eddy resolving observation of the north pacific subtropical mode water abstracthydrographic data obtained by high resolution shipboard observations and argo profiling floats have been analyzed to study the mesoscale structure and circulation of the north pacific subtropical mode water stmw the float data show that in the late winter of 2008 stmw having a temperature of approximately 18 8 17 7 and 16 6 c formed west of 140 e at 140 150 e and east of 150 e respectively in the recirculation gyre south of the kuroshio extension after spring the newly formed stmw gradually shift southward decreasing in thickness simultaneously the stmws of 16 6 and 17 7 c are gradually stirred and then mixed in terms of properties in late fall they seem to be integrated to form a single group of stmws having a temperature centered at 17 2 c such stmw circulation in 2008 is much more turbulent than that in 2006 which was investigated in a previous study the difference between the two years is attributed to the more variable state of the kuroshio extension in 2008 associate

climatology of vertical wind shear over the tropical atlantic abstract the spatiotemporal variability of the 200 850 hpa vertical wind shear over the tropical atlantic is examined for a period of 46 yr this work extends and updates past studies by considering a longer data record as well as a tropospheric deep measure of vertical wind shear composite fields are constructed to illustrate the spatial pattern of the large scale circulation associated with the mean and extreme cases of vertical shear within the tropical atlantic the contemporaneous relationship of vertical shear with el nino southern oscillation enso and sahel precipitation are also examined while the enso shear correlation appears to have slightly strengthened during the past decade the sahel shear correlation has become significantly degraded a combined empirical orthogonal function eof analysis of the zonal and meridional components of the vertical shear reveals interannual and multidecadal modes the leading eof exhibits mainly interannual variability and is highly correlated with enso th

an analysis of moisture fluxes into the gulf of california this study examines the nature of episodes of enhanced warm season moisture flux into the gulf of california both spatial structure and primary time scales of the fluxes are examined using the 40 yr ecmwf re analysis data for the period 1980 2001 the analysis approach consists of a compositing technique that is keyed on the low level moisture fluxes into the gulf of california the results show that the fluxes have a rich spectrum of temporal variability with periods of enhanced transport over the gulf linked to african easterly waves on subweekly 3 8 day time scales the madden julian oscillation mjo at intraseasonal time scales 20 90 day and intermediate 10 15 day time scale disturbances that appear to originate primarily in the caribbean sea western atlantic ocean in the case of the mjo enhanced low level westerlies and large scale rising motion provide an environment that favors large scale cyclonic development near the west coast of central america that over the course of about 2 weeks expands northward along the coast eventually reaching the mouth of the gulf of california where it acts to enhance the southerly moisture flux in that region on a larger scale the development includes a northward shift in the eastern pacific itcz enhanced precipitation over much of mexico and the southwestern united states and enhanced southerly southeasterly fluxes from the gulf of mexico into mexico and the southwestern and central united states in the case of the easterly waves the systems that reach mexico appear to redevelop reorganize on the pacific coast and then move rapidly to the northwest to contribute to the moisture flux into the gulf of california the most intense fluxes into the gulf on these time scales appear to be synchronized with a midlatitude short wave trough over the u s west coast and enhanced low level southerly fluxes over the u s great plains the intermediate 10 15 day time scale systems have zonal wavelengths roughly twice that of the easterly waves and their initiation appears to be linked to an extratropical u s east coast ridge and associated northeasterly winds that extend well into the caribbean sea during their development phase the short 3 8 day and to a lesser extent the intermediate 10 15 day time scale fluxes tend to be enhanced when the convectively active phase of the mjo is situated over the americas

ice sheet control of continental erosion in central and southern chile 36 41 s over the last 30 000 years bulk sediment chemistry from three chilean continental margin ocean drilling program sites constrains regional continental erosion over the past 30 000 years sediments from thirteen rivers that drain the mostly igneous andes and the mostly metamorphic coast range along with existing rock chemistry datasets define terrestrial provenance for the continental margin sediments andean river sediments have high mg al relative to coast range river sediments near 36 s marine sediments have high mg al i e more andean sources during the last glacial period and lower mg al less andean sources during the holocene near 41 s a ti rich source likely from coast range igneous intrusions is prevalent during holocene time whereas high mg al andean sources are more prevalent during the last glacial period we infer that there is a dominant ice sheet control of sediment sources at 36 s andean sourced sediment decreased as andean mountain glaciers retreated after w17 6 ka coincident with local oceanic warming and southward retreat of the patagonian forest and by inference westerly winds at 41 s andean sediment dominance peaks and then rapidly declines at w19 ka coincident with local oceanic warming and the earliest deglacial sea level rise we hypothesize that this decreased flux of andean material in the south is related to rapid retreat of the marine based portion of the patagonian ice sheet in response to global sea level rise as the resulting flooding of the southern portion of the central valley created a sink for andean sediments in this region reversal of the decreasing deglacial mg al trend at 41 s from 14 5 to 13 0 ka is consistent with a brief re advance of the patagonian ice sheet coincident with the antarctic cold reversal

multicore structure of the north pacific subtropical mode water from enhanced argo observations seventeen argo profiling floats with enhanced vertical and temporal sampling were deployed in the kuroshio recirculation gyre in the western north pacific in late march 2014 the subtropical mode water stmw observed in many profiles displays a multicore structure with more than one minima in potential vorticity pv corroborated by vertical covariations in apparent oxygen utilization aou these cores are classified into four submodes according to density and aou the submode waters are typically 100 m thick in which pv varies by 1 10 10 m 1 s 1 and aou by 10 mole kg the stmw multicore structure is most frequently observed in spring gradually taken over by single core profiles into summer the seasonal evolution is suggestive of vertical mixing especially in stmw of lower density

formation and spreading of subtropical mode water in the north pacific a time averaged description of the formation and spreading of north pacific subtropical mode water npstmw is presented the formation of npstmw is studied using transpac expendable bathythermograph data the data are transformed into a stream coordinate system and averaged the coordinate system uses the position of the kuroshio front as its origin maps are presented of the temperature structure and mixed layer distribution in winter relative to the kuroshio front the formation of npstmw occurs in two separate stages cooling and thickening as water flows at the surface in the kuroshio in winter the water is cooled by the intense ocean atmosphere heat flux taking place in the area when water leaves the kuroshio to the south the thermocline underneath becomes deeper convection is able to penetrate deep into the water column and the heat flux acts more to thicken the surface mixed layer rather than reduce the temperature the area south of the kuroshio where relatively homogeneous waters are found is the source region for npstmw at the end of the winter the thick mixed layers are assumed to be covered over by a seasonal thermocline and become npstmw the levitus 1982 data are used to study the way in which npstmw is spread away from its source region by the subtropical circulation the distribution of potential vorticity pv on four npstmw isopycnals is studied with low pv used as a tracer for npstmw the pv reveals a pattern of differential spreading whereby npstmw formed in the western part of the source region is advected to the west after its formation npstmw formed farther east is advected more to the south or east after formation differential spreading allows npstmw to be found in a large part of the northwestern subtropical gyre well away from its source region the distribution of npstmw described by masuzawa 1969 with npstmw getting colder from west to east is explained as a combination of the distribution of npstmw at its source and the way it is spread after it is formed

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

the dynamics of the west african monsoon part v the detection and role of the dominant modes of convectively coupled equatorial rossby waves abstract this study is the last in a series of papers addressing the dynamics of the west african summer monsoon at intraseasonal time scales between 10 and 90 days the signals of convectively coupled equatorial rossby er waves within the summer african monsoon have been investigated after filtering noaa outgoing longwave radiation olr data within a box delineated by the dispersion curves of the theoretical er waves two families of waves have been detected in the 10 100 day periodicity band by performing a singular spectrum analysis on a regional index of er filtered olr for each family the first eof mode has been retained to focus on the main convective variability signal within the periodicity band of 30 100 days an er wave pattern with an approximate wavelength of 13 500 km has been depicted this er wave links the mjo mode in the indian monsoon sector with the main mode of convective variability over west and central africa this confirms the investigations carried out in previous studies wi

a synoptic scale wave of 6 9 day period in the atlantic tropical troposphere during summer 1981 abstract using the ecmwf analyses this study documents a tropospheric synoptic scale wave in the tropical atlantic during summer 1981 it has a 6 9 day period and a westward velocity of about 8 5 longitude per day the wave structure has features similar to a mixed rossby gravity wave it is suggested that it may be a normal mode of the earth atmosphere

characteristics of north african 6 9 day waves during summer 1981 abstract this study applies compositing methods to ecmwf model analyses during july and august 1981 to determine the structure of synoptic scale waves with periods of 6 9 days over northern africa these ware intermittent in time are most regular in period and amplitude west of the greenwich meridian in a narrow longitude band though there is a suggestion of their existence between 15 e and 0 the average wavelength is 5000 km and the westward velocity is 6 7 longitude day 1 the horizontal wind pattern in midtroposphere 700 and 500 hpa consists of two vortices of opposite signs on either side of 12 5 n with maximum perturbation of the zonal wind component at this latitude and maximum perturbation of the meridional wind component at 5 7 5 n and at 17 5 20 n temperature is modulated by the passage of the waves throughout the troposphere this structure is very different from that of the 3 4 day african wave

climatology and decadal variations in multicore structure of the north pacific subtropical mode water the pycnostad of the north pacific subtropical mode water stmw often displays multiple vertical minima in the potential vorticity profile argo profile data from 2004 to 2015 are used to investigate inter annual to decadal variations of the multicore structure climatologically about 24 pycostads of stmw have multicore structure and most of them distribute in the region west of 150 e stmw cores are classified into three sub modes the cold middle and warm ones with potential temperatures of 16 0 17 c 17 18 c and 18 19 5 c respectively the kuroshio extension ke varies between stable and unstable states the unstable ke with large meanders increases the subsurface stratification and shoals the winter mixed layer east of 150 e with warmer temperatures there the dominant stmw type varies from the cold single type in stable ke years making up 72 of the profiles with stmw to the middle single one 53 in unstable years the variation of the dominant stmw type in the region east of 150 e subsequently affects the multicore structure of stmw west of 150 e in a broad region between 130 e and 180 e profiles with stmw are fewer in unstable years but the proportion of multicore profiles increases among stmw profiles this might be due to the split recirculation gyre with a chaotic ke

subtropical mode water variation in the northwestern part of the north pacific subtropical gyre temporal variations of the north pacific subtropical mode water npstmw are studied with the proper temporal resolution for describing seasonal variation using monthly hydrographic data taken near the ogasawara islands npstmw is formed south of the kuroshio and the kuroshio extension in late winter and advected to the ogasawara site by the southwestward westward return flow of the kuroshio recirculation while npstmw is seen at the ogasawara site in almost all seasons npstmw with a higher core temperature is advected to this site in april and one with a colder core follows in and after june until january or february furthermore the npstmw core temperature shows considerable interannual variation this variation is very similar to that found in other regions away from the ogasawara site suggesting that it reflects the larger scale variation of npstmw and that this site would be suitable for monitoring the npstmw core temperature a significant correlation between the npstmw core temperature and the monsoon index which is defined as the difference in the sea level pressure between nemuro japan and irkutsk russia as an indicator of wintertime cooling indicates that npstmw contains a memory of wintertime cooling in the preceding winter

vertical structure of mesoscale eddies in the eastern south pacific ocean a composite analysis from altimetry and argo profiling floats 1 the mean vertical structure of mesoscale eddies in the peru chile current system is investigated by combining the historical records of argo float profiles and satellite altimetry data a composite average of 420 526 profiles acquired by argo floats that surfaced into cyclonic anticyclonic mesoscale eddies allowed constructing the mean three dimensional eddy structure of the eastern south pacific ocean key differences in their thermohaline vertical structure were revealed the core of cyclonic eddies ces is centered at 150 m depth within the 25 2 26 0 kg m 3 potential density layer corresponding to the thermocline in contrast the core of the anticyclonic eddies aes is located below the thermocline at 400 m depth impacting the 26 0 26 8 kg m 3 density layer this difference was attributed to the mechanisms involved in the eddy formation while intrathermocline ces would be formed by instabilities of the surface equatorward coastal currents the subthermocline aes are likely to be shed by the subsurface poleward peru chile undercurrent in the eddy core maximum temperature and salinity anomalies are of 1 c and 0 1 with positive negative values for aes ces this study also provides new insight into the potential impact of mesoscale eddies for the cross shore transport of heat and salt in the eastern south pacific considering only the fraction of the water column associated with the fluid trapped within the eddies each ce and ae has a typical volume anomaly flux of 0 1 sv and yields to a heat and salt transport anomaly of 1 3 1011 w and 3 8 103 kg s 1 respectively

mesoscale eddy effects on the subduction of north pacific mode waters mesoscale eddy effects on the subduction of north pacific mode waters are investigated by comparing observations and ocean general circulation models where eddies are either parameterized or resolved the eddy resolving models produce results closer to observations than the noneddy resolving model there are large discrepancies in subduction patterns between eddy resolving and noneddy resolving models in the noneddy resolving model subduction on a given isopycnal is limited to the cross point between the mixed layer depth mld front and the outcrop line whereas in eddy resolving models and observations subduction takes place in a broader zonally elongated band within the deep mixed layer region mesoscale eddies significantly enhance the total subduction rate helping create remarkable peaks in the volume histogram that correspond to north pacific subtropical mode water stmw and central mode water cmw eddy enhanced subduction preferentially occurs south of the winter mean outcrop with an anticyclonic eddy to the west and a cyclonic eddy to the east the outcrop line meanders south and the thermocline mld shoals eastward as eddies propagate westward the mld shoals shielding the water of low potential vorticity from the atmosphere the southward eddy flow then carries the subducted water mass into the thermocline the eddy subduction processes revealed here have important implications for designing field observations and improving models

generation of african easterly wave disturbances relationship to the african easterly jet abstract the relationship between african easterly waves and the background climatology in which they form is studied using a regional climate model the surface and lateral boundary conditions in the model are manipulated to modify the background climatology especially the african easterly jet and the itcz and the behavior of the waves in these different settings is evaluated three climate simulations are presented with monthly mean lateral and surface boundary conditions one has a strong jet and a strong itcz the second has a strong jet and a weak itcz and the third has a weak jet and a strong itcz in these simulations the presence of wave activity is more closely associated with the concentration of the itcz than the strength of the african easterly jet in particular the simulation with a strong jet accompanied by a weak itcz does not produce significant wave activity but a weak jet with a strong itcz has realistic wave disturbances both the charney stern and the fjortoft necessary conditi

easterly wave regimes and associated convection over west africa and tropical atlantic results from the ncep ncar and ecmwf reanalyses ncep ncar and ecmwf daily reanalyses are used to investigate the synoptic variability of easterly waves over west africa and tropical atlantic at 700 hpa in northern summer between 1979 1995 1979 1993 for ecmwf spectral analysis of the meridional wind component at 700 hpa highlighted two main periodicity bands between 3 and 5 days and 6 and 9 days the 3 5 day easterly wave regime has already been widely investigated but only on shorter datasets these waves grow both north and south of the african easterly jet aej the two main tracks noted over west africa at 5 n and 15 n converge over the atlantic on latitude 17 5 n these waves are more active in august september than in june july their average wavelength phase speed varies from about 3000 km 8 m s 1 north of the jet to 5000 km 12 m s 1 south of the jet rainfall convection and monsoon flux are significantly modulated by these waves convection in the inter tropical convergence zone itcz being enhanced in the trough and ahead of it with a wide meridional extension compared to the 3 5 day waves the 6 9 day regime is intermittent and the corresponding wind field pattern has both similar and contrasting characteristics the only main track is located north of the aej along 17 5 n both over west africa and the atlantic the mean wavelength is higher about 5000 km long and the average phase speed is about 7 m s 1 then the wind field perturbation is mostly evident at the aej latitude and north of it the perturbation structure is similar to that of 3 5 days in the north except that the more developed circulation centers moving more to the north lead to a large modulation of the jet zonal wind component south of the aej the wind field perturbation is weaker and quite different the zonal wind core of the jet appears to be an almost symmetric axis in the 6 9 day wind field pattern a clockwise circulation north of the aej being associated with a counter clockwise circulation south of the jet and vice versa these 6 9 day easterly waves also affect significantly rainfall convection and monsoon flux but in a different way inducing large zonal convective bands in the itcz mostly in the trough and behind it as opposed to the 3 5 day wave regime these rainfall anomalies are associated with anomalies of opposite sign over the guinea coast and the sahelian regions over the continent these waves are more active in june july and in august september over the ocean gate phase i gave an example of such an active 6 9 day wave pattern considered as a sequence of weak easterly wave activity this phase was also a sequence of high 6 9 day easterly wave activity we suggest that the 6 9 day regime results from an interaction between the 3 5 day easterly wave regime maintained by the barotropic baroclinic instability of the aej and the development of strong anticyclonic circulations north of the jet over west africa and both north and south of the jet over the atlantic significantly affecting the jet zonal wind component the permanent subtropical anticyclones azores libya st helena could help initiation and maintenance of such regime over west africa and tropical atlantic based on an a priori period band criterion our synoptic classification has enabled us to point out two statistical and meteorological easterly wave regimes over west africa and tropical atlantic ncep ncar and ecmwf reanalyses are in good agreement the main difference being a more developed easterly wave activity in the ncep ncar reanalyses especially for the 3 5 day regime over the atlantic

case study of a developing african easterly wave during namma an energetic point of view abstract the west african perturbation that subsequently evolved into hurricane helene 2006 during nasa s african monsoon multidisciplinary analysis namma 15 august 14 september 2006 and amma s third special observing period sop 3 15 29 september 2006 has been simulated with the nonhydrostatic meso nh model using parameterized convection the simulated disturbance evolved over west africa and the adjacent eastern tropical atlantic through interactions between different processes at the convective scale mesoscale and synoptic scale the aim of this paper is to quantify the energetics of the simulated disturbance a set of energy equations is first developed in the hydrostatic case to solve the limitations of lorenz s analysis when applied to a finite domain it is shown that this approach is also valid in the compressible and in the anelastic case in order to apply it to the meso nh results application to the simulated pre helene disturbance allows one to determine the most important terms in

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

diagnosis of the mjo modulation of tropical cyclogenesis using an empirical index the modulation of tropical cyclone activity by the madden julian oscillation mjo is explored using an empirical genesis potential gp index composite anomalies of the genesis index associated with the different mjo phases are consistent with the composite anomalies in tc genesis frequency that occur in the same phases indicating that the index captures the changes in the environment that are at least in part responsible for the genesis frequency changes of the four environmental variables that enter the genesis potential index the midlevel relative humidity makes the largest contribution to the mjo composite gp anomalies the second largest contribution comes from the low level absolute vorticity and only very minor contributions come from the vertical wind shear and potential intensity when basin integrated mjo composite anomalies of the gp index are regressed against basin integrated composite anomalies of tc genesis frequency the results differ quantitatively from those obtained from the analogous calculation performed on the annual climatologies in the two quantities the gp index captures the mjo modulation of tc genesis to a lesser degree than the climatological annual cycle of genesis to which it was originally tuned this may be due to weaknesses of the reanalysis or indicative of the importance of precursor disturbances not well captured in the gp index computed from weekly data to the intraseasonal tc genesis frequency fluctuations

differential formation and circulation of north pacific central mode water abstract a repeat hydrographic section along 165 e was analyzed to verify a westward extension of the formation region of the north pacific ocean central mode water cmw suggested by previous synoptic observations and to investigate the relation between the formation region and thermohaline fronts the cmw formation region extends at least as far west as 155 e much farther than recognized in a previous study based on climatology it is located in two interfrontal regions between the kuroshio extension front and the kuroshio bifurcation front kbf and between the kbf and the subarctic front where two types of cmw namely the lighter variety with potential density of 25 8 26 2 kg m 3 and the denser one of 26 3 26 4 kg m 3 are formed how this differential formation of cmw is reflected in its gyrewide distribution was examined using one time sections of the world ocean circulation experiment woce hydrographic program in the north pacific the main circulation paths of the two types of cmw diverge eas

evidence of two regimes of easterly waves over west africa and the tropical atlantic synoptic scale easterly waves at 700 hpa have been studied over west africa and the tropical atlantic for the summers of 1979 1995 spectral analyses fast fourier and wavelet transforms of 700 hpa meridional wind component along 17 5 n enable to point out two band periods between 3 and 5 days and between 6 and 9 days an example of each wave is shown composite analysis confirms the evidence of two such regimes of easterly waves during summer over west africa and the tropical atlantic the 6 9 day wave regime differ from the 3 5 day wave regime by larger anticyclonic cells originated from the libyan and the azores areas and by more northern tracks

on the instability of the african easterly jet and the generation of african waves reversals of the potential vorticity gradient abstract the relationship between the generation of african easterly waves and instability growing in regions with reversed potential vorticity gradients is studied using a regional climate model results indicate that the convective generation of potential vorticity pv due to the meridional and vertical gradients of diabatic heating in the upper and lower troposphere causes a vertically elongated pv anomaly on the southern flank of the african easterly jet this pv maximum at 9 n in the midtroposphere together with a pv minimum near 15 n at lower levels because of dry convection over the sahara reverses the meridional pv gradient between 9 and 15 n which suggests that the zonal flow may be unstable in this region analysis of the seasonal mean eliassen palm flux for african waves indicates that wave energy generated convectively through baroclinic overturning in the upper troposphere propagates downward and triggers barotropic conversions south of the jet and baroclinic conversions below and north

monsoons itczs and the concept of the global monsoon earth s tropical and subtropical rainbands such as intertropical convergence zones itczs and monsoons are complex systems governed by both large scale constraints on the atmospheric general circulation and regional interactions with continents and orography and coupled to the ocean monsoons have historically been considered as regional large scale sea breeze circulations driven by land sea contrast more recently a perspective has emerged of a global monsoon a global scale solstitial mode that dominates the annual variation of tropical and subtropical precipitation this results from the seasonal variation of the global tropical atmospheric overturning and migration of the associated convergence zone regional subsystems are embedded in this global monsoon localized by surface boundary conditions parallel with this much theoretical progress has been made on the fundamental dynamics of the seasonal hadley cells and convergence zones via the use of hierarchical modeling approaches including aquaplanets here we review the theoretical progress made and explore the extent to which these advances can help synthesize theory with observations to better understand differing characteristics of regional monsoons and their responses to certain forcings after summarizing the dynamical and energetic balances that distinguish an itcz from a monsoon we show that this theoretical framework provides strong support for the migrating convergence zone picture and allows constraints on the circulation to be identified via the momentum and energy budgets limitations of current theories are discussed including the need for a better understanding of the influence of zonal asymmetries and transients on the large scale tropical circulation

three dimensional structure and dynamics of african easterly waves part i observations the mean structure of african easterly waves aews over west africa and the adjacent atlantic is isolated by projecting dynamical fields from reanalysis and radiosonde data onto space time filtered satellite derived outgoing longwave radiation these results are compared with previous studies and an idealized modeling study in a companion paper which provides evidence that the waves bear a close structural resemblance to the fastest growing linear normal mode of the summertime basic state flow over africa there is a significant evolution in the three dimensional structure of aews as they propagate along 10 n across west africa at this latitude convection occurs in northerly flow to the east of the greenwich meridian then shifts into the wave trough and finally into southerly flow as the waves propagate offshore into the atlantic itcz in contrast to the north of the african easterly jet along 15 n convection remains in southerly flow throughout the waves trajectory along 10 n over west africa the location of convection is consistent with the adiabatic dynamical forcing implied by the advection of perturbation vorticity by the mean thermal wind in the zonal direction as in the companion paper offshore and along 15 n the relationship between the convection and dynamics is more complex and not as easily explained in terms of dynamical forcing alone

transient simulation of last deglaciation with a new mechanism for bolling allerod warming we conducted the first synchronously coupled atmosphere ocean general circulation model simulation from the last glacial maximum to the bolling allerod ba warming our model reproduces several major features of the deglacial climate evolution suggesting a good agreement in climate sensitivity between the model and observations in particular our model simulates the abrupt ba warming as a transient response of the atlantic meridional overturning circulation amoc to a sudden termination of freshwater discharge to the north atlantic before the ba in contrast to previous mechanisms that invoke amoc multiple equilibrium and southern hemisphere climate forcing we propose that the ba transition is caused by the superposition of climatic responses to the transient co 2 forcing the amoc recovery from heinrich event 1 and an amoc overshoot

mjo and tropical cyclogenesis in the gulf of mexico and eastern pacific case study and idealized numerical modeling the role of the madden julian oscillation mjo in modulating the frequency and location of tropical cyclogenesis over the eastern pacific and the gulf of mexico during august september 1998 is examined during the nonconvective phase of the mjo convection and low level cyclonic vorticity occurred primarily in conjunction with the intertropical convergence zone itcz during the convective phase convection low level cyclonic vorticity and convergence expanded into the northeastern pacific and the gulf of mexico this was accompanied by enhanced eddy kinetic energy and barotropic energy conversions as compared to the nonconvective phase consistent with previous research during the nonconvective phase of the mjo vertical shear was relatively weaker but tropical cyclones tended to form mainly within the itcz on the contrary during the convective phase vertical wind shear exceeded 10 m s 1 over much of this region and tropical cyclone development occurred north of the itcz near the mexican pacific coast and the gulf of mexico idealized numerical experiments are conducted using a barotropic model with time invariant basic states representative of the nonconvective and convective phases of the mjo the simulations indicate that the propagation paths as well as the amplification of the eddies differ substantially between the two phases during the nonconvective phase the waves tend to propagate westward into the eastern pacific during the convective phase stronger southerlies steer the waves into the gulf of mexico the mjo related modulation of tropical cyclogenesis in the eastern pacific and gulf of mexico thus appears to involve anomalous convergence cyclonic vorticity vertical wind shear and differing tracks of easterly waves

climate modulation of north atlantic hurricane tracks the variability of north atlantic tropical storm and hurricane tracks and its relationship to climate variability is explored tracks from the north atlantic hurricane database for the period 1950 2007 are objectively separated into four groups using a cluster technique that has been previously applied to tropical cyclones in other ocean basins the four clusters form zonal and meridional separations of the tracks the meridional separation largely captures the separation between tropical and more baroclinic systems while the zonal separation segregates gulf of mexico and cape verde storms general climatologies of the seasonality intensity landfall probability and historical destructiveness of each cluster are documented and relationships between cluster membership and climate variability across a broad spectrum of time scales are identified composites with respect to cluster membership of sea surface temperature and other environmental fields show that regional and remote modes of climate variability modulate the cluster members in substantially

near synchronous interhemispheric termination of the last glacial maximum in mid latitudes isotopic records from polar ice cores imply globally asynchronous warming at the end of the last glaciation however 10be exposure dates show that large scale retreat of mid latitude last glacial maximum glaciers commenced at about the same time in both hemispheres the timing of retreat is consistent with the onset of temperature and atmospheric co2 increases in antarctic ice cores we suggest that a global trend of rising summer temperatures at the end of the last glacial maximum was obscured in north atlantic regions by hypercold winters associated with unusually extensive winter sea ice

simple solutions for the summer shallow atmospheric circulation over north africa the spring to summer shallow atmospheric circulation over north africa is driven by two desert heat lows dhls one over sahara shl and one over arabia ahl with cyclones embedded in the convective layer capped by mid tropospheric anticyclones the aim of this work is to produce a minimal theoretical framework for these dynamical features in terms of kelvin mixed and planetary mode solutions to a two layer matsuno gill model with a lower rayleigh frictional layer dynamically coupled to an almost frictionless upper layer results show that a dhl drives a walker like cell with rising air over the low and subsiding air to its west with the lower level cyclone to the east of the mid tropospheric anticyclone the latter being bounded to the south west by an unstable easterly jet these features related to frictional differences between the two layers are enhanced by ambient easterly winds in spring the stronger shl drives a cell with rising air over west africa and subsiding over the atlantic the weaker ahl drives a cell with rising air over arabia and subsiding over east africa in summer the stronger ahl drives a cell with rising air over arabia and subsiding over libya and the weaker shl drives a cell with rising air over west sahara and subsiding over the atlantic the concurrent contributions of easterly winds monsoonal low level convergence and seasonal airborne dust warming strengthen the shl making its winds stronger than those of the ahl in addition a third order expansion of the coriolis parameter strengthens the zonal winds and weakens the meridional winds these contributors strengthen anticyclones over the east mediterranean and to the west of gibraltar the ability of the model in representing the main features of the north african atmospheric circulations suggests a potential for better understanding climate dynamics in connected regions mediterranean tropical atlantic

three dimensional structure and dynamics of african easterly waves part iii genesis this paper promotes the view that african easterly waves aews are triggered by localized forcing most likely associated with latent heating upstream of the region of observed aew growth a primitive equation model is used to show that aews can be triggered by finite amplitude transient and localized latent heating on a zonally varying basic state that is linearly stable heating close to the entrance region of the african easterly jet aej is shown to initiate aews downstream the heating leads to an initial trough that reaches the west african coast about 5 7 days later depending on the nature of the heating profile after this a structure that projects strongly onto the leading linear normal mode of the basic state becomes established characterized by a number of westward propagating disturbances that strongly resemble aews the sensitivity of the forced aews to the nature and location of the heating profile is examined aews are most efficiently triggered by heating profiles that establish lower tropospheric circulations close to the entrance region of the aej in the present study this was best achieved by lower tropospheric heating from shallow convection or upper level heating and lower level cooling from a stratiform precipitation profile both profiles have significant heating gradients in the vertical in the mid to lower troposphere this triggering paradigm for the genesis of aews has consequences for the variability and predictability of aews at weather and climate time scales in addition to the nature of the aej often emphasized it is crucial to consider the nature and variability of upstream heating triggers

maintenance of the african easterly jet the maintenance of the african easterly jet aej has been examined using a zonally symmetric general circulation model with simple parametrizations it is shown that the aej is maintained in association with two diabatically forced meridional circulations one associated with surface fluxes and dry convection in the saharan heat low region and one associated with deep moist convection in the intertropical convergence zone equatorward of this the heat low heating which reaches the height of the aej around 700 mb is particularly important in maintaining the aej and its associated meridional gradients in potential vorticity it is concluded that the mean observed aej results from a combination of the diabatically forced meridional circulations which maintain it and easterly waves which weaken it

cosmogenic nuclide exposure ages for moraines in the lago san martin valley argentina at several times during the quaternary a major eastward flowing outlet glacier of the former patagonian ice sheet occupied the lago san martin valley in argentina 49 s 72 w we present a glacial chronology for the valley based on geomorphological mapping and cosmogenic nuclide 10be exposure ages n 10 of boulders on moraines and lake shorelines there are five prominent moraine belts in the lago san martin valley associated with extensive sandar glaciofluvial outwash plains and former lake shorelines cosmogenic nuclide exposure ages for boulders on these moraines indicate that they formed at 14 3 1 7 ka 22 4 2 3 ka 34 4 3 4 ka to 37 6 3 4 ka and possibly 60 3 5 ka and 99 11 ka 1 these dated glacier advances differ from published chronologies from the lago san martin valley based on 14c age determinations from organic sediments and molluscs in meltwater channels directly in front of moraines or in kettleholes within end moraine ridges the moraine boulder ages also point to possible pre lgm glacial advances during the last glacial cycle and a key observation from our data is that the lgm glaciers were probably less extensive in the lago san martin valley than previously thought

african easterly jet barotropic instability waves and cyclogenesis abstract this study investigates the structure of the african easterly jet focusing on instability processes on a seasonal and subseasonal scale with the goal of identifying features that could provide increased predictability of atlantic tropical cyclogenesis the modern era retrospective analysis for research and applications merra is used as the main investigating tool merra is compared with other reanalyses datasets from major operational centers around the world and was found to describe very effectively the circulation over the african monsoon region in particular a comparison with precipitation datasets from the global precipitation climatology project shows that merra realistically reproduces seasonal precipitation over that region the verification of the generalized kuo barotropic instability condition computed from seasonal means is found to have the interesting property of defining well the location where observed tropical storms are detected this property does not appear to be an arti

a subsurface pathway for low potential vorticity transport from the central north pacific toward taiwan island 1 analysis of the simple ocean data assimilation product reveals that the central north pacific 28 n 35 n 150 e 170 w is one of the main formation regions for low potential vorticity water of density between 25 4 and 25 8 it is found that the low potential vorticity water is transported from the central north pacific toward the east of taiwan island along a subsurface pathway following the subtropical gyre circulation and it takes approximately 12 years propagation of pycnocline thickness anomalies is detected along the pathway in association with the decadal variability of the subduction rate

analysis of convection and its association with african easterly waves abstract the association between convection and african easterly wave aew activity over tropical africa and the tropical atlantic during the boreal summer is examined using satellite brightness temperature tb and ecmwf reanalysis datasets spectral analysis using 18 yr of tb data shows significant variance in the 2 6 day range across most of the region within the regions of deep convection this time scale accounts for about 25 35 of the total variance the 2 6 day convective variance has similar amplitudes over western and eastern africa while dynamic measures of aew activity show stronger amplitudes in the west this study suggests that weak aew activity in the east is consistent with initial wave development there and indicates that convection triggered on the western side of the mountains over central and eastern africa near darfur western sudan and ethiopia has a role in initiating aews westward the subsequent development and growth of aews in west africa is associated with stronger cohe

links between tropical cyclone activity and madden julian oscillation phase in the north atlantic and northeast pacific basins abstract the leading intraseasonal mode of atmospheric and oceanic variability the madden julian oscillation mjo influences tropical and extratropical sea level pressure temperature divergent and rotational wind components moisture and deep convection as a 40 to 50 day oscillation the mjo is also known to influence tropical phenomena including tropical cyclone tc activity in various tc basins the links between the mjo and multiple measures of tc activity including genesis landfall and an integrative accumulated cyclone energy ace index were quantified for multiple tc formation basins across the western hemisphere including the north atlantic and northeast pacific ocean and subbasins for the period 1978 2006 using this relatively long 29 yr tc dataset and employing an upper tropospheric mjo diagnostic that is physically meaningful over the entire western hemisphere this study extends existing research on the relationships between the mjo and tcs the noaa climate prediction cente

a role of eddies in formation and transport of north pacific subtropical mode water 1 hydrographic data acquired during 2001 by argo profiling floats deployed in the kuroshio recirculation region are used to verify the inference that mesoscale eddies prevailing in the recirculation region play an important role in the formation and transport of north pacific subtropical mode water npstmw that is the deeper winter mixed layer is formed preferentially where the thermocline is deeper in association with anticyclonic eddies in the succeeding seasons mesoscale eddies retain npstmw during their southwestward movement from the npstmw formation region so that anticylonic eddies contribute substantially to the npstmw transportation the spatial distributions of the mixed layer depth in winter and the npstmw thickness in the succeeding seasons based on the float data suggest that they are affected by mesoscale eddies the float data also provide the statistical relations of these quantities against the thermocline depth which are consistent with our inference

the west african monsoon dynamics part iii the quasi biweekly zonal dipole abstract this paper presents an investigation of the mechanisms giving rise to the main intraseasonal mode of convection in the african monsoon during northern summer here identified as the quasi biweekly zonal dipole qbzd the qbzd is primarily characterized by a quasi stationary zonal dipole of convection whose dimension is larger than the west african monsoon domain with its two poles centered along the guinean coast and between 30 and 60 w in the equatorial atlantic the qbzd dynamical processes within the atlantic africa domain are examined in some detail the qbzd has a dipole pattern associated with a walker type circulation in the near equatorial zonal plane it is controlled both by equatorial atmospheric dynamics through a kelvin wave like disturbance propagating eastward between its two poles and by land surface processes over africa inducing combined fluctuations in surface temperatures surface pressure and low level zonal winds off the coast of west africa when convection is at a min

on the dynamics of the formation of the kelvin cat s eye in tropical cyclogenesis part i climatological investigation abstractmotivated by dunkerton et al a climatological study of 54 developing easterly waves in 1998 2001 was performed time lagged composites in a translating reference frame following the disturbances indicate a weak meridional potential vorticity pv gradient of the easterly jet and a cyclonic critical layer located slightly to the south of the weak pv gradient consistent with previous findings in the marsupial paradigm using a closed pv contour as a criterion for the formation of the cat s eye it was shown that on average it takes 2 6 days for open pv contours to transform to a closed coherent structure bootstrap analysis was then applied to determine the reliability of the easterly wave like pattern in the composite perturbation pv analysis it is suggested that the coexistence of a nonlinear critical layer and a region of weak meridional pv gradient over several days found to occur in only 25 of the easterly waves might be a major factor to distinguish developing and nondeveloping distur

observations of the subtropical mode water evolution from the kuroshio extension system study abstract properties and seasonal evolution of north pacific ocean subtropical mode water stmw within and south of the kuroshio extension recirculation gyre are analyzed from profiling float data and additional hydrographic and shipboard adcp measurements taken during 2004 the presence of an enhanced recirculation gyre and relatively low mesoscale eddy variability rendered this year favorable for the formation of stmw within the recirculation gyre stmw formed from late winter convection that reached depths greater than 450 m near the center of the gyre the lower boundary of stmw corresponding to 25 5 kg m 3 was set by the maximum depth of the late winter mixed layer properties within the deep portions of the stmw layer remained largely unchanged as the season progressed in contrast the upper boundary of the stmw layer eroded steadily as the seasonal thermocline deepened from late april to august vertical eddy diffusivity responsible for this erosion was estimated from a budget analysis of

atlantic sea surface temperatures and tropical cyclone formation abstract it has long been accepted that interannual fluctuations in sea surface temperature sst in the atlantic are associated with fluctuations in seasonal atlantic basin tropical cyclone frequency to isolate the physical mechanism responsible for this relationship a singular value decomposition svd is used to establish the dominant covarying modes of tropospheric wind shear and sst as well as horizontal sst gradients the dominant svd mode of covarying vertical shear and sst gradients which comprises equatorially confined near zonal vertical wind shear fluctuations across the atlantic basin is highly correlated with both equatorial eastern pacific sst anomalies associated with el nino and west african sahel rainfall while this mode is strongly related to tropical storm hurricanes and major hurricane frequency in the atlantic it is not associated with any appreciable atlantic sst signal by contrast the second svd mode of covarying vertical shear and horizontal sst gradient variability wh

on the relationship between african easterly waves and the african easterly jet this idealized modeling study investigates how convectively triggered african easterly waves aews are influenced by the intraseasonal variability of the african easterly jet aej a set of 10 day averaged zonally varying basic states is constructed with the ncep 2 reanalysis 1979 2006 a primitive equation model is used to simulate linear aews on each of these basic states using the same idealized convective heating localized over the darfur mountains as an initial trigger it is shown that the transient response depends strongly on the basic state with the same trigger many configurations of the aej fail to produce a wave disturbance while others produce strong easterly wave structures necessary conditions for the development of strong waves can be characterized by a strong jet a strong vertical shear or a strong and extended potential vorticity reversal in strong wave cases the jet is extended to the south and west and the jet core is aligned with the maximum of surface westerlies maximizing the vertical shear the pattern that is optimal for generating easterly waves also closely resembles the dominant mode of variation of the aej revealed by an empirical orthogonal function eof analysis of the set of basic states

evolution of the north pacific subtropical mode water in anticyclonic eddies anticyclonic eddies aes trap and transport the north pacific subtropical mode water stmw but the evolution of the stmw trapped in aes has not been fully studied due to the lack of eddy tracking subsurface observations here we analyze profiles from special designed argo floats that follow two stmw trapping aes for more than a year the enhanced daily sampling by these argo floats swirling around the eddies enables an unprecedented investigation into the structure and evolution of the trapped stmw in the aes the upper lower thermocline domes up concaves downward and this lens shaped double thermocline encompasses the thick stmw within the eddy core the lighter stmw 25 0 25 2 trapped in aes dissipates quickly after the formation in winter because of the deepening seasonal thermocline but the denser stmw 25 2 25 4 remains largely unchanged except when the ae passes across the izu ridge the enhanced diapycnal mixing over the ridge weakens the denser stmw appreciably while many aes decay upon hitting the ridge some pass through a bathymetric gap between the hachijojima and bonin islands forming a cross ridge pathway for stmw transport by contrast the north pacific intermediate water npiw underneath is deeper than the eddy trapping depth 600 m and hence left behind east of the izu ridge in argo climatology the shallow stmw 400 m intrudes through the gap westward because of the eddy transport while the npiw 800 m is blocked by the izu ridge

analysis of african easterly wave structures and their role in influencing tropical cyclogenesis abstract composite structures of african easterly waves aews that develop into named tropical cyclones in the atlantic are compared and contrasted with nondeveloping aews using the 40 yr ecmwf re analysis era 40 data and satellite brightness temperature between 1979 and 2001 developing aews are characterized by a more distinctive cold core structure two days before reaching the west african coast as they move westward the convective activity increases further in the vicinity of the guinea highlands region at the same time the aew trough increases its vorticity at low levels consistent with a transformation toward a more warm core structure before it reaches the ocean as the aew moves over the ocean convection is maintained in the trough consistent with the observed tropical cyclogenesis the nondeveloping aew has a similar evolution before reaching the coast except that the amplitudes are weaker and there is less convective activity in the guinea highlands region the nondeveloping aew composite

northern hemisphere forcing of the last deglaciation in southern patagonia although the general patterns of deglacial climate change are relatively well constrained how and to what magnitude large parts of the southern hemisphere responded to deglacial forcings remains unknown particularly for the early part of the last deglaciation we investigate the timing and magnitude of early deglacial climate change using cosmogenic 10 be surface exposure ages of moraines deposited by glaciers in the rio guanaco valley adjacent to the southern patagonian ice field at 50 s we demonstrate that the beginning of ice retreat from the local last glacial maximum occurred at 19 7 1 1 ka with significant retreat commencing at 18 9 0 4 ka concurrent with glacier retreat elsewhere in southern patagonia and new zealand and with warming of southern hemisphere middle to high latitudes a third moraine shows that half of the deglacial retreat upvalley had occurred by 17 0 0 3 ka equilibrium line altitudes and climate simulations show 1 5 c of warming in southern patagonia between 18 9 0 4 ka and 17 0 0 3 ka one third of the total estimated deglacial warming relative to present the climate model links this warming to retreat of northern hemisphere ice sheets ca 19 ka through changes in ocean circulation that caused a bipolar seesaw response resulting in southern hemisphere warming and driving initial deglaciation across southern patagonia

on the madden julian oscillation atlantic hurricane relationship abstract the large scale equatorial circulation known as the madden julian oscillation mjo has been shown to impact tropical cyclone activity in several basins around the globe in this paper the author utilizes an mjo index created by wheeler and hendon to examine its impacts on tropical genesis and intensification in the atlantic large differences in frequency and intensity of tropical cyclone activity are seen both in the tropical atlantic as well as in the northwest caribbean and gulf of mexico depending on the mjo phase coherent changes in upper and lower level winds and relative humidity are likely responsible for these differences since the mjo shows potential predictability out to about two weeks the relationships discussed in this paper may be useful for short term predictions of the probability of tropical cyclone activity in the atlantic as a complement to the already available longer term seasonal predictions

effects of mesoscale eddies on subduction and distribution of subtropical mode water in an eddy resolving ogcm of the western north pacific abstract the effects of mesoscale eddies on the subduction and distribution of the north pacific subtropical mode water stmw are investigated using an eddy resolving ocean general circulation model ogcm first the subduction rate is calculated and the contribution of eddies to the subduction of stmw is estimated it is found that eddy subduction significantly contributes to the total subduction of stmw second eddy thickness transport and diapycnal flux are directly diagnosed to investigate the large scale eddy induced transport process of stmw the large southward eddy thickness transport in the stmw core density is consistent with eddy subduction the eddy transport on the isopycnal surface of stmw is directed down the thickness gradient and traverses the mean flow the meridional eddy transport streamfunction indicates two eddy circulation cells south of 30 n associated with the circulation of stmw these cells flatten density surfaces similar to the effect of the gent and mcwilliams gm schem

effect of mesoscale eddies on subtropical mode water variability from the kuroshio extension system study kess abstract forty eight profiling floats have been deployed in the kuroshio extension ke region since may 2004 as part of the kuroshio extension system study kess project by combining the float temperature salinity measurements with satellite altimetry data this study investigates the role played by mesoscale eddies in controlling the property changes in north pacific subtropical mode water stmw following a 3 yr period of low eddy activity in 2002 04 the ke showed a transition to a high eddy kinetic energy state in 2005 this transition is the result of delayed oceanic response to the 2002 shift in the basin scale surface wind forcing in connection with the pacific decadal oscillation the high eddy kinetic energy state of the ke is characterized by successive shedding of strong cold core rings into the recirculation gyre resulting from the interaction of the ke jet with the shatsky rise or the preexisting cutoff rings by transporting northern origin high potential vorticity pv ke water into t

a mechanism for african monsoon breaks mediterranean cold air surges 1 surges of cold air from the mediterranean into northern africa during the boreal summer are documented and their influence on monsoon breaks is analyzed using tropical rainfall measuring mission rainfall estimates and reanalysis products between 1998 and 2006 6 10 cold air surges occurred each summer with low level temperature anomalies ranging from less than 1 k to over 6 k composite analysis indicates that cold air surges over northern africa persist for 2 10 days and travel equatorward at approximately 5 5 m s 1 which is 0 5 1 5 m s 1 faster than the observed climatological low level meridional flow northern african cold surges have characteristics similar to surges observed elsewhere in the world including a hydrostatically induced ridge of surface pressure and an amplified upper tropospheric ridge trough pattern the african cold surge is preceded by the passage of a shortwave trough and an intensification of the upper tropospheric subtropical westerly jet streak over the mediterranean sea these events are associated with increased confluence in the jet entrance region over the central mediterranean an enhanced direct secondary circulation subsidence and low level ageostrophic northerly flow over northeastern africa composite analysis shows that the passage of a cold surge is associated with an enhancement in convective activity over southern algeria western niger northern mali and mauritania 2 to 5 days before the surge reaches the eastern sahel 17 5 n when northeasterly flow channeled between the atlas and ahaggar mountains strengthens and transports relatively moist air from the western mediterranean and eastern north atlantic over the region and increases moisture convergence over western africa north of 20 n over the eastern sahel of sudan and eastern chad the composite results reveal a break in convective activity and decrease in low level convergence when the surge arrives that persists for about 6 days these results offer great promise for improving the short range prediction of rainfall over northern africa

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

a characterization of african easterly waves on 2 5 6 day and 6 9 day time scales abstractthis study shows that the african easterly wave aew activity over the african monsoon region and the northern tropical atlantic can be divided in two distinct temporal bands with time scales of 2 5 6 and 6 9 days the results are based on a two dimensional ensemble empirical mode decomposition 2d eemd of the modern era retrospective analysis for research and applications merra the novel result of this investigation is that the 6 9 day waves appear to be located predominantly to the north of the african easterly jet aej originate at the jet level and are different in scale and structure from the well known low level 2 5 6 day waves that develop baroclinically on the poleward flank of the aej moreover they appear to interact with midlatitude eastward propagating disturbances with the strongest interaction taking place at the latitudes where the core of the atlantic high pressure system is located composite analyses applied to the mode decomposition indicate that the interaction of the

expression of the bipolar see saw in antarctic climate records during the last deglaciation ice core records of climate from greenland and antarctica show asynchronous temperature variations on millennial timescales during the last glacial period 1 the warming during the transition from glacial to interglacial conditions was markedly different between the hemispheres a pattern attributed to the thermal bipolar see saw 2 however a record from the ross sea sector of east antarctica has been suggested to be synchronous with northern hemisphere climate change 3 here we present a temperature record from the talos dome ice core also located in the ross sea sector we compare our record with ice core analyses from greenland based on methane synchronization 4 and find clearly asynchronous temperature changes during the deglaciation we also find distinct differences in antarctic records pointing to differences in the climate evolution of the indo pacific and atlantic sectors of antarctica in the atlantic sector we find that the rate of warming slowed between 16 000 and 14 500 years ago parallel with the deceleration of the rise in atmospheric carbon dioxide concentrations and with a slight cooling over greenland in addition our chronology supports the hypothesis that the cooling of the antarctic cold reversal is synchronous with the bolling allerod warming in the northern hemisphere 14 700 years ago 5 the period from about 8 to 25kyr before present bp includes the climate transition from the last glacial to the holocene as documented from polar ice cores and other climate archives the pattern of climate changes throughout this transition is different between antarctica and the surrounding southern ocean and the northern hemisphere the steady antarctic deglacial warming reaches a first maximum antarctic isotopic maximum aim1 ref 1 followedbyaninterruptiontowardscoolerconditionsduring the antarctic cold reversal acr conversely greenland records show two rapid warming phases at the onset of the dansgaard oeschger 1 do1 event bllingaller dinterstadial b a andthe

the importance of critical layer in differentiating developing from nondeveloping easterly waves abstractrecently asaadi et al found that an easterly wave ew train over the atlantic and eastern pacific is oriented in a southeast northwest direction because of the observed tilt in the easterly jet this tilt results in only one out of four 25 waves to be located at the cyclonic critical layer south of the jet axis in a comoving frame and they subsequently developed into named storms asaadi et al suggested a geometrical view for developing disturbances which is the coexistence of a nonlinear critical layer and a region of weak meridional potential vorticity pv gradient over several days asaadi et al focused on the developing waves and did not investigate the nondeveloping ones to determine whether the nondeveloping ews are not associated with a critical layer a simple objective tracking technique is used to identify ews composite views of the large scale structure and characteristics of nondeveloping ews show that 91 of nondeveloping waves are not located on a critical layer while t

generation of the african easterly jet and its role in determining west african precipitation abstract an examination of analyses and model simulations is used to show that the african easterly jet forms over west africa in summer as a result of strong meridional soil moisture gradients in a series of gcm experiments the imposition of realistic surface wetness contrasts between the sahara and equatorial africa leads to strong positive meridional temperature gradients at the surface and in the lower troposphere the associated easterly shear in the atmosphere is strong enough to establish easterly flow the african easterly jet above the monsoon westerlies at the surface positive temperature gradients associated with the summertime distributions of solar radiation ssts or clouds are not large enough to produce the easterly jet in the absence of soil moisture gradients a thermally direct ageostrophic circulation is identified that can accelerate the largely geostrophic zonal flow and maintain the jet while moisture converges throughout the lower troposphere over east africa moisture divergenc

barotropic aspects of itcz breakdown abstract in satellite images the itcz intertropical convergence zone is sometimes observed to undulate and break down into a series of tropical disturbances tropical cyclones may later develop within these disturbances and move into higher latitudes allowing the itcz to reform it has been proposed that itcz breakdown results from a convectively modified form of combined barotropic and baroclinic instability of the mean flow an unstable mean flow can be produced by itcz convection in just a couple of days in this sense the itcz produces favorable conditions for its own instability and breakdown in this study a nonlinear shallow water model on the sphere is used to simulate barotropic aspects of itcz breakdown in the shallow water model the itcz is simulated by a prescribed zonally elongated mass sink near the equator the mass sink produces a cyclonic potential vorticity pv anomaly that has a reversed meridional pv gradient on its poleward side according to the ripa theorem a flow that has a

fluctuations of outlet and valley glaciers in the southern andes argentina during the past 13 000 years abstract in the southern argentine andes ten advances of valley glaciers were used to reconstruct the late glacial and holocene glacier history the accumulation areas of these glaciers lie in the precordillera and are thus independent of fluctuations of the south patagonian icefield like the viedma outlet glacier the valley glaciers advanced three times during late glacial time 14 000 10 000 yr b p the youngest advance correlates with the younger dryas stade based on two minimum ams 14 c dates of 9588 and 9482 yr b p the second oldest advance occurred before 11 800 yr b p during the first half of the holocene ca 10 000 5000 yr b p advances culminated about 8500 8000 7500 and 5800 5500 yr b p during the second half of the holocene advances occurred between ca 4500 and 4200 yr b p as well as between 3600 and 3300 yr b p in the rio condor valley three subsequent advances have been identified