atmospheric fronts along the east coast of taiwan studied by ers synthetic aperture radar images the existence of quasi stationary alongshore atmospheric fronts typically located 30 70 km off the east coast of taiwan is demonstrated by analyzing synthetic aperture radar sar images of the sea surface acquired by the european remote sensing satellites ers 1 and ers 2 for the data interpretation cloud images from the japanese geostationary meteorological satellite gms 4 and the american terra satellite rain rate maps from ground based weather radars sea surface wind data from the scatterometer on board the quick scatterometer quikscat satellite and meteorological data from weather maps and radiosonde ascents have also been used it is shown that these atmospheric fronts are generated by the collisions of the two airflows from opposing directions one is associated with a weak easterly synoptic scale wind blowing against the high coastal mountain range at the east coast of taiwan and the other with a local offshore wind at the convergence zone where both airflows collide air is forced to move upward which often gives rise to the formation of coast parallel cloud bands there are two hypotheses about the origin of the offshore wind the first one is that it is a thermally driven land breeze katabatic wind and the second one is that it is wind resulting from recirculated airflow from the synoptic scale onshore wind air blocked by the mountain range at low froude numbers is recirculated and flows at low levels back offshore arguments in favor of and against the two hypotheses are presented it is argued that both the recirculation of airflow and land breeze katabatic wind contribute to the formation of the offshore atmospheric front but that land breeze katabatic wind is probably the main cause

on the movement and low level structure of cold fronts abstract this paper presents a review of theoretical and observational studies relating to the low level structure of cold fronts and explores the factors that are pertinent to frontal motion observational studies have shown that in some cases surface cold fronts move at speeds faster than the normal component of the wind at all levels in the lower troposphere and therefore propagate other case studies have shown that the low level flow immediately behind the front and normal to it is faster than the front and that the front has the local structure of a gravity current its speed of movement being well determined by the gravity current speed equation them different types of behavior are related to results of recent theoretical studies and the mechanism by which fronts can propagate is elucidated it is shown that a necessary requirement for propagation is the existence of an alongfront temperature gradient we question the relevance of the gravity current speed equation in general despite its appar

salt weathering simulation using a single immersion technique samples of concrete were subjected in an environmental cabinet to six different diurnal cycles of temperature and humidity change representative of desert surface conditions in the presence of a range of saturated salt solutions the samples were not subjected to repeated immersion or continuous partial immersion as has been the case in most previous experiments breakdown did occur nonetheless the two most effective cycles were one from egypt with a very high daytime maximum and one from the negev with high nocturnal humidity conditions cycles with relatively modest temperature and humidity cycles were ineffective in causing debris liberation

mesoscale anticyclonic circulations in the lee of the central rocky mountains composite analyses of terrain forced mesoscale anticyclonic circulations over southern wyoming and northern colorado are constructed these suggest two different types of circulations based on upstream flow direction the air within type 1 circulations originates to the west of the continental divide and contains little moisture type 2 circulations form in more moist northerly flow and are sometimes associated with snowbands both types tend to form during the afternoon and dissipate after sunset although type 2 events may follow frontal passages and occur at night case studies of one event of each type suggest that anticyclonic vorticity generation occurs within the lowest kilometer above ground level when that layer is nearly vertically mixed in both potential temperature and velocity an analogy with vorticity generation in mixed layer models is considered and it is shown that the conditions for generating negative vorticity in those models are satisfied in each observed case the mixed layer mechanism is also favored as it naturally explains the diurnal tendency of the circulations and may therefore explain the observed late day snowfall maximum along the front range of colorado

deterioration of stone materials in the angkor monuments cambodia the angkor monuments in cambodia are built mainly of sandstone and laterite this paper mainly describes the deterioration of sandstone blocks the sandstone in the monuments can be classified into three types based on the colour texture chemical composition and constituent mineral grey to yellowish brown sandstone red sandstone and greenish greywacke the deterioration is distinct in grey to yellowish brown sandstone because of its low compressive strength high porosity well developed bedding and constituent minerals susceptible to alteration such as feldspar and biotite the main causes of deterioration identified are chemical weathering efflorescence related to bat guano and biodeterioration by the growth of trees algae and lichens an water supply is also indispensable for deterioration

the life cycle of thunderstorm gust fronts as viewed with doppler radar and rawinsonde data abstract this paper presents the time dependent analysis of the thunderstorm gust front with the use of project nimrod data rhi cross sections of reflectivity and doppler velocity are constructed to determine the entire vertical structure the life cycle of the gust front is divided into four stages 1 the formative stage 2 the early mature stage 3 the late mature stage and 4 the dissipation stage a new finding is a horizontal roll detected in the reflectivity pattern resulting from airflow that is deflected upward by the ground while carrying some of the smaller precipitation ahead of the main echo core of the squall line this feature is called a precipitation roll as determined from rawinsonde data the cold air behind the gust front accounts for the observed surface pressure rise calculations confirm that the collision of two fluids produce a nonhydrostatic pressure at the leading edge of the outflow the equation governing the propagation speed of a density current accurately predicts t

a case study of trade wind rainbands and their interaction with the island induced airflow abstract a case study of trade wind rainbands observed on 22 august 1990 during the hawaiian rainband project is presented it shows that the interaction between the morning rainbands and the island induced airflow is important for the evolution of the rainbands in the early morning of 22 august there are two convective periods 0400 0600 and 0700 0900 hst hawaii standard time on the windward side of the island of hawaii for both periods preexisting rain cells are observed in the trade wind flow at least 40 km upstream of the island and move westward toward the island at night and in the early morning the offshore flow opposes the trade winds resulting in a convergent region over the area immediately upstream of the island as the first group of rain cells 0400 0600 hst moves toward the island the low level convergent airflow provides a favorable kinematic background for the enhancement of the coming rain cells these rain cells merge in the convergent zone and become a well defined rainband

spatial and temporal characteristics of warm season convection over pearl river delta region china based on 3 years of operational radar data this study examines the temporal and spatial characteristics and distributions of convection over the pearl river delta region of guangzhou china during the may september warm season using for the first time for such a purpose 3 years of operational doppler radar data in the region results show that convective features occur most frequently along the southern coast and the windward slope of the eastern mountainous area of pearl river delta with the highest frequency occurring in june and the lowest in september among the 5 months the spatial frequency distribution pattern also roughly matches the accumulated precipitation pattern the occurrence of convection in this region also exhibits strong diurnal cycles during may and june the diurnal distribution is bimodal with the maximum frequency occurring in the early afternoon and a secondary peak occurring between midnight and early morning the secondary peak is much weaker in july august and september convection near the coast is found to occur preferentially on days when a southerly low level jet llj exists especially during the meiyu season warm moist and unstable air is transported from the ocean to land by lljs on these days and the lifting along the coast by convergence induced by differential surface friction between the land and ocean is believed to be the primary cause for the high frequency along the coast in contrast the high frequency over mountainous area is believed to be due to orographic lifting of generally southerly flows during the warm season

laboratory simulation of the wick effect in salt weathering of rock the wick effect is the upward migration of saline solutions into rocks and their subsequent crystallization lower carboniferous sandstone blocks of rectangular shape have been subjected to this process in the laboratory using a range of salt types a range of salt concentrations and various mixtures of salts some treatments produced severe disintegration notably sodium carbonate and a mixture of sodium carbonate with magnesium sulphate whereas other salts including sodium chloride and gypsum were much less effective the debris produced by this experimental salt weathering included appreciable quantities of silt sized material which were analysed with a laser granulometer such material could provide a source for desert loess

the role of corsica in initiating nocturnal offshore convection in the region of corsica located in the western mediterranean sea the mean daily lightning activity as an indicator for deep convection in late summer and autumn shows a distinct maximum in mid afternoon and a secondary maximum at night during the night most of the lightning activity is located offshore and near the island s coastline currently there are no observational data which could be used to explain this nocturnal offshore convection but understanding its formation mechanism is important for accurately forecasting the regional weather in this article we explore two possible mechanisms initiating nocturnal offshore convection i convergence with subsequent lifting due to the interaction between drainage winds and the synoptic flow over the sea and ii dynamically induced lee side convergence due to the island barrier effect to this end we perform numerical simulations with the consortium for small scale modeling cosmo model at a convection permitting horizontal grid spacing of 2 8 km for two cases with different synoptic conditions and low level wind directions the simulation results show that the island s drainage flow can either favour or hinder the development of deep convection furthermore convective initiation is very sensitive to terrain elevation and model initialisation time and small changes of these parameters can determine whether deep convection can be successfully simulated

formation and maintenance of a long lived taiwan rainband during 1 3 march 2003 abstracttaiwan rainbands trs defined here as convective lines which form off the mountainous eastern coast of taiwan under weakly synoptically forced weather conditions are a well known mesoscale phenomenon but their formative processes remain the subject of debate this study uses surface and radar observations within the coastal zone of eastern taiwan and ncep reanalysis data to document a long lived tr with a lifetime of 36 h during 1 3 march 2003 to advance the current general understanding of mechanisms responsible for the tr s formation and maintenance detailed analyses indicate that the rainband was initiated by convergence that was produced as low level environmental northeasterly easterly onshore flow encountered topographically blocked northerlies that developed nearshore the northerly blocked flow was observed to weaken and subsequently dissipate because of changing synoptic pressure patterns that caused prevailing southeasterlies southerlies at low levels however colder nearshore ai

the nature and pattern of debris liberation by salt weathering a laboratory study a laboratory simulation of salt weathering was used to ascertain the effects of sodium sulphate and sodium carbonate under negev conditions using a single immersion technique three main points were addressed what are the grain size and textural characteristics of the debris liberated from limestones and a sandstone what do scanning electron microscope observations of the weathered samples tell us about the decay processes involved and how does the rate of debris liberation change during the course of 100 cycles the grain size characteristics of the liberated debris tended to be multimodal and were related to the original petrological characteristics of the rock large amounts of fines were produced which are believed to be analogous to the rock flour of arid areas blistering was also observed scanning electron microscope analysis revealed differences in the style of attack for different rock types and salt treatments and revealed the pattern of salt crystallization in pores and the nature of cracking the rate of debris liberation tended to decline or remain constant through time the reasons for this remain obscure but it is evident that diurnal cycles of temperature and humidity change can cause continuing rock weathering long after the initial input of salt to the rock has taken place

winter monsoon convection in the vicinity of north borneo part i structure and time variation of the clouds and precipitation abstract radar and satellite observations in the vicinity of northern borneo obtained during the international winter monsoon experiment wmonex showed that the convection in that region underwent an extremely regular diurnal cycle over the sea to the north of borneo the general level of convective activity was increased during monsoon surges and during the passages of westward propagating near equatorial disturbances convective activity was decreased during monsoon lulls the diurnal cycle was well defined regardless of whether the general level of convective activity was enhanced or suppressed by synoptic scale events the cycle of convection over the sea was especially well documented it was typically initiated at about midnight when an offshore low level wind began where this wind met the monsoonal northeasterly flow usually just off the coast convective cells formed after midnight the convection continued to develop and by 0800 lst it had evolved into an organized mesoscale system with a

a theory for strong long lived squall lines abstract we study herein the mechanics of long lived line oriented precipitating cumulus convection squall lines using two and three dimensional numerical models of moist convection these models used in juxtaposition enable us to address the important theoretical issue of whether a squall line is a system of special long lived cells or whether it is a long lived system of ordinary short lived cells our review of the observational literature indicates that the latter is the most consistent paradigm for the vast majority of cases but on occasion a squall line may be composed of essentially steady supercell thunderstorms the numerical experiments presented herein show that either type of squall line may develop from an initial line like disturbance depending on the magnitude and orientation of the environmental shear with respect to the line with shallow shear oriented perpendicular to the line a long lived line evolves containing individually short lived cells our analysis of this type o

upstream effects of mesoscale mountains abstract the alpine experiment alpex has revealed that low level air is typically diverted around the alps without reaching the mountaintop in pursuit of an understanding of the physical basis of this phenomenon and of its generality we have explored the characteristics of orographic blocking of a rotating continuously stratified quid as revealed in a simple model problem retaining full nonlinear and transient effects hydrostatic dynamics is assumed and the obstacle is taken to be an infinitely long ridge with height h x the key questions treated are the strength of the upstream deceleration of cross mountain flow and the length scale over which the decelerated region extends by means of scale analysis the controlling parameters are found to be the rossby number ro u fl and the froude number fr nhm u where u is the speed of the oncoming flow f is the coriolis parameter l the mountain half width n the brunt vaisala frequency and hm is the maximum mountain height the scale analysis also

diurnal variation of lee vortices in taiwan and the surrounding area abstract lee vortices have been frequently observed in the wake of mesoscale mountains under a low froude number flow regime during the taiwan area mesoscale experiment tamex a cyclonic vortex was observed to the ice of taiwan by a p 3 aircraft in this paper a numerical simulation is carried out to study this event it is shown that the numerical results are capable of recapturing the detailed features as observed by airplane and surface analysis the simulated surface pressure wind field and ice vortex are in good agreement with observations the diurnal oscillation of cloudiness and precipitation in taiwan is also consistent with the observations under undisturbed conditions during the tamex period under a prevailing southwesterly to westerly summer monsson flow numerical results demonstrate that the observed cyclonic vortex initially develops to the southeast of taiwan after sunset then drifts northeastward the diurnal forcing not only generates land sea breezes but also controls the vortex

on the origin of atmospheric frontal lines off the east coast of taiwan observed on spaceborne synthetic aperture radar images abstract frontal lines having offshore distances typically between 40 and 80 km are often visible on synthetic aperture radar sar images acquired over the east coast of taiwan by the european remote sensing satellites 1 and 2 ers 1 and ers 2 and envisat in a previous paper the authors showed that they are of atmospheric and not of oceanic origin however in that paper they did not give a definite answer to the question of which physical mechanism causes them in this paper the authors present simulations carried out with the fifth generation pennsylvania state university national center for atmospheric research mesoscale model which shows that the frontal lines are associated with a quasi stationary low level convergence zone generated by the dynamic interaction of onshore airflow of the synoptic scale wind with the coastal mountain range of the island of taiwan reversed airflow collides with the onshore flowing air leading to an uplift of air which is often accompanied by the formation of bands

observations of the sea breeze front during cape part i single doppler satellite and cloud photogrammetry analysis abstract an analysis of two sea breeze events on 6 august an onshore flow event and 12 august an offshore flow event 1991 is presented using single doppler observations satellite images and cloud pictures collected during the convection and precipitation electrification cape experiment documentation of the alongfrontal variability at the leading edge of the sea breeze circulation is presented for the first time the horizontal structure of the front was strongly modulated by the near perpendicular intersections of horizontal convective rolls developing in the ambient air out ahead of the sea breeze on 12 august these intersection points also appeared to be preferred locations for cloud development along the front horizontal convective rolls were also documented on 6 august however their orientation was nearly parallel to the sea breeze front as a result extended sections of these rolls appeared to have merged with the front as it propagated inland rather than having distinct intersection po

observations and scale analysis of coastal wind jets abstract blocking of onshore flow by coastal mountains was observed south of vancouver island british columbia by the noaa p 3 aircraft on 1 december 1993 winds increased from 10 m s 1 offshore to 15 m s 1 nearshore and became more parallel to shore in the blocked region which had a vertical scale of 500 m and an offshore scale of 40 50 km these length scale and velocity increases are comparable to theory the flow was semigeostrophic with the coast being hydrodynamically steep that is the coast acts like a wall and the alongshore momentum balance is ageostrophic this is shown by the nondimensional slope parameter the burger number b hmn flm being greater than 1 where hm and lm are the height and half width of the mountain n is the stability frequency and f is the coriolis parameter the height scale is given by setting the local froude number equal to 1 that is hl u n 500 m where u is the onshore component of velocity this scale is appropriate when hl is less than the mountain height

a preliminary morphology of precipitation systems in tropical northern australia a preliminary morphology of convective systems observed in the vicinity of darwin australia is presented several types of tropical convection during monsoonal and break season flow are identified using specific examples and compared with a range of systems observed worldwide in the general context of the bulk richardson number a significant spectrum of convective activity ranging from low shear and low convective available potential energy cape to high shear and moderate to high cape typical of mid latitude severe storms is identified significant differences between monsoonal flow and break season systems are apparent the formation of convective lines perpendicular to the low level shear and the apparent balance between advancing shallow cold pools and the shear are ubiquitous features convective scale downdraughts and mesoscale descent appear to be responsible for redistribution of 700 mb momentum to the planetary boundary layer pel the motion of the break season squall lines appears to result from an equilibrium between the cold pool and the undisturbed environmental pel flow deviations from this balance are hypothesized to result in the observed propagating and non propagating or slow moving modes examples of these modes are given showing the classical continuous development of new cells in a balanced state along the leading edge of long lived squalls and in the propagating case the discontinuous development of new cells on the cold pool ahead of the squall

evolution of downslope flow under strong opposing trade winds and frequent trade wind rainshowers over the island of hawaii abstract the evolution of downslope flow on the windward side of the island of hawaii during 7 8 august 1990 is investigated this period is characterized by atypical strong 11 m s 1 upstream trade winds and frequent nocturnal rainshowers in the late afternoon the onset of downslope flow first occurs on the upper slope which is frequently dominated by orographic clouds with mean weak surface winds on the windward slopes because of island blocking the downslope flow onset occurs after the slope surface becomes negatively buoyant along the hilo coastal areas that are well exposed to decelerating trade wind flow the offshore flow onset there occurs much later 2 h than the hawaiian rainband project harp mean as the drainage front moves slowly from the windward lowlands toward the coast against the atypical strong incoming trade wind flow the downslope flow onset along the coast occurs after a band of trade wind rainshowers has moved over the coast these rainshowers produce evaporatively coole

structure and evolution of numerically simulated squall lines abstract using a three dimensional numerical cloud model we investigate the effects of vertical wind shear on squall line structure and evolution over a wide range of shear magnitudes depths and orientations relative to the line we find that the simulated squall lines are most sensitive to the magnitude of the component of shear perpendicular to the line and that we may reproduce much of the range of observed structures by varying this single parameter for weak shear a line of initially upright to downshear tilted short lived cells quickly tilts upshear producing a wide band of weaker cells extending behind the surface outflow boundary for moderate to strong shear the circulation remains upright to downshear tilted for longer periods of time with vigorous short lived cells confined to a relatively narrow band along the system s leading edge at later times however these systems may also weaken as the circulation tilts upshear for strong deep shears oriented obliquely to the line the squal

effect of stable layer formation over the po valley on the development of convection during map iop 8 during intensive observation period iop 8 of the mesoscale alpine program there was a stable layer of air in the lowest levels of the po valley and just upstream of the apennines in this study the effects of the stable layer on the formation of convection in the southern alpine region were investigated through a series of two dimensional idealized experiments the goals of this study were twofold 1 to determine if stable layer strength affected the placement of convection and 2 to test the notion that the stable layer during iop 8 behaved as an effective mountain to accomplish the first objective three simulations were compared in which the strength of the inversion and low level cooling in the po valley and upstream of the apennines was varied the results of these simulations show that the stronger the inversion and low level cooling the farther south the convection was positioned additionally it was found that convection developed as a result of the formation of a broad region of moist instability over the stable layer cellular convection developed in this region of moist instability the second objective was tested through a simulation where the cold pool was replaced by terrain mmtn as in the reference or stb10 simulation the upslope of the terrain in the mmtn simulation was characterized by a wide zone of moist instability however wave structures to the lee of the apennines were markedly different in the stb10 and mmtn simulations this led to different convective and precipitation patterns with the mmtn simulation exhibiting heavier convection over the po valley while the heaviest convection in stb10 was upstream of the apennines these results suggest that at best the stable layer in the stb10 simulation can only be roughly approximated by terrain

laboratory simulation of rock weathering by salt crystallization and hydration processes in hot arid environments the results of a series of experiments are reported in this paper which were designed to differentiate between the forces of crystal growth and hydration in salt weathering using a single salt hydrate system sodium sulphate five contrasting rock types and several diurnal temperature relative humidity cycles which permitted or inhibited these processes and simulated ground surface climates in hot arid environments it was shown that hydration of sodium sulphate is an effective mechanism of rock disintegration but that it is significantly less destructive than crystal growth pressure crystallization of thenardite na2so4 is in turn more effective in rock weathering than the crystal growth of mirabilite na2so4 10h2o in general rates of disintegration were most rapid where the diurnal temperature range was extreme and relative humidity lowest

a numerical simulation of wind stress and topographic effects on the kuroshio current path near taiwan abstract a semispectral primitive equation model is used to study the effects of wind stress and bottom topography on the meandering of a jet over the continental margin the jet is specified initially as a geostrophic current similar to the kuroshio current supported by the temperature field the intrusion of water from the meandering jet over the continental margin is not only dominated by topographic effects but also enhanced by northerly winds the latter induces an onshore ekman transport which causes surface water in the meandering jet to intrude onto the continental margin lighter water is then carried downward to the deeper ocean through the hydrostatic and topographic boundary layers some subsurface water in the meandering jet also intrudes onto the continental slope and shelf and then rejoins the main stream under the influence of southerly wind surface water in the meandering jet migrates offshore toward the deeper ocean in the ekman layer while subsurface water in the meandering jet in

precipitation and kinematic structure of an oceanic mesoscale convective system part i convective line structure abstract the precipitation thermodynamic and kinematic structure of an oceanic mesoscale convective system is studied using airborne doppler and in situ flight level data collected by the noaa p 3 aircraft the system a well organized stationary north south convective line was located near the east coast of taiwan in part i the basic structure of the line is documented with both datasets a procedure revealing the strengths and weakness of both approaches the doppler data reveal that the warm moist air feeding the line enters from the east side most updrafts associated with the leading edge of the convective line tilt westward below 5 km and then eastward above 5 km this change of tilt corresponds to a change in the sign of the vertical flux of east west momentum to the east of the leading edge a 10 km wide zone of strong mesoscale descent is seen the band is not a complete barrier to the low level southeasterly flow and at times and places along the line the inflowing air can move throu

salt and ice crystallisation in porous sandstones salt and ice crystallisation in the pore spaces causes major physical damage to natural building stones the damaging effect of these processes can be traced back to physically induced stress inside of the rock while crystallizing the increasing scientific research done during the past century has shown that there are numerous parameters that have an influence on the weathering resulting from these processes however the working mechanisms of the stress development within the rock and its material dependency are still subject to discussion this article gives an overview of salt and ice weathering additionally laboratory results of various sandstones examined are presented salt crystallisation tests and freeze thaw tests were done to obtain information about how crystallisation weathering depends on material characteristics such as pore space water transportation and mechanical features simultaneous measuring of the length alternating during the salt and ice crystallisation has revealed detailed information on the development of crystal in the pore spaces as well as the development of stress these findings can help to understand the damaging mechanisms

barrier jets during tamex abstract a barrier jet is frequently found along the northwestern coast of taiwan in the prefrontal southwesterly flow regime during the taiwan area mesoscale experiment tamex it has a maximum wind speed of 14 m s 1 at approximately 1 km above the surface with a vertical wind shear approximately 10 10 3 s 1 below and 4 10 3 s 1 above that altitude during tamex the southwesterly monsoon flow strengthens over taiwan when the low level pressure trough surface front moves toward the southeastern china coast the barrier jet is a result of the stably stratified airflow past an island obstacle under a small froude number o 1 flow regime during the occurrence of a barrier jet a windward pressure ridge is observed along the southwestern coast due to island blocking in low levels the incoming southwesterly flow decelerates off the southwestern coast and moves around the island along the western coast the deflected airflow accelerates northward with a large cross contour wind component down the p

new experimental method to study the combined effect of temperature and salt weathering we would like to thank to the mission sector of the high education ministry egypt and geomateriales 2 s2013 mit 2914 for financial support we also thank rock mechanics laboratory faculty of petroleum and mining engineering suez university egypt and the petrophysics laboratory at the geosciences institute igeo csic ucm research by mg h was supported by a picata postdoctoral fellowship of the moncloa campus of international excellence upm ucm csic

diagnosed characteristics of precipitation systems over taiwan during the may june 1987 tamex abstract characteristics of mei yu precipitating cloud systems over taiwan during the may june 1987 taiwan area mesoscale experiment tamex have been studied using sounding surface precipitation and radar data vertical motion has been computed over the island at 6 h intervals from 13 may to 15 june using a modification of the kinematic method that takes into account the mountainous lower boundary within a four station sounding polygon two primary characteristics of the precipitation have been found first the major rainfall event were linked to the passage of midlatitude disturbances and typically consisted of both deep convective and stratiform components deep convection was primarily prefrontal or frontal while the stratiform precipitation was postfrontal presumably in association with overrunning and orographic lifting second there was a pronounced diurnal variability in the rainfall vertical motion heating q1 and moistening q2 profiles have been used to define the character of the pr

upstream orographic enhancement of a narrow cold frontal rainband approaching the andes abstractupstream orographic enhancement of the rainfall from an extratropical cyclone approaching the andes from the pacific is investigated using the weather research and forecasting wrf model and the tropical rainfall measuring mission trmm precipitation radar the main precipitation from the cyclone over central and coastal chile fell when a narrow cold frontal rainband ncfr interacted with a midlevel layer cloud deck formed from the orographically induced ascent of the prefrontal atmospheric river upstream of the andes model output indicates that low level convergence enhanced the ncfr where it met low level blocked flow near the mountains the ncfr had stronger updrafts with decreasing distance from the mountains and the ncfr produced larger rain accumulations over the land region upstream of the andes than over the open ocean a sensitivity simulation with a 50 reduction in the andes topography for comparison to various west coast mountain ranges of north america demonstrates that the e

reconciliation of crosshole seismic velocities with well information in a layered sedimentary environment in sedimentary environments horizontal fine layering can cause significant complications when analyzing and comparing seismic data with different frequencies and propagation directions at the whitchester test site three boreholes penetrate upper carboniferous cyclical sediments involving interbedded carbonates sandstones and mudstones with seismic velocities ranging from less than 3 0 km s in the mudstones to over 4 5 km s in the carbonates initial crosshole results from two boreholes approximately 200 m deep and 75 m apart showed a poor correlation with the borehole logs recorded in a third intermediate borehole furthermore the tomographic images were inconsistent with the expected geology the objective of this paper is to reconcile the crosshole seismic data with the borehole log information the borehole information must be upscaled to match the resolution of the crosshole experiment however upscaling techniques based on backus averaging lead to the prediction of significant anisotropy of the order of 20 in places with a vertical symmetry axis this anisotropy is a result of a combination of fine layering and the intrinsic mineral anisotropy measured on the core samples although it is the layer induced anisotropy that dominates at the crosshole frequencies of 400 hz this prediction was tested by including anisotropy parameters into the analysis of the crosshole data using anisotropic velocity tomography in the central part of the final anisotropic velocity tomograms where the ray coverage is adequate these crosshole results are consistent with the anisotropy predictions once the anisotropy was properly accounted for the tomographic images are consistent with the layered nature of the geology at the site and they show the location and throw of a known fault in the section we conclude that at this site and at crosshole frequencies seismic layer induced anisotropy plays a significant role and must be accounted for when processing and interpreting crosshole seismic data

doppler radar observation of a land breeze cold front abstract during the early morning hours of ii january 1981 a very narrow intense band of snow which had formed along the leading edge of a land breeze cold front was viewed by cp 4 radar near muskegon michigan the front formed well inland and moved through the area from the northeast shortly after dawn the driving force for the land breeze was the large temperature contrast that existed between radiationally cooled air over the northern highlands of lower michigan and the relatively warm lake modified air near the shore of lake michigan the possibility that the observed snowband was associated with a mesoscale feature other than the land breeze is investigated an analysis of minimum temperatures in the great lakes region for 11 january 1981 shows that a strong temperature gradient existed over western lower michigan this gradient reached a maximum value well inland rather than at the lake shore radar observations show the band to be over 80 km long and only 4 km wide oriented roughly parallel t

statistical location and timing of the convective lines off the mountainous coast of southeastern taiwan from long term radar observations in this study observations from the c band doppler radar on green island which is located off the southeastern coast of taiwan during 1998 2004 were analyzed to investigate the statistical characteristics of the convective lines occurring off the mountainous coast of southeastern taiwan with emphasis on their formative location and timing a total of 211 cases of the lines were identified during the study period it is shown that the lines were clearly a year round phenomenon and five cases occurred per month on average statistical analyses for all identified cases reveal that the formative area of the lines was extended substantially from nearshore regions to at least 100 km offshore with the region of the most frequent formation primarily confined to an elongated zone located 30 km off the coast along coast variations of line formation were also evident and were shown to be closely related to the nearshore terrain features the lines tended to form more frequently during the nighttime hours than the daytime hours with a formative peak between 2000 and 2200 lst minimum formation was found near noon between 1200 and 1400 lst however considerable cases still could be found during the late morning and late afternoon hours more than 70 of the lines 150 cases had a duration of less than 4 h and the mean duration for all lines was calculated to be 3 5 h in addition this study also documented statistical differences in the formative and flow characteristics between the nearshore and offshore lines which are distinguished by offshore distances of formative location that are less or greater than 40 km respectively of particular note the analyses presented strongly suggest that the physical mechanisms contributing to the initiation of the nearshore and offshore lines are fundamentally different

formation of the convective lines off the mountainous coast of southeastern taiwan a case study of 3 january 2004 abstract convective lines frequently occurring off the mountainous coast of southeastern taiwan under weakly synoptically forced weather conditions are one of the most well known mesoscale phenomena in taiwan these lines usually develop close to the coast but frequently can also be observed well offshore while nearshore lines are better understood the formative processes of the offshore lines remain unclear the main objective of this study is to use various available observations e g doppler radar surface and sounding observations quikscat and ncep data collected over southeastern taiwan to investigate a specially chosen case on 3 january 2004 in an attempt to identify possible mechanisms leading to the formation of the offshore lines the studied line was formed 50 60 km away from the southeastern coast of taiwan and oriented south southwest to north northeast and approximately parallel to the coast detailed analyses of the event indicated that the formation of the line did not appear direc

high resolution simulation of a nocturnal narrow convective line off the southeastern coast of taiwan in the mei yu season 1 this study performed high resolution numerical simulation on a convective line that occurred roughly 10 30 km offshore of southeastern taiwan overnight of 14 15 may 1998 three experiments at successively higher resolution 10 2 and 0 5 km but smaller domain were carried out and the narrow line is eventually reproduced it is found that shallow offshore return flow along the coast appeared since daytime due to topographic blocking on the weak prevailing onshore south southeasterly wind producing convergence at their interface near shore during the night mountain breeze further strengthened the offshore flow and convergence and the line initiated once developed downdrafts and outflow boundaries from old clouds triggered new clouds and this was more active along the eastern boundaries against the undisturbed environmental flow thus repeated new cloud formation took place throughout the night and into the next morning

experimental salt weathering of limestones in relation to rock properties a total of 21 different types of british and european mesozoic limestones have been subjected to simulated salt weathering using sodium sulphate na2so4 with the following aims assessment of the relative durabilities of different types of limestone assessment of the importance of modulus of elasticity and other factors in affecting durability and assessment of the use of impulse excitation techniques to monitor changes in rock modulus of elasticity the rocks showed a wide spectrum of durabilities while rocks with high values of modulus of elasticity lower water absorption capacities high densities and low salt uptakes tended to be durable there were anomalies the explanation for which probably lies in their pore structures non destructive testing techniques showed that although the more durable rocks failed to lose weight or to show visual signs of disintegration their modulus of elasticity values did tend to decline indicating a loss in strength copyright 1999 john wiley sons ltd

evolution of katabatic flow on the island of hawaii on 10 august 1990 abstract the data collected on 10 august 1990 from the hawaiian rainband project were analyzed to study the evolution of katabatic flow results from this study show that for a relatively dry case thermal forcing is important to account for the onset evolution depth and offshore extension of the katabatic flow on the windward side of the island of hawaii where the mean winds are weak because of island blocking during the evening transition the initiation of katabatic flow on the windward slopes was mainly driven by the diurnal heating cycle at the windward coast the wind shift was caused by the arrival of the drainage front from the windward lowlands after the arrival of the drainage front at hilo slopewise instability was generated because of rain showers along the coast and diminishing orographic clouds and showers on the slopes along the coast because of the reduced radiative cooling due to cloud cover and vertical mixing associated with rains a warm period was observed at hilo on the slop

the thermal wake of kauai island satellite observations and numerical simulations abstract island thermal effects on the trail cloud band over the central north pacific are investigated for the lee of hawaii using satellite observations and a regional atmospheric model the trail cloud band develops around noon and peaks in cloudiness in the early afternoon the analysis of numerical simulations of the kauai wake suggests that a dynamically induced convergence zone forms in the lee of kauai and oahu maximum elevation at 1 5 and 1 2 km respectively under the trade wind flow the island thermal effect significantly modulates the island wake and creates a diurnal cycle of development and decay in the lee cloud band as solar radiation heats up the island from morning to afternoon warm air moves downstream warm advection from the island in the wake zone increasing the air temperature decreasing the air pressure and enhancing low level wind convergence in favor of the formation of the trail clouds conversely the cold advection during night suppresses cloud formation in the wake t

a field study of seismic attenuation in layered sedimentary rocks ii crosshole data summary a series of crosshole seismic experiments have been performed at the imperial college borehole test site in northumberland england using a detonator source and hydrophone receivers the holes have been drilled through a horizontally layered sequence of carboniferous limestones shales and sandstones estimates of intrinsic q were obtained for frequencies between approximately 500 hz and 1 5 khz a comparison with the results of part i suggests evidence of frequency dependent intrinsic q with attenuation at 1 khz being significantly greater than at 100 hz no change of intrinsic attenuation with ray direction from horizontal oo to 60 was observed however since no high frequency crosshole data for ray angles between 60 and vertical is available we cannot entirely discount the possibility that the difference in intrinsic q estimates from the vertical vsp data part i and the crosshole data is due at least in part to anisotropic intrinsic attenuation

on the dynamics of hawaiian cloud bands island forcing abstract this study focuses on basic island scale forcing mechanisms for the formation and evolution of a band cloud typically present upwind of the island of hawaii by means of numerical experiments and verification of our results against observations and laboratory experiments reported in the literature we show that the band cloud is a complex three dimensional phenomenon which is inseparable from the airflow around the island in particular we demonstrate that the event needs to be analyzed in terms of the basic fluid dynamics of strongly stratified flow past a three dimensional obstacle the band cloud is found to arise primarily from the dynamic interaction of the trade winds with the island the upwind surface flow forms a separation line with an associated stagnation point a low level convergence zone forms along this line resulting in an updraft line if the updrafts are strong enough a band cloud forms formation and characteristics of such a system are mostly controlled by the environmenta

investigation of orographic precipitation over an isolated three dimensional complex topography with a dense gauge network radar observations and upslope model abstractthis study uses a dense rain gauge network radar observations and an upslope model to document the detailed aspects of precipitation over da tun mountain dt of northern taiwan under pre

thunderstorm initiation organization and lifetime associated with florida boundary layer convergence lines abstract the initiation organization and longevity of thunderstorms associated with boundary layer convergence lines in the cape canaveral florida vicinity are examined using data from the convection and precipitation electrification cape experiment the project was conducted during july and august 1991 under low vertical wind shear situations this observational study is based on doppler radar mesonet balloon sounding and satellite data the primary convergence lines studied were the east coast sea breeze front ecsbf and a frequently occurring gust front from the west termed the west coast front wcf that originates with storms initiated by the west coast sea breeze front significantly fewer storms were associated with the ecsbf in comparison to the wcf this was because the convergence with the ecsbf was shallower and weaker and the updrafts were shallow and tilted the environmental winds were generally westerly near the top of the ecsbf and at storm steering level as a result the low le

low frequency radiation from point sources in a fluid filled borehole far field displacement fields have been derived for an impulsive point force acting on a fluid filled borehole wall under the assumption that the borehole diameter is small compared to the wavelength involved the displacements due to an arbitrary source can be computed easily by combining the solutions for the impulsive sources in general the borehole source generates not only longitudinal and vertically polarized shear waves but also horizontally polarized shear waves this study also indicates that only the axisymmetric motion around the borehole due to normal stress is affected by the fluid in the borehole in the long wavelength limit the presence of the fluid does not affect the radiation from tangential sources into the surrounding medium

numerical simulations of the barrier jet over northwestern taiwan during the mei yu season orographic effects on the airflow over taiwan under the prevailing southwesterly monsoon flow are studied using the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 in particular the orographically induced low level strong winds along the northwestern coast of taiwan are simulated in the absence of radiative forcing thermal forcing from the surface and synoptic forcing the momentum balance for the low level strong winds along the northwest coast of taiwan shows that above the mixed layer the alongshore force balance is dominated by the inertial advection term and the pressure gradient force term the significant lagrangian flow acceleration of the northern branch of the deflected airflow along the northwest coast is mainly related to the pressure gradient force as the airflow moves down the orographically induced pressure ridge along the windward coast even though the alongshore pressure gradient force along the northwest coast is largest at the surface the observed and simulated wind profiles show that the wind speed maximum in the vertical of the barrier jet occurs at a height of 800 m primarily due to frictional retardation in the lowest levels within the well mixed layer the alongshore force balance is a threeway balance between inertial advection pressure gradient force and frictional force normal to the northwest coast the force balance is approximately geostrophic in addition the location and the strength of the orographically induced low level strong winds along the northwest coast of taiwan also depend on the impinging angle and the wind speed of the prevailing winds

an investigation into the fundamental relationships between attenuation phase dispersion and frequency using seismic refraction profiles over sedimentary structures despite many attenuation measurements which indicate a linear functional frequency dependence of absorption or constant q 1 in sediments several theories predict no such linear dependence the primary justification for rejecting a first power frequency dependence of attenuation is that it implies that seismic waves cannot propagate causally seismic waves must also travel with some velocity dispersion to satisfy causality yet there is a lack of velocity dispersion measurements in sediments in situ attenuation is caused by two distinct mechanisms anelastic heating and scattering due to interbed multiples apparent or scattering attenuation can produce both frequency dependent and non frequency dependent effects accurate measurements of attenuation and velocity dispersion are difficult it is not surprising that a systematic investigation into the frequency dependence of absorption and velocity has not been made a reinvestigation into two seismic refraction data sets collected over thickly stratifi

the role of saline solution properties on porous limestone salt weathering by magnesium and sodium sulfates saline solution properties viscosity in particular are shown to be critical in salt weathering associated with sodium and magnesium sulfate crystallization in porous limestone the crystallization of sodium and magnesium sulfate within a porous limestone has been studied at a macro and microscale using different techniques including mercury intrusion porosimetry environmental scanning microscopy and x ray computed tomography such analysis enabled the visualization of the crystallization process in situ and at high magnification yielding critical information as to where and how salts crystallize sodium sulfate decahydrate mirabilite tends to crystallize in large pores as euhedral micron sized crystals formed at low supersaturation near to the surface of the stone in contrast magnesium sulfate heptahydrate epsomite tends to precipitate as anhedral wax like aggregates formed at high supersaturation and distributed homogeneously throughout the stone pore system filling large and small pores while the former crystallization behavior resulted in scale formation the latter led to crack development throughout the bulk stone ultimately the contrasting weathering behavior of the two sulfates is explained by considering differences in flow dynamics of solutions within porous materials that are mainly connected with the higher viscosity of magnesium sulfate saturated solution 7 27 cp when compared with sodium sulfate saturated solution 1 83 cp on the basis of such results new ways to tackle salt weathering particularly in the field of cultural heritage conservation are discussed

measurements of earth attenuation from downhole and surface seismic recordings frequency dependent attenuation of compressional waves within the earth has been estimated in the vicinity of wells from 1 spectral power ratios of the coherent events in separate time gates on the seismic section 2 matching a broadband synthetic trace with seismic data at the well and 3 determining the operator that transforms one down up going pulse recorded in the well into another recorded at a deeper shallower level the accuracy of estimation of all three methods was insufficient to estimate attenuation over small depth intervals and it was not possible to distinguish between the contribution due to internal multiples and that of genuine absorption with much confidence spectral ratios from 1 showed a smoother variation with frequency and one more consistent with other estimates when they were compensated for the spectra of the reflectivities over the time gates employed but they did not provide more than a broad indication of attenuation over a substantial depth interval approach 2 was hampered by the restricted durations over which synthetic trace and seismic data can be reliably matched approach 3 gave the best results here matching is a much more powerful tool than the spectral ratio techniques that are commonly applied since it can yield the form of the attenuation operator i e both its amplitude and phase response together with properly defined measures of its accuracy while at the same time it minimizes the influence of noise and local interference effects at each recording level for seismic target depths where internal multiple activity was low the logarithms of the amplitude responses of the estimated attenuation operators decreased approximately linearly with frequency and the phase responses showed no significant dispersion application of approach 3 to downgoing and upgoing waves estimated from a vertical seismic profile revealed the importance of changes in frequency dependent geophone coupling and their effect on values of q determined from downgoing pulses only

structural changes of an outer tropical cyclone rain band encountering the topography of northern taiwan this study utilized ground based doppler radar observations to document the detailed structures of an outer tropical cyclone rainband tcr of typhoon longwang 2005 as the rainband passed over the topography of northern taiwan on 1 october 2005 the tcr was oriented northeast southwest and was roughly parallel to the mountain barrier with a higher lower terrain height in its southern northern landfalling segment during the pre landfall stage the tcr was characterized by convective precipitation on its inner side where the front to rear flow met with the rear to front flow to lift air upward with overturning updraft like signatures significant relatively minor changes in the tcr s structures were evident in the southern northern landfalling segment during the landfalling stage in particular the southern landfalling segment exhibited a much stronger front to rear flow that passed through the region of the rainband resulting in the absence of low level organized convergence and a relatively disorganized nature of precipitation this structural change was shown to be closely related to a significant decrease in the cross barrier flow due to the orographic blocking that occurred as easterly ambient winds encountered local high mountains in the vicinity of the rainband segment as the tcr propagated over the western side of the major topography the low level rear to front flow reappeared due to the collapse of low level orographic blocking and the convergence between the front to rear flow and the rear to front flow tended to rebuild a well organized convective circulation along the rainband results from this case study provide insight into processes that contribute to rapid structural changes in a landfalling tcr over mountainous regions

a numerical modeling study of mesoscale cyclogenesis to the east of the korean peninsula numerical simulations and the analysis of observational data are employed to understand the mesoscale cyclogenesis in a polar airstream that occurred over the sea to the east of the korean peninsula on 28 29 january 1995 the observational analysis shows that a mesoscale low develops over the southeastern east sea japan sea on 29 january 1995 satellite imagery also indicates that a meso b scale vortex forms on the lee side of the northern korean mountain complex kmc which is located in the northern korean peninsula and that a meso a scale cyclone develops over the southeastern east sea at a later time the mesoscale cyclone forms in the lower troposphere with strong baroclinicity and cyclonic circulation under the influence of an upper level synoptic scale cold vortex numerical simulation has captured major features of the observed cyclogenesis very well the cyclogenesis occurs in a progressive manner basically four distinctive stages of the cyclogenesis are identified 1 first a surface pressure trough forms on the lee side of the kmc under a northwesterly synoptic scale flow that is deflected anticyclonically over the kmc 2 second the lee trough deepens further into a strong convergence zone and a meso b scale vortex 3 next the meso b scale vortex develops into a meso a scale vortex as the vortex and the trough begin to move southeastward from the lee of the kmc 4 finally the surface trough deepens into a closed low and the meso a scale vortex becomes collocated with this deepening surface low to form a meso a scale cyclone over the southeastern east sea several sensitivity experiments are performed to isolate the effects of a topography warmer sea surface diurnal thermal forcing and latent heat release during stages 1 and 2 it is found that the kmc and low level baroclinicity are responsible for generating the strong lee trough and vortex during stage 3 the development of the meso a scale vortex is brought on by the tilting of horizontal vorticity and vertical stretching in a synopticscale cyclonic circulation in the final stage the condensational heating plays the key role for the development of the meso a scale cyclone under the influence of an upper level synoptic scale cold vortex the presence of the warm sea surface is found to be a necessary condition for the development of a polar air convergence zone and the mesoscale cyclone it is also found that the low level baroclinicity is essential for the present case of mesoscale cyclogenesis

tropical island convection in the absence of significant topography part i life cycle of diurnally forced convection abstract diurnally forced convection was observed over the tiwi islands north of the australian continent as part of the maritime continent thunderstorm experiment immature peninsula scale 5 15 km sea breezes were observed to initiate moist convection early each day principally through convergence that results from the confluence or collision of peninsula breeze fronts convection initiated by peninsula scale breezes usually fails to organize beyond a small cluster of cells and dissipates as a local event mature island scale 100 km breezes develop by late morning and subsequently play a pivotal role in the forcing and evolution of organized convection the initiation of mesoscale convective systems mcss is observed to be a direct consequence of breeze front collisions for only 20 of the days on which organized convection develops this is referred to as type a forcing and it occurs when normal convective development is delayed or otherwise suppressed type a forcing is nature s backup mech

radar observations of the diurnally forced offshore convective lines along the southeastern coast of taiwan this study documents offshore convective lines along the southeastern coast of taiwan a frequent but poorly understood mesoscale phenomenon that influences coastal weather during the taiwan mei yu season doppler radar and surface observations were gathered from a specially chosen period 11 15 may 1998 when the offshore convective lines were active off the southeastern coast of taiwan these observations were used to show the basic character structure and possible formative processes of offshore convective lines the synoptic environment accompanying these events was found to be relatively undisturbed and featured uniformly prevailing southerly south southeasterly winds in the boundary layer with southwesterlies westerlies aloft examination of radar data during the study period indicates that the lines generally occurred 10 30 km offshore and were characterized by an elongated narrow zone 5 10 km wide of heavy precipitation the lines were oriented roughly parallel to the coastline and generally did not move significantly the intensity of the radar reflectivity associated with the lines exhibited a marked diurnal variation and was closely related to the coastal offshore flow developing at night detailed analyses of an event on 14 15 may 1998 further show the important physical link between the offshore flow and the development of the line the offshore line was found to be located near and immediately ahead of the seaward extent of the offshore flow particularly a very narrow zone 2 km of low level heavy precipitation 40 45 dbz coincided with regions of strong updrafts and convergence where the prevailing southerly onshore flow encountered the cool offshore flow nearshore this offshore flow induced convergence given a stable thermodynamic condition in the lowest 1 km in the inflow region was a crucial low level forcing that provided lifting to trigger moist deep convection in this case the line s precipitation tilt eastward was confined primarily to the warmer inflow side rather than feeding the offshore flow to the west of the line no consistent upshear tilt of updrafts throughout the storm layer was observed which is consistent with the presence of a strong westerly shear in the line s environment both of these observations explain a relatively strong weak modification of low level onshore offshore flow by precipitation additionally a combination of surface and doppler radar observations indicates that the leading edge of the offshore flow moved seaward very slowly at 0 7 m s 1 and possessed a frontal character with notable discontinuities in near surface wind and temperature instead of pressure and dewpoint temperature

convection initiation associated with a sea breeze front a gust front and their collision abstract the initiation of convection associated with a sea breeze front a gust front and their collision is analyzed using data collected in east central florida during the convection and precipitation electrification project in conjunction with satellite surface and rawinsonde information dual doppler radar derived winds are used to determine the three dimensional kinematic factors critical to storm development the gust front which emanated from storms on the western half of the peninsula propagated more rapidly and was deeper than the sea breeze front which originated from the east coast and was characterized by a distinctly scalloped appearance convection associated with the sea breeze front appeared to develop preferentially at the vertices of this scalloped pattern where there were enhanced regions of convergence and upward motion on the gust front a helmholtz shearing instability produced an organized configuration of convergence and updraft maxima along its length however these were

localization and backscattering spectrum of seismic waves in stratified lithology using four sonic well logs from diverse geological environments we analyze the statistics of lithological layers relevant to seismic wave propagation the autocorrelation functions are found to be well approximated by exponentials with correlation lengths generally in the 1 5 to 3 m range we use localization theory to calculate the apparent attenuation caused by random scattering as a function of frequency this attenuation has a peak at 50 to 150 hz with a corresponding localization length of 1 6 to 4 8 km 1 to 3 mi and an apparent q of 120 to 450 at seismic frequencies 20 hz the attenuation is smaller with localization lengths in the 16 to 32 km 10 to 20 mi range and an apparent q of 300 to 700 these values of apparent q are consistent with observations of previous authors who used well log calculations using finite differences we compute synthetic traces for a 20 hz pulse with multiple backscattering from the lithology given by each of the well logs the power spectral density of the trace

velocity and attenuation in sandstone at elevated temperatures and pressures new measurements of seismic velocity and attenuation have been made in the kilohertz frequency range to temperatures of 120 c confining and pore pressure to 200 bars in berea sandstone with increasing temperature shear velocity and attenuation decrease at all pressures in a fully saturated rock the data suggest that thermal relaxation is not a significant loss mechanism under these conditions we propose that dissipation is controlled by a viscous fluid flow mechanism in which a sharp frequency peak in attenuation is shifted from 2khz at room temperature to 8 khz at 120 c as the pore fluid viscosity is decreased with increasing temperature however the velocity decrease is too great to be accounted for by a change of relaxation times a non dispersive temperature softening in shear may control the velocities

the accuracy of estimating q from seismic data a major aim of seismic interpretation is the inference of petrophysical properties of reservoir rocks because the inversion from seismic to petrophysical characteristics is far from unique this task requires a range of seismic parameters prominent among which are seismic velocity impedance and poisson s ratio the inclusion of seismic absorption in this list could add desirable complementary information for example absorption may be more sensitive to clay content than seismic velocity klimento and mccann 1990 however seismic absorption is difficult to measure particularly over depth intervals as short as most reservoir intervals

case study of the leeside mesolow and mesocyclone in tamex abstract an observational study was performed on a leeside mesolow case that occurred 8 june 1987 during the taiwan area mesoscale experiment tamex the case developed as prevailing west southwest winds strengthened and interacted with the terrain of taiwan with a froude number fr u nh increasing from below 0 3 to over 0 5 a quasi stationary mesolow formed to the southeast of taiwan with no closed circulation through most of its 13 h life stages until passage of the mei yu front a stationary and localized mesovortex also formed about 90 km southwest of the low center but little adjustment was observed between the mesolow and the vortex results suggest that airflow at lower levels was blocked and moved around the terrain of the southern central mountain range cmr this led to the formation of low level jets lljs both to the northwest and southeast of taiwan the latter branch provided shear vorticity in the background region of the vortex air parcels at higher levels on the other hand ten

a case study of nocturnal rain showers over the windward coastal region of the island of hawaii abstract nocturnal rain showers over the windward side of the island of hawaii were investigated from the late afternoon of 2 august to the early morning of 3 august 1990 during the hawaiian rainband project harp three types of rainbands produce rainfall peaks over the lowland coastal region during the evening after midnight and along the coast in the early morning in the early evening an inland rainband develops over the lower slopes as a result of orographic lifting and low level forcing along the drainage front as the drainage front progresses toward the coast new rain cells continue to develop along the drainage front these cells move westward with the trade winds aloft and dissipate after the drainage front moves to the hilo coast new cell generation along the drainage front ceases it appears that in the absence of orographic lifting the shallow 0 2 km katabatic flow offshore is not deep enough to lift the low level air to saturation thus the rainband weakens and dissipates it las

the santa cruz eddy part ii mechanisms of formation the formation mechanism of the santa cruz eddy sce is investigated using the fifth generation pennsylvania state university national center for atmospheric research mesoscale model mm5 simulations of 25 26 august 2000 showed that two eddy instances formed on that night a finding supported by observations the two eddies had similar behavior they both formed in the sheltered santa cruz california area and then moved southeastward to finally dissipate after 7 11 h however the first eddy had greater vorticity wind speed horizontal and vertical extents and lifetime than the second eddy numerical simulations showed that the sces are formed by the interaction of the main northwesterly flow with the topographic barrier represented by the santa cruz mountains to the north of monterey bay additional numerical experiments were undertaken with no diurnal heating cycle no molecular or eddy viscosity and no horizontal thermal gradients at ground level in all cases vertical vorticity was still created by the tilting of horizontal vorticity generated by the solenoidal term in the vorticity equation this baroclinic process appeared to be the fundamental formation mechanism for both sces but more favorable conditions in the late afternoon including a south to north pressure gradient flow turning due to the sea breeze and an expansion fan coincided to intensify the first eddy

a field study of seismic attenuation in layered sedimentary rocks i vsp data summary a coherence matching technique was used to estimate q from both real and log derived synthetic vsp data to try to determine the relative contributions of apparent and intrinsic attentuation in layered sedimentary rocks the field experiment was carried out at the imperial college borehole test site in northumberland england the holes have been drilled through a cyclical sequence of the namurian upper limestone group the q analysis indicates that for frequencies from 40 to 200 hz scattering attenuation due to interbed multiples within the horizontally layered sequences is the dominant mechanism and any contribution from intrinsic attenuation is relatively insignificant confirmation of this result is obtained from an analysis of the frequency content of scattered energy in the coda of the downgoing compressional wave although uncertainty bounds on the q values are large these vsp data are not consistent with an intrisic q value as low as 20 which has been estimated from 500 hz to 1 5 khz crosshole data at the same site as described in part ii

the influence of coastal orography the yakutat storm abstract an unforecast windstorm in the vicinity of yakutat alaska on 14 march 1979 illustrates the importance of ageostrophic dynamics within a coastal zone proximal to significant terrain large pressure rises greater than 4 mb 3 h 1 were observed along the southeastern alaska coast after passage of a cold front when the low level geostrophic flow was directed onshore these pressure rises did not occur simultaneously along the coast but rather propagated northward along the coast as a coherent pulse or surge strong surface winds approximately 25 30 m s 1 were observed in the region of laid sea level pressure gradient at the leading edge of the surge and occurred after the passage of the synoptic front although the sparseness of the observations prevent definite conclusions this feature resembles a kelvin wave more than a density current omega dropwindsonde observations collected along the coast of alaska during two other less dramatic situations suggest damming and downslope flow structu