surface pressure disturbance in the ebro valley spain produced by the pyrenees mountains during pyrex in this paper the pressure anomaly created by the pyrenees during the pyrenees experiment pyrex in the ebro valley is studied and analysed in the first part pressure disturbance is obtained during some selected cases of pyrex by subtracting the synoptic component from the pressure registered by microbarographs and regular meteorological stations located in the area as expected from a linear model a low pressure is found for northerly synoptic winds and a high pressure for southerly synoptic winds data shows that the maximum pressure anomaly observed may reach values of the order of 7 hpa pressure anomaly spatial patterns found inside the valley are classified by using principal component analysis pca it is found that the first axes deduced from the pca carried out represent 75 of the variance in pressure data indicating that all the stations analysed observed pressure anomalies in a correlated manner pressure anomalies are then related to incident air characteristics expressed as froude and rossby numbers significant correlation is generally found with these numbers in all cases demonstrating the dynamic origin of the pressure anomaly computed copyright 2007 royal meteorological society

block distributions on itokawa abstract asteroid 25143 itokawa is a small elongated asteroid with two distinct parts the evolution of this two part body has been the source of speculation the scenarios for the formation of this asteroid include two body capture catastrophic disruption and rapid reaccretion yorp spin up and mass shedding and disruption or partial disruption with two body reaccretion in this paper we use the global and regional analyses of block populations and size frequency distributions as evidence of the probable evolutionary history of itokawa the block sample used in this study is believed to be complete for blocks of size 6 m and consists of a sample more than twice as large as previous known studies although block size frequency distributions hint at different evolutionary paths for the head and the body their differences are not statistically significant the distribution of blocks across each body provides clues as to the histories of each body the head is populated in a spherically symmetric fashion while the body has a distinct equatorial peak when considering that the head and the body may have been separate entities for a period of time and estimating a rotational axis using minimum rotational energy considerations the preferential equatorial distribution becomes even more pronounced we interpret this as excellent evidence for the partial disruption of a proto itokawa subsequent planarization of a debris field and reaccretion of the head and the body into its present configuration

autumnal precipitation distribution on the southern flank of the alps a numerical model study of the mechanisms during the autumn there are frequent events of heavy precipitation on the southern slopes of the meso scale alpine chain moreover the accompanying climatology exhibits a distinctive spatial distribution with some meso scale regions of enhanced precipitation such as the wet spot in the vicinity of lago maggiore possible mechanisms to account for the observed spatial distribution are established using a heuristic model based approach it is shown using a mesoscale model that the response to a steady horizontally uniform and moisture laden flow impinging upon a comparatively realistic representation of the alpine chain can reproduce both the overall meso scale precipitation distribution and its meso scale sub structure the nature of the simulated flow regime over around or intermediate is sensitive to the strength of the ambient geostrophic flow and its modification in the planetary boundary layer contrariwise the simulated precipitation distribution in the lago maggiore wet spot is comparatively insensitive to the changes in direction of the incident geostrophic flow from south to south west and in strength in the range 10 30 m s 1 although there is a marked change in the structure of the near alpine flow this systematic precipitation enhancement appears to be related to the relative strength and compensating effects of an easterly barrier jet tracking along the zonally elongated part of the alps and an air stream channelled between the maritime alps and the apennines further evidence to the above interpretation of the meso scale precipitation distribution is given with simulations conducted using a smoothed and schematic representation of the alpine chain likewise the sensitivity to the presence of a lago maggiore like indentation of the topography is tested and evidence is provided of a further indentation induced precipitation enhancement at the local scale copyright 2004 royal meteorological society

modification of precipitation by coastal orography in storms crossing northern california abstract this study compiles and interprets three dimensional weather surveillance radar 1988 doppler wsr 88d data during a 2 5 yr period and examines the typical orographic effects on precipitation mainly associated with winter storms passing over coastal northern california the three dimensional mean reflectivity patterns show echo structure that was generally stratiform from over the ocean to inland over the mountains the flow above the 1 km level was strong enough to be unblocked by the terrain and the mean echo pattern over land had certain characteristics normally associated with an unblocked cross barrier flow both on the broad scale of the windward slopes of the coastal mountains and on the scale of individual peaks of the terrain on the windward side upward sloping echo contours on the scale of the overall region of coastal mountains indicated broadscale upslope orographic enhancement on a smaller scale the mean stratiform echo pattern over the mountains contained a strong embedded core

climatology of barrier jets along the alaskan coast part i spatial and temporal distributions abstract this paper investigates the temporal and spatial climatology of coastal barrier jets in the gulf of alaska the jets are divided into two categories based upon the origin of the air involved classic barrier jets fed primarily by onshore flow and hybrid jets fed primarily by gap flow from the continental interior the analyses are compiled from five years 1998 2003 of synthetic aperture radar images from the radarsat 1 satellite totaling 3000 images thermodynamic and kinematic data from the ncep reanalysis is used in the interpretation of the results the majority of coastal barrier jets occur during the cool season with the coastline near mount fairweather and the valdez cordova mountains experiencing the greatest number of barrier jets hybrid jets are even more strongly restricted to the cool season and are commonly found to the west of cross sound yakutat bay and icy bay some interannual variability in the total number of jets is observed coastal barrier jet formation is associate

terrain trapped airflows and orographic rainfall along the coast of northern california part ii horizontal and vertical structures observed by a scanning doppler radar abstractthis study documents the mean properties and variability of kinematic and precipitation structures associated with orographic precipitation along the coast of northern california in the con

role of eastern ghats orography and cold pool in an extreme rainfall event over chennai on 1 december 2015 chennai and its surrounding region received extreme rainfall on 1 december 2015 a rain gauge in the city recorded 494mm of rainfall within a span of 24 h at least a 100 yr event the convective system was stationary over the coast during the event this study analyzes how the eastern ghats orography and moist processes localized the rainfall era interim data show a low level easterly jet llej over the adjacent ocean and a barrier jet over the coast during the event acontrol simulation with the nonhydrostatic weather research and forecasting wrf model shows that the eastern ghats obstructed the precipitation driven cold pool from moving downstream resulting in the cold pool piling up and remaining stationary in the upwind direction the cold pool became weak over the ocean it stratified the subcloud layer and decelerated the flow ahead of the orography hence the flow entered a blocked regime maximum deceleration of the winds and uplifting happened at the edge of the cold pool over the coast therefore a stationary convective system and maximum rainfall occurred at the coast as a result of orographic blocking propagation of a low pressure system lps was obstructed because of the topographic beta effect the lps subsequently traveled a southward path in a sensitivity experiment without the orography the cold pool was swept downstream by the winds clouds moved inland in the second experiment with no evaporative cooling of rain the cold pool did not form flow as well as clouds moved over the orography

an observation of the surface circulation in a gulf stream frontal perturbation in the period of 3 16 june 1979 a satellite tracked free drifting buoy passed through a gulf stream frontal perturbation and was entrained into a warm filament on the shoreward side of the perturbation significant speed convergence was noted as the buoy passed through the perturbation and approached the counterclockwise turn into the warm filament in the warm filament the buoy drifted to the southwest at speeds of about 0 1 to 0 3 m sec eventually the buoy drifted out of the filament and went westward in an apparent response to wind induced surface drift

interaction of low level flow with the western ghat mountains and offshore convection in the summer monsoon abstract seven year averaged values of percent frequency of occurrence of highly reflective cloud for the months june july and august indicate that offshore convection is a major component of the cloudiness of the southwest monsoon principal areas of convection occur off of the western coats of india burma thailand and the philippines this study concentrates on the area upstream of the western ghats mountains of india analysis of a special boundary layer mission flown during the wmo icsu summer monsoon experiment leads us to believe that partial deceleration of the monsoon flow by upstream blocking effects of the mountains initiates and maintains a vertical and horizontal motion field that could support the observed convection data obtained on this mission allow a large scale momentum budget computation for the subcloud layer which shows pressure deceleration to be significant the budget dominated by advection predicts an increase of average wind speed which is observed the pressure decelera

impact experiments on ice the results of cratering and fragmentation experiments on pure ice are reported the projectiles used are cylindrical aluminum poly carbonate teflon and pyrophyllite fired at velocities between 110 m sec and 680 m sec with kinetic energies at impact between 2 and 500 joules crater diameters pit diameters in the ice were about two times larger than craters in the same energy range in basalts the ratios of pit diameter spall diameter are about three and the ratios of depth of crater spall diameter are between 0 1 and 0 3 which are close to the depth diameter ratios observed in basalts the crater diameter in ice is also well expressed as a single function of the late stage effective energy defined recently by mizutani et al 1983 the specific energy for complete destruction of ice target is about 50 j kg which is two orders of magnitude smaller than that of basalt the present experimental data on cratering and fragmentation of ice show that the impacts associated with the largest craters on callisto and mimas must have severely fractured the whole satellites and that those giant impacts with the kinetic energy of 1023 to 1027 joules probably affected significantly the evolution of the satellites

pressure perturbations and upslope flow over a heated isolated mountain abstract surface and upper air data collected as part of the cumulus photogrammetric in situ and doppler observations cupido experiment during the 2006 monsoon season around the santa catalina mountains in southeast arizona are used to study the diurnal variation of the mountain scale surface convergence and its thermal forcing the thermal forcing is examined in terms of a horizontal pressure gradient force which is derived assuming hydrostatic balance the mountain is 30 km in diameter 2 km high and relatively isolated the environment is characterized by weak winds a deep convective boundary layer in the afternoon and sufficient low level moisture for orographic cumulus convection on most days the katabatic divergent surface flow at night and anabatic convergent flow during the day are in phase with the diurnal variation of the horizontal pressure gradient force which points toward the mountain during the day and away from the mountain at night the daytime pressure deficit over the mo

a numerical study on the effects of taiwan topography on a convective line during the mei yu season abstract during the morning hours on 23 may 2002 a convective line associated with a mei yu front brought heavy rainfall along the coast of central taiwan under favorable synoptic conditions of warm air advection and large convective available potential energy cape of over 3000 m2 s 2 doppler radar observations indicated that deep convection was organized into a linear shape with a northeast southwest orientation along the front about 70 km offshore from taiwan over the northern taiwan strait the system then moved toward taiwan at a slow speed of about 4 m s 1 in the present study the effects of taiwan topography on this convective line and subsequent rainfall distribution were investigated through numerical modeling using the nagoya university cloud resolving storm simulator cress at a 2 km horizontal grid size experiments with different terrain heights of taiwan including full terrain ftrn half terrain htrn and no terrain ntrn were performed the control run using full terrain and co

monsoon convection in the himalayan region as seen by the trmm precipitation radar three dimensional structure of summer monsoon convection in the himalayan region and its overall variability are examined by analyzing data from the tropical rainfall measuring mission trmm precipitation radar over the june september seasons of 2002 and 2003 statistics are compiled for both convective and stratiform components of the observed radar echoes deep intense convective echoes 40 dbz echo reaching heights 10 km occur primarily just upstream south of and over the lower elevations of the himalayan barrier especially in the northwestern concave indentation of the barrier the deep intense convective echoes are vertically erect consistent with the relatively weak environmental shear they sometimes extend above 17 km indicating that exceptionally strong updraughts loft graupel to high altitudes occasionally scattered isolated deep intense convective echoes occur over the tibetan plateau wide intense convective echoes 40 dbz echo 1000 km2 in horizontal dimension also occur preferentially just upstream of and over the lower elevations of the himalayas most frequently in the northwestern indentation of the barrier the wide intense echoes have an additional tendency to occur along the central portion of the himalayas and they seldom if ever occur over the tibetan plateau the wide intense echoes exhibit three mesoscale structures amorphous areas lines parallel to the mountain barrier and arc shaped squall lines perpendicular to and propagating parallel to the steep himalayan barrier the latter are rare generally weaker than those seen in other parts of the world and occur when a midlevel jet is aligned with the himalayan escarpment deep and wide intense convective echoes over the northwestern subcontinent tend to occur where the low level moist layer of monsoon air from the arabian sea meets dry downslope flow in a manner reminiscent of severe convection leeward of the rocky mountains in the central usa as the low level layer of moist air from the sea moves over the hot arid northwestern subcontinent it is capped by an elevated layer of dry air advected off the afghan or tibetan plateau the capped low level monsoonal airflow accumulates instability via surface heating until this instability is released by orographically induced lifting immediately adjacent to or directly over the foothills of the himalayas broad 50 000 km2 in area stratiform echoes occur in the eastern and central portions of the himalayan region in connection with bay of bengal depressions their centroids are most frequent just upstream of the himalayas in the region of the concave indentation of the barrier at the eastern end of the range the steep topography apparently enhances the formation and longevity of the broad stratiform echoes monsoonal depressions provide a moist maritime environment for the convection evidently allowing mesoscale systems to develop larger stratiform echoes than in the western himalayan region copyright 2007 royal meteorological society

surface pressure perturbations produced by an isolated mesoscale topographic barrier part i general characteristics and dynamics abstract this paper presents and analyzes the results of the olympex field experiment during which the operational observational network around the olympic mountains of washington state was enhanced with eleven high accuracy microbarographs it is found that this isolated mesoscale topographic barrier produces both a windward high and lee low at the surface with the latter generally possessing greater amplitude the difference in amplitude between these two features lessens for higher froude numbers the mesoscale pressure perturbation produced by the barrier is highly correlated with the incoming wind speed averaged over a 100 mb layer centered at 850 mb a comparison between the results of this experiment and linear theory reveals that linear theory does quite well in predicting the shape and amplitude of the mesoscale surface pressure perturbations for higher froude numbers this fact and the high correlation of surface pressure perturbations with incoming wind speed suggests that the surface mesos

investigation of microphysical processes occurring in isolated convection during name abstracta major objective of the north american monsoon experiment name was to quantify microphysical processes within convection occurring near the steep topography of northwestern mexico a previous study compared examples of isolated convection using polarimetric radar data and noted a dependence on mixed phase processes via drop freezing and subsequent riming growth along the coastal plain and western slopes with an even greater role of melting ice in rainfall production over the highest terrain despite the higher frequency of these isolated cells compared to organized convective systems the latter were responsible for 75 of rainfall therefore this study seeks to evaluate the role of mesoscale organization on microphysical processes and describes the evolution of these systems as a function of topography similar to isolated convection both warm rain and ice based processes played important roles in producing intense rainfall in organized convection although similarities existed between cell

characteristics of ocean surface winds in the lee of an isolated island observed by synthetic aperture radar abstractcharacteristics of ocean surface winds around an isolated island are examined in relation to atmospheric stability using a synthetic aperture radar sar and rawinsonde sounding observations the sar derived winds on 22 may 2009 indicate a low level jet extending over 30 km behind the island around the time of sar acquisition winds intensified on the leeward side in association with the stabilization of stratified flows which suggests the connection of the sar derived jet with downslope winds a number of sar derived winds elucidate typical wind patterns and their transitions depending on the nondimensional mountain height for cases of large 2 a wake is formed in the lee of the island and low level jets produce strong wind shear on both sides of the wake for cases of relatively small 1 75 although a weak wind region is formed behind the mountain no wind jets develop as a transition of the above two cases a low level jet develops in the lee of the island as in the case on 22 may

experimental impacts into chondritic targets part i disruption of an l6 chondrite by multiple impacts mr after each shot was impacted by a 3 18 mm ceramic sphere at a nominal speed of 2 km s 1 this continued until the mass of the largest remaining piece was less than half the mass of the target presented to that shot ms two chunks of bushveldt gabbro with similar initial masses were also impacted under the same conditions until mr was less than half m0 the two gabbro targets required a total of 1 51 10 7 and 1 75 10 7 erg g 1 to attain 0 27 and 0 33 mr m0 respectively the chondrite however was considerably tougher reaching 0 40 and 0 21 mr m0 only after receiving 2 37 10 7 and 3 10 10 7 erg g 1 respectively the combined ejecta and spallation products from the gabbro impacts were coarser than those from the chondrite and in sufficient quantities that the new surface areas exceeded those from the meteorite until the fifth shot in the chondrite series which was the number of impacts required to disrupt each gabbro target i e mr m0 0 5 unlike the behavior shown in previous regolith evolution series neither gabbro target produced an enhancement in the size fraction reflecting the mean size of the crystals composing the rock about 3 mm an effect possibly related to the width of the shock pulse the original chondrite was so fine grained and fractured and the variance in its grain size distribution so large that effects related to grain size were relegated to the 63 m fraction impacts into alh 85017 produced abundant fine grained debris but otherwise the slopes of its size distributions were comparable to those from other experiments involving natural and fabricated terrestrial targets the characteristic slopes of the chondrite s size distributions however were notably more constant over the entire nine impact series than those from any of the terrestrial targets a testament to the control over comminution apparently exerted by pre existing fractures and other microscopic damage in the meteorite the enhancement in the finer fraction of debris from alh 85017 indicates that ordinary chondrites in solar orbit would be very efficient contributors to the cosmic dust complex at the same time the greater resistance to disruption displayed by ordinary chondrites relative to that exhibited by igneous rocks indicates that a selection effect could be operative between the annealed ordinary chondritic breccias and relatively weaker differentiated meteorites preferential survival from their time in the regoliths of their parent bodies through their transit to earth and passage through the atmosphere suggests that meteorite collections could be biased in favor of the ordinary chondrites

mesoscale organization and structure of orographic precipitation producing flash floods in the lago maggiore region this article investigates the mesoscale precipitation mechanisms affecting the severest flood events observed from 2005 to 2012 in the maggia river located in the lago maggiore region on the southern side of the european alps high resolution volumetric radar data are used to describe the horizontal and vertical structure of precipitation while sounding data depict the airflow conditions the events causing the nine highest peak discharge rates in the river in the last eight years are characterized by the presence of convection which is generally absent in the storms that produced lower peak flow rates during major floods convective cells repeatedly propagate over the watershed over time at large temporal scales precipitation patterns assume the form of an elongated band of precipitation the main reason for the formation of the band is the different direction of the low level and upper level flow in relation to the orientation of the alpine orography when pre frontal moist and conditionally unstable air over the po valley is advected towards the alpine chain by a southsoutheasterly low level jet convection develops over the slopes west of lago maggiore where the low level flow is perpendicular to the terrain orientation convective cells are then transported towards the northeast by the upper level southwesterly steering flow reaching maturity over the maggia watershed this mesoscale process can trigger and maintain moist convection for a long time over the same region statistical analyses show that the strength and stability of the upstream flow at low levels 1 5 km determine to what extent precipitation will be convective a comparison with the mesoscale alpine program intensive observing period map iop precipitation cases shows that map iop 2b and 3 are representative of the type of event that produces the biggest floods in the lago maggiore area

assessing the impact of the tropopause on mountain waves and orographic precipitation using linear theory and numerical simulations abstractthe partial reflection of mountain waves at the tropopause has been studied extensively for its contribution to downslope windstorms but its impact on orographic precipitation has not been addressed here linear theory and numerical simulations are used to investigate how the tropopause affects the vertical structure of mountain waves and in turn orographic precipitation relative to the no tropopause case wave induced ascent above the windward slope of a two dimensional ridge is found to be enhanced or diminished depending on the ratio of the tropopause height to the vertical wavelength of the mountain waves defined here as the nondimensional tropopause height in idealized simulations of flow over both two dimensional and three dimensional ridges variations in are found to modulate the precipitation rate by roughly a factor of 2 under typical atmospheric conditions the sensitivity of precipitation to is related primarily to the depth of windward ascent but also to the location and stren

an observational and numerical study of an intense landfalling cold front along the northwest coast of the united states during coast iop 2 abstract this paper presents an observational and numerical study of an intense wintertime cold front that made landfall along the northwest coast of the united states during iop 2 3 4 dec 1993 of the coastal observation and simulation with topography experiment observations suggest that the offshore frontal zone was associated with two transitions the first characterized by a substantial temperature gradient a nearly vertically oriented wind shift from southwesterly ahead to westerly behind and a convective rainband while the second transition had a slantwise wind shift zone from westerly ahead to northwesterly behind the frontal zone was quite narrow 5 km wide and nearly vertical below 850 mb and its width increased by 1 2 orders of magnitude above 850 mb well before the frontal landfall low level flow to the west of the olympics was associated with geostrophic balance in the cross shore direction and downgradient acceleration in the alongshore direction which contributed to the formation

a comparison of two coastal barrier jet events along the southeast alaskan coast during the sarjet field experiment abstract the southeastern alaskan regional jets experiment investigated the structures and physical processes of barrier jets along the coastal fairweather mountains near juneau alaska from 24 september to 21 october 2004 this paper compares in situ aircraft data and high resolution simulations from the first intensive observation period iop1 which featured a nearly terrain parallel barrier jet classical jet with another coastal jet event iop7 that was influenced by offshore directed gap flows at the coast hybrid jet iop1 featured southerly onshore flow preceding a landfalling trough which was blocked by the coastal terrain and accelerated down the pressure gradient to produce a 5 10 m s 1 wind enhancement in the alongshore direction in the lowest 1 km msl in contrast iop7 featured higher surface pressure and colder low level temperatures to the east inland of the study area than did iop1 which resulted in offshore directed coastal gap flow exiting cross sound below 500 m that turned a

radar observations of precipitation and airflow on the mediterranean side of the alps autumn 1998 and 1999 this study constructs and analyses composite three dimensional fields of doppler radar observed radial velocity and reflectivity for all precipitation events occurring in the lago maggiore region on the mediterranean side of the alps during autumn 1998 and 1999 mean patterns for the two years are in close agreement with each other the radar data are consistent with previous rain gauge studies in showing that the rain was heaviest over the lower windward slopes and decreased toward higher terrain the three dimensional reflectivity fields show that precipitation growth occurred mainly at low altitudes the composite radar data show that the precipitation was most intense when the mean flow around the 2 km level was southerly or south easterly i e when the mean flow was most perpendicular to the alpine barrier sounding data from milan indicated the froude number of the flow upstream of the lago maggiore region when the froude number was high the flow proceeded directly up and over the terrain of the lower alpine slopes under these unblocked conditions the low level flow including the layer from the surface to 2 km above mean sea level rose directly up and over the terrain and the precipitation was greatly enhanced over the lower windward slopes and over the portions of the po valley just upstream of the mountains under unblocked conditions the precipitation enhancement only extended a short distance a few tens of kilometres upstream of the alps when the upstream froude number computed from the milan sounding was low blocked conditions the doppler radial velocities indicated that the low level flow in the layer below 2 km above mean sea level turned cyclonically as it approached the alpine barrier instead of rising over the terrain the composite radar reflectivity data showed less precipitation enhancement directly over the windward slope but in contrast to the unblocked case showed that the precipitation was enhanced 140 km or more upstream of the terrain evidently the low level flow began rising far in advance of the barrier in blocked conditions the 1998 and 1999 autumn data sample further indicates the relative roles of wind speed and stability which are combined in the froude number when the wind speed upstream was strong 8 m s 1 significant precipitation enhancement occurred on the windward slope of the alps in the lago maggiore region regardless of the static stability however the enhancement was far greater under unstable conditions when the wind speed was weak 8 m s 1 the precipitation was generally near or below average except when the stability was low and some patchy enhancement occurred over the po valley just upwind of the alps a diurnal precipitation maximum occurred in the early morning hours 0700 1000 lst possibly where down valley flow converged with synoptic scale up valley flow

a modeling study of orographic convection and mountain waves in the landfalling typhoon nari 2001 in this study the characteristics of mountain induced gravity waves mgws and orographic convection in typhoon nari 2001 and their impacts on the formation of orographic precipitation as nari moved across taiwan s central mountain range cmr are investigated by analyzing the cloud resolving model simulation results in the distant rain band convective cells were triggered frequently on the steep windward slope of cmr and advected downstream simultaneously mgws could exist on the lee side with stable environmental stratification three phases occurred in the mgws convection interaction including the enhancement of mgws and convection breaking and restoring of mgws when the convective cells and mgws were superposed in out of phase the amplitudes of both mgws and convective cells were increased decreased the vertical wavelength of mgws was also increased during the in phase superposition even inducing the further breaking of mgws for the formation of precipitation on the lee side mgws convection interaction contributes on a smaller scale to offset the reduction effect from the larger scale descending moreover convective cells on the windward slope could contribute a large amount of cloud ice and snow particles aloft to seed hydrometeors over the lee side more cloud water was produced by the mgws convection interaction when their amplitudes were increased during the in phase superposition riming and coalescence processes were responsible not only for the windward slope precipitation enhancement but also the secondary precipitation maximum over the lee side therefore the mgws convection interaction could modify the structure of vertical motion and hydrometeors over the lee side and then affect orographic precipitation when nari passed the cmr as nari s eyewall encountered the northern cmr the terrain generated long lasting strong updrafts at the upslope resulting in a doubled rainfall maximum to that in the no terrain sensitivity experiment the downdraft branch of the mgw produced a rain shadow on the lee side copyright 2011 royal meteorological society

high resolution numerical simulations of the convective system observed in the lago maggiore area on 17 september 1999 map iop 2a during intensive observing period iop 2a of the mesoscale alpine programme map a significant convective system developed in the lago maggiore area its evolution is simulated using the meso nh model run over three nested domains with a 2 km horizontal resolution for the finest grid model results are assessed by comparing computed precipitation and model radar reflectivities with observed parameters a control simulation initialized with european centre for medium range weather forecasts analyses and run with the standard microphysical scheme of the model yields fairly realistic results neglecting the ice processes in the microphysical scheme degrades the numerical results whereas significant improvement is obtained when heavy rimed particles are considered to be hail instead of graupel copyright 2003 royal meteorological society

radar observations of intense orographic precipitation associated with typhoon xangsane 2000 abstract with measurements from two ground based doppler radars located in northern taiwan this study documents the detailed aspects of intense orographic precipitation associated with typhoon xangsane 2000 as it moved northward immediately off the eastern coast of taiwan bringing strong low level northeasterly to north northeasterly winds impinging on the mountainous northern coast with relatively good persistent coverage of radar echoes on both inland and upstream regions this particular event provides a unique description of the orographic precipitation and its relationship with orographic geometry strong upstream oncoming flow and the precipitation inherently associated with typhoon circulations in this case the heaviest precipitation was observed to occur primarily over two coastal mountain barriers mount da tun dt and the nangang keelung range nkr barrier dt is an approximately 3d mountain barrier and the nkr adjacent to the southeast of dt is a relatively lower narrower 2d moun

small scale rainfall mechanisms for an idealized convective southerly flow over the alps rain producing flows over the south side of the alps are investigated with an idealized high resolution 2 5 km numerical configuration where only three basic ingredients of typical heavy precipitation situations have been retained 1 a uniform and stationary southerly flow far upstream from the alps which drives 2 a conditionally unstable atmosphere towards 3 the real topography of the alps and the surrounding secondary mountains attention is given to small scale mechanisms of rainfall over the po plain and the alpine slopes these are linked with two orographically induced low level wind jets the easterly barrier wind jet along the southern flank of the alps and a south easterly jet formed over the sea along the south western flank of the apennines and continuing over land up to the alps the specific role of the secondary relief upstream from the alps in inducing or influencing these low level flow features and also in triggering organized convection is studied by means of experiments on the sensitivity to topography the idealized configuration also allows the advantages of a convection resolving model for modelling precipitation distributions at the alpine valley scale to be considered copyright 2007 royal meteorological society

cross barrier flow during orographic precipitation events results from map and improve abstract ground based and airborne doppler radar data collected during passage of frontal rainstorms over the european alps and cascade mountains of oregon are found to exhibit characteristic cross barrier flow and precipitation patterns a stably stratified layer of blocked or partially blocked low momentum flow below mountain crest level is separated from strong cross barrier flow aloft by a concentrated layer of vertical wind shear this shear layer slopes upward toward the mountain crest and persists for several hours as the storm passes over the mountain range this pattern is remarkably similar from case to case and from one mountain range to the other the orographically enhanced precipitation in these cases exhibits stratiform structure marked by a radar bright band which often drops to a lower height indicating locally cooler conditions immediately adjacent to the windward mountain slopes a terrain induced gravity wave produces strong downslope flow and spillover of precipitation onto the

observed mass transports accompanying upstream orographic blocking during map iop8 a mass budget within a domain of 200 km 300 km encompassing the western end of the po river valley in northern italy is performed to examine the relative contributions of the multiple sources of moist airflow in the formation of precipitation for a case of strong upstream blocking observed during intensive observing period eight iop8 of the mesoscale alpine programme map results of this mass budget made possible by horizontally extensive doppler radar observations covering this upstream region reveal that the bulk of the blocked easterly flow undergoes widespread i e mesoscale slow ascent over a region of relatively flat terrain and is ultimately lifted to a level at which it can apparently be entrained into the overriding unblocked southerly component flow as a result the occurrence of profound orographic blocking did not preclude a portion of this low level air from ultimately surmounting the high alpine crest the contribution to this broad mesoscale circulation of smaller scale downslope flows observed within multiple deep alpine river drainages is also investigated by computing observed mass transports emerging from the mouths of several valleys surrounding the lago maggiore region overall the down valley flow is shown to be a relatively minor contributor to the low level mesoscale transports within the po basin but nonetheless one which is important to obtain mass balance in these budget computations copyright 2006 royal meteorological society

airflow within major alpine river valleys under heavy rainfall summary this study documents the aire ow within major alpine river valleys in the presence of precipitation the analysis seeks a conceptual understanding of the effect of rain on the valley e ow ground based and airborne doppler radar and surface data from the mesoscale alpine programme show that during persistent rainy periods the subsidence caused by melting and evaporation of precipitation particles contributes to the formation of a down valley e ow this down valley eow opposes moist southerly e ow aloft which is lifted over the topographic barrier and in which precipitation particles are formed

the influence of mesoscale orography on a coastal jet and rainband abstract the role of mesoscale orography along the central california coast in the development and evolution of a coastal jet and rainband is investigated using a high resolution triply nested nonhydrostatic numerical model comparison of the model simulations which use horizontal grid increments of 5 and 2 km on the inner computational meshes with a coastal mesoscale observation network indicates that the finescale structure of the jet and rainband dynamics are adequately simulated although phase and orientation errors occur the observed and simulated near surface winds have maximum speeds that exceed 22 m s 1 and a direction nearly parallel to the coastline and topography force balance analysis indicates that blocking in the lowest 500 m and flow over the coastal range above this layer contribute to mesoscale pressure perturbations including pressure ridging upstream of the coastal mountains which forces the ageostrophic dynamics of the coastal jet pressure perturbations associated with the to

triple doppler radar analysis of the heavy rain event observed in the lago maggiore region during map iop 2b this paper presents analyses of data collected with three ground based doppler radars during the mesoscale alpine programme map intensive observation period iop 2b from 1900 utc 19 september until 1100 utc 20 september 1999 during this period the synoptic situation was characterized by the propagation of a deep upper tropospheric trough towards the alps as often observed when heavy precipitation occurs on the southern slopes of the alpine massif a frontal cloud system with embedded convective cells passed over northern italy in association with the trough moving rapidly eastwards ahead of the advancing cold front a strong south to south easterly low level flow impinged on the mountains near lago maggiore and produced copious amounts of rain 200mm at several locations an analysis of three dimensional radar derived wind and precipitation fields shows that the most intense precipitation occurred where and when the easterly component of the low to mid level flow was the strongest with however a preferential location on the southern slopes of the alps this phenomenon can be explained by enhanced confluence between the main southerly flow and an intensifying easterly flow and or more favourable orientation of the moist inflow perpendicular to the mountain slopes in addition the propagation of convective cells from the po valley toward the alps led to enhanced precipitation over the mountainous area taking advantage of the approximately two dimensional character of the event the different terms of the water budget are calculated for a series of 25 successive vertical cross sections to analyse the transformation of atmospheric moisture into surface rainfall copyright 2003 royal meteorological society

precipitation sublimation and snow drift in the antarctic peninsula region from a regional atmospheric model 1 a regional atmospheric model with a horizontal grid spacing x of 14 km is used to study the surface mass balance components precipitation sublimation and snow drift in the region of the antarctic peninsula ap an integration is performed for the 7 year period 1987 1993 using a realistic forcing at the lateral model boundaries and at the sea surface output from this integration indicates that the precipitation reaches its maximum value on the northwestern slope of the ap where the upward motion in the atmosphere is largest uplift occurs upstream of the barrier affecting the precipitation distribution over sea the effect of the barrier on the precipitation distribution over the bellingshausen sea might have important implications for the ocean circulation in this region the mean precipitation over the grounded ice of the ap 1 20 m water eq yr 1 is 6 times larger than the mean value over all the grounded ice of antarctica our estimates for the surface sublimation and wind transport of snow over the grounding line toward the sea are 9 and 6 1 of the precipitation respectively in situ data of the wind distribution at three coastal sites located on the northern eastern and western sides of the ap are used to evaluate the modeled wind field which is important for the snow drift calculations for two of the three sites considered the prevailing wind direction and bimodal wind distribution are correctly represented by the model the calculated distribution of accumulation and ablation due to snow drift shows a complex pattern the wind removes snow from the spine of the ap where the near surface flow field diverges whereas deposition occurs mainly on the eastern slopes where the near surface flow field converges an intercomparison between two 7 year integrations at different horizontal resolution x 14 km and x 55 km shows that the precipitation on the northwestern slope is very sensitive to the model resolution in the x 14 km integration precipitation on the northwestern slope is higher than in x 55 km because of higher vertical velocities resulting in a 35 increase in average precipitation over the grounded ice of the ap

summer monsoon convection in the himalayan region terrain and land cover effects during the asian summer monsoon convection occurs frequently near the himalayan foothills however the nature of the convective systems varies dramatically from the western to eastern foothills the analysis of high resolution numerical simulations and available observations from two case studies and of the monsoon climatology indicates that this variation is a result of region specific orographically modified flows and land surface flux feedbacks convective systems containing intense convective echo occur in the western region as moist arabian sea low level air traverses desert land where surface flux of sensible heat enhances buoyancy as the flow approaches the himalayan foothills the soil may provide an additional source of moisture if it was moistened by a previous precipitation event low level and elevated layers of dry warm continental flow apparently cap the low level moist flow inhibiting the release of instability upstream of the foothills the convection is released over the small foothills as the potentially unstable flow is orographically lifted to saturation convectivesystemscontainingbroadstratiformecho occur in the eastern himalayas in association with bay of bengal depressions as strong low level flow transports maritime moisture into the region as the flow progresses over the bangladesh wetlands additional moisture is extracted from the diurnally heated surface convection is triggered as conditionally unstable flow is lifted upstream of and over the foothills the convective cells evolve into mesoscale convective systems mcss with convective and stratiform areas the mcss are advected farther into the himalayan eastern indentation where orographic lifting enhances the stratiform precipitation copyright c 2010 royal meteorological society

survey of a gulf stream frontal filament an assortment of data is used to map and characterize a gulf stream filament during 21 25 april 1980 a filament was captured as it moved through an array of moored current meters on the northeast florida continental shelf current and temperature time series along with satellite vhrr and aircraft art are used to reconstruct the event the event is found to consist of an anticyclonically rotating warm tongue inshore of a cold dome the rotational scheme of the current in the warm tongue is opposite to previous hypotheses upwelling occurs in both the cold dome region and below the warm tongue

a case study of an orographic cyclone south of the alps during the map sop the cyclonic formation of iop15 of the mesoscale alpine programme map 6 7 november 1999 is examined with respect to mesoscale features in the geopotential temperature wind and precipitation fields the effect of orography at different scales is evaluated using a mesoscale meteorological model bolam model errors are determined by comparing standard and special map sop observations with model output an optimal interpolation reanalysis of the initial condition aimed at assimilating mesoscale structures is applied resulting in an overall reduction of the forecast error including position of local scale precipitation maximum in the lago maggiore target area south of the alps different orography representations have an impact on the error patterns since it is shown that the alpine orography largely controls the cyclone growth over the mediterranean particular attention is devoted to the model verification of precipitation and wind fields in the vicinity of the alps where special observations allow for fine scale analysis copyright 2003 royal meteorological society

mechanisms of intense alpine rainfall abstract numerical studies by the authors and others of the 1994 piedmont flood show that the orographically modified flow was a critical element for the production of extraordinary rainfall to uncover the precise mechanism of orographic rainfall occurring in full physics mm5 simulations of the 1994 piedmont flood the authors carried out simulations with the same real data initial and boundary conditions but with the real orography replaced by an idealized one with excellent agreement between real and idealized orography on the rainfall rate versus time in the piedmont area analysis of the idealized orography simulation provides a clear picture of the model s mechanism of orographically induced rainfall as noted in previous studies of the 1994 piedmont case a moist saturated airflow has a reduced effective static stability and tends to flow over the mountains while an unsaturated airstream is stable and tries to flow around toward the left in the northern hemisphere in the 1994 piedmont case t

radar observations and numerical modeling of a precipitating line during map iop 5 abstract during the special observing period of the mesoscale alpine programme a narrow north south oriented frontal precipitation band was observed by two airborne and one operational doppler radar on 4 october 1999 over the friuli target area in northeast italy convective precipitation was mostly concentrated to the south of the eastern alps in regions of smooth orography and warm southerly flow ahead of the cold front while stratiform rain formed above the mountainous chain where a marked cold northerly flow wrapping around the eastern alps progressed southwestward doppler data collected in both convective and stratiform regions of the precipitation line as well as high resolution numerical simulations performed with the nonhydrostatic meso nh model are used to investigate the associated flow structure in connection with the underlying topography the mutually consistent observed and simulated precipitation and wind fields clearly identify low level flow convergence relative to the cold front

orographic effects on precipitating clouds 1 precipitation over and near mountains is not caused by topography but rather occurs when storms of a type that can occur anywhere deep convection fronts tropical cyclones form near or move over complex terrain deep convective systems occurring near mountains are affected by channeling of airflow near mountains capping of moist boundary layers by flow subsiding from higher terrain and triggering to break the cap when low level flow encounters hills near the bases of major mountain ranges mesoscale convective systems are triggered by nocturnal downslope flows and by diurnally triggered disturbances propagating away from mountain ranges the stratiform regions of mesoscale convective systems are enhanced by upslope flow when they move over mountains in frontal cloud systems the poleward flow of warm sector air ahead of the system may rise easily over terrain and a maximum of precipitating cloud occurs over the first rise of terrain and rainfall is maximum on ridges and minimum in valleys if the low level air ahead of the system is stable blocking or damming occurs shear between a blocked layer and unblocked moist air above favors turbulent overturning which can accelerate precipitation fallout in tropical cyclones the tangential winds encountering a mountain range produce a gravity wave response and greatly enhanced upslope flow depending on the height of the mountain the maximum rain may occur on either the windward or leeward side when the capped boundary layer of the eye of a tropical cyclone passes over a mountain the cap may be broken with intense convection resulting

airborne doppler observations of a landfalling cold front upstream of steep coastal orography abstract this study uses airborne doppler radar observations to describe the mesoscale structure and evolution of a cold frontal system as it made landfall on the mountainous coast of oregon and northern california on 1 december 1995 during the coastal observations and simulations with topography experiment this section of coastline constitutes a steep approximately two dimensional north south oriented orographic barrier the front exhibited a northeast southwest orientation and thus intersected the axis of high terrain at an acute angle the along barrier pressure gradient and low level winds increased with time along the coastal zone and reached a maximum as the front made landfall stably stratified prefrontal flow was strongly blocked by the orography resulting in a confluent transition from pervasive southwesterly winds offshore to a narrow zone of accelerated south southwesterly flow near the coast where wind speeds approached 30 m s 1 at a height of 750 m above mean sea level postfrontal flow

effect of the andes cordillera on precipitation from a midlatitude cold front the effects of the andes cordillera the major mountain range in south america on precipitation patterns of baroclinic systems approaching from the southeast pacific remain largely unstudied this study focuses on a case in late may 2008 when an upper level trough and surface cold front produced widespread precipitation in central chile the primary goal was to analyze the physical mechanisms responsible for the structure and evolution of the precipitation weather research and forecasting wrf model simulations indicate that as an upper level trough approached central chile midtropospheric flow below 700 hpa was blocked by the high topography and deflected poleward in the form of a barrier jet this northerly jet had wind maxima in excess of 15 m s 21 was centered around 925 hpa and extended westward 200 km from the mountains it intersected the cold front which approached from the south near the coast thereby increasing convergence along the frontal surface slowing its equatorward progress and enhancing rainfall over central chile another separate region of heavy precipitation formed over the upwind slopes of the cordillera a trajectory analysis confirmed that the barrier jet moved low level parcels from their origin in the moist southeast pacific boundary layer to the coast when model topography was reduced to twenty percent of its original height the cold front advanced more rapidly to the northeast generated less precipitation in central chile between 338 and 368s and produced minimal orographic precipitation on the upwind andean slopes based on these findings the high topography appears responsible for not only orographic precipitation but also for substantially increasing precipitation totals over the central coast and valley

gulf stream fluctuations and meanders over the onslow bay upper continental slope abstract gulf stream fluctuations observed over the 200 and 400 m isobaths off onslow bay north carolina have a prominent weekly time scale the principal fluctuations observed during the 4 month winter experiment are consistent with webster s 1961a description of downstream propagating skewed lateral meanders of the gulf stream over the upper continental slope the subtidal velocity fluctuations were highly coherent over the vertical extent 120 m and over the horizontal extent 64 km of our array the implied downstream propagation speed was 30 km day 1 for the weekly period meanders concurrent satellite images of a sea surface temperature sst meander pattern indicate that subsurface temperature salinity velocity and relative vorticity maxima occurred as meander crests shoreward sst front excursions passed over the experiment site the meandering currents were not coherent with nearby wind stress or coastal sea level fluctuations eddy flux estimates indicate energy conversion from the f

a numerical study of the interaction between the large scale monsoon circulation and orographic precipitation over south and southeast asia abstracta regional climate model is used to simulate the summer monsoon onset in south and southeast asia during the year 2000 to explore the interaction between orographic precipitation and the large scale monsoon circulation in the control run the model uses the u s geological survey topography data and simulates the observed monsoon onset reasonably well in the sensitivity tests mountains are removed within different regions south of the tibetan plateau it is found that the indochina peninsula monsoon onset is closely related to the local wind terrain precipitation interaction while the indian monsoon onset is more controlled by the large scale land sea thermal contrast the sensitivity tests suggest two opposite effects of high terrain on the monsoon circulation and precipitation when the terrain height is below the lifted condensation level lcl the low level westerlies and the orographic precipitation weaken with increasing terrain height due to the surface drag effect when the terrain he

remote sensing of surface pressure on mars with the mars express omega spectrometer 2 meteorological maps 1 surface pressure measurements help to achieve a better understanding of the main dynamical phenomena occurring in the atmosphere of a planet the use of the mars express omega visible and near ir imaging spectrometer allows us to tentatively perform an unprecedented remote sensing measurement of martian surface pressure omega reflectances in the co2 absorption band at 2 m are used to retrieve a hydrostatic estimation of surface pressure see companion paper by forget et al 2007 with a precision sufficient to draw maps of this field and thus analyze meteorological events in the martian atmosphere prior to any meteorological analysis omega observations have to pass quality controls on insolation and albedo conditions atmosphere dust opacity and occurrence of water ice clouds and frosts for the selected observations registration shifts with the mola reference are corrected sea level surface pressure reduction is then carried out in order to remove the topographical component of the surface pressure field three main phenomena are observed in the resulting omega surface pressure maps horizontal pressure gradients atmospheric oscillations and pressure perturbations in the vicinity of topographical obstacles the observed pressure oscillations are identified as possible signatures of phenomena such as inertia gravity waves or convective rolls the pressure perturbations detected around the martian hills and craters may be the signatures of complex interactions between an incoming flow and topographical obstacles highly idealized mesoscale simulations using the wrf model enable a preliminary study of these complex interactions but more realistic mesoscale simulations are necessary the maps provide valuable insights for future synoptic and mesoscale modeling which will in turn help in the interpretation of observations

a laboratory impact study of simulated edgeworth kuiper belt objects abstract this paper reports on a series of laboratory impact experiments designed to provide basic data on how simulated edgeworth kuiper belt objects ekos fragment in an impact event in september october 1997 we carried out 20 low velocity airgun shots at the ames vertical gun range into porous and homogeneous ice spheres using aluminum fractured ice and solid ice projectiles we found that the porous ice targets behaved as strongly as solid ice in collision energy is apparently well dissipated by the void spaces within the target such that these fragile ice structures respond as if they were strong in impacts therefore it would appear that if ekos are porous they are not collisionally weak also our data show that collisional outcomes for low velocity impacts into ice targets depend on the type of projectile used as well as the properties of the target we observed that the degree of fragmentation for a given type of target increases as the strength of the projectile increases aluminum projectiles are far more damaging to the target at the same collisional energy than are solid ice projectiles which in turn are more damaging than fractured ice projectiles one possible explanation for this behavior is the variable depth of penetration of the projectile for the different cases stronger projectiles penetrate more deeply and couple more energy into the target than do weak projectiles based on this if we assume that there has not been significant heating or differentiation in the edgeworth kuiper e k belt the most applicable impact strength for the low velocity e k belt collisions is likely to be that derived from similar target projectile materials impacting each other the laboratory data from this analysis indicate that a value for impact strength 5 10 5 erg cm 3 is appropriate for porous ice targets impacted with solid porous ice projectiles

rain shadow development during the growth of mountain ranges an atmospheric dynamics perspective 1 an idealized atmospheric model is used to explore the links between climate and topography in the development of orographic rain shadows during orogenesis the atmospheric dynamics theory of density stratified fluid flow over topography is used to interpret the results the controlling nondimensional parameter is nh u where n is the brunt vaisala frequency a measure of atmospheric stability h is the terrain relief and u is the initial horizontal wind speed rain shadow development is found to be a nonlinear and nonunique function of both topography and atmospheric state indicating that geological records of orographic aridity cannot be interpreted in terms of relief alone when upstream topography exceeds nh u 1 during surface uplift downstream orographic precipitation vanishes and downstream orographic cloud mass decreases by as much as 90 upstream blocking of air flow can generate a forward projecting rain shadow in which a relatively low ridge nh u 1 may be decoupled from the atmospheric flow by a zone of flow stagnation extending upstream of the high terrain such an effect may occur if the valley separating the two ranges is narrower than the length scale of flow stagnation in the model configuration used here lateral widening of a relatively low nh u 1 range increases downstream cloud mass by up to a factor of 3 these results help to refine interpretations of climate tectonic interactions in shaping the geological record of the sierra nevada and andes

the climatology of small scale orographic precipitation over the olympic mountains patterns and processes the climatology of small scale patterns of mountain precipitation is poorly constrained yet important for applications ranging from natural hazard assessment to understanding the geologic evolution of mountain ranges synthesizing four rainy seasons of high resolution precipitation observations and mesoscale model output from the penn state ncar mm5 reveals a persistent small scale pattern of precipitation over the 10 km wide 800 m high ridges and valleys of the western olympic mountains washington state usa this pattern is characterized by a 50 70 excess accumulation over the ridge crests relative to the adjacent valleys in the annual mean while the model shows excellent skill in simulating these patterns at seasonal time scales major errors exist for individual storms investigation of a range of storm events has revealed the following mechanism for the climatological pattern regions of enhanced condensation of cloud water are produced by ascent in stable flow over the windward slopes of major ridges synoptically generated precipitation grows by collection within these clouds leading to enhanced precipitation which is advected by the prevailing winds instances of atypical patterns of precipitation suggest that under certain conditions during periods with a low freezing level or convective cells fundamental changes in small scale patterns may occur however case studies and composite analysis suggest that departures from the pattern of ridge top enhancement are rare the basic patterns and processes appear robust to changes in temperature winds and background rainfall rates copyright 2008 royal meteorological society

damaging southerly winds caused by barrier jets in the cook strait and wellington region of new zealand abstractstrong southerly winds regularly occur in the cook strait region of new zealand occasionally these winds are strong enough to cause severe damage to property and threaten human life one example of a storm containing such winds is the wellington storm which occurred on 20 june 2013 for this case wind speeds in cook strait were stronger than those observed or forecast elsewhere in the storm even though wind speeds of this intensity are rare storms affecting new zealand with central pressures equal to the wellington storm 976 hpa are not uncommon numerical experiments have been carried out to investigate the possible reasons for the exceptional damaging southerly winds dsws occurring in this storm analyses of the simulations showed that dsws in cook strait for this event were actually barrier jets not gap winds as they appeared the strength of barrier jets in cook strait is sensitive to the precise location of the storm center this explains the uncommon occurrence of dsws in cook

catastrophic disruption of icy bodies with sub surface oceans abstract several icy bodies in the outer solar system have extensive internal oceans in several bodies the oceans are believed to be so extensive they decouple the interior core from the icy surface a major evolutionary driver in the solar system is high speed impacts which lead to cratering or even disruption of the target body here we consider how the presence of an internal ocean modifies the energy density needed to disrupt an icy body with an internal ocean we find that in laboratory experiments on decimetre scale bodies the energy density to cause disruption is 16 25 1 35 j kg 1 compared to 18 0 0 7 j kg 1 for solid ice bodies this suggests that for the purposes of impacts the bodies behave as if a solid with the same density predictions of the lifetimes of such icy bodies against impact disruption thus need not take the interior ocean into account

impacts on asteroids fragmentation regolith transport and disruption abstract we use a numerical hydrocode model to examine the outcomes of various size impacts into targets the sizes of asteroids 951 gaspra and 243 ida which were imaged by the galileo spacecraft a shock wave fractures the asteroid in advance of crater excavation flow thus for impactors larger than 100 m impacting at 5 3 km s 1 tensile strength is unimportant in these bodies whether they are initially intact or are rubble piles because of the shock induced fracture impact results are controlled by gravity therefore these asteroids are much more resistant to catastrophic disruption than predicted by previous estimates which had assumed that strength was controlling these processes for rock targets the rubble and regolith produced by this fracture can be jolted by the impact redistributing surface material and globally erasing craters the crater ejecta can produce tens of meters of regolith per large event likely consisting of 100 m size boulders mixed with smaller particles the response of kilometer size asteroids to impacts is qualitatively different from that of few centimeter targets in terrestrial experiments making prediction based on such experiments difficult the compositional distribution of delivered meteorites depends on the outcomes of such asteroid impacts