reduction in northward incursions of the south asian monsoon since 1400 ad inferred from a mt everest ice core 1 a highly resolved mt everest ice core reveals a decrease in marine and increase in continental air masses related to relatively high summer surface pressure over mongolia and reduction in northward incursions of the summer south asian monsoon since 1400 ad previously published proxy records from lower sites south of the himalayas indicate strengthening of the monsoon since this time these regional differences are consistent with a south north seesaw in convective activity in the asian monsoon region and reflect a southward shift in the mean summer position of the monsoon trough since 1400 ad the change in monsoonal circulation at 1400 ad is synchronous with a reduction in solar irradiance and the onset of the lia this demonstrates a hemispheric scale circulation reorganization at this time and the potential for future large shifts in monsoonal circulation

strontium contents of a porites coral from xisha island south china sea a proxy for sea surface temperature of the 20th century 1 a porites coral collected from xisha island south china sea represents a skeleton secreted in the period from 1906 to 1994 the sr contents of the coral vary linearly with the instrument measured sea surface temperature sst giving a sr thermometer sst 1 9658 x sr 193 26 the reconstructed sst data show that the late 20th century was warmer about 1 degreesc than the early 20th century and that two cooling 1915 1916 and 1947 1948 and three warming 1935 1936 1960 1961 and 1976 1977 shifts occurred in the century the temperature shifts are more pronounced for winters implying a close effect of the west pacific warm pool and asian monsoon and suggesting that the former is a primary force controlling the climatic system of the region results of this study and previously published data indicate a close link of temperature shifts between the boreal summer and the austral winter or the boreal winter and the austral summer the annual sst anomalies in the south china sea and the south pacific reveal the existence of harmonic but opposite sst variations between the two regions on the decadal scale the comparative annual sst anomalies for the south china sea and for the equatorial west pacific show a similarity in temperature variations implying that the south china sea climate is coherent with climatic regime of the tropical west pacific

a reconstructed dynamic indian monsoon index extended back to 1880 the authors present a reconstruction of summer june july august mean dynamic indian monsoon index dimi back to 1880 based on a large number of historical surface observation data as well as information from the upper air data the reconstruction shows a satisfying skill in terms of both the value of reduction of error and an evaluation against other independent monsoon indices the skill of reconstruction increases over time with more predictor data in particular upper level data becoming available a comparison with the observed all indian summer monsoon rainfall index airi shows a high consistence in both inter decadal and inter annual variability the reconstruction shows stronger than normal monsoon during the 1880s 1915 1925 around 1920 and 1930 1945 around 1940 as the airi the el nino southern oscillation enso monsoon relationship is reasonably captured in the reconstruction powers concentrating within quasi biennial band stand out in the reconstruction as well as in the airi a comparison of the reconstruction against an atmospheric general circulation model simulation with specified sst and external forcing agents spanning 1901 1999 indicates a slightly higher reproducibility of monsoon circulation than monsoon rainfall in terms of interannual variability the relationship between the asian continent warming and the enso monsoon connection is also discussed by using the new dynamic index

variability of the low level cross equatorial jet of the western indian ocean since 1660 as derived from coral proxies 1 using monthly seasonally resolved coral proxies from the indian ocean basin we statistically reconstruct the june july august jja low level jet in western indian ocean from 1660 1957 with skillful estimates for high and low frequencies the el nino southern oscillation enso signals are reasonably captured the strength of the jet significantly increases from the late 17th century to late 19th century the decreasing in reconstructed jet in 20th century disagrees with previous studies which indicated an enhancement of southern asian summer monsoon sasm in association with the rapid global warming the jet reconstructions are useful for understanding of sasm variability and the validation of historical monsoon simulation

a 780 year annually resolved record of indian ocean monsoon precipitation from a speleothem from south oman 1 meteorological records of monsoon rainfall in the indian ocean are generally less than 100 years long the relative brevity of these records makes it difficult to investigate monsoon variation on decadal and centennial timescales to determine what factors influence the intensity of rainfall on these timescales or to place possible changes in the twentieth century into a broader historical context development of a geologic proxy for rainfall that records annual variation in the monsoon over much longer time periods than are covered by instrumental records would be a significant step forward we have developed an annually resolved record of monsoon rainfall variation for the past 780 years based on annual layer thickness and stable isotope analyses of a laminated stalagmite from southern arabia our results show that monsoon variation over the past century is not outside of the range of the past 800 years decreasing monsoon rainfall over the past century is related to increasing sea surface temperature in the indian ocean spectral analyses of the record are dominated by cycles that are similar to those observed in records of solar activity on centurial timescales decadal to interannual cycles in the record appear to originate in the tropical pacific ocean index terms 3344 meteorology and atmospheric dynamics paleoclimatology 3354 meteorology and atmospheric dynamics precipitation 1854 1620 global change climate dynamics 3309 1699 global change general or miscellaneous keywords monsoon paleoclimate rainfall indian ocean speleothem oxygen isotopes

measurements of turbulence transfer in the near surface layer over the antarctic sea ice surface from april through november in 2016 the surface energy budget over the antarctic sea ice from 8 april 2016 through 26 november 2016 are presented from april to october sensible heat flux sh and subsurface conductive heat flux g were the heat source of surface while latent heat flux le and net radiation flux rn were the heat sink of surface our results showed larger downward sh due to the warmer air in our site and upward le due to the drier air and higher wind speed in our site compared with sheba data however the values of sh in n ice2015 campaign which located at a zone with stronger winds and more advection of heat in the arctic were comparable to our results under clear skies the values of aerodynamic roughness length z0m and scalar roughness length for temperature z0h being 1 9 10 3 m and 3 7 10 5 m were suggested in this study it is found that snow melting might increase z0m our results also indicate that the value of log z0h z0m was related to the stability of stratification in addition several representative parameterization schemes for z0h have been tested and a couple of schemes were found to make a better performance

parametrizing the antarctic stable boundary layer synthesizing models and observations the accurate representation of the stable boundary layer sbl is a key issue for weather prediction and climate models the sbl exerts a crucial influence controlling heat moisture and momentum fluxes between the surface and the rest of the atmosphere some of the world s most stably stratified boundary layers develop on the antarctic continent the british antarctic survey has observed the boundary layer at their halley station for the past several decades previous work investigating stable boundary layers has tended to take either a purely observational or purely modelling based approach in this thesis a novel three way methodology has been developed which uses the halley observations alongside single column model scm and large eddy simulation les techniques to examine two case studies the les and observations were first used together to establish the correct initial conditions and forcings for each case study very close agreement was generally achieved between the les and observations particularly for the first case study this approach represents a powerful framework for verifying scm and les results against a range of in situ observations the choice of stability function is an important decision for column based parameterizations of the sbl four schemes were tested in the scm providing persuasive evidence for the use of shorter tailed stability functions the les data was also used to extract implied stability functions these experiments reinforced the conclusion that shorter tailed stability functions offered improved performance for the antarctic stable boundary layer the wind turning angle was defined as the difference between the geostrophic and near surface wind directions a slightly larger wind turning angle was found with the les and scm results presented in this thesis as compared to previous work this difference might be explained by the shallowness of

flow of variably fluidized granular masses across three dimensional terrain 2 numerical predictions and experimental tests numerical solutions of the equations describing flow of variably fluidized coulomb mixtures predict key features of dry granular avalanches and water saturated debris flows measured in physical experiments these features include time dependent speeds depths and widths of flows as well as the geometry of resulting deposits three dimensional 3 d boundary surfaces strongly influence flow dynamics because transverse shearing and cross stream momentum transport occur where topography obstructs or redirects motion consequent energy dissipation can cause local deceleration and deposition even on steep slopes velocities of surge fronts and other discontinuities that develop as flows cross 3 d terrain are predicted accurately by using a riemann solution algorithm the algorithm employs a gravity wave speed that accounts for different intensities of lateral stress transfer in regions of extending and compressing flow and in regions with different degrees of fluidization field observations and experiments indicate that flows in which fluid plays a significant role typically have high friction margins with weaker interiors partly fluidized by pore pressure interaction of the strong perimeter and weak interior produces relatively steep sided flat topped deposits to simulate these effects we compute pore pressure distributions using an advection diffusion model with enhanced diffusivity near flow margins although challenges remain in evaluating pore pressure distributions in diverse geophysical flows riemann solutions of the depth averaged 3 d coulomb mixture equations provide a powerful tool for interpreting and predicting flow behavior they provide a means of modeling debris flows rock avalanches pyroclastic flows and related phenomena without invoking and calibrating rheological parameters that have questionable physical significance

some measurements of turbulence over an antarctic ice shelf profiles of wind speed temperature and turbulent fluxes of heat and momentum in the lowest 32 m have been measured at a station on an antarctic ice shelf during the antarctic winter the surface layer often shows strong static stability with temperature gradients as large as 1 km 1 in the lowest few metres the surface inversion is destroyed during periods of high wind speed but the wind profile shows significant deviation from the expected logarithmic form under such conditions measurements of stress at 5 m indicate that the roughness length of the snow surface is about lo 4 m at 5 m height the variations of the dimensionless wind shear m and potential temperature gradient t agree with previously determined forms of the monin obukhov similarity functions above 5 m the behaviour of m and t is only qualitatively similar and surface layer similarity theory does not provide a good description of the profiles turbulence length scales have been deduced from vertical velocity power spectra under near neutral conditions the ratio of turbulence length scale to measurement height is observed to decrease with increasing height of measurement this observation is consistent with the variation of turbulence length scale with height implied by the measurements of m it is suggested that the stability of the overlying atmosphere restricts the depth of the turbulent boundary layer and hence the length scales of turbulence within this layer increasing stability causes a decrease of turbulence length scales at all levels the ratios of turbulence kinetic energy to stress and temperature variance to heat flux are examined measurements are somewhat scattered but the distribution of values varies little with height or stability the form of the distribution suggests that large scale motions possibly internal gravity waves may be playing an important role in boundary layer processes

the seasonal cycle of sublimation at halley antarctica we have used micrometeorological data collected at halley research station antarctica to estimate monthly totals of snow sublimation direct sublimation from the snow surface is calculated using bulk transfer formulae while the sublimation of blowing snow is estimated using a model for suspended particle number density and individual particle sublimation rates during the winter months sublimation losses are negligible but between november and march sublimation removes around 25 of the snowfall surface sublimation and sublimation of blowing snow make roughly equal contributions to this total estimates of sublimation using micrometeorological data agree well with estimates made from daily snow stake measurements

monsoon tropical ocean interaction in a network of coral records spanning the 20th century abstract the 20th century evolution of basin wide gradients in surface ocean properties provides one essential test for recent models of the interaction between the asian monsoon and the tropical ocean because various feedback mechanisms should result in characteristic regional patterns of variability although the instrumental record of climate variability in the tropics is essentially limited to the last few decades the stable isotopic composition of living corals provides an effective means for extending the instrumental observations here we present two coral isotopic records from the indonesian maritime continent and we use these records with other previously published records to describe i the relationship between western pacific and central pacific climate variability over the past century with special emphasis on the biennial band and ii the strength of the west east indian ocean dipole we find that the amplitude of the biennial cycle in the pacific did not vary inversely with the strength of enso el nino southern oscillation as might be expected from some models of monsoonal feedback on the central pacific instead the biennial variability was modulated on decadal timescales throughout much of the pacific we also show that the zonal oxygen isotopic gradient in the indian ocean coral records was significantly correlated with central pacific sea surface temperature on a variety of timescales thus it is likely that this coral dipole was a product of strong enso like teleconnections over the indian ocean as opposed to being the result of unique indian ocean or monsoonal dynamics

granular mass flows and coulomb s friction in shear cell experiments implications for geophysical flows 1 granular mass flows of rock fragments are studied in the lab by means of a high speed video camera at 2000 frames per second these granular flows are generated using beds of pumice fragments positioned on a rough rotating disk whose angular velocity is controlled by a motor the experimental apparatus allows an understanding of the arrangement of the particles in granular mass flows with relatively small and relatively large values of the savage number the savage number represents the ratio between grain collision stresses and gravitational grain contact stresses in particular these flows develop a basal layer of agitated and colliding particles underneath a relatively rigid upper layer our experimental results suggest the validity on average of the coulomb s relationship between shear and normal forces at the base of granular mass flows irrespective of their savage number value in coulomb s equation the shear stresses do not depend on the shear rate we expect the coulomb friction law to be valid also in moving pyroclastic flows our experiments suggest that the collisions and subsequent comminution of pumice fragments in moving pyroclastic flows could provide ash for the overriding ash clouds in our experiments the amount of ash generated by particle particle and particle boundary interactions increases as the value of the savage number increases in nature part of this ash may also simply move toward the base of the flows because of kinetic sieving

interaction between the enso and the asian monsoon in a coral record of tropical climate the oxygen isotopic composition of a banded coral from the western equatorial indian ocean provides a 150 year long history of the relation between the el nino southern oscillation enso phenomenon and the asian monsoon interannual cycles in the coral time series were found to correlate with pacific coral and instrumental climate records suggesting a consistent linkage across ocean basins despite the changing frequency and amplitude of the enso however decadal variability that is characteristic of the monsoon system also dominates the coral record which implies important interactions between tropical and midlatitude climate variability one prominent manifestation of this interaction is the strong amplitude modulation of the quasi biennial cycle

correlation between the oxygen isotope record from dasuopu ice core and the asian southwest monsoon during the last millennium long high resolution proxy records are valuable for understanding asian southwest monsoon asm dynamics on decadal to centennial timescales a millennium long d 18 o ice core record from the central himalayas provides an opportunity to study the asm variability on decadal to centennial timescales the dasuopu ice core d 18 o record indicates that a relatively warm period corresponding with the medieval warm period lasted from ad 1140s to 1390s a notable warming trend is apparent from 1800s to 1990s and several cool periods occurred between ad 1010 1130s 1290 1330s 1400 1460s 1520s 1590 1630s 1740s and 1770 1790s comparisons with other high resolution monsoon proxy records from the arabian sea south oman and southern china reveal a high correspondence between temperature changes in the central himalayas and the asm variability during the last 1000 years a pronounced warming trend since ad 1670 coincides with an abrupt transition from a weak to a strong intensity of the asm the thermal conditions in the himalayas and on the tibetan plateau and associated glacial boundary conditions may have been predominantly responsible for variations of the asm intensity and for a latitudinal movement in the mean position of the itcz on decadal to centennial timescales r 2007 elsevier ltd all rights reserved

a numerical model of blowing snow around an antarctic building the accumulation of drifting snow around buildings in regions of severe climate has important implications on their design and location this paper studies one such building at a station run by the british antarctic survey and located on the brunt ice shelf at the edge of the antarctic continent four previous stations have bccn built in the area the buildings of which werc designed to becomc covercd in snow and all have been crushed within a few years the current station halley v consists of three buildings which are all raised from the ice shelf by means oflegs they were designed in such a way that the action of the wind blowing underneath the buildings would keep them clear of snow this paper describes a model which predicts the shape and position of drift formation and then compares the results with those observed at halley this modd is a first attempt to address the problem and as such the paper can be considered to be a progress report improvements arc currently being made as part of continuing research it is found that there is some qualitative agreement and possible reasons for a few quantitative discrepancies are discussed both the model and the true data show clearly that the new design is very effective in prolonging the useful life of the buildings

deep soil temperature as proxy for surface air temperature in a coupled model simulation of the last thousand years 1 the relationship between terrestrial deep soil temperature tdst and surface temperature sat at interannual and centennial timescales has been investigated in a simulation of the last millennium with a three dimensional climate model driven by estimations of historical external forcing tdst is loosely related to borehole temperature profiles which have been recently used to reconstruct long term temperature trends in the last centuries recently questions about the validity of boreholes based reconstructions have been raised in the simulation at interannual time scales the connection between tdst and sat is stable being stronger in the summer half year than in the winter half year at long timescales annual tdsl is a good proxy for annual sat and their variations are almost indistinguishable from each other both tdsl and terrestrial sat overestimate the variations of global mean sat this may be a source for the disagreement between statistical reconstructions of global sat and terrestrial borehole measurements

solar influence on the indian ocean monsoon through dynamical processes 1 the result of paleoclimate studies on the relationship between the indian monsoon and solar activity inferred from the analysis of stalagmites in oman is confirmed by using a modern meteorological dataset from 1958 1999 the present result suggests that the solar influence on monsoon activity is not due to a change in radiative heating in the troposphere but rather originates from the stratosphere through modulation of the upwelling in the equatorial troposphere which produces a north south seesaw of convective activity over the indian ocean sector during summer higher precipitation over arabia and india thus occurs during high solar activity

depressurization of fine powders in a shock tube and dynamics of fragmented magma in volcanic conduits abstract samples of fine glass beads mean grain size equal to 38 and 95 m have been depressurized within a vertical shock tube these short lived rapid decompressions resemble discrete cannon like vulcanian explosions and produce two phase flows that are inhomogeneous in density in both vertical and horizontal directions because of the presence of bubble like heterogeneities we suggest that also volcanic flows may present similar inhomogeneities in density in the experimental apparatus the flow velocities increase from approximately 1 to 13 m s when the pressure drop increases from approximately 200 to 900 mbar a physical model of the initial velocities of expansions in the shock tube has been applied to a range of volcanic overpressures between 0 1 and 20 mpa suggesting initial velocities of volcanic flows caused by the removal of a rock plug in volcanic conduits between 25 and 400 m s during the experiments at large pressure drops as the mixture expands and moves up the tube the flow front becomes highly irregular and bubble like heterogeneities form the shape of these bubbles becomes distorted and stretched in the turbulent flow during the experiments at relatively small pressure drops the sample oscillates when the particles after the expansion flow back and bounce upward again jets with diameter smaller than that of the tube are ejected from the oscillating samples generating independent pulses large bubble like heterogeneities whose diameter is a significant fraction of the tube diameter can also discretize the flows similar mechanisms in real volcanoes may produce pulse like ejections of gas particle mixtures out of the vent

antarctic boundary layer parametrization in a general circulation model 1 d simulations facing summer observations at dome c the parametrization of the atmospheric boundary layer abl is critical over the antarctic plateau for climate modelling since it affects the large scale temperature inversion and the katabatic winds this study challenges state of the art parametrizations used in general circulation models to represent the clear sky summertime diurnal cycle of the abl at dome c antarctic plateau the laboratoire de meteorologie dynamique zoom model is run in a 1d configuration on the fourth gewex atmospheric boundary layers study case simulations are analysed and compared to observations giving insights into the sensitivity of one model that participates to the intercomparison exercise snow albedo and thermal inertia are calibrated leading to better surface temperatures using the so called thermal plume model improves the momentum mixing in the diurnal abl in stable conditions four turbulence schemes are tested best simulations are those in which the turbulence cuts off above 35m in the middle of the night highlighting the contribution of the longwave radiation in the abl heat budget however the nocturnal surface layer is not stable enough to distinguish between surface fluxes computed with different stability functions the absence of subsidence in the forcings and an underestimation of downward longwave radiation are identified to be likely responsible for a cold bias in the nocturnal abl apart from model specific improvements the paper clarifies on which are the critical aspects to improve in general circulation models to correctly represent the summertime abl over the antarctic plateau

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

measurement and parameterization of aerodynamic roughness length variations at haut glacier d arolla switzerland spatial and temporal variations in aerodynamic roughness length z0 on haut glacier d arolla switzerland during the 1993 and 1994 ablation seasons are described based on measure ments of surface microtopography the validity of the microtopographic z0 measurements is established through comparison with independent vertical wind profile z0 measurements over melting snow slush and ice the z0 variations are explained through correlation and regression analyses using independent measurements of meteorological and surface variables and parameterizations are developed to calculate z0 variations for use in surface energy balance melt models several independent variables successfully explain snow z0 variation through their correlation with increasing surface roughness caused by ablation hollow formation during snow melt non linear parameterizations based on either accumulated melt or accumulated daily maximum temperatures since the most recent snowfall explain over 80 of snow z0 variation the z0 following a fresh snowfall on an ice surface is parameterized based on relationships with the underlying ice z0 snow depth and accumulated daily maximum temperatures none of the independent variables were able to successfully explain ice z0 variation although further comparative studies are needed the results lend strong support to the microtopo graphic technique of measuring z0 over melting glacier surfaces

modes of climate variability synthesis and review of proxy based reconstructions through the holocene abstract modes of climate variability affect global and regional climates on different spatio temporal scales and they have important impacts on human activities and ecosystems as these modes are a useful tool for simplifying the understanding of the climate system it is crucial that we gain improved knowledge of their long term past evolution and interactions over time to contextualise their present and future behaviour we review the literature focused on proxy based reconstructions of modes of climate variability during the holocene i e the last 11 7 thousand years with a special emphasis on i proxy based reconstruction methods ii available proxy based reconstructions of the main modes of variability i e el nino southern oscillation pacific decadal variability atlantic multidecadal variability the north atlantic oscillation the southern annular mode and the indian ocean dipole iii major interactions between these modes and iv external forcing mechanisms related to the evolution of these modes this review shows that modes of variability can be reconstructed using proxy based records from a wide range of natural archives but these reconstructions are scarce beyond the last millennium partly due to the lack of robust chronologies with reduced dating uncertainties technical issues related to proxy calibration and difficulty elucidating their stationary impact or not on regional climates over time while for each mode the available reconstructions tend to agree at mutidecadal timescales they show notable disagreement on shorter timescales beyond the instrumental period the reviewed evidence suggests that the intrinsic variability of modes can be modulated by external forcing such as orbital solar volcanic and anthropogenic forcing the review also highlights some modes experience higher variability over the instrumental period which is partly ascribed to anthropogenic forcing these features stress the paramount importance of further studying their past variations using long climate proxy records for the progress of climate science

aircraft observations of the ekman layer during the joint air sea interaction experiment results are presented from an observational study of the mid latitude atmospheric boundary layer over the sea the data were obtained mainly by instrumented aircraft as part of the joint air sea interaction experiment jasin the eight occasions chosen for study are characterized by small surface buoyancy fluxes and the conditions are well described as near neutral and barotropic in the absence of low level inversions a well mixed ekman layer is observed on each occasion but is limited to a depth of approximately 0 2u f accurate measurements of horizontal gradients including pressure together with improved wind observations and turbulent flux measurements enabled each of the terms of the momentum balance to be evaluated throughout the depth of this layer these terms were found to balance quite closely were well described by ekman scaling and were consistent with the requirements of the measured turbulent kinetic energy balance the latter suggests that the main shear production terms are dissipated locally and that little is exported to upper levels in the ekman layer to enable significant deepening by entrainment although only a slight increase in instability appears to be needed to alter this balance conditions in which such boundary layer structure might be observed are suggested values of various coefficients used in schemes for relating surface fluxes to mean quantities cd ce cg a b are derived and compared with previous measurements spectral analysis reveals that most of the turbulent transport is confined to a distinct high wavenumber region whose characteristics vary as a function of ekman layer depth and stability parameters this is superimposed on larger scale fluctuations which do not vary appreciably within the ekman layer and which therefore dominate the variances in the upper regions as the intensity of the smaller scale turbulence decreases strongly with height finally further implications of this interpretation are discussed with particular reference to the heat and water vapour balance these imply that removal of water vapour from the ekman layer is accomplished by transfer related to cloud activity marking a significant change in the mechanism of turbulent transport at the top of this layer the relationship between these and similar results obtained concurrently by different methods is also discussed

palaeoclimatic interpretation of high resolution oxygen isotope profiles derived from annually laminated speleothems from southern oman high resolution stable isotope profiles of three contemporaneously deposited stalagmites from a shallow cave in southern oman provide an annually resolved record of indian ocean monsoon rainfall variability for the past 780 years uranium series age dating and counts of annual growth bands enable an excellent age calibration although modern speleothems do not grow in perfect isotopic equilibrium oxygen isotope ratios 18o are a proxy for the amount of monsoon rainfall this is supported by the statistically significant correlation between 18o and the thickness of annual bands whereas 18o is inversely correlated with annual band thickness additionally overlapping 18o profiles are very similar in pattern and range indicating that sample specific noise did not blur the climatic signal the longest oxygen isotope profile derived from stalagmite s3 clearly shows the transition at 1320 ad from a generally wetter medieval warm period to a drier little ice age that lasted from approximately ad 1320 1660 in southern oman the decrease in monsoon rainfall since the 1960s is also obvious in meteorological records from northern africa and india indicating that our speleothem based rainfall records do not only reflect local monsoon rainfall variability

east asian monsoon evolution and reconciliation of climate records from japan and greenland during the last deglaciation abstract east asian monsoon eam evolution during the last deglaciation has been shown repeatedly to be aligned with paleoclimatic changes in the north atlantic based on climate reconstructions comparing asian speleothem records with greenland ice cores in contrast to this finding paleoclimatic reconstructions based on lake suigetsu sediment cores suggest that past eam variability in japan was not always coherent with climatic variability recorded in greenland ice cores we resolve this discrepancy using an absolute dated stalagmite 18 o record that covers the period between 15 5 and 10 7 thousand years before present ka before ad 1950 this stalagmite record is from nearby maboroshi cave japan and shows climate changes that are synchronous with those of chinese caves and greenland ice cores our results support an effective teleconnection between low and high latitudinal climate systems during the transitions into the bolling allerod ba warming at 14 6 ka and the younger dryas cooling at 12 8 ka in the north atlantic however our results also indicate monsoonal intensification during the ba coincident with decreasing temperatures in greenland from 14 6 to 12 8 ka we explain this decoupling as a result of the interhemispheric bipolar seesaw climate system discrepancies between lake suigetsu radiocarbon age data sets and other radiocarbon calibration archives can also be removed when our maboroshi record is used to adjust the lake suigetsu age model as well as resolving temporal ambiguities in the lake suigetsu paleoclimate record

high resolution palaeoclimatology of the last millennium a review of current status and future prospects this review of late holocene palaeoclimatology represents the results from a pages clivar intersection panel meeting that took place in june 2006 the review is in three parts the principal high resolution proxy disciplines trees corals ice cores and documentary evidence emphasizing current issues in their use for climate reconstruction the various approaches that have been adopted to combine multiple climate proxy records to provide estimates of past annual to decadal timescale northern hemisphere surface temperatures and other climate variables such as large scale circulation indices and the forcing histories used in climate model simulations of the past millennium we discuss the need to develop a framework through which current and new approaches to interpreting these proxy data may be rigorously assessed using pseudo proxies derived from climate model runs where the answer is known the article concludes with a list of recommendations first more raw proxy data are required from the diverse disciplines and from more locations as well as replication for all proxy sources of the basic raw measurements to improve absolute dating and to better distinguish the proxy climate signal from noise second more effort is required to improve the understanding of what individual proxies respond to supported by more site measurements and process studies these activities should also be mindful of the correlation structure of instrumental data indicating which adjacent proxy records ought to be in agreement and which not third large scale climate reconstructions should be attempted using a wide variety of techniques emphasizing those for which quantified errors can be estimated at specified timescales fourth a greater use of climate model simulations is needed to guide the choice of reconstruction techniques the pseudo proxy concept and possibly help determine where given limited resources future sampling should be concentrated

experiments on the flow behaviour of granular materials at high velocity in an open channel a series of laboratory flume experiments has been conducted to investigate the flow behaviour of dry sand at high velocities the first incentive for this experimental programme was an attempt to explain the high mobility of apparently dry masses of rapidly moving broken rock during rock avalanches sturzstroms test velocities of over 5 m s and most other parameters of the tests were found to be dimensionally similar to those for a typical rock avalanche yet the conclusion was negative even the most rapid of the experiments indicated flow behaviour which is in conformity with the constant volume uniform coulomb friction relationship as applicable to slow shearing this conclusion was confirmed independently both by direct measurements of base friction and mean density of the flows and by detailed observations of flow uniformity acceleration and velocity profiles the surprising mobility of st umlrzstroms therefore requires a different explanation une serie de tests a canaux a ete entreprise dans le

a glimpse of the quaternary monsoon history from india and adjoining seas abstract the evolution of the monsoon is briefly summarized taking into account previous studies conducted on both terrestrial and marine records recovered from the indian subcontinent and the adjoining seas while the initiation of the monsoon is debated it seems clear that a major intensification of the summer monsoon occurred at 8 2 ma a seasonal monsoon circulation with distinct summer and winter monsoon phases was established at 2 8 ma in the late quaternary the summer monsoon weakens during glacial periods as compared to interglacial periods the centennial to sub centennial scale changes in the monsoon during both glacial and interglacial periods suggest strong links between high latitude processes and the tropical monsoon and its role in modulating northern hemispheric climate the glacial terminations are marked by weak monsoon activity the summer monsoon weakened during the middle holocene after the early holocene optimum a change in the monsoon intensity though alters the salinity of the seas surrounding india the quantitative paleosalinity reconstructions still have large associated uncertainties and an effort should be made to lower them

modelling temperature variations in polar snow using daisy a physics based snow model has been calibrated using data collected at halley bay antarctica during the international geophysical year variations in snow temperature and density are well simulated using values for the model parameters within the range reported from other polar field experiments the effect of uncertainty in the parameter values on the accuracy of the predictions is no greater than the effect of instrumental error in the input data thus this model can be used with parameters determined a priori rather than by optimization the model has been validated using an independent data set from halley bay and then used to estimate 10 m temperatures on the antarctic peninsula plateau over the last half century

wind profiles in the stable boundary layer and the effect of low relief wind profiles through the stable boundary layer are presented the data were collected at a site located in a shallow river valley and show evidence of upstream effects near the edge of the valley the wind speed profiles are consistent with a non dimensional shear om 1 3z l for z l 0 5 changes in wind speed and direction are found to occur over a greater depth than the depth of the turbulent nocturnal boundary layer estimated from various diagnostic formulae

studies of internal gravity waves at halley base antarctica using wind observations at halley base which is situated on the brunt ice shelf in antarctica internal gravity waves are frequently observed in the stably stratified atmospheric boundary layer in this paper time series of wind speed and direction at a height of 8 m observed from three meteorological masts are used to determine some of the physical properties of the waves such as their wavelengths phase speeds and directions of propagation the relationship of the results to various theories of the generation of internal gravity waves is considered it is shown that the waves do not usually propagate in the direction of the surface wind typically the direction of propagation is rotated about 45 clockwise from the wind vector the waves most frequently propagate from a direction of about 135 which is perpendicular both to the hinge line line where the ice shelf meets the land and to the ridges in the ice shelf suggesting a topographic influence it is shown that the waves obey a dispersion relation similar to that for neutral trapped internal gravity waves

use of conventional stability parameters during swell the situation with swell is of climatological importance over the baltic sea since swell is present during as much as 40 of the time in this study two periods with unstable and two periods with stable stratification and wind following swell are investigated data are taken at a small flat island in the baltic sea during unstable stratification the turbulent structure shows great resemblance to the free convective boundary layer and scales with the boundary layer height since surface heat flux is too small to support the high levels of turbulence present inactive turbulence is probably the dominating source for the stably stratified layer there are smaller differences between data with and without swell the turbulence is mainly transported upward into the atmosphere with the aid of pressure fluctuations induced by the waves for most of the data with swell the gradients are smaller than for growing sea during unstable conditions the wind gradients are negative indicating the presence of a wave driven wind the gradients increase with increasing height above the surface the drag coefficient is smaller than is usually found for both stable and unstable stratification and varies very little with wind and stratification there are only small variations in the heat transfer coefficients with changing stratification but they are significantly different for stable and unstable stratification

the dynamics of idealized katabatic flow over a moderate slope and ice shelf summary a non hydrostatic numerical weather prediction model has been employed to simulate idealized katabatic flows over a moderate slope and adjoining ice shelf the topography of coats land and the adjoining brunt ice shelf antarctica has been used this is typical of much of the antarctic coastline the regional atmospheric modeling system version 4 3 has been adapted for simulations over compacted snow most notably through changes to the multi layer soil model the simulations are initialized using clear sky conditions and at rest on the slope a shallow katabatic flow develops the winds becoming approximately steady on the slope by 12 h the peak downslope winds are about 7 m s 1 at 30 m above the snow surface the katabatic flow depth ranges from 50 to 100 m down the slope over the ice shelf the katabatic flow peters out while a pool of cold air develops primarily through sensible heat loss into the surface and partially balancing the net radiative heat loss to space near surface and sounding data from the model simulations compare well with archetypal and typical katabatic flow observations especially after some tuning of the model s turbulence parametrization an analysis of the downslope flow dynamics shows the buoyancy force is generally balanced by the inertial force except towards the foot of the slope where it is balanced by upslope forces related to gradients in the potential temperature deficit and katabatic layer height caused by the pool of cold air over the ice shelf over time the cooling of the ice shelf boundary layer leads to an apparent retreat of the katabatic flow from the ice shelf and some way up the slope the dynamical analysis explains the surface climatology observed such that the persistent katabatic winds of coats land rarely reach the brunt ice shelf the simulated katabatic flow moves from shooting to tranquil towards the foot of the slope this transition acts to trigger a train of internal gravity waves which propagate energy upwards away from the katabatic flow jump previous studies have also found shooting to tranquil katabatic flow transitions so to generalize these findings would suggest that internal gravitywave generation is ubiquitous around much of coastal antarctica and greenland

control of near surface winds over an antarctic ice shelf simple models are used to assess the factors controlling near surface winds over an antarctic ice shelf observations from halley station and an automatic weather station situated close to the coastal slopes adjoining the brunt ice shelf are presented these suggest that katabatic flows originating over the continental slopes adjust more quickly to the regional easterly flow over the ice shelf than is predicted by these simple models it is suggested that nonlinear mechanisms such as hydraulic jumps or internal gravity wave radiation could lead to flow adjustment on the short space and time scales observed in contrast with the present observations katabatic flows have been observed to propagate across the ross ice shelf for great distances with little modification however in this latter region the topography favors the formation of intense channeled katabatic flow while the katabatic flow onto the brunt ice shelf is unconfined and consequently much weaker

supercritical channel flow in the coastal atmospheric boundary layer idealized numerical simulations numerical simulations of supercritical coastal flows were performed with a three dimensional nonlinear hydrostatic meso scale model with a higher order turbulence closure the purpose was to resolve questions from previous studies related to terrain forcing idealized terrain representing northern california was used this facilitated testing of hypotheses in a simple fashion it was found that the angle by which the coast turns away from the flow regulates the acceleration in the expansion fan and determines how far downstream the maximum in the wind speed is located simulations with curved coastlines confirmed that the gradual curvature of the coastal mountains north of cape mendocino is sufficient to excite an expansion fan a decreasing height of the terrain along the coast lead to an increased acceleration of the flow largest when the slope of the terrain was confined to the change in coastline orientation a cape perpendicular to the main coastal mountains significantly blocked the flow even when as low as half the upstream marine atmospheric boundary layer mbl depth moreover a realistic cape caused gravity wave breaking these simulations confirmed that the local terrain at cape mendocino is responsible for the collapse of the mbl in shelter cove one striking feature in this study was that the flow started to accelerate far upstream of the change in coastline orientation even in supercritical conditions this phenomenon was most pronounced in the cases with the highest wind speeds using normalized wind speed and the bernoulli function from calculated back trajectories it was concluded that this feature is not due to deviations from linearity or from the shallow water concept

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

deuterium excess record in a southern tibetan ice core and its potential climatic implications a 55 m long ice core drilled close to bedrock from mt noijin kangsang on the southern tibetan plateau in summer 2007 was annually dated covering the period of 1864 2006 ad the stable isotope ratios 18o and d of the ice core were measured and thereby the deuterium excess d was calculated by d d 8 18o for the individual ice samples results show that the d values of the ice samples were predominantly controlled by the moisture sources the significant increasing trend of annual mean d values along the ice core is mainly related to the rapid warming of the tropical indian ocean although the tendency is subjected to the modulation by the western derived moisture the decreasing indian monsoon precipitation on the southern tibetan plateau physically linked with the increasing tropical indian ocean sst reduced the share of monsoon precipitation in the annual total accumulation making an additional contribution to the significant increase of annual mean d in the noijin kangsang ice core with high values during the past 143 years

past monsoon rainfall variations in peninsular india recorded in a 331 year old speleothem an actively growing stalagmite collected from a cave located in the hills of the western ghats in the uttar kannada district of karnataka india has been studied for stable isotope ratios of oxygen and carbon width of growth layers and grey level changes distinct carbonate layers alternate coarse and compact are seen in cross section each couplet of compact and coarse layer is found to represent a single year a total of 331 such couplets has been counted indicating that the stalagmite started growing in ad 1666 and continued until it was sampled stable isotope ratios of oxygen i 18o and carbon i 13c show variations ranging from 13 6 to 7 9 and from 2 7 to 1 6 respectively we have reconstructed past rainfall changes of the cave site using the amount effect in i 18o of rain speleothem i 18o and instrumental rainfall data from the associated climate subdivision show a significant correlation r 0 62 decadal average several sharp spikes of enrichment and depletion in 18o are indicative of the past deficiency and excess in rainfall most of the severe drought years recorded independently by meteorological observations are found registered in the stalagmite layers during the 331 year period rainfall was highest at ad 1666 and lowest around ad 1900 the stalagmite generated past rainfall record can serve as a reasonable proxy for testing monsoon models