model based estimation of wind fields over the ocean from wind scatterometer measurements i development of the wind field model for pt ii see ibid vol 28 no 3 p 361 373 1990 a parametric model for near surface mesoscale wind fields suitable for use in a model based approach to estimate the wind field over a large region of the scatterometer measurement swath from measurements of the radar backscatter of the ocean s surface is discussed the assumptions made in developing the model are described and the accuracy of the resulting model is evaluated the model is based only on scatterometer data and is computationally tractable consisting of a linear equation relating the near surface wind field to a vector of model parameters which is estimated from the scatterometer measurements tradeoffs in the accuracy of the model and the number of unknown parameters are considered

the roles of co2 and orbital forcing in driving southern hemispheric temperature variations during the last 21 000 yr abstract transient climate model simulations covering the last 21 000 yr reveal that orbitally driven insolation changes in the southern hemisphere combined with a rise in atmospheric pco2 were sufficient to jump start the deglacial warming around antarctica without direct northern hemispheric triggers analyses of sensitivity experiments forced with only one external forcing component greenhouse gases ice sheet forcing or orbital forcing demonstrate that austral spring insolation changes triggered an early retreat of southern ocean sea ice starting around 19 18 ka bp the associated sea ice albedo feedback and the subsequent increase of atmospheric co2 concentrations helped to further accelerate the deglacial warming in the southern hemisphere implications for the interpretation of southern hemispheric paleoproxy records are discussed

atlantic meridional overturning circulation during the last glacial maximum the circulation of the deep atlantic ocean during the height of the last ice age appears to have been quite different from today we review observations implying that atlantic meridional overturning circulation during the last glacial maximum was neither extremely sluggish nor an enhanced version of present day circulation the distribution of the decay products of uranium in sediments is consistent with a residence time for deep waters in the atlantic only slightly greater than today however evidence from multiple water mass tracers supports a different distribution of deep water properties including density which is dynamically linked to circulation

some observational constraints on the global scale wind systems of mars wind direction measurements from a variety of indicators taken over several mars years and covering the entire planet have been collected these include observations of lee wave clouds not previously studied the data exhibit a high degree of consistency and seasonal reproducibility making it possible to interpret most of the observations in terms of the zonally symmetric circulation of mars we examine these data in the context of the constraints the observed wind directions place upon the thermal and polar cap mass flux fields which force the flows within the limitations of the data set mid and high latitude winds appear to be controlled by the thermal field during mid and late summer and winter and in the northern hemisphere during early spring and early summer at other times the cap flows dominate at high latitudes the strongest yearly winds are probably generated by cap formation in the north and cap recession in the south the hemispheric asymmetry seems to result primarily from the effects of global dust storms on the north polar cap turning of the prograde wind from poleward to equatorward in midautumn is observed consistent with reduced poleward mass flux and increased meridional temperature gradient at that time the latitudinal extent of the equatorial hadley cell when observed is probably larger than that predicted by nearly inviscid models of low latitude circulation the cross equational hadley cell and high latitude poleward flows which occur in both hemispheres during the summer seasons may set additional constraints on the thermal forcing mechanisms at these times

rapid changes of glacial climate simulated in a coupled climate model abrupt changes in climate termed dansgaard oeschger and heinrich events have punctuated the last glacial period approximately 100 10 kyr ago but not the holocene the past 10 kyr here we use an intermediate complexity climate model to investigate the stability of glacial climate and we find that only one mode of atlantic ocean circulation is stable a cold mode with deep water formation in the atlantic ocean south of iceland however a warm circulation mode similar to the present day atlantic ocean is only marginally unstable and temporary transitions to this warm mode can easily be triggered this leads to abrupt warm events in the model which share many characteristics of the observed dansgaard oeschger events for a large freshwater input such as a large release of icebergs the model s deep water formation is temporarily switched off causing no strong cooling in greenland but warming in antarctica as is observed for heinrich events our stability analysis provides an explanation why glacial climate is much more variable than holocene climate

measurements of winds on mars with hubble space telescope images in 2003 opposition the winds of mars at the water cloud level are measured by tracking cloud features in sequential high resolution hubble space telescope uv images for 5 days during the perihelion season in 2003 global circulation model gcm predictions are in general agreement with the observations for the zonal wind component but reveal significant differences for the meridional component

wind direction alias removal studies of seasat scatterometer derived wind fields owing to the antenna configuration and the biharmonic nature of the anisotropic return of the probing radar the seasat scatterometer wind reports consist of as many as four wind directions at each point of observation a systematic methodology is proposed for selection of the true direction from among these in the absence of any in situ observations the techniques employed are those familiar to meteorological analysts they were subjected to rigorous testing for the jasin workshop with two teams performing independent analyses the agreement of the two analyses was striking comparison with wind directions from the jasin data set and those estimated from the analyzed pressure field show agreement largely within the seasat specifications it is concluded that the methodology employed is suitable for seasat scatterometer data users

evaporation effects on the formation of martian gullies abstract in order to investigate the formation of martian gullies and the stability of fluids on mars we examined about 120 gully images twelve hirise images contained a sufficient number of transverse aeolian ridges tars associated with the gullies to make the following measurements overall gully length length of the alcove channel and apron and we also measured the frequency of nearby tars six of the 12 images examined showed a statistically significant negative correlation between overall gully length alcove channel and apron length and tar frequency previous experimental work from our group has shown that at temperatures below 200 k evaporation rate increases by about an order of magnitude as wind speed increases from 0 to 15 m s thus the negative correlations we observe between gully length and dune frequency can be explained by formation at temperatures below 200 k where wind speed evaporation is a factor governing gully length in these cases evaporation of the fluid carving the gully was a constraint on their dimensions cases where there is no correlation between gully length and tar frequency can be explained by formation at temperatures 200 k the temperatures are consistent with global circulation model and thermal emission spectrometer tes data for these latitudes the temperatures suggested by these trends are consistent with the fluid responsible for gully formation being a strong brine such as fe 2 so 4 3 which has a eutectic temperature of 200 k we also find that formation timescales for gullies are 10 5 10 6 years

meltwater pulse 1a from antarctica as a trigger of the bolling allerod warm interval meltwater pulse 1a mwp 1a was a prominent feature of the last deglaciation which led to a sea level rise of 20 meters in less than 500 years concurrent with mwp 1a was the onset of the bolling allerod interstadial event 14 600 years before the present which marked the termination of the last glacial period previous studies have been unable to reconcile a warm northern hemisphere with mwp 1a originating from the laurentide or fennoscandian ice sheets with the use of a climate model of intermediate complexity we demonstrate that with mwp 1a originating from the antarctic ice sheet consistent with recent sea level fingerprinting inferences the strength of north atlantic deep water nadw formation increases thereby warming the north atlantic region and providing an explanation for the onset of the bolling allerod warm interval the established mode of active nadw formation is then able to respond to subsequent freshwater forcing from the laurentide and fennoscandian ice sheets setting the stage for the younger dryas cold period the melting of continental ice sheets during the last deglaciation provided a freshwater source to the ocean that affected global sea level and the strength of the thermohaline circulation an exceptionally large melting event inferred from far field relative sea level records occurred

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

waves encircling the summer southern pole of mars observed by mgs tes 1 distinct atmospheric disturbances with zonal wave number 1 were found in the summer southern polar region of mars using the mars global surveyor mgs thermal emission spectrometer tes retrieved temperatures provided by nasa our investigations show that the polar disturbances exist during summer ls 250 270 in three consecutive martian years these disturbances have phase structures tilted westward with height and connected with near surface temperature anomalies whose maxima and minima are largely fixed to those of the surface temperature associated with the axially asymmetric polar cap such a wave structure is consistent with stationary planetary waves that are forced by axially asymmetric surface temperature anomaly and propagate upward in weak eastward winds flowing over the polar cap

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

wind field model based estimation of seasat scatterometer winds a model based approach to estimating near surface wind fields over the ocean from seasat scatterometer sass measurements is presented the approach is a direct assimilation technique in which wind field model parameters are estimated directly from the scatterometer measurements of the radar backscatter of the ocean s surface using maximum likelihood principles the wind field estimate is then computed from the estimated model parameters the wind field model used in this approach is based on geostrophic approximation and on simplistic assumptions about the wind field vorticity and divergence but includes ageostrophic winds nine days of sass data were processed to obtain unique wind estimates comparisons in performance to the traditional two step point wise wind retrieval followed by ambiguity removal wind estimate method and the model based method are provided using both simulated radar backscatter measurements and actual sass measurements in the latter case the results are compared to wind fields determined using subjective ambiguity removal while the traditional approach results in missing measurements and reduced effective swath width due to fore aft beam cell coregistration problems the model based approach uses all available measurements to increase the effective swath width and to reduce data gaps the results reveal that the model based wind estimates have accuracy comparable to traditionally estimated winds with less noise in the directional estimates particularly at low wind speeds in addition wind fields generated using the model based procedure can be used to detect and correct ambiguity removal errors in ambiguity removed point wise wind fields a separate procedure based only on the wind field model can also be used as a data quality check to detect errors in point wise ambiguity removal

the role of the north atlantic drift in the millennial timescale glacial climate fluctuations abstract the greenland ice core records show that the overall cold climate of the last glacial period was repeatedly interrupted by short rapid warmings the events known as dansgaard oeschger d o events are strongly imprinted in the north atlantic marine records suggesting that they were linked to north atlantic circulation changes however the causes of the d o events are poorly understood and they represent one of the most intriguing puzzles of the last glacial period in order to investigate a possible mechanism we have studied variations in the distribution of benthic and planktonic foraminifera oxygen isotopes and ice rafted debris during the last glacial period in eight cores from the north atlantic and the nordic seas taken at mid depth from 853 to 1760 m the parameters indicate in agreement with previous studies that the circulation system during the interstadials resembled the present system atlantic surface water flowed north into the nordic seas where most of it sank through convection and as cold deep water flowed back into the north atlantic during the stadials a halocline was established in the nordic seas and in the northernmost part of the north atlantic and the outflow from the nordic seas stopped however below the cold light surface layer the relatively warm water of the north atlantic drift continued to flow across the north atlantic and into the nordic seas here warming up the deep water masses we suggest that the warm water gradually made the water column unstable the pivotal abrupt climate warmings were caused by sudden upwelling of the deep warm water masses causing overturning of the entire water column and onset of convection

long cloud observations on mars and implications for boundary layer characteristics over slopes viking orbiter images of mars show several instances of long continuous cloud formations on the slopes of arsia and pavonis mons we have searched all the images of the planet for occurrences of such formations only in the tharsis region were long clouds unambiguously identified we have measured the times and locations of occurrence the wavelengths and when possible the apparent velocity of motion of these clouds we have also tabulated the wavelengths of patches of ripple clouds that are often found with the long formations the long clouds are observed only in the early morning hours suggesting that they are associated with drainage winds due to a cold planetary boundary layer we develop simple mathematical models to examine various aspects of such boundary layer winds these allow us to construct a complete and self consistent explanation of all the observed features of the cloud formations we use the results to characterize some physical properties of the mars boundary layer there is strong downslope flow in the boundary layer on the high slopes of both volcanos in the saddle region between the peaks the flow slows and undergoes a hydraulic jump producing the long clouds downstream of the jump standing internal gravity waves can exist and are excited by flow over surface irregularities small variations in their observed wavelengths behind the jump may be attributed to variation in the flow speed and depth finally we can account for the location of the jumps by the variation of relative strength of the boundary layer flows on the two volcanos

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

southern ocean origin for the resumption of atlantic thermohaline circulation during deglaciation during the two most recent deglaciations the southern hemisphere warmed before greenland at the same time the northern atlantic ocean was exposed to meltwater discharge which is generally assumed to reduce the formation of north atlantic deep water yet during deglaciation the atlantic thermohaline circulation became more vigorous in the transition from a weak glacial to a strong interglacial mode here we use a three dimensional ocean circulation model to investigate the impact of southern ocean warming and the associated sea ice retreat on the atlantic thermohaline circulation we find that a gradual warming in the southern ocean during deglaciation induces an abrupt resumption of the interglacial mode of the thermohaline circulation triggered by increased mass transport into the atlantic ocean via the warm indian ocean and cold pacific ocean water route this effect prevails over the influence of meltwater discharge which would oppose a strengthening of the thermohaline circulation a southern ocean trigger for the transition into an interglacial mode of circulation provides a consistent picture of southern and northern hemispheric climate change at times of deglaciation in agreement with the available proxy records

high resolution atmospheric observations by the mars odyssey thermal emission imaging system high resolution observations of atmospheric phenomena by the mars odyssey thermal emission imaging system themis during its first mapping year are presented an atmospheric campaign was implemented on the basis of previous spacecraft imaging this campaign however proved of limited success this appears to be due to the late local time of the odyssey orbit the locations of activity at 4 6 p m appear to be different from those at 2 p m ironically images targeting the surface were more useful for study of the atmosphere than those images specifically targeting atmospheric features while many previously recognized features were found novel themis observations included persistent clouds in the southern polar layered deposits dust or condensate plumes on the northern polar layered deposits dust plumes as constituent parts of local dust storms and mesospheric clouds the former two features tend to be aligned parallel and normal to polar troughs respectively suggesting a wind system directed normal to troughs and radially outward from the center of the polar deposits this is consistent with katabatic drainage of air off the polar deposits analogous to flow off antarctica the observation of dust lifting plumes at unprecedented resolution associated with local dust storms not only demonstrates the importance of mean wind stresses as opposed to dust devils in initiation of dust storms but is also seen to be morphologically identical to dust lifting in terrestrial dust storms as odyssey moves to earlier local times we suggest that the atmospheric campaign from the first mapping year be repeated

comparative carbon cycle dynamics of the present and last interglacial changes in temperature and carbon dioxide during glacial cycles recorded in antarctic ice cores are tightly coupled however this relationship does not hold for interglacials while climate cooled towards the end of both the last eemian and present holocene interglacials co2 remained stable during the eemian while rising in the holocene we identify and review twelve biogeochemical mechanisms of terrestrial vegetation dynamics and co2 fertilization land use wildfire accumulation of peat changes in permafrost carbon subaerial volcanic outgassing and marine origin changes in sea surface temperature carbonate compensation to deglaciation and terrestrial biosphere regrowth shallow water carbonate sedimentation changes in the soft tissue pump and methane hydrates which potentially may have contributed to the co2 dynamics during interglacials but which remain not well quantified we use three earth system models esms of intermediate complexity to compare effects of selected mechanisms on the interglacial co2 and 13co2 changes focusing on those with substantial potential impacts namely carbonate sedimentation in shallow waters peat growth and in the case of the holocene human land use a set of specified carbon cycle forcings could qualitatively explain atmospheric co2 dynamics from 8 ka bp to the pre industrial however when applied to eemian boundary conditions from 126 to 115 ka bp the same set of forcings led to disagreement with the observed direction of co2 changes after 122 ka bp this failure to simulate late eemian co2 dynamics could be a result of the imposed forcings such as prescribed caco3 accumulation and or an incorrect response of simulated terrestrial carbon to the surface cooling at the end of the interglacial these experiments also reveal that key natural processes of interglacial co2 dynamics shallow water caco3 accumulation peat and permafrost carbon dynamics are not well represented in the current esms global scale modeling of these long term carbon cycle components started only in the last decade and uncertainty in parameterization of these mechanisms is a main limitation in the successful modeling of interglacial co2 dynamics

curvilinear features in the southern hemisphere observed by mars global surveyor mars orbiter camera abstract we have used the complete set of mars global surveyor mgs mars daily global maps mdgms to study martian weather in the southern hemisphere focusing on curvilinear features including frontal events and streaks frontal events refer to visible events that are morphologically analogous to terrestrial baroclinic storms mdgms show that visible frontal events were mainly concentrated in the 210 300 e 60 150 w sector and the 0 60 e sector around the southern polar cap during l s 140 250 and l s 340 60 the non uniform spatial and temporal distributions of activity were also shown by mgs thermal emission spectrometer transient temperature variations near the surface streaks refer to long curvilinear features in the polar hood or over the polar cap they are an indicator of the shape of the polar vortex streaks in late winter usually show wavy segments between the 180 meridian and argyre model results suggest that the zonal wave number m 3 eastward traveling waves are important for their formation

mars atmospheric dynamics as simulated by the nasa ames general circulation model 2 transient baroclinic eddies a large set of experiments performed with the nasa ames mars general circulation model gcm have been analyzed to determine the properties structure and dynamics of the simulated transient baroclinic eddies the mars gcm simulations span a wide range of seasonal dates and dust loadings and include a number of special sensitivity experiments e g with flat topography there is strong transient baroclinic eddy activity in the extratropics of the northern hemisphere during the northern autumn winter and spring seasons the eddy activity remains strong for very large dust loadings though it shifts northward the eastward propagating eddies are characterized by zonal wavenumbers of 1 4 and periods of 2 10 days in several simulations the eddy variance is dominated by a single zonal wavenumber and a narrow range of periods the longer wavenumbers 1 and 2 transient eddies have a very deep vertical structure exhibiting a maximum kinetic energy density at the model top 45 50 km in many of the simulations in a simulation for early northern spring the eddies are quite shallow however the transient eddies generate the bulk of their energy baroclincally via large meridional and vertical heat fluxes at both lower and upper levels this is despite the fact that their vertical structure is typically close to equivalent barotropic above the lowest 10 km the eddies also appear to generate a substantial amount of energy barotropically via large meridional momentum fluxes at both lower and upper levels in the tropics and northern subtropics at upper levels 25 50 km there are strong transient eddy motions with structures resembling those characteristic of inertially unstable modes this eddy activity appears to be a response to the forcing of a region of marginal inertial stability by the extratropical transient baroclinic eddies as the wavenumbers and periods are the same as those in the extratropics a major surprise is the presence of very weak transient eddy activity in a number of the southern winter simulations it appears that this is partly a consequence of the stabilizing effects of the zonally symmetric topography in the gcm but it also must be associated with certain aspects of the zonal mean circulation in southern winter this is indicated by the presence of relatively large amplitude eddies in simulations for early southern autumn and spring and in a southern winter solstice simulation incorporating a different topography derived from the mars digital terrain model this topography differs from that used in most of the gcm simulations in not being characterized by steep symmetric slopes which are stabilizing to baroclinic instability in southern high latitudes it is hypothesized that the very large extent of the southern seasonal polar cap and high elevations in the south both might contribute to weakening the transient eddy activity large zonally symmetric topography in the northern hemisphere of the mars gcm also appears to have a strong impact on the transient eddies acting to increase the dominant zonal wavenumbers and phase speeds the properties of the gcm baroclinic eddies in the northern extratropics are compared in detail with analogous properties inferred from viking lander meteorology observations the gcm eddies are found to be very similar to those observed in most respects a notable exception is that the eddy amplitudes in the highly dusty gcm simulations are much larger than those observed by viking during the 1977 winter solstice dust storm this is almost certainly at least partly due to the relatively small latitudinal expansion of the hadley circulation in the highly dusty gcm experiments

the effect of obliquity driven changes on paleoclimate sensitivity during the late pleistocene some studies suggest that specific equilibrium climate sensitivity s might be state dependent reanalyzing existing paleodata of global mean surface temperature tg and radiative forcing r of co2 and land ice albedo for the last 800 000 years we show that this state dependency of s is only found if tg is based on reconstructions and not when tg is based on model simulations furthermore during times of decreasing obliquity periods of land ice sheet growth and sea level fall the multi millennial component of reconstructed tg is diverging from atmospheric co2 while in simulations both variables vary more synchronously for a reconstruction based extrapolation of s to the future we eliminate these periods due to an expected sea level rise consequently s determined from proxy based reconstructions without these data with strong tg co2 divergence is less state dependent or even constant state independent and yields into an equilibrium warming for 2 co2 of 1 9 3 8 k

orographic control of storm zones on mars low pressure cyclones and their accompanying frontal systems in the middle latitudes of the earth s troposphere develop travel eastwards and decay preferentially within latitudinally and longitudinally confined geographical regions known as storm zones1 these zones can be readily identified in the circulation statistics of terrestrial weather systems2 mars like the earth is a rapidly rotating solid planet and has a seasonally varying shallow atmosphere large scale orography and in a broadly defined context continental structures3 although there are also important differences between the two planets travelling weather systems do exist on mars3 this raises the question of whether storm zones also occur there and if so by what mechanisms here we report the results of numerical simulations of global atmospheric circulation patterns on mars we find that storm zones can exist during the northern winter and that continental scale orography rather than surface thermal contrasts is the main factor determining the development of these zones storm zones on mars should play an important role in the martian climate cycle4 5 by influencing the transport of for example heat momentum water vapour and atmospheric dust3 6 8 towards the poles

forced waves in the martian atmosphere from mgs tes nadir data abstract we have analyzed the temperature retrievals from mars global surveyor mgs thermal emission spectrometer tes nadir spectra to yield latitude height resolved maps of various atmospheric forced wave modes as a function of season for a full mars year among the isolated wave modes is the zonal mean time mean temperature which we used to derive zonal mean zonal winds and stationary wave quasi geostrophic indices of refraction diagnostic of their propagation the diurnal kelvin wave was isolated in the data with results roughly consistent with models wilson and hamilton 1996 j atmos sci 33 1290 1326 the s 1 and s 2 stationary waves were found to have significant amplitude in ducts extending up the winter polar jets while the s 3 stationary wave was found to be confined to near the surface the s 1 stationary wave was found to have little phase tilt with height during northern winter but significant westward phase tilt with height in the southern winter this indicates that the wave carries heat poleward slightly more than that found in barnes et al 1996 j geophys res 101 12 753 12 776 the s 1 stationary wave is likely the dominant mechanism for eddy meridional heat transport for the southern winter we noted that the phase of the s 2 stationary wave is nearly constant with time but that the s 1 stationary wave moved 90 of longitude from fall to winter and back in spring in the north while interannual variability is not yet addressed overall these results provide the first comprehensive benchmark for forced waves in mars s atmosphere against which future atmospheric models of mars can be compared

quasi periodic dust events in the summertime south polar region of mars abstract a hovmoller diagram analysis of the dust optical depth measured by the mars global surveyor thermal emission spectrometer shows the occurrence of quasi periodic westwardly propagating disturbances with timescales of 10 20 sols during summer in the south polar region of mars dust clouds emerge repeatedly around the region with a latitude of around 70 80 s and a longitude of 240 300 e move westward at speeds of 3 6 m s 1 reach the region with a longitude of 60 120 e and finally disappear this longitude range coincides with elevated terrains in the south polar region and in this region an increase of dust optical depth encircling the south pole is also observed this implies that the quasi periodic dust events will contribute to the enhancement of the atmospheric dust loading in this region these dust events might be related to baroclinic instability caused by the thermal contrast across the co2 cap edge or the horizontal advection or vertical convection with radiative dynamical feedback the westward movement of the dust clouds suggests steady westward winds blowing in the near surface layer where the quasi periodic dust lifting is expected to occur such a westward cap edge flow will be created by the coriolis force acting on the flow from the ice side to the regolith side

north polar frontal clouds and dust storms on mars during spring and summer the complete archive of mars global surveyor mgs mars orbiter camera moc mars daily global maps mdgm are used to study north polar clouds and dust storms that exhibit frontal structures during the spring and summer ls 0 180 results show that frontal events generally follow the edge of the polar cap during spring and mid late summer with a gap in the distribution in early summer the exact duration and timing of the gap vary from year to year ten to twenty percent of spring and summer time frontal events exhibit complex morphologies distinct temperature signatures are associated with features observed in images in many but not all cases the general travel paths of the frontal events are eastward around the polar cap westward paths exist only at the edge of the polar cap in late spring early summer occasionally the paths curve toward or away from the polar cap in certain longitude sectors

atlantic subsurface temperatures response to a shutdown of the overturning circulation and consequences for its recovery abstract using the coupled climate model of intermediate complexity climber 3 changes in the vertical thermal structure associated with a shutdown of the atlantic meridional overturning circulation amoc are investigated when north atlantic deep water formation is inhibited by anomalous freshwater forcing intermediate depth ventilation can remain active and cool the subsurface water masses i e the cold case however if intermediate ventilation is completely suppressed relatively warm water coming from the south penetrates to a high northern latitude beneath the halocline and induces a strong vertical temperature inversion between the surface and intermediate depth i e the warm case both types of temperature anomalies emerge within the first decade after the beginning of the freshwater perturbation the sign of subsurface temperature anomaly has a strong implication for the recovery of the amoc once the anomalous freshwater forcing is removed while the amoc recovers from the cold case

martian clouds observed by mars global surveyor mars orbiter camera we have made daily global maps that cover both polar and equatorial regions of mars for ls 135 360 and 0 111 using the mars global surveyor mgs mars orbiter camera moc red and blue wide angle swaths taken from may 1999 to january 2001 we study the seasonal distribution of condensate clouds and dust clouds during roughly 1 martian year using these daily global maps we present the development and decay of the tropical cloud belt and the polar hoods the spatial and temporal distributions of lee waves and spiral clouds and an unusual aster cloud above the volcanoes consisting of rays around a central disk like the flower the tropical cloud belt contains mostly fibrous clouds during northern spring early summer and convective clouds during middle late northern summer the detailed development and decay of the tropical cloud belt is nonuniform in longitude two distinct stormy periods in late summer precede the formation of the north and south circumpolar hoods the north polar storms in late summer resemble baroclinic frontal systems on earth but contain both dust and condensate clouds spiral clouds occur only in the northern high latitudes and only during northern spring and summer the north polar hood displays a stationary wave number two structure during the fall and winter the south polar hood has fewer streak clouds and lee wave clouds than the north polar hood during this particular year the lee wave cloud abundance in the south had two peaks in early fall and late winter and the lee wave cloud abundance in the north had one peak in early fall

observations of the initiation and evolution of the 2001 mars global dust storm 1 a global dust storm occurred on mars between june and october 2001 the storm began near hellas just before southern spring equinox ls 177 local storms likely forced by a combination of slope flow and ice cap thermal contrasts were observed to propagate along the northwestern rim of hellas apparently triggering the global storm cap edge storm activity for much of late southern winter was similar in 2001 to one mars year earlier however a very large storm propagated into the basin just after ls 177 subsequently the total area of storm activity in 2001 was roughly double that of the previous year for about 10 days dust lifting was limited to the hellas region as additional storms propagated into hellas activity built and extended northward into syrtis and eastward into hesperia it is not clear whether transport or spreading of lifting were of greatest importance for expansion at ls 185 the storm began to spread rapidly to the east along a line from the southern pole to the northern tropics essentially no storm propagation to the west occurred yielding strong zonal asymmetry of expansion as the dust storm reached the western edge of tharsis secondary dust lifting centers developed in daedalia and solis southeastern tharsis subsequently the storm rapidly encompassed the planet by ls 193 once fully global the syria solis daedalia lifting center appeared to dominate on the basis of cloud top morphology with hellas quiescent by ls 212 lifting could no longer be discerned thereafter dust haze appeared uniform and diffuse and decay appeared to have set in

deconstructing terminations i and ii revisiting the glacioeustatic paradigm based on deep water temperature estimates benthic and planktonic oxygen isotope 18occ and mg ca analyses in two cores from the northeast atlantic have permitted the reconstruction of surface and deep water temperature tdw and 18o 18ow variations across the last two deglaciations these records allow the timing of de glacial melt water pulses reaching the northeast atlantic to be compared with the evolution of local deep water tdw 18ow conditions although each glacial termination is unique in detail a similar pattern of hydrographic change is reconstructed for both deglaciations with the first major decrease in deep water 18ow due to sea level and or purely local deep water change occurring in parallel with the onset of intensely cold glacial surface water temperatures and prior to a terminal ice rafting and melt water event the evolution of deep water across both de glaciations involved two transient incursions of cold low 18o water into the deep northeast atlantic the second of which was particularly pronounced each time these pulses of cold deep water are interpreted to reflect the incursion of water directly analogous to modern antarctic bottom water aabw and containing a significant component of brine rejected during sea ice formation the results presented here show that the same type of transient changes in deep water circulation that occurred across termination i also occurred across termination ii and that as a result of these deep ocean changes the timing of each benthic 18o termination cannot precisely reflect the timing of de glacial sea level change as many palaeoceanographic interpretations and some controversies are prone to assume such imprecision in timing especially may well extend to marine isotope stage mis boundaries in general as a principle of hydrographic variability and its expression in the geological record

results of the imager for mars pathfinder windsock experiment the imager for mars pathfinder imp windsock experiment measured wind speeds at three heights within 1 2 m of the martian surface during pathfinder landed operations these wind data allowed direct measurement of near surface wind profiles on mars for the first time including determination of aerodynamic roughness length and wind friction speeds winds were light during periods of windsock imaging but data from the strongest breezes indicate aerodynamic roughness length of 3 cm at the landing site with wind friction speeds reaching 1 m s maximum wind friction speeds were about half of the threshold of motion friction speeds predicted for loose fine grained materials on smooth martian terrain and about one third of the threshold of motion friction speeds predicted for the same size particles over terrain with aerodynamic roughness of 3 cm consistent with this and suggesting that low wind speeds prevailed when the windsock array was not imaged and or no particles were available for aeolian transport no wind related changes to the surface during mission operations have been recognized the aerodynamic roughness length reported here implies that proposed deflation of fine particles around the landing site or activation of duneforms seen by imp and sojourner would require wind speeds 28 m s at the pathfinder top windsock height or 31 m s at the equivalent viking wind sensor height of 1 6 m and wind speeds 45 m s above 10 m these wind speeds would cause rock abrasion if a supply of durable particles were available for saltation previous analyses indicate that the pathfinder landing site probably is rockier and rougher than many other plains units on mars so aerodynamic roughness length elsewhere probably is less than the 3 cm value reported for the pathfinder site

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

a state dependent quantification of climate sensitivity based on paleodata of the last 2 1 million years the evidence from both data and models indicates that specific equilibrium climate sensitivity s x the global annual mean surface temperature change tg as a response to a change in radiative forcing x r x is state dependent such a state dependency implies that the best fit in the scatter plot of tg versus r x is not a linear regression but can be some non linear or even non smooth function while for the conventional linear case the slope gradient of the regression is correctly interpreted as the specific equilibrium climate sensitivity s x the interpretation is not straightforward in the non linear case we here explain how such a state dependent scatter plot needs to be interpreted and provide a theoretical understanding or generalization how to quantify s x in the non linear case finally from data covering the last 2 1 myr we show that due to state dependency the specific equilibrium climate sensitivity which considers radiative forcing of co2 and land ice sheet li albedo s co2 li is larger during interglacial states than during glacial conditions by more than a factor two

removal of ambiguous wind directions for a ku band wind scatterometer using three different azimuth angles the seasat a satellite scatterometer sass sensor demonstrated very successfully that ku band scatterometers can make accurate synoptic measurements of surface wind speed over the ocean because sass provided normalized radar cross section nrcs measurements from only two azimuths however the harmonic relationship of nrcs with azimuth results in up to four ambiguous wind directions the primary improvement to be incorporated in a next generation scatterometer design such as navy remote ocean sensing system nross is the addition of a third azimuth look at each sampled cell with this and other instrument improvements preliminary studies indicate that wind direction ambiguities aliases could successfully be removed in at least 80 percent of the cases furthermore these studies show that in over 90 percent of the wind solutions the two most probable solutions correctly identify the wind streamlines methods were studied which could examine typical streamline patterns derived from scatterometers using continuity or pattern recognition techniques to determine which of the possible two wind directions was correct in addition unambiguous solutions were sought for cases where streamlines were not correctly defined this paper describes several approaches for such alias removal algorithms these algorithms were developed with the aid of simulated three beam scatterometer ambiguous wind solution data based on noss conditions over a known windfield the resulting algorithms were evaluated using a different set of simulated orbital data but withholding the true winds

importance of aeolian processes in the origin of the north polar chasmata mars abstract a detailed examination of the location and orientation of sand dunes and other aeolian features within the north polar chasmata indicates that steep scarps strongly influence the direction and intensity of prevailing winds these steep scarps are present at the heads and along the margins of the north polar chasmata topographic profiles of the arcuate head scarps and equator facing wall of chasma boreale reveal unusually steep polar slopes ranging from 6 30 the relatively steep sloped 8 sinuous scarp at the head of two smaller chasmata located west of chasma boreale exhibits an obvious resistant cap forming unit scarp retreat is occurring in places where the cap unit is actively being undercut by descending slope winds low albedo surfaces lacking sand dunes or dust mantles are present at the base of the polar scarps a 100 300 m deep moat located at the base of the scarps corresponds with these surfaces and indicates an area of active aeolian scour from descending katabatic winds small local dust storms observed along the equator facing wall of chasma boreale imply that slope wind velocities in chasma boreale are sufficient to mobilize dust and sand sized particles in the polar layered deposits pld two amphitheater forms located above the cap forming unit of the sinuous scarp and west of chasma boreale may represent an early stage of polar scarp and chasma formation these two forms are developing within a younger section of polar layered materials the unusually steep scarps associated with the polar chasmata have developed where resistant layers are present in the pld offering resistance during the headward erosion and poleward retreat of the scarps steep slopes that formed under these circumstances enhance the flow of down scarp katabatic winds on the basis of these observations we reject the fluvial outflood hypothesis for the origin of the north polar chasmata and embrace a wind erosion model for their long term development in the aeolian model off pole katabatic winds progressively remove materials from the steep slopes below chasmata scarps undermining resistant layers at the tops of scarps and causing retreat by headward erosion assuming a minimum age for the onset of formation of chasma boreale 105 yr results in a maximum volumetric erosion rate of 0 35 km 3 yr 1 removal of this volume of material from the equator facing wall and head scarps of chasma would require a rate for scarp retreat of 0 5 m yr 1

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos

cloud tracked winds for the first mars global surveyor mapping year we have measured winds using cloud motion in consecutive mars global surveyor mgs mars orbiter camera moc wide angle global map swaths taken during the first mapping year l s 135 360 111 we present a total of 11 200 wind vectors collected in the north polar region during l s 135 195 late summer early fall and l s 20 55 mid spring and in the south polar region during l s 337 10 late summer early fall for cases with good coverage we also present the derived mean zonal and meridional winds and the associated eddies the speed of the zonal winds in 60 n 70 n increases at 0 6 m s l s in late northern summer and that in 60 s 70 s increases at a rate of 0 7 m s l s in late southern summer the latitudinal distribution of zonal wind within 50 n 75 n from mid northern summer to early northern fall indicates that winds at higher latitudes are generally weaker than those at lower latitudes but the rate of increase with time is faster at higher latitudes there is a cyclonic gyre in the 90 w 0 30 e sector in the north polar region there are large scale waves in the weekly mean meridional wind and in the biweekly mean eddy momentum flux and eddy kinetic energy fields in the north polar region from mid to late summer the cloud tracked winds in the north are generally consistent with winds calculated by general circulation model at the water condensation level derived from mgs thermal emission spectrometer tes observations but appear stronger than the gradient winds derived from tes assuming no flow at the surface

intermediate depth warming in the tropical atlantic related to weakened thermohaline circulation combining paleoclimate data and modeling results for the last deglaciation 1 benthic foraminiferal oxygen isotope ratios from two sediment cores recovered at 426 and 1299 m water depth in the eastern and western tropical atlantic show that a slowdown of the thermohaline circulation thc during heinrich event h1 and the younger dryas was accompanied by rapid and intense warming of intermediate depth waters millennial scale covariations of low paleosalinities in the subpolar north atlantic with decreased benthic oxygen isotope ratios in the eastern tropical atlantic throughout the past 10 000 years suggest that thc weakening might be related to middepth warming during the holocene period as well climate model experiments simulating a strong reduction of the thc in the atlantic ocean under present day and glacial conditions reveal that the increase of temperature in the middepth tropical and south atlantic is a common feature for both climatic states caused by a reduced ventilation of cold intermediate and deep waters in conjunction with downward mixing of heat from the thermocline from the similarity of the paleoclimatic records with the model simulations we infer that the characteristic pattern of temperature change in the atlantic ocean related to weakened thermohaline circulation can serve as an indicator of present day and future thc slowdown

model based estimation of wind fields over the ocean from wind scatterometer measurements ii model parameter estimation for pt i see ibid vol 28 no 3 p 349 360 1990 the feasibility of a model based approach to wind field estimation is discussed in this approach the parametric model for near surface mesoscale wind fields developed in pt i is used the parameters of the model are estimated from the wind scatterometer measurements the wind field estimate is then computed from the estimated model parameters unlike the traditional pointwise approach this approach takes advantage of the inherent correlation in the winds at different sample points to estimate the wind field more accurately and resolve directional ambiguity the accuracies of wind field estimates obtained using the traditional pointwise estimation scheme and the model based approach using simulated scatterometer measurements are compared

revision of the epica dome c co2 record from 800 to 600 kyr before present the european project for ice coring in antarctica dome ice core from dome c edc has allowed for the reconstruction of atmospheric co2 concentrations for the last 800 000 years here we revisit the oldest part of the edc co2 record using different air extraction methods and sections of the core for our established cracker system we found an analytical artifact which increases over the deepest 200 m and reaches 10 1 2 4 ppm in the oldest deepest part the governing mechanism is not yet fully understood but it is related to insufficient gas extraction in combination with ice relaxation during storage and ice structure the corrected record presented here resolves partly but not completely the issue with a different correlation between co2 and antarctic temperatures found in this oldest part of the records in addition we provide here an update of 800 000 years atmospheric co2 history including recent studies covering the last glacial cycle