modelling glacial climatic millennial scale variability related to changes in the atlantic meridional overturning circulation a review abstract since the discovery of glacial abrupt variability in greenland and the north atlantic about two decades ago its modelling remains a conceptual and technical challenge while the global climatic signature of heinrich events can reasonably be ascribed to the fresh water discharge related to the massive iceberg armadas released by the laurentide ice sheet in the north atlantic the existence of such a triggering mechanism is elusive as far as dansgaard oeschger type variability is concerned even if other mechanisms have been proposed the majority of modelling attempts to better understand glacial climate variability has assumed it to be linked to abrupt variations in the atlantic meridional overturning circulation amoc in this review we introduce the rationale behind this approach i e the possible existence of several deep ocean circulation equilibria associated with distinct climate signatures we then review the published fresh water hosing experiments and the mechanisms at work to explain the climate differences related to the different amoc states most of these works have been performed under pre industrial boundary conditions the few hosing experiments run under glacial conditions show that the sensitivity of the climate system to fresh water hosing is very dependent on the background climate state in order to rigourously compare several types of experiments equilibrium runs vs transient runs with pre industrial vs glacial boundary conditions we present experiments especially run for this review with two climate models of intermediate complexity uvic and loveclim although there are similarities between the responses simulated by these models there are also many differences which would benefit being compared to reconstructions such as those presented in this special issue however a strict comparison will require to consider boundary conditions as realistic as possible for marine isotopic stage 3 modelling glacial variability to compare model results with paleoclimatic data remains a big challenge

spatial fingerprint and magnitude of changes in the atlantic meridional overturning circulation during marine isotope stage 3 pronounced millennial scale climate variability during marine isotope stage 3 mis3 is considered to be linked to changes in the state of the atlantic meridional overturning circulation amoc i e a warm interstadial cold stadial state corresponds to a strong weak amoc based on a series of freshwater hosing extraction experiments with the state of the art community climate system model version 3 we construct a global spatial fingerprint of oceanic temperature anomalies in response to amoc changes under mis3 boundary conditions highest sensitivity to amoc changes especially in summer is found in northeastern north atlantic sea surface temperature but a characteristic temperature fingerprint is also found at subsurface levels after testing significance of the linear sea surface temperature sst amoc regressions the model results are combined with paleo sst records to estimate the magnitude of millennial scale dansgaard oeschger amoc variations during mis3 the results suggest a mean difference in amoc strength between interstadial and non heinrich stadial states of 9 2 1 2 sv 1

dendrogeomorphic reconstruction of past snow avalanche events in bâlea glacial valley făgăras massif southern carpathians romanian carpathians abstract snow avalanches are a major hazard in the southern carpathians romanian carpathians and cause damage to transportation routes or infrastructure and losses of human lives in these mountains the scientific understanding of avalanches is still poor the main objectives of this study were to reconstruct spatio temporal patterns of avalanche events to complement written records in the b lea glacial valley located in the central part of northern slope of the f g ras massif and to identify the winter weather conditions responsible for avalanche occurrence using a dendrogeomorphologic approach the analysis was based on tree ring series from 293 affected picea abies trees in four avalanche tracks our results from tree ring records yielded 24 and 17 snow avalanches in the 1867 2012 chronology in first and second track 24 and 12 snow avalanches in the 1870 2012 chronology in third and in fourth track the tree ring based analysis of the 586 extracted increment cores allowed the identification of 853 growth disturbances related to past avalanche activity the most frequent response is found as reaction wood 64 1 followed by abrupt growth changes 20 6 traumatic resin ducts 13 and callus tissue 2 3 a total of 77 event years with aai 10 were reconstructed the reconstruction revealed five high magnitude avalanches aai 30 25 medium magnitude avalanches 20 aai 30 and 47 small magnitude avalanches 10 aai 20 the return period values vary between 16 7 and 23 6 years based on the reconstructed chronologies our analyses identified 13 cases of synchronicity of events with aai 10 this synchronicity indicates the decisive role of local weather conditions which are responsible for the occurrence of extreme snow avalanches the weather conditions triggering extreme avalanche correspond with high amounts of snowfall and consequently thick snowpack even if the largest snowfalls are not necessarily associated with extreme avalanches

timing of millennial scale climate change at siple dome west antarctica during the last glacial period using atmospheric methane and the isotopic composition of o2 as correlation tools we place the dd record of ice from the siple dome west antarctica ice core on a precise common chronology with the gisp2 greenland ice core for the period from 9 to 57 ka the onset of major millennial warming events in siple dome preceded major abrupt warmings in greenland and the pattern of millennial change at siple dome was broadly similar though not identical to that previously observed for the byrd ice core also in west antarctica the addition of siple dome to the database of well dated antarctic paleoclimate records supports the case for a coherent regional pattern of millennial scale climate change in antarctica during much of the last ice age and glacial interglacial transition

changing influence of antarctic and greenlandic temperature records on sea level over the last glacial cycle we use a simple model to analyse the relationship between ice core temperature proxy data and global ice volume eustatic sea level data over the last glacial cycle lgc by allowing the temperature forcing to be a mix of greenlandic and antarctic signals we optimise the proportion of this mixing to fit sea level data we find that sea level forcing is best represented by a mix of antarctic and greenlandic temperature signals through the whole glacial cycle we suggest that a distinct bipolar switch occurs which links eustatic sea level more closely with the antarctic like variability during the glacial period mis 4 3 and 2 and more closely to the greenland like variability during the last termination ti and the interglacial periods holocene and mis 5 this switch may be caused by the spatio temporal distribution of ice sheet collapse perhaps linked to glacial to interglacial changes in deep water distribution in the ocean which in turn drive changes in pole ward heat and moisture transport

results of paleoecological studies in the loess region of szeged othalom se hungary abstract new results of sedimentological magnetic susceptibility geochemical radiocarbon and malacological analysis from a typical and an infusion loess section are presented from se hungary the geologic and geomorphologic value of the area is that aeolian typical loess accumulated on sand dunes that formed during mis3 while in the interdune depressions on the top of lacustrine deposit series infusion loess developed as the two types of loess interfinger it is the first demonstration that the two types of loess formed during the same time period isochron in different environments heterotype at the end of mis3 and during mis 2 between 33 000 13 000 cal bp a temperate steppe forest steppe environment characterized the loess surface of the se great hungarian plain during the first interstadial phase of mis2 a pinus sylvestris charcoal rich paleosol layer developed on the loess covered surface of a wind blown sand hummock while in the interdune depressions a pond phase developed after the formation of the paleosol layer on the surface of the loess covered wind blown sand hummock during the heinrich 2 event vertigo modesta vallonia tenuilabris indicate a cold steppe forest steppe environment and a deeper and colder lake phase in the interdune depressions after that a short microinterstadial phase developed and a pupilla triplicata chondrula tridens dominated temperate steppe forest steppe environment evolved on the terrestrial surface between 23 000 21 000 cal bp after 21 000 cal bp in the last glacial maximum lgm the environment completely changed the average dust accumulation accelerated and coarse silt 0 02 0 06 mm became dominant as a result the lake stage transformed to a marshy environment while on the land area shade loving including closed forest environment preferring mollusca taxa appeared such as vestia turgida vitrina pellucida and mastus venerabilis based on the mollusca fauna composition humidity increased during the cooling of the lgm horizon forestation started and a boreal forest steppe evolved at the study site during the post lgm the interdune depressions filled and aeolian loess layers developed formation of the infusion loess occurred between 24 000 17 000 cal bp loess formation lasted until the beginning of the late glacial maximum last permafrost maximum and ended in a forest steppe environment with boreal central european holarctic palearctic and continental mollusc fauna elements

mesoscale to microscale simulations over complex terrain with the immersed boundary method in the weather research and forecasting model abstractimprovements to the weather research and forecasting wrf model are made to enable multiscale simulations over highly complex terrain with dynamically downscaled boundary conditions from t

patterns of deglacial warming in the pacific ocean a review with emphasis on the time interval of heinrich event 1 abstract based on a compilation of currently available records of past sea surface temperature sst variability estimated from a variety of different proxies the regional scale deglacial sst development in the pacific ocean is tentatively classified into four endmember types the subtropical and tropical pacific is characterized by a continuous deglacial warming without marked interruption during the time interval of heinrich event 1 h1 whereas the subarctic north pacific exhibits centennial scale warm cold oscillations during this time interval sst records from marginal seas of the pacific show a deglacial warming interrupted by a cooling event coeval with h1 followed by a marked bolling sst increase a single sst record from the southwestern subantarctic pacific displays a continuous deglacial warming across h1 followed by an antarctic cold reversal type cooling during the allerod thus in contrast to the deglacial sst development in the atlantic which has been inferred to be overwhelmingly driven by the redistribution of heat through changes in the meridional overturning circulation moc none of the open oceanic pacific sst records reviewed here displays any obvious and or dominant response to the reduction of the moc and or the reorganization of atmospheric circulation during h1 within the limits of absolute chronologies all tropical and subtropical pacific sst records show an onset of deglacial warming at 19 1 ka coeval with the onset of the deglacial rise in sea level

interhemispheric air temperature phase relationships in the nonlinear dansgaard oeschger oscillation it has previously been suggested that the southern ocean might act as a thermal reservoir in mediating the relationship between the northern and southern hemisphere air temperature signals during a dansgaard oeschger cycle on the basis of a climate model based analysis we demonstrate on the contrary that it is equatorial and subtropical north atlantic thermocline waters that act so as to integrate and damp the northern hemisphere signal to fix the amplitude and phase of the southern hemisphere counterpart to the more intense north atlantic component of the oscillation the dynamics of the southern ocean component of the atlantic meridional overturning circulation are critical in explaining the evolution of the interhemispheric temperature phase relationships european project for ice coring in antarctica dronning maud land inferred air temperature variations are in phase with sea surface temperatures north of the antarctic sea ice edge suggesting that it is via a fast atmospheric pathway that this temperature signal is transmitted into the antarctic ice core record

beyond the bipolar seesaw toward a process understanding of interhemispheric coupling abstract the thermal bipolar ocean seesaw hypothesis was advanced by stocker and johnsen 2003 as the simplest possible thermodynamic model to explain the time relationship between dansgaard oeschger do and antarctic isotope maxima aim events in this review we combine palaeoclimate observations theory and general circulation model experiments to advance from the conceptual model toward a process understanding of interhemispheric coupling and the forcing of aim events we present four main results 1 changes in atlantic heat transport invoked by the thermal seesaw are partially compensated by opposing changes in heat transport by the global atmosphere and pacific ocean this compensation is an integral part of interhemispheric coupling with a major influence on the global pattern of climate anomalies 2 we support the role of a heat reservoir in interhemispheric coupling but argue that its location is the global interior ocean to the north of the antarctic circumpolar current acc not the commonly assumed southern ocean 3 energy budget analysis indicates that the process driving antarctic warming during aim events is an increase in poleward atmospheric heat and moisture transport following sea ice retreat and surface warming over the southern ocean 4 the antarctic sea ice retreat is itself driven by eddy heat fluxes across the acc amplified by sea ice albedo feedbacks the lag of antarctic warming after amoc collapse reflects the time required for heat to accumulate in the ocean interior north of the acc predominantly the upper 1500 m before it can be mixed across this dynamic barrier by eddies

effects of glacial meltwater in the giss coupled atmosphere ocean model 2 a bipolar seesaw in atlantic deep water production the relationship between the northern hemisphere and southern hemisphere deep water circulation systems is explored in experiments with gradual and impulsive freshwater input through the st lawrence with sufficient freshwater volume input 50 sv years north atlantic deep water nadw cessation occurs as does substantial cooling in the northern hemisphere the colder temperatures are accompanied by increased mass and sea level pressure in the northern hemisphere with corresponding lower pressure in the southern hemisphere the low pressure response occurs at high southern latitudes consistent with the antarctic annular mode the leading mode of variability in the current climate stronger winds associated with this increased cyclonicity intensify the antarctic circumpolar current acc with heat flux divergences in the south atlantic and convergences and warming in the indian ocean weddell sea bottom water production increases in response to the south atlantic high latitude cooling and sea ice growth hence acting as a seesaw with the decreasing nadw and even global antarctic bottom water increases although not as strongly the initial seesaw response occurs within a few years although it takes some 100 years to maximize due to the response time of the acc the south atlantic cooling occurs approximately in phase with the north atlantic so the seesaw is not in temperature within that ocean basin however warming in portions of the southern indian ocean occurs out of phase with the northern hemisphere cooling nadw does not resume of its own accord once complete cessation occurs even when freshwater input is stopped but when increased evaporation is used to force nadw formation temporarily weddell sea bottom water decreases accordingly

interhemispheric space time attributes of the dansgaard oeschger oscillations between 100 and 0 ka the persistence stability and interhemispheric phasing of the dansgaard oeschger do climate oscillation over the last glacial period 0 100 ka has been evaluated in oxygen isotope records of three polar ice cores grip gisp2 and byrd station and a midlatitude deep sea core from the north atlantic ocean md95 2042 the results show that do oscillations in atmospheric conditions occurred in both northern and southern polar ice records although in the southern records the oscillations had at most only ca one tenth the power of those in the north the do oscillations first appeared duringmarine isotope stage mis 4 and the average spectral power of the northern hemisphere do oscillations increased markedly during mis 3 30 38 ka the do mode in the gisp2 record is confined to the frequency band 1 1 59 kyr to 1 1 37 kyr but in the grip record the mode exhibits strong frequency splittingover a band that is wider by ca 50 time frequency analysis shows that in grip the do mode underg oes a frequency modulation that is phase locked with the earth s obliquity cycle this modulation does not appear in nearby gisp2 in the north atlantic marine record do oscillations behaved somewhat differently appearingsporadically duringmis 5 and 4 the planktonic do oscillations increased in spectral power duringmis 3 leadingpeak power in the gisp2 record by ca 3 kyr do oscillations were relatively stable in all five records duringmis 3 they could not be detected unequivocally in any of the records duringthe holocene 0 11 ka at other times the do mode in all of the records was amplitude modulated by earth s orbital parameters finally interhemispheric phasingof do oscillations over 10 90 ka was assessed between the byrd station and gisp2 records and between the benthic and planktonic records of core md95 2042 coherency studies reveal an apparent time lead of byrd do oscillations over gisp2 by 384770 yr 2s level and of the north atlantic benthic over planktonic do oscillations by 208733 yr this apparent time lead of the southern over the northern temperature proxies is likely the consequence of the distinctive harmonic shapes affecting the northern rectangular vs southern triangular do oscillations the actual northern southern relationship as suggested by modelling and other recent data studies is most probably in simple antiphase cross phase of 1801 r 2002 published by elsevier science ltd

coupling of the hemispheres in observations and simulations of glacial climate change abstract we combine reconstructions climate model simulations and a conceptual model of glacial climate change on millennial time scales to examine the relation between the high latitudes of both hemispheres a lead lag analysis of synchronised proxy records indicates that temperature changes in greenland preceded changes of the opposite sign in antarctica by 400 500 yr a composite record of the dansgaard oeschger events shows that rapid warming cooling in greenland was followed by a slow cooling warming phase in antarctica the amplitudes rates of change and time lag of the interhemispheric temperature changes found in the reconstructions are in excellent agreement with climate model simulations in which the formation of north atlantic deep water is perturbed the simulated time lag between high northern and southern latitudes is mainly determined by the slow meridional propagation of the signal in the southern ocean our climate model simulations also show that increased deep water formation in the north atlantic leads to a reduction of the antarctic circumpolar current through diminishing meridional density gradients in the southern ocean we construct a simple conceptual model of interhemispheric dansgaard oeschger oscillations this model explains major features of the recorded temperature changes in antarctica as well as the general shape of the north south phase relation found in the observations including a broad peak of positive correlations for a lead of antarctica over greenland by 1000 2000 yr the existence of this peak is due to the regularity of the oscillations and does not imply a southern hemisphere trigger mechanism contrary to previous suggestions our findings thus further emphasise the role of the thermohaline circulation in millennial scale climate variability

climate correlations between greenland and antarctica during the past 100 000 years the ice cores recovered from central greenland by the grip1 2 and gisp23 projects record 22 interstadial warm events during the part of the last glaciation spanning 20 105 kyr before present the ice core from vostok east antarctica records nine interstadials during this period4 5 here we explore links between greenland and antarctic climate during the last glaciation using a high resolution chronology derived by correlating oxygen isotope data for trapped o2 in the gisp2 and vostok cores we find that interstadials occurred in east antarctica whenever those in greenland lasted longer than 2 000 years our results suggest that partial deglaciation and changes in ocean circulation are partly responsible for the climate teleconnection between greenland and antarctica ice older than 115 kyr in the gisp2 core shows rapid variations in the 18o of o2 that have no counterpart in the vostok record the age depth relationship and thus the climate record in this part of the gisp2 core appears to be significantly disturbed

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

instability of glacial climate in a model of the ocean atmosphere cryosphere system in contrast to the relatively stable climate of the past 10 000 years during glacial times the north atlantic region experienced large amplitude transitions between cold stadial and warm interstadial states in this modeling study we demonstrate that hydrological interactions between the atlantic thermohaline circulation thc and adjacent continental ice sheets can trigger abrupt warming events and also limit the lifetime of the interstadial circulation mode these interactions have the potential to destabilize the thc which is already more sensitive for glacial conditions than for the present day climate thus providing an explanation for the increased variability of glacial climate

a terrain following coordinate with smoothed coordinate surfaces an alternative form for a height based terrain following coordinate is presented here that progressively smoothes the coordinate surfaces with height to remove smaller scale steeper terrain structure from the surfaces testing this approach in comparison with traditional and hybrid terrain following formulations in resting atmosphere simulations demonstrates that it can significantly reduce artificial circulations caused by inaccuracies in the horizontal pressure gradient term the simulations also suggest that some further improvementintheaccuracyofthehorizontalpressuregradienttermscanbeachievedusingasimplifiedversion of mahrer s approach which can be implemented with little increase in computational cost or complexity

southern ocean deep convection as a driver of antarctic warming events simulations with a free running coupled climate model show that heat release associated with southern ocean deep convection variability can drive centennial scale antarctic temperature variations of up to 2 0 c the mechanism involves three steps preconditioning heat accumulates at depth in the southern ocean convection onset wind and or sea ice changes tip the buoyantly unstable system into the convective state antarctic warming fast sea ice albedo feedbacks on annual decadal timescales and slow southern ocean frontal and sea surface temperature adjustments to convective heat release on multidecadal century timescales drive an increase in atmospheric heat and moisture transport toward antarctica we discuss the potential of this mechanism to help drive and amplify climate variability as observed in antarctic ice core records

modelling carbon cycle feedbacks during abrupt climate change abstract past climate both before and after the last glacial maximum was marked by a series of abrupt transitions from cold to warm states associated with significant changes in atmospheric co2 mechanisms which led to these transitions most likely include variability in the thermohaline circulation thc as inferred from deep sea sediment records in this study we investigate the changes in atmospheric co2 concentration that arise during abrupt climate change events this is accomplished through our use of meltwater pulse scenarios applied to an ocean atmosphere sea ice model coupled to an inorganic carbon component we perform transient simulations with increased freshwater discharge to high latitude regions in both hemispheres from a glacial equilibrium climate to simulate meltwater episodes we find that changes in ocean circulation and carbon solubility lead to significant increases in atmospheric co2 concentrations when we simulate meltwater episodes in both hemispheres the magnitude of increase in atmospheric co2 is between 10 and 40 ppmv which accounts for some of the changes in co2 as recorded in the ice core records

antarctic and global climate history viewed from ice cores a growing network of ice cores reveals the past 800 000 years of antarctic climate and atmospheric composition the data show tight links among greenhouse gases aerosols and global climate on many timescales demonstrate connections between antarctica and distant locations and reveal the extraordinary differences between the composition of our present atmosphere and its natural range of variability as revealed in the ice core record further coring in extremely challenging locations is now being planned with the goal of finding older ice and resolving the mechanisms underlying the shift of glacial cycles from 40 000 year to 100 000 year cycles about a million years ago one of the great mysteries of climate science a discussion of past antarctic and global climate history as seen from antarctic ice cores with an outlook on future goals and drilling priorities

three dimensional cut cell modelling for high resolution atmospheric simulations owing to the recent rapid development of computer technology the resolution of atmospheric numerical models has increased substantially with the use of next generation supercomputers atmospheric simulations using horizontal grid intervals of o 100 m or less will gain popularity at such high resolution more of the steep gradients in mountainous terrain will be resolved which may result in large truncation errors in those models using terrain following coordinates in this study a new three dimensional 3d cartesian coordinate non hydrostatic atmospheric model is developed a cut cell representation of topography based on finite volume discretization is combined with a cell merging approach in which small cut cells are merged with neighbouring cells either vertically or horizontally in addition a block structured mesh refinement technique is introduced to achieve a variable resolution on the model grid with the finest resolution occurring close to the terrain surface the model successfully reproduces a flow over a 3d bell shaped hill that shows a good agreement with the flow predicted by the linear theory the ability of the model to simulate flows over steep terrain is demonstrated using a hemisphere shaped hill the advantage of a locally refined grid around the hill with cut cells at the terrain surface is also demonstrated the model reproduces smooth mountain waves propagating over varying grid resolution without introducing large errors associated with the change of mesh resolution at the same time the model shows a good scalability on the locally refined grid

power laws and snow avalanches 1 this paper presents evidence of frequency size power laws in several groups of snow avalanche paths other natural hazards such as earthquakes and forest fires exhibit similar power law relationships in addition an analysis of the response of one group of snow avalanche paths to storms through time demonstrates a power law between the response of the system and the binned frequency of those responses our results as well as our experience with these complex non linear systems are consistent with self organized criticality the practical implication of this work is that the frequency size relationship for small and medium sized avalanches may be useful for quantifying the risk of large snow avalanches within a group of avalanche paths

climate connections between the hemisphere revealed by deep sea sediment core ice core correlations abstract correlation of southern ocean deep sea sediment core records with ice core records of polar climate delineates with unprecedented detail the relationship between high latitude climate and the ocean s thermohaline circulation over the last 80 000 years our observations suggest that while north atlantic deep water variability manifests itself clearly in southern ocean nutrient proxy records over periods as short as 500 yr this deep water variability did not promote a direct link between climate variability in the high latitudes of the two hemispheres on millennial timescales in particular the proxy records indicate that on average northern hemisphere climate fluctuations lagged those of the southern hemisphere by 1500 yr

an atlantic pacific ventilation seesaw across the last deglaciation it has been proposed that the rapid rise of atmospheric co2 across the last deglaciation was driven by the release of carbon from an extremely radiocarbon depleted abyssal ocean reservoir that was vented to the atmosphere primarily via the deep and intermediate overturning loops in the southern ocean while some radiocarbon observations from the intermediate ocean appear to confirm this hypothesis others appear to refute it here we use radiocarbon measurements in paired benthic and planktonic foraminifera to reconstruct the benthic planktonic 14c age offset i e ventilation age of intermediate waters in the western equatorial atlantic our results show clear increases in local radiocarbon based ventilation ages during heinrich stadial 1 hs1 and the younger dryas yd these are found to coincide with opposite changes of similar magnitude observed in the pacific demonstrating a seesaw in the ventilation of the intermediate atlantic and pacific oceans that numerical model simulations of north atlantic overturning collapse indicate was primarily driven by north pacific overturning we propose that this atlantic pacific ventilation seesaw would have combined with a previously identified north atlantic southern ocean ventilation seesaw to enhance ocean atmosphere co2 exchange during a collapse of the north atlantic deep overturning limb whereas previous work has emphasized a more passive role for intermediate waters in deglacial climate change merely conveying changes originating in the southern ocean we suggest instead that the intermediate water seesaw played a more active role via relatively subtle but globally coordinated changes in ocean dynamics that may have further influenced ocean atmosphere carbon exchange

interglacials of the last 800 000 years interglacials including the present holocene period are warm low land ice extent high sea level end members of glacial cycles based on a sea level definition we identify eleven interglacials in the last 800 000 years a result that is robust to alternative definitions data compilations suggest that despite spatial heterogeneity marine isotope stages mis 5e last interglacial and 11c 400 ka ago were globally strong warm while mis 13a 500 ka ago was cool at many locations a step change in strength of interglacials at 450 ka is apparent only in atmospheric co2 and in antarctic and deep ocean temperature the onset of an interglacial glacial termination seems to require a reducing precession parameter increasing northern hemisphere summer insolation but this condition alone is insufficient terminations involve rapid nonlinear reactions of ice volume co2 and temperature to external astronomical forcing the precise timing of events may be modulated by millennial scale climate change that can lead to a contrasting timing of maximum interglacial intensity in each hemisphere a variety of temporal trends is observed such that maxima in the main records are observed either early or late in different interglacials the end of an interglacial glacial inception is a slower process involving a global sequence of changes interglacials have been typically 10 30 ka long the combination of minimal reduction in northern summer insolation over the next few orbital cycles owing to low eccentricity and high atmospheric greenhouse gas concentrations implies that the next glacial inception is many tens of millennia in the future

simulating the ice thickness distribution in a coupled climate model climate simulations in a global coupled model are investigated using a dynamic thermodynamic sea ice and snow model with sophisticated thermodynamics and a subgrid scale parameterization for multiple ice thicknesses in addition to the sea ice component the model includes a full primitive equation ocean and a simple energy moisture balance atmosphere we introduce a formulation of the ice thickness distribution that is lagrangian in thickness space the method is designed to use fewer thickness categories because it adjusts to place resolution where it is needed most and it is free of diffusive effects that tend to smooth eulerian distributions experiments demonstrate that the model does reasonably well in simulating the mean arctic climate we find the climate of the arctic and northern north atlantic is sensitive to resolving the ice thickness distribution when comparing the model results to a simulation with a two level sea ice model the ice thickness distribution causes ice export through fram strait to be more variable and more strongly linked to meridional overturning in the north atlantic ocean the lagrangian formulation of the ice thickness distribution allows for the inclusion of a vertical temperature profile with relative ease compared to an eulerian method we find ice growth rates and ocean surface salinity differ in our model with a well resolved vertical temperature profile in the ice and snow and an explicit brine pocket parameterization compared to a simulation with semtner zero layer thermodynamics although these differences are important for the climate of the arctic the effects of an ice thickness distribution are more dramatic and extend into the northern north atlantic sensitivity experiments indicate that five ice thickness categories with 50 cm vertical temperature resolution capture the effects of the ice thickness distribution on the heat and freshwater exchange across the surface in the presence of sea ice in these simulations

a simulation study of kelvin waves interacting with synoptic events during december 2016 in the south china sea and maritime continent abstractthis study evaluates the model simulation of interaction between convectively coupled tropical disturbances in the south china sea scs and maritime contin mc the model for prediction a

a study of multiple tropopause structures caused by inertia gravity waves in the antarctic abstractmultiple tropopauses mts defined by the world meteorological organization are frequently detected from autumn to spring at syowa station 69 0 s 39 6 e the dynamical mechanism of mt events was examined by observations of the first mesosphere stratosphere troposphere mst radar in the antarctic the program of the antarctic syowa mst incoherent scatter is radar pansy and of radiosondes on 8 11 april 2013 the mt structure above the first tropopause is composed of strong temperature fluctuations by a detailed analysis of observed three dimensional wind and temperature fluctuation components it is shown that the phase and amplitude relations between these components are consistent with the theoretical characteristics of linear inertia gravity waves igws numerical simulations were performed by using a nonhydrostatic model the simulated mt structures and igw parameters agree well with the observation in the analysis using the numerical simulation data it is seen that igws were generate

climate response to external sources of freshwater north atlantic versus the southern ocean abstract the response of an atmosphere ocean general circulation model aogcm to perturbations of freshwater fluxes across the sea surface in the north atlantic and southern ocean is investigated the purpose of this study is to investigate aspects of the so called bipolar seesaw where one hemisphere warms and the other cools and vice versa due to changes in the ocean meridional overturning the experimental design is idealized where 1 sv 1 sv 106 m3 s 1 of freshwater is added to the ocean surface for 100 model years and then removed in one case the freshwater perturbation is located in the atlantic ocean from 50 to 70 n in the second case it is located south of 60 s in the southern ocean in the case where the north atlantic surface waters are freshened the atlantic thermohaline circulation thc and associated northward oceanic heat transport weaken in the antarctic surface freshening case the atlantic thc is mainly unchanged with a slight weakening toward the end of the integration this w

atmospheric co2 concentration from 60 to 20 kyr bp from the taylor dome ice core antarctica a high resolution record of the atmospheric co2 concentration from 60 to 20 thousand years before present kyr bp based on measurements on the ice core of taylor dome antarctica is presented this record shows four distinct peaks of 20 parts per million by volume ppmv on a millennial time scale good correlation of the co2 record with temperature reconstructions based on stable isotope measurements on the vostok ice core antarctica is found

interhemispheric atlantic seesaw response during the last deglaciation the asynchronous relationship between millennial scale temperature changes over greenland and antarctica during the last glacial period has led to the notion of a bipolar seesaw which acts to redistribute heat depending on the state of meridional overturning circulation within the atlantic ocean here we present new records from the south atlantic that show rapid changes during the last deglaciation that were instantaneous within dating uncertainty and of opposite sign to those observed in the north atlantic our results demonstrate a direct link between the abrupt changes associated with variations in the atlantic meridional overturning circulation and the more gradual adjustments characteristic of the southern ocean these results emphasize the importance of the southern ocean for the development and transmission of millennial scale climate variability and highlight its role in deglacial climate change and the associated rise in atmospheric carbon dioxide

simulated resumption of the north atlantic meridional overturning circulation slow basin wide advection and abrupt local convection abstract the resumption process of the north atlantic meridional overturning circulation moc is investigated in a series of freshwater hosing experiments using a comprehensive coupled climate model four different freshwater perturbations are applied to the north atlantic between 50 n and 70 n leading to a substantial weakening of moc and an expansion of winter sea ice cover over the greenland iceland norwegian gin seas deactivating the freshwater forcing leads to a two phase recovery of the moc the first phase is a slow basin wide advection process whereas the second phase is an abrupt decadal scale transition located in the north atlantic the slow basin wide advection process to an intermediate state of the moc is characterized by a restart of the deep water production in the area of the subpolar gyre and the irminger basin however the ice cover over the gin seas remains whereas the surface density gradually increases in the gin seas on a century time scale the length of this intermediate state depends on the strength of freshwater perturbation which determines the magnitude of the meridional density gradient in the north atlantic the second transition phase is triggered by a model specific density threshold reached in the gin seas when passed the moc abruptly intensifies by 60 within 60 80 years the analysis shows that this abrupt intensification only depends on surface salinity in the gin seas the model results reveal that the simulated sea ice retreat in the gin seas and a rapid increase of the greenland air temperature of the second phase of the resumption of the moc are similar in amplitude to temperature proxies observed during dansgaard oeschger events of the last ice age

last glacial maximum lgm primary productivity in the northern north atlantic oceanthis article is one of a series of papers published in this special issue on the theme polar climate stability network to reconstruct oceanic primary productivity in the northern north atlantic ocean during the last glacial maximum lgm we have applied the modern analogue technique to dinocyst assemblages using a northern hemisphere database that includes 1171 reference sites the reconstructions were made in lgm sediments 21 2 ka of a set of 62 cores collected from 36 n to 75 n here we present the compilation of reconstructed seasonal and annual productivity during the lgm results show lower mean annual productivity during the lgm than at present in the northern north atlantic at most high latitude locations lgm productivity has been estimated at 200 gc m 2 a 1 with extremely low values 100 gc m 2 a 1 in the labrador sea baffin bay and along the margins of greenland such low values might be the result of reduced atlantic meridional overturning circulation and stratified water that characterized the glacial episode of the north atlantic ocean

radiocarbon evidence for alternating northern and southern sources of ventilation of the deep atlantic carbon pool during the last deglaciation recent theories for glacial interglacial climate transitions call on millennial climate perturbations that purged the deep sea of sequestered carbon dioxide via a bipolar ventilation seesaw however the viability of this hypothesis has been contested and robust evidence in its support is lacking here we present a record of north atlantic deep water radiocarbon ventilation which we compare with similar data from the southern ocean a striking coherence in ventilation changes is found with extremely high ventilation ages prevailing across the deep atlantic during the last glacial period the data also reveal two reversals in the ventilation gradient between the deep north atlantic and southern ocean during heinrich stadial 1 and the younger dryas these coincided with periods of sustained atmospheric co2 rise and appear to have been driven by enhanced ocean atmosphere exchange primarily in the southern ocean these results confirm the operation of a bipolar ventilation seesaw during deglaciation and underline the contribution of abrupt regional climate anomalies to longer term global climate transitions

australasian monsoon response to dansgaard oeschger event 21 and teleconnections to higher latitudes abstract dansgaard oeschger d o cycles were the most prominent abrupt climate events of the last glacial period whose impact was most strongly felt in the high latitudes of the north atlantic region the climate links between the north atlantic the asian and american tropics and antarctica during these cycles are well documented however the potential role of the indo pacific warm pool and australasian monsoon system in propagating climate impacts across the hemispheres is still unclear here we use tandem measurements of oxygen isotopes in calcite and fluid inclusions as well as carbon isotope ratios from multiple stalagmites from liang luar cave flores southern indonesia to examine the monsoon response to d o event number 21 87 000 84 000 years ago the longest and warmest event recorded in greenland ice cores the record shows that there was a rapid decline in monsoon rainfall in indonesia during d o21 warming in greenland and cooling in antarctica at around the same time the east asian monsoon was intensified indicating that the intertropical convergence zone itcz shifted abruptly to the north during this event our record also shows that there was a 2 3 c increase in local air temperature which would have acted to increase primary productivity and promote the generation of soil carbon for methanogenesis therefore our findings indicate that itcz positioning in tropical australasia through its influence on large scale oceanic atmospheric circulation played a key role in transmitting the abrupt climate signal between the hemispheres thereby facilitating the rapid rise of atmospheric co 2 and ch 4 concentrations during d o21 that ultimately led to global warming and the demise of the mis5b stadial

antarctic climate signature in the greenland ice core record a numerical algorithm is applied to the greenland ice sheet project 2 gisp2 dust record from greenland to remove the abrupt changes in dust flux associated with the dansgaard oeschger d o oscillations of the last glacial period the procedure is based on the assumption that the rapid changes in dust are associated with large scale changes in atmospheric transport and implies that d o oscillations in terms of their atmospheric imprint are more symmetric in form than can be inferred from greenland temperature records after removal of the abrupt shifts the residual dejumped dust record is found to match antarctic climate variability with a temporal lag of several hundred years it is argued that such variability may reflect changes in the source region of greenland dust thought to be the deserts of eastern asia other records from this region and more globally also reveal antarctic style variability and suggest that this signal is globally pervasive this provides the potential basis for suggesting a more important role for gradual changes in triggering more abrupt transitions in the climate system

an idealized model of the world ocean part i the global scale water masses abstract a primitive equation three dimensional numerical model of the ocean employing idealized versions of the real topography and surface boundary conditions is used to study the water mass structure of the world ocean in particular the response of the model to three fundamental changes in boundary conditions is investigated in an attempt to identify the mechanisms in the model which are responsible for the establishment of the largest scale features of the global water mass structure with the drake passage closed thermohaline driving alone and a fresh north atlantic surface salinity specified only the coarsest aspects of the observed t and s structure are reproduced and the entire world ocean below the thermocline is dominated by water formed at the southern boundary the salinity configuration in particular lacks much of its observed structure in this case when the drake passage is opened the resulting circumpolar flow serves to isolate the extreme southern ocean this allows waters of no

sediment instability on the portuguese continental margin under abrupt glacial climate changes last 60 kyr abstract it is well established that orbital scale sea level changes generated larger transport of sediments into the deep sea during the last glacial maximum than the holocene however the response of sedimentary processes to abrupt millennial scale climate variability is rather unknown frequency of distal turbidites and amounts of advected detrital carbonate are estimated off the lisbon setubal canyons core md03 2698 at 4602 mwd within a chronostratigraphy based on radiometric ages oxygen isotopes and paleomagnetic key global anomalies we found that 1 higher frequency of turbidites concurred with northern hemisphere coldest temperatures greenland stadials gs including heinrich h events but more than that an escalating frequency of turbidites starts with the onset of global sea level rising and warming in antarctica and culminates during h events at the time when rising is still in its early mid stage and the atlantic meridional overturning circulation amoc is re starting this short time span coincides with maximum gradients of ocean surface and bottom temperatures between gs and antarctic warmings antarctic isotope maximum aim 17 14 12 8 4 2 and rapid sea level rises 2 trigger of turbidity currents is not the only sedimentary process responding to millennial variability land detrital carbonate with a very negative bulk 18o signature enters the deep sea by density driven slope lateral advection accordingly during gs 3 possible mechanisms to create slope instability on the portuguese continental margin are sea level variations as small as 20 m and slope friction by rapid deep and intermediate re accommodation of water masses circulation 4 common forcing mechanisms appear to drive slope instability at both millennial and orbital scales

paleocean circulation during the last deglaciation a bipolar seesaw hughen et al 1998 have documented that during the first 200 years of younger dryas time the 14c content of atmospheric co2 increased by 50 and that during the remainder of this 1200 year duration cold event it steadily declined the initial increase in 14c c was likely the result of a reduction in the atlantic s conveyor circulation however were the subsequent radiocarbon decline due to the rejuvenation of this potent heat pump then it is difficult to understand why the climate conditions in the northern atlantic basin remained cold throughout the younger dryas modeling exercises by stocker and wright 1996 mikolajewicz 1998 and schiller et al 1998 show that if the conveyor is terminated the transfer of radiocarbon into the deep sea shifts to the southern ocean thereby stabilizing the atmospheric 14c c ratio paleoclimatic evidence from the antarctic continent suggests that this model based scenario might have been played out in the real world while the younger dryas cooling has been documented in many places around the world including new zealand denton and hendy 1994 sowers and bender 1995 using their 18o in o2 based correlation between the ice core 18o in ice records for antarctica and greenland have demonstrated that in antarctica the younger dryas was a time of maximum warming the point of this paper is that the steep rise in 18o rise in antarctic ice which commenced close to the onset of the younger dryas might have been caused by heat released to the atmosphere in response to an increase in deep sea ventilation in the southern ocean

the transition from the last glacial period in inland and near coastal antarctica recent studies suggested that during the transition out of the last glacial period one near coastal site in antarctica showed a response similar to that of greenland and unlike that of central antarctica here we present a new high resolution record of calcium from dome c antarctica changes in flux of calcium an indicator of dust input from other continents should be synchronous across the region and probably the continent using ca to synchronise records we find that the main warming at the near coastal site of taylor dome was slower than suggested previously and similar to that of central antarctica until there is further evidence it is still a reasonable hypothesis that antarctic climate behaved more or less as a single unit during the transition

submillennial variations in ocean conditions during deglaciation based on diatom assemblages from the southwest atlantic we present a high resolution paleoceanographic record of deglaciation based on diatom assemblages from a core located just south of the polar front in the southwest atlantic core kc073 is from a sediment drift at the mouth of the falkland trough and contains sediments from the last glacial maximum lgm to present dated using radiocarbon dates on bulk organic matter and radiolarian stratigraphy the site lies along the path of the antarctic circumpolar current acc and immediately downstream of where north atlantic deep water nadw is entrained into the acc significant variations in ocean conditions are reflected in high amplitude changes in diatom concentrations and assemblage composition the diatom assemblage at the lgm indicates that winter sea ice extent was at least 5 farther north than present until at least 19 0 ka calendar years and summer sea ice may have occasionally extended over the site but for the most part it lay to the south during deglaciation chaetoceros resting spores crs dominate the diatom assemblage with valve concentrations in excess of 500 106 valves per gram submillennial scale variations in the numbers of crs and thalassiosira antarctica occur throughout the late deglacial and dominate the changes in diatom concentration we propose that the influx of crs is controlled by the flow of nadw over the falkland plateau as such our data provide unique evidence that nadw impacted on this sector of the southern ocean during deglaciation during the holocene the sedimentation rate dramatically reduced we suggest that the acc flow increased over the site and inhibited settling and winnowed the surface sediments

synchronous climate changes in antarctica and the north atlantic central greenland ice cores provide evidence of abrupt changes in climate over the past 100 000 years many of these changes have also been identified in sedimentary and geochemical signatures in deep sea sediment cores from the north atlantic confirming the link between millennial scale climate variability and ocean thermohaline circulation it is shown here that two of the most prominent north atlantic events the rapid warming that marks the end of the last glacial period and the bolling allerod younger dryas oscillation are also recorded in an ice core from taylor dome in the western ross sea sector of antarctica this result contrasts with evidence from ice cores in other regions of antarctica which show an asynchronous response between the northern and southern hemispheres

stratospheric analysis and forecast errors using hybrid and sigma coordinates abstractpast investigations have documented large divergent wind anomalies in stratospheric reanalyses over steep terrain which were attributed to discretization errors produced by the terrain following sigma vertical coordinate in the forecast model however forecasting experiments have reported negligible differences in skill between sigma and hybrid coordinate models this leads to the paradoxical conclusion that discretization errors in the forecast model yield significant stratospheric analysis errors but insignificant stratospheric forecast errors the authors reexamine this issue by performing two forecast assimilation experiments that are identical except for the vertical coordinate one uses a sigma coordinate and the other uses a hybrid coordinate the sigma coordinate analyses exhibit large divergent wind anomalies over terrain that extend from the surface to the model top and distort explicitly resolved orographic gravity waves above the tropopause divergent wind errors are suppressed

a 70 kyr sea surface temperature record off southern chile ocean drilling program site 1233 1 we present the first high resolution alkenone derived sea surface temperature sst reconstruction in the southeast pacific ocean drilling program site 1233 covering the major part of the last glacial period and the holocene the record shows a clear millennial scale pattern that is very similar to climate fluctuations observed in antarctic ice cores suggesting that the southern hemisphere high latitude climate changes extended into the midlatitudes involving simultaneous changes in air temperatures over antarctica sea ice extent extension of the antarctic circumpolar current and westerly atmospheric circulation a comparison to other midlatitude surface ocean records suggests that this antarctic millennial scale pattern was probably a hemisphere wide phenomenon in addition we performed sst gradient reconstructions over the complete latitudinal range of the pacific eastern boundary current system for different time intervals during the last 70 kyr the main results suggest an equatorward displaced subtropical gyre circulation during marine isotope stages 2 and 4

using a maximum simplicity paleoclimate model to simulate millennial variability during the last four glacial periods abstract many studies have documented the existence of millennial scale variability in the earth system during the last glacial period an increasing number of studies document the occurrence of similar millennial variability during glacial periods previous to the last one here we use the simplest possible thermal bipolar seesaw model to consider this variability for the last four glacial periods we invert this model and use the high pass filtered vostok stable isotope records to make a first tentative attempt to estimate high latitude n hemisphere temperature variability over the last four glacial periods beyond the reach of greenland ice core records the model result is compared against the vostok methane record which shows rapid variations in parallel to greenland temperature records during the last glacial period a further comparison is carried out against the planktonic oxygen isotope of north atlantic core odp 980 there is agreement between the records on the existence of similar millennial scale variability during the last three glacial periods with very similar characteristics to the variability during the last glacial cycle

large fluctuations of dissolved oxygen in the indian and pacific oceans during dansgaard oeschger oscillations caused by variations of north atlantic deep water subduction a s and s h were supported by the paleoclimate program of the national science foundation as part of the paleovar project atm 0602395

debris flow activity and snow avalanches in a steep watershed of the valais alps switzerland dendrogeomorphic event reconstruction and identification of triggers debris flows and snow avalanches are common processes in the headwaters of steep watersheds worldwide in forested areas dendrogeomorphic analyses of trees affected by debris flows and snow avalanches have regularly been used to date past events previous studies have however almost never focused on both processes at once as snow avalanche impacts cannot easily be distinguished from debris flow scars in a similar way tree ring studies have often been limited to conifers and sites colonized with broad leaved forests have been widely disregarded we report on a case from the valais alps switzerland where past debris flow and snow avalanche activity was dated with intraseasonal precision using different broad leaved and conifer trees in total the analysis of 171 cores 34 wedges and 11 crosssections from 93 trees allowed identification of 20 debris flow and 3 snow avalanche events between a d 1930 and 2008 results also indicate that some of the events would have been missed without the sampling of broad leaved trees

palaeoclimatology fresh angle on the polar seesaw during the last glacial period climatic variation in the northern and southern hemispheres was evidently linked modelling work points to freshwater discharge into the north atlantic as a driving factor

spatio temporal reconstruction of snow avalanche activity using tree rings pierres jean jeanne avalanche talus massif de l oisans france snow avalanches are a major threat in many parts of the alps where they periodically damage infrastructure disrupt transportation corridors or even cause loss of life nonetheless the spatial behavior of past avalanche activity and the analysis of areas affected during particular events remain often imprecise it was therefore the purpose of this study to reconstruct spatio temporal patterns of past avalanche activity on a forested avalanche talus in the french alps pierres jean jeanne talus massif de l oisans france a total of 232 european larches larix decidua mill with clear signs of snow wasting events was analyzed and growth disturbances gd related to avalanche activity was assessed such as tangential rows of traumatic resin ducts the onset of compression wood or abrupt growth suppression and release in total 901 gd were identified in the tree ring samples indicating that 20 high magnitude avalanches occurred between ad 1919 and 1994 the mean return period of snow avalanches was 4 years with a 26 probability that an avalanche occurs in any particular year interpolated maps allowed for explicit spatial estimates of return periods throughout the talus showing a rapid increase of return frequency from 2 5 to 50 years with increasing distance from the talus apex the distribution of avalanche years seems to be quite homogeneous in time with a gap between 1951 and 1959 snowfall from a nearby meteorological station saint christophe en oisans 10 km from the study site indicated that the five most recent high magnitude events on record occurred due to above average snowfall anomalies in december and january associated with abnormally low air temperatures findings suggest that a strong snow metamorphism under high temperature gradients in january could explain the occurrence of high magnitude snow avalanches 2010 elsevier b v all rights reserved

limited area atmospheric modeling using an unstructured mesh abstracta regional configuration of the atmospheric component of the model for prediction across scales mpas a is described and evaluated it employs horizontally unstructured spherical centroida

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

comparison of terrain following and cut cell grids using a nonhydrostatic model abstractterrain following coordinates are widely used in operational models but the cut cell method has been proposed as an alternative that can more accurately represent atmospheric dynamics over steep orography because the type of grid is usually chosen during model implementation it becomes necessary to use different models to compare the accuracy of different grids in contrast here a c grid finite volume model enables a like for like comparison of terrain following and cut cell grids a series of standard two dimensional tests using idealized terrain are performed tracer advection in a prescribed horizontal velocity field a test starting from resting initial conditions and orographically induced gravity waves described by nonhydrostatic dynamics in addition three new tests are formulated a more challenging resting atmosphere case and two new advection tests having a velocity field that is everywhere tangential to the terrain following coordinate surfaces these new tests present a challenge

stochastic resonance in the north atlantic large abrupt changes between warm and cold modes of north atlantic climate exhibit spectral power at 1500 years yet some climatic changes were linked to outburst floods and other events that are unlikely to have been truly periodic we hypothesize that a weak periodic forcing has combined with noise from ice sheet related events to cause the observed mode switches this stochastic resonance hypothesis predicts a recurrence pattern between warmings that is distinct from the predictions of simple periodic and stochastic models and at least some other models the ice isotopic data from central greenland ice cores are consistent with the stochastic resonance hypothesis but not with other models we have tested we thus support arguments for the existence of a periodicity of 1500 years in the north atlantic climate system and for the importance of ice sheet events in forcing north atlantic changes

radiocarbon calibration beyond 20 000 14c yr b p by means of planktonic foraminifera of the iberian margin we present a new set of 14c ages obtained by accelerator mass spectrometry ams on planktonic foraminifera from a deep sea core collected off the iberian margin md952042 this site at 37 n is distant from the high latitude zones where 14c reservoir age is large and variable many independent proxies alkenones magnetic susceptibility ice rafted debris foraminifera stable isotopes abundances of foraminifera pollen and dinoflagellates show abrupt changes correlative with dansgaard oeschger and heinrich events of the last glacial period the good stratigraphic agreement of all proxies from the fine to the coarse size fractions indicates that the foraminifera 14c ages are representative of the different sediment fractions to obtain reliable 14c ages of foraminifera beyond 20 000 14c yr b p we leached the shells prior to carbonate hydrolysis and subsequent analysis for a calendar age scale we matched the iberian margin u37k profile with that of greenland summit 18o both are proxies for temperature which in models varies synchronously in the two areas the match creates no spurious jumps in sedimentation rate and requires only a limited number of tie points except for ages older than 40 000 14c yr b p greenland s gisp2 and grip records yield similar calendars the 14c and imported calendar ages of the iberian margin record are then compared to data from lacustrine annual varves and from corals and speleothems dated by u th previously used to extend the calibration beyond 20 000 14c yr b p the new record follows a smooth pattern between 23 000 and 50 000 cal yr b p we find good agreement with the previous data sets between 23 000 and 31 000 cal yr b p in the interval between 33 000 and 41 000 cal yr b p for which previous records disagree by up to 5000 cal yr the iberian margin record closely follows the polynomial curve that was previously defined by an interpolation of the coral ages and runs between the lake suigetsu and the bahamian speleothem data sets

large arctic temperature change at the wisconsin holocene glacial transition analysis of borehole temperature and greenland ice sheet project ii ice core isotopic composition reveals that the warming from average glacial conditions to the holocene in central greenland was large approximately 15 c this is at least three times the coincident temperature change in the tropics and mid latitudes the coldest periods of the last glacial were probably 21 c colder than at present over the greenland ice sheet

oceanic carbon and water masses during the mystery interval a model data comparison study 1 the mystery interval 17 5 14 5 ka bp is characterized by a large decline in atmospheric 14c synchronous with an increase in atmospheric co2 the most widely accepted hypothesis to explain these observed shifts involves the existence of an isolated old ocean carbon reservoir that was subsequently ventilated here we use the uvic earth system climate model to locate a potential carbon rich and 14c depleted water mass under 17 5 ka bp boundary conditions we then investigate two mechanisms for the potential ventilation of such a reservoir namely the weakening of the north atlantic meridional overturning due to iceberg calving and latitudinal shifts in southern hemisphere westerlies shw due to southern hemispheric warming we find that simulations derived from an equilibrium state forced with present day shw and moderate north atlantic deep water nadw formation are in better agreement with atmospheric and ocean 14c reconstructions than simulations derived from an equilibrium state forced with a northward shifted shw belt resulting in a shut down of the atlantic meridional overturning and formation of north pacific deep water for simulations with present day shw the oldest water masses are found in the north pacific although the southern ocean cannot be ruled out as a potential mystery reservoir according to our simulations the strength of atlantic overturning is the dominant mechanism in increasing the ocean atmosphere carbon flux while shifting shw results in a rearrangement of deep ocean carbon largely between the atlantic and pacific basins in our best case scenario the model can account for 58 of the atmospheric co2 increase and 48 of the atmospheric 14c decline while the rate of ventilation and the age of ventilated water masses are comparable with observations the ventilation in the model could not be sustained long enough to account for the full excursion seen in paleodata

phase relationships between antarctic and greenland climate records comparison of climate records from antarctic and greenland ice cores shows that the two regions respond asynchronously during millennial scale climate changes the apparent out of phase relationship between the records has been described as a climate seesaw in which cooling in the northern hemisphere is balanced by warming in the southern hemisphere the same relationship has also been attributed to the initiation of climate change events in the southern hemisphere rather than the north atlantic as is conventionally assumed a simple statistical approach band pass filtering combined with lag correlation tests used to examine the phase relationships in more detail shows that neither an anti phase nor a phase lag relationship adequately describes the observations whereas antarctic and greenland climate records do exhibit approximate anti phase behavior about 50 of the time they are generally in phase during cooling a phase lead of southern hemisphere climate of 1000 1600 years is statistically indistinguishable from a lag of 400 800 years whether for dansgaard oeschger heinrich or longer duration events the seesaw or southern lead appearance of the data arises from the fundamentally different characteristics of the climate time series most importantly the absence of rapid warming events in antarctica comparable to those in greenland to be consistent with the observations climate models will need to capture these characteristics in addition to reproducing the correct phase relationships

hybrid mass coordinate in wrf arw and its impact on upper level turbulence forecasting abstractalthough a terrain following vertical coordinate is well suited for the application of surface boundary conditions it is well known that the influences of the terrain on the coordinate sur

high latitude salinity effects and interhemispheric thermohaline circulations a general circulation model for the ocean is used to investigate the interaction between the global scale thermohaline circulation and the salinity distribution it is shown that an equatorially asymmetric circulation can be maintained even under equatorially symmetric basin geometry and surface forcing multiple equilibrium solutions are obtained for the same forcing by perturbing the high latitude salinity field in an otherwise equatorially symmetric initial condition the timescale of the transition from the symmetric circulation to an asymmetric circulation depends critically on the sign of the initial salinity perturbation

evaluating implementations of the immersed boundary method in the weather research and forecasting model abstractthe terrain following coordinate system used by many atmospheric models can cause numerical instabilities due to discretization errors as resolved terrain slopes increase and the grid becom

a global perspective on last glacial maximum to holocene climate change while the abrupt climate events of the last deglaciation are well defined in ice core records from the polar regions of both hemispheres their manifestation elsewhere is less well constrained here we compile 104 high resolution paleoclimate records to characterize the timing and spatial pattern of climate change during the last deglaciation this compilation indicates relatively concurrent timing of the last glacial maximum lgm peak glacial conditions and the altithermal peak interglacial conditions in the northern 22 1 4 3 ka and 8 0 3 2 ka and southern 22 3 3 6 ka and 7 4 3 7 ka hemispheres suggesting the hemispheres were synchronized by greenhouse gases local insolation and or northern hemisphere induced ocean circulation changes the magnitude of the glacialeinterglacial temperature change increases with latitude reflecting the polar amplification of climate change with a likely minimum global mean cooling of ww4 9 c during the lgm relative to the altithermal empirical orthogonal function eof analysis of 71 records spanning 19e11 ka indicates that two modes explain 72 of deglacial climate variability eof1 61 of variance shows a globally near uniform pattern with its principal component pc1 strongly correlated with changes in atmospheric co2 e of2 11 of variance exhibits a bipolar seesaw pattern between the hemispheres with its principal component pc2 resembling changes in atlantic meridional overturning circulation strength eof analysis of 90 records from 15 to 11 ka indicates that northern and southern modes of climate variability characterize the younger dryas bolling allerod interval these modes dominate at the higher latitudes of each hemisphere and exhibit a complex interaction in the tropics the magnitude of the younger dryas climate anomaly cooler drier increases with latitude in the northern hemisphere with an opposite pattern warmer wetter in the southern hemisphere reflecting a general bipolar seesaw climate response global mean temperature decreased by w0 6 c during the younger dryas therefore our analysis supports the paradigm that while the younger dryas was a period of global climate change it was not a major global cooling event but rather a manifestation of the bipolar seesaw driven by a reduction in atlantic meridional overturning circulation strength

roles of deep and shallow convection and microphysics in the mjo simulated by the model for prediction across scales the november event of the madden julian oscillation mjo during the dynamo field campaign was simulated using the global compressible nonhydrostatic model for prediction across scales mpas with global coarse 60 and 15 km and regional the indian ocean cloud permitting 3 km meshes the purpose of this study is to compare roles of parameterized deep and shallow cumulus and microphysics in mjo simulations two cumulus schemes were used tiedtke and grell freitas the deep and shallow components of tiedtke scheme can be turned on and off individually the results reveal that microphysics alone without cumulus parameterization is able to produce strong signals of the mjo in precipitation with 3 km mesh and weak mjo signals with 15 km mesh a shallow scheme tiedtke along with microphysics strengthens the mjo signals but makes them less well organized on large scales a deep cumulus scheme can either improve the large scale organization of mjo precipitation produced by microphysics and shallow convection tiedtke or impair them grell freitas the deep scheme of tiedtke cannot reproduce the mjo well without its shallow counterpart the main role of shallow convection in the model is to transport moisture upward to the lower mid troposphere by doing so it removes dry biases in the lower mid troposphere a distinct feature in simulations with weak or no mjo signals and enhances total precipitation and diabatic heating produced by microphysics and deep cumulus schemes changing model grid spacing from 60 to 15 km makes a little difference in the model fidelity of reproducing the mjo all roles of shallow convection in 15 km simulations with parameterized deep convection cannot be reproduced in 3 km simulations without parameterized deep convection results from this study suggest that we should pay more attention to the treatment of shallow convection and its connection to other parameterized processes for improving mjo simulations in other words a holistic approach should be taken that consider parameterization of shallow cumulus microphysics boundary layer as well as deep cumulus as a whole for model improvement

modelling the concentration of atmospheric co2 during the younger dryas climate event the younger dryas yd dated between 12 7 11 6 ky bp in the grip ice core central greenland is a distinct cold period in the north atlantic region during the last deglaciation a popular but controversial hypothesis to explain the cooling is a reduction of the atlantic thermohaline circulation thc and associated northward heat flux as triggered by glacial meltwater recently a ch4 based synchronization of grip 18o and byrd co2 records west antarctica indicated that the concentration of atmospheric co2 coatm2 rose steadily during the yd suggesting a minor influence of the thc on coatm2 at that time here we show that the coatm2 change in a zonally averaged circulation biogeochemistry ocean model when thc is collapsed by freshwater flux anomaly is consistent with the byrd record cooling in the north atlantic has a small effect on coatm2 in this model because it is spatially limited and compensated by far field changes such as a warming in the southern ocean the modelled southern ocean warming is in agreement with the anti phase evolution of isotopic temperature records from grip northern hemisphere and from byrd and vostok east antarctica during the yd 13c depletion and po4 enrichment are predicted at depth in the north atlantic but not in the southern ocean this could explain a part of the controversy about the intensity of the thc during the yd potential weaknesses in our interpretation of the byrd co2 record in terms of thc changes are discussed

modeling and simulation of glacier avalanche a case study of gayari sector glaciers hazards assessment glacier avalanches are natural hazards that could damage infrastructures and threaten lives in high altitude mountainous terrains on april 7 2012 a massive ice avalanche struck a pakistani base at gayari sector saltoro valley and buried killed 148 soldiers and civilians keeping in view the catastrophe a study was designed with the objectives to 1 model and simulate the gayari sector glacier avalanche incident in terms of height extent velocity pressure and momentum 2 generate hazard risk assessment of possible other glacier avalanches in the saltoro valley through modeling and simulation and 3 suitability analysis of current camp sites and recommendation of new safe camps sites locations in the saltoro valley to simulate the gayari sector glacier event and other glacier possible avalanches a physical process based rapid mass movements ramms was used the ramms has two main components i e voellmy salm vs model and random kinetic energy which deals with variables such as avalanche height and the mean avalanche velocity during the course of simulation the suitability analysis of current camp sites were achieved using weighted overlay analysis with different constraints in arcgis spatial analyst the ramms model simulation of the gayari avalanche event predicted a maximum velocity of 74 ms 1 generating a pressure of 5074 kpa and attaining a height of 45 m whereas the predicted debris volume on the ground was 3 8145 million m 3 a good agreement was found between actual debris height and extent as compared with the ramms model output the ramms model simulated all the potential tributary glacier avalanches of saltoro valley very well the weighted overlay analyses in arcgis spatial analyst revealed that the existing camp sites are safe and were not threatened by the glacier avalanche hazard however it was recommended that the gayari camp should not be constructed at the same location and should be relocated to the proposed safe camp sites identified in this research study the proposed methodology developed in the current study could be applied in the siachen conflict zone for avalanche hazard risk analysis of all the camp sites located in the valley

a theory for the surface atlantic response to thermohaline variability abstract the response of the upper warm limb of the thermohaline circulation in the north atlantic to a rapid change in deep water formation at high latitudes is investigated using a reduced gravity ocean model changes in deep water formation rate initiate kelvin waves that propagate along the western boundary to the equator on a timescale of months the response in the north atlantic is therefore rapid the southern hemisphere response is much slower limited by a mechanism here termed the ldquo uatorial buffer since to leading order the flow is in geostrophic balance the pressure anomaly decreases in magnitude as the kelvin wave moves equatorward where the coriolis parameter is lower together with the lack of sustained pressure gradients along the eastern boundary this limits the size of the pressure field response in the southern hemisphere interior adjustment is by the westward propagation of rossby waves but only a small fraction of the change in thermohaline circulation strength is commun

atmospheric co2 forcing on glacial thermohaline circulation and climate 1 a coupled climate model study indicates the paleoclimate record of glacial thermohaline circulation thc and reversed deep sea temperature salinity t s distribution in the atlantic can be explained largely by lower glacial atmospheric co2 alone the reduced co2 leads to increased southern ocean wintertime sea ice cover and salinity increased production of dense antarctic bottom water aabw enhanced cold and saline aabw penetration into the deep north atlantic increased oceanic vertical stability and reduced north atlantic deep water nadw circulation the dominant role of co2 forcing during the glacial implies a positive feedback between the southern ocean regulated thc and the glacial global carbon cycle

timing of millennial scale climate change in antarctica and greenland during the last glacial period a precise relative chronology for greenland and west antarctic paleotemperature is extended to 90 000 years ago based on correlation of atmospheric methane records from the greenland ice sheet project 2 and byrd ice cores over this period the onset of seven major millennial scale warmings in antarctica preceded the onset of greenland warmings by 1500 to 3000 years in general antarctic temperatures increased gradually while greenland temperatures were decreasing or constant and the termination of antarctic warming was apparently coincident with the onset of rapid warming in greenland this pattern provides further evidence for the operation of a bipolar see saw in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales

analyzing the grell freitas convection scheme from hydrostatic to nonhydrostatic scales within a global model abstractthe authors implemented the grell freitas gf parameterization of convection in which the cloud base mass flux varies quadratically as a function of the convective updraft fraction in the global nonhydrostatic model for prediction across scales mpas they evaluated the performance of gf using quasi uniform meshes and a variable resolution mesh centered over south america the resolution of which varied between hydrostatic 50 km and nonhydrostatic 3 km scales four day forecasts using a 50 km and a 15 km quasi uniform mesh initialized with gfs data for 0000 utc 10 january 2014 reveal that mpas overestimates precipitation in the tropics relative to the tropical rainfall measuring mission multisatellite precipitation analysis data results of 4 day forecasts using the variable resolution mesh reveal that over the refined region of the mesh gf performs as a precipitating shallow convective scheme whereas over the coarse region of the mesh gf acts as a conventional deep convective scheme a

synchronization of polar climate variability over the last ice age in search of simple rules at the heart of climate s complexity evidence is presented supporting the hypothesis of polar synchronization which states that during the last ice age and likely in earlier times millennial scale temperature changes of the north and south polar regions were coupled and synchronized the term synchronization as used here describes how two or more coupled nonlinear oscillators adjust their initially different natural rhythms to a common frequency and constant relative phase in the case of the polar regions heat and mass transfer through the intervening ocean and atmosphere provided the coupling as a working hypothesis polar synchronization brings new insights into the dynamic processes that link greenland9s dansgaard oeschger do abrupt temperature fluctuations to antarctic temperature variability it is shown that consistent with the presence of polar synchronization the time series of the most representative abrupt climate events of the last glaciation recorded in greenland and antarctica can be transformed into one another by a 2 phase shift with antarctica temperature variations leading greenland9s this plus the fact that remarkable close simulations of the time series are obtained with a model consisting of a few nonlinear differential equations suggest the intriguing possibility that there are simple rules governing the complex behavior of global paleoclimate

enso suppression due to weakening of the north atlantic thermohaline circulation changes of the north atlantic thermohaline circulation thc excite wave patterns that readjust the thermocline globally this paper examines the impact of a freshwater induced thc shutdown on the depth of the pacific thermocline and its subsequent modification of the el nino southern oscillation enso variability using an intermediate complexity global coupled atmosphere ocean sea ice model and an intermediate enso model respectively it is shown by performing a numerical eigenanalysis and transient simulations that a thc shutdown in the north atlantic goes along with reduced enso variability because of a deepening of the zonal mean tropical pacific thermocline a transient simulation also exhibits abrupt changes of enso behavior depending on the rate of thc change the global oceanic wave adjustment mechanism is shown to play a key role also on multidecadal time scales simulated multidecadal global sea surface temperature sst patterns show a large degree of similarity with previous climate reconstructions suggesting that the observed pan oceanic variability on these time scales is brought about by oceanic waves and by atmospheric teleconnections

processes governing the recovery of a perturbed thermohaline circulation in hadcm3 abstract in an experiment with the latest version of the hadley centre climate model the model response has been analyzed after the thermohaline circulation thc in the atlantic ocean has been suppressed the suppression is induced by a strong initial perturbation to the salinity distribution in the upper layer of the northern north atlantic the model is then allowed to adjust freely salinity gradually increases and deep water formation in the greenland and norwegian seas restarts later also in the labrador sea the meridional overturning recovers after about 120 yr in the first few decades when the overturning is very weak surface air temperature is dominated by cooling of much of the northern hemisphere and weak warming of the southern hemisphere leading to maximum global cooling of 0 9 c the disruption to the atmosphere s radiation balance results in a downward flux anomaly at the top of the atmosphere maximally 0 55 w m 2 in the first decade then decreasing with the thc recovery the processes

reply to comment on a nonhydrostatic version of the penn state ncar mesoscale model validation tests and simulations of an atlantic cyclone and cold front

ice core age dating and paleothermometer calibration based on isotope and temperature profiles from deep boreholes at vostok station east antarctica an interpretation of the deuterium profile measured along the vostok east antarctica ice core down to 2755 m has been attempted on the basis of the borehole temperature analysis an inverse problem is solved to infer a local geophysical metronome the orbital signal in the surface temperature oscillations expressed as a sum of harmonics of milankovich periods by correlating the smoothed isotopic temperature record to the metronome a chronostratigraphy of the vostok ice core is derived with an accuracy of 3 0 4 5 kyr the developed timescale predicts an age of 241 kyr at a depth of 2760 m the ratio 13d 13t i between deuterium content and cloud temperature fluctuations at the top of the inversion layer is examined by fitting simulated and measured borehole temperature profiles the conventional estimate of the deuterium temperature slope corresponding to the present day spatial ratio 9 per mil oc is confirmed in general however the mismatch between modeled and measured borehole temperatures decreases noticeably if we allow surface temperature responsible for the thermal state of the ice sheet to undergo more intensive precession oscillations than those of the inversion temperature traced by isotope record with this assumption we obtain the long term temporal deuterium temperature slope to be 5 8 6 5 per mil oc which implies that the glacial interglacial temperature increase over central antarctica was about 15oc in the surface temperature and 10oc in the inversion temperature past variations of the accumulation rate and the corresponding changes in the ice sheet surface elevation are simultaneously simulated

precise interpolar phasing of abrupt climate change during the last ice age a new ice core from west antarctica shows that during the last ice age abrupt northern hemisphere climate variations were followed two centuries later by a response in antarctica suggesting an oceanic propagation of the climate signal to the southern hemisphere high latitudes