the evolution of regional seismicity between large earthquakes 1 we describe a simple model that links static stress coulomb modeling to the regional seismicity around a major fault unlike conventional coulomb stress techniques which calculate stress changes we model the evolution of the stress field relative to the failure stress background seismicity is attributed to inhomogeneities in the stress field which are created by adding a random field that creates local regions above the failure stress the inhomogeneous field is chosen such that when these patches fail the resulting earthquake size distribution follows a gutenburg richter law immediately following a large event the model produces regions of increased seismicity aftershocks where the overall stress field has been elevated and regions of reduced seismicity where the stress field has been reduced stress shadows the high stress levels in the aftershock regions decrease due to loading following the main event combined with the stress shadow from the main event this results in a broad seismically quiet region of lowered stress around the epicenter pre event seismicity appears as the original stress shadows finally fill as a result of loading the increase in seismicity initially occurs several fault lengths away from the main fault and moves inward as the event approaches as a result of this effect the seismic moment release in the region around the future epicenter increases as the event approaches synthetic catalogues generated by this model are virtually indistinguishable from real earthquake sequences in california and washington

numerical diagnosis of a small quasi tropical cyclone over the western mediterranean dynamical vs boundary factors a small quasi tropical cyclone occurred on 12 september 1996 over the western mediterranean intense convective activity over the region during this period also produced a tornado outbreak in the balearic islands and torrential precipitation over eastern mainland spain mesoscale model runs properly simulate the cyclone formation and show convection and heavy precipitation following the cyclone trajectory during its eastward progression a sensitivity study examining the upper level dynamic forcing latent and sensible heat fluxes from the sea and orography is conducted a potential vorticity pv inversion technique is used to reduce the amplitude of the upper level trough in the model initial conditions the results show that neither the orography nor the sensible heat flux from the sea play a significant role during this particular cyclone development conversely both the latent heat flux and the upper level trough are shown to be crucial for low level cyclogenesis features common to hurricane like polar lows are found for the cyclone and an analysis of the precise role of the upper level structures and the convective development is conducted a factor separation technique is used to determine the individual effects of the aforementioned factors as well as their interaction at the first stage of the cyclogenesis the upper level pv anomaly enhanced the low level circulation of the synoptic scale low and enhanced the latent heat flux from the sea during its mature stage the circulation associated with the small scale cyclone enhanced the latent heat flux from the sea thereby helping to maintain the development of deep convection and inducing further cyclone deepening by diabatic heating this scenario has many similarities with the air sea interaction instability mechanism thus the joint action of the upper level anomaly as a spin up agent and the latent heat flux as a sustainer of convection emerges as the primary factor for the genesis and evolution of the small quasi tropical cyclone copyright 2003 royal meteorological society

sensitivity of a heavy rain producing western mediterranean cyclone to embedded potential vorticity anomalies the development and track of a surface cyclone that produced heavy precipitation in the western mediterranean region on 28 29 september 1994 is numerically simulated using a mesoscale model diagnostic calculations reveal that surface pressure falls and upward motion occur in response to a well defined pattern of upward quasi geostrophic forcing at all tropospheric levels in addition convective instability and low tropospheric water vapour flux convergence are significant over the western mediterranean and therefore the environment is highly supportive for convection development the appreciable dynamical forcing at upper levels appears to be associated with two positive potential vorticity pv anomalies that are embedded within the large scale trough and rotate about each other motivated by the fact that the small scale features of the pv field are more prone to analysis or forecast error than the large scale components a sensitivity study is conducted in order to analyse the dependence of the mesoscale forecast on the initial intensity and position of the two embedded pv centres this is accomplished by first applying a piecewise pv inversion technique which allows the balanced flow associated with each pv centre to be calculated and then the inverted mass and wind fields are used to modify the model initial conditions eight simulations are run after doubling or removing one or both anomalies sensitivity to intensity and eight other simulations after displacing the anomalies towards or away from the iberian peninsula sensitivity to position the results exhibit a clear dependence of the track and shape of the surface cyclone and its associated pattern of low tropospheric warm air advection on the characteristics of the pv anomalies therefore spatial details of the mesoscale forecast are shown to be highly sensitive to the precise structure of the upper level dynamic forcing nevertheless for the full set of arbitrarily defined initial conditions one or several low pressure systems develop in the western mediterranean area and heavy precipitation always occurs on the other hand there is an overall tendency of the simulations to favour cyclone development leeward of the atlas mountain range and local rainfall enhancements over the exposed mountains of eastern spain the relative roles of the orography and sea surface latent heat flux versus the action of the upper level pv centres are examined by means of additional simulations

models of coastally trapped disturbances during the spring and summer the climatological northerly flow along the u s west coast is occasionally interrupted by transitions to southerly flow that have a limited offshore scale and appear to be manifestations of marine layer flow that is rotationally trapped by the coastal mountains existing climatological and observational studies suggest that a synoptic scale offshore flow initiates these coastally trapped disturbances ctds using idealized simulations produced with a 3d nonhydrostatic model the authors find that an imposed offshore flow will produce ctds in idealized coastal environments the imposed flow first weakens the prevailing northerly flow in the marine layer and lowers the pressure at the coast the marine layer flow around this low pressure evolves toward geostrophic balance but is retarded as it encounters the coastal mountains to the south of the low and subsequently deepens the marine layer in this region the elevated marine layer then begins progressing northward as a kelvin wave and later may steepen into a bore or gravity current this progression being the ctd many observed features accompanying ctds are found in the numerical simulations including the formation of a mesoscale pressure trough offshore and deep southerlies in the ctd at the coast stability in the atmosphere above the marine layer can give rise to topographically trapped rossby waves and stronger ctd winds in these stable conditions propagation of wave energy away from the disturbance does not preclude strong quasi steady propagating ctds

lgm ice sheet extent in the weddell sea evidence for diachronous behavior of antarctic ice sheets abstract inaccessibility due to harsh weather conditions and perennial sea ice has resulted in the weddell sea being one of the more under studied regions of antarctica re examination of existing cores and unpublished multibeam bathymetric data provide new insight into the lgm configuration of the ice sheet in the region sediment cores from the eastern continental shelf where the east antarctic ice sheet eais drains display a retreat stratigraphy with distal glacimarine sediments overlying proximal glacimarine sediments and till the distinction between distal and proximal glacimarine sediments is based on degrees of marine influence based on grain size distributions and foraminiferal abundance and diversity glacimarine sediments yielded ams radiocarbon ages that span the past 30 476 cal yr bp indicating that retreat of the eais from the continental shelf occurred prior to the lgm multibeam swath bathymetry data show mega scale glacial lineations in two troughs on the southern continental shelf which indicates the existence of two ice streams draining the west antarctic ice sheet wais more subtle lineations within filchner trough imply more sluggish flow across bedrock and older strata within this trough although there are no radiocarbon ages to absolutely constrain the timing of this grounding event on the southern continental shelf we interpret the lineations as lgm age based on their pristine nature this interpretation is consistent with results from other sectors of the west antarctic continental shelf where compelling evidence for significant wais advance during the lgm exists in the weddell sea this apparent diachronous behavior of the eais and wais is consistent with results from onshore studies

how do asperities fracture an experimental study of unbroken asperities abstract the fracture of a shear fault containing several unbroken asperities in a granitic porphyry is examined in detail via acoustic emission ae data collected by a high speed multi channel waveform recording system the experimental results reveal that a quasi static nucleation of the shear faulting corresponds to the fracture of coupled asperities on the fault plan aes caused by the fracture of individual asperities exhibit similar characteristics to the sequence for natural earthquakes including foreshock mainshock and aftershock events foreshocks initiated at the edge of the asperity occur with an event rate that increases according to a power law of the temporal distance to the mainshock and with a decreasing b value from 1 1 to 0 5 one or a few mainshocks then initiate at the edge of the asperity or the front of the foreshocks the aftershock period is characterized by a remarkable increase and subsequent gradual decrease in b value and a decreasing event rate obeying the modified omori law which has been well established for earthquakes the fracture of neighboring asperities is then initiated after the mainshock of a particular asperity presumably due to redistribution of the strain energy accumulated within an asperity which is released by the mainshock resulting in enhancement of the stress concentration around the nearest neighboring intact asperities the progressive fracturing of multiple coupled asperities during the nucleation of shear faulting results in short term precursory fluctuations in both b value and event rate which may prove useful information in the prediction of failure of the main fault plane of seismic earthquakes

sustained increase in ice discharge from the amundsen sea embayment west antarctica from 1973 to 2013 we combine measurements of ice velocity from landsat feature tracking and satellite radar interferometry and ice thickness from existing compilations to document 41 years of mass flux from the amundsen sea embayment ase of west antarctica the total ice discharge has increased by 77 since 1973 half of the increase occurred between 2003 and 2009 grounding line ice speeds of pine island glacier stabilized between 2009 and 2013 following a decade of rapid acceleration but that acceleration reached far inland and occurred at a rate faster than predicted by advective processes flow speeds across thwaites glacier increased rapidly after 2006 following a decade of near stability leading to a 33 increase in flux between 2006 and 2013 haynes smith pope and kohler glaciers all accelerated during the entire study period the sustained increase in ice discharge is a possible indicator of the development of a marine ice sheet instability in this part of antarctica key points sustained ase mass flux increase 77 since 1973 thwaites accelerated by 33 during the last 6 years speed changes are pervasive and rapid major implications for ice flow modeling 2014 american geophysical union all rights reserved

shear margins in glaciers and ice sheets analytical and numerical techniques are used to examine the flow response of a sloped slab of power law fluid power n subjected to basal boundary conditions that vary spatially across the flow direction as for example near an ice stream margin with planar basal topography the primary assumption is that basal shear stress is proportional to the basal speed time a spatially variable slip resistance the ratio of mean basal speed to the speed originating from shearing through the thickness denoted as r gives a measure of how slippery the bed is the principal conclusion is that a localized disturbance in slip resistance affects the basal stress and speed in a zone spread over a greater width of the flow in units of ice thickness h the spatial scale of spreading is proportional to a single dimensionless number r n r n 1 1 n 1 derived from n and r the consequence for a shear zone above a sharp jump in slip resistance is that the shearing is spread out over a boundary layer with a width proportional to r n for an ice stream caused by a band of low slip resistance with a half width of wh the margins influence velocity and stress in the central part of the band depending on r n in comparison to w three regimes can be identified which for n 3 are quantified as follows low r defined as r 3 1w for which the boundary layers from both sides bridge across the full flow width and the driving stress in the center is supported almost entirely by side drag intermediate r for which the driving stress in the center is supported by a combination of basal and side drag shear zones that are narrower than predicted on the basis of this theory r 3 would require localized softening of the ice to explain the concentration of deformation at a shorter scale

depiction of upper lower vortex interaction associated with extratropical cyclogenesis abstract using observed data and model simulations an attempt is made to verify that baroclinic instability can be viewed as an interaction and mutual amplification of a pair of upper and lower tropospheric potential vorticity pv perturbations this view has recently been advanced by hoskins et al and mcintyre two episodes from march and may 1989 encompassing two lee cyclogenetic events east of the rocky mountains and one over the central gulf states are selected to demonstrate this concept in order to depict the low level pv maximum which forms infinitely thin sheets of infinite pv the display of pv in cartesian space is replaced by a display of absolute vorticity in isentropic space perspective computer drawings of iso surfaces of absolute vorticity in three dimensional space are found to be a convenient means of conveying the desired information

development and tropical transition of an alpine lee cyclone part i case analysis and evaluation of numerical guidance abstract the development and tropical transition tt of a subsynoptic scale cyclone in the gulf of genoa during the mesoscale alpine project map demonstration of probabilistic hydrological and atmospheric simulation of flood events in the alpine region d phase project is investigated using analyses and model simulations cyclogenesis occurs in association with the passage of a synoptic scale trough and attendant surface cold front across the alps on 15 november 2007 an embedded coherent tropopause disturbance ctd plays an important role in promoting the initial development of the lower level vortex by simultaneously providing quasigeostrophic forcing for ascent and reducing the bulk column stability over warm mediterranean waters persistent convection thereafter erodes the ctd as the storm transitions into a hurricane like vortex in addition to this upper level forcing a pair of diabatically generated lower level cyclonic potential vorticity pv features associated with distinct flow regimes i

on the role of a rossby wave train during the extratropical transition of hurricane helene 2006 three successive interactions of hurricane helene 2006 with a rossby wave train during the extratropical transition of helene over the north atlantic were investigated numerical experiments were performed with different horizontal resolutions and configurations over a domain that stretches from the eastern pacific to the western mediterranean to encompass helene and the whole rossby wave train in particular a cloud resolving run offered an explicit representation of strong diabatic effects involved in the three successive interactions while the circulation and moisture anomaly of helene were essential to its own reintensification it is shown that the rossby wave train played an important role in the track and intensity of helene and in explosive cyclogenesis downstream first the rossby wave train steered helene in such a way that a small difference in phasing resulted in large errors in the track of helene only a run at kilometre scale was able to correctly forecast the 5 day track of helene second through the formation of three filaments the rossby wave train created a quasi diurnal cycle in the intensity of helene helene responded with strong diabatic activity that prevented the superposition of an upstream trough and enhanced a downstream ridge finally model errors in the outflow of helene propagated downstream with the group speed of the rossby wave train leading to the loss of predictability of a tropical like cyclone over the mediterranean this study suggests that in addition to the horizontal resolution uncertainty from the model microphysics and from initial conditions need to be characterized to improve mid range forecast downstream from an extratropical transition copyright 2012 royal meteorological society

kinematic constraints on glacier contributions to 21st century sea level rise on the basis of climate modeling and analogies with past conditions the potential for multimeter increases in sea level by the end of the 21st century has been proposed we consider glaciological conditions required for large sea level rise to occur by 2100 and conclude that increases in excess of 2 meters are physically untenable we find that a total sea level rise of about 2 meters by 2100 could occur under physically possible glaciological conditions but only if all variables are quickly accelerated to extremely high limits more plausible but still accelerated conditions lead to total sea level rise by 2100 of about 0 8 meter these roughly constrained scenarios provide a most likely starting point for refinements in sea level forecasts that include ice flow dynamics

insights into spatial sensitivities of ice mass response to environmental change from the searise ice sheet modeling project ii greenland searise greenland

sensitivity of 21st century sea level to ocean induced thinning of pine island glacier antarctica 1 pine island glacier pig antarctica is rapidly losing mass supporting arguments that it may play a major role in 21st century sea level rise yet this glacier s quantitative contribution to sea level based on theoretical and computational models is poorly known we have developed a basin scale glaciological model to examine the sensitivity of pig to a range of environmental forcings while oceanic melt likely played the leading role in recent thinning and retreat we find that the particular grounding line geometry with an extended ice plain in the 1990s made it susceptible to such forcing our model further indicates that while the rate of grounding line retreat should diminish soon the glacier s mass loss may continue at rates similar to or moderately elevated from the present while substantial our model derived maximum rate of 2 7 cm century is considerably smaller than previous heuristically derived bounds on the sea level contribution

recent antarctic ice mass loss from radar interferometry and regional climate modelling observed estimates of ice losses in antarctica combined with regional modelling of ice accumulation in the interior suggest that east antarctica is close to a balanced mass budget but large losses of ice occur in the narrow outlet channels of west antarctic glaciers and at the northern tip of the antarctic peninsula

seismicity patterns before the m 5 8 2002 palermo italy earthquake seismic quiescence and accelerating seismicity abstract seismic quiescence and accelerating seismic energy release are considered as possible spatio temporal patterns of the preparation process of the 6 september 2002 palermo italy earthquake m 5 8 the detailed properties of the quiescence are analyzed applying the rtl algorithm the rtl algorithm is based on the analysis of the rtl prognostic parameter which is designed in such a way that it has a negative value if in comparison with long term background there is a deficiency of events in the time space vicinity of the tested point the rtl parameter increases if activation of seismicity takes place the rtl algorithm identified that a seismic quiescence started from the beginning of november 2001 and reached its minimum at the end of may 2002 the palermo 2002 earthquake occurred 2 months after the rtl parameter restored its long term background level the application of a log periodic time to failure model gives a predicted in retrospect magnitude m 6 2 main shock on 5 may 2002

dynamics of ice stream temporal variability modes scales and hysteresis 1 understanding the mechanisms governing temporal variability of ice stream flow remains one of the major barriers to developing accurate models of ice sheet dynamics and ice climate interactions here we analyze a simple model of ice stream hydrology coupled to ice flow dynamics and including drainage and basal cooling processes analytic and numerical results from this model indicate that there are two major modes of ice stream behavior steady streaming and binge purge variability the steady streaming mode arises from friction stabilized subglacial meltwater production which may also activate and interact with subglacial drainage the binge purge mode arises from a sufficiently cold environment sustaining successive cycles of thinning induced basal cooling and stagnation low prescribed temperature at the ice surface and weak geothermal heating typically lead to binge purge behavior while warm ice surface temperature and strong geothermal heating will tend to produce steady streaming behavior model results indicate that modern siple coast ice streams reside in the binge purge parameter regime near a subcritical hopf bifurcation to the steady streaming mode numerical experiments exhibit hysteresis in ice stream variability as the surface temperature is varied by several degrees our simple model simulates heinrich event like variability in a hypothetical hudson strait ice stream including dynamically determined purge time scale till freezing and basal cooling during the binge phase these findings are an improvement on studies of both modern and paleo ice stream variability and provide a framework for interpreting complex ice flow models

steep reverse bed slope at the grounding line of the weddell sea sector in west antarctica the bed of the west antarctic ice sheet is in places more than 1 5 km below sea level1 2 it has been suggested that a positive ice loss feedback may occur when an ice sheet s grounding line retreats across a deepening bed1 2 3 applied to the west antarctic ice sheet this process could potentially raise global sea level4 by more than 3 m hitherto attention has focussed on changes at the siple coast5 6 7 and amundsen sea embayment8 9 10 sectors of west antarctica here we present radio echo sounding information from the ice sheet s third sector the weddell sea embayment that reveals a large subglacial basin immediately upstream of the grounding line the reverse bed slope is steep with about 400 m of decline over 40 km the basin floor is smooth and flat with little small scale topography that would delay retreat indicating that it has been covered with marine sediment5 11 and was previously deglaciated upstream of the basin well defined glacially carved fjords with bars at their mouths testify to the position of a former ice margin about 200 km inland from the present margin evidence so far suggests that the weddell sea sector of the west antarctic ice sheet has been stable but in the light of our data we propose that the region could be near a physical threshold of substantial change

the challenge of the sudan in 1974 chevron overseas petroleum inc was granted a license to explore for oil and gas in the interior of the sudan the original contract area was 199 227 square miles which has been reduced by later relinquishment to the current area of 99 961 square miles for comparison the area is about the size of the state of wyoming

a reconciled estimate of ice sheet mass balance we combined an ensemble of satellite altimetry interferometry and gravimetry data sets using common geographical regions time intervals and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of earth s polar ice sheets we find that there is good agreement between different satellite methods especially in greenland and west antarctica and that combining satellite data sets leads to greater certainty between 1992 and 2011 the ice sheets of greenland east antarctica west antarctica and the antarctic peninsula changed in mass by 142 49 14 43 65 26 and 20 14 gigatonnes year 1 respectively since 1992 the polar ice sheets have contributed on average 0 59 0 20 millimeter year 1 to the rate of global sea level rise

cosmogenic nuclide exposure ages from the pensacola mountains adjacent to the foundation ice stream antarctica we describe glacial geological observations and cosmogenic nuclide exposure ages from the schmidt williams and thomas hills in the pensacola mountains of antarctica adjacent to the foundation ice stream fis our aim is to learn about changes in the thickness and grounding line position of the antarctic ice sheet in the weddell sea embayment between the last glacial maximum lgm and the present glacial geological observations from all three regions indicate that currently ice free areas were covered by ice during one or more past ice sheet expansions and that this ice was typically frozen to its bed and thus non erosive permitting the accumulation of multiple generations of glacial drift cosmogenic nuclide exposure age data from glacially transported erratics are consistent with this interpretation in that we observe both i samples with holocene exposure ages that display a systematic age elevation relationship recording lgm to present deglaciation and ii samples with older and highly scattered apparent exposure ages that were deposited in previous glacial interglacial cycles and have experienced multiple periods of surface exposure and ice cover holocene exposure ages at the thomas and williams hills upstream of the present grounding line of the fis show that the fis was at least 500 m thicker prior to 11 ka and that 500 m of thinning took place between 11 and 4 ka however exposure age data from the schmidt hills downstream of the present grounding line of the fis show no evidence for lgm thickening of the fis and in fact provide some evidence that the fis could have been no more than 200 m thicker than present at the lgm if all these observations are correct they imply that the lgm and early holocene ice surface slope in the vicinity of the present grounding line was steeper than present which is inconsistent with glaciological model predictions of possible lgm ice sheet configurations specifically scenarios in which the lgm grounding line of the fis advanced to the outer continental shelf appear inconsistent with exposure age data from the schmidt hills whereas scenarios in which the fis grounding line did not advance at the lgm appear inconsistent with exposure age data from the williams and thomas hills

earthquakes induced by water injection at 3 km depth within the rongchang gas field chongqing china 1 unwanted water amounting more than 1 million m 3 has been injected intermittently at a pumping pressure of 2 1 2 9 mpa over hydrostatic at 2 6 2 9 km depth within the rongchang gas field western chongqing china since july 1988 the injections have induced more than 32 000 surface recorded earthquakes including 2 of m l 5 14 of m l 4 and more than 100 of m l 3 up until the end of 2006 we examined the epidemic type aftershock sequence etas model and the temporal evolution of several statistics of the earthquake sequence the random component in the etas model can be considered as an indicator of fluid driven activity while the rate of omori law type aftershocks indicates stress triggering of the preceding earthquakes we observed three distinct seismic activity phases that were coincident with different injection periods phase i corresponds to initial injections with low injection rate long time interval and shows a vast majority of omori type events and only 8 externally forced activity phase ii corresponds to a period of high injection rates and shows intense earthquake activity characterized by a high percentage 45 of fluid driven earthquakes phase iii demonstrates decreasing seismicity as a result of a lowering in the injection rate more than 70 of earthquakes occurred randomly over time indicating the dominance of external triggering the physical mechanism that induced the rongchang earthquake sequence was a change in coulomb s failure stress caused by pore pressure diffusion and transformed from seismic slip of preceding earthquakes a pressure increase of 2 1 2 9 mpa at the injection well is more than sufficient to induce failure within the local formations

indicators of critical point behavior prior to rock failure inferred from pre failure damage abstract to investigate possible indicators of critical point behavior prior to rock failure the statistical properties of pre failure damage were analyzed based on acoustic emission events ae recorded during the catastrophic fracture of typical rock samples under differential compression aes were monitored using a high speed 32 channel waveform recording system time dependent statistics including the energy release rate b value of the magnitude frequency distribution fractal dimension and spatial correlation length scl of the ae hypocenters were calculated for each data set each parameter is a function of the time to failure and thus can be treated as an indicator of the critical point it is clear that the pre failure damage evolution prior to catastrophic failures in several common rock types is generally characterized by 1 accelerated energy release 2 a decrease in fractal dimension and scl with a subsequent precursory increase and 3 a decrease in b value from 1 5 to 0 5 for hard rocks and from 1 1 to 0 8 for soft rocks such s c cataclasite however each parameter also reveals more complicated temporal evolution due to either the heterogeneity of the rock mass or the micro mechanics of shear fracturing this confirms the potential importance of integrated analysis of two or more parameters for successfully predicting the critical point the decreasing b value and increasing energy release may prove meaningful for intermediate term prediction while the precursory increase in fractal dimension and scl may facilitate short term prediction

thickening of the ice stream catchments feeding the filchner ronne ice shelf antarctica 1 earlier ice sheet mass balance estimates disagree with satellite altimeter measured thickening of the catchment area that feeds the filchner ronne ice shelf antarctica in an effort to reconcile these differences we generated a new flux gate mass balance estimate using improved elevation and velocity data our results show a 39 26 gton yr thickening whereas earlier flux gate results indicated minor thinning our results are consistent with altimeter derived estimates of elevation change this suggests that altimeter observed thickening on the east antarctic plateau may be the result of some combination of a 20th century accumulation increase and a continuing response to the 50 accumulation increase that began in the early holocene

earthquake source nucleation as self organization process abstract the theory of an earthquake source nucleation is discussed based on the assumption that self organization of damage process takes place in the zone of an earthquake source nucleation the theory incorporates the damage rheology framework of lyakhovsky et al and the approach of phenomenology theory of second order phase transition namely the free energy governing the process of an earthquake source nucleation depends on two collective variables and in addition to the strain tensor eij the variable quantifies the fracture of the medium and the variable quantifies the interaction effect of cracks the region s is associated with a potential source of an earthquake if the damage variable exceeds the critical value cr 1 inside s the important feature of a potential source is that interaction of fractures causes acceleration of damage process inside the region of potential source and the material should lose stability primarily in this region interaction of fractures results also in occurrence of a residual stress caused by nonuniformity of fracture density the appearance and development of the potential source result in increase of intensity of damage process not only in the region of potential source but also in a certain neighborhood of the last it is compatible with such observed effects as acceleration of seismic energy release and growth of correlation length of weak seismicity before large earthquake transition of potential source to the stage of avalanche unstable fracturing is associated with instability generated by explosive increase of interaction of fractures when the damage variable exceeds the second critical value cr 2 inside s

coupling of ice shelf melting and buttressing is a key process in ice sheets dynamics 1 increase in ice shelf melting is generally presumed to have triggered recent coastal ice sheet thinning using a full stokes finite element model which includes a proper description of the grounding line dynamics we investigate the impact of melting below ice shelves we argue that the influence of ice shelf melting on the ice sheet dynamics induces a complex response and the first naive view that melting inevitably leads to loss of grounded ice is erroneous we demonstrate that melting acts directly on the magnitude of the buttressing force by modifying both the area experiencing lateral resistance and the ice shelf velocity indicating that the decrease of back stress imposed by the ice shelf is the prevailing cause of inland dynamical thinning we further show that feedback from melting and buttressing forces can lead to nontrivial results as an increase in the average melt rate may lead to inland ice thickening and grounding line advance

development and tropical transition of an alpine lee cyclone part ii orographic influence on the development pathway abstract the development and subsequent tropical transition of a subsynoptic scale cyclone over the gulf of genoa gog on 15 november 2007 led to the rapid onset of tropical storm force winds near the islands of corsica and sardinia this study evaluates the influence of two key ingredients on the cyclogenesis event a near surface warm potential temperature perturbation in the lee of the alps and a mountain scale potential vorticity pv banner a high resolution modeling system is used to perform a set of attribution tests in which modifications to the alpine orography control the presence of the cyclogenetic ingredients when either feature exists in the initial state a gog cyclone develops even when the alpine barrier is removed however when neither the warm perturbation nor the pv banner is present there is insufficient lower level pv to couple with the upper level trough to promote cyclogenesis a conceptual model involving the complimentary interaction of the two pv features is presented that

rift basins of interior sudan petroleum exploration and discovery in early 1975 chevron overseas petroleum inc commenced what became a major petroleum exploration effort in previously unexplored interior sudan with the cooperation of the sudanese government chevron has acquired a vast amount of geological and geophysical data during the past 12 years these data include extensive aeromagnetic and gravity surveys 36 040 mi 58 000 km of seismic data and 86 wells this information has defined several large rift basins now recognized as a major part of the central african rift system the sedimentary basins of interior sudan are characterized by thick nonmarine clastic sequences of jurassic cretaceous and tertiary age over 45 000 ft 13 716 m of sediment was deposited in the deepest trough and extensive basinal areas are underlain by more than 20 000 ft 6 096 m of sedimentary rocks the depositional sequences include thick lacustrine shales and claystones floodplain claystones and lacustrine fluvial and alluvial sandstones and conglomerates those lacustrine claystones deposited in a suboxic environment provide good oil prone source rocks reservoir sandstones have been found in a wide variety of nonmarine sandstone facies the extensional tectonism that formed these basins began in the jurassic early cretaceous movement along major fault trends continued intermittently into the miocene this deformation resulted in a complex structural history that led to the formation of several deep fault bounded troughs major interbasinal highs and complex basin flanks this tectonism has created a wide variety of structures many of which have become effective hydrocarbon traps during the past eight years several important oil discoveries have been made significant accumulations have been delineated in the heglig and unity areas where estimated recoverable reserves are 250 300 million bbl of oil

visibility graph analysis of the 2003 2012 earthquake sequence in the kachchh region of western india a visibility graph vg is a rather novel statistical method in earthquake sequence analysis it maps a time series into networks or graphs converting dynamical properties of the time series into topological properties of networks by using the vg approach we defined the parameter window mean interval connectivity time that informs about the mean linkage time between earthquakes we analysed the time variation of in the aftershock depleted catalogue of kachchh gujarat western india seismicity from 2003 to 2012 and we found that i changes through time indicating that the topological properties of the earthquake network are not stationary and ii appeared to significantly decrease before the largest shock m5 7 that occurred on march 7 2006 near the gedi fault an active fault in the kachchh region

correlation length as an indicator of critical point behavior prior to a large earthquake abstract a large earthquake preparation is often manifested in correlation of seismicity in an area whose characteristic dimension greatly exceeds a dimension of source of main shock zoller et al g zoller s hainzl j kurths observation of growing correlation length as an indicator for critical point behavior prior to large earthquakes j geophys res 106 2001 2167 2176 show the growth of correlation length of earthquakes prior to nine large earthquakes in california according to a power low we argue that the algorithm of correlation length estimation proposed by zoller et al g zoller s hainzl j kurths observation of growing correlation length as an indicator for critical point behavior prior to large earthquakes j geophys res 106 2001 2167 2176 can result in a decrease of correlation length preceding its precursory growth before large earthquakes if the area in which earthquake activity is correlated grows with time during a main shock preparation the correlation length analysis of acoustic emission events recorded in laboratory experiments on destruction of rocks and correlation length analysis of intermediate magnitude earthquakes in the area of large earthquakes preparation on kamchatka and in italy confirms the theoretical argument this effect can be considered as an additional premonitory pattern of large earthquake preparation

a physically based climatology of the occurrence and intensification of australian east coast lows abstractthe subtropical part of the eastern australian seaboard experiences intense cyclonic activity the severe damage caused by the intense storms in the region known as east coast lows ecls

geological constraints on antarctic palaeo ice stream retreat submarine landforms preserved in bathymetric troughs on the antarctic continental shelf show that the style of ice stream retreat across the shelf following the last glacial maximum varied between different troughs three styles of retreat are inferred from the geological evidence rapid episodic and slow rapid retreat by ice stream floatation and calving is recorded by the preservation of a landform assemblage of unmodified streamlined subglacial bedforms including mega scale glacial lineations msgls that record streaming flow along these troughs these elongate bedforms are not overprinted by recessional glacial landforms formed transverse to ice flow such as moraines or grounding zone wedges and overlying deglacial sediments are thin a second type of landform assemblage consists of msgls overprinted or interrupted by transverse grounding zone wedges this assemblage implies episodic retreat between successive grounding zone positions the third type of landform assemblage is that of numerous closely spaced recessional moraines and intermittent grounding zone wedges that overlie and interrupt msgls this assemblage records the slow retreat of grounded ice across the shelf variation in the style of ice stream retreat between the different bathymetric troughs indicates that antarctic palaeo ice streams did not respond uniformly to external forcing at the end of the last glacial cycle rather their diachronous retreat reflects the dominance of local controls in the form of bathymetry and drainage basin size more broadly these data show that retreat of marine based ice sheets in areas of reverse bed slope is not necessarily catastrophic and they provide important constraints for numerical models that attempt to predict the dynamics of large polar ice sheets copyright 2008 john wiley sons ltd

sea level as a stabilizing factor for marine ice sheet grounding lines climate change could potentially destabilize marine ice sheets which would affect projections of future sea level rise1 2 3 4 specifically an instability mechanism5 6 7 8 has been predicted for marine ice sheets such as the west antarctic ice sheet that rest on reversed bed slopes whereby ice sheet thinning or rising sea level leads to irreversible retreat of the grounding line however existing analyses of this instability mechanism have not accounted for deformational and gravitational effects that lead to a sea level fall at the margin of a rapidly shrinking ice sheet9 10 11 here we present a suite of predictions of gravitationally self consistent sea level change following grounding line migration our predictions vary the initial ice sheet size and also consider the contribution to sea level change from various subregions of the simulated ice sheet using these results we revisit a canonical analysis of marine ice sheet stability5 and demonstrate that gravity and deformation induced sea level changes local to the grounding line contribute a stabilizing influence on ice sheets grounded on reversed bed slopes we conclude that accurate treatments of sea level change should be incorporated into analyses of past and future marine ice sheet dynamics

ice sheet grounding line dynamics steady states stability and hysteresis 1 the ice sheet ice shelf transition zone plays an important role in controlling marine ice sheet dynamics as it determines the rate at which ice flows out of the grounded part of the ice sheet together with accumulation this outflow is the main control on the mass balance of the grounded sheet in this paper we verify the results of a boundary layer theory for ice flux in the transition zone against numerical solutions that are able to resolve the transition zone very close agreement is obtained and grid refinement in the transition zone is identified as a critical component in obtaining reliable numerical results the boundary layer theory confirms that ice flux through the grounding line in a two dimensional sheet shelf system increases sharply with ice thickness at the grounding line this result is then applied to the large scale dynamics of a marine ice sheet our principal results are that 1 marine ice sheets do not exhibit neutral equilibrium but have well defined discrete equilibrium profiles 2 steady grounding lines cannot be stable on reverse bed slopes and 3 marine ice sheets with overdeepened beds can undergo hysteresis under variations in sea level accumulation rate basal slipperiness and ice viscosity this hysteretic behavior can in principle explain the retreat of the west antarctic ice sheet following the last glacial maximum and may play a role in the dynamics of heinrich events

mesoscale numerical study of two cases of long lived quasi stationary convective systems over eastern spain a set of mesoscale numerical simulations using the pennsylvania state university national center for atmospheric research model is used to investigate two cases of extreme precipitation over eastern spain both cases 3 4 november 1987 and 20 october 1982 were characterized by quasi stationary mesoscale convective systems that developed over the valencia region and lasted more than 30 and 12 h respectively rainfall totals in 24 h exceeded 800 mm on 3 4 november and 400 mm on 20 october at some localities of that region the first event occurred within a weak and very stagnant synoptic pattern under a persistent easterly northeasterly low level jet stream impinging on the valencian orography in contrast the second case involved a westwardmoving surface low driven by an upper level jet streak which evolved along the northern edge of an upperlevel cutoff low over north africa in both cases the mesoscale model forecast spatial details of the precipitation field reasonably accurately as well as capturing its long duration but underestimated the storm total precipitation model output fields suggest that the development of a surface mesolow by latent heat release as well as lee cyclogenesis induced by the atlas mountains could have played an important role in both events by providing low level convergence and enhanced upslope winds thus a factor separation technique is used to explore this issue for the event of 3 4 november 1987 latent heat is decisive for explaining the precipitation maximum over central valencia and the atlas orography induces rainfall enhancement over the same zone for the event of 20 october 1982 the latent heat release is again shown to be important whereas the atlas mountains orography factor appears to inhibit rainfall this is the first time that it has been documented that the atlas induced modulation of the surface pressure field is not a positive factor for heavy precipitations over eastern spain this exceptional case may be due to a negative interaction between the atlas mountains and the upper level dynamics and frontal forcing for this event

switch of flow direction in an antarctic ice stream fast flowing ice streams transport ice from the interior of west antarctica to the ocean and fluctuations in their activity control the mass balance of the ice sheet the mass balance of the ross sea sector of the west antarctic ice sheet is now positive that is it is growing mainly because one of the ice streams ice stream c slowed down about 150 years ago1 here we present evidence from both surface measurements and remote sensing that demonstrates the highly dynamic nature of the ross drainage system we show that the flow in an area that once discharged into ice stream c has changed direction now draining into the whillans ice stream formerly ice stream b this switch in flow direction is a result of continuing thinning of the whillans ice stream and recent thickening of ice stream c further abrupt reorganization of the activity and configuration of the ice streams over short timescales is to be expected in the future as the surface topography of the ice sheet responds to the combined effects of internal dynamics and long term climate change we suggest that caution is needed when using observations of short term mass changes to draw conclusions about the large scale mass balance of the ice sheet

ice flow of the antarctic ice sheet we present a reference comprehensive high resolution digital mosaic of ice motion in antarctica assembled from multiple satellite interferometric synthetic aperture radar data acquired during the international polar year 2007 to 2009 the data reveal widespread patterned enhanced flow with tributary glaciers reaching hundreds to thousands of kilometers inland over the entire continent this view of ice sheet motion emphasizes the importance of basal slip dominated tributary flow over deformation dominated ice sheet flow redefines our understanding of ice sheet dynamics and has far reaching implications for the reconstruction and prediction of ice sheet evolution

distributed damage faulting and friction we present a formulation for mechanical modeling of geological processes in the seismogenic crust using damage rheology the seismogenic layer is treated as an elastic medium where distributed damage modifying the elastic stiffness evolves as a function of the deformation history the model damage rheology is based on thermodynamic principles and fundamental observations of rock deformation the theoretical analysis leads to a kinetic equation for damage evolution having two principal coefficients the first is a criterion for the transition between strength degradation and recovering healing and is related to friction the second is a rate coefficient of damage evolution which can have different values or functional forms for positive degradation and negative healing evolution we constrain these coefficients by fitting model predictions to laboratory data including coefficient of friction in sawcut setting intact strength in fracture experiments first yielding in faulting experiments under three dimensional strain onset and evolution of acoustic emission and dynamic instability the model damage rheology accounts for many realistic features of three dimensional deformation fields associated with an earthquake cycle these include aseismic deformation gradual strength degradation development of process zones and branching faults around high damage areas strain localization brittle failure and state dependent friction some properties of the model damage rheology e g cyclic stick slip behavior with possible accompanying creep are illustrated with simplified analytical results the developments of the paper provide an internally consistent framework for simulating long histories of crustal deformation and studying the coupled evolution of regional earthquakes and faults this is done in a follow up work

marine geological constraints for the grounding line position of the antarctic ice sheet on the southern weddell sea shelf at the last glacial maximum abstract the history of grounded ice sheet extent on the southern weddell sea shelf during the last glacial maximum lgm and the timing of post lgm ice sheet retreat are poorly constrained several glaciological models reconstructed widespread grounding and major thickening of the antarctic ice sheet in the weddell sea sector at the lgm in contrast recently published onshore data and modelling results concluded only very limited lgm thickening of glaciers and ice streams feeding into the modern filchner and ronne ice shelves these studies concluded that during the lgm ice shelves rather than grounded ice covered the filchner and ronne troughs two deep palaeo ice stream troughs eroded into the southern weddell sea shelf here we review previously published and unpublished marine geophysical and geological data from the southern weddell sea shelf the stratigraphy and geometry of reflectors in acoustic sub bottom profiles are similar to those from other west antarctic palaeo ice stream troughs where grounded ice had advanced to the shelf break at the lgm numerous cores from the southern weddell sea shelf recovered sequences with properties typical for subglacially deposited tills or subglacially compacted sediments these data sets give evidence that grounded ice had advanced across the shelf during the past thereby grounding in even the deepest parts of the filchner and ronne troughs radiocarbon dates from glaciomarine sediments overlying the subglacial deposits are limited but indicate that the ice grounding occurred at the lgm and that ice retreat started before 15 1 corrected 14c kyrs before present bp on the outer shelf and before 7 7 corrected 14c kyrs bp on the inner shelf which is broadly synchronous with ice retreat in other antarctic sectors the apparent mismatch between the ice sheet reconstructions from marine and terrestrial data can be attributed to ice streams with very low surface profiles similar to those of ice plains that had advanced through filchner trough and ronne trough at the lgm considering the global sea level low stand of 130 m below present a low surface slope of the expanded lgm ice sheet in the southern weddell sea can reconcile grounding line advance to the shelf break with limited thickening of glaciers and ice streams in the hinterland this scenario implies that ice sheet growth in the weddell sea sector during the lgm and ice sheet drawdown throughout the last deglaciation could only have made minor contributions to the major global sea level fluctuations during these times

implications of a statistical physics approach for earthquake hazard assessment and forecasting there is accumulating evidence that distributed seismicity is a problem in statistical physics seismicity is taken to be a type example of self organized criticality this association has important implications regarding earthquake hazard assessment and forecasting a characteristic of a thermodynamic system is that it exhibits a background noise that is self organized in the case of a dilute gas this self organization is the maxwell boltzmann distribution of molecular velocities in seismicity it is the gutenberg richter frequency magnitude scaling this scaling is fractal observations favor the hypothesis that smaller earthquakes in moderate sized regions occur at rates that are only weakly dependent on time thus the rate of occurrence of smaller earthquakes can be extrapolated to assess the hazard of larger earthquakes in a region we obtain the rate of occurrence of earthquakes with m 4 in 1 1 areas from the neic catalog using only this data we produce global maps of the seismic hazard observations also favor the hypothesis that the stress level at which an earthquake occurs is a second order critical point as a critical point is approached correlations extend over increasingly larger distances in terms of seismicity the approach to a critical point is associated with an increase in the rate of occurrence of intermediate sized earthquakes prior to a large earthquake this precursory activation has been shown to exhibit power law scaling and to occur over a region about ten times larger than the rupture length of the large earthquake analyses of the spinoidal behavior associated with second order critical points predict the power law increase in seismic activity prior to a characteristic earthquake this precursory activation provides the basis for intermediate range earthquake forecasting

interpretation of the effect of mountains on synoptic scale baroclinic waves abstract linear and nonlinear simulations of idealized baroclinic waves interacting with topography are examined in the context of quasigeostrophy the purpose is to provide a simple conceptual interpretation of the transients resulting from this interaction a perturbation expansion is employed with the small parameter being proportional to topographic slope to isolate fundamentally different topographic effects and show how they enter systematically at each order first and second order corrections appear to capture the essence of the topographic effect for all cases considered even for values of the small parameter as large as 0 5 and are qualitatively useful for a parameter value of unity results indicate the importance of surface rossby wave dynamics at first order near the mountain and downshear from the mountain a distance inversely proportional to the growth rate of the most unstable mode of the system the second order correction projects onto the initial baroclinic wave being primarily

a deglacial model for antarctica geological constraints and glaciological modelling as a basis for a new model of antarctic glacial isostatic adjustment abstract we present a new reconstruction of the antarctic ice sheets between 20 ka bp and the present day our reconstruction is derived using a numerical model to generate a physically consistent ice surface across the whole of the continent we define the extent of the ice sheet at five time slices 20 15 10 5 and 0 ka bp assuming an equilibrium state for the 20 ka bp time slice and a transient state for the deglacial time slices the evolution of the ice sheet within the numerical model is driven by variations in temperature accumulation rate and relative sea level in order to reconstruct the concave profile of the ice sheet in marine grounded regions such as the ross and weddell seas we force our model to develop channels of faster flow by defining greater basal sliding along the trajectory of former ice streams we find a strong dependence upon the basal sliding parameters and also the position of the grounding line we use an extensive data base of geological and glaciological data to constrain our ice sheet reconstruction grounding line extent is prescribed from marine geological data and we test ice sheet thickness against onshore geological data at 62 sites of the five time slices considered our 20 ka bp reconstruction is the best constrained by data and has an rms misfit of 147 6 m when compared to observations of ice thickness change between 20 ka bp and the present day across all time slices there are large regions of the ice sheet which are poorly constrained especially after 20 ka bp we estimate the spatial distribution of uncertainty in our ice sheet reconstruction and note that the solutions are least reliable in regions of complex topography we predict that the antarctic ice sheets contributed 9 1 5 m of eustatic sea level to the global ocean between 20 ka bp and the present and our reconstruction with minimum misfit contributes 8 m eustatic sea level during this period these values which we argue are an upper bound are lower than many previous estimates the reconstructed pattern of ice unloading can serve as a new input for glacial isostatic models

a vortical hot tower route to tropical cyclogenesis abstract a nonhydrostatic cloud model is used to examine the thermomechanics of tropical cyclogenesis under realistic meteorological conditions observations motivate the focus on the problem of how a midtropospheric cyclonic vortex a frequent by product of mesoscale convective systems during summertime conditions over tropical oceans may be transformed into a surface concentrated warm core tropical depression as a first step the vortex transformation is studied in the absence of vertical wind shear or zonal flow within the cyclonic vorticity rich environment of the mesoscale convective vortex mcv embryo the simulations demonstrate that small scale cumulonimbus towers possessing intense cyclonic vorticity in their cores vortical hot towers vhts emerge as the preferred coherent structures the vhts acquire their vertical vorticity through a combination of tilting of mcv horizontal vorticity and stretching of mcv and vht generated vertical vorticity horizontally localized and exhibiting conve

a depositional model for seismo turbidites in confined basins based on ionian sea deposits abstract this study investigates ionian sea seismo turbidite st deposits that we interpret to be triggered by major historic earthquakes and tsunamis in the calabrian arc st beds can be correlated with the ad 1908 mw 7 24 messina ad 1693 mw 7 41 catania and ad 1169 mw 6 6 eastern sicily earthquakes while two previously unknown turbidites might have been generated by the ad 1818 mw 6 23 catania and ad 1542 mw 6 77 siracusa earthquakes textural micropaleontological geochemical and mineralogical signatures of sts reveal cyclic patterns of sta stb stc and std sedimentary units for each earthquake with an associated tsunami the sta unit contains multiple st stacks with different mineralogy geochemistry foraminiferal assemblages and sedimentary structures that are deposited from synchronous multiple slope failures and turbidity currents the stb homogenite graded mud unit overlying the sta unit is deposited by the waning flows of the multiple turbidity currents that are trapped in the ionian sea confined basin the stc laminated and marine sourced unit results from seiching of the confined water mass that appears to be generated by earthquake ruptures combined with tsunami waves the std unit is a tsunamite cap deposited by the slow settling suspension cloud created by tsunami wave backwash erosion of the shoreline and continental shelf this tsunami process interpretation is based on the textural gradation of the upper unit and a more continental source of the tsunamite cap which includes c n 10 and the presence of inner shelf foraminifera with a lack of abyssal species this interpretation is in agreement with the lack of a tsunamite cap for the turbidite likely linked to the ad 1542 historic earthquake that is not associated with a tsunami the new sedimentologic criteria identifies the final seiche and tsunamite cap deposits of sts and provides a model that can now be tested in other locations to better understand the different depositional processes of seismo turbidites in confined basins

recent dramatic thinning of largest west antarctic ice stream triggered by oceans a growing body of observational data suggests that pine island glacier pig is changing on decadal or shorter timescales these changes may have far reaching consequences for the future of the west antarctic ice sheet wais and global sea levels because of pig s role as the ice sheet s primary drainage portal we test the hypothesis that these changes are triggered by the adjoining ocean specifically we employ an advanced numerical ice flow model to simulate the effects of perturbations at the grounding line on pig s dynamics the speed at which these changes are propagated upstream implies a tight coupling between ice sheet interior and surrounding ocean

tropical transition of an unnamed high latitude tropical cyclone over the eastern north pacific abstractin early november 2006 an unnamed tropical cyclone tc formed via the tropical transition tt process at 42 n over the eastern north pacific an extratropical cyclone ec developing downstream of a thinning upper tropospheric trough over the eastern north pacific served as the precursor disturbance that would ultimately undergo tt the tt of the unnamed tc was extremely unusual occurring over 16 c sea surface temperatures in a portion of the eastern north pacific basin historically devoid of tc activity this paper 1 identifies the upper and lower tropospheric features linked to the formation of the ec that transitions into the unnamed tc 2 provides a synoptic overview of the features and processes associated with the unnamed tc s tt and 3 discusses the landfall of the weakening cyclone along the west coast of north america as observed in previous studies of tt the precursor ec progresses through the life cycle of a marine extratropical frontal cyclone developing a bent back warm fr

topographic control on the post lgm grounding zone locations of the west antarctic ice sheet in the whales deep basin eastern ross sea abstract after the last glacial maximum lgm the antarctic ice sheet retreated several hundred kilometers from the outer continental shelf an overall backstepping stratal pattern of grounding zone wedges gzws indicates that the post lgm retreat occurred in a step wise fashion each gzw records a prior interval of ice stream sedimentation during which the location of paleo grounding zone i e the former seaward limit of flowing ice grounded to the seafloor was relatively stationary here we investigate whether the locations of post lgm grounding zone stillstands in the whales deep basin wdb of the eastern ross sea were controlled by the antecedent topography the bindschadler ice stream formerly occupied the wdb we used 7500 km of seismic reflection data to create a depth converted map of the lgm unconformity that was sub glacially eroded when the wais was grounded at the continental shelf edge i e prior to the deposition of the post lgm gzws our mapping shows that the first three paleo grounding zones were located slightly downstream of relatively low relief obstacles on the lgm unconformity the subsequent four grounding zones were located above a low relief saddle on the lgm unconformity at a bottleneck constriction in the width of the paleo ice stream basin these observations support the general hypotheses that post lgm grounding zone locations were at least partly controlled by the antecedent subglacial topography we cannot exclude the possibility that other factors may have also been important however the results suggest that models seeking to accurately predict the changing extent of grounded ice in response to ongoing climate changes should incorporate highly resolved maps of the existing subglacial topography as well as considerations as to how subglacial topography evolves in response to contemporaneous ice stream erosion and sedimentation

widespread rapid grounding line retreat of pine island thwaites smith and kohler glaciers west antarctica from 1992 to 2011 we measure the grounding line retreat of glaciers draining the amundsen sea sector of west antarctica using earth remote sensing ers 1 2 satellite radar interferometry from 1992 to 2011 pine island glacier retreated 31 km at its center with most retreat in 2005 2009 when the glacier ungrounded from its ice plain thwaites glacier retreated 14 km along its fast flow core and 1 to 9 km along the sides haynes glacier retreated 10 km along its flanks smith kohler glaciers retreated the most 35 km along its ice plain and its ice shelf pinning points are vanishing these rapid retreats proceed along regions of retrograde bed elevation mapped at a high spatial resolution using a mass conservation technique that removes residual ambiguities from prior mappings upstream of the 2011 grounding line positions we find no major bed obstacle that would prevent the glaciers from further retreat and draw down the entire basin 2014 american geophysical union all rights reserved

studies on temporal and spatial variation of microseismic activities in a deep metal mine abstract aiming at forecasting techniques of ground pressure hazards in deep metal mines a microseismic monitoring system was established at a deep stope in hongtoushan copper mine in china based on theories of geophysics and rock mechanics a forecasting approach was introduced using microseismic multi parameters including cumulative apparent volume energy index spatial correlation length fractal dimension and b value the approach was used to predict large scale fractures and ground pressure hazards in rock masses the results showed that microseismic activities were very weak before mining commenced however activities became significant when mining started when mining finished microseismic activities remained at a higher level for about one week then became weakened before large scale fractures occurred all microseismic multi parameters behaved differently the apparent volume and spatial correlation length were continually increasing while energy index fractal dimension and b value were gradually dropping to their minimum values therefore these parameters could be used as precursory indicators for great ground pressure hazards comprehensive analysis on microseismic multi parameters changes could improve reliability of forecasting which is of great significance to deep metal mines in managing ground pressure failure risks

analysis of tropical like cyclones over the mediterranean sea through a combined modeling and satellite approach 1 several mediterranean vortices with characteristics similar to tropical cyclones are analyzed by means of numerical simulations satellite products and lightning data numerical analysis suggests that the broad tropical like cyclone category includes in reality a set of different cyclones ranging from very small and weak vortices to larger and stronger cyclones one case displays a much longer persistence of tropical features than the other events the analysis of the tracks identifies two preferred areas of occurrence the ionian sea and the balearic islands the satellite analysis of cloud top height and retrieved rainfall indicates that the stage characterized by the most intense convective activity and rainfall anticipates the mature phase when the cyclone is more intense and characterized by tropical features during which convection is shallower and rainfall weaker this result is confirmed by a preliminary analysis of the lightning activity

a numerical model of interactions between a polar ice stream and the ocean application to ice stream e west antarctica a time dependent numerical model has been developed to study the dynamics of a polar ice stream grounded below sea level the model was applied to ice stream e one of the two most active ice streams draining the ross sea sector of the west antarctic ice sheet the retarding force or back stress from the floating ross ice shelf needed to hold the model grounding line in dynamic equilibrium was found to compare closely with retarding force mapped from field data by earlier investigators this implies that the grounding line of ice stream e is in fact close to dynamic equilibrium neither advancing nor retreating rapidly if the ice stream and its catchment area are approximately in mass balance sensitivity tests showed that the model ice stream is more sensitive to changes in back stress from the ice shelf than to changes in the accumulation rate changes in back stress can be caused by changes in the average thickness of the ice shelf the model was used to simulate retreat of the ice stream from the edge of the continental shelf in the ross sea during the holocene period of rising sea level the sea floor was assumed to be isostatically depressed but to remain rigid during retreat the effect of the assumed retreat history of the ross ice shelf on the computed timing of grounding line retreat was investigated by considering several alternative ice shelf histories the results support the conclusion of earlier investigators that the ross ice shelf caused the grounding line to stop retreating near its present position after extensive retreat during the holocene in addition the timing of retreat of the calving front of the ross ice shelf exerted major influence on the timing of retreat of the ice stream grounding line

colliding cascades model for earthquake prediction a wide set of premonitory seismicity patterns is reproduced on a numerical model of seismicity and their performance in the prediction of major model earthquakes is evaluated seismicity is generated by the colliding cascades model recently developed by the authors the model has a hierarchical structure it describes the interaction of two cascades a direct cascade of loading which is applied to the top largest element and transfers down the hierarchy and an inverse cascade of failures which goes up the hierarchy from the smaller to the larger elements these cascades collide and interact loading leads to failures while failures release and redistribute the loading three basic types of earthquake precursors are considered i the clustering of earthquakes in space and time ii the intensity of earthquake sequences and iii the correlation distance between earthquakes patterns of the first two types are used in intermediate term earthquake prediction algorithms patterns of the third type are found in the colliding cascades model although they were hypothesized previously they have not been validated by observations for each precursor we explore what is called an error diagram showing the total duration of alarms the rate of failures to predict and the rate of false alarms

predictability of a mediterranean tropical like storm downstream of the extratropical transition of hurricane helene 2006 the extratropical transition et of a tropical cyclone is known as a source of forecast uncertainty that can propagate far downstream the present study focuses on the predictability of a mediterranean tropical like storm medicane on 26 september 2006 downstream of the et of hurricane helene from 22 to 25 september while the development of the medicane was missed in the deterministic forecasts from the european centre for medium range weather forecasts ecmwf initialized before and during et it was contained in the ecmwf ensemble forecasts in more than 10 of the 50 members up to 108 h lead time the 200 ensemble members initialized at 0000 utc from 20 to 23 september were clustered into two nearly equiprobable scenarios after the synoptic situation over the mediterranean in the first and verifying scenario helene was steered northeastward by an upstream trough during et and contributed to the building of a downstream ridge a trough elongated farther downstream toward italy and enabled the development of the medicane in 9 of 102 members in the second and nonverifying scenario helene turned southeastward during et and the downstream ridge building was reduced a large scale low over the british isles dominated the circulation in europe and only 1 of 98 members forecasted the medicane the two scenarios resulted from a different phasing between helene and the upstream trough sensitivity experiments performed with the meso nh model further revealed that initial perturbations targeted on helene and the upstream trough were sufficient in forecasting the warm core medicane at 84 and 108 h lead time

marine ice sheet collapse potentially under way for the thwaites glacier basin west antarctica resting atop a deep marine basin the west antarctic ice sheet has long been considered prone to instability using a numerical model we investigated the sensitivity of thwaites glacier to ocean melt and whether its unstable retreat is already under way our model reproduces observed losses when forced with ocean melt comparable to estimates simulated losses are moderate 1 mm per year of sea level rise collapse in the different simulations within the range of 200 to 900 years

the dynamical structure of intense mediterranean cyclones this paper presents and analyzes the three dimensional dynamical structure of intense mediterranean cyclones the analysis is based on a composite approach of the 200 most intense cyclones during the period 1989 2008 that have been identified and tracked using the output of a coupled ocean atmosphere regional simulation with 20 km horizontal grid spacing and 3 hourly output it is shown that the most intense mediterranean cyclones have a common baroclinic life cycle with a potential vorticity pv streamer associated with an upper level cyclonic rossby wave breaking which precedes cyclogenesis in the region and triggers baroclinic instability it is argued that this common baroclinic life cycle is due to the strongly horizontally sheared environment in the mediterranean basin on the poleward flank of the quasi persistent subtropical jet the composite life cycle of the cyclones is further analyzed considering the evolution of key atmospheric elements as potential temperature and pv as well as the cyclones thermodynamic profiles and rainfall it is shown that most intense mediterranean cyclones are associated with warm conveyor belts and dry air intrusions similar to those of other strong extratropical cyclones but of rather small scale before cyclones reach their mature stage the streamer s role is crucial to advect moist and warm air towards the cyclones center these dynamical characteristics typical for very intense extratropical cyclones in the main storm track regions are also valid for these mediterranean cases that have features that are visually similar to tropical cyclones

interaction of potential vorticity anomalies in extratropical cyclogenesis part i static piecewise inversion the relative importance of various potential vorticity pv perturbations and their mutual interactions associated with the superstorm of 12 14 march 1993 are investigated by applying a piecewise pv inversion diagnostic system to a 36 h simulation of the storm it is shown that the contributions from all pv anomalies to the surface development increase with time although their relative significance varies during the rapid deepening stage in general the upper level dry pv anomalies contribute the most to the rapid deepening of the storm followed in order by the lower level thermal anomaly and latent heat release comparing the pv anomalies and their inverted circulations reveals that there exists a favorable phase tilt between the upper and lower level anomalies that allows lower and upper level mutual interactions in which the circulations associated with the upper level pv anomalies enhance the lower level anomalies and vice versa in addition to the vertical interactions lateral interactions are also present among the upper level pv anomalies and the background flow it is also found that the background flow advection dominates the vortex vortex and vortex background flow interactions in the deepening of the storm the vortex vortex interactions of the two upper level positive pv anomalies cause the negative tilt of the main upper level trough during the rapid deepening period

antarctic ice sheet loss driven by basal melting of ice shelves accurate prediction of global sea level rise requires that we understand the cause of recent widespread and intensifying glacier acceleration along antarctic ice sheet coastal margins atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves potentially limiting their ability to buttress the flow of grounded tributary glaciers indeed recent ice shelf collapse led to retreat and acceleration of several glaciers on the antarctic peninsula but the extent and magnitude of ice shelf thickness change the underlying causes of such change and its link to glacier flow rate are so poorly understood that its future impact on the ice sheets cannot yet be predicted here we use satellite laser altimetry and modelling of the surface firn layer to reveal the circum antarctic pattern of ice shelf thinning through increased basal melt we deduce that this increased melt is the primary control of antarctic ice sheet loss through a reduction in buttressing of the adjacent ice sheet leading to accelerated glacier flow the highest thinning rates occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of antarctic ice shelves through ocean upwelling in the amundsen and bellingshausen seas and atmospheric warming on the antarctic peninsula this implies that climate forcing through changing winds influences antarctic ice sheet mass balance and hence global sea level on annual to decadal timescales

numerical analysis of a mediterranean hurricane over southeastern italy abstract the presence of a subsynoptic scale vortex over the mediterranean sea in southeastern italy on 26 september 2006 has been recently documented by the authors the transit of the cyclone over land allowed an accurate diagnosis of the structure of the vortex based on radar and surface station data showing that the cyclone had features similar to those observed in tropical cyclones to investigate the cyclone in greater depth numerical simulations have been performed using the weather research and forecasting wrf model set up with two domains in a two way nested configuration model simulations are able to properly capture the timing and intensity of the small scale cyclone moreover the present simulated cyclone agrees with the observational analysis of this case identifying in this small scale depression the typical characteristics of a mediterranean tropical like cyclone an analysis of the mechanisms responsible for the genesis development and maintenance of the cyclone has also been p

modelling west antarctic ice sheet growth and collapse through the past five million years changes in earth s orbit are known to influence climate shifts from cold glacials to warm interglacials how the vast west antarctic ice sheet responds to these fluctuations is uncertain but because its collapse could raise sea levels by about 5 metres of great interest naish et al have analysed the and 1b ocean sediment core extracted from beneath the ross ice shelf as part of the andrill drilling project and find evidence that the ice sheet collapsed periodically during the early pliocene 3 5 million years ago when atmospheric co2 levels were similar to or slightly higher than today s the pattern of collapse suggests an influence of approximately 40 000 year cycles in the tilt of earth s rotational axis obliquity also in this issue of nature in a numerical modelling study focused on the past 5 million years in antarctica david pollard and robert deconto combine ice sheet land supported and ice shelf water supported modelling approaches to simulate the movement of the grounding line the border between land and sea ice their results show that over the past 5 million years the west antarctic ice sheet transitioned between full intermediate and collapsed states in just a few thousand years this means that the ice sheet is likely to disintegrate if ocean temperatures in the area rise by 5 c if the west antarctic ice sheet wais melted sea levels would rise by about 5 m such changes are thought to have occurred in the past but could not be simulated by models pollard and deconto combine ice sheet with ice shelf modelling and show that over the past 5 million years the wais transitioned among full intermediate and collapsed states in only a few thousand years suggesting possible disintegration of the wais if ocean temperatures in the area rise by 5 c the west antarctic ice sheet wais with ice volume equivalent to 5 m of sea level1 has long been considered capable of past and future catastrophic collapse2 3 4 today the ice sheet is fringed by vulnerable floating ice shelves that buttress the fast flow of inland ice streams grounding lines are several hundred metres below sea level and the bed deepens upstream raising the prospect of runaway retreat3 5 projections of future wais behaviour have been hampered by limited understanding of past variations and their underlying forcing mechanisms6 7 its variation since the last glacial maximum is best known with grounding lines advancing to the continental shelf edges around 15 kyr ago before retreating to near modern locations by 3 kyr ago8 prior collapses during the warmth of the early pliocene epoch9 and some pleistocene interglacials have been suggested indirectly from records of sea level and deep sea core isotopes and by the discovery of open ocean diatoms in subglacial sediments10 until now11 however little direct evidence of such behaviour has been available here we use a combined ice sheet ice shelf model12 capable of high resolution nesting with a new treatment of grounding line dynamics and ice shelf buttressing5 to simulate antarctic ice sheet variations over the past five million years modelled wais variations range from full glacial extents with grounding lines near the continental shelf break intermediate states similar to modern and brief but dramatic retreats leaving only small isolated ice caps on west antarctic islands transitions between glacial intermediate and collapsed states are relatively rapid taking one to several thousand years our simulation is in good agreement with a new sediment record andrill and 1b recovered from the western ross sea11 indicating a long term trend from more frequently collapsed to more glaciated states dominant 40 kyr cyclicity in the pliocene and major retreats at marine isotope stage 31 1 07 myr ago and other super interglacials

non uniform scaling features in central italy seismicity a non linear approach in investigating seismic patterns and detection of possible earthquake precursors 1 the detrended fluctuation analysis dfa is a powerful method for capturing scaling behavior in nonstationary time series using an appropriate instability index it is possible to identify and quantify deviations from uniform power law scaling which suggest the presence of changing dynamics in the system under study in this context the scaling behavior of the 1981 2007 seismicity in umbria marche central italy which is one of the most seismically active areas in italy was investigated significant deviations from uniform power law scaling in the seismic temporal fluctuations were revealed mostly linked with the occurrence of rather large earthquakes or seismic clusters

calibrated prediction of pine island glacier retreat during the 21st and 22nd centuries with a coupled flowline model a flowline ice sheet model is coupled to a box model for cavity circulation and configured for the pine island glacier an ensemble of 5000 simulations are carried out from 1900 to 2200 with varying inputs and parameters forced by ocean temperatures predicted by a regional ocean model under the a1b business as usual emissions scenario comparison is made against recent observations to provide a calibrated prediction in the form of a 95 confidence set predictions are for monotonic apart from some small scale fluctuations in a minority of cases retreat of the grounding line over the next 200 yr with huge uncertainty in the rate of retreat full collapse of the main trunk of the pig during the 22nd century remains a possibility

basal topographic controls on the stability of the west antarctic ice sheet lessons from foundation ice stream using observations of basal topography ice thickness and modern accumulation rates we use theory and a dynamic flowline model to examine the sensitivity of antarctica s foundation ice stream to changes in sea level accumulation and buttressing at the grounding line our sensitivity studies demonstrate that the steep upward sloping basal topography inland from the grounding line serves to stabilize retreat of the ice stream while the upward sloping submarine topography downstream from the grounding line creates the potential for significant advance under conditions of modest sea level lowering and or increased accumulation rate extrapolating from foundation ice stream many nearby weddell sea sector ice streams are in a similar configuration suggesting that the historical and projected responses of this sector s ice streams may contrast with those in the amundsen or ross sea sectors this work reaffirms that the greatest concerns for rapid west antarctic ice sheet wais retreat are locations of reverse slopes muted basal topography and limited lateral support

a numerical study of an extreme cold air outbreak over the labrador sea sea ice air sea interaction and development of polar lows in this paper the ability of the mm5 mesoscale forecast model to simulate the air sea interaction boundary layer development and mesoscale structure associated with a cold air outbreak over the labrador sea is investigated the case chosen was one for which research aircraft data and satellite imagery are available for validation the default surface layer parameterization included in the model is shown to grossly overestimate the magnitude of the air sea interaction resulting in forecasts of boundary layer growth and mesoscale development that differ substantially from observations it is also shown that a representation of the inhomogeneities in sea ice cover results in a significant improvement in simulations of the air sea interaction boundary layer development and mesoscale structure both within the marginal ice zone and downstream over the open ocean finally the mesoscale cyclones or polar lows observed in the wake of the cold air outbreak are shown to be coupled to the evolution of an upper tropospheric potential vorticity anomaly that was advected over the region the model simulations suggest that mm5 most probably due to inaccuracies in and the limited resolution of the analyzed fields that supply the initial and boundary conditions to the model was unable to correctly simulate the development and track of this anomaly and this ultimately led to an incorrect forecast of the polar lows finite amplitude behavior

changes in the west antarctic ice sheet the portion of the west antarctic ice sheet that flows into the ross sea is thinning in some places and thickening in others these changes are not caused by any current climatic change but by the combination of a delayed response to the end of the last global glacial cycle and an internal instability the near future impact of the ice sheet on global sea level is largely due to processes internal to the movement of the ice sheet and not so much to the threat of a possible greenhouse warming thus the near term future of the ice sheet is already determined however too little of the ice sheet has been surveyed to predict its overall future behavior

a cyclone phase space derived from thermal wind and thermal asymmetry abstract an objectively defined three dimensional cyclone phase space is proposed and explored cyclone phase is described using the parameters of storm motion relative thickness asymmetry symmetric nonfrontal versus asymmetric frontal and vertical derivative of horizontal height gradient cold versus warm core structure via the thermal wind relationship a cyclone s life cycle can be analyzed within this phase space providing substantial insight into the cyclone structural evolution an objective classification of cyclone phase is possible unifying the basic structural description of tropical extratropical and hybrid cyclones into a continuum stereotypical symmetric warm core tropical cyclone and asymmetric cold core extratropical cyclone life cycles are illustrated using 1 navy operational global atmospheric prediction system nogaps operational analyses and 2 5 ncep ncar reanalyses the transitions between cyclone phases are clearly illustrated within the phase space including extratro

the 2005 hurricane season an echo of the past or a harbinger of the future 1 recent atlantic hurricane activity raises several questions for example why was the 2005 season so early and active and are there similarities with the past we show that parallels exist between 2005 and previously active years tropical atlantic sea surface temperature sst anomalies beginning in winter aided the formation of early storms on longer timescales sst sea level pressure and zonal winds exhibit multidecadal variability weaker easterlies during the positive phase of the atlantic multidecadal oscillation amo result via ocean atmosphere interactions in warmer water and increased hurricane activity however individual active years appear independent of the amo phase

storm related sedimentation influenced by coastal configuration in the stratigraphic record of a tectonically active shelf upper pleistocene le castella terrace italy abstract analysis of patterns of coastal circulation and sediment dispersal is an essential step for the study of controlling factors influencing the long term dynamics of coastal systems modern settings offer the possibility to monitor relevant parameters over relatively short time spans however geological examples complement this perspective by providing a time averaged record where longer trends and stratigraphically significant processes can be evaluated this study investigates the shallow marine deposits of le castella terrace upper pleistocene southern italy to document how patterns of circulation influenced by coastline configuration can affect the preserved millennial scale depositional record of a progradational shoreline system the regressive portion of the le castella terrace deposits developed during a relative sea level highstand and falling stage consists of a progradational wedge mainly composed of redistributed skeletal particles of a coeval shallow water carbonate factory preservation of the morphology of the paleocoastline and abundant current related sedimentary structures allow reconstruction of the predominant sediment dispersal dynamics responsible for the formation of this sedimentary wedge facies and paleocurrent analysis indicate offshore and alongshore sediment transport modes consistent with coastal circulation driven by storms normally incident to the shoreline and a sharp change in coastline orientation this coastal inflection influenced circulation patterns causing flow separation and eddy formation in the lee of the curved coastline syndepositional tectonic deformation also affected the architecture of the preserved deposits controlling the nucleation and development of a clinostratified body and determining localized lateral stratigraphic variability this study illustrates how transient but recurrent circulation patterns associated with changes in coastal orientation and related to high energy storm events can leave a predominant signature in the stratigraphic record of microtidal shallow marine successions

single link cluster analysis as a method to evaluate spatial and temporal properties of earthquake catalogues summary single link cluster analysis is a straightforward method to quantitatively measure the degree of clustering or isolation of groups of elements in a set such as a catalogue of earthquakes to apply single link cluster analysis to a set of n earthquakes individual earthquakes are first linked to their nearest neighbours to form event sub groups the process is then repeated and each sub group linked to its nearest neighbour recursively until n 1 links are found to join all the earthquakes this paper shows how knowledge of these links can be used to divide a group of earthquakes into any number of spatial clusters with various modifications this analysis can identify earthquake nests isolated events aftershock sequences and zones of seismic quiescence to illustrate this method we apply it to i a global data set of 2178 earthquakes having mb of 5 8 or greater reported by the international seismological centre isc between 1964 and february 1986 and ii sets of earthquakes having mb of 4 9 and greater as reported by the isc occurring in central america and in the aleutians to facilitate comparison with real data this study also investigates the distribution of link lengths for synthetic events placed randomly on 1 d circular line 2 d circular area and 3 d spherical volume geometries if we remove links between nuclear explosions from the isc data the resulting link distribution is quite similar to that for synthetic events placed along a 1 d fault for the shortest links the similarity improves markedly if the synthetic fault has a finite width or if relative location errors cause events to be located away from the fault trace with a standard deviation of about 15 km

insights into spatial sensitivities of ice mass response to environmental change from the searise ice sheet modeling project i antarctica atmospheric oceanic and subglacial forcing scenarios from the sea level response to ice sheet evolution searise project are applied to six three dimensional thermomechanical ice sheet models to assess antarctic ice sheet sensitivity over a 500 year timescale and to inform future modeling and field studies results indicate i growth with warming except within low latitude basins where inland thickening is outpaced by marginal thinning ii mass loss with enhanced sliding with basins dominated by high driving stresses affected more than basins with low surface slope streaming ice and iii mass loss with enhanced ice shelf melting with changes in west antarctica dominating the signal due to its marine setting and extensive ice shelves cf minimal impact in the terre adelie george v oates and victoria land region of east antarctica ice loss due to dynamic changes associated with enhanced sliding and or sub shelf melting exceeds the gain due to increased precipitation furthermore differences in results between and within basins as well as the controlling impact of sub shelf melting on ice dynamics highlight the need for improved understanding of basal conditions grounding zone processes ocean ice interactions and the numerical representation of all three key points sensitivity study of antarctica to atmospheric oceanic and subglacial forcings different sectors of antarctica are vulnerable to the forcings atmospheric forcing lead to a growth but dynamic forcing lead to a mass loss 2013 american geophysical union all rights reserved

stability of the west antarctic ice sheet in a warming world equivalent to 0 28 to 0 56 mm yr 1 sea level rise with the rate growing over at least the past two decades 1 4 these observations intensify concerns about the ice sheet s stability that were first raised more than four decades ago 5

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen

upper ocean response to hurricane gilbert the evolving upper ocean response excited by the passage of hurricane gilbert september 14 19 1988 was investigated using current and temperature observations acquired from the deployment of 79 airborne expendable current profilers axcps and 51 airborne expendable bathythermographs from the national oceanic and atmospheric administration wp 3d aircraft in the western gulf of mexico the sea surface temperatures ssts mixed layer depths and bulk richardson numbers were objectively analyzed to examine the spatial variability of the upper ocean response to gilbert net decreases of the ssts of 3o 4oc were observed by the profilers as well as by the airborne infrared thermometer airt along the flight tracks and advanced very high resolution radiometer avhrr imagery the axcps indicated a marked cooling from 29oc to about 25 5oc on september 17 1988 which was about 1 2 inertial periods ip following storm passage this pool of cooler water 3 5 o was located further downstream in the hurricane wake by september 19 2 7 ip following the storm as a result of the near inertial currents in the mixed layer while there was a bias of about 0 6oc and 1 7oc between the in situ and avhrr derived ssts respectively both the avhrr images and the objectively analyzed fields indicated a rightward bias in the upper ocean cooling that extended from the storm track to about 4rmax where rmax the radius of maximum winds is equal to 50 km the larger sst offset of 1 7oc was due to the difference between the time of the avhrr image and the time of the aircraft experiment on september 19 the ssts derived from the avhrr images and the airt also indicated large gradients between the cold wake and the warm eddy in the central gulf of mexico the mixed layer deepened by about 30 35 m on the right side of the track during the storm and 1 2 ip later with little evidence of continued deepening afterward the mixed layer current vectors demonstrate that a strong near inertially rotating current was excited by the passage of gilbert with maxima of about 1 1 4 m s 1 the currents observed during and subsequent to 1 2 ip the storm diverged from the storm track whereas the mixed layer current vectors 2 7 ip after storm passage converged toward the track with relative maxima of 0 8 1 m s 1 this alternating pattern of convergence and divergence of the mixed layer current was associated with the upwelling and downwelling cycles of the baroclinic response considerable current shear existed between the mixed layer and the thermocline currents in the cool wake between the storm track and the 4rmax estimates of the bulk richardson numbers ranged between 0 2 and 1 0 during gilbert and at 1 2 ip which suggests that enhanced current shears were responsible for some of the mixed layer deepening

an air sea interaction theory for tropical cyclones part ii evolutionary study using a nonhydrostatic axisymmetric numerical model abstract in part i of this study an analytical model for a steady state tropical cyclone is constructed on the assumption that boundary layer air parcels are conditionally neutral to displacements along the angular momentum surfaces of the hurricane vortex the reversible thermodynamics implied by this assumption allows the mature storm to be thought of as a simple carnot engine acquiring heat at the high temperature ocean surface and losing heat near the low temperature tropopause although the oceanic heat source is universally recognized as the sine qua non for the mature hurricane there is also wide acceptance of conditional instability of the second kind cisk which makes no specific reference to surface heat fluxes as the formative mechanism this ambivalence is seen in that all numerical simulation studies find it essential to have transfer from the ocean surface yet all start from a conditionally unstable atmosphere the hypothesis put forward in part i based on the steady state theory is t

century scale discharge stagnation and reactivation of the ross ice streams west antarctica 1 flow features on the surface of the ross ice shelf west antarctica record two episodes of ice stream stagnation and reactivation within the last 1000 years we document these events using maps of streaklines emerging from individual ice streams made using visible band imagery together with numerical models of ice shelf flow forward model experiments demonstrate that only a limited set of discharge scenarios could have produced the current streakline configuration according to our analysis whillans ice stream ceased rapid flow about 850 calendar years ago and restarted about 400 years later and macayeal ice stream either stopped or slowed significantly between 800 and 700 years ago restarting about 150 years later until now ice stream scenarios emphasized runaway retreat or stagnation on millennial timescales here we identify a new scenario century scale stagnation and reactivation cycles as well as lateral communication with adjacent ice streams through thickness changes on lightly grounded ice plains this introduces uncertainty into predictions for future sea level withdrawals by the west antarctic ice sheet which are based in part on recent slowing of whillans ice stream and the stagnant condition of kamb ice stream