aeolian desertification in china s northeastern tibetan plateau understanding the present through the past abstract under a background of a significantly warming climate current aeolian desertification in china s northeastern tibetan plateau netp has been widely studied but disagreements related to its causes continue to persist in order to understand the present through the past this study determined the various phases of aeolian desertification in the netp based on the statistical analysis of 40 optically stimulated luminescence osl aeolian sand dates from 23 aeolian sections because the redistribution of aeolian sand by wind processes can reduce the number of older sand dates this research only affects exactly the past millennium following this we analyzed the relationships between aeolian desertification phases in conjunction with reconstructed climatic data results revealed three distinct aeolian desertification phases that approximately correspond to 1480 ce 1680 ce and 1800 ce respectively by comparing these dates to well established paleoclimate records we determined that these three aeolian desertification phases all occurred under a cold and dry climate background accordingly aeolian desertification in the netp today under its current warm and wet climate background can therefore be attributable to irrational human activities rather than rising temperatures accordingly we can infer that under the current warmer and wetter climate background aeolian desertification in the netp today can be reversed as long as human activities remain moderate even without the implementation of artificial revegetation initiatives

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones viii a model for the seeder feeder process in warm frontal rainbands abstract previous field studies have indicated that warm frontal rainbands form when ice particles from a seeder cloud grow as they fall through a lower level feeder cloud in this paper we present results from a parameterized numerical model of the growth processes that can lead to the enhancement of precipitation in a seeder feeder type situation the model is applied to two types of warm frontal rainbands in the first type 1 situation the vertical air motions are typical of those associated with slow widespread lifting in the vicinity of warm fronts in the second type 2 situation the vertical air motions are stronger and more characteristic of the mesoscale the model simulations show that in the type 1 situations the growth of the seed ice crystals within the feeder zone is due to vapor deposition the feeder zone in this case is slightly sub saturated with respect to water due to the presence of the seed crystals in regions where the feeder zone is not seeded from aloft snow cryst

downwind aeolian sediment accumulations associated with lake level variations of the qinghai lake during the holocene northeastern qinghai tibetan plateau many lakes in the qinghai tibetan plateau qtp have aeolian sands distributed in their downwind shores however it has been rarely systemically investigated on whether the downwind dune sand and lake evolved in association with each other or they evolved independently here we take the well known qinghai lake and its downwind sand area as a case study to investigate the issue of water sand interaction grain size magnetic susceptibility and geochemical data along with optically stimulated luminescence osl ages suggest that the downwind eastern shore sandy lands co varied with the lake level fluctuations or lake extension changes of the qinghai lake during the holocene epoch during the early holocene lake lowstands 11 9 ka ka is 1000 years vast areas of exposed lacustrine sediments were eroded by prevailing westerly winds therefore causing sand to accumulate at the eastern shore bajada areas along the west piedmonts of the riyue mount and to expand along the daotang river valley in contrast during the mid to late holocene lake highstands 7 1 2 ka eastern shore dune sands were largely stabilized and loess accumulated and even paleosol developed leading to substantial shrinkage of the eastern shore sandy lands in addition using gis tool we reconstructed the spatial extensions of the lake during highstand mid holocene and lowstand early holocene and eastern shore desert range of early holocene as a result this study indicates a close connection between the lakes in qtp and the aeolian sands downwind

the role of snow sublimation in frontogenesis recent work on the influence of moist processes at synoptic fronts has shown how condensation heating can be a strong and even a dominant factor in their development at mesoscale lines of convection the heating is again dominant but it is thought that cooling by the evaporation of precipitation is also a crucial factor in their development and propagation although most simple models of synoptic fronts do not attempt to simulate diabatic cooling accurately data from the fronts 87 experiment have identified evidence of a strong mesoscale downdraught below a synoptic frontal surface there has been speculation that such a downdraught is forced by the sublimation of falling snow since snow is more efficient at cooling the atmosphere for a given precipitation rate than evaporation of rain rainfall parametrizations are likely to underestimate the influence of such cooling in this paper a suitable parametrization of diabatic cooling based on the assumption of small stability to slantwise convection is used to simulate a band of snow sublimation in developing fronts the semi geostrophic equations are employed in the study of fronts which are formed by deformation or horizontal shear of the geostrophic winds it is found that the cooling has little influence on the large scales of motion and does not greatly accelerate the formation of frontal singularity however the cross frontal flows in the vicinity of the cooling are modified strongly with the formation of a narrow downdraught of comparable dimensions and intensity to that suggested by the experimental data the cooling has a weak influence on all the fields at a larger distance from the front this is discussed in the context of the large scale or geostrophic response to lines of convection

effects of melting on frontogenesis abstract frontal precipitation systems are simulated with a 2d cloud model including ice phase microphysics despite the use of idealized frontogenetic forcing in the simulations some observed characteristics of frontal zones and their associated cloud and precipitation fields are reproduced in the simulations the effects of melting snow on surface frontogenesis is investigated it is found that the cooling effects of melting snow significantly accelerate surface frontogenesis in winter storm environments especially when the melting layer is close to the surface however the steady state surface frontal strength in the model is not sensitive to the melting effects finescale thermal and kinematic perturbations inside the frontal zone near the melting level quite similar to those recently reported in the literature are evident in the model results analysis of the model results suggests that cooling from melting snow may induce these thermal and kinematic perturbations and may enhance baroclinicity

holocene climatic changes revealed by aeolian deposits from the qinghai lake area northeastern qinghai tibetan plateau and possible forcing mechanisms previous palaeoclimatic studies in the northeastern qinghai tibetan plateau netp during the holocene mainly using lake sediments have deepened our understanding of the climatic system in this remote region the timing and forcing mechanisms of climatic change in this region are still controversial however aeolian sand and silt deposits which are widely distributed in the netp can be readily dated by optically stimulated luminescence osl techniques and reveal the sensitive response of the landscape to climatic change in this study aeolian sand and loess at six sites around qinghai lake were studied to reconstruct millennial scale climatic changes during the holocene multiproxy data along with 24 osl age determinations show that low effective moisture and aeolian activity occurred at c 13 ka 10 9 1 ka and 8 9 7 8 ka periods of greater effective moisture may have occurred at 11 ka and 9 ka and there is evidence for a previously undocumented wet climate at 4 3 ka these results show that mi

wind energy environments and aeolian sand characteristics along the qinghai tibet railway china abstract the qinghai tibet railway qtr the longest high altitude railway in the world is frequently damaged by windblown sand because of strong winds and abundant sand based on detailed wind data in situ observations of windblown sand and field wind tunnel simulations along the qtr this paper aims to clarify the characteristics of windblown sand with increasing altitude and to show the dynamical environment of sand activities the predominant wind is unidirectional along the qtr in cold high environments sand transport rate increases with increasing wind velocity but decreases exponentially with increasing height in the windstream as the altitude increases the threshold velocity for sand movement linearly increases with altitude and the sand transport per unit width decreases gradually the results can be used to guide the design of sand control structures both in the study area and in other areas suffering from windblown sand

an environmental gradient of vegetative controls upon channel planform in the source region of the yangtze and yellow rivers abstract alluvial reaches in the source region of the yangtze and yellow rivers located atop the qinghai tibetan plateau and mostly at elevations that are typically higher than 3500 m have similar slope and valley setting conditions however alluvial reaches in the source region of the yangtze river exhibit predominantly braided channel planforms while equivalent reaches in the source region of the yellow river have more diverse planform morphologies including anastomosing braided anabranching braided and anabranching anastomosing reaches the regional gradient of variation in riparian vegetation and interactions between vegetation development and hydrologic process are shown to be major factors influencing this difference in channel planforms a short period above freezing coincident with recurrent yet pulsed flows in the source region of the yangtze river suppress riparian vegetation growth promoting the development of braided channel morphologies in contrast a milder climate coincident with less variable flows in the source region of the yellow river permit the establishment of different forms of riparian vegetation thereby supporting the development of a wider range of channel planform morphologies

holocene aeolian activity in the zoige basin northeastern tibetan plateau china abstract the zoige basin is located in the northeastern tibetan plateau at an altitude of around 3500 m to fully understand and assess the current status and future trend of aeolian activity in the zoige basin it is necessary to reveal the history of aeolian activity of this region in this study 11 optically stimulated luminescence osl ages from three typical sections were used to reconstruct the history of aeolian activities in the region during the holocene the results of the chronologies show that the oldest osl age 10 27 0 81 ka occurred in the early holocene but aeolian sediment deposition primarily occurred in the late holocene after around 3 20 0 33 ka in the whole holocene the aeolian activities of the zoige basin occurred contemporaneously with nearby sites in the northeastern tibetan plateau episodic weak aeolian activities were recorded in nearby sites in the northeastern tibetan plateau however we postulate here that the combination of a flat low lying landscape along with higher precipitation during the mid holocene resulted in this area being relatively insensitive to short term arid climatic changes and aeolian activity

the role of latent heating in warm frontogenesis the role of latent heating from individual cloud processes associated with one part of a springtime extratropical cyclone the warm front is assessed using high resolution modelling condensation and cloud droplet nucleation are the largest sources of latent heat along the frontal surface and together produce rates of horizontal frontogenesis that are of the same order of magnitude as the deformation and tilting terms at mid levels however near the surface latent heating does not cause strong frontogenesis in the vertical stabilization caused by condensation and cloud nucleation is nearly everywhere higher than stabilization caused by dry dynamics and is the primary process through which high static stability is found along the frontal surface the frontogenesis and static stability tendency equations are combined to form an expression for the frontal slope tendency while dynamic processes lead to increases in frontal slope latent heating often counteracts this tendency this indicates that the direct effect of latent heating on the thermal structure of the front is to decrease the slope and in that sense weaken the warm front

the environmental effects of the uplift of the qinghai xizang plateau the intense upheaval of the qinghai xizang plateau took place 2 ma bp the terraces of the yellow river in the lanzhou region and its upper sections provide a record of the uplift of the plateau the interaction of glaciation cycles resulting from climatic changes and pulsating tectonic upheavals are both involved in the record of environmental change across the plateau three tectonic climatic events which are termed respectively the qinghai xizang movement the huanghe yellow river movement and the gonghe movement occurred 2 1 5 1 0 and 0 15 ma bp the upheaval of the qinghai xizang plateau was the trigger mechanism of the asian monsoon the loess plateau was formed in the monsoon triangle of east asia human origins and human evolution may have been stimulated by the uplift of the qinghai xizang plateau

the front range blizzard of 1990 part i synoptic and mesoscale structure abstract over 1 m of snow fell in the foothills of southeast wyoming and northeast colorado during the storm of 6 7 march 1990 the heavy snowfall combined with strong winds to product blizzard conditions resulting in major highways being closed for several days the heaviest snow fell in the vicinity of a narrow northerly barrier jet that developed in place along the front range of the colorado rockies strong warm air advection from the southeast was observed during the development of the barrier jet there was no cold air advection from the north rapid intensification of the barrier jet took place only after precipitation started and was concurrent with the development of heavy precipitation a mesoscale front marked the transition from southeasterly to northerly flow this front remained very close to the rain snow line and progressed toward the east at 1 2 m s 1 for about 15 h melting precipitation appears to be the dominant process contributing to the development of the barrier jet and mesoscale f

aeolian sediments on the north eastern tibetan plateau abstract aeolian sediments on the tibetan plateau are an important archive of palaeoclimatic information this study presents a detailed analysis of sediments from the donggi cona catchment on the north eastern part of the tibetan plateau long and short distance sediment transport leads to a complex pattern of aeolian sediment deposition that depends on climatic changes as well as on the availability of sediments based on the largest dataset of osl datings 51 from a single catchment on the tibetan plateau so far different periods of increased sediment transport have been reconstructed increased aeolian deposition in this high elevation environment started in the early holocene with the accumulation of sands from around 10 5 to 7 ka loess sediments have been preserved from a period from 10 5 to 7 5 ka both archives are related to the strengthening of the asian summer monsoons characterized by wetter and warmer climate this change in climate supported the trapping of aeolian sediments under full monsoon conditions from around 9 ka onwards fluvial processes resulted in erosion of the aeolian archives and the formation of colluvial sediments until 6 ka a dry and cooler climate resulted in the reactivation of dune sands from 3 ka to present possibly in combination with stronger human influence aeolian sediments on the tibetan plateau therefore indicate two different climatic modes during the early holocene wetter conditions were favourable to retain aeolian sediments the reactivation of sediment in the late holocene due to small scale disturbances in the vegetation cover points to a cooler and drier climate

infiltrated clays in fluvial jurassic sandstones of reconcavo basin northeastern brazil abstract fluvial sandstones and conglomerates of the sergi formation a jurassic unit of reconcavo basin northeastern brazil contain significant amounts of interstitial detrital clays which are interpreted as the product of early mechanical infiltration developed in an arid semi arid environment within such an environment the lowered water table allowed muddy waters of episodic runoff to infiltrate through the coarse alluvium concentrating the clays in the upper phreatic zone near the sources of influent seepage petrographic textures considered to be typical of mechanically infiltrated mi clays are herein presented using examples from the sergi formation these textures include 1 ridges and bridges 2 geopetal fabrics 3 loose aggregates 4 anisopachous coatings of tangentially accreted lamellae cutans 5 massive aggregates and 6 shrinkage patterns developed during diagenesis in addition their detrital aspect as revealed by sem observations and the presence of impurities in the interior of the clay aggregates were also used as evidence for the interpreted origin of the clays in most hydrocarbon reservoirs in the sergi formation the clays described in this paper are among the main controls on porosity and permeability distribution commonly zones with maximum clay concentration are the main internal permeability barriers within the sergi formation reservoirs

holocene climatic change revealed by aeolian deposits from the gonghe basin northeastern qinghai tibetan plateau a climate record for the gonghe basin in the northeastern qinghai tibetan plateau during the holocene period was determined from a 3 90 m aeolian deposit as revealed by the variation of proxies including sedimentary facies magnetic susceptibility the total organic carbon toc content grain size and geochemical parameters the regional climatic evolution during this period can be divided into the following stages there was a cold and dry phase in 11 8 10 1 ka probably related to the younger dryas yd event prior to the holocene an optimum stage with relatively warmer and wetter climate dominated the region between 10 1 ka and 8 7 ka the climate tended to relatively dry condition from 8 7 ka to 4 7 ka although weak paleosol weakly developed paleosol developed during this period this is inconsistent with the megathermal maximum in the holocene or holocene optimum a relatively warm and wet climate emerged in 4 7 0 7 ka and an obviously cold and dry stage emerged since 0 7 ka thereafter the regional climate became warmer in addition eight cold events were recorded including the yd event around 11 8 ka 9 8 9 5 ka 9 2 8 7 ka 8 1 7 6 ka 7 0 6 1 ka 5 3 4 7 ka 3 1 1 5 ka and since 0 7 ka these events are coincident with cold phases revealed by aeolian depositions and lake records in the northeastern qinghai tibetan plateau and also with the evidence of deteriorated climate phases in the high and low latitudes of the northern hemisphere on a millennial scale such as in hongyuan peat and drift ice tracers in the north atlantic ocean in the holocene

an 800 ky proxy record of climate from lake sediments of the zoige basin eastern tibetan plateau abstract we present the results of magnetic susceptibility geochemical and pollen analyses of a 120 m long core of lacustrine and fluvial sediments from the zoige basin eastern tibetan plateau palaeomagnetic dating indicates that the sediment sequence spans the last ca 800 ky the magnetic susceptibility record appears to be related to global ice volume over this period and this relationship is used to produce a tentative revised chronology for the sediment sequence the various climate proxies show a pattern of periodic variations over the last 800 ky bp the date of 500 ky bp is a significant boundary prior to this date the climate proxies show a pattern of more frequent variability after 500 ky bp the variations are of lower frequency and higher amplitude the results also indicate that marine oxygen isotope stage 13 was an unusually intense interglacial in the eastern tibetan plateau and chinese loess plateau areas

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones xiii structure of a warm front abstract mesoscale measurement from radars aircraft and rawinsondes and synoptic and satellite data are used to provide a detailed description of a warm front as it approached the washington coast in many respects the warm front was consistent with the classical model temperature rises were concentrated within a forward sloping frontal zone winds veered with height and lapse rates were more stable within the frontal zone clouds and precipitation were produced by upglide over the warm frontal surface and as the warm front approached clouds lowered and precipitation generally increased however in several important respects the warm front differed from the classical picture air flowed through the warm front and the warm frontal zone also the warm frontal zone had a staircase profile with some segments nearly horizontal and other segments with steep slopes finally precipitation was by no means uniformly distributed instead it occurred in both irregular and banded shaped mesoscale features

palaeoenvironmental implications of a holocene sequence of lacustrine peat sediments from the desert loess transitional zone in northern china abstract a high resolution lacustrine peat record from the desert loess transitional zone in northern china was obtained to reconstruct holocene environmental change in the region ams 14c dates are used to provide a chronology the results indicate that the site was a desert environment before 12 2 cal kyr bp and was then occupied by a paleolake which started to shrink with a wetland occurring from 6 2 to 3 0 cal kyr bp subsequently the site became a seasonally water filled depression based on the lithology and measurements of grain size and total organic carbon content the climate changed from arid to humid at 12 2 cal kyr bp and became more humid after 8 3 cal kyr bp from 6 2 to 3 0 cal kyr bp precipitation decreased but the climate remained at an optimum after 3 0 cal kyr bp the climate was dry overall but with several humid intervals a comparison of paleoclimatic records from lacustrine and aeolian deposits from the region reveals a discrepancy about the nature of the early holocene climate and we conclude that this is because lacustrine sediments responded more sensitively to precipitation than aeolian deposits when the temperature was low the environmental evolution of the region was synchronous with changes in the asian summer monsoon asm but temperature also played a key role in the early holocene

dolomitization and silicification in low energy lacustrine carbonates paleogene madrid basin spain abstract repetitive sequences of carbonate deposits occurrence include in the lower part of the paleogene carbonate unit northeast border of the madrid basin have been studied defining regressive lacustrine sequences and early diagenetic processes binocular microscopic examination scanning electron microscopic energy dispersive x ray observations and x ray diffraction analyses joint to isotopic studies 18 o and 13 c have been used to characterise the facies and environments the sequences consist of a lower uncemented carbonate mud unit calcitic or dolomitic in composition and an upper carbonate unit arenites bioclastic limestones and microbial laminated limestones with cherts visual features vertical prismatic structures fissures massive nodulization rhizoliths brecciation and microscopic features micrite micronodules vug porosity circumgranular cementation gypsum lenticular crystals outline pedogenic processes these features found locally in bioclastic and microbial laminated limestones or in dolomite uncemented muds define respectively palustrine limestones or dolocretes facies analysis allows us to define several lacustrine sub environments basinal littoral eulittoral and supralittoral and characterises different types of shallowing upward lacustrine sequences either with or without subaerial exposure the isotopic values of the bioclastic and microbial laminated limestone from 5 77 to 6 78 for 13 c and from 5 25 to 5 53 for 18 o and those of uncemented calcitic muds from 5 80 to 7 01 for 13 c and from 4 98 to 5 58 for 18 o establish that both types of carbonates precipitated in equilibrium with meteoric waters in the palustrine carbonate deposits the 13 c values suggest a strong organic contribution the dolomitization that only affected the uncemented carbonate muds is early interpreted because of the structural and compositional characteristics of the dolomite micro rhombic dolomicrite nearly stoichiometric and poorly ordered and because the calculated average 18 o dol cal for calcitic and dolomitic uncemented muds is about 6 the 18 o isotopic values indicate that the dolomite precipitated from water that was slightly more enriched in heavy isotopes than the calcite because of an increase in evaporation rates nodules and nodular levels of cherts occur in the upper units of littoral and eulittoral sequences probably as a consequence of the existence of microbial mats that could include the silica source according to their mineralogy opal ct and quartz moganite and structures double nodules lamination and bioturbation three types of chert are described tb mb and wo these types define three general stages of silicification during the early diagenesis from the recently buried to the postcompactation of carbonate deposits the 18 o values of quartz show that the silicification and ageing of opaline phases occurred from meteoric waters which were lighter than the calcite or dolomite precipitating waters the cherts included in palustrine limestones show 18 o values of quartz that record more evaporated waters than those of the general stages of silicification

osl chronology and palaeoclimatic implications of aeolian sediments in the eastern qaidam basin of the northeastern qinghai tibetan plateau abstract aeolian sediments are widely distributed in the hyper arid qaidam basin and are good palaeoclimatic records due to limited age control aeolian processes and their relevance to palaeoclimatic change are poorly understood in this study we present 28 optically stimulated luminescence osl ages for both loess 14 samples and aeolian sand 14 samples from 8 profiles in eastern qaidam basin eqb in order to provide a detailed chronology for understanding the timing of aeolian processes and associated environmental conditions we reconstructed the history of aeolian activity in the eqb since deglaciation by combining osl chronologies lithologic stratigraphy and grain size analysis the results indicate that 1 aeolian sand underlying the loess accumulated at ca 12 4 11 5 ka and 10 8 ka but not during the last glacial maximum 2 loess accumulation started at 10 ka and lasted to 0 45 ka at least while most of the loess was deposited during 8 4 5 ka 3 palaeoclimates in the eqb are inferred to be arid during 12 4 11 5 ka relatively humid during 10 8 ka humid during 8 4 5 ka and relatively arid during 4 5 0 45 ka and 4 evolution of aeolian sediments were mainly controlled by effective moisture and also affected by local topography

the kinematics of orographic airflow during sierra storms abstract two case studies of the kinematics of the airflow over the sierra barrier are presented the observations consisted of rawinsondes and single doppler rhi and velocity azimuth display vad analysis of ppi scans the rhi scans were made orthogonal to the nearly two dimensional sierra barrier the cloud in the first case study contained a strong stable layer at 0 c while the second storm was highly unstable the radar bright band and soundings near the radar indicated that an 250 m thick 0 c isothermal layer was present in response to the diabatic process of melting when the bright band was impinging upon the barrier the associated 0 c isothermal layer was inferred to expand until it finally reached the ground at that point it was 1 km in depth direct thermodynamic soundings am presented for a similar situation which agrees with the modified soundings inferred for this study the resulting effects on the airflow and precipitation are discussed the unstable case contained a line of deep conve

holocene aeolian activity in the headwater region of the yellow river northeast tibet plateau china a first approach by using osl dating abstract the headwater region of the yellow river hryr is the catchment upstream of duoshi gorge covering an area of 29 588 km2 the hryr is located in the northeastern tibet plateau with an altitude higher than 4000 m above sea level and is especially sensitive to climate change since the late 19th century the mean annual temperature in tibet plateau has increased sharply as a result of increasing air temperature a significant number of environmental problems have occurred during the past decades including aeolian desertification in recent decades aeolian desertification has become a severe environmental problem in the tibet plateau due to permafrost degradation because permafrost plays an important role in maintaining the grassland vegetation with the increase in ground temperature the aeolian activity in the hryr is likely to become more serious however the history of aeolian activity in the hryr remains unknown due to a lack of chronological studies in this study 15 optical stimulated luminescence osl ages from three typical sections were used to reveal the history of aeolian activities in the hryr during the holocene all of the osl ages were late holocene and the oldest age is 2 13 0 16 ka bp the relative young osl ages and deep aeolian sediment indicated very high sedimentation rates in the late holocene especially after around 1 ka bp the intensive aeolian activity and low toc content indicate a drier climate in the late holocene the well sorted sediments and similar grain size distributions of the three sections imply their similar wind regimes based on the evolution history of the yellow river s headward erosion it is inferred that little aeolian activity occurred in this region during the early and mid holocene

diagenesis of late miocene micritic lacustrine carbonates madrid basin spain mud grade lacustrine limestones of miocene age from the madrid basin spain reveal varied and complex diagenetic histories microporous micrites occur as well as micrites with anhedral mosaics the micrites have recrystallized from a metastable precursor in part under sub oxic meteoric diagenetic conditions probably before extensive karstification in the pliocene the absence of aragonite relics their mainly micritic microfabric low sr content and covariant trend of sr and mg suggest that the micrites formed from mainly high magnesian calcite muds lacustrine micrites can be compared to marine forms and criteria used to assess the composition of the marine precursor muds can be applied to lacustrine limestones to complement other techniques to identify original lake water compositions

eolianite grain size distributions as a proxy for large changes in planetary atmospheric density a digitized version of the ahlbrandt 1979 global dune dataset and data for distributions in figure are available at https github com erikgoosmann aeoliandata

a numerical investigation of squall lines part i the control experiment abstract a two dimensional anelastic cloud resolving numerical model was used to simulate squall systems large domain and fine grid resolutions were utilized so that both the convective and mesoscale components of squall lines could be handled adequately detailed cloud microphysics including the ice phase and the coriolis force have been included in the basic model both the life cycle and storm structure of observed squall systems have been simulated successfully some details in the observed precipitation and kinematic characteristics of squall lines such as the locations of front to rear jet core the base of the stratiform cloud the formation of a transition zone and the organized mesoscale updraft have been simulated by the model the storm generated meso scale low pressure center located behind the convective updraft has been shown to be instrumental in the initiation and maintenance of the mesoscale circulation and the associated trailing stratiform region diagnostically the horizontal

chemical weathering of fluvial sediments during alluvial storage the macuapanim island point bar solimoes river brazil abstract modification of sediment composition by chemical weathering depends both on the overall intensity of weathering and on its duration at macuapanim island solimboes river amazon main channel brazil a number of alluvial deposits have been exposed to intense tropical weathering for differing lengths of time in the very fine sand fraction the detrital component shows a steady and marked increase in compositional maturity with increasing sediment age immature sands of arkosic to litharenitic composition show a progressive loss of lithic fragments feldspars and accessory minerals with a concomitant enrichment in quartz this process produces first cycle sands whose detrital component is of quartz arenite composition among the salts quartz is enriched over time relative to more nstable phases particularly plagioclase this enrichment is probably largely caused by the destruction of plagioclase through chemical weathering but silt size quartz may also be produced through the breakdown of sedimentary and metasedimentary lithic fragments in the sand fraction in the clay fraction an increase in the relative abundance of smectite accompanies the breakdown of volcanic lithic fragments in the sand fraction and probably reflects the degradation of volcanic glass the clay fractions of the oldest samples examined contain less smectite somewhat more kaolinite and markedly more vermiculite as compared to younger samples but an extensively leached cation poor clay fraction analogous to the quartz dominated silts and sands is never attained the compositional mat rity of the clay fraction is everywhere lower than that of associated silts and sands perhaps because of a continual influx into the clay fraction of immature cation rich clays derived from the physical breakdown of lithic fragments in coarser size fractions this effect is enhanced by the translocation of fines whereby younger less weathered fine material is juxtaposed with older more mature coarse material in the lower levels of the alluvial stratigraphy reworking of floodplains during channel migration results in the reincorporation of older material stored on the floodplains into the sediment load if sediments have been intensely weathered during storage on the floodplain then the result will be a net dilution and replacement of younger relatively immature sands transported by the river by older more mature material from the floodplain the relative proportion of the older sands in the bedload will increase downstream resulting in a progressive downstream increase in the compositional maturity of the bedload of the river

a 7 ka climatic variability record inferred from peat bog sediments in the north of bayan har mountains northeastern tibetan plateau reconstructions of the holocene especially the mid holocene climatic and environmental changes may serve as an analogue for future scenarios about 7 ka of holocene climatic variability in the north of bayan har mountains on the northeastern tibetan plateau is reconstructed using grain size magnetic susceptibility geochemical parameters and accelerator mass spectrometry 14c chronology from peat bog sediments the peat s source is found to be aeolian sediments climatic variability from the peat bog sediments during the last 7 3 ka can be divided into four stages warm and wet from 7 3 to 5 7 cal ka bp cool and dry semi wet from 5 7 to 2 5 cal ka bp relatively cool and wet from 2 5 to 1 1 cal ka bp and cold and dry from 1 1 cal ka bp to present mid late holocene climate in the north of bayan har mountains was significantly unstable during the last 7 3 ka and characterized by five centennial scale oscillations 6 2 6 0 4 3 3 9 2 5 2 1 1 7 1 4 and 0 7 0 2 cal ka bp this mid late holocene climate recorded by peat bog deposits is consistent with most lacustrine sediment records in the north of bayan har mountains and its adjacent areas these lacustrine sediments indicated that the climate on the northeastern tibetan plateau was warm and humid in the early holocene cold and dry after the mid holocene ca 7 5 6 0 cal ka bp and relatively cool and wet in the late holocene

the effect of climate warming and permafrost thaw on desertification in the qinghai tibetan plateau abstract four sets of remote sensing images from 1987 1994 2000 and 2006 50 years of meteorological and soil moisture data corresponding to different desertified lands were combined with populations and livestock data to analyze the process and cause of desertification in a portion of the qinghai tibetan plateau qtp it showed that surface soil temperature in the region has increased at an average rate of 0 6 c per decade between 1980 and 2005 the thawing days on the surface have increased by 60 days from 1983 to 2001 and the depth of the seasonal thawing layer has increased by 54 cm 102 cm and 77 cm in april may and june respectively from 1983 to 2003 as a result the upper soil layer has become drier due to the thickening active layer and soil water infiltration these changes in turn have inhibited the growth of alpine meadow vegetation that has shallow root systems it is concluded that climate warming and permafrost thawing have caused desertification in grazing regions of the qinghai tibetan plateau qtp

timing and provenance of loess in the sichuan basin southwestern china abstract loess like sediments locally called the chengdu clay are widely distributed in the sichuan basin at the eastern margin of the tibetan plateau tp southwest china geomorphology sedimentology pedology grain size distributions and quartz oxygen isotopic ratios collectively demonstrate the aeolian origin of the chengdu clay and its main source area on the tp evidence also supports its transport by the westerlies and the tibetan winter monsoon the magnetostratigraphy of the huagai loess section of the chengdu clay on the highest river terrace of the anchang he river indicates that the sediments began accumulating at about 825 ka bp this suggests the establishment of a circulation system similar to the present day system related to the rapid uplift of the tp at that time

mesoscale circulations forced by melting snow part i basic simulations and dynamics abstract the melting of snow extracts latent heat of fusion from the environment the basic response of the atmosphere to this cooling by melting mechanism is investigated by using a nonlinear two dimensional numerical model it is found that the resultant melting induced circulations consist of a forced downdraft which spreads out laterally like a gravity current and transients which are gravity waves the characteristics of these mesoscale thermally driven circulations are studied under idealistic atmospheric conditions model results show that the melting associated with realistic precipitation rates up to 10 mm h 1 can induce horizontal wind perturbations of several meters per second and vertical motions of tens of centimeters per second since the gravity waves and the cold outflow current propagate away from the source they can have significant dynamic effects on the environment remote from the precipitation region moreover the melting induced near o c isothermal layer in the atmosphere alters

holocene aeolian activity and climatic change in qinghai lake basin northeastern qinghai tibetan plateau abstract aeolian deposits in the qinghai lake basin on the northeastern qinghai tibetan plateau netp were studied in order to reconstruct changes in aeolian activity related to climatic changes over the last 12 5 ka we used 20 optically stimulated luminescence and conventional radiocarbon dates to construct chronological frameworks for four aeolian sections the results indicate that aeolian activity occurred episodically at 12 5 ka 11 2 ka 9 0 ka 8 5 ka 5 5 ka 2 6 2 4 ka and 1 0 9 ka paleosols developed mainly during 9 5 4 ka the field stratigraphy of the sections together with measurements of grain size magnetic susceptibility ms and total organic carbon toc indicate that aeolian activity was strong during the last glacial period following the younger dryas yd holocene interglacial conditions began to develop in the qinghai lake basin at 12 ka with the strengthened asian summer monsoon asm and the decrease in insolation the climate became warm and humid according to the record of aeolian activity the early holocene can be divided into two intervals before and after 9 5 ka aeolian activity remained strong from 12 ka 9 5 ka although the climate was more humid than that of the last glacial period between 9 5 ka and 8 5 ka the aeolian activity weakened and the climate became warm and wet but variable following the mid holocene climatic optimum the climate became significantly drier at 4 ka and aeolian activity strengthened again overall the asm dominated aeolian activity in the qinghai lake basin during the holocene with enhanced aeolian activity corresponding to a weakened asm paleosol development exhibited a lagged response to the strengthened asm and therefore aeolian sand layers in the section do not always indicate a cold and dry climate

cherts with moganite in continental mg clay deposits an example of false magadi type cherts madrid basin spain abstract during the miocene the madrid basin was a closed basin in which a succession of alluvial and lake deposits were replaced by different types of crusts mainly calcretes dolocretes and silcretes in a geographically restricted area to the south mg clay deposits were precipitated in ponds on the sand flats a discontinuous nodular and stratiform mg rich chert appears at the top of the mg clay deposits and displays visual mineralogical and petrological characteristics that are very different from the other silcretes of the madrid basin as revealed by x ray diffraction the cherts consist mainly of quartz and moganite which are commonly found in magadi type cherts the petrological characteristics reveal that the chert consists of a groundmass crossed by several networks of quartz veins the groundmass is formed by mosaic quartz with different sizes of crystals usually less than 20 m and length slow chalcedony the presence of gridwork extinction patterns the differentiation of silica flakes and the preservation of the micromorphological characteristics of the mg clay deposits indicate an early replacement by quartz and moganite the quartz networks show veins of different shapes rectilinear irregular branched and v shaped sizes from a few microns to several millimeters and textures mainly megaquartz microquartz and length slow chalcedony the v shaped veins and some irregular and branched veins are considered to be a consequence of the silicification of cracks in the host rocks the other veins represent silica filling cracks that formed by shrinkage during the various stages of chert formation many macroscopic attributes e g some kinds of cracks mineralogical features the presence of moganite and petrological characteristics e g rectilinear or gridwork orientation of quartz crystals are similar to those of magadi type cherts in spite of this the origin and the environment of formation of this mg rich chert which crystallized by silicification of mg clays during deposition of silcrete are very different from those of the typical pleistocene magadi cherts of african lakes a pronounced shrinkage during silicification in a zone just below the water table and the presence of the moganite are the two factors that caused these mg rich cherts to appear similar to magadi type cherts

geomorphological and palaeoclimate dynamics recorded by the formation of aeolian archives on the tibetan plateau abstract aeolian sediments are an important archive for palaeoclimate reconstructions on the tibetan plateau the accumulation of aeolian sediments and the formation of palaeosols are used as a proxy for dry and wet phases respectively during the last decade the number of osl optically stimulated luminescence ages of aeolian sediments has been rapidly increasing this study summarises the results from more than 300 individual osl ages despite the widespread occurrence of aeolian sediments on the tibetan plateau nearly all osl samples are located on the northeastern and the southern part in most regions the strongest accumulation occurred during the late glacial and in the early holocene this coincides with the strengthening of the asian summer monsoon on the tibetan plateau and wetter climate conditions after the relatively dry glacial times the development of a sufficient vegetation cover acting as a sediment trap seems to be an important requirement for the preservation of aeolian archives short dry periods like the younger dryas led to a more enhanced aeolian accumulation without destruction of previously formed archives in some regions the formation of palaeosols occurred mainly during the wet early and mid holocene but the number of ages is relatively small in contrast a second phase of aeolian accumulation during the late holocene was related to the weakening of the asian summer monsoon and drier climate conditions this indicates that the reaction of aeolian accumulation on the tibetan plateau depends on the previous climate state a comparison between the osl ages from aeolian sands and loess deposits yields a different timing of deposition of these two sediment types while the sand deposits in different basins resemble wet and dry phases loess deposits show no common signal between the analysed areas this indicates an influence of local factors such as varying source areas and erosive processes on the slopes in general the aeolian archives in the high mountain environment are governed by numerous factors besides the climatic influence

quaternary evolution of a meandering gravel bed river in central spain the river jarama is a medium sinuosity meandering river with gravel bedload throughout the quaternary it developed a large number of terraces in a repetitive sequence of aggradation stability degradation stability stages which are studied in the middle reach of the river applying geomorphological and sedimentological methods as well as kadiocarbon dating techniques the upper terrace system of earliest pleistocene to mid pleistocene age forms isolated fragments vertically disconnected and colluviated and their sequential distribution of facies implies lateral shifting of channels and a welldeveloped flood plain the middle terrace system of mid to late pleistocene age has differentiated levels in the upstream reaches while downstream they condense giving a thick multi episodic series corresponding to the tectonic tilting of the basin classical point bar fining upward sequences of a medium to high sinuosity river with gravels and sands as bedload are clearly differentiated in them a major degradation stage follows this group of terraces with an incision of up to 30 m then during a relatively long period of stability a forest of riparian species developed prior to the last aggradational stage of the lower terrace system the aggradation resulted in a fining upward sequence where lateral accretion is clearly visible in the gravels due to migration of the medium to low sinuosity river sedimentation continued and was active up to the 1950s but since then intense anthropogenic modifications led to renewed incision of the river

landscape analysis of the huang he headwaters ne tibetan plateau patterns of glacial and fluvial erosion the large scale geomorphology of the huang he yellow river headwaters centered around the bayan har shan 5267 m asl in the northeastern part of the tibetan plateau is dominated by an uplifted

timing and spatial distribution of loess and loess like sediments in the mountain areas of the northeastern tibetan plateau abstract most studies on landscape evolution on the tibetan plateau during the late quaternary have mainly focused on using lacustrine records however mantles of sandy silt and paleosols also provide valuable archives for reconstructing holocene paleoenvironmental change yet little is known about the distribution and timing of these late quaternary aeolian sediments to enhance understanding and knowledge of aeolian sediments in tibet and to help reconstruct the nature of late glacial through mid holocene landscape development a loess paleosol sequence the suohuduo section located at the eastern margin of the tibetan plateau at about 4000 m above sea level is examined using sedimentological geochemical and geochronological methods a chronostratigraphy is established using nine optically stimulated luminescence and one radiocarbon ages sedimentation increased during the late glacial and the early holocene with an upwards fining of sediments in the lower part of the section two mid holocene paleosols that date to about 8 5 ka to 7 ka and 5 5 ka to 4 ka reflect more humid climate conditions during the mid holocene than earlier times the upper part of the section is mainly silt which reflects a more open landscape with higher aridity since 4 to 3 ka this time these data support evidence for similar climate paleoenvironmental change in adjacent regions on the tibetan plateau

composition of modern stream sand derived from a mixture of sedimentary and metamorphic source rocks henares river central spain the henares river central spain flows westward from the iberian range mesozoic sedimentary rocks under semiarid climatic conditions in the middle and lower reaches the henares river receives sediment from three tributaries canamares bornova and sorbe rivers that drain the central system paleozoic crystalline rocks low grade metamorphic rocks and minor amounts of mesozoic sedimentary rocks modern sands from the henares river and its tributaries offer an excellent opportunity to evaluate the importance of lithology and physiography in determining detrital modes from mixed metamorphic and sedimentary source terrain sand modes from the henares river and its tributaries are quartzolithic they plot in a restricted area on a qmflt diagram with low contents of feldspar and variable amounts of quartz and carbonate metamorphic and minor siliciclastic lithic fragments higher feldspar abundances in the canamares and bornova stream sands are related to the erosion of gneissic rocks by contrast sands from sorbe river are low in feldspar reflecting the absence of coarse metamorphic sources thus proportions of bedrock lithologies in the drainage sub basins are the main control on detrital modes of the tributaries in addition slope acts on the sand productivity of source rocks sedimentary source rocks in the upper reaches of the three tributaries have a poor productivity in the carbonate lithic fragments lsc compared with the lsc productivity of sedimentary sources located downstream with higher relief the percentage of bedrock types in the source area versus petrographic indices lm l lss l and lsc l provide a useful contrast between source and sand composition in the tributaries thus the high content of metamorphic lithic grains in the lithic grain population over represents this lithology slate plus schist at the source terrain lithic grains from sedimentary clastic sources generate few recognizable grains lss in the lithic grain population local supplies from carbonate sources may produce important increases of lsc in short reaches of the channels sand compositions in the henares river seem to be very homogeneous in a qmflt diagram with only minor differences caused by the supplies from the tributaries these differences can be modeled in terms of end member mixing processes between henares detritus and detritus from the relevant tributary these mixing processes are more evident when lithic grain contents lmlvls and lmlsslsc diagrams are compared changes produced by inputs from the canamares bornova and sorbe rivers are not permanent along the henares course an important homogenization of henares sand composition takes place by the mixing of tributary deposits with previously deposited henares river terraces abrasion during transport does not appear to cause significant changes in the sand composition along the henares river

assessment of aeolian desertification trends from 1975 s to 2005 s in the watershed of the longyangxia reservoir in the upper reaches of china s yellow river abstract global climate change will affect the ecology and environment of the qinghai tibet plateau thus increasing attention is being paid to the aeolian desertification that is occurring in the watershed that supplies the longyangxia reservoir in the upper reaches of china s yellow river we must assess the aeolian desertification trends before developing a plan to restore the region s degraded eco environment in this study land suffered from aeolian desertification was classified into four levels slight moderate severe and extremely severe using a series of indices interpretation of landsat mss and tm data from 1975 s 1989 s and 2005 s was used to establish databases of aeolian desertified land at these three times we then derived the aeolian desertification trends during the study period by overlaying the consecutive databases and we analyzed the driving factors responsible for the observed aeolian desertification the results show a total of 1 721 478 02 ha of aeolian desertified land in 2005 s accounting for 13 of the region s total area from 1975 s to 1989 s the area of aeolian desertified land increased by 229 307 26 ha which represents a 15 increase compared to the 1975 s area and from 1989 s to 2005 s the area of aeolian desertified land decreased by 19 079 87 ha which represents a 1 decrease compared to the 1989 s area the main driving factors responsible for this increased aeolian desertification were climate factors high wind velocity and an increase in annual temperature combined with low precipitation and high evaporation as well as unsustainable human activities and inappropriate policy measures a series of key national projects initiated to combat degradation of the study area s eco environment led to a decrease of aeolian desertified land through obvious restoration of vegetation

climate change vegetation history and landscape responses on the tibetan plateau during the holocene a comprehensive review abstract numerous studies of changes in the climate vegetation and landscape responses of the tibetan plateau tp during the holocene have been published in recent decades however several conflicting interpretations are evident within these studies and a comprehensive review of the topic is needed to reconcile them and thus to provide an improved understanding of the history and forcing mechanisms of holocene environmental changes within the region here we review the evidence for changes in climate temperature precipitation moisture vegetation and landscape attributes glacier and eolian activity on the tp during the holocene our main conclusions are as follows 1 the patterns of holocene mean annual temperature change on the tp remain controversial however an early to middle holocene summer temperature maximum is evident which coincided with high summer insolation and a strengthening of the indian summer monsoon ism this suggests that the summer land sea thermal gradient impacted by the temperature of the tp may be an important factor driving orbital scale ism changes 2 lake level records indicate an optimum in moisture conditions on the southwestern sw tp in the early holocene while on the northeastern ne tp the optimum occurred in the middle to late holocene this out of phase or anti phased relationship may be linked to the role of the ism in dominating precipitation on the sw tp while the westerlies and east asian summer monsoon dominated the precipitation on the ne tp 3 most of the lake sediment based stable isotope records 18o and leaf wax d exhibit a pattern similar to that of stalagmite 18o records from monsoonal asia reflecting the dominance of large scale patterns of atmospheric circulation rather than localized moisture changes reflected by lake level records 4 a synthesis of pollen records reveals that the extent of forest was maximal in the mid holocene while from the early holocene onwards alpine steppe shrunk and alpine meadow and desert gradually expanded 5 evidence of glacier advance increased slightly during the early holocene decreased during the mid holocene and then increased substantially after 3 ka bp 6 the integrated ages of eolian sand and loess from the ne tp reveal that eolian activity intensified during the early and late holocene site inter comparisons reveal that regional climate change played a major role in modulating changes in vegetation and other landscape attributes overall producing holocene climate reconstructions for the entire tp remains a major challenge even though much progress has been made further improvements in terms of the spatial coverage of high resolution paleoclimatic records with robust chronological control and a deeper understanding of the specific climatic significance of several climatic proxies will facilitate an improved understanding of how the monsoon and the westerlies interacted and their impacts on vegetation and landscape changes on the tp

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones xvi three dimensional airflow and vertical vorticity budget for a warm front abstract the three dimensional structure of a warm front and its precipitation features are caused using due doppler radar data and supporting mesoscale measurements evidence is presented to support a staircase like structure of the warm frontal surface and significant flow of air through front from the warm side the cyclonic vertical vorticities within both the principal banded and nonbanded precipitation features were very weak the primary source of the vertical vorticity appears to have been advected horzontally from behind the frontal zone by a strong low level inflow vortex streteching was generally weak tilting terms is in the vorticity budget were primarily sinks kinematic factors that must have played a role in the formation of the banded and irregular precipitation feature associated with this front are discussed and some generalizations are made to other preciptations systems

modelling precipitation in frontal rainbands the main aim of this study is to establish the ability of a simple parametrization to represent adequately the microphysical processes acting in frontal rainbands in order to do this we compare it with a more detailed parametrization in conditions typical of warm frontal and narrow cold frontal rainbands simulations using a 2 dimensional diagnostic model indicate that a mixed phase parametrization is required in dynamical models of high resolution

mesoscale circulations forced by melting snow part ii application to meteorological features abstract various authors have proposed that the cooling associated with melting precipitation contributes significantly to the dynamics of mesoscale precipitation systems in this study we use the numerical model described in part i of this paper to investigate the effects of the cooling by melting mechanism in three specific situations rain snow boundaries the production of deep 0 c isothermal layers and the trailing stratiform region associated with mesoscale convective systems it is found that melting in the vicinity of a rain snow boundary produces a thermally indirect mesoscale vertical circulation that may be responsible for enhanced precipitation near a rain snow boundary melting in the presence of warm air advection above the melting layer and cold advection at and below it are necessary for producing deep 0 c layers within realistic times the dynamic effects of cooling associated with melting and evaporation in the stratiform region of a mature squall line system produce a mesoscale circul

the structure water budget and radiational features of a high latitude warm front abstract on 30 september 1994 an arctic low pressure system passed over the southern beaufort sea area of northern canada and research aircraft observations were made within and around the warm front of the storm this study is unique in that the warm front contained subzero centigrade temperatures across the entire frontal region the overall structure of the warm front and surrounding region was similar to midlatitude storms however the precipitation rates liquid water content magnitudes horizontal and vertical winds vertical wind shear turbulence and thermal advection were very weak in addition a low level jet and cloud bands were aligned parallel to the warm front near neutral stability occurred within and around the front and conditional symmetric instability was likely occurring a steep frontal region resulted from strong coriolis influences that in turn limited the amount of cloud and precipitation ahead of the system the precipitation efficiency of the storm was high 60 but is beli

dynamical effects of ice sublimation in a frontal wave the dynamical role of ice sublimation in weather systems is briefly reviewed observations are presented from the fronts and atlantic storm track experiment fastex intensive observation period 16 that show variations of static stability humidity and mesoscale circulation corresponding to those associated theoretically with sublimation of ice precipitation it is thus suggested that the observations display the mechanism proposed by clough and franks in which forward mesoscale flows are associated with moist adiabatic descent supported by the sublimation cooling this mechanism was suggested as an important stage in the evolution of many mesoscale rain bands a set of three model simulations of the event has been made with versions of the mel office s unified model of these a mesoscale model integration with 11 km resolution and 45 levels clearly displays the symptoms and is diagnosed to demonstrate its consistency with the clough franks mechanism an integration omitting the cooling due to sublimation differs significantly from the full model experiment in the structure of low level wind fields frontal troughs and mesoscale precipitation distribution il is also demonstrated that the static stability transition mesoscale circulation and mid tropospheric potential vorticity perturbations are substantially weakened in this integration thus confirming that the clough franks mechanism is also operating in the numerical weather prediction nwp model we deduce from these studies that ice precipitation and its sublimation has a major role in determining mesoscale circulation and structure in mid latitude weather systems affecting stratification and the formation of features such as fronts and rain bands these are substantially affected by the fall and evaporation of ice crystals which are both important to temperature and moisture transports and the behaviour of nwp models on time scales of hours to days in our integrations dynamical feedback due to sublimation cooling coincided with extreme negative potential vorticity values and potentially conditional symmetric instability hence the anticyclonic motion occurring in the cloud head or deep cloud of the moist warm sector as in this case in moist warm sectors a substantial role for sublimation may be anticipated more generally particularly for air trajectories receiving most ice precipitation we suggest that the described phenomenon be referred to as sublimation enhanced descent or sed it is concluded that in view of tins demonstrated sensitivity substantial attention should be given to refining microphysical parametrizations in nwp models and that radar and sounding observations from the fastex experiment provide a suitable basis for validating these schemes

observations and numerical simulations of the origin and development of very large snowflakes abstract the canadian atlantic storms program casp ii field experiment was conducted near st john s newfoundland canada during january march 1992 and it focused on the nature of winter storms analyses of casp ii aircraft surface satellite and radar observations collected during an intensive study of the origin and development of 9 mm h 1 precipitation containing 4 5 cm diameter snowflakes are compared in this article with results of the mm5 mesoscale and mitchell microphysical models mm5 simulations of the thermal kinematic and bulk microphysical fields were in good agreement with the observations this comparison provided the basis for extending the spatial and temporal scales of the aircraft observations to a larger scale domain using the model results the mitchell analytical numerical model was used to improve the understanding of the microphysical processes that led to the development of the very large snowflakes a synthesis of results using the different techniques leads to the co

late quaternary aeolian activity in gonghe basin northeastern qinghai tibetan plateau china abstract aeolian deposits at four sites in the gonghe basin were used to reconstruct the history of aeolian activity over the late quaternary these deposits include well sorted aeolian sand paleosols and or loess aeolian sand represents dune field expansion and or dune buildup whereas paleosols indicate stabilization of dunes accompanying ameliorated vegetation cover on the basis of 25 dates by optically stimulated luminescence osl it appears that aeolian activities occurred episodically at 33 5 20 3 13 9 11 8 11 0 9 4 7 8 and 5 7 5 5 ka which is largely consistent with the recent findings from the adjacent semi arid areas aeolian sand mobility occurring during the early to mid holocene conflicts with a climatic optimum inferred from lacustrine records in the northeastern qinghai tibetan plateau this inconsistency may be resolved by interpreting aeolian activity as a response to decreased effective moisture due to enhanced evaporation induced by higher summer insolation at that time together with local terrain and its effects on moisture our results suggest that aeolian sand and paleosol cannot be simply ascribed to regional dry and wet climates respectively and they most likely reflect changes in effective moisture

late glacial and holocene development of lake donggi cona north eastern tibetan plateau inferred from sedimentological analysis abstract sediments of lake donggi cona on the northeastern tibetan plateau were studied to infer changes in the lacustrine depositional environment related to climatic and non climatic changes during the last 19 kyr the lake today fills a 30 8 km big and 95 m deep tectonic basin associated with the kunlun fault the study was conducted on a sediment core transect through the lake basin in order to gain a complete picture of spatio temporal environmental change the recovered sediments are partly finely laminated and are composed of calcareous muds with variable amounts of carbonate micrite organic matter detrital silt and clay on the basis of sedimentological geochemical and mineralogical data up to five lithological units lu can be distinguished that document distinct stages in the development of the lake system the onset of the lowermost lu with lacustrine muds above basal sands indicates that lake level was at least 39 m below the present level and started to rise after 19 ka possibly in response to regional deglaciation at this time the lacustrine environment was characterized by detrital sediment influx and the deposition of siliciclastic sediment in two sediment cores upward grain size coarsening documents a lake level fall after 13 cal ka bp possibly associated with the late glacial younger dryas stadial from 11 5 to 4 3 cal ka bp grain size fining in sediment cores from the profundal coring sites and the onset of lacustrine deposition at a litoral core site 2 m water depth in a recent marginal bay of donggi cona document lake level rise during the early to mid holocene to at least modern level in addition high biological productivity and pronounced precipitation of carbonate micrites are consistent with warm and moist climate conditions related to an enhanced influence of summer monsoon at 4 3 cal ka bp the lake system shifted from an aragonite to a calcite dominated system indicating a change towards a fully open hydrological lake system the younger clay rich sediments are moreover non laminated and lack any diagenetic sulphides pointing to fully ventilated conditions and the prevailing absence of lake stratification this turning point in lake history could imply either a threshold response to insolation forced climate cooling or a response to a non climatic trigger such as an erosional event or a tectonic pulse that induced a strong earthquake which is difficult to decide from our data base

gravel washing wastes from jarama river deposits spain an undervalued natural raw material this work presents the main characteristics of 97 quarry wastes collected in 23 gravel pits from the jarama river area madrid province spain in this area more than 2 5 106 ton of silty clay waste are generated every year and no applications have as yet been defined for them this work is the first systematic study of the fine fractions generated from the jarama river quaternary deposits playing part in the comprehension of this complex terrace systems quartz potassium feldspar plagioclase calcite and complex mixtures of phyllosilicates such as smectite illite kaolinite chlorite and illite smectite mixed layer have been detected two sets of waste which are recognized according to the calcite content have been directly related with the terrace level beneficed in the jarama river and the position along the valley calcite concentrates in the wastes produced in the lower course where henares and tajuna tributaries promote an extensive change in the geochemistry of underground water and locally in the petrology of quarried conglomerates this clear distinction by location between calcite bearing and calcite free wastes is essential for potential applications such as soil conditioning raw materials for brick or tiles etc the wastes studied can be considered as a potential source of industrial raw materials because of their uniformity and large volume this suggestion is now being carried out with an attempt at assessing the possibilities of using these mining wastes as ceramic raw materials

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

dry or humid mid holocene humidity changes in arid and semi arid china abstract spatial changes of effective moisture during the mid holocene have been reconstructed based on the compilation of recently published paleoclimate records including ice core lake level pollen assemblage and loess paleosol records both geological data and the spatial pattern indicate that it was dry in deserts during the mid holocene but the timing of the beginning and end of dry intervals differs from place to place deserts having higher aridity index values remain dry longer dry intervals during the mid holocene are more possibly asynchronous than synchronous in arid and semi arid china in the xinjiang region except in sites located in deserts the climate is generally wet during 7000 5000 a bp in the northern qinghai tibetan plateau effective moisture in most sites began to decrease after 5000 a bp the climate became dry after 4000 a bp except in the deserts in the loess plateau and the inner mongolia plateau