structure of a cold front over the ocean the kinematic and thermodynamic structure of a strong cold front over the gulf of alaska has been determined using aircraft dropsonde and radiosonde data obtained during the storm transfer and response experiment synoptic scale analysis using the sawyer eliassen secondary circulation equation shows that friction and diabatic heating as well as the geostrophic forcing are important in accounting for the secondary circulation at the front a fine scale analysis with horizontal resolution of 700m and vertical resolution of 100 m shows strong relative inflow of warm boundary layer air toward the front from the east and a weaker inflow of cold air from the west updraught velocities of greater than 6 m s 1 over a 2 km width were measured at 875 mb near the leading edge of the front the frontogenetical effects of confluence turbulent mixing and tilting of isentropic surfaces are evaluated in the region of the front and compared with the results of previous studies the high resolution of the thermodynamic fields provides new data for comparison with high resolution numerical models

equilibrium line altitudes on reconstructed lgm glaciers of the northwest barguzinsky ridge northern baikal russia abstract the spatial extent of the last glacial maximum lgm glaciers mis 2 in the northwest of the barguzinsky ridge has previously been mapped geographical information system gis computing of the glaciers quantitative parameters allowed us to use various methods to evaluate the former equilibrium line altitudes elas for the 10 largest glaciers elas on reconstructed glaciers were calculated using four common methods 1 the median elevation of glaciers meg 2 the toe to headwall altitude ratio thar 3 the accumulation area ratio aar and 4 gefer s method the results suggest that the mean macroclimatic lgm background ela for the area studied was about 1200 145 m above present sea level and the mean ela depression relative to modern conditions was about 1100 m tentative estimates suggest that the reconstructed glaciers could have existed in a drier about 1 5 times drier than present environment if the mean summer air temperature was about 8 9 c lower than present day

finescale vertical structure and dynamics of some dryline boundaries observed in ihop abstract several radar fine lines all with a humidity contrast were sampled in the central great plains during the 2002 international h2o project ihop this study primarily uses aircraft and airborne millimeter wave radar observations to dynamically interpret the presence and vertical structure of these fine lines as they formed within the well developed convective boundary layer in all cases the fine line represents a boundary layer convergence zone this convergence sustains a sharp contrast in humidity and usually in potential temperature across the fine line the key question addressed herein is whether at the scale examined here 10 km the airmass contrast itself in particular the horizontal density virtual potential temperature difference and resulting solenoidal circulation is responsible for the sustained convergence and the radar fine line for the 10 cases examined herein the answer is affirmative

evidence from lake baikal for siberian glaciation during oxygen isotope substage 5d abstract the paleoclimatic record from bottom sediments of lake baikal eastern siberia reveals new evidence for an abrupt and intense glaciation during the initial part of the last interglacial period isotope substage 5d this glaciation lasted about 12 000 yr from 117 000 to 105 000 yr b p according to correlation with the specmap isotope chronology lithological and biogeochemical evidence of glaciation from lake baikal agrees with evidence for the advance of ice sheet in northwestern siberia during this time period and also with cryogenic features within the strata of kazantzevo soils in southern siberia the severe 5d glaciation in siberia was caused by dramatic cooling due to the decrease in solar insolation as predicted by the model of insolation changes for northern asia according to milankovich theory coupled with western atmospheric transport of moisture from the open areas of northern atlantic and arctic seas which became ice free due to the intense warming during preceeding isotope substage 5e other marine and continental records show evidence for cooling during 5d but not for intense glaciation late pleistocene glaciations in the northern hemisphere may have begun in northwestern siberia

airborne doppler radar and sounding analysis of an oceanic cold front abstract an analysis of a cold front over the eastern atlantic ocean based on airborne doppler wind syntheses and dropsonde data is presented the focus and unique aspect of this study is a segment of the front that was near the center of the cyclone the dual doppler wind synthesis of the frontal zone combined with an average dropsonde spacing of 30 km covers a total distance of 450 km in the cross frontal direction the finescale resolution and areal coverage of the dataset are believed to be unprecedented the cold front was characterized by a distinct wind shift and a strong horizontal temperature gradient the latter was most intense aloft and not at the surface in contrast to the classical paradigm of surface cold fronts the shear of the alongfront component of the wind was relatively uniform as a function of height within the frontal zone this observation is contrary to studies suggesting that frontal zones decrease in intensity above the surface the surface convergence within the frontal zon

glacier dynamics in the southern part of east siberia russia from the final part of the lgm to the present based on from biogeochemical proxies from bottom sediments of proglacial lakes abstract in the present study we have reconstructed glacier dynamics based on the high 1 0 5 mm resolution x ray fluorescence spectrometry scanning the fourier transform infrared technique and 14c dating used in the analyses of the lake bottom sediments fluvioglacial deposits and a peat bog situated on east siberian mountains east sayan baikal barguzin and kodar ridges between 51 723 n 100 601 e and 56 885 n 117 580 e we have found what the largest glacier deposits on the baikal shoreline so called tompuda end moraine formed in two stages the first stage occurred until ca 12 cal ka bp then there was a short pause the second stage ended by 9 5 cal ka bp azarova glacier kodar ridge retreated upwards the kodar ridge by ca 11 cal ka bp it may indicate that the bolling allerod warming was very evident and it was a trigger for these deglacial events in east siberia it is most likely that remains of the late pleistocene glaciers were cardinally shrunk or fully disappeared during the holocene thermal optimum in the southern part of east siberia climate conditions were suitable for glacier formation after 3 cal ka bp however if there were new glaciers in the middle holocene their sizes were likely to be less than 1 km2 for this reason these glaciers should have completely melted during the roman and medieval warm periods it is most likely small glaciers observed at present in the south of east siberia were mainly formed during the little ice age

impact of glacier changes on ecosystem of proglacial lakes in high mountain regions of east siberia russia mountain lakes in east siberia have been studied for recent changes in water chemistry turbidity and diatom assemblages preserved in bottom sediments we performed a regional analysis of the relative effect of climate and glacier changes on change in diatom diversity and supply of meltware in proglacial lakes we analysed sediment records from east siberian glacier lakes using geochemical and diatoms proxies we found that dramatic changes in communities and abundance of diatoms and biogenic proxy could be induced by low nutrient concentrations in glacial lakes and high turbidity due to active degradation of glaciers and snow patches as a result of the global increase in temperature in the northern hemisphere our evidences show that diatoms have been gradually decreased since ca the 1880s a significant tendency towards diatom reducing occurred at high summer regional temperatures this tendency may be attributed to the fact that glaciers and snow patches thawed actively in east siberia during ca 1880 1958 which was induced by the beginning of the recent warming ca 1850 1860 and a long period of relatively warm regional climate from ca 1900 to 1960

water level changes in lake baikal siberia tectonism versus climate relative changes in the level of lake baikal amounting to hundreds of meters in quaternary time are well documented data presented here show that tectonic displacements of the lake outlet or former shoreline features are entirely sufficient to explain these relative lake level changes in contrast the morphology and hydrology of the lake make its level hydrologically insensitive to climate change available evidence indicates that throughout the past several hundred thousand years lake baikal was a dilute through flowing lake controlled by the level of its outlet on the basis of geologic data alone climatic effects on lake level whatever their magnitude are difficult to separate from those caused by active rift tectonism however consideration of 1 the hydrologic budget of the lake and 2 the configuration of the outlet suggests that potential lake level fluctuations due solely to climate change were less than about 2 m

snowline depression in the tropics during the last glaciation five primary methods have been used to reconstruct pleistocene snowlines or equilibrium line altitudes elas in the tropics 23 53n 23 53s during the last glaciation but each has inherent errors that limit the accuracy of the results additional potential errorsin determiningela depression involveestimates of modernsnowline altitude datingresolution topographicreconstructionof former glaciers orographic e ects the presence of rockfall debris on glaciers and calculation of regional ela gradients eustatic sea level lowering during the last glaciation is an additional factor in uencing estimates of ela depression ela in cases where modern snowline lies above a mountain summit only a minimum value for ela can be obtained at 12 tropical sites in africa the americas to 103s latitude and paci c islands estimates of average ela range from 440 to 1400m but most fall in the range of 800 1000m mean 1 900 135m in a regional study of ela depression in the southern tropical andes 8 223s an average ela of ca 920 250m has been reported based on the assumption that glacier mass balance was controlled solely by ablation season temperature and assuming a full glacial temperature lapse rate of 63c km depression of mean annual temperature in glaciated alpine areas was ca 5 4 0 83c if adjusted for a sea level fall of 120m at the glacial maximum this value is reduced to 4 7 0 83c the gure is based on the unlikely assumption that accumulation on alpine glaciers has been invariant nevertheless it is similar to values of temperaturedepresson 5 6 43c for the last glaciationobtainedfrom variousterrestrial sites but contrasts with tropical sea surface temperature estimates that are only 1 33c cooler than present 2001 elsevier science ltd all rights reserved

biological nitrate utilization in south siberian lakes baikal and hovsgol during the last glacial period the influence of climate change on primary productivity abstract stable nitrogen isotope ratios 15 n in sediment cores recovered from two siberian lakes baikal and hovsgol are determined in order to evaluate the biologically mediated nitrogen cycle from the last glacial period to the postglacial period the ranges of 15 n values from the two lakes are similar varying from 2 8 to 6 7 the high values of 15 n around 6 during the last glacial maximum lgm 26 5 19 cal ka bp indicate that a larger fraction of the available nitrate in both lakes was utilised by phytoplankton a cool and dry climate during the lgm may have limited the input of terrestrial nitrate resulting in the use of a large fraction of the nitrate and low productivity in both lakes the use of a smaller fraction of the nitrate by phytoplankton in both lakes after the lgm 19 12 cal ka bp is reflected in the lower 15 n values down to 3 0 the increase in summer insolation after the lgm caused increased vertical mixing of the lake water column which transported nitrate upwards from the deeper waters and into the photic zone the reduced rate of nitrogen consumption after the lgm indicates that nitrate was more readily available to phytoplankton at this time and did not limit their activities this change suggests that other factors limited phytoplankton activity during this period at the climatic transition between oxygen isotope stages 2 and 1 around 11 5 cal ka bp the rapid increase in 15 n from 3 0 to 6 0 reflected a rapid increase in nitrate utilization at this transition increases in precipitation and lake levels which were associated with the increased intensity of the east asian monsoon may have brought a large influx of nutrients required by the phytoplankton into the lakes from the watershed this hydrological change led to increased phytoplankton activity in both lakes resulting in increased nitrate consumption the 15 n data obtained here from the sediments of lakes baikal and hovsgol suggest that the nitrogen cycle in the siberian region is strongly linked to hydrological changes across the asian continent which are related to global climate change

late quaternary lake level changes of lake el gygytgyn ne siberia abstract lake el gygytgyn is situated in a 3 6 ma old impact crater in northeastern siberia presented here is a reconstruction of the quaternary lake level history as derived from sediment cores from the southern lake shelf there a cliff like bench 10 m below the modern water level has been investigated deep water sediments on the shelf indicate high lake levels during a warm mid pleistocene period one period with low lake level prior to marine oxygen isotope stage mis 3 has been identified followed by a period of high lake level 10 m above present in the course of mis 2 the lake level dropped to 10 m at the end of mis 2 the bench was formed and coarse beach sedimentation occurred subsequently the lake level rose rapidly to the holocene level changes in water level are likely linked to climate variability during relatively temperate periods the lake becomes free of ice in summer strong wave actions transport sediment parallel to the coast and towards the outlet where the material tends to accumulate resulting in lake level rise during cold periods the perennial lake ice cover hampers any wave activity and pebble transport keeping the outlet open and causing the lake level to drop

the effect of large scale flow on low level frontal structure and evolution in midlatitude cyclones abstract observational and modeling studies documented in the literature indicate that the large scale flow has an important effect on the structure and evolution of low level fronts in midlatitude cyclones the purpose of this paper is to address the role of the large scale flow on low level cyclone frontal structure and evolution through a combined observational and idealized modeling approach analyses of two observed cyclone cases embedded in large scale diffluence and confluence respectively are presented to illustrate two possible cyclone frontal structures and evolutions specifically the cyclone moving into a diffluent high amplitude ridge becomes meridionally elongated and possesses a strong meridionally oriented cold front and a weak warm front the cold front rotates into the warm front forming an occluded front in the manner of the norwegian cyclone model as indicated by the narrowing of the thermal ridge connecting the warm sector to the cyclone center in contrast the cyclone moving i

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

asymmetric late pleistocene glaciations in the north basin of the baikal rift russia new morphological sedimentological and radiocarbon data of quaternary deposits from the northern baikal rift document at least three extensive late pleistocene glaciations at 50 ka 40 35 ka and 26 13 ka respectively during these periods valley glaciers advanced from the high rift shoulders 2500 m down to the present day coast of lake baikal 456 m in places the glaciers advanced beyond the present day shoreline into the lake basin as indicated by large moraines exposed in steep cliffs along the lakeshore furthermore stratigraphic relations between lacustrine sequences and glacial deposits as well as 14 c ages of two palaeo shorelines 10 and 4 m above the present lake level show that the last and the penultimate glaciations were followed by relative lake highstands these land based observations document a significant influence of late pleistocene glaciations on the sedimentary development of this lacustrine rift basin the northern baikal rift is characterized by an asymmetric half graben geometry that controls river drainage and sedimentation this asymmetry greatly influenced the development and spatial distribution of pleistocene glaciers on both rift margins on the western flank tilted fault blocks parallel to the rift served as topographic barriers for valley glaciers advancing toward the lake basin only in two locations glaciers could reach the present day coast on the eastern rift flank in contrast structure and drainage conditions allowed the development of numerous consequent streams providing thoroughfares and space for recurrent valley glaciations thus the glaciers on the eastern flank could advance beyond the present day lakeshore into the lake basin in numerous locations these observations indicate that asymmetric rift structure in combination with the effects of global cooling were the important controls on the pleistocene glacial development of the baikal rift

numerical study of horizontal shear instability waves along narrow cold frontal rainbands abstractthe effects of variations in low level ambient vertical shear and horizontal shear on the alongfront variability of narrow cold frontal rainbands ncfrs that propagate into neutral and slightly unstable environments are investigated through a series of idealized cloud resolving simulations in cases initialized with slightly unstable sounding and weak ambient cross frontal vertical shears core gap structures of precipitation along ncfrs occur that are associated with wavelike disturbances that derive their kinetic energy mainly from the mean local vertical shear and buoyancy however over a wide range of environmental conditions core gap structures of precipitation occur because of the development of a horizontal shear instability hsi wave along the ncfrs the growth rate and amplitude of the hsi wave decrease significantly as the vertical shear of the ambient cross front wind is reduced these decreases are a consequence of the enhancement of the low level local vertical shear immediately beh

a high resolution diatom record of the palaeoclimates of east siberia for the last 2 5 my from lake baikal abstract two parallel drilling cores bdp96 1 200 m and bdp96 2 100 m have been taken from top of the underwater akademichesky ridge in lake baikal and dated by paleomagnetic techniques these cores are part of the baikal drilling project kuzmin et al 1997a b diatom analysis of the first 100 m of these sediments reveals that they store a 2 5 myr high resolution continuous record of the palaeoclimates of east siberia sediments belonging to warmer climates have a high content of diatom algae frustules whereas those belonging to global glaciations are diatom barren the record of upper pleistocene 500 kyr bp strongly correlates with the oceanic specmap curve and contains distinct 100 41 23 and 19 kyr periods as revealed by fourier analysis diversity of diatom species was small in pliocene abrupt and frequent changes of the climate in pleistocene resulted in frequent dramatic changes in the diatom communities the extant dominating endemics cyclotella minuta and aulacoseira baicalensis became important in lake baikal 760 kyr and less than 120 kyr bp respectively

an observational and modeling study of the interaction of low level southwesterly flow with the olympic mountains during coast iop 4 abstract this paper presents an observational and modeling study of the three dimensional flow and precipitation around the olympic mountains of northwest washington state for a case of relatively steady south southwesterly flow this study utilized data from coast iop 4 the fourth intensive observing period during the coastal observation and simulation with topography field experiment that took place during 9 10 december 1993 one of the most important data sources was the noaa p 3 aircraft which provided flight level data reflectivity and doppler winds as it flew around the olympics features that were mapped successfully with the noaa p 3 included flow splitting around the windward pressure ridge strong southeasterlies to approximately 25 m s 1 northeast of the olympics caused by downgradient acceleration into the lee trough the rapid transition from strong southeasterlies to lighter easterlies 5 10 m s 1 in the strait of juan de fuca strong downslope flow and a hydraulic jump like transiti

balancing the last glacial maximum lgm sea level budget abstract estimates of post last glacial maximum lgm sea level rise are not balanced by the estimated amount of ice melted since the lgm we quantify this missing ice by reviewing the possible contributions from each of the major ice sheets this missing ice amounts to 18 1 9 6 m of global sea level rise ocean expansion accounts for 2 4 0 3 m of this discrepancy while groundwater could contribute a maximum of another 1 4 m to this offset after accounting for these two potential contributors to the sea level budget the shortfall of 15 6 9 6m suggests that either a large reservoir of water e g a missing lgm ice sheet has yet to be discovered or current estimates of one or more of the known lgm ice sheets are too small included within this latter possibility are potential inadequacies of current models of glacial isostatic adjustment

a simple model for the synoptic analysis of cold fronts a split cold front model with an over running upper front or humidity front ahead of a surface front or humidity front is shown to provide a useful representation of the principal characteristics of many katafronts the use of such a model leads to more consistent analyses especially of cloud and rain than are achieved using unmodified classical concepts

glaciers and meltwater flux to lake baikal during the last glacial maximum abstract maximal 3d ice extent during mis 2 around lake baikal has been reconstructed using glacial landforms in the field aerial photos satellite images and gis analysis this regional glacial maximum is correlated 18 kyr bp with the global lgm based on available 14 c dates cosmogenic 10 be exposure ages correlation of lakeshore moraines with two raised shorelines and the ird record in lake sediments total ice area was 13 000 km 2 and ice volume 2000 km 3 1800 km 3 in water equivalent ice distribution was controlled by topography and ice fields with valley glaciers spreading to adjacent depressions locally ice caps with outlet glaciers existed averaged regional ela is estimated to be 1290 240 m with the ela depression at approximately 1340 m more acceptable regional scenario of the lgm precipitation reduction by 25 50 implies that summer temperature decreased by 6 12 c along with an increased solid fraction in precipitation up to 85 there were primary climatic controls for glaciation meltwater supply as a strong controller of lgm water budget 60 of total water input to the lake is estimated to have been from 6 4 to 9 0 km 3 yr 1 7 9 times less than present day river input preliminary balance estimation shows that during full glacial stage lake baikal was overflowing with the angara river output as 4 9 km 3 yr 1 and with lake level close to that today lake level drop down to the depth of 40 m is recorded by geological and geophysical evidence perhaps explaining the abrupt increase in effective evaporation in the lake watershed at the start of mis 2 24 18 ky bp

morphology and evolution of cold frontal misocyclones a numerical simulation of an intense narrow cold frontal rain band ncfr is presented this front was associated with localized wind damage as it moved eastwards across the united kingdom on 24 september 2007 the model used was the operational and research weather research and forecasting advanced research wrf arw mesoscale model initialized with global forecast system gfs operational model output data the simulation produced a front strongly resembling that seen in radar imagery and conforming to previous studies and conceptual models of the ana cold front in the simulation a strong surface horizontal wind speed maximum is located along the southern flank of a misocyclone this is shown to be typical of a number that form along the front using trajectory analysis descending cold air parcels which originate in the rear inflow jet and accelerate within the circulation of the misocyclone are identified as the origin of the strongest winds in addition to the localized strong straight line winds circumstantial evidence is presented for the possible occurrence of weak tornadogenesis the results are discussed in relation to recent studies of ncfrs squall lines and misocyclones copyright 2009 royal meteorological society

25 years 1981 2005 of equilibrium line altitude and mass balance reconstruction on glacier blanc french alps using remote sensing methods and meteorological data annual equilibrium line altitude ela and surface mass balance of glacier blanc ecrins region french alps were reconstructed from a 25 year time series of satellite images 1981 2005 the remote sensing method used was based on identification of the snowline which is easy to discern on optical satellite images taken at the end of the ablation season in addition surface mass balances at the ela were reconstructed for the same period using meteorological data from three nearby weather stations a comparison of the two types of series reveals a correlation of r 0 67 at the 0 01 level of significance furthermore the surface mass balances obtained from remote sensing data are consistent with those obtained from field measurements on five other french glaciers r 0 76 p 0 01 also consistent for glacier blanc is the total mass loss 10 8mw e over the studied period however the surface mass balances obtained with the remote sensing method show lower interannual variability given that the remote sensing method is based on changes in the ela this difference probably results from the lower sensitivity of the surface mass balance to climate parameters at the ela

palaeoenvironmental history of lake baikal during the last 23000 years abstract a sediment core recovered from lake baikal was studied in an attempt to elucidate the palaeoenvironmental history of an intra continental lake under the control of last glacial to post glacial climatic fluctuations the lake conditions were characterised by subdued primary production and increased turbidity conditions during the last glacial maximum terrestrial vegetation and the development of soil layers were reduced in the drainage areas the deglaciation suggested by increased terrigenous sand influx and biological productivity took place at around 18 000 yr b p responding to the increased insolation in the northern hemisphere high latitude the onset of wet and warm conditions at ca 12 000 yr b p brought on a maximum of aquatic production and forestal expansion between 7 000 and 6 000 yr b p since 5 000 yr b p enhanced blooming of diatoms has occurred due to an increased nutrient supply and dissolved silica input into the lake

observations of the finescale structure of a dryline during vortex 95 abstract the three dimensional finescale structure of a dryline observed over the texas panhandle during the verification of the origins in tornadoes experiment vortex on 6 may 1995 is presented high resolution observations documenting dryline evolution were collected from midafternoon while it moved slowly eastward until late afternoon as it retrogressed back to the west dryline variability in the horizontal along line direction was revealed by airborne doppler radar observations from the national center for atmospheric research electra doppler radar and ground based measurements from the nearby wsr 88d at amarillo texas this variability was created as the dryline interacted with horizontal convective rolls forming west of the dryline the rolls intersected the dryline at periodic locations creating radar reflectivity and vertical velocity maxima more importantly clouds initiated at these intersection points additional dryline variability was generated through the interaction of the low level fl

vegetation response in the southern lake baikal region to abrupt climate events over the past 33calkyr abstract we reconstructed vegetation changes and fire events in the southern lake baikal region over the past 33 cal kyr using a sediment core from the buguldeika saddle southern lake baikal to examine vegetation response to past short term climate variations herbs such as artemisia and asteraceae were dominant just before the last glacial maximum lgm low pollen accumulation rates pars with little herb pollen indicate sparse herbaceous vegetation cover during the lgm picea expanded after the bolling interval suggesting expansion of riparian areas and shrub alnus rapidly increased during the following allerod interval abies and pinus subgen haploxylon began to increase at the beginning of the holocene and pinus subgen diploxylon has been highly dominant since the middle holocene the vegetation change after the lgm is similar to that from other sites in the lake baikal region but the responses to short term climate events are pronounced fluctuations in herb elements and vegetation cover as indicated by the par correspond to the younger dryas yd cooling event the decline in the par and increase in herb taxa were remarkable at the beginning of the yd but larix and picea trees were distributed in river valleys near lake baikal in the latter half the rapid expansion of betula and artemisia following frequent fires in the early holocene may have been in response to the 8 2 cal ka bp cooling event from these findings the southern lake baikal region including the selenga river basin may possibly have been more sensitive than other parts of the region to abrupt climate changes

radar observations of wind shear splitting within evolving atmospheric kelvin helmholtz billows summary the high resolution radar at chilbolton was used to measure the velocity structure of large amplitude kelvinhelmholtz billows within a precipitating warm frontal zone a deep layer of frontal shear was observed to split into thin layers of more concentrated shear displaying the characteristic braided structure previously reported within clear air radar reflectivity patterns and attributed to a splitting of the thermal stratification the billows were situated within a region of strong wind veer with height and they were orientated at right angles to the mean flow such that air parcels within them were tending to follow helical trajectories up the inclined frontal zone radar scans normal to the axes of the billows at different distances from their origin close to the position of the surface warm front provided an indication of the evolution of the split shear structure

late quaternary climatic control of lake baikal russia turbidite systems implications for turbidite systems worldwide lake baikal russia contains a variety of turbidite systems in different tectonic and depositional settings that provide tests for the role of quaternary climatic change on turbidite system growth during pleistocene glacial climates all types of systems exhibit increased sediment supply high sedimentation rates high net sand percent thick sand turbidites and progradation during holocene interglacial climate all systems exhibit reduced sediment supply and retreat seismic profiles from the large selenga fan and small tompuda fan show 1 maximum fan growth during the late pleistocene glacial melt time where lobes and large channels reached the distal outer fan and 2 fan retreat during the transition to the fully developed holocene interglacial climate for example the selenga fan surface lobes backstepped 55 km from the distal outer fan to the distal inner fan and the large outer fan surface channel 750 m wide 20 m levee relief evolved to a smaller surface channel 450 m wide 13 m levee relief that extended only to the end of the inner fan these results show that quaternary climate controls the growth of the lake baikal turbidite systems in a setting where there are no significant water level changes which often are cited as the main control on turbidite system growth the lake baikal and other marine turbidite systems suggest that climatic control of sediment supply unrelated to sea level lowering and tectonic effects may have been a much more important control for turbidite systems than previously believed not only during the pleistocene but perhaps also for ancient systems

lake level changes during the past 100 000 years at lake baikal southern siberia abstract lake level changes inferred from seismic surveying and core sampling of the floor of lake baikal near the selenga river delta can be used to constrain regional climatic history and appear to be correlated to global climate changes represented by marine oxygen isotope stages mis the reflection pattern and correlation to the isotope stages indicate that the topset and progradational foreset sediments of the deltas formed during periods of stable lake levels and warm climatic conditions during warm stages the lake level was high and during cold stages it was low the drop in the lake level due to cooling from mis 5 through mis 4 is estimated to be 33 38 m from mis 3 through mis 2 it fell an additional 11 15 m because the lake level is chiefly controlled by evaporation and river input we infer that more water was supplied to lake baikal during warm stages

the frontal hydraulic head a micro α scale 1 km triggering mechanism for mesoconvective weather systems abstract measurements from the noaa boulder atmospheric observatory bao 300 m tower the national center for atmospheric research ncar sabreliner aircraft and the noaa goes 5 satellite give evidence for the cross front scale collapse of nonprecipitating surface cold frontal zones to horizontal distances of 1 km or less the leading edges of these frosts possess the characteristic structure of density current flows an elevated hydraulic head followed by a turbulent wake vertical motions at the frontal heads exceed 5 m s 1 at 300 m agl the ascent at the frontal head may act as a 1 km scale triggering mechanism for the release of potential instability and the formation of intense squall line mesoconvection

effects of surface drag on fronts within numerically simulated baroclinic waves abstract a comparative analysis of simulations of baroclinic waves with and without surface drag is presented with particular reference to surface features as in recent studies the present simulations show that compared to simulations with no drag those with surface drag are less inclined to develop a secluded warm sector and that drag weakens the warm front while the cold front remains strong the authors demonstrate that analogous effects occur when ekman pumping is used in nonlinear quasigeostrophic numerical simulations of unstable baroclinic waves in a channel however since the quasigeostrophic model produces symmetric highs and lows in the unstable baroclinic wave the cold and warm fronts are therefore also symmetric and hence equally affected by the ekman pumping the different effect that friction has on the warm front with respect to the cold front in the primitive equation simulations is fundamentally related to the tendency for the lows to be strong and narrow and the highs weak and br

mesoscale dynamics of cold fronts structures described by dropsoundings in fronts 87 the fronts 87 project was a european experiment to make mesoscale observations to deduce the dynamics of active cold fronts approaching north west europe with a minimum of orographic influences in this paper data from dropsoundings made by the meteorological office s c 130 research aircraft are analysed the aircraft flew a pattern with 4 or 5 runs oriented approximately at right angles to the front but with each run displaced in the along front direction by about 100 km the dropsondes gave soundings to a height of approximately 7 km with a cross frontal spacing of 20 km at best and 60 km on average between 30 and 50 soundings were made in each event over an area of 500 500 km2 these data are unique in their mesoscale resolution over a synoptic scale region this was made possible by the ability to track up to 5 sondes in the air at any time several new aspects of cold front dynamics have been identified from these data the approach here is to treat each run as an instantaneous cross frontal section the discussion is centred on the hypotheses postulated before the experiment these were intended to allow verification or refutation of aspects of models of frontal dynamics such as those embodied in semi geostrophic theory a minimal and purely objective analysis has been performed on the data presented here but the high resolution of the dropsonde observations permits evaluation of differentiated quantities such as potential vorticity pv with some confidence issues raised here include the degree of thermal wind balance the structure of conserved variables such as equivalent potential temperature and absolute momentum the cross frontal circulation and the role of diabatic processes such as the evaporation of snow and the potential vorticity structure on the mesoscale and its interpretation the intention is to present an integrated view of the dynamical structure of fronts in the light of theoretical rather than conceptual or airflow models

anelastic modeling of explosive cyclogenesis abstract a three dimensional anelastic model is used to perform simulations of explosive cyclones the major goals are 1 to investigate the importance of horizontal resolution on the simulation of mesoscale features during explosive cyclogenesis using a very high resolution nonhydrostatic model and 2 to determine the impact of the destabilization of the lower troposphere by strong surface fluxes on the development of the storm the results from six experiments are presented the main conclusions are 1 by using analytic initial conditions based on typical wintertime conditions prior to explosive cyclogenesis it is possible to obtain very realistic simulations of rapid cyclogenesis 2 the use of high horizontal resolution is important in simulating the mesoscale features of rapidly deepening cyclones in particular the structure of the intense warm front observed ahead of the cyclone is very sensitive to changes in horizontal resolution 3 the destabilization of the lower troposphere prior to the pe

catastrophic events in the quaternary outflow history of lake baikal abstract lake baikal is earth s deepest lake and an iconic site of scientific study this vast basin holds sedimentary archives of environmental change dating back to the miocene and its array of palaeoshorelines and surrounding relief record the past 1 3 ma of lake levels and outflows here we present an extensive review of previous work alongside a new set of observations concerning the quaternary development of lake baikal with special focus on lake level fluctuations and the formation and evolution of the lake s three known outlets the sequence of shoreline terraces indicates that lake levels were both higher and lower in the past lake baikal stood 200 m higher during the last interglacial i e marine isotope stage mis 5e and dropped to 40 m below present day during the last glacial maximum mis 2 the relative lake level variations reflect climate factors and gradual or sudden coseismic tectonic impacts on the elevation of the lake s outlet thresholds three successive outlets are known i the palaeo goloustnaya manzurka associated with the manzurka alluvium ii the palaeo irkut and iii the currently active angara river outlet we propose that the manzurka alluvium is the product of catastrophic events in lake baikal the sudden possibly coseismic collapse of the 15 3 km goloustnaya fault block into lake baikal triggered a mega tsunami that thrust overwash deposits across neighbouring drainage divides above lake baikal and the valleys of the goloustnaya manzurka river system the age of the manzurka alluvium remains poorly constrained but the mega tsunami is potentially traceable to an unconformity in drill core sediments at 0 8 1 0 ma although older late pliocene and younger 125 ka ages have also been proposed the irkut outlet existed between mis 6 and mis 5 when lake level was 200 m higher than present 640 650 masl and a large bay extended into the tunka rift at baikal s south west tip lake baikal retreated from the tunka rift when lake level fell by up to 100 m in early mis 5e we propose that the lake level fall is connected to a partial collapse of primorsky ridge at listvenichny bay which caused baikal to overspill into the angara river thereby forming a new outlet the release of a 4000 km3 megaflood down the angara river valley caused large scale modification and reworking of valley fills mis 5e at the end of mis 2 further collapse of primorsky ridge lowered the outlet threshold an additional 50 60 m and prompted a second megaflood down the angara river valley which left a widespread unconformity where horizontal bedded sands dated at 11 8 13 4 ka overlie cryoturbated deposits of the earlier megaflood the central role of catastrophic processes at lake baikal suggests that rather than being rare events coseismic landsliding and mega tsunami may be more frequent than hitherto recognised

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

structure of the cold front observed in sesame ave iii and its comparison with the hoskins bretherton frontogenesis model abstract a cold front which passed through the dense network of the sesame ave severe environmental storms and mesoscale experiment atmospheric variability experiment on 25 26 april 1979 was investigated rawinsonde data collected from 23 special stations and 19 national weather service stations at three hour intervals for a 24 hour period were used along with hourly surface data radar summary charts and goes east satellite images severe storms formed along the surface front during this period the analysis focused on the vertical circulation across the frontal surface at low levels the major features of the cold frontal system that emerged from an analysis of this unique data set include a familiar direct vertical circulation with moist warm air ascending just above the surface front however the upgliding motion was intercepted by a secondary circulation at middle levels the analysis result was compared with model predictions of hoskins and bretherton 1972 as calculated by blumen 1980 sever

organic matter geochemical signatures of sediments of lake ngoring qinghai tibetan plateau a record of environmental and climatic changes in the source area of the yellow river for the last 1500 years abstract the climate history of the source area of the yellow river sayr is important to understanding the pacing and processes of climate evolution on the northeastern qinghai tibetan plateau qtp to date results of research in this alpine region are limited herein we provide a first lacustrine record from the largest freshwater lake on the qtp that archives climatic and environmental variations in the sayr for the last 1500 yr the bulk organic carbon and nitrogen isotopic compositions 13corg and 15ntot are combined with atomic carbon nitrogen c n ratios to indicate that the sedimentary organic matter in lake ngoring originates from autochthonous algae and that the terrestrial input is minor comparison of the record of organic carbon isotope values with published records of ice accumulation rate iar of dunde and guliya glaciers from the northern qtp the total solar irradiance tsi 18o variations in the greenland ice core and biologically sensitive indicators c37 4 alkenone crenarchaeol and bgdgt concentrations from lake qinghai indicate that variations in the 13corg values in lake ngoring sediments reflect lake level fluctuations that are associated with variations in the amount of precipitation and glacier meltwater on the sayr high lake level phases indicated by positive shifts of 13corg values correspond to higher values of the north atlantic oscillation index naoi and lower values of the southern oscillation index soipr this relation suggests that the hydrologic history in the sayr is linked to changes in the indian monsoon and the westerlies and that both air masses delivered more moisture to the sayr during high tsi stages in contrast variations in the 15ntot values resemble the multiple paleoclimate proxy records obtained from ice cores peat sequences lake sediments and integrated paleo records from other qtp sites suggesting that the 15ntot values archived in lake ngoring sediments provide a history of past lake water temperature variations that is consistent with the variation history of the temperature dependent parameters from regional paleo climatic studies global climatic events including the dark ages cold period the medieval climate anomaly the little ice age and modern warming in 20th century could be clearly observed in the 15ntot variations in general the 13corg and 15ntot values in lake ngoring sediments appear to be useful indicators for paleo environment and paleo climate reconstructions in alpine oligotrophic freshwater lakes such as this one

crustal structure and apparent tectonic underplating from receiver function analysis in south island new zealand we utilize seismic converted phases on more than 700 receiver functions calculated for 42 stations in the south island new zealand to infer crustal and uppermost mantle structure we determine the crustal thickness from direct observations of conversion from the moho interface and infer zone of the maximum thickness being located along the axis of the southern alps just east from the alpine fault the crustal root widens from north to south in the direction perpendicular to the alpine fault and appears to have an asymmetric structure stations in the alpine portion of island show evidence for prominent midcrustal conversions significant crustal thickening is developed in response to both the convergent component of the motion on the alpine fault and subduction in the fiordland region we propose two models for a strong uppermost mantle conversion that occurs at depths between 33 and 83 km on 16 stations and forms a large continuous feature along the east coast and in the central portions of the south island our preferred model attributes upper mantle conversion to tectonically underplated oceanic crust formed by late oligocene miocene spreading between the australian and pacific plates which was detached from the australian plate and tectonically underplated under the south island an alternative model attributes the upper mantle conversions to long lived seismic fabric created by subduction of the gondwanaland margin

the role of meltwater in glacial processes abstract water plays a dominant role in many glacial processes and the erosional depositional and climatic significance of meltwaters and associated fluvioglacial processes cannot be overemphasized at its maximum extent c 20 000 years ago the volume of the laurentide ice sheet was 33 106 km3 about the same as the volume of all ice present today on planet earth the bulk of this was released as water in little more than 10 000 years pulses of meltwater flowing to the atlantic ocean from large ice dammed lakes altered thermohaline circulation of the world s oceans and global climate one such discharge event via hudson bay at 8200 years bp released 160 000 km3 of water in 12 months global sea levels recovered from glacial maximum low stands reached at about 20 000 years ago at an average rate of 15 m per thousand years but estimates of shorter term rates suggest as much as 20 m sea level rise in 1000 years and for short periods rates as high as 4 m per hundred years meltwaters played a key role in lubricating ice sheet motion and thus areal abrasion across the inner portions of the ice sheet where it slid over rigid crystalline bedrock of the canadian shield the recharge of meltwater into the ice sheets bed was instrumental in generating poorly sorted diamict sediments till by sliding induced shearing and deformation of overpressured sediment and soft rock the transformation of overpressured till into hyperconcentrated slurries in subglacial channels may have generated a highly effective erosional tool for selective overdeepening and sculpting of bedrock substrates some workers credit catastrophic subglacial megafloods with the formation of drumlins and flutes on till surfaces subglacial melt river systems were instrumental in reworking large volumes of glaciclastic sediment to marine basins it has been estimated that less than 6 of the total volume of glaciclastic sediment produced during the pleistocene remains on land fluvioglacial and glaciolacustrine sediments and landforms dominate large tracts of the glacial landscape in north america the recharge of subglacial meltwater into underlying bedrock and sediment aquifers created transient reversals in the long term equilibrium flow directions of basinal fluids with regard to pre pleistocene glacial record meltwaters moved enormous volumes of terrestrial glaciclastic sediment to marine basins and thus played a key role in preserving a record of glaciation a record otherwise almost entirely lost on land

the life cycle of an extratropical marine cyclone part ii mesoscale structure and diagnostics abstract this is the second of two articles describing the evolving structure and selected physical processes within an intense extratropical marine cyclone observed during the experiment on rapidly intensifying cyclones over the atlantic erica field program part i describes the 24 h frontal cyclone evolution through 6 h horizontal analyses of observations taken by specially deployed observing systems from air land and sea part ii presents frontal scale and precipitation structures and physical processes from analyses based primarily on research aircraft observations taken during three phases of the cyclone s life cycle horizontal analyses at 350 m above ground level describe the cyclone s mesoscale frontal baroclinic structure and associated flow patterns the vertical structure and evolution of the cyclone s cold front warm front and bent back front are illustrated in cross sectional analyses of potential temperature wind velocity potential vorticity pv front relative transverse flow vecto

structure of a warm front helsinki testbed observations and model simulation abstractthe purpose of this study is to document the structure of a warm front in northeast europe identify the effects that the finnish coastline has on the evolution of the front and investigate factors that influence the speed that the warm front moves at within and above the boundary layer the warm front formed over estonia traveled northward across the gulf of finland and then crossed the southern coastline of finland surface based measurements from the helsinki testbed are analyzed together with output from a high resolution numerical weather prediction model application of research to operations at mesoscale arome during the early stages of development the warm front interacted with a stationary baroclinic zone and consequently evolved into an s shape as the front approached the southern coast of finland the temperature gradient at 1000 hpa increased as it merged with a diabatically generated temperature gradient at 1000 hpa the front stalled at the coastline due to friction enh

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones part v the substructure of narrow cold frontal rainbands abstract the organization and structure of a narrow cold frontal rainband ncfr on the small mesoscale and the microscale have been investigated through quantitative radar reflectivity doppler radar observations airborne observations and surface measurements the ncfr was composed of small mesoscale regions of heavy precipitation called precipitation cores pcs oriented at an angle to the synoptic scale cold front in horizontal cross section the pcs were roughly elliptical in shape areas of lighter precipitation called gap regions grs separated the pcs the pcs were so oriented that their loading edges were regions of strong low level convergence the weather associated with the passage of a pc resembled that of a squall line gust front with concurrent windshifts and pressure checks occurring 5 min before heavy precipitation and a fall in temperature the changes in surface weather that accompanied the passage of a gr were more variable but tended to be less marked than for pcs thus the se

reconstruction of the late glacial and holocene history of lake oron eastern siberia russia based on high resolution reflection seismic data high resolution seismic data have been used to study the sedimentary infill of lake oron we have tested the idea that glacial lake vitim could be formed when glaciers descending from the kodar mountains blocked the vitim river at lake oron the five seismic facies types shallow pelagic mudslide and turbidite rock sandslide and alluvial or glacial fan facies and five seismic units were identified in the sedimentary infill of lake oron however features that could represent moraines were not observed on the seismic profiles and along the shoreline of lake oron it is very likely that terminal moraines did not dam the vitim river up to 840 60 m a s l at the end of the last glacial maximum lgm we assume that the oron depression was mainly dry and glaciers lobes could be located close to the eastern edge of lake oron in valleys of the sygykta kultushnaya and kamennaya rivers during the lgm intensive inflow of meltwater and river input into lake oron began since ca 18 ka bp after ca 5 ka bp the supply of surface water into the lake sharply reduced

airborne radar observations of a cold front during fastex1 abstract a detailed analysis using airborne doppler radars of an oceanic cold front associated with precipitation core and gap regions is presented the precipitation cores appear to form as a result of the combined effects of horizontal shearing instability and the advection of hydrometeors by the core relative winds in contrast to previous schematic models it is shown that a strong surface discontinuity does not exist along the entire length of the precipitation core the southern section of the core can be accompanied by an abrupt discontinuity and lighter precipitation while the northern section can be associated with more slowly changing variables but heavier precipitation the peak updrafts at the leading edge of the front appeared to be primarily driven by frictional convergence and the acceleration of the vertical vorticity in the boundary layer the overall motion of the cold front was not well predicted using density current theory even though the kinematic structure of the front resembled cla

reconstruction of glacier fluctuations in the east sayan baikalsky and kodar ridges east siberia russia during the last 210 years based on high resolution geochemical proxies from proglacial lake bottom sediments we have presented results of study of bottom sediments of the proglacial lakes enriched with meltwater of peretolchin glacier the east sayan ridge chersky glacier the baikalsky ridge and glaciers of the kodar ridge bottom sediments formed from the end of the little ice age to 2013 were investigated with time resolution in year season using x ray fluorescence with synchrotron radiation and inductively coupled plasma mass spectrometry depth age models of the cores were estimated from year laminate layers using 210pb and 137cs chronology intense glacier thawing was calculated from the amount of clastic matter supplied by glacier meltwater into proglacial lakes a high content of some elements was closely associated with clastic material e g rb zr nb y or th in bottom sediments and most likely these elements affected the intensity of glacier melting we have defined three periods in significant increase of glacier flow melting during the last 210 years the first period ca 1800 1890 supply of suspended material by meltwater into lake ekhoy the east sayan ridge and lake preobrazhenskoe the kodar ridge was not intense until 1850 and 1875 respectively however the rate of meltwater supply into lake izumrudnoe the baikalsky ridge was high during the little ice age and it is likely attributed to local moisture from lake baikal the regional glacier water balances were most likely positive during the second period ca 1890 1940 the third period ca 1940 till present was characterised by moderate melting rate of glaciers located on the kodar and baikalsky ridges in contrast to peretolchin glacier that demonstrated the highest rate of melting and changes in outlines during this period

reconstruction of glacier advance in northern baikal area east siberia russia in the pleistocene inferred from mitochondrial dna polymorphisms of baikal grayling salmonidae thymallus baicalensis the study of allopatric speciation or geographic speciation expressed by dna polymorphisms can be successfully used in paleogeography reconstructions in this study we have tested the idea that grayling from lake baikal could migrate following chersky glacier retreat to the baikalsky mountains and were isolated by this glacier in glacial lake gitara in the pleistocene in order to estimate the initial isolate time of this population we compared the control region mtdna polymorphism of lake gitara grayling with that known for the lake baikal region all fish from lake gitara have the same mtdna haplotype one of the most represented among lake baikal grayling indicating that the isolation of the population in lake gitara could happen not earlier than 335 90 ka this age estimations do not contradict the records from bottom sediments of lake baikal and glacial tills of the northern baikal area which suggest that glacial advance to lake baikal reached its maximum extent in mis 8 samarovskoe glaciation

the detailed record of climatic events during the past 75 000yrs bp from the lake baikal drill core bdp 93 2 abstract by correlating the pronounced interstadial type diatom peak with mis 3 the high resolution and well dated record bdp 93 2 from the selenga delta area of lake baikal complements the classical long paleoclimatic records from academician ridge which lack the pronounced mis 3 warm signal this correlation helps to resolve the age model controversies related to this interstadial interval the content and c n ratios of total organic carbon as well as its stable isotope composition and diatom abundance reveal high frequency oscillatory variations reflecting the more unstable conditions of mis 3 interstadial in the lake baikal region as compared with the holocene interglacial an important part of the regional climatic instability during the past 75 000 yrs bp revealed for the first time in the baikal record is the recurrence of the abrupt erosional events leading to the deposition of the detrital carbonate material at the hemipelagic bdp 93 site there were at least five such events at mis 5 4 transition in the middle of mis 4 and three during mis 3 stratigraphic and ams radiocarbon age models allow the baikal erosional carbonate events to be confidently correlated to the intervals of heinrich layers in the north atlantic this correlation suggests a surprisingly strong climatic teleconnection of the remote mid continent baikal location with the dansgaard oeschger events and the bond cycles in the north atlantic region