rise in frequency of surface melting at siple dome through the holocene evidence for increasing marine influence on the climate of west antarctica 1 a new melt layer history from siple dome west antarctica indicates notable late holocene summertime warming visual stratigraphic analyses of the 1004 m ice core identified 62 years with melt layers melting events began around 11 7 ka followed by a period of no melting from 8 8 6 6 ka melt layer frequency increased from 6 6 ka to the present with the 1000 year average melt layer frequency reaching a maximum of 2 at 0 8 ka we use our millennial scale archive of melt events as a unique seasonal paleothermometer to elucidate changes in west antarctic holocene summer climate our calibration suggests the change in melt frequency from 0 to 2 may represent a summer temperature increase of 2 c from the middle to late holocene this temperature change cannot be explained entirely by local change in ice elevation or summer insolation and is in contrast to east antarctic climate records which show peak warmth in the early holocene followed by stable or decreasing temperature we interpret the rise in melt frequency as evidence of an increasing marine influence on the ross sea sector of west antarctica although the surface elevation of siple dome has not changed greatly the continued lateral retreat of the west antarctic ice sheet from its last glacial maximum configuration across the outer continental shelf and the delayed drawdown in ice thickness from the adjacent coastal marie byrd land region in conjunction with periods of increased cyclogenesis perhaps related to variations in enso would allow a moderated maritime climate to more easily reach west antarctica

holocene reef growth dynamics on kodakara island 29 n 129 e in the northwest pacific abstract the spatial distribution of modern coral reefs in the northwest pacific nwp is restricted to approximately 30 n understanding the high latitude reef growth process and its correlation to climate change may provide important insights into future reef growth at even higher latitudes in response to global warming we conducted field surveys and obtained seven cores from the raised reefs of kodakara island 29 n 129 e in the nwp to determine the changes in and response of reef growth dynamics to millennial scale climate change through the holocene to reconstruct the timing of the reef growth 37 coral ages were determined using accelerator mass spectrometry ams radiocarbon dating the island is characterized by three holocene reef terraces terraces i to iii which were uplifted ca 2 4 ka 1 0 0 4 ka and in the modern era three growth hiatuses occurred circa 5 9 5 8 ka 4 4 4 0 ka and 3 3 3 2 ka which correlate with millennial scale climate changes hamanaka et al 2012 the reef growth began at least 8 ka relatively rapid vertical growth of 3 6 3 3 m kyr 1 occurred between 8 and 6 ka the reef started growing near land and then gradually extended seaward the reef growth around the reef slope decelerated after 6 ka and most likely coincided with the first and second hiatuses detected landward in contrast with the reef flat which resumed its growth after the third hiatus event the reef mound accretion on the slope ceased definitively terrace i was uplifted ca 2 4 ka the reef growth reactivated ca 1 3 ka and the reef grew at a rate of 9 1 m kyr 1 between 1 3 and 1 0 ka this rate is the fastest growth recorded in this study this time interval corresponds to the medieval climatic anomaly mca the cause of the delayed reef growth between 2 4 and 1 4 ka remains unclear but it may imply the existence of a late holocene hiatus due to a weaker kuroshio current kc ca 1 7 ka and to strong el nino southern oscillation enso activity between 2 and 1 5 ka in the east pacific the timing of the hiatuses agrees with the weakening of the kc and the more frequent el nino events during the positive phase of the pacific decadal oscillation pdo whereas the rapid growth coincides with la nina conditions such as the mca during the negative phase of the pdo our results indicate that the climate event at approximately 4 ka caused the largest change in the reef growth and it may have affected reefs throughout the pacific region specifically the enso and pdo phases may have impacted the reef growth and kc behavior

the neglected indo gangetic plains low level jet and its importance for moisture transport and precipitation during the peak summer monsoon accurately simulating the indo asian monsoon iam using atmospheric general circulation models agcms is challenging but crucial this study uses reanalysis products erai jra55 and har to highlight an easterly low level barrier jet along the indo gangetic plain referred from here as ig llj which we identify as the primary moisture transport mechanism for the northeastern branch of the iam we show that the ncar family of agcms cam does not capture this circulation until 1 2 degree or greater spatial horizontal resolution is used the ig llj develops due to a persistent low pressure system centered over the ganges basin and is enhanced by the himalayas using diabatic heating rates and the moist froude number as diagnostics we find that in cam this branch of the iam displays two different dynamical regimes as a function of resolution at low resolution the atmosphere near the himalayas is statically unstable diabatic heating is strong and the moisture flow is southwesterly from the arabian sea and moves over the terrain unblocked at high resolution the moist static stability near the hm is stable diabatic heating is weak and the flow primarily enters easterly from the bay of bengal and moves parallel to the terrain blocked during the summer season the low resolution cam is locked into the unblocked mode which has serious implications for interpreting topography monsoon interactions for a broader context we demonstrate that more than half of the cmip5 models do not capture the ig llj which further highlights model data mismatch across the iam region

stepwise onset of monsoon weather observed in the nepal himalaya mountain weather changes in the nepal himalaya were intensively examined during the 2003 monsoon onset using in situ datasets observed by multiple automatic weather stations aws distributed across the coordinated enhanced observing period ceop himalaya reference site at locations with significant differences in altitude onset of monsoon rainfall characterized as nighttime precipitation was initiated simultaneously at all stations with the occurrence and migration of a monsoon depression in the north of the bay of bengal satellite infrared images detected evident suppression of diurnal cloud development after the onset about two weeks prior to the onset the mountain weather abruptly changed such that the daytime valley wind at lower elevations weakened associated with morning clouds and the nighttime southerly wind began at upper elevations the timing corresponded with the weakening of the westerly wind over the himalaya due to the northward shift of the upper subtropical jet stream the time lag between the precipitation onset and the change in the mountain weather was confirmed by 9 yr of in situ aws data the mechanism of nighttime southerly winds at high elevations is also discussed in relation to large scale monsoon flow and local circulation

intercomparison of deep convection over the tibetan plateau asian monsoon region and subtropical north america in boreal summer using cloudsat calipso data abstractdeep convection in the tibetan plateau southern asian monsoon region tp samr is analyzed using cloudsat and cloud aerosol lidar and infrared pathfinder satellite observations calipso data for the boreal summer season june august from 2006 to 2009 three subregions are defined the tp the southern slope of the plateau pss and the samr and deep convection properties such as occurrence frequency internal vertical structure system size and local environment are compared among these subregions to cast them in a broader context four additional regions that bear some similarity to the tp samr are also discussed east asia ea tropical northwestern pacific nwp and western and eastern north america wna and ena respectively the principal findings are as follows 1 compared to the other two subregions of the tp samr deep convection over the tp is shallower less frequent and embedded in smaller size convection systems but the cloud tops are more densely packed these characteristi

a possible enso signal in the ross sea an examination of the observational record in the ross sea over the period 1982 1994 indicates that there is a statistically significant relationship between the ross sea sea surface temperature sst and the enso signal in the tropical pacific during this period the ross sea ssts lag the enso signal by 2 4 months with the highest correlation coefficient occurring with a lag of 3 months observations of the sea ice concentration during 1982 1994 also indicate a relation between the sea ice concentration in the ross sea and the enso cycle with reduced sea ice concentrations in el nino years

post glacial sea level rise from a coral record at huon peninsula papua new guinea dating of coral reef terraces can provide a record of changes in sea level which should be pronounced during the transition between glacial and interglacial periods cores drilled from coral reefs at barbados in the equatorial west atlantic1have revealed the sea level changes that occurred during the younger dry as event at the end of the last glacial maximum 11 000 yr bp it has not been known however whether pacific coral reefs can grow at a rate sufficient to keep up with the rise in sea level during such a transition here we report results obtained from a 52 m drill core from the post glacial reef at huon peninsula papua new guinea spanning the interval from 7 000 to 11 000 14c yr bp which show that coral growth kept pace while the relative sea level rose by 50m although the tectonic environment is very different from that at barbados the two records compare well when corrections are made for local tectonic uplift showing that sea level rise was similar at both locations the rate of rise was greatest between 9 000 and 10 00014c yr bp corresponding to the time of the younger dryas

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

katabatic wind in opposing flow abstract this paper presents a one dimensional model of katabatic winds in ambient flow and examines types of possible solutions results presented in dimensionless form indicate that 1 cooling along a slope with upslope ambient flow can lead to tranquil flow speed less than gravity wave speed solutions characterized by appreciable entrainment and 2 the onset time of katabatic winds is particularly sensitive to the retarding effects of opposing flow and reduced cooling rates model results present a plausible explanation for observed delays in the onset time of downslope flow of up to 8 h after sunset along certain humid tropical slopes

on the forcing of planetary scale rossby waves by antarctica the propagation of rossby waves forced at high latitudes into middle and low latitudes is studied using the barotropic vorticity equation on the sphere ray tracing theory indicates that fundamental differences exist between the response of an atmosphere initialized with typical northern hemisphere winter flow and typical southern hemisphere winter flow to such a forcing with a substantial response more likely for the southern hemisphere case integrations with a fully nonlinear barotropic model confirm this suggestion and indicate that away from the local forcing region linear theory provides a good description of the response the most notable feature in the steady solutions is a split of the mid latitude jet close to new zealand the location of this split coincides well with a region where blocking is observed to be prevalent in the southern hemisphere

hemispheric atmospheric variations and oceanographic impacts associated with katabatic surges across the ross ice shelf antarctica numerical simulations and surface based observations show that katabatic winds persistently converge toward and blow across the siple coast part of west antarctica onto the ross ice shelf about 14 of the time during winter april to august 1988 thermal infrared satellite images reveal the horizontal propagation of this negatively buoyant katabatic airstream for about 1000 km across the ice shelf to its northwestern edge a trajectory that nearly parallels the transantarctic mountains this takes place when the pressure field supports such airflow and is caused by synoptic scale cyclones that decay near and or over marie byrd land the northwestward propagation of the katabatic winds is accompanied by other changes in the hemispheric long wave pattern an upper level ridge develops over wilkes land resulting in an enhancement of the split jet in the pacific ocean then more frequent and or intensified synoptic scale cyclones are steered toward marie byrd land where they become nearly stationary to the northeast of the climatological location the resulting isobaric configuration accelerates the katabatic winds crossing siple coast and supports their horizontal propagation across the ross ice shelf an immediate impact of this katabatic airflow that crosses from the ice shelf to the ross sea is expansion of the persistent polynya that is present just to the east of ross island this polynya is a conspicuous feature on passive microwave images of antarctic sea ice and plays a central role in the salt budget of water masses over the ross sea continental shelf the impact of this katabatic airflow upon mesoscale cyclogenesis over the south pacific ocean is also discussed

teleconnections in the southern hemisphere abstract teleconnections are calculated from monthly mean anomalies of sea level pressure and 500 mb geopotential height for the southern hemisphere 10 90 s for five month winter and summer seasons the monthly means were calculated from australian analyses for the period from june 1972 to november 1980 zonally averaged anomalies at both sea level and 500 mb display an out of phase relation between low and high latitudes and in midlatitudes are negatively correlated with anomalies in the subtropics and polar regions in winter a striking zonal wavenumber 3 pattern is found over the southern ocean anomalies in 500 mb geopotential heights at 50 s 95 e 58 s 150 w and 38 s 15 w exhibit strong positive correlations while showing weaker negative correlations with heights over antarctica and in low latitudes a similar pattern appears in sea level pressure in summer anomalies in 500 mb geopotential height over the three subtropical continents appear to occur out of phase with anomalies over the su

isotope evidence for secondary sulfide precipitation along the marsyandi river nepal himalayas abstract we present sulfur and oxygen isotope data from 41 samples of dissolved riverine sulfate from along 65 km of the marsyandi river in the northern himalayas coupled sulfur and oxygen isotopic composition of riverine sulfate 34 s so 4 and 18 o so 4 respectively yield unique constraints on the source of sulfur to the river system the headwaters of the marsyandi river have light 34 s so 4 and 18 o so 4 which requires that the source of sulfate to the river is through the anoxic weathering of pyrite likely via fe3 the 34 s so 4 and 18 o so 4 of sulfate in tributaries to the marsyandi increase downstream which could result either from inputs from evaporites or bacterial sulfate reduction with subsequent sulfide precipitation in warmer and wetter catchments either of these processes could result in heavy 34 s so 4 and 18 o so 4 of the residual river sulfate elemental ratios such as sr ca and ca so4 suggest as previous studies have also concluded that evaporite weathering is not important in the marsyandi river we conclude that the isotope data is most consistent with the onset of bacterial sulfate reduction and secondary sulfide precipitation in the soils in the warmer and wetter downstream catchments our results have implications for understanding the source of sulfate to the ocean as well as the redox and acidity budget within rapidly eroding catchments

the southern oscillation part vi anomalies of sea level pressure on the southern hemisphere and of pacific sea surface temperature during the development of a warm event abstract the paper shows the discrete mean three month anomalies of sea level pressure on the southern hemisphere during the year before and the year of a warm event in the southern oscillation together with associated anomalies of sea surface temperature in the south pacific 0cean the two sets anomalies develop in a parallel and physically logical sequence over the south pacific ocean in conjunction with changes in the south pacific convergence zone nearly all of the southern hemisphere responds to the southern oscillation but the response is largest in the australia south pacific sector large anomalies of sea level pressure form well ahead of any on the northern hemisphere and this observation together with the conspicuous anomalies in the region of australia and the south pacific suggest that the origin of the southern oscillation must be sought in this region

late holocene reef ecosystem baseline field evidence from the raised reef terraces of kodakara and kikai islands ryukyu islands japan abstract to better understand and evaluate how present day and future reef ecosystems are being impacted by natural climate change and human activity it is important to establish reef ecosystem baselines from paleoecological records here we present paleoecological data including coral cover and genus and species composition for two raised reef islands kodakara and kikai islands located in the ryukyu islands japan covering the last 2 4 and 4 1 kyr respectively evidence of a mean cover of 20 40 coral on pristine reefs at the study sites was found for a millennial scale period of ocean environment stability in terms of sea level solar radiation and sea surface temperature this coral cover has been maintained on the modern reef at kikai island since at least 4 1 kyr ago the coral community was a reef crest upper reef slope community with acropora and goniastrea as the dominant genera and acropora digitifera and goniastrea retiformis as the dominant species from the late holocene to present millennial scale persistence of a digitifera and g retiformis may have been influenced by a strong kuroshio current increased genetic diversity and an increased potential for adaptation to environmental conditions our coral cover and species composition results provide important information for the development of effective reef restoration plans in light of the likely future degradation of reefs

a pronounced continental scale diurnal mode of the asian summer monsoon abstract a pronounced continental scale diurnal mode of the asian summer monsoon is mapped using data from recent satellites meteosat 5 and trmm these datasets were available at high temporal resolutions a result that stands out is the diurnal divergent circulation that in the afternoon hours has an ascending lobe over north central india and has a descending lobe that reaches out radially toward central china the southern part of china the equatorial indian ocean and the western arabian sea the reverse circulation is clearly seen during the early morning hours this diurnal pulsation of continental scale divergent circulation appears to be an integral part of the monsoon another finding relates to the diurnal slowing down and speeding up of the tibetan high circulations especially in the southern flanks where the tropical easterly jet resides and exhibits a pulsation of intensity the amplitude of pulsation was found to reach up to 7 m s 1 thus this continental scale change appears to be a prono

sea ice atmosphere signal of the southern oscillation in the weddell sea antarctica abstract composite analysis of weekly ship and shore observations of the weddell sea pack ice for extreme events of the southern oscillation so occurring in the 1929 62 period reveals strong variations in ice water concentrations in the early and late summer melt season substantially reduced ice concentrations more open water occur in december and early january of warm el nino events yr0 compared with the summer before yr 1 and appear connected with the change to a stronger cyclonic atmospheric circulation over higher latitudes of the south atlantic similarly consistent meteorology sea ice associations appear to characterize the mid to late summer of warm so events yr0 compared with yr0 of cold events there is some evidence that the regionally dependent pressure and wind reversals and possibly the associated sea ice concentration changes in the weddell sector have become more marked during so events occurring since about the early 1950s some corroboration of changes in the sea ice

coseismic and postseismic creep in the andaman islands associated with the 2004 sumatra andaman earthquake 1 two field campaigns march 2005 and march 2006 for measurements of biological indicators and eyewitness accounts confirm that large coseismic and postseismic surface deformation occurred over the andaman islands in association with the 2004 sumatra andaman earthquake amount of uplift was as large as 1 3 m in the islands off nw coast and decreased to ese with a zone of subsidence in the se andaman the coseismic deformation did not generate large seismic waves or tsunamis indicating that slip was much slower than that off sumatra the coseismic uplift was followed by postseismic subsidence which was evidenced by local residents to have occurred within two months after the earthquake a simple dislocation model explains the deformation pattern by a coseismic rupture 50 km wide with its down dip limit 130 km east of the trench axis followed by an up dip propagation of the rupture front for about 10 km

high precision and high resolution carbonate 230th dating by mc icp ms with sem protocols abstract to facilitate the measurement of u th isotopic compositions suitable for high precision and high resolution 230th dating of coral and speleothem carbonates secondary electron multiplier sem protocol techniques for multicollector inductively coupled plasma mass spectrometry mc icp ms have been developed the instrumental sensitivities are 1 2 with a precision of 1 2 2 for abundance determination of 50 200 fg 234u 1 4 ng 238u or 230th this method features chemistry refinements improvements to procedural and instrumental blanks spectral inference reductions and careful consideration of non linear sem behavior measurement consistency of this mc icp ms combined with previous mass spectrometric results on u th standards and a variety of carbonates demonstrates the validity of the sem protocol method for fossil corals a routine u th isotopic determination at permil level precision requires only 10 50 mg of carbonate as little as 200 mg of young coral with an age of less than 20 yr can be dated with a precision of 0 3 0 8 yr about 20 200 mg speleothem samples with sub ppm to ppm u are required to earn a 5 precision on ages from 5 to 100 kyr requirement of small sample size 10 100s mg carbonate can permit high temporal resolution to date speleothems with slow growth rates i e 1 10 mm kyr this high precision 230th chronology is critical to accurately establish age models date events and splice geochemical proxy time series records from multiple samples in the fields of paleoclimatology and paleoceanography the u th isotopic determination techniques described here can also be applied to different environmental samples such as waters rocks and sediments

cloud to ground lightning observations from toga coare selected results and lightning location algorithms abstract recently observations of electrified oceanic convection and associated cloud to ground cg lightning were obtained over the tropical western pacific ocean during toga coare tropical ocean global atmosphere coupled ocean atmosphere response experiment during coare observations of convection were made using a variety of instrument platforms including ship and airborne doppler radars an advanced lightning direction finder aldf network and a shipborne inverted electric field mill this study focuses on data collected by the coare aldf network fusion of those data with observations and the methods used to calculate accurate cg return stroke locations analysis of cg lightning data and doppler radar data indicates that lightning producing oceanic convection is characterized by deep vertically developed convective cells with radar reflectivities exceeding 30 dbz above the height of the 10 c level in several cases a peak in cg frequency occurred coincident with the descent of precipitation

low frequency of southern asian monsoon variability using a 295 year record from the dasuopu ice core in the central himalayas 1 a better understanding of the spatial and temporal variability of rainfall in the himalayas should be extremely important to improve our understanding of asian monsoon dynamics there is little that is understood about rainfall variability at the high himalayas with elevation over 7000 m a s l here a high resolution snow accumulation record from a well dated dasuopu ice core from central himalayas reflects low frequency variability of monsoon precipitation over the last 295 year multidecadal to centennial variations in the dasuopu snow accumulation dsa are in phase out of phase with that in monsoon rainfall of northeast indian nepal and bangladesh southern india over the period 1901 1995 the record shows the monsoon in central himalayas had weakened in 18th century and strengthened throughout much of 19th and early 20th century and then weakening again from early 1920s to the present

the vertical structure and development of the enso anomaly mode during 1979 1989 abstract the latest two pacific basinwide warm episodes 1982 83 and 1986 87 exhibit some common features in their development and vertical structure these features are examined by multivariate empirical orthogonal function analysis of the interannual variability of the ocean atmosphere system along equatorial indian and pacific oceans the updraft and downdraft branches of the anomalous walker circulation originate over the western pacific and the eastern indian ocean respectively the early development of basinwide warming is characterized by the strengthening of a cross equatorial low level southerly component over the eastern pacific and the enhancement of convection and boundary layer westerlies over the western pacific the structure of the enso anomaly mode changes from the cold to the warm phase of the southern oscillation this is attributed to its eastward migration and the intrinsic longitudinal dependence of the vertical structure the latter results from the east west contrast of the air s

antarctic pressure and temperature anomalies surrounding the minimum in the southern oscillation index the purpose of our research is to analyze surface pressure and temperature patterns in antarctica for relationships with the el nino southern oscillation enso using monthly anomalies of surface pressure and temperature in antarctica lag correlations are made to the southern oscillation index soi and annual composites are created for years where enso is in a warm phase comparisons are made to annual composites for nonwarm phase years and to six individual enso warm phases occurring between 1957 and 1984 we found a sharp change in the sign of the pressure and temperature anomalies between the year before and the year after the minimum in the soi we hypothesize that the temperature and pressure anomaly patterns are related through a thickness argument to the 500 mbar southern hemispheric flow and the australian branch of the southern oscillation

deciphering the contrasting climatic trends between the central himalaya and karakoram with 36 years of wrf simulations glaciers over the central himalaya have retreated at particularly rapid rates in recent decades while glacier mass in the karakoram appears stable to address the meteorological factors associated with this contrast 36 years of climate forecast system reanalyses cfsr are dynamically downscaled from 1979 to 2015 with the weather research and forecasting wrf model over high mountain asia at convection permitting grid spacing 6 7 km in all seasons cfsr shows an anti cyclonic warming trend over the majority of high mountain asia but distinctive differences are observed between the central himalaya and karakoram in winter and summer in winter and summer the central himalaya has been under the influence of an anti cyclonic trend which in summer the downscaling shows has reduced cloud cover leading to significant warming and reduced snowfall in recent years contrastingly the karakoram has been near the boundary between large scale cyclonic and anti cyclonic trends and has not experienced significant snowfall or temperature changes in winter or summer despite significant trends in summer of increasing cloud cover and decreasing shortwave radiation this downscaling does not identify any trends over glaciers in closer neighboring regions to the karakoram e g hindu kush and the western himalaya where glaciers have retreated as over the central himalaya indicating that there are other factors driving glacier mass balance that this downscaling is unable to capture while this study does not fully explain the karakoram anomaly the identified trends detail important meteorological contributions to the observed differences between central himalaya and karakoram glacier evolution in recent decades

biogeography of holocene coral species in the western indian ocean abstract understanding the relationship between coral biogeography and reef development is a key topic in sedimentology and paleoecology although the knowledge of coral reef growth and internal facies patterns during the holocene has increased since the 1970s the biogeography of holocene coral species in the indo pacific regions remains poorly constrained in this study we examined quantitative records of coral species based on data from five cores retrieved from two holocene reefs in the western indian ocean la pointe au sable reef on mauritius island and toliara reef on madagascar our results indicate that the dominant reef building corals on both reefs were isopora palifera acropora robusta abrotanoides complex some corals e g the a robusta abrotanoides complex and acropora digitifera from 6 ka were found in mauritius whereas these were not identified in the cores from madagascar before 1 5 1 ka this delay may have been controlled by ocean currents and or the competency period of the coral larvae a comparison of these coral assemblages with those in other regions seychelles mayotte ryukyu islands palau islands papua new guinea the great barrier reef new caledonia and vanuatu showed that i palifera was common in all of the studied regions whereas goniastrea retiformis probably migrated recently to mauritius and madagascar in response to prevailing surface ocean currents including the south equatorial current and the agulhas current one explanation for the late arrival of g retiformis to the study sites could be that the competency period of g retiformis larvae is shorter than that of i palifera moreover our quantitative analysis suggests that a given population size during the holocene may have contributed to the abundance of species in modern reefs this study emphasizes the need for further quantitative research on holocene coral species in other regions to better understand the temporal and spatial patterns of coral biogeography

mid holocene coral community data as baselines for understanding contemporary reef ecological states land use changes and associated deteriorations in water quality are cited as major drivers of marine ecosystem change and can modify community abundance and diversity on coral reefs this study uses palaeoecological data derived from a mid holocene age coral reef in the wet tropics region of australia s great barrier reef to develop a record of coral community composition and diversity from a period that significantly pre dates european settlement in the region major changes in catchment sediment and nutrient yields since european settlement have been documented and thus the data presented provides a baseline against which to compare contemporary ecological datasets natural variations in coral assemblage composition as preserved in core records clearly occurred in this mid holocene reef and were associated with the reef shallowing to sea level as it accreted vertically comparisons between modern and mid holocene coral community data from equivalent water depths did not reveal marked shifts in coral community composition and diversity suggesting the long term persistence of a resilient coral assemblage over these time periods

trumpet shaped topography modulation of the frequency vertical structures and water path of cloud systems in the summertime over the southeastern tibetan plateau a perspective of daytime nighttime differences

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

holocene sea level record from corals reliability of paleodepth indicators at ishigaki island ryukyu islands japan abstract holocene sea level change provides direct evidence of the melting of ice sheets however our understanding of the timing and course of such change is limited by a lack of information regarding environmental condition of corals for example holocene sea level curves are compiled based on water depths estimated from the occurrence of a small number of coral species as species identification is difficult work the error associated with this method of estimating sea level exceeds 2 5 m in addition there generally occurs a difference in the living water depth of corals between high energy reefs and low to moderate energy reefs this difference in living water depth also results in an error in reconstructed sea level curves in the present study we analyzed drill core and recorded the vertical distribution of corals at the high energy ibaruma reef and low to moderate energy fukido reef ishigaki island ryukyu islands japan analyses of corymbose acropora a digitifera massive goniastrea g retiformis massive pocillopora p verrucosa massive platygyra p ryukyuensis and other corals enables the accurate reconstruction of a sea level curve because these species are distributed in a narrow range with a weighted mean m w error of between 0 5 and 2 5 m these observation data from ibaruma and fukido reefs can be used to reconstruct holocene sea level curves based on drill core data from ibaruma reef however the two reefs yield contrasting sea level curves the curve reconstructed based on data from fukido reef is several meters deeper than that reconstructed based on data from ibaruma reef this discrepancy reflects the different energy levels of the two reefs high energy at ibaruma reef and low to moderate energy at fukido reef therefore the accurate reconstruction of a holocene sea level curve requires the identification of species from drill core and observations of the vertical distribution of species at the present day reef at a location close to the drilling site the holocene sea level curve reconstructed based on drill core data from ibaruma reef reveals a rapid sea level rise of approximately 7 5 m kyr 1 between 8000 and 6000 cal years bp the rate of sea level rise decreased from 7 5 to 3 5 m kyr 1 between 6000 and 5000 cal years bp a mid holocene highstand occurred at around 5000 cal years bp at a level of approximately 3 2 5 m above the present mean sea level the increase in ocean volume corresponding to this sea level rise indicates that melting of the antarctic ice sheet continued beyond 6000 cal years bp as most of the northern hemisphere ice sheets had melted by 6000 cal years bp resulting in sea levels similar to those of the present day

diurnal winds in the himalayan kali gandaki valley part i observations abstract the diurnal wind system of the kali gandaki valley in nepal was explored in september and october 1998 in a field campaign using pilot balloons as the main observational tool this valley connects the plateau of tibet with the indian plains the river crosses the himalayas forming the deepest valley on earth intense upvalley winds blow up this valley during the day observations were made along the river at various spots selected between the exit point from the himalayas and the source close to the plateau of tibet the strongest upvalley winds were found between marpha and chuksang with typical speeds of 15 20 m s 1 the upvalley wind sets in first at the ground but an upvalley wind layer of 1000 2000 m depth forms quickly after the onset this deep inflow layer persists up to lo manthang a town located a few kilometers south of the plateau of tibet deceleration in the late afternoon and evening also appears to commence near the ground weak drainage flow forms late in the night the causes o

regional seasonal and diurnal variations of extreme convection in the south asian region abstract temporal and spatial variations of convection in south asia are analyzed using eight years of tropical rainfall measuring mission trmm precipitation radar pr data and ncep reanalysis fields to identify the most extreme convective features three types of radar echo structures are defined deep convective cores contiguous 3d convective echo 40 dbz extending 10 km in height represent the most vertically penetrative convection wide convective cores contiguous convective 40 dbz echo over a horizontal area 1000 km2 indicate wide regions of intense multicellular convection and broad stratiform regions stratiform echo contiguous over an area 50 000 km2 mark the mesoscale convective systems that have developed the most robust stratiform regions the preferred locations of deep convective cores change markedly from india s east coast in the premonsoon to the western himalayan foothills in the monsoon they form preferentially in the evening and over land as near surface moist flow is cap

the polar expression of enso and sea ice variability as recorded in a south pole ice core an annually dated ice core recovered from south pole 2850ma s l in 1995 that covers the period1487 1992 was analyzed for the marine biogenic sulfur species methanesulfonate ms empirical orthogonal function analysis is used to calibrate the high resolution ms series with associated environmental series for the period of overlap 1973 92 utilizing this calibration we present a 1500 year long proxy record of the polar expression of the el ni o southern oscillation enso and southeastern pacific sea ice extent variations these records reveal short term periods of increased 1800 50 1900 40 and decreased sea ice extent 1550 1610 1660 1710 1760 1800 in general increased decreased sea ice extent is associated with a higher lower frequency of el ni o events

the large scale circulation and heat sources over the tibetan plateau and surrounding areas during the early summer of 1979 part i precipitation and kinematic analyses abstract the time evolution of the large scale precipitation low level 850 mb wind moisture and vertical motion fields over the tibetan plateau and surrounding areas during a 40 day period from late may to early july 1979 is studied based on the objectively analyzed fgge level ii b data set during this period the general circulation over east asia undergoes a distinct change characterizing the onset of the summer monsoon circulation the tibetan plateau exerts profound orographic and thermal influences upon the low level wind field the inflow towards the eastern part of the plateau with a marked diurnal change in its intensity is the most prominent feature of the low level wind field the areas of organized precipitation are well related to synoptic systems seen in the 850 mb flow the quasi stationary burma india trough the disturbances forming on the trough the mei yu baiu front and the transverse trough extending eastward from the plateau there is a sharp contrast between the western an

monitoring the monsoon in the himalayas observations in central nepal june 2001 abstract the monsoon himalayan precipitation experiment mohprex occurred during june 2001 along the south slopes of the himalayas in central nepal radiosondes were launched around the clock from two sites one in the marsyandi river basin on the eastern footslopes of the annapurna range and one farther to the southwest near the border with india the flights supported rainfall and other hydrometeorological observations including surface winds from the marsyandi network that has been operated in this region since the spring of 1999 the thermodynamic profiles obtained from the soundings support the observed nocturnal maximum in rainfall during the monsoon with total column moisture and instability maximized just before rainfall peaks coinciding with the appearance of a monsoon depression over central india the onset of the monsoon in this region was characterized by a weeklong weakening of the upper level westerlies and an increase in moisture and convective instability the vertical structure of

climate variability in west antarctica derived from annual accumulation rate records from itase firn ice cores thirteen annually resolved accumulation rate records covering the last 200 years from the pine island thwaites and ross drainage systems and the south pole are used to examine climate variability over west antarctica accumulation is controlled spatially by the topography of the ice sheet and temporally by changes in moisture transport and cyclonic activity a comparison of mean accumulation since 1970 at each site to the long term mean indicates an increase in accumulation for sites located in the western sector of the pine island thwaites drainage system accumulation is negatively associated with the southern oscillation index soi for sites near the ice divide and periods of sustained negative soi 1940 42 1991 95 correspond to above mean accumulation at most sites correlations of the accumulation rate records with sea level pressure slp and the soi suggest that accumulation near the ice divide and in the ross drainage system may be associated with the mid latitudes the post 1970 increase in accumulation coupled with strong slp accumulation rate correlations near the coast suggests recent intensification of cyclonic activity in the pine island thwaites drainage system

modeled antarctic precipitation part ii enso modulation over west antarctica the impacts of the el nino southern oscillation enso on the antarctic region are of special importance in evaluating the variability and change of the climate system in high southern latitudes in this study the enso signal in modeled precipitation over west antarctica since 1979 is evaluated using forecast precipitation from several meteorological analyses and reanalyses additionally a dynamical retrieval method drm for precip itation is applied over the last two decades the southern oscillation index soi has an overall anticorrelation with precipitation over the west antarctic sector bounded by 758 908s 1208w 1808 while it is positively correlated with precipitation over the south atlantic sector bounded by 658 758s 308 608w decadal variations are found as the relationship between the soi and west antarctic precipitation is stronger in the 1990s than that in the 1980s the polar front jet stream west antarctic precipitation and the soi show a well ordered correspondence during the 1990s as the jet zonal speed is negatively correlated to the soi and positively correlated to west antarctic precipitation these relationships are weaker during the 1980s consistent with the change in sign of the correlation between the soi and west antarctic precipitation the decadal variations are apparently related to changes in the quasi stationary eddies that determine the local onshore and offshore flow over west antarctica

atmospheric teleconnections involving the southern ocean 1 i review the characteristic patterns of low frequency interannual and subdecadal variation in atmospheric circulation over the southern hemisphere sh extratropics and their climatic associations e g temperature precipitation winds sea surface temperatures ssts and sea ice conditions for the southern ocean the considerable spatial and temporal limitations of the observational database have strongly conditioned the pace of our understanding of sh teleconnections particularly for the pacific sector where the tropical el nino southern oscillation enso exerts a dominant influence an enso signal appears in the intensity interannual variations of the amundsen sea mean low pressure asl jet streams and long waves these variations comprise the so called pacific south america psa teleconnection patterns of low frequency variability in sh circulation that are mostly extratropical in origin but which can interact with enso are dominated by the zonally symmetric high latitude mode or antarctic oscillation aao the aao involves an alternation of atmospheric mass between middle and high southern latitudes a zonally asymmetric mode of wave number 1 is represented by an oscillation in pressure height between australian and south american sectors depicted by a trans polar circulation index a significant wave number 2 oscillation in the coupled atmosphere ocean ice system or antarctic circumpolar wave acw has a similar periodicity to enso and is strongest in the pacific sw atlantic sectors atmospheric teleconnections involving the southern ocean including those to enso show evidence of recent changes and the climatic implications of these are discussed

diurnal winds in the himalayan kali gandaki valley part ii modeling abstract the penn state ncar mesoscale model mm5 is used to simulate and better understand the wind observations in the kali gandaki valley reported in the first part of this paper the kali gandaki river originates in nepal near tibet flows southward through the mustang basin crosses the himalayas in a gorge and descends to the lowlands of nepal extremely strong diurnal upvalley flow in the gorge and the basin alternates with rather weak drainage flow in the night as proposed in part i the mustang basin and the tibetan plateau can be considered as an elevated heat source driving the upvalley flow during the day however the extreme strength of the diurnal upvalley winds and the order of magnitude asymmetry between day and night cannot be explained with a simple plateau circulation theory the model is successful in simulating almost all aspects of the observations the simulations strongly suggest that the observed acceleration of the upvalley winds near the entrance to the mustang basin is linked

isolating the role of surface evapotranspiration on moist convection along the eastern flanks of the tropical andes using a quasi idealized approach abstractthe contribution of surface evapotranspiration et to moist convection cloudiness and precipitation along the eastern flanks of the tropical andes eads was investigated using the weather research and forecasting wrf model with nested simulations of selected weather conditions down to 1 2 km grid spacing to isolate the role of surface et numerical experiments were conducted using a quasi idealized approach whereby at every time step the surface sensible heat effects are exactly the same as in the reference simulations whereas the surface latent heat fluxes are prevented from entering the atmosphere energy balance analysis indicates that surface et influences moist convection primarily through its impact on conditional instability because it acts as an important source of moist entropy in this region the energy available for convection decreases by up to approximately 60 when the et contribution is withdrawn in contrast when convective motion is not thermally driven or under condit

diurnal variation of surface airflow and rainfall frequencies on the island of hawaii abstract the high resolution portable automated mesonet data from the hawaiian rainband project are used to document the circulation over the entire island of hawaii for the first time it is shown that the surface airflow and rainfall occurrences over the island are strongly modulated by the diurnal heating cycle most areas over the island show daytime upslope and nighttime downslope components separated by morning and evening transitions on the windward slope the onset of the downslope upslope wind during the evening morning transition starts on the slopes and progresses downward the effects of island blocking are also evident on the windward slopes of mauna kea and mauna loa the mean winds are weak 1 m s 1 due to flow deceleration flow splitting occurs in the hilo bay area as the trade winds are forced to move around the island on the lee side the trade winds are absent for stronger trade wind days the island blocking is more significant with a higher surface pressure 0 2 0 5 hpa on

the interconnected global climate system a review of tropical polar teleconnections abstractthis paper summarizes advances in research on tropical polar teleconnections made roughly over the last decade elucidating el nino southern oscillation enso impacts on high latitudes has remained an important focus along different lines of inquiry tropical to polar connections have also been discovered at the intra seasonal timescale associated with madden julian oscillations mjo on the timescale of decades changes in mjo phases can result in temperature and sea ice changes in the polar regions of both hemispheres moreover the long term changes in sst of the western tropical pacific tropical atlantic and north atlantic ocean have been linked to the rapid winter warming around the antarctic peninsula while sst changes in the central tropical pacific have been linked to the warming in west antarctica rossby wave trains emanating from the tropics remain the key mechanism for tropical and polar teleconnections from intraseasonal to decadal timescales enso related tropical sst anomal

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

a pole to pole west pacific atmospheric teleconnection during august 1 an observational analysis is presented that reveals an august teleconnection involving both the northern hemisphere nh and the southern hemisphere sh the teleconnection includes three primary anomalies in the monthly average surface pressure field 1 a high southern latitude component including wilkes land antarctica the nearby southern ocean and the ross sea 2 a sh midlatitude component near australia and new zealand and 3 a nh subtropical component over the extreme western pacific ocean surface pressure for the sh high latitude anomaly is negatively correlated to the other two primary anomalies the sh midlatitude and nh subtropical component are positively correlated furthermore the teleconnection is correlated to surface pressure near the aleutian islands the teleconnection anomalies result from tropical convection on intraseasonal timescales monsoon rainfall over east asia during august is correlated to the teleconnection furthermore august precipitation at several other locations in the nh and sh is modulated by the teleconnection two different sets of numerical experiments with the national center for atmospheric research ncar community climate model version 2 ccm2 show a similar appearing teleconnection during late boreal summer the modeled teleconnection however is forced from high southern latitudes

climate variability in the amundsen and bellingshausen seas satellite data reveal a 20 decline in sea ice extent in the amundsen and bellingshausen seas in the two decades following 1973 this change is negatively correlated with surface air temperatures on the west side of the antarctic peninsula which have increased 0 58c decade21 since the mid 1940s the recession was strongest during summer when monthly average minima in 1991 92 removed much of the incipient multiyear ice over the continental shelf this would have lowered the regional mean ice thickness impacting snow ice formation brine production and vertical heat flux the northern ice edge contracted by 18 of latitude in all seasons from 1973 79 to 1987 93 returning toward mean conditions in 1993 95 the decline included multiyear cycles of several years in length superimposed on high interannual variability a review of atmospheric forcing shows winds consistent with mean and extreme ice extents and suggests links to larger scale circulation changes in the south pacific historical ocean measurements are sparse in this sector but mixed layer depths and upper pycnoclines beneath the sea ice resemble those in the weddell sea weaker surface currents or changes in the upwelling of circumpolar deep water on the continental shelf could have contributed to the anomaly persistence

investigating tropospheric effects and seasonal position variations in gps and doris time series from the nepal himalaya summary geodetic time series from continuous gps cgps and 1 doris stations across the himalaya of central nepal show strong seasonal fluctuations observed on the horizontal and vertical components because the fluctuations determined at the different stations have similar phase but different amplitudes these observations would imply that the secular shortening across the range is modulated by a seasonal strain given the geographic and climatic setting there is however a possibility that the gps positions be biased by tropospheric effects we process these data using two different software packages and two different analysis strategies our analysis shows evidence for 1 strong seasonal fluctuation of zenithal delays consistent with in situ meteorological data and two strong horizontal tropospheric gradients in particular in the ew direction that is parallel to the mountain front at gumba also detected in doris results we show that the tropospheric effects cannot however be the source of the observed seasonality of horizontal strain this study supports the view that the seasonal strain in the himalaya is real and probably driven by seasonal surface load variations our study adds support to the view that seasonal variations of seismicity in the himalaya reflects seasonal variations of geodetic strain

a radar and electrical study of tropical hot towers abstract radar and electrical measurements for deep tropical convection are examined for both break period and monsoonal regimes in the vicinity of darwin australia break period convection consists primarily of deep continental convection whereas oceanic based convection dominates during monsoonal periods associated with the monsoon trough over darwin order of magnitude enhancements in lightning flash rates for the break period regime are associated with 10 20 db enhancements in radar reflectivity in the mixed phase region of the convection compared with the monsoonal regime the latter differences are attributed to the effect of convective available potential energy cape and its nonlinear influence on the growth and accumulation of ice particles aloft which are believed to promote charge separation by differential particle motions cape in turn is largely determined by the boundary layer wet bulb temperature modest differences 1 3 c in wet bulb potential temperature between land and s

forcing of the antarctic circumpolar wave by el nino southern oscillation teleconnections we address several issues regarding the antarctic circumpolar wave acw these include the extent to which the acw is related to el nino southern oscillation enso cycles and the need to reconcile differences between the observed zonal wavenumber 2 pattern and the wavenumber 3 pattern found in coupled ocean atmosphere models in the present study we revisit the sea surface temperature sst signal of the observed acw we find that the associated sst variations may be decomposed into several empirical orthogonal functions eofs that are linearly independent the first four eofs describe 84 of the total variance on timescales of 3 7 years and superposition of sst signals of the four eofs reproduces sst signals of the observed acw given that eof analysis can only describe standing oscillations we then employ complex eof ceof analysis suitable for studying propagating waves the first two ceofs denoted ceofsst1 and 2 account for 70 of the total variance and the sst variability reconstructed from them again reproduces the observed acw the real part of ceofsst1 44 of the total variance is similar to the first real eof eofsst1 both eofsst1 and ceofsst1 may be identified with enso and have a wavenumber 2 zonal pattern in the southern middle to high latitudes ceofsst1 is the major constituent of the acw in the period of 1981 1997 the associated atmospheric circulation displays a pacific south america psa pattern statistical analyses demonstrate that the psa pattern teleconnected to enso is the major mechanism that forces this principal constituent of the acw ceofsst2 26 of the total variance has a zonal wavenumber 3 pattern in the same latitude band similar to that simulated by several coupled models we suggest that if enso is not adequately resolved in coupled models but structures with zonal wavenumber 3 pattern are then the modeled acw would appear to have a zonal wavenumber 3 pattern

holocene climate variability in antarctica based on 11 ice core isotopic records a comparison is made of the holocene records obtained from water isotope measurements along 11 ice cores from coastal and central sites in east antarctica vostok dome b plateau remote komsomolskaia dome c taylor dome dominion range d47 km105 and law dome and west antarctica byrd with temporal resolution from 20 to 50 yr the long term trends possibly reflect local ice sheet elevation fluctuations superimposed on common climatic fluctuations all the records confirm the widespread antarctic early holocene optimum between 11 500 and 9000 yr in the ross sea sector a secondary optimum is identified between 7000 and 5000 yr whereas all eastern antarctic sites show a late optimum between 6000 and 3000 yr superimposed on the long time trend all the records exhibit 9 aperiodic millennial scale oscillations climatic optima show a reduced pacing between warm events typically 800 yr whereas cooler periods are associated with less frequent warm events pacing 1200 yr

enso related variability of the southern hemisphere winter storm track over the eastern pacific atlantic sector abstract the interannual variability associated with the enso of winter storm tracks over the region extending from the eastern south pacific ocean across south america to the south atlantic ocean is described using 39 yr of data from the ncep reanalysis data base tropical sea surface temperature anomalies associated with enso induce large scale atmospheric circulation anomalies over large areas of the southern hemisphere in particular positive height anomalies dominate the bellingshausen sea during warm events and consistently a weakening of the eddy activity at low levels is found to the west of the antarctic peninsula during el nino en the storm track evidences an equatorward shift over the subtropical pacific ocean and a slight strengthening in the central atlantic ocean time lagged correlation analysis applied to anomalies of the 300 hpa meridional wind at selected base points was used to study the structure and propagation characteristics of the waves during en waves emanating from the at

spectral analysis of seismic noise induced by rivers a new tool to monitor spatiotemporal changes in stream hydrodynamics to 20 db relative to m s 2 hz for all the stations located along a steep 30 km long narrow and deeply incised channel of the trisuli river a major trans himalayan river the early summer increase in high frequency energy is modulated by a 24 h periodicity where the minimum of seismic noise level is reached around noon and the maximum is reached late in the evening a detailed study of seismic noise amplitude reveals a clear correlation with both regional meteorological and hydrological data along the trisuli river seasonal increase in ambient noise coincides with the strong monsoon rainfall and a period of rapid melting of snow and ice in the high elevations the observed 24 h cyclicity is consistent with the daily fluctuation of the precipitation and river discharge in the region river induced seismic noise is partly generated by stream turbulence but this mechanism fails to explain the observed clockwise hysteresis of seismic noise amplitude versus water level this pattern is better explained if a significant part of the observed seismic noise is caused by ground vibrations generated by bed load transport this points out the potential of using background seismic noise to quantify in continuous river bed load and monitor its spatial variations which remain difficult with classical approaches

continuous reef growth during the last 23 cal kyr bp in a tectonically active zone vanuatu southwest pacific abstract at urelapa island vanuatu sea level rise and a tectonic uplift of 3 mm yr 1 have controlled water depth and the colonization and reef development on a substrate from 23 until 6 cal kyr bp analysis of coralgal assemblages offers insights on the mode of reef growth and on water depth over the reef for the studied period those assemblages precisely dated by the 230 th 234 u method give valuable information on the rate and timing of sea level rise since the last glacial maximum the urelapa reef sequences are characterized by upwards replacement of reef frameworks which indicates changes in wave energy through time the sudden acceleration of sea level rise associated with meltwater pulse 1b at around 11 3 cal kyr bp is marked by a change in reef growth strategy from a keep up mode to a catch up mode we examine the delay in timing of the occurrence of suitable substrates the role of paleoceanographic factors and the influence of possible jumps in sea level

the surface windfield over the antarctic ice sheets the intense radiative cooling of air over the ice slopes of antarctica generates a surface wind regime that is strongly controlled by topography and plays a key role in determining the behaviour of the atmosphere and ocean in high southern latitudes1 7 resultant surface winds are intimately linked to the orientation of the ice terrain fig 1 and display the highest degree of persistence found on earth the close coupling between wind and topography allows estimation of the former if the latter is known with some precision here we report on time averaged near surface airflow over the antarctic continent during winter diagnosed from a recent accurate synthesis of terrain slopes and from estimates of the lower atmospheric temperature structure the simulated drainage pat tern exhibits strong spatial variability with the airflow concentrated into several zones near the coastal margin these confluence regions are responsible for strong persistent katabatic winds over downstream coastal stretches and are indicative of zones of greatest katabatic potential

sea level pressure variability in the amundsen sea region inferred from a west antarctic glaciochemical record using european center for medium range weather forecasts ecmwf numerical operational analyses sea ice extent records and station pressure data we investigate the influence of sea level pressure variability in the amundsen sea region on a west antarctic siple dome glaciochemical record empirical orthogonal function analysis of the high resolution siple dome multivariate ice core chemical time series record sdeof1 documents lower tropospheric transport of sea salt aerosols to the site during 1985 1994 the sdeof1 record of high low aerosol transport corresponds to anomalously low high sea level pressure slp in the amundsen sea region spatial correlation patterns between ecmwf monthly slp fields and the annual sdeof1 record suggest that a majority of sea salt aerosol is transported to siple dome during spring september october and november analysis of zonal and meridional wind fields supports the slp sdeof1 correlation and suggests the sdeof1 record is sensitive to changes in regional circulation strength no relationship is found between sea ice extent and the sdeof1 record for the period 1973 1994 to investigate the sdeof1 record prior to ecmwf coverage a spring transpolar index stpi is created using normalized slp records from the new zealand and south america antarctic peninsula sectors and is significantly correlated at least 95 c l with the sdeof1 record on an annual r 5 0 32 p 0 001 and interannual 3 years r 5 0 51 p 0 001 basis dominant periodicities 3 3 and 7 1 years in the annual sdeof1 record 1890 1994 a d suggest that a portion of the recorded interannual variability may be related tropical extratropical enso teleconnections changes in the periodic structure of the full 850 1994 a d siple dome record suggests a shift in slp forcing during the little ice age 1400 1900 a d interval

vertical motion diabatic heating and rainfall characteristics in north australia convective systems very high frequency wind profiler data are used to study the vertical draught structure within 13 tropical mesoscale convective systems mcss near darwin australia during the 1989 90 and 1990 91 wet seasons these studies are supported by single doppler radar soundings and surface rainfall data to correlate radar reflectivity thermal buoyancy and surface rainfall patterns with vertical air motion structures because of darwin s unique location at the southern tip of the maritime continent vertical draughts in both the monsoon maritime and monsoon break continental convective regimes can be observed the break regime mcss six in total were all squall lines characterized by a leading line of convection with heavy precipitation and trailing stratiform rainfall containing a characteristic radar bright band these mcss exhibited a pronounced life cycle pattern and were all sampled by the profiler in the mature to dissipating stages in contrast the monsoon systems seven in total were composed of regions of stratiform cloud with embedded convective bands which moved on shore in the monsoonal flow results from the darwin rain gauge network indicated that the majority of the total rainfall in each mcs break and monsoon was associated with the convective portion of the system the break regime mcss were all characterized by a low level 4 km updraught peak associated with convective cells on the leading edge of each squall line trailed by deeper convective updraughts in the middle and upper troposphere for the monsoon cases the lower troposphere convective updraughts were typically less than those in the squall lines yet were stronger in the upper troposphere the low level differences in the convective updraughts were consistent with the smaller virtual temperature excess in the monsoon soundings as well as the larger vertical radar reflectivity gradients observed in monsoon convection consistent with the differences in vertical air motion patterns diabatic heating and moistening profiles for the monsoon mcss were characterized by a higher level heating and drying peak compared with the break mcss the results have important implications for cumulus parametrizations in numerical models since the large scale circulation is sensitive to the vertical distribution of diabatic heating in tropical mcss