convective momentum transport by rainbands within a madden julian oscillation in a global nonhydrostatic model with explicit deep convective processes part i methodology and general results abstractthe convective momentum transport cmt properties of 13 215 rainbands within a madden julian oscillation mjo event simulated by a global nonhydrostatic model are examined cmt vectors which represent horizontal accelerations to the mean winds due to momentum flux convergences of deviation winds are derived for each rainband the cmt vectors are composited according to their locations relative to the mjo center while a similar number of rainbands are detected in the eastern and western halves of the mjo convective envelope cmt vectors with large zonal components are most plentiful between 0 and 20 to the west of the mjo center the zonal components of the cmt vectors exhibit a coherent directionality and have a well organized three layer structure positive near the surface negative in the low to midtroposphere and positive in the upper troposphere in the low to midtroposphere where the longitudinal difference in the mean zonal wind across the mjo is 10 m s 1 on average the net acceler

structure and evolution of the 22 february 1993 toga coare squall line organization mechanisms inferred from numerical simulation abstract mechanisms responsible for meso and convective scale organization within a large tropical squall line that occurred on 22 february 1993 during the tropical ocean global atmosphere coupled ocean atmosphere response experiment are investigated using a three dimensional numerical cloud model the squall line occurred in an environment typical of fast moving tropical squall lines characterized by moderate convective available potential energy and moderate to strong vertical shear beneath a low level jet with weak reverse vertical shear above a well simulated aspect of the observed squall line is the evolution of a portion of its leading convective zone from a quasi linear to a three dimensional bow shaped structure over a 2 h period this transition is accompanied by the development of both a prominent mesoscale vortex along the northern edge of the 40 60 km long bow shaped feature and elongated bands of weaker reflectivity situated rearward and oriented transverse to the leading edge within enha

a dual doppler radar study of longitudinal mode snowbands part i a three dimensional kinematic structure of meso γ scale convective cloud systems within a longitudinal mode snowband abstract observations of snowstorms were carried out around ishikari bay hokkaido japan from december 1991 to february 1992 on 15 january 1992 a longitudinal mode snowband was observed by a dual doppler radar system the snowband was composed of meso scale 20 km convective cloud systems the three dimensional kinematic structures and organization processes of the meso scale systems were studied in detail strong band parallel winds appeared in the upper north rear of the meso scale systems since their speed was faster than that of the cellular radar echoes the winds formed rear to front currents increasing in volume and speed the rear to front currents developed into meso scale and penetrated toward the lower front and lower south of the systems consequently the rear to front currents caused strong meso scale convergence and the enhancement of updrafts at their leading edges the transport of the band parallel momentum greatly contributed to the successive development of new convec

effect of stone content on water flow velocity over loess slope non frozen soil abstract stony soils are commonly found worldwide and are considerably studied for their hydrological characteristics and effect on soil erosion water flow velocity is an important parameter in understanding the effect of stone content on hydrodynamics and soil erosion in this study laboratory experiments were used to measure rill flow velocity by using electrolyte tracer method under different hydraulic conditions flow rates of 1 2 4 and 8 l min slope gradients of 5 10 15 and 20 and stone mass contents amounting to 0 10 20 and 50 nine sensors which were 1 m apart along the 8 m long rill were used to measure flow velocity by tracing solute transport measured flow velocity increased with slope gradient and flow rate the highest increase in flow velocity was measured from 15 to 20 which were also affected by flow rate effects of discharge rate on flow velocity presented the largest difference when flow rate increased from 2 l min to 8 l min at slope gradients higher than 5 the effects of different factors were quantified by a regression model with high accuracy of 0 99 maximum flow velocity of water was predicted at 15 23 of stone content flow velocity increased with 0 15 23 of stone content but decreased at higher values this study aims at further understanding the hydrodynamics of soil erosion and sediment transport behaviors in hillslopes with different stone contents to obtain information for quantifying soil erosion on stony slopes

organization of oceanic convection during the onset of the 1998 east asian summer monsoon the organizational modes of convection over the northern south china sea scs during the onset of the summer monsoon are documented using radar and sounding data from the may june 1998 south china sea monsoon experiment scsmex the onset occurred in mid may with a rapid increase in deep convection over a 10 day period accompanied by a major shift in the circulation over the east asian region analysis of bureau of meteorology research centre bmrc radar data from dongsha island reveals a wide range of organizational modes of convection over the northern scs proximity sounding data indicate that lower and middle level vertical wind shears exerted a dominant control over the orientation of convective lines within mesoscale convective systems in this region as has been found in the australian monsoon region and the equatorial western pacific the results are consistent with the conceptual model of lemone et al based on the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare except two new organizational modes have been identified shear parallel bands for strong low level shear and weak midlevel shear when there is weak instability and the air is dry aloft and shear parallel bands for strong shears in both layers when the shear vectors are in the same direction midlatitude influences namely the passage of troughs over southern china likely contributed to these two additional modes the stratiform rain fraction from the convective systems during the monsoon onset period was relatively small 26 compared to the estimated average of about 40 for the entire tropics this small fraction is attributed to the weak instability during the onset period and relatively dry air in the upper troposphere

the structure and classification of numerically simulated convective storms in directionally varying wind shears abstract using a three dimensional numerical cloud model we investigate the effects of directionally varying wind shear on convective storm structure and evolution over a wide range of shear magnitudes as with a previous series of experiments using unidirectional wind shear profiles weisman and klemp the current results evince a spectrum of storm types ranging from short lived single cells at low shears multicells at intermediate shears to supercells at high shears with a clockwise curved hodograph the supercellular growth is confined to the right flank of the storm system while multicellular growth is favored on the left flank an analysis of the dynamic structure of the various cells reveals that the quasi steady supercell updrafts are strongly enhanced by dynamically induced pressure gradients on the right flank of the storm system we use this feature along with other related storm characteristics such as updraft rotation to propose a dynamically based storm classification scheme following

notes and correspondence convective eddy momentum tendencies in long cloud resolving model simulations abstract domain average momentum budgets are examined in several multiday cloud resolving model simulations of deep tropical convection in realistic shears the convective eddy momentum tendency f neglected in many global circulation models looks broadly similar in two and three dimensional simulations it has a large component in quadrature with the mean wind profile tending to cause momentum profile features to descend this component opposes and exceeds in magnitude the corresponding large scale vertical advective tendency which would tend to make features ascend in convecting regions the portion of f in phase with the mean wind is isolated by vertically integrating f u yielding a kinetic energy tendency that is overwhelmingly negative the variation of this energy damping with shear flow kinetic energy and convection intensity measured by rain rate gives a cumulus friction coefficient around 40 to 80 per centimeter of rain in 3d runs large scatter reflects the effects of varying co

research paperseffect of stone content on water flow velocity over loess slope frozen soil soils in high altitude or latitude regions are commonly rich in stone fragments which are frequently frozen the hydrodynamics of water flow over frozen stony slopes must be investigated to understand soil erosion and sediment transportation the objective of this laboratory experiments was to measure water flow velocity over frozen slopes with different stone contents by using electrolyte trace method the experiments were performed under slope gradients of 5 10 15 and 20 flow discharge rates of 1 2 4 and 8 l min and stone contents of 0 10 20 and 50 on mass basis nine equidistant sensors were used to measure flow velocity along flume from the top of the slope results indicated that stone content significantly affected flow velocity under increasing slope gradient the increase in stone content rapidly reduced the flow velocity the flow velocities over frozen slopes were 1 21 to 1 30 times of those over non frozen slopes under different slope gradients and flow rates when the stone content increased from 0 to 20 proportions gradually decreased from 52 to 25 and 13 additionally flow velocities over frozen and non frozen soil slopes became gradually similar with increasing stone content this study will help elucidate the hydrodynamics soil erosion and sediment transport behaviors of frozen or partially unfrozen hillslopes with different stone contents

velocity of water flow along saturated loess slopes under erosion effects abstract rainfall or snow melted water recharge easily saturates loose top soils with a less permeable underlayer such as cultivated soil slope and partially thawed top soil layer and thus may influence the velocity of water flow this study suggested a methodology and device system to supply water from the bottom soil layer at the different locations of slopes water seeps into and saturates the soil when the water level is controlled at the same height of the soil surface the structures and functions of the device the components and the operational principles are described in detail a series of laboratory experiments were conducted under slope gradients of 5 10 15 and 20 and flow rates of 2 4 and 8 l min 1 to measure the water flow velocities over eroding and non eroded loess soil slopes under saturated conditions by using electrolyte tracing results showed that flow velocities on saturated slopes were 17 to 88 greater than those on non saturated slopes flow velocity increased rapidly under high flow rates and slope gradients saturation conditions were suitable in maintaining smooth rill geomorphology and causing fast water flow the saturated soil slope had a lubricant effect on the soil surface to reduce the frictional force resulting in high flow velocity the flow velocities of eroding rills under different slope gradients and flow rates were approximately 14 to 33 lower than those of non eroded rills on saturated loess slopes compared with that on a saturated loess slope the eroding rill on a non saturated loess slope can produce headcuts to reduce the flow velocity this study helps understand the hydrodynamics of soil erosion and sediment transportation of saturated soil slopes

numerical archetypal parameterization for mesoscale convective systems abstractvertical shear commonly organizes atmospheric convection into coherent multiscale structures the associated countergradient vertical transport of horizontal momentum by organized convection can enhance the wind shear and transport kinetic energy upscale however organized convection and its upscale effects are not represented by traditional mass flux based parameterizations the present paper sets the archetypal dynamical models originally formulated by the second author into a parameterization context by utilizing a nonhydrostatic anelastic model with segmentally constant approximation nam sca using a two dimensional framework as a starting point nam sca spontaneously generates propagating tropical squall lines in a sheared environment high numerical efficiency is achieved through a novel compression methodology the numerically generated archetypes produce vertical profiles of convective momentum transport that are consistent with the analytic archetype

application of heat pulse injections for investigating shallow hyporheic flow in a lowland river 1 hyporheic zone processes can have significant impact on groundwater and surface water resources detailed knowledge of exchange flow patterns is crucial for understanding the ecohydrological and biogeochemical functioning of river corridors in particular small scale hyporheic exchange flow is still poorly understood partially because of the lack of adequate in situ monitoring technology this paper investigates the spatial heterogeneity of hyporheic exchange flow in a lowland river at multiple scales it demonstrates the conjunctive use of active heat pulse tracing at shallow depths 15 cm and vertical hydraulic gradients vhg at 120 150 cm streambed depth for improving the understanding of hyporheic exchange flow processes generally positive vhg indicated a regional dominance of groundwater up welling high and temporally variable vhg were used to identify confined conditions caused by low conductivity layers in the subsurface low connectivity while locations with lower and temporally less variable vhg indicated free groundwater up welling high connectivity in highly conductive sediments a heat pulse sensor hps was applied for identifying shallow hyporheic flow at three locations representative for high versus low streambed connectivity shallow hyporheic flow patterns were found to be spatially heterogeneous subsurface flow could only partially be explained by streambed topography surface water infiltration and horizontal flow coincided with inhibited groundwater up welling whereas locations with high streambed connectivity were characterized by increased up welling the combined information of spatiotemporal vhg variability and flow vector frequency distribution by hps has the potential to improve the understanding of impacts of streambed topography and subsurface stratification on hyporheic flow patterns

numerical simulation of tornadogenesis in a high precipitation supercell part i storm evolution and transition into a bow echo abstract a nested grid primitive equation model rams version 3b was used to simulate a high precipitation hp supercell which produced two weak tornadoes six telescoping nested grids allowed atmospheric flows ranging from the synoptic scale down to the tornadic scale to be represented in the simulation all convection in the simulation was initiated with resolved vertical motion and subsequent condensation latent heating from the model microphysics no warm bubbles or cumulus parameterizations were used part i of this study focuses on the simulated storm evolution and its transition into a bow echo the simulation initially produced a classic supercell that developed at the intersection between a stationary front and an outflow boundary as the simulation progressed additional storms developed and interacted with the main storm to produce a single supercell this storm had many characteristics of an hp supercell and eventually evolved into a bow echo with a rotating comma head structure an analysi

dynamical influence of microphysics in tropical squall lines a numerical study abstract based on environmental conditions of the 22 and 23 june squall lines during the convection profonde tropicale in 1981 copt81 experiment in west africa a series of numerical simulations are performed with a two dimensional nonhydrostatic cloud model to examine the dynamical effect of microphysics in tropical squall lines the role of ice phase microphysics strongly depends on ambient conditions for the environment of strong convective instability the ice phase is important regarding the system scale structure but is not important to the convective scale dynamics on the other hand the ice influence is crucial to the squall line convective system if the environment has a weak convective instability and is almost saturated at low levels

seasonal migration of itcz precipitation across the equator why can t gcms simulate it 1 the secondary meridional circulation induced by convective momentum transport cmt within the ascending branch of the hadley circulation is a missing dynamical mechanism that can cause common failure of general circulation models gcms in simulating seasonal migration of the intertropical convergence zone itcz precipitation maximum across the equator this failure is manifested by the model bias that the precipitation peak remains north of the equator during november march the cmt induced secondary circulation characterized by strong downward motion along the equatorial belt and upward motion south and north of the belt tends to modify the meridional distribution of precipitation with the strongest impacts during boreal winter and spring a 20 year gcm simulation with the cmt parameterization successfully reproduces the observed seasonal migration of the itcz precipitation across the equator with the peaks near 8 n during boreal summer and near 8 s during boreal winter

parametrization of momentum transport by convection ii tests in single column and general circulation models diagnostics derived from cloud resolving model simulations in part i of this study relating to the vertical transport of horizontal momentum by convection are used to develop a parametrization of convective momentum transports for deep convection based upon the mass flux convection scheme discussed by gregory and rowntree the importance of cloud pressure gradients to the flow within the cloud is emphasised and a simple method of representing their effect is suggested the scheme is able to reproduce the fluxes derived from the cloud resolving model studies where cloud organization by the flow is unimportant inclusion of the parametrization in a version of the meteorological office unified model demonstrates that convective momentum transports play a large role in the momentum balance of the atmosphere generally simulation of the mean atmospheric circulation by the unified model is improved by the inclusion of such transports

analytic representation of the large scale organization of tropical convection the pivotal role of mesoscale organization on the large scale coherence of tropical convection is represented by a nonlinear dynamical model the general model consists of two interlocked systems a mesoscale parameterization of organized convection and a two layer model of large scale equatorial dynamics the lower layer dynamics is rossby gyre like whereas outflow from organized convection maintains the upper layer circulation the transports of zonal momentum in the vertical and meridional directions are key processes an archetype of the general model in spite of being brutally simplified represents the convective organization momentum transport and equatorial superrotation realized by the cloud resolving convection parameterization or superparameterization explicit approach developed by grabowski the mesoscale parameterization is an analytic equivalent of the cloud system resolving models used in this computational approach finally issues in parameterizing convective organization are discussed

a unified convection scheme unicon part i formulation abstractthe author develops a unified convection scheme unicon that parameterizes relative i e with respect to the grid mean vertical flow subgrid vertical transport by nonlocal asymmetric turbulent eddies unicon is a process based model of subgrid convective plumes and mesoscale organized flow without relying on any quasi equilibrium assumptions such as convective available potential energy cape or convective inhibition cin closures in combination with a relative subgrid vertical transport scheme by local symmetric turbulent eddies and a grid scale advection scheme unicon simulates vertical transport of water species and conservative scalars without double counting at any horizontal resolution unicon simulates all dry moist forced free and shallow deep convection within a single framework in a seamless consistent and unified way it diagnoses the vertical profiles of the macrophysics fractional area plume radius and number density as well as the microphysics production and evaporati

high resolution simulation of mean convection and its intraseasonal variability over the tropics in the mri jma 20 km mesh agcm abstract tropical mean convection and its organization on different spatiotemporal scales in a simulation using the meteorological research institute japan meteorological agency mri jma global atmospheric general circulation model agcm at 20 km resolution tl959l60 has been investigated comparison with two lower resolution simulations of 120 km tl159l40 and 180 km tl95l40 shows that convection climatological fields and moist stability over the indian ocean and south pacific convergence zone are better represented in tl959l60 than in lower resolution simulations however the simulated three dimensional structure of the walker and hadley cells and the vertical structure of convective heating do not show marked improvement relative to lower resolution simulations the amplitude and phase speed of convectively coupled equatorial waves show that although the kelvin waves the observed hierarchical structure of cloud clusters associated with the madden julian oscillation mjo convection and th

effects of convective processes on gcm simulations of the madden julian oscillation abstract weak temporal variability in tropical climates such as the madden julian oscillation mjo is one of major deficiencies in general circulation models gcms the uncertainties in the representation of convection and cloud processes are responsible for these deficiencies with the improvement made to the convection scheme the iowa state university isu gcm which is based on a version of the ncar community climate model is able to simulate many features of mjo as revealed by observations in this study four 10 yr 1979 88 isu gcm simulations with observed sea surface temperatures are analyzed and compared to examine the effects of the revised convection closure convection trigger condition and convective momentum transport cmt on the mjo simulations the modifications made in the convection scheme improve the simulations of amplitude spatial distribution eastward propagation and horizontal and vertical structures especially for the coherent feature of eastward propagating convection a

characterization of momentum transport associated with organized moist convection and gravity waves abstract tropical convection is inherently multiscalar involving complex fields of clouds and various regimes of convective organization ranging from small disorganized cumulus up to large organized convective clusters in addition to being a crucial component of the atmospheric water cycle and the global heat budget tropical convection induces vertical fluxes of horizontal momentum there are two main contributions to the momentum transport the first resides entirely in the troposphere and is due to ascent descent and organized circulations associated with precipitating convective systems the second resides in the troposphere stratosphere and farther aloft and is caused by vertically propagating gravity waves both the convective momentum transport and the gravity wave momentum flux must be parameterized in general circulation models yet in existing parameterizations these two processes are treated independently this paper examines the relationship between the convective momentum transport and

microplate tectonics along a superfast seafloor spreading system near easter island there is a growing easter microplate between the pacific and nazca plates the eastern and western boundaries of the microplate are actively spreading and propagating north and south respectively the northern and southern boundaries are broad transform zones most of the interior of the microplate contains the sort of oblique sheared structures characteristic of zones of transferred lithosphere between propagating and failing spreading centres

regional variation of morphology of organized convection in the tropics and subtropics 1 properties of organized convection with large horizontal area 1000 km2 and with different horizontal structures in the tropics and subtropics are investigated by using 14 years of tropical rainfall measuring mission observations first the convective features cfs are defined as contiguous areas of convective precipitation detected by the tropical rainfall measuring mission precipitation radar using the minor and major axes of fitted ellipses the morphology of the cfs are described as closer to a circular or a line shape regional variations and the properties of organized convection are examined with cfs with area 1000 km2 after categorizing them by their shapes organized convection tends to have larger extent and a higher fraction of near circular shapes over land than over ocean shallow organized convection with maximum radar echo top height below 4 5 km is found mainly over ocean and some coastal regions of all tropical oceans most shallow organized convection is found over the east pacific the fraction of line shaped organized convection is higher over the ocean than over land and is higher in the subtropics than in the tropics more convective lines are found in winter than in summer over oceans but more in summer over land organized convective lines are slightly less convectively intense indicated by lower 30 dbz echo top heights and warmer 37 ghz brightness temperatures than those with near circular shapes orientations of organized convective lines are often aligned with fronts dry lines warm ocean currents coastlines and mountain slopes over the subtropics organized convective lines are tilted more east west over land and more north south over oceans the largest and the most intense convective lines are found over central africa argentina and southeast u s over land and over several warm currents in subtropical oceans

doppler radar observations of an asymmetric mesoscale convective system and associated vortex couplet abstract a study of the 28 may 1985 asymmetric mesoscale convective system mcs observed during pre storm is presented dual doppler analysis revealed a well defined cyclonic mesovortex in the northern portion of the stratiform region in accord with previous studies on this type of circulation at maximum extent the closed cyclonic circulation had a diameter of approximately 80 km and a depth of 7 km a smaller anticyclonic circulation was present to the south of the cyclonic vortex counterrotating vortices in asymmetric mcss have been identified in recent modeling studies however prior to this study observational confirmation of the anticyclonic vortex has been elusive

comparative study of erosion processes of thawed and non frozen soil by concentrated meltwater flow abstract investigating the erosion processes of freeze thaw affected soils caused by concentrated snow glacier meltwater flow can be challenging experimental data can help improve our understanding and modeling of the phenomenon laboratory experiments were conducted to assess the effects of slope gradient and flow rate on soil erosion by concentrated meltwater flow over thawed and non frozen soil surfaces flumes were filled with the silty sandy soil materials collected from a watershed delta formed by deposited sediments before being saturated and stored in a freezer to freeze the soil after the soil was completely frozen the flumes were taken out of the freezer and placed in the experimental hall to thaw the soil for a period of sufficient length until all the soil materials were thawed similarly flumes which were filled with the same soil in the same procedures without undergoing the freezing and thawing process were used for the comparative experiments meltwater was simulated with a tank filled with ice water mixture to supply water flow at a temperature of 0 c the erosion experiments involved four slope gradients of 5 10 15 and 20 and three flow rates of 1 2 and 4 l min with seven rill lengths of 0 5 1 0 2 0 3 0 4 0 5 0 and 6 0 m as determined by the distance between the water inlets and exit sill sediment concentrations at the seven locations formed a rill erosion process which increased exponentially with rill length to approach a limiting value the sediment concentrations were positively correlated with flow rate and slope gradient however the effect of flow rate on sediment concentration was not as significant as that of slope gradient the effect of flow rate on sediment concentration decreased with the increase in slope gradient the maximum sediment concentrations in water flow over thawed slopes were higher than those over non frozen slopes results from these experiments will be useful for estimating erosion model parameters for predicting erosion by meltwater

comparison between a three dimensional simulation and doppler radar data of a tropical squall line transports of mass momentum heat and moisture abstract results from a detailed three dimensional cloud model are extensively compared with doppler radar data in the case of a fast moving tropical squall line observed during the copt81 experiment the comparisons use a two dimensional statistical analysis in which we consider each four dimensional field as the sum of a two dimensional averaged vertical field and a four dimensional residual field representative of along line and temporal fluctuations these fluctuations are analyzed by computing the time average of spatial variances and the temporal variance of spatial averages the results indicate good agreement in both quality and quantity particularly for the vertical velocity and line normal wind the consequences of this agreement are two fold first a physical and comprehensive model of the convective part of a tropical squall line emerges that is coherent with both observations and simulations this conceptual model emphasizes the importance of along line fluctuations second it is possib

influence of upper tropospheric inertial stability on the convective transport of momentum this study verifies the apparent high positive correlation between environmental and convection relative inertial stability and the transport of momentum by deep convection we evaluate the hypothesis that convection structurally aligns itself to best access the region of lowest upper tropospheric inertial stability while forming the lowest convective updraught relative inertial stability a numerical experiment evaluates variations in the structure behaviour and momentum transport characteristics of deep convection across the tropical plume genesis region in the eastern pacific this unique region forms as a precursor to tropical plume genesis and possesses spatially varying very low upper tropospheric inertial stability the potential vorticity locally reaches zero or becomes slightly negative in the northern hemisphere our results show that the vertical transport of horizontal momentum is predictable given knowledge of the inertial stability fields immediately surrounding the convection it is conjectured that the preferred mode of convective organization squall line dominated versus more three dimensional near the intertropical convergence zone is a function of the ambient inertial stability therefore as the convection organizes itself it selects the most efficient access to regions of lowest inertial stability to enable its upper tropospheric outflow copyright 2003 royal meteorological society

systematic variation of drop size and radar rainfall relations time histories of the characteristics of the drop size distribution of surface disdrometer measurements collected at kapingamarangi atoll were partitioned for several storms using rain rate r reflectivity factor z and median diameter of the distribution of water content d0 this partitioning produced physically based systematic variations of the drop size distribution dsd and z r relations in accord with the precipitation types viewed simultaneously by a collocated radar wind profiler these variations encompass the complete range of scatter around the mean z r relations previously reported by tokay and short 1996 for convective and stratiform rain and demonstrate that the scatter is not random the systematic time or space variations are also consistent with the structure of mesoscale convective complexes with a sequence of convective transition and stratiform rain described by various authors there is a distinct inverse relation between the coefficient a and the exponent of the z r relations which has been obscured in prior work because of the lack of proper discrimination of the rain types contrary to previous practice it is evident that there is also a distinct difference in the dsd and the z r relations between the initial convective and the trailing transition zones the previously reported z r relation for convective rain is primarily representative of the transition rain that was included in the convective class the failure of present algorithms to distinguish between the initial convective and the trailing transition rains causes an erroneous apportionment of the diabatic heating and cooling and defeats the primary intent of discriminating stratiform from convective rains

physical mechanisms for the maintenance of gcm simulated madden julian oscillation over the indian ocean and pacific abstractthe kinetic energy budget is conducted to analyze the physical processes responsible for the improved madden julian oscillation mjo simulated by the iowa state university general circulation models isugcms the modified deep convection scheme that includes the revised convection closure convection trigger condition and convective momentum transport cmt enhances the equatorial 10 s 10 n mjo related perturbation kinetic energy pke in the upper troposphere and leads to a more robust and coherent eastward propagating mjo signal in the mjo source region the indian ocean 45 120 e the upper tropospheric mjo pke is maintained by the vertical convergence of wave energy flux and the barotropic conversion through the horizontal shear of mean flow in the convectively active region the western pacific 120 e 180 the upper tropospheric mjo pke is supported by the convergence of horizontal and vertical wave energy fluxes over the central eastern pacific 180 120 w where convection is s

the geometry of propagating rifts abstract the kinematics of two different processes are investigated both of which have been described as rift propagation courtillot uses this term to describe the change from distributed to localised extension which occurs during the early development of an ocean basin the term localisation is instead used here to describe this process to distinguish it from hey s type of propagation localisation generally leads to rotation of the direction of magnetisation to hey propagation means the extension of a rift into the undeformed plate beyond a transform fault detail surveys of the galapagos rift have shown that the propagating and failing rifts are not connected by a single transform fault but by a zone which is undergoing shear the principal deformation is simple shear and the kinematics of this deformation are investigated in some detail the strike of most of the lineations observed in the area can be produced by such deformation the mode of extension on the propagating rift appears to be localised for some periods but to be distributed for others neither simple kinematic arguments nor stretching of the lithosphere with conservation of crust can account for the observed variations in water depth

dye tracer technique for rill flows by velocity profile measurements abstract water flow on hillslope soil surface supplies energy which is required to detach soil particles to transport and deposit sediments therefore flow velocity is a key variable related to hillslope hydrodinamics of soil erosion processes among the different methods available for measuring velocity of shallow interrill and rill flow the trace technique is widely used trace technique is applied by adding a material salt magnetic material water isotope floating object and then measuring the speed of the material to travel a known distance from the injection point when flow velocity is measured using a dye tracing method the mean velocity is calculated by multiplying the measured surface velocity of the leading edge of the tracer plume by a correction factor which was generally empirically deduced the main uncertainty of the dye tracing technique stands in the estimate of this correction factor which is the ratio between the mean flow velocity and the surface velocity the main goal of this paper is establishing a theoretical relationship for calculating the correction factor by using a power velocity profile at first the developed analysis demonstrated that the correction factor only depends on the exponent of the power velocity distribution eq 5 then this theoretical expression of the correction factor was applied using the velocity profiles measured by baiamonte and ferro for the condition of sediment free flow in motion on a rough bed and by coleman for a sediment laden flow moving on a smooth flume using the correction factor values calculated by the velocity measurements carried out for the sediment free flow in motion on a rough bed the relationship between the correction factor and roughness height was established in agreement with a previous study by ali et al for a sediment free flow the correction factor increases with roughness height finally the velocity profile measurements carried out for a sediment laden flow in motion on a smooth bed were used to state the effect of sediment load on the correction factor this last analysis allowed to conclude in agreement with li and abrahams and zhang et al that the correction factor decreases when the sediment load increases

using a thermal tracer to estimate overland and rill flow velocities flow velocity is a basic hydraulic property of surface flows and its precise calculation is necessary for process based hydrological models such as soil erosion and rill development models as well as for modelling sediment and solute transport by runoff this study presents a technique based on infrared thermography to visualize very shallow flows and allow a quantitative measurement of overland flow and rill flow velocities laboratory experiments were conducted to compare the traditional dye tracer technique with this new thermal tracer technique by injecting a combined tracer heated dye into shallow flowing surface water the leading edge tracer velocities estimated by means of infrared video and by the usual real imaging video were compared the results show that thermal tracers can be used to estimate both overland and rill flow velocities since measurements are similar to those resulting from using dye tracers the main advantage of using thermography was the higher visibility of the leading edge of the injected tracer compared with the real image videos copyright 2013 john wiley sons ltd

modern erosion rates in the high himalayas of nepal abstract current theories regarding the connections and feedbacks between surface and tectonic processes are predicated on the assumption that higher rainfall causes more rapid erosion to test this assumption in a tectonically active landscape a network of 10 river monitoring stations was established in the high himalayas of central nepal across a steep rainfall gradient suspended sediment flux was calculated from sampled suspended sediment concentrations and discharge rating curves accounting for solute and bedload contributions the suspended sediment fluxes were used to calculate watershed scale erosion rates that were then compared to monsoon precipitation and specific discharge we find that in individual watersheds annual erosion rates increase with runoff in addition our data suggest average erosion rate increases with discharge and precipitation across the entire field site such that the wetter southern watersheds are eroding faster than the drier northern watersheds the spatially non uniform contemporary erosion rates documented here are at odds with other studies that have found spatially uniform long term rates 10 5 10 6 yr across the pronounced rainfall gradient observed in the region the discrepancy between the modern rates measured here and the long term rates may be reconciled by considering the high erosional efficiency of glaciers the northern catchments were much more extensively glacierized during the pleistocene and therefore they likely experienced erosion rates that were significantly higher than the modern rates we propose that in the northern watersheds the high rates of erosion during periods of glaciation compensate for the low rates during interglacials to produce a time averaged rate comparable to the landslide dominated southern catchments

meltwater erosion process of frozen soil as affected by thawed depth under concentrated flow in high altitude and cold regions changes in thawed depth of frozen soil caused by diurnal and seasonal temperature fluctuations are commonly found in high altitude and latitude regions of the world this is of great importance in terms of its impact on hydrologic and erosion processes there is a need for experimental data to improve our knowledge and modeling of the phenomenon laboratory experiments were conducted in beijing to assess the impacts of thawed depth slope gradient and flow rate on soil erosion by concentrated meltwater flow over underlying frozen soil layer flumes were filled with soil collected from watershed deposited sediments before being saturated and frozen after the soil was completely frozen flumes were taken out of storage to thaw the frozen soil from top to designed depths meltwater was simulated with a tank filled with ice cubes to supply water flow at approximately 0 c the erosion experiments involved four thawed depths of 1 2 5 and 10 cm three slope gradients of 5 10 and 15 and three flow rates of 1 2 and 4 l min with seven rill lengths of 0 5 1 2 3 4 5 and 6 m sediment laden water samples were collected at the lower end of the flume for determination of sediment concentration which showed that it increased exponentially with rill length to approach a maximum value the sediment concentrations were closely correlated with thawed soil depth flow rate and slope gradient shallower thawed depths produced more sediments than thick thawed depths however the effect of flow rate on sediment concentration was not as great as slope gradient which declined with increases in slope gradient results from these experiments are useful for understanding the effect of thawed depth on erosion process in thawed soils subject to freezing and for estimating erosion model parameters

parameterization of convective momentum transport in highly baroclinic conditions the organization of convection by vertical shear strongly affects the transport of horizontal momentum yet the concept of organization has received little attention in convective parameterization here the focus is on open cellular convection in cold air outbreaks under strongly baroclinic conditions that occur to the rear of midlatitude cyclones the principles derived herein are envisaged to apply to baroclinic advection at large in similar shear flows open cellular convection forced by surface fluxes of sensible and latent heat and organized by unidirectional shear is simulated using a three dimensional cloud resolving numerical model the effects of the in cloud pressure field organization and shear on momentum transport are quantified for the simulated clouds a simple analytic model of blocked overturning provides dynamical insight into downgradient momentum transport by the simulated three dimensional cumulonimbus ensemble the overturning circulation having vorticity of the same sign as the ambient shear maintains the far field flow while the blocking effect decelerates in cloud momentum the combined effect is to maintain the mean flow somewhat below its undisturbed value the numerical results and analytic predictions are used to evaluate and interpret two parameterization schemes for convective momentum transport used in operational global weather prediction and climate models at the u k meteorological office and the european centre for medium range weather forecasts finally the authors comment on how the downgradient momentum transport by three dimensional cumulus convection contrasts with momentum mixing concepts as well as countergradient momentum transport by two dimensional squall lines

precipitation and kinematic structure of an oceanic mesoscale convective system part i momentum transport and generation abstract this is the second paper of a two part series documenting the structure of and momentum transport by a subtropical mesoscale convective system near taiwan using doppler radar data and in situ data from the noaa p 3 part i defines the basic system structure and evolution in part ii the momentum transport by the system is estimated and related to system structure and the momentum budget for a portion of the embedded convective band is evaluated profiles of the vertical flux of horizontal momentum are constructed from in situ data doppler radar data and both combined in a coordinate system with u normal to the line and positive eastward since the low level air is feeding the line from the east differences in the fluxes from the two sources appear to be mainly due to an underestimation of the mean vertical velocity from the doppler radar data the discrepancy results partially from the concentration of convergence in the boundary layer precisely where the doppler cannot adequately sample t

multiscale waves in an mjo background and convective momentum transport feedback abstractthe authors use linear analysis for a simple model to study the evolution of convectively coupled waves ccws in a background shear and background moisture mimicking the observed structure of the madden julian oscillation mjo this is motivated by the observation in an idealized setting of intraseasonal two way interactions between ccws and a background wind it is found here that profiles with a bottom heavy moisture content are more favorable to the development of mesoscale squall line like waves whereas synoptic scale ccws are typically more sensitive to the shear strength the mjo envelope is thus divided into three regions in terms of the types of ccws that are favored an onset region in front that is favorable to kelvin waves a mature or active region in the middle in which squall lines are prominent and the stratiform and decay phase region in the back that is favorable to westward inertia gravity wig waves a plausible convective momentum transport cmt feedback is then provide

comparison of rill flow velocity over frozen and thawed slopes with electrolyte tracer method summary freeze thaw erosion is the primary soil water erosion form in high altitude and or high latitude regions the water flow velocity along an eroding rill over frozen and thawed slopes is vital to understanding of rill erosion hydrodynamics this study experimentally measured rill flow velocity over frozen and thawed slopes using electrolyte trace method under pulse boundary model the experiments used three flow rates of 1 2 and 4 l min 1 three slope gradients of 5 10 and 15 the temperature of the rill flow water was supplied at 0 c as controlled with ice water mixture seven sensors were used to measure flow velocity by tracing the solute transport process at 10 110 210 310 410 510 and 610 cm distances from the electrolyte injection position the measured velocity became steady at a distance of about 3 m from the electrolyte injection location where the effect of the pulse boundary condition on the analytic solution to the partial differential equation becomes negligible results showed that flow velocity increased with slope gradient and flow rate on frozen slopes a significant effect was observed on the steepest slope or at the highest flow rate over the thawed slope which changed slightly on the gentle slopes and low flow rates flow velocity was about 25 30 and 40 higher on the frozen soil than on the thawed slope at 5 10 and 15 slopes and about 30 higher over the frozen slope at all flow rates this study demonstrates that water over a frozen slope flows much faster than over a thawed slope this study helps in the study and further understanding of the hydrodynamics of soil erosion and sediment transport behaviors of frozen and thawed slopes

mechanism for northward propagation of boreal summer intraseasonal oscillation convective momentum transport 1 this study demonstrates that the momentum transport by cumulus convection plays a significant role in the organization and northward propagation of intraseasonal iso convection anomalies over the indian and western pacific regions during boreal summer a version of seoul national university s atmosphere ocean coupled general circulation model simulates northward propagation when convective momentum transport cmt is implemented the northward propagation disappears when cmt is disabled an axially symmetric shallowwatermodel withaparameterized cmtis used to understand the role of cmt in the northward propagation of iso the basic mechanism of northward propagation is the lower level convergence to the north of convection which is induced by the secondary meridional circulation associated with large momentum mixing by convection in the region of large mean vertical shear a large meanverticalshearexistsinsouthasianregionduringboreal summer citation kang i s d kim and j s kug 2010 mechanism for northward propagation of boreal summer intraseasonal oscillation convective momentum transport geophys res lett 37 l24804 doi 10 1029 2010gl045072

organized convection parameterization for the itcz abstractmesoscale convective systems mcss are of fundamental importance in the dynamics of the atmospheric circulation and the climate system they are often observed to develop over significant terrain in ambient shear flows in midlatitudes and embedded within the madden julian oscillation mjo and convectively coupled equatorial wave ccew envelopes as well as in the intertropical convergence zone itcz yet general circulation models gcms fail to resolve these systems and their underlying convective parameterizations are not directed to represent organized circulations shear parallel mcss which are common in the itcz have a three dimensional structure and as such present a serious modeling challenge here a previously developed multicloud model mcm is modified to parameterize mcss one of the main modifications is the parameterization of stratiform condensation to capture extended stratiform outflows which characterize mcss resulting from strong upper level jets linear analysis show

heat moisture and momentum budgets of isolated deep midlatitude and tropical convective clouds as diagnosed from three dimensional model output part ii sensitivity to ice phase and small changes in ambient shear strength and low level moisture supply abstract this project uses a three dimensional anelastic cloud model with a simple ice phase parameterization to evaluate the feedback of isolated deep convective clouds over a horizontal scale comparable to one grid cell in typical mesoscale numerical weather prediction models a more specific focus in this paper is the sensitivity of the feedback to modest changes in the initial vertical wind shear intensity and low level moisture supply as well as to the ice phase two parallel sets of comparative simulations are run for a quasi steady severe oklahoma supercell thunderstorm in strong vertical wind shear versus a weaker less persistent and narrower tropical atlantic cumulonimbus with a slowly decaying and pulsating updraft in much weaker shear the horizontal reynolds averaging approach of anthes is adopted to diagnose the budgets for heat moisture and horizontal momentum several similarities and differences between the midlatitude and tropical control experiments were delineated in part i the ma

momentum transport by a line of cumulonimbus abstract the vertical transport of horizontal momentum normal to a line of cumulonimbus observed during gate on 14 september 1974 is against the vertical momentum gradient contrary to the predictions of mixing length theory data from repeated aircraft passes normal to the line s axis at heights from 0 15 to 5 5 km are used to document the flux and determine its source the flux is concentrated in roughly a 25 km wide active zone just behind the leading edge of the line in kilometer scale convective updrafts accelerated upward by buoyancy and toward the rear of the line by mesoscale pressure forces the fall in mesoscale pressure from the leading edge to the rear of the active zone is mainly hydrostatic resulting from relatively high virtual temperatures and the 60 degree tilt of the leading edge from the vertical with the clouds at the surface well ahead of those aloft evaluation of the terms in the momentum flux generation equation confirms that the above process reflected by the velocity buoyan

on the mass flux representation of vertical transport in moist convection abstractthis study investigates to what extent the convective fluxes formulated within the mass flux framework can represent the total vertical transport of heat and moisture in the cloud layer and whether the same approach can be extended to represent the vertical momentum transport using large eddy simulations less of six well documented cloud cases including both deep and shallow convection two methods are used to decompose the les resolved vertical fluxes decompositions based on the coherent convective features using the mass flux top hat profile and by two dimensional fast fourier transform 2d fft in terms of wavenumbers the analyses show that the convective fluxes computed using the mass flux formula can account for most of the total fluxes of conservative thermodynamic variables in the cloud layer of both deep and shallow convection for an appropriately defined convective updraft fraction a result consistent with the mass flux dynamic view of moist convection and previous studies however

what are the sources of mechanical damping in matsuno gill type models the matsuno gill model has been widely used to study the tropical large scale circulations and atmosphere ocean interactions however a common critique of this model is that it requires a strong equivalent linear mechanical damping to get realistic wind response and it is unclear what could provide such a strong damping above the boundary layer this study evaluates the sources and strength of equivalent linear mechanical damping in the walker circulation by calculating the zonal momentum budget using 15 yr 1979 93 of daily global reanalysis data two different reanalyses ncep ncar and 15 yr ecmwf re analysis era 15 give qualitatively similar results for all major terms including the budget residual whose structure is consistent with its interpretation as eddy momentum flux convergence by convective momentum transport cmt the walker circulation is characterized by two distinct regions a deep convection region over the indo pacific warm pool and a shallow convection region over the eastern pacific cold tongue these two regions are separated by a strong upper tropospheric ridge and a strong lower tropospheric trough in the central pacific the resultant pressure gradient forces on both sides require strong approximately 5 10 days damping to balance them because coriolis force near the equator is too small to provide the balance in the deep convection region the damping is provided by cmt and advection together in both the upper and lower troposphere in the shallow convection region on the other hand the damping is provided mainly by advection in the upper troposphere and by cmt in the lower troposphere in other words the upperlevel tropical easterly jet and the low level trade wind are both braked by cmt these results support the use of strong damping in the matsuno gill type models but suggest that the damping rate is spatially inhomogeneous and the cmt related damping increases with the strength of convection implications for gcm s simulation of tropical mean climate are discussed

hot spot ridge crest convergence in the northeast pacific evolution of the juan de fuca ridge during the past 7 m y has been reconstructed taking into account both the propagating rift history and migration of the spreading center in the absolute fixed hot spot reference frame northwestward migration of the spreading center at a rate of 30 km m y has resulted in progressive encroachment of the ridge axis on the cobb hot spot and westward jumping of the central third of the ridge axis more recently than 0 5 ma seamounts in the cobb eickelberg chain are predicted to display systematic variations in morphology and petrology and a reduction in the age contrast between the edifice and underlying crust as a result of the ridge axis approach relative seamount volumes also indicate that magmatic output of the hot spot varied during this interval with a reduction in activity between 2 5 and 4 5 ma compared with relatively more robust activity before and after this period spatial relationships determined in this reconstruction allow hypotheses relating hot spot activity and rift propagation to be evaluated in most cases rift propagation has been directed away from the hot spot during the time period considered individual propagators show some reduction in propagation rate as separation between themore propagating rift tip and hot spot increases but cross comparison of multiple propagators does not uniformly display the same relationship no obvious correlation exists between propagation rate and increasing proximity of the hot spot to the ridge axis or increasing hot spot output taken together these observations do not offer compelling support for the concept of hot spot driven rift propagation however short term reversals in propagation direction at the cobb offset coincide with activity of the heckle melting anomaly suggesting that local propagation effects may be related to excess magma supply at the ridge axis less

convective momentum transport in a simple multicloud model for organized convection abstractconvective momentum transport cmt is the process of vertical transport of horizontal momentum by convection onto the environmental flow the significance of cmt from mesoscale to synoptic and planetary scale organized cumulus convection has been established by various theoretical and observational studies a new strategy mimicking the effect of unresolved mesoscale circulation based on the weak temperature gradient wtg approximation with a gaussian profile to redistribute the heating due to parameterized cumulus convection at the subgrid scale is adopted here to construct a cmt parameterization for general circulation models gcms two main regimes of cmt are considered an upscale squall line regime and a downscale non squall line regime an exponential probability distribution is used to select which of these two effects is active conditional on the state of the large scale shear the shear itself is used as a measure of the persistence of mesoscale organized circulation due to the presen

measurement of rill and ephemeral gully flow velocities and their model expression affected by flow rate and slope gradient abstract water flow velocities in rill and ephemeral gully are useful for estimating hydrodynamics in the study on soil erosion laboratory experiments were conducted to measure erosive rill and ephemeral gully flow velocities including nine unit width flow rates of 0 17 0 33 0 67 1 33 2 67 5 33 10 67 21 33 and 42 67 10 3 m2 s 1 and five slope gradients of 8 7 17 6 26 8 36 4 and 46 6 on sandpaper slope glued with silt loam soil materials to imitate fixed rill and ephemeral gully beds using an electrolyte tracer method the flow velocities measured in this research ranged from 0 31 to 3 34 m s 1 for sediment free water flow the flow velocity fitted well with unit width flow rate and slope gradient by a power function yielding an improved model with higher coefficient of determination than that related flow velocity to flow rate alone the improved model is applicable for flow velocity and soil erosion predictions

roles of barotropic convective momentum transport in the intraseasonal oscillation both observational data analysis and model simulations suggest that convective momentum transport cmt by cumulus convection may play a significant role in the intraseasonal oscillations iso by redistributing atmospheric momentum vertically through fast convective mixing process the authors present a simple theoretical model for the iso by parameterizing the cumulus momentum transport process in which the cmt tends to produce barotropic wind anomalies that will affect the frictional planetary boundary layer pbl in the model with equatorial easterly vertical wind shear vws it is found that the barotropic cmt tends to select most unstable planetary scale waves because cmt suppresses the equatorial ekman pumping of short waves which reduces the shortwave instability from the pbl moisture convergence and accelerates the shortwave propagation the model with subtropical easterly vws has behavior that can be qualitatively different from the model with equatorial easterly vws and has robust northward propagation the basic mechanism of this northward propagation is that the cmt accelerates the barotropic cyclonic wind to the north of iso which will enhance the precipitation by pbl ekman pumping and favor the northward propagation the simulated northward propagation is sensitive to the strength and location of the seasonal mean easterly vws these results suggest that accurate simulation of the climatological mean state is critical for reproducing the realistic iso in general circulation models

an improved method for shallow water flow velocity measurement with practical electrolyte inputs summary the measurement of shallow water flow velocity is of interest to hill slope hydrology and soil erosion mechanics lei et al lei t xia w zhao j 2005 method for measuring velocity of shallow water flow for soil erosion with an electrolyte tracer journal of hydrology 301 139 145 proposed an electrolyte pulse method for the purpose but found that the velocity measured at short distances from the salt injector was not as well estimated as those further away from the injector though it is desirable to estimate velocity at short distances for the purpose of portable device development in this study the system was improved over the previous development an additional sensor was added at the salt injection location to register the input signal as the actual boundary condition function instead of using the pulse assumption two function forms a normal distribution function normal model and a sine function sine model were suggested to approximate the measured boundary conditions these two determined boundary models were used to fit the experimentally obtained data using the least square method to determine the model parameters of the boundary conditions the determined normal model and the sine model were both used to solve the transport processes as the convolution integrals of the pulse response and the actually determined boundary functions so as to determine the shallow water flow velocity laboratory experiments were conducted to get data to verify the proposed methods and computational procedures the experiment device included a flume 4 m long and 15 cm wide a solute injector a data logger for control and data acquisition and a computer with specially designed software for data measurement and velocity estimation the experiments involved three flow rates 12 24 and 48 l min 1 and three slope gradients 4 8 and 12 six sensors were used to measure the solute transport processes at 5 30 60 90 120 and 150 cm from the location where the salt solute was injected into the water flow the solutions of both the normal model and sine model fitted the measured data very well for all the experimental conditions the velocities at different distances from the salt solution injector and under different flow rates and slope gradients as computed by the two models were almost identical which indicated the feasibility of the method and the computational procedures as well as the two suggested models for velocity estimation the velocity values estimated by the normal and sine models agreed also with those measured by using the floating objects and the volumetric method these demonstrated the rationality of the improved methods for shallow water flow velocity measurement the results will be useful to design a practical system for the measurement of shallow water flow velocity

stochastic models for convective momentum transport the improved parameterization of unresolved features of tropical convection is a central challenge in current computer models for long range ensemble forecasting of weather and short term climate change observations theory and detailed smaller scale numerical simulations suggest that convective momentum transport cmt from the unresolved scales to the resolved scales is one of the major deficiencies in contemporary computer models here a combination of mathematical and physical reasoning is utilized to build simple stochastic models that capture the significant intermittent upscale transports of cmt on the large scales due to organized unresolved convection from squall lines properties of the stochastic model for cmt are developed below in a test column model environment for the large scale variables the effects of cmt from the stochastic model on a large scale convectively coupled wave in an idealized setting are presented below as a nontrivial test problem here the upscale transports from stochastic effects are significant and even generate a large scale mean flow which can interact with the convectively coupled wave

analysis of cloud resolving model simulations for scale dependence of convective momentum transport abstractwe use 3d cloud resolving model crm simulations of two mesoscale convective systems at midlatitudes and a simple statistical ensemble method to diagnose the scale dependency of convective

midtropospheric anticyclonic vortex street associated with a cloud band near a cold front abstract the characteristics and formation mechanism of an anticyclonic vortex street of meso scale which appeared near a cold front around the ryukyu islands japan on 11 april 1995 were examined by an analysis of observational data a numerical simulation and a linear stability theory the vortex street was generated near the midtroposphere on the north edge of a cloud band along the cold front the diameter of individual vortices was 70 km and the interval between vortices was 100 200 km the phase speed of the vortices was nearly equal to the wind speed at the 400 hpa level the cloud band was accompanied by a weak wind region in which the along front wind was about 15 m s 1 weaker than that in the environment a region of large anticyclonic horizontal shear 10 4 s 1 existed on the north side of this weak wind region to examine a detailed structure and formation mechanism of the weak wind region a numerical simulation was performed regions of active convection and convective cloud bands

convective momentum transport and perturbation pressure field from a cloud resolving model simulation this study uses a 2d cloud resolving model to investigate the vertical transport of horizontal momentum and to understand the role of a convection generated perturbation pressure field in the momentum transport by convective systems during part of the tropical ocean and global atmosphere coupled ocean atmosphere response experiment toga coare intensive observation period it shows that convective updrafts transport a significant amount of momentum vertically this transport is downgradient in the easterly wind regime but upgradient during a westerly wind burst the differences in convective momentum transport between easterly and westerly wind regimes are examined the perturbation pressure gradient accounts for an important part of the apparent momentum source in general it is opposite in sign to the product of cloud mass flux and the vertical wind shear with smaller magnitude examination of the dynamic forcing to the pressure field demonstrates that the linear forcing representing the interaction between the convective updrafts and the large scale wind shear is the dominant term while the nonlinear forcing is of secondary importance thus parameterization schemes taking into account the linear interaction between the convective updrafts and the large scale wind shear can capture the essential features of the perturbation pressure field the parameterization scheme for momentum transport by zhang and cho is evaluated using the model simulation data the parameterized pressure gradient force using the scheme is in excellent agreement with the simulated one the parameterized apparent momentum source is also in good agreement with the model simulation other parameterization methods for the pressure gradient are also discussed

organized convective systems in the tropical western pacific as a process in general circulation models a toga coare case study we examine the large scale effects of organized convective systems in the tropical western pacific observed during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare in a case study approach we examine realizations of a supercluster associated with the onset of the december 1992 westerly wind burst in the t213 operational medium range weather forecasting model of the european centre for medium range weather forecasts ecmwf we idealize a supercluster as a hierarchy of three interacting scales namely organized cumulonimbus c 1 mesoscale convective systems c 2 and the supercluster component c 3 it is shown that the ecmwf model represents this hierarchy as a c 3 like surrogate whose influence dominates the effect of parametrized convection this causes over prediction of the model tendencies which in the case of zonal momentum is explained in elementary terms the structure of the resolved scale momentum flux is explained by moncrieff s 1992 archetypal theory of organized convection which has been verified against observations and cloud resolving model data sets the parametrization of subgrid scale convective momentum flux in the ecmwf model based on a momentum mixing concept produces subgrid scale tendencies that are physically different from transports associated with cumulonimbus convection in a shear flow we outline a strategy for parametrizing the momentum flux by the c 1 component based on the archetypal model the c 2 component which is part resolved and part parametrized is at odds with the assumptions of scale separation underpinning parametrization it is argued that this component should be represented as part of the prognostic treatment of convectively generated cirrus finally we suggest cloud resolving modelling studies to further quantify the structure and large scale impact of superclusters in a westerly wind burst environment ranging from idealized models to models having data assimilation capability

mesoscale convective systems 1 mesoscale convective systems mcss have regions of both convective and stratiform precipitation and they develop mesoscale circulations as they mature the upward motion takes the form of a deep layer ascent drawn into the mcs in response to the latent heating and cooling in the convective region the ascending layer overturns as it rises but overall retains a coherent layer structure a middle level layer of inflow enters the stratiform region of the mcs from a direction determined by the large scale flow and descends in response to diabatic cooling at middle to low levels a middle level mesoscale convective vortex mcv develops in the stratiform region prolongs the mcs and may contribute to tropical cyclone development the propagation of an mcs may have a discrete component but may further be influenced by waves and disturbances generated both in response to the mcs and external to the mcs waves of a larger scale may affect the propagation velocity by phase locking with the mcs in a cooperative mode the horizontal scale of an mcs may be limited either by a balance between the formation rate of convective precipitation and dissipation of stratiform precipitation or by the rossby radius of the mcv the vertical redistribution of momentum by an mcs depends on the size of the stratiform region while the net vertical profile of heating of the large scale environment depends on the amount of stratiform rain regional variability of the stratiform rain from mcss affects the large scale circulation s response to mcs heating

propagating rift explanation for the tectonic evolution of the northeast pacific the pseudomovie abstract we have developed a new computer graphic technique to use in reconstructing plate tectonic evolution and to make movies illustrating this evolution using this technique we have deciphered the evolutionary history of the juan de fuca area in the northeast pacific and show that a combination of seafloor spreading and rift propagation can explain this seemingly complex area as a simple consequence of the interaction of two rigid plates

the tropospheric response to tropical and subtropical zonally asymmetric torques analytical and idealized numerical model results abstractthe tropospheric response to prescribed tropical and subtropical zonally asymmetric torques which can be considered as idealizations of vertical momentum transfers by orographic gravity waves or convection is investigated the linear analytical gill model response to westward upper tropospheric torques is compared to the response to a midtropospheric heating which is a familiar point of reference the response to an equatorial torque projects onto a kelvin wave response to the east that is of opposite sign to the response to the east of the heating at upper levels in contrast the torque and heating both produce rossby gyres of the same sign to the west of the forcing and the zonal mean streamfunction responses are identical when the forcings are shifted into the northern hemisphere the streamfunction responses have opposite signs there is upwelling in the southern northern hemisphere in response to the torque heating the nonlinear response to westward torques was explored in idealized

a method for estimating momentum fluxes of deep precipitating convection using profiling doppler radar 1 this paper outlines a novel approach for obtaining estimates of momentum fluxes for deep precipitating convection this method relies on data collected by vertically incident profiling doppler radars but may be applied to aircraft or space based radar systems this work represents a significant step forward toward the evaluation of convective momentum transports across regional scales using data from operational satellite systems e g the tropical rainfall measuring mission trmm instrument the new method is demonstrated as convective momentum flux terms and are estimated for deep convection occurring during the third convection and atmospheric moisture experiment camex 3 which was conducted during august and september 1998 these terms contain the most information on the momentum transported in the updrafts and downdrafts of cumulus convection key to the method is that the tilt and orientation of the convective drafts relative to earth s surface are quantified from radar information into perturbation horizontal wind components once an accurate storm motion estimate is provided for perturbation vertical velocities the evaluation of drop size diameters from radar reflectivities and the subsequent evaluation of terminal velocities of hydrometeors and draft motions are necessary information toward applying this technique doppler velocity measurements from the upward looking rd 69 disdromet disdrometer joss waldvogel disdrometer calibrated 915 mhz profiler are used to test the procedures for estimating w the method is tested against numerically simulated convection using the university of wisconsin nonhydrostatic modeling system uw nms mesoscale and cloud resolving model the radar estimated momentum fluxes are found to match in sign and relative magnitude through the depth of the convective clouds studied compared to those obtained from model simulation

a systemic analysis of multiscale deep convective variability over the tropical pacific the multiscale tropical deep convective variability over the pacific ocean is examined with the 4 month highresolution deep convection index derived from satellite imagery with a systemic view the complex itbb phenomenon is described with succinct parameters known as generalized dimensions associated with the correlation structures embedded in the observed time series with higher order dimensions emphasizing extreme convective events it is suggested that convective activities of lifetimes ranging from 1 h to 21 days have interdependence across scales that can be described by a series of power laws hence a spectrum of generalized dimensions that is the time series is multifractal the spatiotemporal features of the time series is ii t t bb bb preliminarily examined by changing the spatial domain from 0 1 83 0 18 to 25 83 258 the multifractal features are weakened with increasing strength of spatial averaging but cannot be eliminated furthermore the data itbb has the property of long range dependency implying that its autocorrelation function decays with a power law in contrast to the zero or exponentially decaying autocorrelation functions for white and commonly used red noise processes generated from autoregressive models physically this means that intensified convection tends to be followed by another intensified event and vice versa for weakened events or droughts such tendency is stronger with larger domain averaging probably due to more complete inclusion of larger scale variability that has more definite trends such as the supercloud clusters associated with the madden julian oscillation mjo the evolution of cloud clusters within an mjo event is studied by following the mjo system across the analysis domain for 21 days convective activities along the front center and rear parts of the mjo event continuously intensify while approaching the date line indicating multifractal features in the range of 1 h to about 5 10 days convective activity along the front and rear edges of the mjo event are more intermittent than in the center the multifractal features of the time series can be approximated by the random multiplicative cascade itbb processes suggesting likely mechanisms for the multiscale behavior and casting concern on the predictability time scale of the observed phenomena

sea beam deep tow investigation of an active oceanic propagating rift system galapagos 95 5 w we have tested and corroborated the propagating rift hypothesis with high resolution sea beam and deep tow data collected over the galapagos 95 5 w propagating rift system the propagating rift is continuously breaking through the cocos plate at a velocity of about 50 km m y with an azimuth of about 273 away from the galapagos hotspot this process transfers cocos lithosphere to the nazca plate including the preexisting spreading center which fails as it is gradually preempted by the propagating rift the spreading center azimuth is being changed by about 8 clockwise by this rift propagation the active propagating and failing rift axes overlap by about 15 km and are joined by a broad and anomalously deep zone of nonrigid plate deformation rather than by a transform fault although rift propagation is continuous on a scale of a few kilometers 50 000 years and lithospheric transferral from one plate to the other occurs mostly continuously as the preexisting rift fails it breaks into discrete segments the geometry of seafloor fabric and tectonic elements such as active and failed rifts the v shaped pattern of pseudofaults and the oblique tectonic fabric in the sheared zone of transferred lithosphere are observed as predicted this quantitative verification provides strong support for the propagating rift hypothesis

the evolution of propagating rifts the magnetic survey carried out by mason and raff1 2 off the north west coast of the us has been central to the development of many of the concepts of seafloor spreading and plate tectonics recently hey and wilson3 have again used this survey to illustrate hey s suggestion4 that ridge segments sometimes increase their length by propagation this process leads to a characteristic pattern of magnetic anomalies offset by discontinuities which hey called pseudofaults because unlike fracture zones they fig 1 were never plate boundaries we demonstrate here how the geometry of the pseudofaults magnetic anomalies and the failed rift can be worked out using velocity triangles and the concept of stability this method was originally developed to understand the evolution of triple junctions between three plates5

detailed tectonics near the tip of the galapagos 95 5 w propagator how the lithosphere tears and a spreading axis develops a model for propagation of an active spreading axis into preexisting lithosphere has been developed based on intensive detailed studies using seamarc ii sea beam deep tow and alvin near the tip of the propagator growing westward at 52 km m y along the east west trending galapagos spreading axis near 95 5 w initial lithospheric rifting appears to be accommodated along reactivated roughly east west abyssal hill faults at the tectonic tip extension leads to downdropping of a keystone block which is pervasively cut by normal faults and fissures the initial volcanism initial volcanic tip occurs about 6 5 km behind the tectonic tip as basalt erupts through these fissures covering most of the keystone block the neovolcanic axial tip occurs another 4 5 km back at the western termination of a well defined axial pillow ridge along which volcanism is localized spreading along the propagator axis accelerates to the full rate 29 mm yr half rate at the full rate tip interpreted to be 10 km behind the neovolcanic axial tip or 21 km behind the tectonic tip a complex pattern of strain in the tip area results from the interaction of plate spreading transform shear stress crack propagation dynamic depression of the western end of the axial valley and the transform zone and variations in the strength thickness heterogeneity and anisotropy of the lithosphere southwesterly curvature of the neovolcanic axis near its tip is inferred to result primarily from the response of young thin weak relatively homogeneous lithosphere to counterclockwise rotation of the maximum tensional stress direction relative to the spreading direction due to the influence of shear stress from the transform zone similar stress interactions likely occur at the tectonic tip but are inferred to be accommodated in this older thick strong heterogeneous and anisotropic lithosphere by oblique slip along a set of left stepping reactivated preexisting east west abyssal hill structures although on a time scale of 106 years the overall process of propagation is mostly continuous rifting at the tectonic tip appears discontinuous at a scale of 1500 m or 30 000 years based on the east west spacing of grabens formed as rifting begins the scale of discontinuity of propagation of the neovolcanic axis is 3 5 km or 50 000 100 000 years based on the distribution of northeast trending features interpreted as beheaded western terminations of paleoneovolcanic axes the extension involved in rifting is 10 20 based on summing the horizontal normal separation of all normal faults and fissures integrated and averaged over the zone of rifting these values are approximately doubled if simple shear listric faulting is dominant rather than pure shear normal faulting

discharges of turbid water during mini surges of variegated glacier alaska u s a discharges of water sediment and dissolved impurities from variegated glacier ala ska were monitored in the early summers of 1980 and 1981 during the occurrence of mini surg es sea sonal trends weat her related eve nts and diurnal variat ions similar to behavior of other temperat e gl acier streams were found the prin cipal effect in the stream associated with mini surge occurrence was a brief discharge of extremely turbi d water the turbidity is assumed to be introduced into the basal hydraulic system by initiation of the fast motion of a mini surge at a time and locat ion on the upper glacier known from oth er meas ure ments the mean water velocity in the hydraulic system over the int erven ing distance is thereby determined 0 3 m s i the mean water velocity together with the water discharge 16 m3 s 1 at the terminus places con straints on the distribution of water velocity u and total cros s sectional area at of the flow paths along the gl acier base this leads to the con clusion that within the zone of mini surge occurrence in its unpe rturbed state u is about 0 1 m s 1 or possibly less at is about 10 2 m2 or possibly more and it must be divided into a very large number of small passag eways be blocked by constrict ions or both the total water cro ss se ction corresponds to a layer 0 1 2 m thick when spr ead unifo rmly over the glacier width the water velocity is clos e to or less than the propa gation velo city of the mini s urges bet ween the zone affected by mini surges and the stream a dyna mically less active lower section of the glacier is proba bly underlain by a small number of conduits in which the water velocity may be very high 2 m s i water di scharge follo wing the mini surges puts an upper limit on water storage changes ass ociated with the anomalous ice motion

simulated convective lines with parallel stratiform precipitation part i an archetype for convection in along line shear abstract this article the first of two describing convective lines with parallel stratiform ps precipitation addresses the basic kinematic and precipitation features of these systems the ps mode appears to be the preferred organizational structure in environments with line parallel vertical wind shear this archetype for long lived convective systems has received relatively little attention to date and yet it is frequently implicated in flash flooding because it entails both the along line movement of hydrometeors and back building convective development as a reality check this paper presents conventional observations of the wind and reflectivity fields associated with an archetypal ps system from 2 may 1997 thereafter analyses of idealized numerical simulations serve as the basis for a more detailed investigation of ps systems internal structures and processes the observations and simulations suggest several unique aspects of the ps structure the environment s vertically sheared 3d wind prof

scale interactions involved in the initiation structure and evolution of the 15 december 1992 mcs observed during toga coare part ii mesoscale and convective scale processes abstract this paper the second of a series documents the precipitation and kinematic and thermodynamic structure of a tropical mesoscale convective system observed by instrumented aircraft on 15 december 1992 during toga coare radar derived precipitation fields indicate that the studied system consists of two subsystems s1 and s2 characterized by distinct internal dynamics and morphological structures the retrieved kinematic and thermodynamic structures are compared in detail with the synoptic scale characteristics described in part i of this paper so as to evaluate the scale interactions involved in the internal organization of this convective system it is shown essentially that the synoptic scale circulation governs the mesoscale and convective scale motions and therefore determines the internal organization of the selected system in particular this study highlights the major role played by the synoptic scale vertical wind shear in the internal structure of this tropical mesoscale system m

effects of vertical wind shear on the cumulus transport of momentum observations and parameterization abstract dynamical effects of organized cumulus convection on its environment with vertical wind shear are studied analyses of the wind field and momentum budget residual for mesoscale convective systems observed during sesame and pre storm reveal systematic differences in the vertical transport of horizontal momentum between mesoscale convective complex mcc and squall line cases in the mcc a distinct minimum in wind speed appears over the area of intense convection and the momentum budget residual acts to decelerate the environmental wind and to reduce the upper level vertical shear therefore the inferred vertical transport of momentum in the mcc is downgradient in the upper layer on the other hand in the squall line there is no wind speed minimum and the upper level vertical shear of the line normall component of the environmental wind increases as convection develops thus the vertical transport of momentum normal to the squall line is upgradient in the upper layer although the transport of

field measurement of the velocity of overland flow using dye tracing a new method of computing the mean velocity of overland flow using dye tracing is proposed in which a specified cross section is divided into zones of relatively uniform flow characteristics termed partial sections the mean surface velocity for each partial section is determined by timing the passage of injected dye and this figure is multiplied by 0 67 0 70 or 0 80 depending on whether the flow is laminar transitional or turbulent to give mean velocity the mean velocity for the entire cross section is calculated by multiplying the mean velocity of each partial section by its cross sectional area summing the products for all the partial sections and dividing by the total area of the cross section a field test shows that mean velocity derived in this manner differs from mean velocity derived by the discharge method i e by dividing discharge measured volumetrically by cross sectional area by an average of only 7 07 per cent thus the partial section technique appears to provide a reliable method of estimating mean velocity of overland flow

mesoscale motion fields associated with a slowly moving gate convective band abstract the structure of the convective band of 14 september in the dense gate observing array is determined using wind and thermodynamic data primarily from multiple aircraft penetrations which are well distributed in the vertical and in time the well defined mesoscale features in the line which are 10 40 km in scale quasi two dimensional and persist for several hours determine the distribution of the convective scale features which are 5 km or less in size three dimensional not generally detectable for more than one flight leg at the leading edge a 30 km zone of strong ascent is computed from two dimensional continuity here lifting of the ambient air creates a favorable environment not found elsewhere for deep cumulonimbus clouds to develop their updrafts are weak 2 4 m s 1 on the average behind the updraft zone below 3 4 km is a broad descent zone it corresponds to the stratiform rain area and has little convection and some drying at lower levels on the average the mass flux by

multiscale interactions in an idealized walker cell analysis with isentropic streamfunctions abstracta new approach for analyzing multiscale properties of the atmospheric flow is proposed in this study for that the recently introduced isentropic streamfunctions are employed here for scale decomposition with haar wavelets this method is applied subsequently to a cloud resolving simulation of a planetary walker cell characterized by pronounced multiscale flow the resulting set of isentropic streamfunctions obtained at the convective meso synoptic and planetary scales capture many important features of the across scale interactions within an idealized walker circulation the convective scale is associated with the shallow congestus and deep clouds which jointly dominate the upward mass flux in the lower troposphere the synoptic and planetary scales play important roles in extending mass transport to the upper troposphere where the corresponding streamfunctions mainly capture the first baroclinic mode associated with large scale overturning circulation the intermediate scale features of

method for measuring velocity of shallow water flow for soil erosion with an electrolyte tracer abstract measurement of the velocity of shallow water flow on a hill slope is of great importance in soil erosion studies electrolyte tracers have been tried to estimate mean velocity of water flow with the velocity of the leading edge of the solute propagation multiplied with a somewhat arbitrary correction factor in this study an analytical solution of solute tracer transport was formulated to serve as the mathematical foundation for measuring shallow water flow velocity to estimate the flow velocity a procedure was advanced in the procedures the analytical solution is fitted with the measured propagation curve and given the the least square estimation of velocity a detailed mathematical description is outlined for this purpose experimental results are given to show the feasibility of the method including the analytical solution and the estimation procedures this study provides the theoretical foundation for measuring the velocity of shallow water flow and for studies of overland solute transport

convection over the pacific warm pool in relation to the atmospheric kelvin rossby wave abstract deep convection over the western tropical pacific warm pool is analyzed in terms of its relation to the atmospheric kelvin rossby wave which dominates the large scale flow during the austral summer the study uses doppler radar data collected by aircraft and ship radars during different time periods in the tropical ocean global atmosphere coupled ocean atmosphere response experiment to characterize the mesoscale circulations of organized convective cloud systems occurring throughout the season the study focuses on convection in two contrasting phases of the wave the westerly onset region just west of the point within the wave where low level easterlies change to westerlies and the strong westerly region or westerly wind burst lying between the large scale counterrotating gyres of the kelvin rossby wave in the westerly onset region the zonal wind component had midlevel easterlies overlying low level westerlies in the strong westerly region a deep layer of westerlies extended from the

marine tectonics processes at mid ocean ridges the use of multibeam echo sounders and various side looking sonar systems has greatly increased our knowledge and understanding of mid ocean ridge mor processes since the last iugg review on mid ocean ridge research macdonald 1983 the extensive use of swath mapping tools such as sea beam deep tow seamarc i and ii the application of multichannel seismic reflection techniques to the detection of axial magma chambers and the use of satellite data in the study of oceanic lithosphere have rejuvenated marine tectonics and have generated and stimulated a large number of important contributions this review will focus on what we feel were the major developments in marine tectonics with an emphasis on mid ocean ridges in the last four years certain topics such as marine seismicity and satellite studies are only briefly mentionned for reference and will be covered in greater detail in other reviews because of the exponential growth in the number of publications related to mors during 1982 1986 only a few references pertinent to each of the major research topics will be quoted in the text as examples but the reader will find an extensive bibliography at the end of the text references published prior to 1982 were added only where appropriate

crustal structure and kinematics of the tammar propagating rift system on the mid atlantic ridge from seismic refraction and satellite altimetry gravity the tammar segment of the mid atlantic ridge forms a classic propagating system centred about two degrees south of the kane fracture zone the segment is propagating to the south at a rate of 14 mm yr 1 15 per cent faster than the half spreading rate here we use seismic refraction data across the propagating rift sheared zone and failed rift to investigate the crustal structure of the system inversion of the seismic data agrees remarkably well with crustal thicknesses determined from gravity modelling we show that the crust is thickened beneath the highly magmatic propagating rift reaching a maximum thickness of almost 8 km along the seismic line and an inferred from gravity thickness of about 9 km at its centre in contrast the crust in the sheared zone is mostly 4 5 6 5 km thick averaging over 1 km thinner than normal oceanic crust and reaching a minimum thickness of only 3 5 km in its nw corner along the seismic line it reaches a minimum thickness of under 5 km the pmp reflection beneath the sheared zone and failed rift is very weak or absent suggesting serpentinisation beneath the moho and thus effective transport of water through the sheared zone crust we ascribe this increased porosity in the sheared zone to extensive fracturing and faulting during deformation we show that a bookshelf faulting kinematic model predicts significantly more crustal thinning than is observed suggesting that an additional mechanism of deformation is required we therefore propose that deformation is partitioned between bookshelf faulting and simple shear with no more than 60 per cent taken up by bookshelf faulting

simulation modeling and dynamically based parameterization of organized tropical convection for global climate models abstracta new approach for treating organized convection in global climate models gcms referred to as multiscale coherent structure parameterization mcsp introduces physical and dynamical effects of organized convection that are missing from contemporary parameterizations the effects of vertical shear are approximated by a nonlinear slantwise overturning model based on lagrangian conservation principles simulation of the april 2009 madden julian oscillation event during the year of tropical convection yotc over the indian ocean using the weather research and forecasting wrf model at 1 3 km grid spacing identifies self similar properties for squall lines mcss and superclusters embedded in equatorial waves the slantwise overturning model approximates this observed self similarity the large scale effects of mcsp are examined in two categories of gcm first large scale convective systems simulated in an aquaplanet model are approximated by slantwise overturning with attention to convective mome

an explicit representation of vertical momentum transport in a multiscale modeling framework through its 2 d cloud resolving model component in this study an explicit representation of vertical momentum transport by convective cloud systems including mesoscale convective systems mcss is proposed and tested in a multiscale modeling framework mmf the embedded cloud resolving model crm provides vertical momentum transport in one horizontal direction the vertical momentum transport in the other direction is assumed to be proportional to the vertical mass flux diagnosed from the crm in addition to the effects of entrainment and detrainment in order to represent both upgradient and downgradient vertical momentum transports the orientation of the embedded crm must change with time instead of being stationary typically in mmfs the orientation is determined by the stratification of the lower troposphere and environmental wind shear introducing the variation of the orientations of the embedded crm is responsible for reducing the stationary anomalous precipitation and many improvements improvements are strengthened when the crm simulated vertical momentum transport is allowed to modify the large scale circulation simulated by the host general circulation model these include an improved spatial distribution amplitude and intraseasonal variability of the surface precipitation in the tropics more realistic zonal mean diabatic heating and drying patterns more reasonable zonal mean large scale circulations and the east asian summer monsoon circulation and an improved annual mean implied meridional ocean transport in the southern hemisphere further tests of this convective momentum transport parameterization scheme will be performed with a higher resolution mmf to further understand its roles in the intraseasonal oscillation and tropical waves monsoon circulation and zonal mean large scale circulations

coupling of convective momentum transport with convective heating in global climate simulations abstract the effects of convective momentum transport cmt on global climate simulations are examined in this study comparison between two sets of 20 yr 1979 98 integration using the ncar community climate model version 3 ccm3 illustrates that the inclusion of cmt in the convection scheme systematically modifies the climate mean state over the equatorial region the convective momentum tendencies slow down the equatorward flow at higher latitudes near the surface and weaken the equatorial convergence and convection this reduces the convective heating and drying around the equator and produces an improved meridional distribution within the upward branch of the hadley circulation the major heating peak during the boreal winter is moved to south of the equator at about 10 s which is closer to the heat budget residuals of the ecmwf reanalysis data the responses of meridional wind to the reduced heating result in the secondary meridional circulation within the intertropical convergence zone

the role of momentum transport in the motion of a quasi idealized mesoscale convective system abstract momentum transport is examined in a simulated midlatitude mesoscale convective system mcs to investigate its contribution to mcs motion momentum budgets are computed using model output to quantify the role of specific processes in determining the low level wind field in the system s surface based cold pool results show that toward the leading convective line of the mcs and near the leading edge of the cold pool the momentum field is most strongly determined by the vertical advection of the storm induced perturbation wind across the middle rear of the system the wind field is largely a product of the pressure gradient acceleration and to a lesser extent the vertical advection of the background environmental i e base state wind the relative magnitudes of the vertical advection terms in an eulerian momentum budget suggest that for gust front driven systems downward momentum transport by the mcs is a significant driver of mcs motion and potentially severe surface winds results furthe

developing a magnetic tracer to study soil erosion abstract soil erosion is commonly measured as the quantity of sediment leaving a plot or watershed the techniques for measuring soil erosion patterns and sediment redistribution within plots or watersheds by direct monitoring are very limited the objective of this study was to develop a direct and non intrusive tracer method to study the sources patterns and rates of erosion and deposition of sediments in erosion plots the magnetic tracer developed in this study consisted of polystyrene plastic beads embedded with a magnetic powder magnetite the magnetized beads with a mean weight diameter of 3 2 mm and particle density of about 1 2 g cm 3 were uniformly mixed with soil and tested in the laboratory using simulated rainfall and inflow studies to simulate the interrill and rill components of soil erosion respectively in the interrill and rill experiments the tracer was transported in the same proportion it was initially mixed with the soil given this fact a magnetometer which measures the soil s magnetic susceptibility could be used to identify areas of deposition or detachment the magnetic susceptibility would be increased or reduced depending on whether deposition or detachment occurs to simulate detachment and deposition a magnetometer was tested for different tracer concentrations and different thickness of soil containing the tracer the magnetometer promises to be a sensitive accurate and useful tool to study the spatial variation of soil erosion when magnetic tracers are used

king s trough reactivated pseudo fault of a propagating rift summary a compilation of magnetic data in the western north atlantic shows that seafloor spreading magnetic anomalies 26 to 18 are dislocated across a pseudo fault with a direction mirroring that of king s trough it is interpreted that this feature and king s trough were formed by northward propagation of the rift initiated by a hotspot that created the azores biscay rise the rift propagation stopped when king s trough became part of the plate boundary between eurasia and iberia at chron 17 most of the present day structure of king s trough was created by extensional motion across this plate boundary from chron 17 to 9 6c