a synthesis of hydrochemistry with an integrated conceptual model for groundwater in the hexi corridor northwestern china abstract although many studies have investigated the recharge and evolution of groundwater in the hexi corridor northwestern nw china they describe individual sites such as jinchang jiuquan dunhuang and others considering the similarity of these sites a systematic review of the entire hexi corridor is lacking this paper compares and summarizes previous studies in the hexi corridor to provide a regional perspective of the isotopic characteristics and hydrochemical composition of groundwater in unconfined aquifers groundwater is recharged by snow and ice melt water from the qilian mountains local precipitation can be neglected therefore the groundwater belongs to a unique hydrological cycle model in the hexi corridor referred to as snow and ice melt water groundwater system the dominant anion species changes from hco3 in front of the mountains to so42 in the middle basin and cl at the basin boundary along the groundwater flow direction and tds increases gradually owing to evaporation a major hydrogeochemical process is the dissolution of minerals from the aquifer in the recharge area changing to cation exchange reactions in the discharge area confined groundwater was recharged mainly in the late pleistocene and middle holocene at colder temperatures than those of modern times thus it is non renewable in addition to dissolution the hydrochemical composition of confined groundwater is also affected by cation exchange reactions the hydrogeochemical categories of the confined groundwater are simple and stable in the present study a conceptual model is established on the basis of the analyses presented which has important implications for water resource management in the hexi corridor the inter basin water allocation program should continue in order to achieve optimal utilization of water resources but groundwater exploitation should be limited as much as possible additionally on the basis of the review and integration of previous research the regional groundwater cycle patterns in the hexi corridor are illustrated in the present study and new research questions are identified for future work

isotopic and geochemical evidence of recharge sources and water quality in the quaternary aquifer beneath jinchang city nw china multiple isotopic and hydrogeochemical tracers were utilized to understand the recharge sources and geochemical evolution of groundwater in the quaternary aquifer beneath jinchang city and the adjacent gobi desert area the groundwater shows markedly depleted stable isotopic composition compared to modern rainfall the signature of groundwaters from jinchang and the northern gobi desert area differ clearly from that of the alluvial fan in the south yongchang basin and modern rainfall and has lower or non detectable 3 h activity implying that the aquifer is likely maintained by palaeowater this groundwater in the gobi desert has a 14 c age older than 12 ka indicating that the groundwater resources are non renewable the build up of dissolved solids through evaporation is a major control on groundwater composition and the dominant anion species change systematically from hco 3 so 4 2 to cl but cations from weathering of albite calcite dolomite and gypsum also make a significant contribution the scientific results have important implications for groundwater management in jinchang city and as well as in the shiyang river basin under china s west development strategy it is recommended that the water allocation program of diverting water from the dongda river to the minqin basin be reconsidered c 2010 elsevier ltd all rights reserved

environmental isotopic and hydrochemical study of groundwater in the ejina basin northwest china the study investigates the groundwater evolution and its residence time in the ejina basin northwest china according to isotope and hydrochemical analyses results the groundwater chemistry is mainly controlled by the dissolution of halite glauber s salt gypsum dolomite and calcite also influenced by other processes such as evaporation ion exchange and deposition based on tritium content in atmospheric precipitation and by adopting a model with exponential time distribution function the mean residence time of the unconfined aquifer groundwater with fairly high tritium activities 21 49 tu is evaluated the results show that these groundwaters have low residence time 5 120 years and are renewable in contrast the deep confined groundwaters are tritium free and radiocarbon values range from 18 3 to 26 7 pmc according to the most commonly used 14c correction models the radiocarbon groundwater ages were calculated which yield ages of approximately 4 087 9 364 years bp isotopic signatures indicate formation of deep confined groundwaters in a colder and wetter climate during the late pleistocene and holocene it is suggested that long term rational water usage guide should be set up for the heihe river basin as a whole to permit a considerable discharge to the ejina basin

hydrochemical characteristics and salinity of groundwater in the ejina basin northwestern china a hydrochemical investigation was conducted in the ejina basin to identify the hydrochemical characteristics and the salinity of groundwater the results indicate that groundwater in the area is brackish and are significantly zonation in salinity and water types from the recharge area to the discharge area the ionic ration plot and saturation index si calculation suggest that the silicate rock weathering and evaporation deposition are the dominant processes that determine the major ionic composition in the study area most of the stable isotope 18o and d compositions in the groundwater is a meteoric water feature indicating that the groundwater mainly sources from meteoric water and most groundwater undergoes a long history of evaporation based on radioactive isotope tritium 3h analysis the groundwater ages were approximately estimated in different aquifers the groundwater age ranges from less than 5 years between 5 years and 50 years and more than 50 years within 1 km of the river water influence zone the groundwater recharges from recent heihe river water and the groundwater age is about less than 5 years in shallow aquifer from 1 km to 10 km of the river water influence zone the groundwater sources from the mixture waters and the groundwater age is between 5 years and 50 years in shallow aquifer the groundwater age is more than 50 years in deep confined aquifer

hydrogeochemical controls and usability of groundwater in the semi arid mayo tsanaga river basin far north province cameroon deuterium 18o major ions and dissolved silica in groundwater from semi arid mayo tsanaga river basin in the far north province cameroon were used to trace hydrogeochemical processes that control their concentrations and to explore for usability of the water electrical conductivity ranges from 57 2 581 s cm with alternating low and high values along the hydraulic gradient waters from piedmont alluvium show low concentrations in major cations which peak in mg within basalt na within plain alluvium and ca within basalt and the sandy limani yagoua ridge the initial dominant groundwater composition is cahco3 which did not evolve within the basalt and piedmont alluvium but evolved to nahco3 in the granite and plain alluvium the main processes controlling the major ions composition include the following 1 dissolution of silicates and fluorite 2 precipitation of fluorite and carbonate 3 cation exchange of ca in water for na in clay 4 and anthropogenic activities the d and 18o ratios vary from 35 to 0 7 and 5 3 to 1 1 respectively the lowest and highest isotope ratios are observed in groundwater within the downstream sandy limani yagoua ridge and the upstream graintes respectively variation in isotope ratios depends on altitude effect of 0 48 per 100 m between 600 and 850 m asl and on evaporation which had insignificant effect on the water salinity seventy percent of the groundwater shows poor drinking quality and 90 is suitable for irrigation

research aircraft observations and numerical simulations of a warm front approaching vancouver island abstract the mesoscale structure of the low level flow and the character of the turbulence are investigated for a warm front as it approached the prominent terrain of the pacific northwest in the vicinity of vancouver island flight level and airborne doppler radar measurements collected from a national oceanic and atmospheric administration p 3 research aircraft on 9 december 1995 during the coastal observation and simulation with topography experiment and high resolution numerical simulations performed with the naval research laboratory s nonhydrostatic coupled ocean atmosphere mesoscale prediction system coamps model have been used to document the warm front as it approached the coast and the structure of cool air trapped along vancouver island this air mass was capped by a flat thin transition zone of enhanced static stability and vertical wind shear the flow within the trapped air mass was oriented parallel to the terrain of vancouver island but appears to have been more an outflow from the s

groundwater recharge history and hydrogeochemical evolution in the minqin basin north west china the minqin basin is a type area for examining stress on groundwater resources in the gobi desert and has been investigated here using a combination of isotopic noble gas and chemical indicators the basin is composed of clastic sediments of widely differing grain size and during the past half century over 10 000 boreholes have been drilled with a groundwater decline of around 1 m a 1 modern diffuse recharge is unlikely to exceed 3 mm a 1 as determined using unsaturated zone profiles and cl mass balance a small component of modern 50 a groundwater is identified in parts of the basin from 3h 3he data probably from irrigation returns a clear distinction is found between modern waters with median 18o values of 6 5 0 5 and most groundwaters in the basin with more depleted isotopic signatures radiocarbon values as pmc range from 0 6 to 85 modern but it is difficult to assign absolute ages to these although a value of 20 modern c probably represents the late pleistocene to holocene transition the 13c compositions remain near constant throughout the basin median value of 8 1 13c and indicate that carbonate reactions are unimportant and also that little reaction takes place there is a smooth decrease in 14c activity accompanied by a parallel increase in 4he accumulations from s n across the basin which define the occurrence of a regional flow system noble gas temperatures indicate recharge temperatures of about 5 6 c for late pleistocene samples which is some 2 3 c cooler than the modern mean annual air temperature and the recharge temperature obtained from several holocene samples groundwaters in the minqin basin have salinities generally below 1 g l and are aerobic containing low fe but elevated concentrations of u cr and se mean values of 27 5 5 8 and 5 3 g l 1 respectively nitrate is present at baseline concentrations of around 2 mg l 1 but there is little evidence of impact of high no3 from irrigation returns strontium isotope and major ion ratios suggest that silicate reactions predominate in the aquifer the results have important implications for groundwater management in the minqin and other water stressed basins in nw china a region so far destined for rapid development the large proportion of the water being used at present is in effect being mined and significant changes are urgently needed in water use strategy

factors governing cellular convection in orographic precipitation the development of shallow cellular convection in warm orographic clouds is investigated through idealized numerical simulations of moist flow over topography using a cloud resolving numerical model buoyant instability a necessary element for moist convection is found to be diagnosed most accurately through analysis of

groundwater recharge environments and hydrogeochemical evolution in the jiuquan basin northwest china the groundwater recharge environments and hydrogeochemical characteristics in the quaternary aquifer of jiuquan basin was investigated using a combination of chemical indicators stable isotopes and radiocarbon dating the d excess values of winter precipitation and surface water revealed that the meltwater from snow and ice played the dominant role in the basin s surface water supply the unconfined groundwater showed gradual enrichment of heavy isotopes along the flow path but delta o 18 and delta h 2 values were similar to those of surface water suggesting recent recharge as a result of rapid seepage along rivers combined with the effects of high evaporation the c 14 pmc values of unconfined groundwater was between 71 5 and 90 9 and since 80 modern carbon probably represents the upper limit of initial c 14 activity this suggests that the groundwater is relatively young the confined groundwater was depleted in heavy isotopes coupled with low c 14 values similar to 20 53 indicating that the groundwater was mainly recharged as palaeowater during the late pleistocene and holocene epochs under a cold climate the surface water and most groundwater samples were fresh rather than saline with tds 490 and 1000 mg l 1 respectively the chemistry of unconfined groundwater changed from hco3 dominated to no dominant ions and then to so42 dominated moving along the flow path from the jiuquan jiayuguan basin to the jinta basin and the confined water was so42 dominated the results have important implications for groundwater management in the basin where a high proportion of the water being used is in effect being mined i e extracted faster than its replacement rate thus significant changes are urgently needed in the regional water use strategy c 2012 elsevier ltd all rights reserved

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

three dimensional mesoscale circulation within a convective post frontal system possible role of conditional symmetric instability for triggering convective motion the role of the conditional symmetric instability csi in the formation of convective systems in the cold airmass located at the rear of a secondary cold frontal system is evaluated this study is based on observations made on 4 june 1984 during the french experiment landes fronts 84 in particular the mesoscale three dimensional circulation deduced from doppler radar data within one of these convective systems is studied in detail and compared with that predicted by the csi theory in spite of the fact that on the one hand notable convective scale motion masks the mesoscale circulation and that on the other hand the synoptic scale circulation is poorly described this comparison shows that among the various theories involved at the mesoscale only csi gives a proper account of the observed mesoscale circulation

a numerical study of the along line variability of a frontal squall line during pre storm despite considerable progress in the understanding of two dimensional structures of squall lines little attention has been paid to the along line variability of these convective systems in this study the roles of meso and larger scale circulations in the generation of along line variability of squall lines are investigated using an 18 h prediction of a frontal squall line that occurred on 26 27 june 1985 during pre storm preliminary regional experiment for stormscale operational research meteorology it is shown that the canadian regional finiteelement rfe model reproduces reasonably well a number of surface and vertical circulation structures of the squall system as verified against available network observations these include the initiation propagation and dissipation of the squall system surface pressure perturbations and cold outflow boundaries a midlevel mesolow and an upper level mesohigh a front to rear ftr ascending flow overlying an intense rear to front rtf flow and a leading convective line followed by stratiform precipitation regions it is found that across line circulations at the northern segment of the squall line differ significantly from those at its southern segment including the different types of precipitation the absence of the rtf flow and midlevel mesolow and the early dissipation of organized convection in the northern part the along line variability of the squall s circulations results primarily from the interaction of convectively generated perturbations with a midlevel baroclinic trough the large scale trough provides an extensive rtf flow component in the southern portion of the squall system and an ftr flow component in the north whereas the midlevel mesolow tends to enhance the rtf flow to the south and the ftr flow to the north of the mesolow during the mature to decaying stages the along line variability of the squall s circulations appears to be partly responsible for the generation of different weather conditions along the line such as the development of an upper level stratiform region in the southern segment and a midlevel cloud region in the northern portion of the squall line

multiple precipitation mechanisms over mountains observed by airborne doppler radar during map iop5 abstract this study uses airborne doppler radar measurements from the special observing period of the mesoscale alpine programme map to document the detailed airflow and precipitation structure over the mountainous regions near the border of northeastern italy and slovenia as a cold frontal system moved eastward and encountered the eastern alps on 4 october 1999 during map iop5 in contrast to previously documented map cases the environmental conditions associated with this case are characterized by a deep layer of strong convective instability in the lower troposphere and by a cold northeasterly continental flow coming down from the mountains the so called bora wind along the southeastern alps over the study region there are two primary mountain barriers the julian alps oriented roughly west east with a peak mountain height of 2500 m and a significant variation in terrain height along its length and the other the dinaric alps a relatively lower mountain range oriented northwest southeast

using hydrochemical and isotopic data to determine sources of recharge and groundwater evolution in an arid region a case study in the upper middle reaches of the shule river basin northwestern china understanding sources of recharge and mechanisms for hydrogeochemical evolution of groundwater in the shule river basin an arid inland river basin in northwestern china is essential for successful water resource management sources of water and associated groundwater recharge processes were investigated using hydrogeological hydrogeochemical and isotopic methods the study area was divided into three parts changma the shule valley and the beishan area the hydrogeochemical and isotopic analysis results show that groundwater in changma mainly originated from precipitation in the qilian mountains lateral flow from changma is the primary recharge mechanism while direct recharge by infiltration of precipitation can be neglected in the shule valley minerals within the aquifer material e g halite calcite dolomite and gypsum dissolve into water that recharges the groundwater system therefore strong linear relationships were found between na and cl and between ca2 mg2 and so42 hco3 with stoichiometry ratios of approximately 1 1 in both cases groundwater quality in the region is generally good with low salinity and hardness local precipitation is the only source of recharge for groundwater in the beishan area low groundwater velocity and dry climatic conditions suggest that dissolution of minerals from the aquifer material controls hydrogeochemical evolution water rarely travels from the beishan area to the shule valley therefore almost all the groundwater in the shule valley originates from changma global climate change and loss of glaciers in the qilian mountains may lead to a reduction of recharge therefore the groundwater resources of the shule valley must be managed to sustain water supply

handbook of environmental isotope geochemistry vol 1 the terrestrial environment a p fritz and j ch fontes editors elsevier amsterdam 1980 xii 532 pp u s 90 25 dfl 185 00

airborne doppler observations of a cold front in the vicinity of vancouver island abstract this study uses airborne doppler radar and flight level measurements from the coastal observations and simulations with topography experiment to examine the detailed mesoscale structure of an oceanic cold front upstream of vancouver island on 13 december 1993 these aircraft observations show that there were dramatic differences in frontal structure and movement between nearshore and offshore regions presumably due to the effects of blocking by the terrain the aircraft observations are considered in two parts since the behavior of the front evolved over the flight period during the early and middle portion of the flight the low level flow east of the front was out of the south southeast in the nearshore region rather than southerly as found farther offshore the nearshore segment of the front was oriented south north and appeared to be stationary the zone of orographic influence was found to extend to a region 20 km offshore and confined primarily to the lowest 1 5 km msl in distinct c

hydrochemistry and controlling mechanism of lakes in permafrost regions along the qinghai tibet engineering corridor china abstract lakes are the main water resource for migrating animals and herdsmen in permafrost regions along the qinghai tibet engineering corridor qtec and play a crucial role in regulating the balance between regional surface water and groundwater hydrochemical properties also affect the soil environment ecological conditions and hydrological cycle in this study 127 water samples were collected from lakes to analyze hydrochemistry characteristics the results are discussed in the context of relationships between water chemistry and local conditions including climate topography and geology the results showed that 43 3 of lakes are fresh 19 7 are brackish 18 9 are saline 17 3 are brine and only 0 8 are bitter the dominant cation is na followed by mg2 ca2 and k the dominant anion is cl followed by so42 and hco3 in the northern section of study region whereas ca2 na and hco3 are the dominant ions in the lakes of the southern section the higher concentrations of carbonate in the southern lakes reflect contributions from groundwater discharge in contrast the higher concentrations of sodium chloride and sulfate in the northern section indicate that they are dominated by the interaction of evaporates additionally cation exchange precipitation and dissolution have also modified the distribution of hydrochemical compositions thermokarst processes in particular have induced changes in the hydrochemistry of lake waters in the permafrost regions of the qtec in that the ion concentrations are closely related to ground ice content in the context of persistent climatic warming and steadily increasing anthropogenic activities the salinity of lakes along the qtec is likely to increase in the future

towards sustainable development of the environmentally degraded arid rivers of china a case study from tarim river increases in water resources development and utilization over the last 30 years have led to significant environmental and hydrological degradation of the tarim river basin water discharge in the lower reaches has been seriously compromised a total of 300 km of the lower reach has been drained between the 1950s and 1970s the water table fell from 2 3 to 4 10 m between the years 1960 and 1980 and the annual rate of fall of the water table was 20 cm from 1980 to the present the area populated by populus euphtatica has declined by two thirds and the biomass has decreased by half between the years 1958 and 1978 in the tarim river basin from the 1950s to the 1990s the area of p euphtatica e angustifolia forest the main tree species of the region declined by 3 820 km2 in the lower reaches of the tarim river basin while the shrub and meadow area declined by 200 km2 such hydrological changes have resulted in a marked degradation of aquatic habitats and have caused substantial land desertification a total of 12 300 km2 of desertified lands formed between the 1960s and 1990s during the past 30 years the salt content of the tarim river has increased gradually according to observational data from the alar hydrological station the maximum salt content in 1960 was 1 28 g l 1 but in 1981 1984 it reached 4 0 g l 1 and in 1998 was 7 8 g l 1 based on the present organic carbon content in desertified lands total emissions of c into the atmosphere in the last 30 years have been 112 2 tg representing 28 3 of organic carbon in the 0 1 0 m soil layer due to the hydrological degradation among factors contributing to these problems human activities are fore most solving these problems will require raising the level of scientific and technological expertise in the monitoring conservation protection and rehabilitation of water resources and associated habitats presently the greatest priority is to expand and improve water conservation studies

the retreat of glaciers in response to recent climate warming in western china glaciers in china are primarily located in the tibetan plateau tp and surrounding high mountains the chinese glacier inventory indicates that there are 46 377 glaciers in western china meteorological records indicate that air temperature in western china has risen by 0 2 c per decade since 1951 and 1998 was the warmest year precipitation in the region increased by 5 10 per decade from 1953 to 1997 using remote sensing and geographic information system methods we have monitored the changes in 5000 glaciers over the past 50 years we conclude that 80 of glaciers in western china have retreated losing 4 5 of their combined areal coverage although some glaciers have advanced in addition regional differences characterize glacier changes over the past few decades for example glaciers in the central and northwestern tp were relatively stable while glaciers in the mountains surrounding the tp experienced extensive wastage mass balance variations for some glaciers show accelerated ice shrinkage in the last two decades

an observational and numerical study of a cold front interacting with the olympic mountains during coast iop5 abstract this paper documents the three dimensional flow and precipitation structures associated with a weak cold front interacting with the olympic mountains and the subsequent development of a puget sound convergence zone this study utilizes data collected during coast iop5 the fifth intensive observing period of the coastal observation and simulation with topography field experiment that took place on 11 12 december 1993 one of the most important data sources was a noaa p 3 aircraft which provided flight level data radar reflectivity and doppler winds as it circumnavigated the olympics initially frontal passage along the western foothills of the olympics was accompanied by a 2 3 c temperature drop a rapid wind shift to northwesterlies and an intense line of precipitation 35 45 dbz however the wind shift and associated precipitation structures attenuated when the front began to ascend the windward slopes of the olympics surface and p 3 observations document the deformation of the front

active thrusting and folding in the qilian shan and decoupling between upper crust and mantle in northeastern tibet fieldwork south of the city of gaotai gansu province china shows that active shortening of surface sediments in the foothills of the yumu shan a large fore mountain of the qilian shan at the northeastern edge of tibet involves both overthrusting and flexural slip folding north of this mountain we found and mapped a prominent north facing thrust scarp that offsets a holocene fan sloping gently 3 4 to the north part of this scarp appears to be related to the m 7 5 180 a d earthquake that may have led to the demise of the han dynasty city of luo tuo chen in the hexi corridor a set of 10 100 150 m long profiles measured across this scarp 3 2 m high on the average can be made to fit the diffusion degraded morphology of a surface break related to the 180 a d event using a value of about 3 3 m 2 10 3 yr for the mass diffusivity of fanglomerates in this part of gansu province smaller mountain facing scarps on a terrace capped foothill result from bedding slip concurrent with active folding of underlying steeply northdipping plioquaternary sandstone and conglomerate beds holocene uplift rates along the yumu shan which is only one of the qilian shan ranges are estimated to be between 0 4 and 1 9 mm yr which implies that much of the mountain formed in the quaternary the periclinal structure of the plioquaternary envelope under which the paleozoic core of the yumu shan plunges towards the west suggests that the whole 3200 m high mountain is a basement ramp anticline mountains striking parallel to the yumu shan with similar structure and comparable or greater sizes north and south of the hexi corridor probably also correspond to recent crustal ramp anticlines this implies that the wide mountainous upper crustal wedge making the northeastern edge of the tibet qinghai plateau is detached from the underlying lower crust and upper mantle

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones ix some effects of orography on rainbands abstract the effects of orography on the mesoscale structures and precipitation processes in warm frontal warm sector wide cold frontal narrow cold frontal and post frontal rainbands in four pacific cyclones are described the rainbands were tracked with a doppler radar as they approached the washington coast and then for 150 km inland as they passed over topographic features ranging from modest hills to mountain ranges the rainbands were affected in a variety of ways by orography ranging from dissipation to formation and precipitation from the bands was enhanced and reduced in different situations these effects are discussed with respect to the large scale flow mesoscale air motions and precipitation growth mechanisms

relevance of conditional symmetric instability in the interpretation of wide cold frontal rainbands a case study 20 may 1976 comparisons are made between the characteristics of rainbands observed in a frontal system using a c band doppler radar and dynamical mechanisms relevant on the mesoscale 100 km the orientation of these rainbands nearly aligned with the thermal wind suggests that symmetric instability may play a role in their formation this possible explanation of the precipitation is discussed

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

spatial structure of rainfall in mid latitude cold front systems abstract experimental evidence and physical interpretation of rainfall spatial distribution associated with cold front systems in an inland region 2282 km 2 of the mediterranean area are provided by using a representation on the meso local scale postfrontal and prefrontal storm ensembles consisting of thirty two and seven components respectively were considered for postfrontal storms the distribution of storm total depth was found to be mainly determined by small mesoscale precipitation areas of random nature with orographic effects that in the average were represented by a ratio of 1 5 between rainfall depth over the hills and in a lowland area just upwind of them however despite the basic role of random effects it was possible to divide the study region into a restricted number of homogenous zones whose structure appears to be linked with orography for prefrontal storms the orographic enhancement was more considerable with the above ratio expressed by a value of 2 5 the enhancement was limited by the absence of contributions to surface rainfall due to a seeder feeder process the occurrence of an effect of inhibition of forced uplift which accompanied both the storm types and was caused by fairly modest orography is also discussed such a mechanism frequently produced a weakening or dissipation of pre existing precipitation and may take on an important role in problems of rainfall analysis over real basins

hydrogeochemical investigation in an arid region of iran tabas central iran groundwater is the most important source of water supply in iran and understanding the geochemical evolution of groundwater is important for sustainable development of the water resources in tabas area a total of 29 samples of groundwater in tabas area have been analyzed for ions and major elements groundwater of the study area is characterized by the dominance of na cl water type groundwater was generally acidic to high alkaline with ph ranging from 5 42 to 10 75 the tds as a function of mineralization characteristics of the groundwater ranged from 479 to 10 957 mg l with a mean value of 2 759 mg l the ca2 mg2 so42 and hco3 were mainly derived from the dissolution of calcite dolomite and gypsum the cu pb and zn ions are not mobile in recent ph eh but these conditions controlled dissolved se v and mo in groundwater the as is released in groundwater as a result of the weathering of sulfide minerals like arsenopyrite

evolution of a cold front encountering steep quasi 2d terrain coordinated aircraft observations on 8 9 december 2001 during improve 2 abstract research aircraft observations from the 8 9 december 2001 case of the second phase of the improvement of microphysical parameterization through operational verification experiment improve 2 describe the evolution of a wide cold frontal rainband wcfr during its eastward advance from the pacific coastline to a point 200 km inland over the cascade mountains of oregon this analysis has two objectives first to illustrate the rapid weakening of the circulation associated with a landfalling wcfr and the relationship of these changes to terrain induced airflow modifications and second to quantify the degree to which this weakening impacted cloud microphysical properties such as liquid water content ice particle concentrations and precipitation rate the kinematic structure of the wcfr is detailed using doppler radar observations from a noaa p 3 aircraft while some concomitant cloud microphysical properties are documented using flight level measurements from the university of washington convai

deuterium excess in an east antarctic ice core suggests higher relative humidity at the oceanic surface during the last glacial maximum a continuous deuterium excess profile d d 8 18o was obtained from the dome c ice core spanning 32 000 yr it exhibits significant variations over this period in particular d was 4 5 lower around 18 000 yr bp than over the past 7 500 yr interpreted as reflecting higher relative humidity estimated 90 over the oceanic areas providing moisture for antarctic precipitation

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

hydrochemical characteristics of groundwater in the zhangye basin northwestern china the zhangye basin located in arid northwest china is an important agricultural and industrial center in recent years rapid development has created an increased demand for water which is increasingly being fulfilled by groundwater abstraction detailed knowledge of the geochemical evolution of groundwater and water quality can enhance understanding of the hydrochemical system promoting sustainable development and effective management of groundwater resources to this end a hydrochemical investigation was conducted in the zhangye basin types of shallow groundwater in the zhangye basin were found to be hco3 hco3 so4 2 so4 2 hco3 so4 2 cl cl so4 2 and cl the deep aquifer groundwater type was found to be hco 3 so 4 2 throughout the entire area ionic ratio and saturation index calculations suggest that silicate rock weathering and evaporation deposition are the main processes that determine the ionic composition in the study area the suitability of the groundwater for irrigation was assessed based on the us salinity laboratory salinity classification and the wilcox diagram in the study area the compositions of the stable isotopes 18o and d in groundwater samples were found to range from 4 00 to 9 28 and from 34 0 to 65 0 respectively these values indicate that precipitation is the main recharge source for the groundwater system some local values indicate high levels of evaporation tritium analysis was used to estimate the ages of the different groundwaters the tritium values of the groundwater samples varied from 3 13 to 36 62 tu the age of the groundwater at depths of less than 30 m is about 5 10 years the age of the groundwater at depths of 30 50 m is about 10 23 years the age of the groundwater at depths of 50 100 m is about 12 29 years for groundwater samples at depths of greater than 100 m the renewal time is about 40 years

airborne dual doppler observations of an intense frontal system approaching the pacific northwest coast airborne doppler radar data collected off the pacific northwest coast by a noaa wp 3d orion aircraft over an 8 h period on 8 december 1993 during the coastal observations and simulations with topography experiment reveal the mesoscale structure of an intense frontal system while it was well offshore and as it approached within 20 km of the oregon coastline during the offshore stage a portion of the narrow coldfrontal rainband was characterized by deep convective cores pseudo dual doppler analyses characterize the kinematic and precipitation structure of the deep convection pseudo dual doppler analyses describe the subsequent evolution of the narrow cold frontal rainband as it approached to within 20 km of the oregon coast deformation of the frontal zone appeared to cause the dissipation of one of three precipitation cores contained within the dual doppler area the precipitation cores and the strong convergence zone associated with the front conformed to some degree to the shape of the coastline near cape blanco oregon as the front neared the coast changes in the prefrontal flow that occurred as the front approached the coast were qualitatively consistent with theoretical and numerical studies of upstream orographic influence comparison of pseudo dual doppler derived velocity profiles with idealized numerical model calculations suggests that the nearshore evolution of the frontal rainband was significantly affected by an upstream influence of the coastal orography

the role of vertically propagating gravity waves forced by melting induced cooling in the formation and evolution of wide cold frontal rainbands abstractrealistic mesoscale model simulations using the weather research and forecasting wrf model and idealized dry simulations were used to study the mechanisms responsible for the formation and evolution of wide cold frontal rainbands wcfrs associated with a wintertime cyclone that moved onto the washington coast the wrf simulation reproduced observed characteristics of three successively formed wcfrs including their spacing and movement as well as the timing of the formation of two wcfrs behind the first sensitivity experiments showed that melting induced cooling in the stratiform precipitation area behind the surface cold front was essential for the formation of the first and second wcfrs whereas the third wcfr was formed by the release of potential instability within an ascent forced by upper level frontogenesis enhanced frontal updrafts responsible for the first and second wcfrs were created by a superposition of a broad updraft caused by frontal dynamics and upward propagating gravity wav