a comparison of inner and outer spiral rainbands in a numerically simulated tropical cyclone abstractthe simulated inner and outer spiral rainbands in a tropical cyclone are compared in this study the inner rainbands are generally active immediately outside the eyewall in the rapid filamentation zone while the outer rainbands are active in regions outside about 3 times the radius of maximum wind the inner rainbands are characterized by the convectively coupled vortex rossby waves the movement of the outer rainbands follows the low level vector winds associated with the azimuthally averaged low level flow and the radially outward cross band flow caused by the downdraft induced cold pool in the boundary layer convective cells in outer rainbands are typical of convective systems and move cyclonically and radially outward inward at large small radii net upward vertical mass transports vmts appear throughout the depth of the troposphere in the whole inner rainband region while net downward vmts are found below 4 km height in the outer rainband region in the whole inner rainband region on

distribution of helicity cape and shear in tropical cyclones abstract the previous study of helicity cape and shear in hurricane bonnie 1998 was extended to all eight tropical cyclones sampled by nasa during the convection and moisture experiments camex storms were categorized as having large or small ambient vertical wind shear with 10 m s 1 as the dividing line in strongly sheared storms the downshear mean helicity exceeded the upshear mean by a factor of 4 as in the previous study the helicity differences resulted directly from the tropical cyclone response to ambient shear with enhanced in up out flow and veering of the wind with height present downshear cape in strongly sheared storms was 60 larger downshear mean inflow near the surface and the depth of the inflow layer each were 4 times larger downshear at more than 30 of observation points outside the 100 km radius in the downshear right quadrant midlatitude empirical parameters indicated a strong likelihood of supercells no such points existed upshear in highly sheared storms much small

varves of the dead sea sedimentary record abstract the sedimentary record of the dead sea provides an exceptional high resolution archive of past climate changes in the drought sensitive eastern mediterranean levant a key region for the development of humankind at the boundary of global climate belts moreover it is the only deep hypersaline lake known to have deposited long sequences of finely laminated annually deposited sediments i e varves of varied compositions including aragonite gypsum halite and clastic sediments vast efforts have been made over the years to decipher the environmental information stored in these evaporitic clastic sequences spanning from the pleistocene lake amora to the holocene dead sea a general characterisation of sediment facies has been derived from exposed sediment sections as well as from shallow and deep water sediment cores during high lake stands and episodes of positive water budget mostly during glacial times alternating aragonite and detritus laminae aad facies were accumulated whereas during low lake stands and droughts prevailing during interglacials laminated detritus ld facies and laminated halite lh facies dominate the sequence in this paper we i review the three types of laminated sediments of the dead sea sedimentary record aad ld and lh facies ii discuss their modes of formation deposition and accumulation and their interpretation as varves and iii illustrate how dead sea varves are utilized for palaeoclimate reconstructions and for establishing floating chronologies

the governing dynamics of the secondary eyewall formation of typhoon sinlaku 2008 abstractthrough successful convection permitting simulations of typhoon sinlaku 2008 using a high resolution nonhydrostatic model this study examines the role of peripheral convection in the storm s secondary eyewall formation sef and its eyewall replacement cycle erc the study demonstrates that before sef the simulated storm intensifies via an expansion of the tangential winds and an increase in the boundary layer inflow which are accompanied by peripheral convective cells outside the primary eyewall these convective cells which initially formed in the outer rainbands under favorable environmental conditions and move in an inward spiral play a crucial role in the formation of the secondary eyewall it is hypothesized that sef and erc ultimately arise from the convective heating released from the inward moving rainbands the balanced response in the transverse circulation and the unbalanced dynamics in the atmospheric boundary layer along with the positive feedback between these processes

monument creek debris flow 1984 implications for formation of rapids on the colorado river in grand canyon national park a recent debris flow in monument creek illustrates the nature of debris flows in small tributaries and their hydrologic effects on the colorado river in grand canyon national park a debris avalanche originated in the permian esplanade sandstone of the supai group during intense rainfall on july 27 1984 and fell 600 m into monument creek forming a 7 m high barrier across the channel the subsequent debris flow traveled 4 5 km to the colorado river and achieved velocities of 3 4 to 4 0 m s and a peak discharge of 100 to 120 m 3 s the flow consisted of a main pulse followed by subsequent pulses of debris flow or hyperconcentrated flow the main pulse moved boulders as large as 2 7 m in diameter and deposition at the mouth of monument creek enlarged the fan surface and significantly constricted the colorado river most of the major rapids on the colorado river in grand canyon national park appear to be maintained by episodic debris flows

the influence of land surface heterogeneities on cloud size development abstractthis study analyzes the effects of land surface heterogeneities at various horizontal scales on the transition from shallow to deep convection and on the cloud size distribution an idealized case of midlatitude summertime convection is simulated by means of large eddy simulations coupled to an interactive land surface the transition is accelerated over heterogeneous surfaces the simulation with an intermediate patch size of 12 8 km exhibits the fastest transition with a transition time two thirds that over a homogeneous surface a similar timing is observed for the precipitation onset whereas the total accumulated rainfall tends to increase with patch size the cloud size distribution can be approximated by a power law with a scale break the exponent of the power law is independent of the heterogeneity scale implying a similar cloud cover between the simulations in contrast the scale break varies with patch size the size of the largest clouds does not scale with the boundary layer height

convection initiation aided by lake breeze convergence over the niagara peninsula abstractobservations from the 2015 environment and climate change canada pan parapan american science showcase ecpass and real case cloud resolving numerical simulations with the weather researc

initiation of deep convection over an idealized mesoscale convergence line abstractthis study performs cloud resolving simulations of cumulus convection over an idealized surface based convergence zone to investigate the mechanisms and sensitivities of deep convection initiation forced by mesoscale ascent the surface convergence forms in response to a localized diurnal heating anomaly over an otherwise homogeneous and unheated surface producing a strong boundary layer updraft over the center of the heat source this updraft gives rise to a line of cumuli that gradually deepen and in some cases transition into deep convection to statistically investigate the factors controlling this transition a new thermal tracking algorithm is developed to follow incipient cumulus cores as they ascend through the troposphere this tool is used to isolate the impacts of key environmental parameters cloud layer lapse rate midlevel humidity etc and initial core parameters near cloud base horizontal area vertical velocity etc on the ultimate cloud top height in general the initial

the characteristic time scale for basin hydrological response using radar data abstract the transformation of rainfall into runoff at a basin outlet is the combined effect of many hydrological processes which occur at a wide range of spatial and temporal scales however determining the scale of the combined hydrological response of the basin is still problematic and concepts for its definition are yet to be identified in this paper high resolution meteorological radar data are used for the determination of a characteristic temporal scale for the hydrological response of the basin the response time scale t s t s is defined as the time scale at which the pattern of the time averaged radar rainfall hietograph is most similar to the pattern of the measured outlet runoff hydrograph the existence of such similarity at a relatively stable time scale for a specific basin indicates that it is an intrinsic property of the basin and is related to its hydrological response the identification of the response time scale is carried out by analysis of observations only without assuming a specific rainfall runoff model t s is examined in four small basins 10 100 km 2 in israel the spatial scale is assumed as the entire basin for all analyzed basins a stable response time scale is identified relatively short time scales are found for the urban and arid basins 15 30 min while for the rural basins longer time scale are identified 90 180 min the issues of relationship between the response time scale and basin properties and modeling at the response time scale have yet to be determined

palaeomagnetic remanences in high grade metamorphic rocks of the everest region indication for late miocene crustal doming summary high grade metamorphic rocks of the upper amphibolite to granulite facies in the higher himalayan crystalline hhc were studied for their appropriateness for palaeomagnetic investigations sampling and fieldwork was accomplished on a south north transect at 87 ei n the khumbu region south of everest paragenesis of iron sulphides and oxides was found to be variableduetodifferentsourcerocksandmetamorphicconditionsinthisarea unblockingtemperature ranges isothermal remanence acquisition low temperature magnetic properties and microscopic observations confirm the presence of pyrrhotite and magnetite two remanence componentswereseparatedwithunblockingtemperatureintervalsof250 330 cand370 550 c which can be attributed to characteristic remanent magnetizations chrm of monoclinic pyrrhotite chrm pyr and magnetite chrm mag respectively mainly the chrm pyr showed a consistent demagnetization behaviour probably residing in pyrrhotite particles within the single domain to pseudo single domain range normal and reverse polarities were observed partly co existing within the unblocking spectrum of single specimens this i supports a thermoremanent trm origin of the chrm pyr and ii indicates that the time span of remanence acquisition was long enough to average out palaeosecular variation the age of the chrm pyr can be related tothe last metamorphic cooling event at the early to late miocene boundary 16 ma the chrm mag is probably a secondary chemical or thermochemical remanence acquired byhydrothermalprocessesduringretrogression chrm pyr andchrm mag directionsaresimilar suggesting that pyrrhotite and magnetite were magnetized approximately contemporaneously separation of the sampling area into three sectors reveals a south north trend with i variable block rotations in the southernmost part close to the main central thrust five sites ii no rotation in the area between lukla and namche 10 sites and iii a significant clockwise rotation n 5 sites d i 42 3 29 4 k 20 7 95 17 2 along the imja khola north of namche we interpret the clockwise rotation as an apparent rotation due to tilting by crustal doming in the everest region this doming obviously occurred north of a fault zone located at around namche and was not affecting the region south of it the clockwise sense of the apparent vertical axis rotation indicates that the area north of namche is located at the western side of the dome structure where westward tilting around a subhorizontal axis occurred best fit tilt direction 277 tilt angle 51

anatomy of a pressure induced ferromagnetic to paramagnetic transition in pyrrhotite implications for the formation pressure of diamonds 1 meteorites and diamonds encounter high pressures during their formation or subsequent evolution these materials commonly contain magnetic inclusions of pyrrhotite because magnetic properties are sensitive to strain pyrrhotite can potentially record the shock or formation pressures of its host moreover pyrrhotite undergoes a pressure induced phase transition between 1 6 and 6 2 gpa but the magnetic signature of this transition is poorly known here we report room temperature magnetic measurements on multidomain and single domain pyrrhotite under nonhydrostatic pressure magnetic remanence in single domain pyrrhotite is largely insensitive to pressure until 2 gpa whereas the remanence of multidomain pyrrhotite increases 50 over that of initial conditions by 2 gpa and then decreases until only 33 of the original remanence remains by 4 5 gpa in contrast magnetic coercivity increases with increasing pressure to 4 5 gpa below 1 5 gpa multidomain pyrrhotite obeys neel theory with a positive correlation between coercivity and remanence above 1 5 gpa it behaves single domain like yet distinctly different from uncompressed single domain pyrrhotite the ratio of magnetic coercivity and remanence follows a logarithmic law with respect to pressure which can potentially be used as a geobarometer owing to the greater thermal expansion of pyrrhotite with respect to diamond pyrrhotite inclusions in diamonds experience a confining pressure at earth s surface applying our experimentally derived magnetic geobarometer to pyrrhotite bearing diamonds from botswana and the central african republic suggests the pressures of the pyrrhotite inclusions in the diamonds range from 1 3 to 2 1 gpa these overpressures constrain the mantle source pressures from 5 4 to 9 5 gpa depending on which bulk modulus and thermal expansion coefficients of the two phases are used

characterization of hematite α fe2o3 goethite α feooh greigite fe3s4 and pyrrhotite fe7s8 using first order reversal curve diagrams 1 first order reversal curve forc diagrams have become a standard tool in rock magnetism yet magnetite is the only magnetic mineral that is well characterized using forc diagrams we present forc diagrams for predominantly single domain sd synthetic aluminous hematite a fe2 xalxo3 and goethite a feal ooh and natural greigite fe3s4 and pyrrhotite fe7s8 to constrain interpretation of forc diagrams from natural samples hematite and goethite have low spontaneous magnetizations and negligible magnetic interactions while greigite and pyrrhotite have higher spontaneous magnetizations and can have strong magnetic interactions the coercivity of hematite systematically increases with al content only for samples produced using the same synthesis method but it is variable for samples produced with different methods even for similar al content this precludes use of magnetic coercivity alone to quantify the al content of natural hematites goethite has much higher coercivity than hematite for all measured samples sd and superparamagnetic sp behavior is common in natural greigite samples with peak coercivities ranging from

numerical simulation of cyclone sidr using a cloud resolving model characteristics and formation process of an outer rainband abstractcyclone sidr one of the most devastating tropical cyclones that resulted in several thousand deaths and substantial damages developed in the north indian ocean and made landfall over the bangladesh coast on 15 november 2007 observation and simulation results show that sidr was embedded in a nonuniform environment and contained an intense outer rainband to the east of its center and a significant frontal band to the northwest a detailed study of the outer rainband is performed by numerical simulation the eastern band was a long quasi straight shape in the meridional direction that remained stationary relative to the cyclone center this band was composed of convective cells that developed southeast of the center within a synoptic scale convergence zone and propagated along the band toward the northeast quadrant the speed of the downwind propagating cells was greater than that of the cyclone which resulted in a convective cluster northeast of the center only the downwind portion of the band

objective convective updraft identification and tracking part 1 structure and thermodynamics of convection in the rainband regions of two hurricane simulations to better understand the life cycles of convective elements in numerical model simulations a convective updraft tracking algorithm dubbed the statistical and programmable objective updraft tracker spout is developed spout identifies updraft cores in horizontal slices through a given model data set links these cores in three dimensions to form vertically coherent updrafts and then tracks updrafts in time via estimates of the mean local advection spout is evaluated in idealized hurricane simulations from both the regional atmospheric modeling system rams and weather research and forecasting wrf in both simulations spout indicates most updrafts live less than 60 min but some can persist for over 2 h updrafts are typically manifested as shallow cumulus cumulus congestus and deep cumulonimbus overall there is reasonable agreement between the vigor of convection and the amount of localized conditional convective instability also the majority of updrafts attain a tilted structure that is in accordance with the localized vertical wind shear nonetheless there are striking differences between models with the higher resolution wrf simulation producing around twice as many updrafts as rams moreover the wrf updrafts are significantly weaker this paper highlights the utility of spout for studying convective life cycles in high resolution numerical simulations and provides some basic features of convection in two hurricane simulations

hydrometeorological controls and erosive response of an extreme alpine debris flow on 29 august 2003 an intense convective storm system affected the fella river basin in the eastern italian alps producing rainfall peaks of approximately 390 mm in 12 h the storm triggered an unusually large debris flow in the ungauged rio cucco basin 0 65 km2 with a volume of approximately 78 000 m3 the analysis of the time evolution of the rainstorm over the basin has been based on rainfall estimates from radar observations and data recorded by a raingauge network detailed geomorphological field surveys carried out both before and after the flood of august 2003 and the application of a distributed hydrological model have enabled assessment of flood response estimation of erosion volumes and sediment supply to the channel network the accounts of two eyewitnesses have provided useful elements for reconstructing the time evolution and the flow processes involved in the event liquid peak discharge estimates cluster around 20 m3 s 1 km 2 placing this event on the flood envelope curve for the eastern italian alps the hydrological analysis has shown that the major controls of the flood response were the exceptional cumulated rainfall amount required to exceed the large initial losses and the large rainfall intensities at hourly temporal scales required to generate high flood response at the considered basin scale observations on the deposits accumulated on the alluvial fan indicate that although the dominant flow process was a debris flow sheetflood also contributed to fan aggradation and fluvial reworking had an important role in winnowing debris flow lobes and redistributing sediment on the fan surface this points out to the large discharge values during the recession phase of the flood implying an important role for subsurface flow on runoff generation of this extreme flash flood event copyright 2009 john wiley sons ltd

incision of alluvial channels in response to a continuous base level fall field characterization modeling and validation along the dead sea abstract the dramatic lake level drop of the dead sea during the twentieth century 30 m provides a field scale experiment in transport limited incision of gravel bed channels in response to quasi continuous base level fall at approximately constant rate we apply a one dimensional numerical incision model based on a linear diffusion equation to seven ephemeral channels draining into the dead sea the model inputs include the measured twentieth century lake level curve annual shoreline location i e annual channel lengthening following the lake level drop reconstructed longitudinal profiles of each of the channels based on mapped and surveyed terraces and the current profiles of the active channels the model parameters included the diffusion coefficient and the upstream derived sediment flux both were first calibrated using a set of longitudinal profiles of known ages and then validated using additional sets of longitudinal profiles the maximum at station total incision observed at each of the studied channels was significantly less then the total lake level drop and varied in response to both drainage area and lake bathymetry the model applied predicted degradation rates and the pattern of degradation with high accuracy this suggests that sediment flux in the modeled channels is indeed linearly dependent on slope further support for this linear dependency is provided by a linear correlation between the diffusion coefficient and the mean annual rain volume over each basin a proxy for discharge the model presented could be a valuable tool for planning in rapid base level fall environments where incision may risk infrastructure

a convective cell in a hurricane rainband abstract on 10 october 1983 the two noaa wp 3d aircraft completed a mission designed to provide airborne doppler radar data for a convective cell embedded in a weak rainband on the trailing side of hurricane raymond comparisons of the wind field produced from the pseudo dual doppler radar technique with in situ wind measurements suggest that the larger convective scale feature may be resolved if the sampling time is kept to a minimum the convective cell was found to move downband faster than any environmental winds but slightly slower than the winds found in the reflectivity core that delineates the cell in the core of the cell the tangential wind is increased and the radial inflow turns to outflow with respect to the circulation center the flow field demonstrates that the downband stratiform portion of a rainband is not from cells currently active since the updraft detrains upwind relative to the cell but rather it is due to the fallout from ice particles placed into the upper troposphere by clouds t

the roles of asymmetric inflow forcing induced by outer rainbands in tropical cyclone secondary eyewall formation abstractthis study analyzes the secondary eyewall formation sef process in an idealized cloud resolving simulation of a tropical cyclone in particular the unbalanced boundary layer response to asymmetric inflow forcing induced by outer rainbands orbs is examined in order to understand the mechanisms driving the sustained convection outside the primary eyewall during the early phase of sef the enhancement of convection in the sef region follows the formation and inward contraction of an orb the azimuthal distribution of the enhanced convection is highly asymmetric but regular generally along a half circle starting from the downwind portion of the orb it turns out that the descending radial inflow in the middle and downwind portions of the orb initiates maintains a strong inflow in the boundary layer the latter is able to penetrate into the inner core region sharpens the gradient of radial velocity and reinforces convergence consequently warm and moist air is continuously lifted up at the lead

geologic versus wildfire controls on hillslope processes and debris flow initiation in the green river canyons of dinosaur national monument abstract as in many areas of high relief debris flows are an important process linkage between hillslopes and the green river in the canyons of the eastern uinta mountains yet the physical conditions that lead to debris flow initiation are unknown a recent episode of enhanced debris flow and wildfire activity provided an opportunity to examine the geomorphic impact of fire and the processes by which weathered bedrock is transported to the green river field investigations and analysis of elevation and precipitation data were undertaken in 15 catchments with recent debris flows to determine how surficial geology wildfire topography bedrock strength and meteorology influence hillslope processes the recent debris flows were triggered by intense summer rainstorms the dominant debris flow initiation mechanism the firehose effect occurred when overland flow generated on bedrock hillslopes cascaded down steep cliffs onto colluvium causing failure sixty percent of the debris flows occurred in unburned catchments however 15 of the burned catchments in the study area produced debris flows over the study period whereas only 7 of the unburned catchments did thus fire was not the primary driver of debris flows but fire related events did contribute to the increased debris flow activity the geomorphic impact of wildfire in the eastern uinta mountains is not as great as in transport limited settings with regolith mantled hillslopes the strong rocks and dry climate of the study area cause hillslopes to be very steep and weathering limited with high runoff ratios and a dearth of regolith as a result there is little vegetation and thus we hypothesize that burning does little to change hillslope processes the suite of hillslope processes in the eastern uintas are like those documented in the similarly dry grand canyon but differ from other locations in the western u s where wildfire is a primary control on debris flow processes

mechanisms for the generation of mesoscale vorticity features in tropical cyclone rainbands a high resolution tropical cyclone model with explicit cloud microphysics has been used to investigate the dynamics and energetics of tropical cyclone rainbands analysis of the vorticity interactions that occur within the simulated rainbands demonstrates that couplets of cyclonic anticyclonic mesovortices can be produced in outer bands the primary source of this vorticity is the upward tilting of system generated horizontal vorticity by diabatic heating gradients the vertical heating gradient in the stratiform cloud also creates a potential vorticity pv dipole that accelerates the tangential flow and develops a midlevel jet the strength of the jet is enhanced by the vortex pair that is oriented radially across the rainband the fourier decomposition of the absolute vorticity field shows two counterpropagating vortex rossby waves associated with the rainband the wave located on the inner side of the band transports energy toward the vortex center the outer wave is made up of high wavenumbers and uses the vorticity gradients generated by the rainband the results support the hypothesis that the heating profile in the stratiform regions of rainbands generates cyclonic pv across the freezing level which develops a midlevel jet this mechanism creates a vorticity gradient that enables the propagation of vortex rossby waves that could allow the rainbands to interact with the mean flow and potentially influence the evolution of the storm by contributing to the symmetric component of vorticity and the development of secondary eyewalls

a numerical investigation of the eyewall evolution in a landfalling typhoon abstract an interesting eyewall evolution occurred in typhoon zeb 1998 when it devastated luzon the eyewall of zeb contracted before landfall and broke down and weakened after landfall then a much larger new eyewall formed and strengthened as it left luzon and reentered the ocean the fifth generation pennsylvania state university ncar mesoscale model mm5 with four nested domains was used to perform numerical experiments to understand the effects of terrain and land surface variation on the observed eyewall evolution results show that the presence of luzon plays a critical role in the observed eyewall evolution quite different from the conventional concentric eyewall replacement the eyewall replacement that occurred in typhoon zeb was triggered by the mesoscale landmass and terrain variation with a horizontal scale similar to the core of the typhoon in typhoon zeb the original eyewall contracted and broke down because of enhanced surface friction after landfall the outer eyewall was triggered

low temperature magnetic properties of monoclinic pyrrhotite with particular relevance to the besnus transition monoclinic pyrrhotite fe7s8 owes its ferrimagnetism to an ordered array of fe vacancies its magnetic properties change markedly around 30 k in what is known as the besnus transition plausible explanations for the besnus transition are either due to changes in crystalline anisotropy from a transformation in crystal symmetry or from the establishment of a two phase system with magnetic interaction between the two phases to help resolve this discrepancy we measured hysteresis loops every 5a degrees and backfield curves every 10a degrees in the basal plane of an oriented single crystal of monoclinic pyrrhotite at 300 k and every 2 k from 50 k through the besnus transition until 20 k between 50 and 30 k hysteresis loops possess double inflections between crystallographic a axes and only a single inflection parallel to the a axes magnetization energy calculations and relative differences of the loops show a sixfold symmetry in this temperature range we propose that the inflections stem from magnetic axis switching which is both field and temperature dependent in a manner somewhat analogous to an isotropic point where magnetocrystalline constants change their sign the besnus transition is best characterized by changes in magnetic remanence and coercivity over a 6a degrees temperature span 28 34 k with a maximum rate of change at 30 k a surprising yet puzzling finding is that the coercivity ratio becomes less than unity below the transition when fourfold symmetry arises because the changes in magnetic parameters are linked to the crystal structure we conclude the besnus transition owes its origin to a distortion of the crystallographic axes below 30 k rather than an apparition of a two phase system an isothermal magnetization of natural pyrrhotite cycled from room temperature to successively lower temperatures through the besnus transition decreases 2 4 times less than equivalent grain sizes of magnetite with less than a 10 per cent loss in remanence between 300 and 150 k in pseudo single domain psd pyrrhotite as psd monoclinic pyrrhotite carries the magnetic remanence in some meteorites it is likely that low temperature cycling in space then warming to ambient conditions at the earth s surface will have only a minor influence on palaeointensity values derived from those meteorites

debris flow deposition and reworking by the colorado river in grand canyon arizona 1 flow regulation by large dams affects downstream flow competence and channel maintenance debris flows from 740 tributaries in grand canyon arizona transport coarse grained sediment onto debris fans adjacent to the colorado river these debris fans constrict the river to form rapids and are reworked during river flows that entrain particles and transport them downstream beginning in 1963 flood control operations of glen canyon dam limited the potential for reworking of aggraded debris fans we analyzed change in debris fans at the mouths of 75 mile and monument creeks using photogrammetry of aerial photography taken from 1965 to 2000 and supplemented with ground surveys performed from 1987 to 2005 our results quantify the debris fan aggradation that resulted from debris flows from 1984 to 2003 volume area and river constriction increased at both debris fans profiles of the two debris fans show that net aggradation occurred in the middle of debris fans at stages above maximum dam releases and surface shape shifted from concave to convex dam releases above power plant capacity partially reworked both debris fans although reworking removed much less sediment than what was added by debris flow deposition large dam releases would be required to create additional reworking to limit the rate of debris fan aggradation in grand canyon

essential dynamics of secondary eyewall formation abstractthe authors conduct an analysis of the dynamics of secondary eyewall formation in two modeling frameworks to obtain a more complete understanding of the phenomenon the first is a full physics three dimensional mesoscale model in which the authors examine an idealized hurricane simulation that undergoes a canonical eyewall replacement cycle analysis of the mesoscale simulation shows that secondary eyewall formation occurs in a conditionally unstable environment questioning the applicability of moist neutral viewpoints and related mathematical formulations thereto for studying this process of tropical cyclone intensity change the analysis offers also new evidence in support of a recent hypothesis that secondary eyewalls form via a progressive boundary layer control of the vortex dynamics in response to a radial broadening of the tangential wind field the second analysis framework is an axisymmetric nonlinear time dependent slab boundary layer model with radial diffusion when this boundary l

the dependence of numerically simulated convective storms on vertical wind shear and buoyancy abstract the effects of vertical wind shear and buoyancy on convective storm structure and evolution are investigated with the use of a three dimensional numerical cloud model by varying the magnitude of buoyant energy and one directional vertical shear over a wide range of environmental conditions associated with severe storms the model is able to produce a spectrum of storm types qualitatively similar to those observed in nature these include short lived single cells certain types of multicells and rotating supercells the relationship between wind shear and buoyancy is expressed in terms of a nondimensional convective parameter which delineates various regimes of storm structure and in particular suggests optimal conditions for the development of supercell type storms applications of this parameter to well documented severe storm cases agree favorably with the model results suggesting both the value of the model in studying these modes of convection as well as the value of this representation i

hydrometeorological triggers of periglacial debris flows in the zermatt valley switzerland since 1864 1 the triggering of debris flows depends on a critical combination of available unconsolidated material and water supply in periglacial environments debris flows are generally triggered by liquefaction of loose material in a channel or by progressive erosion during a large release of water here we link an unusually dense and highly resolved database on periglacial debris flows with meteorological records dating back to ad 1864 to reconstruct 150 yr of rainstorms that triggered debris flows at high elevation sites source area elevations ranging from 2000 to 4545 m a s l in the swiss alps analysis is based on a tree ring derived frequency series of debris flows from eight torrents as well as on daily records from three meteorological stations and runoff data from four river gauging stations results show that the debris flow season at these high altitude sites now is much longer may to october than it used to be in the late nineteenth century when activity was limited to june september debris flows early in the season are generally triggered by lower rainstorm totals 20 mm day than those occurring later in the season because early season snowmelt adds considerable amounts of water to the system and therefore facilitates debris flow formation debris flows in may june july and august are triggered primarily by short duration high intensity rainstorms local thunderstorms whereas late season september october debris flows are commonly related to longer lasting advective rainstorms

boundary layer structure and dynamics in outer hurricane rainbands part i mesoscale rainfall and kinematic structure abstract results of hurricane boundary layer experiments conducted in outer rainbands of hurricanes josephine 1984 and earl 1986 are presented comparisons of precipitation and kinematic structures in these storms and in hurricane floyd 1981 indicate that principal rainbands have common characteristic mesoscale and convective scale features in the boundary layer the two dimensional mesoscale structure suggests that these rainbands are made up of a linear aggregate of cellular reflectivity elements on the inner upshear side of the band and stratiform rain on the outer downshear side the bands are oriented perpendicular to the shear above the boundary layer and cells move downband at about 85 of the density weighted mean wind speed of the 0 2 6 km layer the boundary layer wind field is strongly influenced by the rainband with alongband and crossband wind maxima located on the outer side of the band axis and minima 4 8 km to the inner side maximum crossband convergence and cyclonic shear vor

initiation of convection over the black forest mountains during cops iop15a doppler on wheels radar observations made during the convective and orographically induced precipitation study cops on 12 august 2007 showed that precipitating clouds only developed between the north south orientated murg and nagold valleys of the northern black forest the clouds produced moderate precipitation the weather research and forecasting wrf model run at 700 m horizontal resolution in the inner domain was able to simulate the location of the precipitation insight is therefore gained into the physical mechanisms responsible for the initiation and development of the convection convergence lines resulting from thermally driven flows constrained the initial location of the convection within warm and moist cores produced by heating on elevated surfaces the heaviest precipitation was later produced by secondary convection which was initiated within the cores at the boundary between cold pool outflows and thermal flows copyright 2011 royal meteorological society

response of alluvial fan systems to the late pleistocene to holocene climatic transition contrasts between the margins of pluvial lakes lahontan and mojave nevada and california usa abstract dated shorelines of late pleistocene pluvial lakes lahontan great basin desert northwest nevada and mojave mojave desert eastern california provide timelines for the assessment of alluvial fan sedimentation at the lake margins during the late pleistocene to early holocene two sets of alluvial fan systems have been mapped the stillwater fans feeding lake lahontan and the zzyzx fans feeding lake mojave their contrasting morphologies suggest different responses of the two fan systems to late pleistocene to early holocene climatic change at the time the stillwater fan systems underwent minimal sedimentation with the catchment hillslopes apparently stable the zzyzx fans experienced major changes in water and sediment supply from the catchment hillslopes there was a major phase of hillslope debris flow activity followed by fanhead trenching and distal fan progradation both areas were wetter and colder in the late pleistocene than they are today but during the transition to the holocene the zzyzx area was more likely to experience intense rains associated with the monsoonal penetration of warm moist tropical air into the southwest vegetation reconstructions for the late pleistocene to the early holocene suggest that catchment hillslopes in the mojave supported a desert shrub vegetation but those in the stillwaters supported juniper woodland and grasses at low elevations and pine at higher elevations contrasts in hillslope vegetation cover together with storm activity may account for the different responses of the alluvial fans to climatic change during the pleistocene to holocene climatic transition after the falls in lake levels of lakes lahontan and mojave in the early holocene both areas underwent aridification resulting in reductions in hillslope vegetation cover increased storm runoff led to fanhead trenching and distal progradation of the alluvial fans variations in fan style at that time may relate primarily to base level conditions resulting from different gradients on the exposed lake shores

the evolution of convective storms initiated by an isolated mountain ridge abstractthe evolution of convective storms over the black hills an isolated mountain ridge in south dakota and wyoming and a regional convection hotspot is investigated using a 10 yr observational climatology and quasi idealized numerical simulations radar observed diurnally forced mountain convection events are classified according to their maximum cell track length and duration which are quantified using an automated cell tracking algorithm environmental conditions during these events are obtained from operational radiosonde and model analysis data these data suggest that mountain forced convective cells generally struggle to survive in the convectively inhibited flow downwind of the black hills those cells that do survive downwind prefer environments with strong bulk vertical shear over the 0 6 km layer which favors organized multicellular or supercellular convection under slightly weaker shear the cells tend to dissipate rapidly as they propagate downwind relatively weak winds aloft when c

supercells and mesocyclones in outer rainbands of hurricane katrina 2005 1 this study documents and describes supercells embedded within the outer rainbands of hurricane katrina 2005 radar reflectivity and velocity data collected on 29 august 2005 by weather surveillance radar 1988 doppler radars were used to track the supercells radar analysis indicates that the supercells were characterized by heavy precipitation collocated with band relative mesocylonic circulations containing strong vorticity and a wind speed enhancement to their northeast atmospheric soundings and dual doppler derived shear suggest that environmental conditions were comparable to those in previous hurricane spawned supercell studies twenty three storms from 0300 0900 utc were tracked and single and dual doppler radar analyses were used to examine characteristics such as shear and rotational velocity remarkably the majority of the supercells formed over the gulf of mexico rather than over land which contrasts with previous studies furthermore the ground relative wind speeds of these potentially tornadic mesocyclones in the outer rainbands could have been category 4 intensity despite sustained winds in katrina s eyewall only reaching category 3 at landfall

concentric eyewall formation in typhoon sinlaku 2008 part ii axisymmetric dynamical processes abstractin part i of this study the association between the secondary eyewall formation sef and the broadening of the outer swirling wind in typhoon sinlaku 2008 was documented the findings from part i help lay the groundwork for the application of a newly proposed intensification paradigm to sef part ii presents a new model for sef that utilizes this new paradigm and its axisymmetric view of the dynamics the findings point to a sequence of structure changes that occur in the vortex s outer core region culminating in sef the sequence begins with a broadening of the tangential winds followed by an increase of the corresponding boundary layer bl inflow and an enhancement of convergence in the bl where the secondary eyewall forms the narrow region of strong bl convergence is associated with the generation of supergradient winds in and just above the bl that acts to rapidly decelerate inflow there the progressive strengthening of bl inflow and the generation of an effective adverse radial force

mesoscale and convective structure of a hurricane rainband abstract the mesoscale thermodynamic kinematic and radar structure of a hurricane floyd rainband observed on 7 september 1981 is presented data are from 26 aircraft passes through the rainband from 150 to 6400 m a composite technique which presents rainband structure as a function of distance from the storm circulation center reveals inflow from the outer edge of the band and a partial barrier to this flow below 3 km in the direction parallel to rainband orientation radar reveals cellular reflectivity structure on the upwind and central portions of the rainband the frequency of cellular precipitation decreases in favor of stratiform precipitation further downwind as the band spirals gradually towards the eyewall in the radial direction a decrease of 12 k in e is observed across the rainband in the subcloud layer convective scale up and downdrafts that are associated with cellular reflectivity structure are hypothesized to be responsible for the thermodynamic modification of the cloud and subc

discrepancies between experimental observations in natural and synthetic samples abstract the evidence is reviewed by comparing the data obtained from synthetic samples with those derived from natural samples of magnetic minerals present in rocks it is shown that there are many issues which are still unresolved some suggestions are made concerning the future direction of rock magnetic research such as the need for intensified studies of natural samples the aim of this note is not to disclose anything new but rather to open up some lines of thought and draw attention to questions and ideas that may have been lurking in our minds from the very beginnings of paleomagnetism

the influence of debris flow rheology on fan morphology owens valley california we have investigated factors controlling the surface morphology of debris flow fans comprising the bajada along the western slope of owens valley california these fans have average slopes of 4 an extensive network of abandoned boulder lined channels rough undulatory surfaces near the range front and smooth distal surfaces field relationships and mechanical considerations indicate that the channels of the bajada are products of fluvial incision and not debris flow scour this is significant because detailed geomorphic maps indicate that the channels strongly influence the pattern of debris flow deposition the locus of debris flow deposition on a channelized fan surface is set by the interaction of debris flows with the channel system and is controlled by channel size channel gradient flow volume flow hydrograph and flow rheology debris flow behavior is most directly controlled by variations in bulk sediment concentration and its influence on flow rheology whereas low sediment concentration debris flows tend to smooth the surface of the lower fan spreading into thin sheets and filling channels and surface undulations repeated deposition of high sediment concentration debris flows produces the rugged topography of the upper fan the texture of the fan surface rough or smooth is determined by the relative volumetric importance of these two types of debris flow in addition channel avulsions and the associated long term shifting of depositional loci are driven by in channel deposition of debris flows with the highest sediment concentrations these debris flows therefore play a critical role in determining both the structure of the channel network and the long term pattern of deposition on the fan surface as a whole we infer that the frequency distribution of debris flow rheologies set by source terrain geology and hydrology is an important control on fan morphology

convectively generated potential vorticity in rainbands and formation of the secondary eyewall in hurricane rita of 2005 abstracteyewall replacements in mature tropical cyclones usually cause intensity fluctuations one reason for eyewall replacements remaining a forecasting challenge is the lack of understanding of how secondary eyewalls form this study uses high resolution full physics model forecast fields of hurricanes katrina and rita 2005 to better understand potential vorticity pv generation in the rainbands and the role that convectively generated pv played in the formation of a secondary eyewall in hurricane rita previous studies have focused on dynamic processes in the inner core and or the effects of certain specified pv distributions however the initial development of a concentric pv ring in the rainband region has not been fully addressed katrina and rita were extensively observed by three research aircraft during the hurricane rainband and intensity change experiment rainex which was designed to study the interaction of the rainbands and the inner core rita developed a secondary eyewall and went

kinematic structure of convective scale elements in the rainbands of hurricanes katrina and rita 2005 1 airborne doppler radar data collected during the hurricane rainband and intensity change experiment rainex show the convective scale air motions embedded in the principal rainbands of hurricanes katrina and rita these embedded convective cells have overturning updrafts and low level downdrafts originating at 2 4 km that enter the rainband on its radially outward side and cross over each other within the rainband as well as a strong downdraft emanating from upper levels 6 km on the radially inward side these vertical motion structures repeat from one convective cell to another along each rainband the resulting net vertical mass transport is upward in the upwind portion of the band and greatest in the middle sector of the principal rainband where the updraft motions contribute generally to an increase of potential vorticity below the 3 4 km level because the convective cells in the middle sector are systematically located radially just inside the secondary horizontal wind maximum shwm the local increase in vorticity implied by the convective mass transport is manifest locally as an increase in the strength of the shwm at midlevels 4 km the overturning updrafts of the convective cells tilt stretch and vertically transport vorticity such that the convergence of the vertical flux of vorticity strengthens the vorticity anomaly associated with the shwm this process could strengthen the shwm by several meters per second per hour and may explain how high wave number convective scale features can influence a low wave number feature such as the principal rainband and subsequently influence the primary vortex

the indication of martian gully formation processes by slope area analysis the formation process of recent gullies on mars is currently under debate this study aims to discriminate between the proposed formation processes pure water flow debris flow and dry mass wasting through the application of geomorphological indices commonly used in terrestrial geomorphology high resolution digital elevation models dems of earth and mars were used to evaluate the drainage characteristics of small slope sections data from earth were used to validate the hillslope debris flow and alluvial process domains previously found for large fluvial catchments on earth and these domains were applied to gullied and ungullied slopes on mars in accordance with other studies our results indicate that debris flow is one of the main processes forming the martian gullies that were being examined the source of the water is predominantly distributed surface melting not an underground aquifer evidence is also presented indicating that other processes may have shaped martian crater slopes such as ice assisted creep and solifluction in agreement with the proposed recent martian glacial and periglacial climate our results suggest that within impact craters different processes are acting on differently oriented slopes but further work is needed to investigate the potential link between these observations and changes in martian climate

petrography and shock related remagnetization of pyrrhotite in drill cores from the bosumtwi impact crater drilling project ghana rock magnetic and magnetic mineralogy data are presented from the international continental scientific drilling program icdp drill cores lb 07a and lb 08a of the bosumtwi impact structure in order to understand the magnetic behavior of impact and target lithologies and their impact related remagnetization mechanism basic data for the interpretation of the magnetic anomaly patterns and the magnetic borehole measurements as well as for new magnetic modeling are provided magnetic susceptibility 150 500 10 6 si and natural remanent magnetization 10 3 10 1 a m are generally weak but locally higher values up to 10 6 10 3 si and 43 a m occur sixty three percent of the investigated rock specimens show q values above 1 indicating that remanence clearly dominates over induced magnetization which is a typical feature of impact structures ferrimagnetic pyrrhotite is the main magnetite phase which occurs besides minor magnetite and a magnetic phase with a curie temperature between 330 and 350 c interpreted as anomalous pyrrhotite coercive forces are between 20 and 40 mt brecciation and fracturing of pyrrhotite is a common feature confirming its pre impact origin grain sizes of pyrrhotite show a large variation but the numerous stress induced nanostructures observable by transmission electron microscopy tem are assumed to behave as single domain grains we suggest that the drilled rocks lost their pre shock remanence memory during the shock event and acquired a new stable remanence during shock induced grain size reduction the observed brittle microstructures indicate temperatures not higher than 250 c which is below the curie temperature of ferrimagnetic pyrrhotite 310 c

effectiveness of exceptional rainstorms on a small mediterranean basin abstract a comprehensive investigation of rainstorms and their consequent impacts on landscape evolution is geomorphologically important but only scant information may be available on exceptional events because parameters on synoptic conditions rainstorm landforms and hydrology for such events may be incomparable with previous knowledge we studied an exceptional storm on april 2 2006 in the ramot menashe region israel our investigation of rainfall landslides debris flows and channel suggests the effectiveness of such an event on the development of basin scale morphology the storm caused damage and casualties although it covered relatively narrow strips neither direct rainfall nor runoff measurements exist for the most severely affected area of ramot menashe but the geomorphologic evidence combined with high resolution meteorological radar data provides the basic understanding of the processes and hazardous conditions which prevailed at the time in the storm core based on estimation from meteorological radar data 263 mm of rain fell within 3 h with a maximum intensity of 220 mm h 1 for 10 min triggering both sporadic landslides at the soil bedrock contact on the upper slopes and widespread landslides at the fractured massive bedrock contact on the lower slopes the 1st order channels on the alternation of chalk and marl also underwent erosion and the produced sediment deposited on alluvial fans at the confluence with the main channel the specific peak discharges for catchment size of 0 3 10 km2 were 11 to 73 m3 s 1 km 2 higher than any recorded floods in the mediterranean climatic region of israel the effectiveness of the flood for geomorphic work represented by shear stress and stream power per unit boundary area reached 87 398 n m 2 and 212 2134 w m 2 respectively this kind of analysis can be applied to hazard prediction in other areas under similar geomorphological conditions

magnetic characterization of non ideal single domain monoclinic pyrrhotite and its demagnetization under hydrostatic pressure up to 2 gpa with implications for impact demagnetization here we present a comprehensive magnetic characterization of synthesized non ideal single domain sd monoclinic pyrrhotite fe 7 s 8 the samples were in the form of a powder and a powder dispersed in epoxy non ideal refers to a powder fraction of predominantly sd size with a minor contribution of small pseudo single domain grains such non ideal sd pyrrhotite was found to be a remanence carrier in several types of meteorites carbonaceous chondrites snc which justifies the usage of synthetic compositions as analogous to natural samples data were collected from 5 to 633 k and include low field magnetic susceptibility 0 thermomagnetic curves major hysteresis loops back field remanence demagnetization curves first order reversal curves forcs alternating field and pressure demagnetization of saturation isothermal remanent magnetization sirm low temperature data such as zero field cooled and field cooled remanence datasets together with room temperature sirm cooling warming cycles as well as xrd and mossbauer spectra the characteristic besnus transition is observed at 33 k forc diagrams indicate interacting sd grains the application of hydrostatic pressure up to 2 gpa using nonmagnetic high pressure cells resulted in the demagnetization of the sample by 32 38 repeated cycling from 1 8 gpa to atmospheric pressure and back resulted in a total remanence decrease of 44 after 3 cycles pressure demagnetization experiments have important implications for meteorite paleomagnetism and suggest that some published paleointensities of meteorites with non ideal sd monoclinic pyrrhotite as remanence carrier may be lower limits because shock demagnetization was not accounted for

initiation of convective storms at radar observed boundary layer convergence lines abstract the origin of 653 convective storms occurring over a 5000 km2 area immediately east of the colorado rocky mountains from 18 may to 15 august 1984 was examined seventy nine percent of the 418 storms that initiated within the study area occurred in close proximity to radar observed boundary layer convergence lines this percentage increased to 95 when only the more intense storms 60 dbze were considered colliding convergence lines initiated new storms or intensified existing storms in 71 of the cases a new storm took a median time of 24 min to grow to 30 dbz following line collision the convergence lines ranged in length between ten and several hundred kilometers both radar and mesonet stations indicated that the primary convergence was concentrated in a zone 0 5 to 5 km in width these lines were characterized on doppler radar as thin lines of enhanced reflectivity between 0 and 20 dbze and as a line of strong radial or azimuthal gradient in doppler velocity these lines were observed ev

palaeomagnetic results from the tibetan sedimentary series of the manang area north central nepal summary the remanent magnetization of palaeozoic and mesozoic carbonates from the tibetan sedimentary series tss of the manang area north of the annapurna range north central nepal has been investigated the tss forms part of the tectonic unit between the indian eurasian plate boundary in the north and the main central thrust mct in the south apart from a present field direction three remanence components have been separated a normal polarity post folding remanence negative fold test is carried by pyrrhotite the core corrected mean direction for five sites with 47 specimens from silurian devonian rocks is decl 312 9 incl 58 3 95 17 6 k 19 8 the origin of this component is not understood a more precisely determined reversed polarity post folding remanence 99 per cent negative fold test is also carried by pyrrhotite the core corrected mean direction for 12 sites with 229 specimens from carboniferous triassic rocks is decl 196 4 incl 65 9 95 3 2 k 183 one site of lower carinan age shows in addition to the pyrrhotite component a second stable remanence direction carried by magnetite the fold test is 99 per cent positive and there is a high probability that the remanence is of detrital origin the bedding corrected direction for one site with 40 specimens is decl 334 3 incl 54 1 95 4 2 k 30 2 palaeolatitude 34 6 s the direction of the magnetite component coincides with other triassic palaeodirection data from the literature and the inclination suggests a palaeoposition of the tss at the northern margin of india at this time the northern extent of india in the triassic cannot be reconstructed from the data because of the strong anticlockwise rotation 48 of stable india since this time the inclination of the reverse polarity pyrrhotite component is 19 steeper than expected from the maximum northern position of the area this suggests a regional northward tilt along the mct which is supported by steep inclinations found in other areas declination data for the reverse polarity pyrrhotite component and for the magnetite component deviate clockwise from expected values for the area by 23 34 calculated from the indian apwp utilizing klootwijk conaghan powell s 1985 rotational underthrusting model the minimum magnitude of continental underthrusting between the tss and stable india at the longitude of central nepal 84 e has been calculated from the declination of our reverse polarity pyrrhotite component a possible range of 520 1100 km results from consideration of different tectonic models

initiation conditions for debris flows generated by runoff at chalk cliffs central colorado abstract we have monitored initiation conditions for six debris flows between may 2004 and july 2006 in a 0 3 km 2 drainage basin at chalk cliffs a band of hydrothermally altered quartz monzonite in central colorado debris flows were initiated by water runoff from colluvium and bedrock that entrained sediment from rills and channels with slopes ranging from about 14 to 45 the availability of channel material is essentially unlimited because of thick channel fill and refilling following debris flows by rock fall and dry ravel processes rainfall exceeding i 6 61 d 0 77 where i is rainfall intensity mm h and d is duration h was required for the initiation of debris flows in the drainage basin the approximate minimum runoff discharge from the surface of bedrock required to initiate debris flows in the channels was 0 15 m 3 s colluvium in the basin was unsaturated immediately prior to antecedent and during debris flows antecedent volumetric moisture levels in colluvium at depths of 1 cm and 29 cm ranged from 4 9 and 4 7 respectively during debris flows peak moisture levels in colluvium at depths of 1 cm and 29 cm ranged from 10 20 and 4 12 respectively channel sediment at a depth of 45 cm was unsaturated before and during debris flows antecedent moisture ranged from 20 22 and peak moisture ranged from 24 38 although we have no measurements from shallow rill or channel sediment we infer that it was unsaturated before debris flows and saturated by surface water runoff during debris flows our results allow us to make the following general statements with regard to debris flows generated by runoff in semi arid to arid mountainous regions 1 high antecedent moisture levels in hillslope and channel sediment are not required for the initiation of debris flows by runoff 2 locations of entrainment of sediment by successive runoff events can vary within a basin as a function of variations in the thickness of existing channel fill and the rate of replenishment of channel fill by rock fall and dry ravel processes following debris flows and 3 rainfall and simulated surface water discharge thresholds can be useful in understanding and predicting debris flows generated by runoff and sediment entrainment

impact of consecutive extreme rainstorm events on particle transport case study in a sonoran desert range western usa abstract quantifying erosion rates in different landscape settings provides insight into how landforms change under different climatic tectonic and anthropogenic influences sediment traps designed to capture grus detached from granitic hill crests of an arid sonoran desert mountain range were placed prior to every precipitation event over a three year period just above rills that drain areas between 18 and 68 m 2 the slopes are underlain by moderately to strongly weathered granitic rocks to a depth of about a meter within this 3 year window a 1000 year precipitation event followed 27 days later by a 500 year event detached granitic grus in amounts far greater than previous storms capturing between 22 and 63 the average amount transported in the previous 59 rain events indicating the non linear nature of the response of grus detachment to precipitation intensity considering every precipitation event over a 3 year period no detachment occurred from events with less than 2 mm of total rainfall and only minimal erosion occurred from rainfall events with totals between 2 and 10 mm with durations typically less than 30 min detachment increased greatly with rain intensities of 36 mm h or more grus detachment from these arid crests increases with drainage area a higher percentage of exposed soil and steeper slopes 87 sr 86 sr ratios reveal that suspended sediment transported from hill crest to trap derives from recycled dust and not the local granite bedrock

pyrrhotite varieties from the 9 1 km deep borehole of the ktb project we used transmission electron microscopy tem to study pyrrhotite from the german continental deep drilling kontinentale tiefbohrung ktb project our goals were to determine the distribution of structure types with depth and to establish relationships between the bulk thermomagnetic behavior and the microstructures of pyrrhotite in samples from the deep section of the borehole 9080 m below surface which is equivalent to an in situ temperature of similar to 260 degrees c the dominant variety of pyrrhotite is 1c that has a mostly disordered vacancy distribution faint diffuse superstructure reflections in the selected area electron diffraction saed patterns indicate some nc like ordering occurs probably in small domains in addition to the disordered pyrrhotite a 5c type is also present according to bulk thermomagnetic measurements pyrrhotite grains from 9080 m are antiferromagnetic at room temperature we attribute this behavior to the dominance of the disordered 1c type in the upper section of the hole at 564 and 2325 m several pyrrhotite varieties occur but the 4c type is most common in agreement with the ferrimagnetic character of most pyrrhotite grains optical microscopy of pyrrhotite grains that are covered with a magnetic colloid reveal intergrown ferrimagnetic and antiferromagnetic lamellae tem images show that these grains are intergrowths of 4c 5c and nc types we interpret these microstructural variations to be responsible for the variation in magnetic properties within single pyrrhotite grains

modern extreme storms and the rainfall thresholds for initiating debris flows on the hyperarid western escarpment of the dead sea israel intense rainstorms cause debris flows on escarpments in hyperarid environments in contrast with more temperate environments there have been no direct observations on rainfall intensities and durations required for initiating debris flows in hyperarid environments here we report rainfall volume and intensities acquired by gauge and radar measurements for two successive storms along the hyperarid the first of the two analyzed storms occurred on 2 november 1995 during this storm two convective cells rained sequentially within a 5 h period at the lower reaches of the nahal david and the nahal arugot that dissects the western escarpment of the dead sea israel this storm triggered debris flows in 38 small 2 and high gradient drainage basins along the escarpment total rainfall volume and spatial distribution were determined by 10 cumulative rain gauges that were also used to calibrate rainfall intensity distributions from radar data for this storm region and landscape rainfall intensities exceeding 30 mm h for a duration of 1 h were required to initiate debris flows a second storm in the same area on 17 18 october 1997 allowed the evaluation of the results determined from the 1995 storm in this second more regional storm maximum rainfall intensities were 19 27 mm h for a duration of 45 min these values lower than the 30 mm h minimal threshold defined in the previous storm are consistent with the occurrence of only three debris flows the small number of debris flows resulted from the concentration of the highest intensities of rainfall on the desert plateau and not directly on top of the canyon walls most first to third order basins draining the dead sea escarpment contain evidence of zero to three late holocene 30 mm h and durations of at least 1 h the small number of debris flows that has occurred during the late holocene indicates that such events are rare at the scale of individual drainage basins

magnetic transition at 30 34 kelvin in pyrrhotite insight into a widespread occurrence of this mineral in rocks abstract a characteristic magnetic transition at 30 34 k is shown to provide a powerful tool for the identification of pyrrhotite with concentration down to 10 ppm through the same low temperature techniques as applied to magnetite and hematite extended down to liquid helium temperature a review of rock magnetic and petrological data on pyrrhotite suggests that this mineral should be considered as a major carrier of paleomatnetic signals unblocking temperature up to 350 c and extreme resistance against af may be encountered in fine grained pyrrhotite

tropical cyclone motion and evolution in vertical shear abstract the motion and the evolution of tropical cyclone like vortices in an environmental flow with vertical shear are investigated using a baroclinic primitive equation model the study focuses on the fundamental dynamics of a baroclinic vortex in vertical shear the influence of vortex structure and the role of diabatic heating the results show that the initial response of the vortex to the vertical shear is to tilt downshear as soon as the tilt develops the upper level anticyclonic and lower level cyclonic circulations begin to interact with each other as a result of these interactions the tilted axis of the vortex reaches a stable state after an initial adjustment which varies with the structure of the vortex its environmental flow shear and the cumulus convective heating the motion of an adiabatic vortex in vertical shear is controlled by both the steering of the environmental flow and vertical coupling mechanisms most of the vortices move with the environmental flow at about 650 hpa or

debris flows as geomorphic agents in the huachuca mountains of southeastern arizona abstract numerous debris flows occurred in the huachuca mountains of southeastern arizona during the summer rainy season of 1988 in areas that were burned by a forest fire earlier in the summer debris flows occurred following a major forest fire in 1977 as well suggesting a causal link between fires and debris flows abundant evidence of older debris flows preserved along channels and in mountain front fans indicates that debris flows have occurred repeteadly during the late quaternary in this environment soil development in sequences of debris flow deposits indicates that debris flows probably recur over time intervals of several hundred to a thousand years in individual drainage basins in the study area surface runoff in the steep drainage basins of the huachuca mountains is greatly enhanced following forest fires as the hillslopes are denuded of their vegetative cover water and sediment eroded from the hillslope regolith are rapidly introduced into the upper reaches of tributary channels by widespread rilling and slope wash during rainfall events this influx of water and sediment destabilizes regolith previously accumulated in the channel triggering debris flows that scour the channel to bedrock in the upper reaches following a debris flow the scoured trapezoidally shaped channel gradually assumes a swale shape and the percentage of exposed bedrock declines as material is introduced from the slopes debris flows do a tremendous amount of work in a very short time however and are the major channel forming events where the tributary channels enter larger trunk channels the debris flows serve as the main source of very coarse sediment the local slope and coarse particle distribution of the trunk channel depend on the competence of water flows in the channel to transport the material introduced by debris flows where the smaller channels drain directly to the mountain front debris flows create extensive alluvial fans which dominate the morphology of the basin range boundary time intervals between debris flows in the drainage basins of the huachuca mountains are probably controlled by complex interactions among climate forest fires and slope processes fires destroy the protective vegetation that stabilizes the upper catchment slopes and inhibits erosion however not every fire that burns a catchment causes debris flows because sufficient weathered material must accumulate in the upper channel reaches to initiate a large debris flow if such accumulation has not occurred the material introduced to a channel following a forest fire will move only a short distance down the channel thus the episodic nature of debris flows probably depends on rates of slope weathering and erosion which are in turn controlled by climate both directly and through vegetation and forest fires

lake levels and sequence stratigraphy of lake lisan the late pleistocene precursor of the dead sea lake lisan the late pleistocene precursor of the dead sea existed from 70 000 to 15 000 yr b p it evolved through frequent water level fluctuations which reflected the regional hydrological and climatic conditions we determined the water level of the lake for the time interval 55 000 15 000 cal yr b p by mapping offshore nearshore and fan delta sediments by application of sequence stratigraphy methods and by dating with radiocarbon and u series methods during the studied time interval the lake level fluctuated between 340 and 160 m below mean sea level msl between 55 000 and 30 000 cal yr b p the lake evolved through short term fluctuations around 280 290 m below msl punctuated at 48 000 43 000 cal yr b p by a drop event to at least 340 m below msl at 27 000 cal yr b p the lake began to rise sharply reaching its maximum elevation of about 164 m below msl between 26 000 and 23 000 cal yr b p then it began dropping and reached 300 m below msl at 15 000 cal yr b p during the holocene the lake corresponding to the present dead sea stabilized at ca 400 m below msl with minor fluctuations the hypsometric curve of the basin indicates that large changes in lake area are expected at above 403 and 385 m below msl at these elevations the lake level is buffered lake lisan was always higher than 380 m below msl indicating a significantly large water contribution to the basin the long and repetitious periods of stabilization at 280 290 m below msl during lake lisan time indicate hydrological control combined with the existence of a physical sill at this elevation crossing this sill could not have been achieved without a dramatic increase in the total water input to the lake as occurred during the fast and intense lake rise from 280 to 160 m below msl at 27 000 cal yr b p

sticky thermals evidence for a dominant balance between buoyancy and drag in cloud updrafts abstractthe vertical velocities of convective clouds are of great practical interest because of their influence on many phenomena including severe weather and stratospheric moistening however the magnitudes of forces giving rise to these vertical velocities are poorly understood and the dominant balance is in dispute here an algorithm is used to extract thousands of cloud thermals from a large eddy simulation of deep and tropical maritime convection using a streamfunction to define natural boundaries for these thermals the dominant balance in the vertical momentum equation is revealed cloud thermals rise with a nearly constant speed determined by their buoyancy and the standard drag law with a drag coefficient of 0 6 contrary to suggestions that cloud thermals might be slippery with a dominant balance between buoyancy and acceleration cloud thermals are found here to be sticky with a dominant balance between buoyancy and drag

experimental evaluation of magnetic interaction in pyrrhotite bearing samples pyrrhotite bearing metamorphic limestones have recently experienced an increasing relevance in paleomagnetic research simple univectorial remanences document the metamorphic uplift whereas more complex multicomponent ptrms may constrain its age for a successful application of the latter it is important to estimate the degree of magnetic interactions to ensure the additivity of individual ptrm segments we therefore have subjected the sized dispersed suite 5 250m of tte pyrrhotite to forc analysis and

paleoremanence dispersal across a transpressed archean terrain deflection by anisotropy or by late compression the quetico belt is an archean metasedimentary terrain sandwiched between greenstone subprovinces a single regional schistosity is subparallel to magnetic foliation defined by anisotropy of low field magnetic susceptibility ams and anisotropy of anhysteretic remanence aarm aligned micas are the primary cause of ams aligned pyrrhotite is the sole cause of aarm each magnetic subfabric is due to minerals that grew in overlapping intervals in the strain history their slight obliquity may be due to crystallization during noncoaxial strain magnetic fabric ellipsoids suggest varying severity of flattening very strong flattening on the northern boundary less severe on the southern boundary and least severe in the interior the interior and the southern boundary of the belt stretched horizontally and the shortening direction varies gradually from ns in the north to nnw in the south the paleomagnetic record carried by pyrrhotite shows characteristic remanences dispersed around a great circle subparallel to the regional schistosity and magnetic foliations late stress effects rotated paleoremanences into this pattern we discount deflection of the paleofield by anisotropy the pattern of dispersal indicates uniaxial oblate flattening of the region with nnw sse shortening late in the metamorphic cooling history 300 c this postdates schistosity ams and aarm fabrics but it is controlled by the same kinematic pattern

magnetic properties of synthetic analogues of pyrrhotite ore in the grain size range 1 24 µm summary iron and sulphur in proportions appropriate to fe 7 s 8 were reacted in evacuated quartz tubes for 24 hr at 500 c quenching produces predominantly hexagonal pyrrhotite whereas further prolonged annealing at 250 c produces monoclinic pyrrhotite we mainly report the properties of material cooled from 500 ca t 10 c min 1 which is predominantly monoclinic but probably contains hexagonal pyrrhotite together with pyrite fes 2 this material which we refer to as non ideal pyrrhotite may be a better analogue of pyrrhotite ore than ideal synthetic monoclinic pyrrhotite the samples were characterized by x ray mossbauer evect and thermomagnetic analyses the slow cooled non ideal monoclinic pyrrhotite exhibits thermal stability intermediate between monoclinic and hexagonal pyrrhotites one striking observation is that the deviation from ideal monoclinic pyrrhotite increases with decreasing particle size particles about 1 mm in size have a low saturation magnetization value of about 6 am2 kg 1 indicating a lower concentration of ferrimagnetic monoclinic pyrrhotite saturation magnetization 18 am2 kg 1 than particles of about 6 mm and above saturation magnetization 12 am2 kg 1 on the other hand magnetization process parameters coercive force ratio of saturation remanence to saturation magnetization coercive force of remanence median destructive and inductive fields the magnetic susceptibility follow well behaved power law dependences on particle size similar to monoclinic pyrrhotite magnetic domain patterns in the slow cooled non ideal pyrrhotite are similar in type and style to those observed in synthetic monoclinic pyrrhotite and in natural pyrrhotite particles in rocks dynamic observations of domain walls in changing external alternating and direct magnetic fields are consistent with macroscopic obser vations of magnetization change with field the critical size for the monodomain multidomain transition in synthetic monoclinic pyrrhotite at about 1 mm is essentially the same as that previously determined for natural pyrrhotite grains in rocks the observations suggest that the domain walls lie normal to the c axis of the structure consistent with the known magnetocrystalline anisotropy symmetry of monoclinic pyrrhotite the type and style of the magnetic microstructures of hexagonal pyrrhotite are quite diverent from those of monoclinic pyrrhotite the domain patterns are on a much smaller scale wavy and sometimes resemble those of a hexagonal material such as magnetoplumbite or cobalt

increased frequency of torrential rainstorms during a regional late holocene eastern mediterranean drought identifying climates favoring extreme weather phenomena is a primary aim of paleoclimate and paleohydrological research here we present a well dated late holocene dead sea sediment record of debris flows covering 3 3 to 1 9 cal ka bp twenty three graded layers deposited in shallow waters near the western dead sea shore were identified by microfacies analysis these layers represent distal subaquatic deposits of debris flows triggered by torrential rainstorms over the adjacent western dead sea escarpment modern debris flows on this escarpment are induced by rare rainstorms with intensities exceeding 30 mm h 1 for at least one hour and originate primarily from the active red sea trough synoptic pattern the observed late holocene clustering of such debris flows during a regional drought indicates an increased influence of active red sea troughs resulting from a shift in synoptic atmospheric circulation patterns this shift likely decreased the passages of eastern mediterranean cyclones leading to drier conditions but favored rainstorms triggered by the active red sea trough this is in accord with present day meteorological data showing an increased frequency of torrential rainstorms in regions of drier climate hence this study provides conclusive evidence for a shift in synoptic atmospheric circulation patterns during a late holocene drought

reconstructing low levels of lake lisan by correlating fan delta and lacustrine deposits abstract reconstruction of paleo shorelines of lake lisan the late pleistocene precursor of the dead sea is based on sequence stratigraphy of fan delta and lacustrine deposits that are exposed at the perazim valley southwest of the dead sea the shoreline sediments are physically correlated with lacustrine aragonites their ages are determined by u series dating to establish a lake level curve for the time interval between 55 and 35 kyr during most of this period lake lisan was at a relatively low level which fluctuated between 280 and 290 m below sea level m bsl the minimum lake stand 330 m bsl was reached at 47 kyr and lasted for 3 4 kyr this episode is marked by a depositional hiatus in the section and formation of an erosional channel the studied period correlates with the global marine isotope stage 3 the low stand of lake lisan during most of this period indicates relative dry climatic conditions in the region

domain structure of natural fine grained pyrrhotite in a rock matrix diabase the domain structure of natural pyrrhotite grains in a devonian diabase was studied with the bitter pattern technique examples are shown of the domain structure of large d 100 m true multidomain grains intermediate 10 d 40 m pseudo single domain grains and ore grains with less than four domains down to the transition from the two domain to the single domain state plate shaped domains prevail for all sizes of ore grains closure domains are only rarely formed non magnetic inclusions and surface irregularities impede the domain wall mobility as expected resulting in an often quite considerable spread of muscopic coercive forces in the large grains intergrowths of chemically only slightly different phases of pyrrhotite which cannot be distinguished in a reflected light muscope seem to be responsible for entirely stationary pseudo domain walls in low dc fields domain wall displacements as well as spin rotations within the basal plane of easy magnetization are probably the dominant magnetization processes in pseudo single domain and multidomain particles

effects of under resolved convective dynamics on the evolution of a squall line abstractsimulations of a squall line observed on 20 may 2011 during the midlatitude continental convective clouds experiment mc3e using 750 and 250 m horizontal grid spacing are performed the h

tropical convection the effects of ambient vertical and horizontal vorticity we present a series of idealized numerical model experiments to investigate aspects of deep convection in tropical depressions including the effects of boundary layer wind structure on storm structure especially on vertical vorticity production and updraught splitting and the combined effects of horizontal and vertical shear on vertical vorticity production with and without background rotation in warm cored disturbances such as tropical depressions the vertical shear and horizontal vorticity change sign at some level near the top of the boundary layer so that unlike in the typical middle latitude supercell storm the tilting of horizontal vorticity by a convective updraught leads not only to dipole patterns of vertical vorticity but to a reversal also in sign of the updraught rotation with height this finding has implications for understanding the merger of convectively induced vorticity anomalies during vortex evolution ambient cyclonic horizontal shear and or cyclonic vertical vorticity favour amplification of the cyclonically rotating gyre of the dipole consistent with an earlier study storm splitting occurs in environments with pure horizontal shear as well as pure vertical shear but the morphology of splitting is different in both situations splitting is found to require a relatively unstable sounding and relatively strong wind shear

characteristics of convective processes and vertical vorticity from the tropical wave to tropical cyclone stage in a high resolution numerical model simulation of tropical cyclone fay 2008 abstractthe statistics of convective processes and vertical vorticity from the tropical wave to tropical cyclone stage are examined in a high resolution simulation of tropical cyclone fay 2008 the intensity of vertical velocity follows approximately the truncated lognormal distribution in the model simulation which is consistent with previous observational studies the upward motion at the pregenesis stage is weaker compared to mature hurricanes or midlatitude thunderstorms the relatively strong upward velocities occupying a small areal fraction make a substantial contribution to the upward mass and moisture fluxes and condensation it is also found that upward motion and downward motion both intensify with time but the former is stronger than the latter and the mean vertical motion and the mean vertical mass flux thus increase with time by contrast the maximum anticyclonic vorticity is comparable to the maximum cyclonic vorticity in magnitude both cyclonic vorticity and anticyclonic vorticity in

vertical motion characteristics of tropical cyclones determined with airborne doppler radial velocities abstract vertical motions in seven atlantic hurricanes are determined from data recorded by doppler radars on research aircraft the database consists of doppler velocities and reflectivities from vertically pointing radar rays collected along radial flight legs through the hurricane centers the vertical motions are estimated throughout the depth of the troposphere from the doppler velocities and bulk estimates of particle fallspeeds portions of the flight tracks are subjectively divided into eyewall rainband stratiform and other regions characteristics of the vertical velocity and radar structure are described as a function of altitude for the entire dataset and each of the four regions in all of the regions more than 70 of the vertical velocities range from 2 to 2 m s 1 the broadest distribution of vertical motion is in the eyewall region where 5 of the vertical motions are 5 m s 1 averaged over the entire dataset the mean vertical velocity is upward at all altitudes mean downward mot

cloud resolving simulations of deep convection over a heated mountain abstract cloud resolving numerical simulations of airflow over a diurnally heated mountain ridge are conducted to explore the mechanisms and sensitivities of convective initiation under high pressure conditions the simulations are based on a well observed convection event from the convective and orographically induced precipitation study cops during summer 2007 where an isolated afternoon thunderstorm developed over the black forest mountains of central europe but they are idealized to facilitate understanding and reduce computational expense in the conditionally unstable but strongly inhibited flow under consideration sharp horizontal convergence over the mountain acts to locally weaken the inhibition and moisten the dry midtroposphere through shallow cumulus detrainment the onset of deep convection occurs not through the deep ascent of a single updraft but rather through a rapid succession of thermals that are vented through the mountain convergence zone into the deepening cloud mass emerging t

alpine debris flows triggered by a 28 july 1999 thunderstorm in the central front range colorado on 28 july 1999 about 480 alpine debris flows were triggered by an afternoon thunderstorm along the continental divide in clear creek and summit counties in the central front range of colorado the thunderstorm produced about 43 mm of rain in 4 h 35 mm of which fell in the first 2 h several debris flows triggered by the storm impacted interstate highway 70 u s highway 6 and the arapahoe basin ski area we mapped the debris flows from color aerial photography and inspected many of them in the field three processes initiated debris flows the first process initiated 11 of the debris flows and involved the mobilization of shallow landslides in thick often well vegetated colluvium the second process which was responsible for 79 of the flows was the transport of material eroded from steep unvegetated hillslopes via a system of coalescing rills the third which has been termed the firehose effect initiated 10 of the debris flows and occurred where overland flow became concentrated in steep bedrock channels and scoured debris from talus deposits and the heads of debris fans these three processes initiated high on steep hillsides 30 in catchments with small contributing areas 8000 m2 however shallow landslides occurred on slopes that were significantly less steep than either overland flow process based on field observations and examination of soils mapping of the northern part of the study area we identified a relation between the degree of soil development and the process type that generated debris flows in general areas with greater soil development were less likely to generate runoff and therefore less likely to generate debris flows by the firehose effect or by rilling the character of the surficial cover and the spatially variable hydrologic response to intense rainfall rather than a threshold of contributing area and topographic slope appears to control the initiation process in the high alpine of the front range because debris flows initiated by rilling and the firehose effect tend to increase in volume as they travel downslope these debris flows are potentially more hazardous than those initiated by shallow landslides which tend to deposit material along their paths

downward remagnetization of a 74 m thick zone in lake sediments from palaeo lake idaho nw united states locating the gauss matuyama geomagnetic boundary within a dual polarity zone

mesoscale and convective scale characteristics of mature hurricanes part ii inner core structure of hurricane allen 1980 abstract the eyewall structure of hurricane alien is examined from analyses of multiple aircraft data on two days 5 and 8 august 1980 these data sets are unique in that for the first time three instrumented aircraft executed coordinated radial penetrations of the eyewall at multiple levels the data collected on 5 august illustrate the persistence of various features on horizontal scales 10 km over several hours composite cross sections constructed from the 8 august data show similar structure although the eye diameter had decreased to less than half that of 5 august the convergence of air in the eyewall was highly two dimensional this convergence supported organized ascent that was along the inner edge of the high reflectivity region and displaced inward several kilometers from the radius of maximum wind rmw a mean eyewall updraft of 5 6 m s 1 is computed from integration of the two dimensional continuity equation embedded within the two dimensional eyewall were cores of high reflectivity t

conditions for generation of fire related debris flows capulin canyon new mexico comparisonoftheresponsesofthreedrainagebasinsburnedbythedomefireof1996innewmexicoisusedtoidentifythe hillslope channelandfirecharacteristicsthatindicateasusceptibilityspecificallytowildfire relateddebrisflow summer thunderstorms generated three distinct erosive responses from each of three basins the capulin canyon basin showed widespreaderosivesheetwashandrillingfromhillslopes andseverefloodingoccurredinthechannel thenorthtributary basin exhibited extensive erosion of the mineral soil to a depth of 5 cm and downslope movement of up to boulder sized material andatleastonedebrisflowoccurredinthechannel negligiblesurfacerunoffwasobservedinthesouthtributary basin thenegligiblesurfacerunoffobservedinthesouthtributarybasinisattributedtothelimitedextent andseverityof the fire in that basin the factors that best distinguish between debris flow producing and flood producing drainages are drainage basin morphology and lithology a rugged drainage basin morphology an average 12 per cent channel gradient andsteep roughhillslopescoupledwithcolluviumandsoilweatheredfromvolcaniclasticandvolcanicrockspromotedthe generation of debris flows a less rugged basin morphology an average gradient of 5 per cent and long smooth slopes mantled with pumice promoted flooding flood and debris flow responses were produced without the presence of waterrepellentsoils thecontinuityandseverityoftheburnmosaic theconditionoftheriparianvegetation theconditionofthe fibrous root mat accumulations of dry ravel and colluvial material in the channel and on hillslopes and past debris flow activity appearedtohavelittlebearingonthedistinctiveresponsesofthebasins publishedin2000byjohnwiley sons ltd

sedimentologic and geomorphic variations in storm generated alluvial fans howgill fells northwest england in june 1982 a storm with a return period greater than 100 yr but lasting less than 2 5 hr destabilized hillslopes and produced a suite of geomorphologically and sedimentologically diverse alluvial fans thirteen major fans were deposited at the tributary junctions between small 2 catchments and two north flowing headwater streams of the river lune northwest england storm generated fans spread over or became inset into older stable fans and produced localized vertical accretion of as much as 3 m and lateral accretion of as much as 100 m sedimentary processes operating during deposition involved debris flow transitional flow and streamflow six facies types are recognized on the basis of depositional topography sedimentary texture and fabric and matrix content viscous debris flow d1 dilute debris flow d2 transitional flow t1 fluvial bars and lobes s1 s2 and fluvial sheet gravels s3 regionally streamflow deposition prevails over debris flow deposition and type s3 facies has the greatest areal extent temporal and spatial variations in facies deposition during the storm however resulted from water sediment ratio variations fan deposition involved an early phase of debris flow to transitional flow due to large inputs of sediment from hillslope failures this was followed by a systematic change to more dilute conditions resulting in streamflow deposition and eventually in channel incision a significant amount of geomorphic work and complex variations in sedimentary processes during the storm resulted in part from extensive overland flow and hillslope destabilization discriminant analyses indicate that catchment size channel gradient and percentage of area eroded during the storm controlled whether debris flow or streamflow facies dominated a fan sequence smaller steeper catchments had a greater percentage of the area yielding sediment and are dominanted by debris flows whereas larger catchments produced more runoff resulting in dilution and streamflow the results indicate that the facies sequences and fan entrenchment in the howgill fells which are typically considered products of longer term climatic change or tectonics in other localities are here primarily affected by thresholds related to catchment geomorphology by the type of sediment available and by the position within the storm cell

late quaternary weathering erosion and deposition in nahal yael israel an impact of climatic change on an arid watershed in their seminal paper in 1979 bull and schick proposed a conceptual model for the geomorphic response to pleistocene to holocene climate change based on the hyperarid nahal yael watershed in the southern negev desert in this model the change from semiarid late pleistocene to hyperarid early holocene climates reduced vegetation cover increased the yield of sediment from slopes and accelerated aggradation of terraces and alluvial fans the model is now over 30 yr old and during this time chronologic paleoenvironmental and hydrogeomorphic research has advanced here we reevaluate the model using data acquired in nahal yael over the 30yr since the original model was proposed recent studies indicate that the late pleistocene climate was hyperarid and a transition from semiarid to hyperarid climates did not occur the revised chronology reveals a major 35 20 ka episode of accelerated late pleistocene sediment production on slopes with lower rates probably already at ca 50ka due to increased frequency of wetting drying cycles caused by frequent extreme storms and floods between 35 and 27 ka without lag time these sediments were transported and aggraded in depositional landscape components fluvial terraces and alluvial fans this intensified sediment production and delivery phase is unrelated to the pleistocene holocene transition the depositional landforms were rapidly incised between 20 and 18 ka since and or soon after this last glacial maximum lgm incision most material leaving the basin originated from sediments stored in depositional landforms and was not produced from bedrock using these new data we propose a revision to the bull and schick model in this hyperarid environment our revision suggests that the model should include the frequent storms and floods responsible for a late pleistocene pulse of intense weathering due to numerous cycles of wetting and drying on slopes and coeval sediment transport to fluvial terraces and alluvial fans we also discuss the common use and pitfalls of using the bull and schick conceptual model to explain observations in diverse arid environments usually without sufficient data on basin specific stratigraphic chronologic paleoenvironmental and paleoclimatic information

fire and alluvial chronology in yellowstone national park climatic and intrinsic controls on holocene geomorphic processes we employed a systemwide approach a large and robust set of radiocarbon ages and modern process analogs to interpret the holocene history of forest fire related sedimentation and overall alluvial activity in northeastern yellowstone national park debris flow and flood events following the 1988 fires provided facies models for interpreting the stratigraphic record of fire related sedimentation within valley side alluvial fans of soda butte creek fire related deposits make up approximately 30 of the late holocene fan alluvium fifty 14 c ages on fire related events cluster within the intervals of 3300 2900 2600 2400 2200 1800 and 1400 800 yr b p and suggest earlier episodes of large fires and fan aggradation around 7500 5500 and 4600 4000 yr b p a major pulse of fire related debris flow activity between 950 and 800 yr b p coincided with the height of the widely recognized medieval warm period ca a d 1050 1200 instrumental climate records over the last 100 yr in yellowstone imply that the intensity and interannual variability of summer precipitation are greater during warmer periods enhancing the potential for severe short term drought major forest fires and storm generated fan deposition along lower soda butte creek fill cut terrace treads were created by lateral migration of channels and accumulation of overbank sediments ca 8000 yr b p terrace level t1a 7000 5600 t1b 3100 2600 t2 2000 1300 t3 and post 800 yr b p t4 these periods coincide with overbank sedimentation on slough creek and the lamar river but alternate with intervals of fire related fan deposition implying a strong climatic control local paleoclimatic data suggest cooler effectively wetter conditions during terrace tread formation in warmer drier intervals reduced average runoff in axial streams results in meander belt narrowing concurrent channel incision may be caused by infrequent large floods greater resistance to downcutting however allowed fewer terraces to be formed along slough creek and the lamar river alluvial systems in northeastern yellowstone show a clear response to millennial scale climatic cycles wherein alluvial fans aggrade and prograde over flood plains in drier periods axial streams widen their flood plains and trim back the fans during wetter periods small scale climatic fluctuations of the holocene thus had substantial impact on postglacial landscapes in northeastern yellowstone

domain wall dynamics in 4c pyrrhotite at low temperature summary monoclinic 4c pyrrhotite fe7s8 is ferrimagnetic due to an ordered defect structure with alternating vacancy and vacancy free sublattices its low temperature magnetic transition near 35k is characterized by the distinct increase in coercivity and remanent magnetization the increase of these parameters has been attributed to changes in the domain wall structure we present static and dynamic magnetization data of a powder sample to study the domain wall dynamics across the low temperature transition the amplitude dependent ac susceptibility and the ferromagnetic resonance spectroscopy indicate that the hardening of the domain wall pinning at the transition occurs simultaneously with the decrease in initial saturation remanent magnetization these two effects are explained by the enhanced inhomogeneity of the bulk material caused by the persistency of the ordered vacancies and by newly formed defects due to localized distortion of fe ii sites in the vacancy free sublattice the generated localized defects are the link between the domain wall dynamics and the low temperature transition in 4c pyrrhotite

secondary eyewall formation and eyewall replacement cycles in a simulated hurricane effect of the net radial force in the hurricane boundary layer abstractmultiple secondary eyewall formations sefs and eyewall replacement cycles ercs are simulated with the fifth generation pennsylvania state university psu national center for atmospheric research ncar mesoscale model mm5 at horizontal grid spacing of 0 67 km the simulated hurricane is initialized from a weak synthetic vortex in a quiescent environment on an f plane after spinup and rapid intensification the hurricane enters a mature phase during which the intensity change is relatively slow convective clouds then organize into a ring with a secondary tangential wind maximum at radii beyond the hurricane s primary eyewall this secondary eyewall se then contracts and strengthens the primary eyewall weakens and is eventually replaced by the se the hurricane grows in size and the radius of maximum wind rmw increases as similar ercs repeat 5 times during the simulation two existing hypotheses on sef are evaluated using the simulation output then model diagnostics are used to revea

volumetric analysis and hydrologic characterization of a modern debris flow near yucca mountain nevada abstract on july 21 or 22 1984 debris flows triggered by rainfall occurred on the southern hillslope of jake ridge about 6 km east of the crest of yucca mountain nevada rain gages near jake ridge recorded 65 mm and 69 mm on july 21 and 20 mm and 17 mm on july 22 rates of rainfall intensity ranged up to 73 mm h on the twenty first and 15 mm h on the twenty second digital elevation models with 2 0 m grid node spacing measured from pre storm and post storm aerial stereo photographs were used to map hillslope erosion and the downslope distribution of debris volumetric calculations indicate that about 7040 m 3 of debris was redistributed on the 49 132 m 2 hillslope study area during the two day storm period about 4580 m 3 65 of the eroded sediment was deposited within the study area and the remaining 35 was deposited outside the study area in a short tributary to fortymile wash and in the wash itself the maximum and mean depths of erosion in the study area were about 1 8 m and 5 cm respectively the mean depths of erosion on the upper and middle hillslope were 27 cm and 4 cm respectively the mean depth of deposition on the lower hillslope was 16 cm analysis of the values of cumulative precipitation in the context of the precipitation frequency atlas of the national oceanic and atmospheric administration indicates that precipitation from the main storm on july 21 was more than double that expected on average once during a 100 year period the relations of precipitation intensity duration developed from data recorded at a nearby precipitation gage indicate a storm interval of 500 years or greater the amount of erosion caused by such a storm is primarily dependent on three variables storm intensity development of the drainage network on the hillslope and the amount of available colluvium additionally the erosive ability of successive storms of equal intensity will decrease because such storms would tend to progressively isolate and reduce the amount of colluvium available the preservation of pleistocene deposits on hillslopes of yucca mountain in general indicates that erosional events that strip 5 of the available hillslope colluvium must be quite rare we conclude that the recurrence interval of an erosional event comparable to the july 1984 event is probably much longer than 500 years

mineralogical change and self reversed magnetizations in pyrrhotite resulting from partial oxidation geophysical implications abstract low field thermomagnetic studies performed on natural and synthetic pyrrhotite samples showed that a very low oxygen fugacity is already sufficient to start the transformation into magnetite at 500 c the quantity of magnetite produced is a function of the oxidation time during which the temperature is maintained the remanent magnetization acquired by the magnetite during its formation in the applied field is a chemical remanent magnetization crm in the case of partial oxidation the close coexistence of pyrrhotite and magnetite in a single grain may produce a self reversed thermoremanent magnetization in pyrrhotite upon cooling in zero field if the initial pyrrhotite is hexagonal oxidation is necessary to obtain the transformation into the monoclinic variety which may also show the self reversed trm in contrast to the natural samples in synthetic pyrrhotite the magnetite produced by oxidation carries a crm but shows no self reversal upon cooling to room temperature a model for a self reversal and structural change processes following oxidation is presented in which the size and the shape of pyrrhotite grains play an important role the consequences for palaeomagnetism and magnetic anomaly interpretation are discussed

did plinian eruptions in california lead to debris flows in nevada an intriguing stratigraphic connection a common association of thin late holocene mono and inyo crater tephra beds buried by debris flows within a 250 km long corridor of western nevada suggests that there has been at times a genetic link between these two otherwise independent processes the unambiguous depositional relations and the undisturbed character of the tephra beds at more than 20 sites indicate that tephra deposition was often followed by burial under debris flows produced by intense precipitation considering that average return periods are hundreds of years for such storms it is highly improbable that this stratigraphic association is random coincidence we propose that the most plausible explanation for this association is that some plinian ash columns produced intense thunderstorms resulting in large debris flows that buried the tephra beds

a large eddy simulation study of moist convection initiation over heterogeneous surface fluxes this study uses large eddy simulations to investigate processes of moist convection initiation ci over heterogeneous surface fluxes surface energy balance is imposed via a 1808 phase lag of the surface moisture flux relativetothesensibleheatflux suchthattherelativelywarmsurfaceisrelativelydry andtherelatively coolsurfaceisrelativelywet as shownin previoussimulations amesoscalecirculationformsin thepresence of surface flux heterogeneity which coexists with turbulent fluctuations the mesoscale convergence zone of this circulation develops over the relatively warm surface and this is where clouds first form convection initiation occurs sooner as the amplitude of the heterogeneity increases and as the surface moisture increases i e bowen ratio decreases shallow clouds initiate when boundary layer heights zi become greater than the lifting condensation level lcl deep precipitating clouds initiate when the lcl and level of free convection lfc are roughly the same when averaged over the relatively warm surface which is equivalent tothemeanconvectiveinhibition cin becomingnearlyzero fromtheperspectiveoftheentire mesoscale domain cases with strongly heterogeneous surfaces have a wider distribution of both zi and lcl thus a comparison of zi with lcl over a mesoscale area i e within one mesoscale model grid box may lead to misleading conclusions about ci and cloud base height it is also shown that as the amplitude of the surfaceflux heterogeneity increases the mesoscale convergence zone becomes narrower and stronger furthermore ci occurs earlier over relatively wet surfaces partly because turbulent eddies are more vigorous owing to slightly greater buoyancy