the vertical profile of winds on titan the huygens probe landed on titan on 14 january this year and seven papers published in this issue record the encounter they describe a world that resembles a primitive earth complete with weather systems and geological activity the huygens on titan section opens with an overview of the descent and landing and a news and views piece tomasko et al describe the dry riverbed and drainage channels seen during huygens descent evidence that liquid methane falls as rain or erupts from cryovolcanoes periodically flooding the surface this paper includes the images used on the cover to the huygens section niemann et al measured the abundances of isotopes of argon nitrogen and carbon in the atmosphere and conclude that there is no evidence that titan s methane comes from biological activity fulchignoni et al obtained precise measurements of temperature and pressure from the upper atmosphere right down to the surface on the way down huygens recorded evidence for lightning zarnecki et al report that the probe landed on a relatively smooth surface of icy grains with the consistency of wet clay or sand isral et al report that the aerosols in titan s clouds have solid cores made from complex organic molecules containing carbon and nitrogen and bird et al found that on average titan s winds blow in the same direction as the moon rotates and that close to the surface these winds are very weak travelling at around walking speed one of titan s most intriguing attributes is its copious but featureless atmosphere the voyager 1 fly by and occultation in 1980 provided the first radial survey of titan s atmospheric pressure and temperature1 2 and evidence for the presence of strong zonal winds3 it was realized that the motion of an atmospheric probe could be used to study the winds which led to the inclusion of the doppler wind experiment4 on the huygens probe5 here we report a high resolution vertical profile of titan s winds with an estimated accuracy of better than 1 m s 1 the zonal winds were prograde during most of the atmospheric descent providing in situ confirmation of superrotation on titan a layer with surprisingly slow wind where the velocity decreased to near zero was detected at altitudes between 60 and 100 km generally weak winds 1 m s 1 were seen in the lowest 5 km of descent

climate instability during the last interglacial period recorded in the grip ice core isotope and chemical analyses of the grip ice core from summit central greenland reveal that climate in greenland during the last interglacial period was characterized by a series of severe cold periods which began extremely rapidly and lasted from decades to centuries as the last interglacial seems to have been slightly warmer than the present one its unstable climate raises questions about the effects of future global warming

the atmosphere of titan an analysis of the voyager 1 radio occultation measurements abstract two coherently related radio signals transmitted from voyager 1 at wavelengths of 13 cm s band and 3 6 cm x band were used to probe the equatorial atmosphere of titan the measurements were conducted during the occultation of the spacecraft by the satellite on november 12 1980 an analysis of the differential dispersive frequency measurements did not reveal any ionization layers in the upper atmosphere of titan the resolution was approximately 3 10 3 and 5 10 3 electrons cm 3 near the evening and morning terminators respectively abrupt signal changes observed at ingress and egress indicated a surface radius of 2575 0 0 5 km leading to a mean density of 1 881 0 002 g cm 3 for the satellite the nondispersive data were used to derive profiles in height of the gas refractivity and microwave absorption in titan s troposphere and stratosphere no absorption was detected the resolution was about 0 01 db km at the 13 cm wavelength the gas refractivity data which extend from the surface to about 200 km altitude were interpreted in two different ways in the first it is assumed that n 2 makes up essentially all of the atmosphere but with very small amounts of ch 4 and other hydrocarbons also present this approach yielded a temperature and pressure at the surface of 94 0 0 7 k and 1496 20 mbar respectively the tropopause which was detected near 42 km altitude had a temperature of 71 4 0 5 k and a pressure of about 130 mbar above the tropopause the temperature increased with height reaching 170 15 k near the 200 km level the maximum temperature lapse rate observed near the surface 1 38 0 10 k km corresponds to the adiabatic value expected for a dry n 2 atmosphere indicating that methane saturation did not occur in tbis region above the 3 5 km altitude level the lapse rate dropped abruptly to 0 9 0 1 k km and then decreased slowly with increasing altitude crossing zero at the tropopause for the n 2 atmospheric model the lapse rate transition at the 3 5 km level appears to mark the boundary between a convective region near the surface having the dry adiabatic lapse rate and a higher stable region in radiative equilibrium in the second interpretation of the refractivity data it is assumed instead that the 3 5 km altitude level corresponds to the bottom of a ch 4 cloud layer and that n 2 and ch 4 are perfectly mixed below this level these assumptions lead to an atmospheric model which below the clouds contains about 10 ch 4 by number density the temperature near the surface is about 95 k arguments concerning the temperature lapse rates computed from the radio measurements appear to favor models in which methane forms at most a limited haze layer high in the troposphere

analysis of cassini cirs limb spectra of titan acquired during the nominal mission i hydrocarbons nitriles and co2 vertical mixing ratio profiles observations of the composite infrared spectrometer cirs during the entire nominal cassini mission 2004 2008 provide us with an accurate global view of composition and temperature in the middle atmosphere of titan between 100 and 500 km we investigated limb spectra acquired at 0 5 cm 1 resolution at nine different latitudes between 56 s and 80 n with a better sampling in the northern hemisphere where molecular abundances and temperature present strong latitudinal variations from this limb data acquired between february 2005 and may 2008 we retrieved the vertical mixing ratio profiles of c2h2 c2h4 c2h6 c3h8 ch3c2h c4h2 c6h6 hcn hc3n and co2 we present here for the first time the latitudinal variations of the c2h6 c3h8 co2 c2h4 and c6h6 vertical mixing ratios profiles some molecules such as c2h6 or c3h8 present little variations above their condensation level the other molecules except co2 show a significant enhancement of their mixing ratios poleward of 50 n c2h4 is the only molecule whose mixing ratio decreases with height at latitudes below 46 n regions depleted in c2h2 hcn and c4h2 are observed around 400 km 0 01 mbar and 55 n we also inferred a region enriched in co2 located between 30 and 40 n in the 2 0 7 mbar pressure range at 80 n almost all molecules studied here present a local minimum of their mixing ratio profiles near 300 km 0 07 mbar which is in contradiction with global circulation models that predict constant with height vertical profiles due to subsidence at the north pole 2009 elsevier inc all rights reserved

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

transient diapycnal mixing and the meridional overturning circulation abstract an idealized three dimensional model of buoyancy forced flow in a single hemisphere is used to investigate whether transient diapycnal mixing can sustain the meridional overturning circulation in the annual mean mixing transience had little effect on the meridional overturning when mixing occurred on basin boundaries the overturning strength was found to be insensitive to mixing transience for mixing that was highly localized in space away from basin boundaries oceanic meridional mass and heat transport decreased as mixing became more transient the increased sensitivity in the highly localized case is likely due to the inhibition of surface heat flux into the thermocline the dynamic response to transient mixing featured large scale internal oscillations that increased in amplitude with the transience of mixing but were confined to the tropics and had little effect on the overturning cell through midlatitudes these results indicate that transient diapycnal mixing with a distribution sug

seasonal evolution of titan s stratosphere during the cassini mission titan s stratosphere exhibits significant seasonal changes including break up and formation of polar vortices here we present the first analysis of mid infrared mapping observations from cassini s composite infrared spectrometer cirs to cover the entire mission ls 293 93 2004 2017 mid northern winter to northern summer solstice the north polar winter vortex persisted well after equinox starting break up around ls 60 and fully dissipating by ls 90 absence of enriched polar air spreading to lower latitudes suggests large scale circulation changes and photochemistry control chemical evolution during vortex break up south polar vortex formation commenced soon after equinox and by ls 60 was more enriched in trace gases than the northern mid winter vortex and had temperatures 20 k colder this suggests early winter and mid winter vortices are dominated by different processes radiative cooling and subsidence induced adiabatic heating respectively by the end of the mission ls 93 south polar conditions were approaching those observed in the north at ls 293 implying seasonal symmetry in titan s vortices

a damped decadal oscillation in the north atlantic climate system a simple stochastic atmosphere model is coupled to a realistic model of the north atlantic ocean a north south sst dipole with its zero line centered along the subpolar front influences the atmosphere model which in turn forces the ocean model by surface fluxes related to the north atlantic oscillation the coupled system exhibits a damped decadal oscillation associated with the adjustment through the ocean model to the changing surface forcing the oscillation consists of a fast wind driven positive feedback of the ocean and a delayed negative feedback orchestrated by overturning circulation anomalies the positive feedback turns out to be necessary to distinguish the coupled oscillation from that in a model without any influence from the ocean to the atmosphere using a novel diagnosing technique it is possible to rule out the importance of baroclinic wave processes for determining the period of the oscillation and to show the important role played by anomalous geostrophic advection in sustaining the oscillation

titan s atmosphere from voyager infrared observations iii vertical distributions of hydrocarbons and nitriles near titan s north pole abstract the temperature structure and vertical distributions of minor stratospheric constituents in titan s north polar region have been inferred from the study of voyager 1 infrared spectra the data were recorded at grazing incidence over the limb and cover an approximate vertical range of 100 300 km the upper stratospheric temperature is retrieved from an analysis of the 7 7 m methane band in which the emission originates mainly from pressure levels between 0 01 and 5 mbar 120 and 375 km we find the thermal profile at 70 n to be significantly colder by 20 k than the equatorial one vertical distributions of the following absorbers were derived from the best fits obtained in the spectral region 200 1400 cm 1 for three different data sets corresponding to three different altitudes above the satellite s surface c 2 h 2 c 4 h 2 c 2 h 6 c 3 h 4 hcn hc 3 n and c 2 n 2 the mixing ratios of these species increase with height suggesting their formation in the upper stratosphere and above the abundances of c 3 h 8 and c 2 h 4 could only be obtained near the 1 5 mbar level when compared to the abundances derived at the equator we find the nitriles hc 3 n and c 2 n 2 and some of the hydrocarbons c 2 h 4 c 3 h 4 and c 4 h 2 to be considerably enhanced in the north polar region the upper limit of the co 2 abundance obtained near the north pole indicates a depletion of this gas with respect to the equator by a factor of at least 2 current available photochemical models are insufficient to interpret these observations

latitudinal transport by barotropic waves in titan s stratosphere i general properties from a horizontal shallow water model abstract we present a numerical study of barotropic waves in titan s stratosphere based on a shallow water model the forcing of the zonal flow by the mean meridional circulation is represented by a relaxation towards a barotropically unstable wind profile the relaxation profile is consistent with observations and with previous results from a 3d general circulation model the time constant of the forcing that best matches the northward eddy transport of zonal momentum from the 3d model is 5 titan days the eddy wind field is a zonal wavenumber 2 wave with a peak amplitude about 10 of the mean wind speed the latitudinal transport of angular momentum by the wave tends to keep the flow close to marginal stability by carrying momentum upgradient from the core of the jets into the low latitudes although the strongest eddy motions occur at the latitudes of the wind maxima the strongest mixing takes place at the barotropically unstable regions close to 30 and spanning about 30 in latitude an eddy mixing time constant of the order of 1 titan day is inferred within these regions and of a few tens of days within regions of stable flow horizontal gradients in transient tracer fields are less than 10 of the latitudinal gradient of the meridional tracer profile cassini s detection of such waves could provide a direct observation of wind speeds at stratospheric levels

the eemian interglaciation in northwestern germany abstract hundreds of small lakes became filled with eemian deposits following the retreat of saalian ice in northwestern germany weakly expressed climate oscillations have been inferred from some local pollen records of late saalian sediments sea level stood 7 m below the current northwest german sea level datum nn during the interglacial climate optimum and decreased afterward a uniform vegetational succession of the eemian mixed forests correlated with marine isotope stage mis 5e terminated with the demise of boreal woodlands marked by a steep increase in nonarboreal pollen this is the onset of the early weichselian herning stade correlated with mis 5d no sharp climate oscillations during the eemian have been documented in the ending phase of the interglaciation the climate deteriorated gradually dominant heath and grass tundras point to a substantial decline of summer temperature during the herning stade sea level then stood at 40 m nn sedimentological considerations supported by counts of partly varved deposits indicate that the eemian lasted about 10 000 11 000 yr and the herning for several millennia

a review of numerical ocean modeling 1983 1986 midlatitude mesoscale and gyre scale for the years 1983 to the present numerical modeling of midlatitude ocean circulation on the mesoscale and gyre scale is reviewed numerical results have shown great similarity to recent thermocline theories but also some important differences in particular ventilation of the pool zone caused by convective processes is substantial also solutions employing explicitly resolved eddies differ significantly from their equilibrium counterparts inverse methods have provided improved estimates of meridional heat transport and tropical upwelling of tracers the crucial influence of the western boundary on the circulation of the gyre interior is beginning to be understood research has focused on the conditions for radiation by jets the relationship between a jet s structure and its stability and the generation of deep mean flows by eddy activity near the surface constraints on the structure of isolated vortices imposed by instability mechanisms have been explored with new balanced models which provide an inexpensive but accurate alternative to primitive equation models for many oceanic processes transport of salinity by gulf stream rings has been found to be comparable to the effects of evaporation and precipitation in the slope water it has also been shown that radial circulation in warm core rings cannot be disregarded as a possible cause of ring spin down in anticipation of a dramatic increase in the oceanic observational data base from altimetry scatterometry tomography and in situ measurement new modeling techniques for data assimilation and prediction are beginning to be developed

generation of a buoyancy driven coastal current by an antarctic polynya descent and spreading of high salinity water generated by salt rejection during sea ice formation in an antarctic coastal polynya is studied using a hydrostatic primitive equation three dimensional ocean model called the proudman oceanographic laboratory coastal ocean modeling system polcoms the shape of the polynya is assumed to be a rectangle 100 km long and 30 km wide and the salinity flux into the polynya at its surface is constant the model has been run at high horizontal spatial resolution 500 m and numerical simulations reveal a buoyancy driven coastal current the coastal current is a robust feature and appears in a range of simulations designed to investigate the influence of a sloping bottom variable bottom drag variable vertical turbulent diffusivities higher salinity flux and an offshore position of the polynya it is shown that bottom drag is the main factor determining the current width this coastal current has not been produced with other numerical models of polynyas which may be because these models were run at coarser resolutions the coastal current becomes unstable upstream of its front when the polynya is adjacent to the coast when the polynya is situated offshore an unstable current is produced from its outset owing to the capture of cyclonic eddies the effect of a coastal protrusion and a canyon on the current motion is investigated in particular due to the convex shape of the coastal protrusion the current sheds a dipolar eddy

the latitudinal distribution of clouds on titan clouds have been observed recently on titan through the thick haze using near infrared spectroscopy and images near the south pole and in temperate regions near 40 s recent telescope and cassini orbiter observations are now providing an insight into cloud climatology to study clouds we have developed a general circulation model of titan that includes cloud microphysics we identify and explain the formation of several types of ethane and methane clouds including south polar clouds and sporadic clouds in temperate regions and especially at 40 in the summer hemisphere the locations frequencies and composition of these cloud types are essentially explained by the large scale circulation

recent changes in the north atlantic it has long been recognized that the atlantic meridional overturning circulation moc is potentially sensitive to greenhouse gas and other climate forcing and that changes in the moc have the potential to cause abrupt climate change however the mechanisms remain poorly understood and our ability to detect these changes remains incomplete four main interrelated types of ocean change in particular are associated in the literature with greenhouse gas forcing these are a slowing of moc overturning rate changes in northern seas which might effect a change in atlantic overturning including changes in the freshwater flux from the arctic and changes in the transport and or hydrographic character of the northern overflows which ventilate the deep atlantic a change in the trans ocean gradients of steric height both zonal and meridional which might accompany a change in the moc and an intensification of the global water cycle though as yet we have no direct measure of the freshwater flux passing from the arctic to the atlantic either via the canadian arctic archipelago or along the east greenland shelf and no direct measure yet of the atlantic overturning rate we examine a wide range of time series from the existing hydrographic record for oceanic evidence of the other anticipated responses large amplitude and sustained changes are found or indicated by proxy over the past three to four decades in the southward transport of fresh waters along the labrador shelf and slope in the hydrography of the deep dense overflows from nordic seas in the transport of the eastern overflow through faroe bank channel and in the global hydrologic cycle though the type and scale of changes in ocean salinity are consistent with an amplification of the water cycle we find no convincing evidence of any significant concerted slowdown in the atlantic overturning circulation

convective mixing and the thermohaline circulation abstract an idealized three dimensional model of buoyancy driven flow in a single hemisphere is used to investigate the relationship between the meridional overturning and the efficiency by which convective mixing eliminates static instability in the fast limit mixing timescale hours to weeks the meridional overturning is not rate limited by the efficiency of convective mixing if convective mixing is made less efficient the model s meridional overturning strength increases moreover the dominant downwelling occurs not at the highest surface density hence the deep ocean is relatively buoyant the numerical results are explained by the different influences of convective mixing and downward advection on the deep ocean heat budget they underscore the fundamentally three dimensional nature of the meridional overturning in addition the narrowness of deep downwelling is related to the geostrophic dynamics of deep temperature anomalies near the eastern wall the model results presented here are in con

diagnostics of titan s stratospheric dynamics using cassini cirs data and the 2 dimensional ipsl circulation model abstract the dynamics of titan s stratosphere is discussed in this study based on a comparison between observations by the cirs instrument on board the cassini spacecraft and results of the 2 dimensional circulation model developed at the institute pierre simon laplace available at http www lmd jussieu fr titandbase rannou p lebonnois s hourdin f luz d 2005 adv space res 36 2194 2198 the comparison aims at both evaluating the model s capabilities and interpreting the observations concerning 1 dynamical and thermal structure using temperature retrievals from cassini cirs and the vertical profile of zonal wind at the huygens landing site obtained by huygens dwe and 2 vertical and latitudinal profiles of stratospheric gases deduced from cassini cirs data the modeled thermal structure is similar to that inferred from observations cassini cirs and earth based observations however the upper stratosphere above 0 05 mbar is systematically too hot in the 2d cm and therefore the stratopause region is not well represented this bias may be related to the haze structure and to misrepresented radiative effects in this region such as the cooling effect of hydrogen cyanide hcn the 2d cm produces a strong atmospheric superrotation with zonal winds reaching 200 m s 1 at high winter latitudes between 200 and 300 km altitude 0 1 1 mbar the modeled zonal winds are in good agreement with retrieved wind fields from occultation observations cassini cirs and huygens dwe changes to the thermal structure are coupled to changes in the meridional circulation and polar vortex extension and therefore affect chemical distributions especially in winter polar regions when a higher altitude haze production source is used the resulting modeled meridional circulation is weaker and the vertical and horizontal mixing due to the polar vortex is less extended in latitude there is an overall good agreement between modeled chemical distributions and observations in equatorial regions the difference in observed vertical gradients of c 2 h 2 and hcn may be an indicator of the relative strength of circulation and chemical loss of hcn the negative vertical gradient of ethylene in the low stratosphere at 15 s cannot be modeled with simple 1 dimensional models where a strong photochemical sink in the middle stratosphere would be necessary it is explained here by dynamical advection from the winter pole towards the equator in the low stratosphere and by the fact that ethylene does not condense near the winter pole 80 n some compounds c 4 h 2 c 3 h 4 exhibit an interior minimum in the observed abundance vertical profiles whereas 2d cm profiles are well mixed all along the atmospheric column this minimum can be a diagnostic of the strength of the meridional circulation and of the spatial extension of the winter polar vortex where strong descending motions are present in the summer hemisphere observed stratospheric abundances are uniform in latitude whereas the model maintains a residual enrichment over the summer pole from the spring cell due to a secondary meridional overturning between 1 and 50 mbar at latitudes south of 40 50 s the strength as well as spatial and temporal extensions of this structure are a difficulty that may be linked to possible misrepresentation of horizontally mixing processes due to the restricted 2 dimensional nature of the model this restriction should also be kept in mind as a possible source of other discrepancies

a simplified general circulation model for a baroclinic ocean with topography part i theory waves and wind driven circulations a new type of ocean general circulation model with simplified physics is described and tested for various simple wind driven circulation problems the model consists of the vorticity balance of the depth averaged flow and a hierarchy of equations for vertical moments of density and baroclinic velocity the first vertical density moment is the vertically integrated potential energy which is used to describe the predominant link between the barotropic and the baroclinic oceanic flow in the presence of sloping topography tendency equations for the vertical moments of density and baroclinic velocity and an appropriate truncation of the coupled hierarchy of moments are derived that together with the barotropic vorticity balance yield a closed set of equations describing the barotropic baroclinic interaction barbi model of the oceanic circulation idealized companion experiments with a numerical implementation of the barbi model and a primitive equation model indicate that wave propagation properties and baroclinic adjustments are correctly represented in barbi in midlatitudes as well as in equatorial latitudes furthermore a set of experiments with a realistic application to the atlantic southern ocean system reproduces important aspects that have been previously reported by studies of gyre circulations and circumpolar currents using full primitive equation models

high resolution climate records from the north atlantic during the last interglacial the two deep ice cores recovered by the grip1 and gisp22 projects at summit greenland agree in detail over the past 100 000 years3 and demonstrate dramatic climate variability in the north atlantic region during the last glacial before the current period of holocene stability this glacial climate instability has subsequently been documented in the marine sedimentary record of surface ocean conditions in the north atlantic4 before 100 kyr ago the two ice core records are discrepant however casting doubt on whether the oxygen isotope fluctuations during the last interglacial eemian seen in the grip core1 5 represent a true climate signal here we present high resolution records of foraminiferal assemblages and ice rafted detritus from two north atlantic cores for the interval 65 kyr to 135 kyr ago extending the surface ocean record back to the eemian the correlation between our records and the greenland ice core records is good throughout the period in which the two ice cores agree suggesting a regionally coherent climate response during the eemian our marine records show a more stable climate than that implied by the grip ice core suggesting that localized phenomena may be responsible for the variability in the latter record during the eemian

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

climatic interpretation of terrestrial malacofaunas of the last interglacial in southeastern france abstract the sequence of the ruisseau de l amourette in the french alps covering the isotope stages 5e 5d 5c and part of 5a and 6 was studied for terrestrial mollusks correspondence analysis of the mollusk assemblages permits reconstruction of temperature and moisture trends using knowledge of the modern ecology of the recognized species the classic environmental succession of the last interglacial early glacial wurmian is recognized the eemian sub stage 5e suggests warm and moist conditions it is followed by the cold melisey i sub stage 5d showing moisture variation from dry in the lower part to moist in the upper part the mollusk equivalent of st germain i and ii also indicates warm and moist conditions the melisey ii stadial sub stage 5b is missing but may be reflected by the deposition of barren gravel layers all these environmental oscillations agree with the fluctuations described in the literature however stage 5e indicates a particular trend as the mollusks recorded two well individual cool events which seem to correspond to variations identified in various west european continental records however as no particular cold indicator species were identified these events cannot be related to strong climatic fluctuations as emphasized in the early studies of the greenland grip ice core or in north atlantic and western european records

improved general circulation models of the martian atmosphere from the surface to above 80 km we describe a set of two new generation general circulation models of the martian atmosphere derived from the models we originally developed in the early 1990s the two new models share the same physical parameterizations but use two complementary numerical methods to solve the atmospheric dynamic equations the vertical resolution near the surface has been refined and the vertical domain has been extended to above 80 km these changes are accompanied by the inclusion of state of the art parameterizations to better simulate the dynamical and physical processes near the surface boundary layer scheme subgrid scale topography parameterization etc and at high altitude gravity wave drag in addition radiative transfer calculations and the representation of polar processes have been significantly improved we present some examples of zonal mean fields from simulations using the model at several seasons one relatively novel aspect previously introduced by wilson 1997 is that around northern winter solstice the strong pole to pole diabatic forcing creates a quasi global angular momentum conserving hadley cell which has no terrestrial equivalent within such a cell the coriolis forces accelerate the winter meridional flow toward the pole and induce a strong warming of the middle polar atmosphere down to 25 km this winter polar warming had been observed but not properly modeled until recently in fact thermal inversions are generally predicted above one and often both poles around 60 70 km however the mars middle atmosphere above 40 km is found to be very model sensitive and thus difficult to simulate accurately in the absence of observations

numerical experiments with a wind and buoyancy driven two and a half layer upper ocean model we describe numerical experiments with a limited domain 15 67 n 65 west to east coarse resolution two and a half layer upper ocean model the model consists of two active variable density layers a niiler and kraus 1977 type mixed layer and a pycnocline layer which overlays a semipassive deep ocean the mixed layer is forced with a cosine wind stress and haney type heat and precipitation evaporation fluxes which were derived from zonally averaged climatological levitus 1982 surface temperatures and salinities for the north atlantic the second layer is forced from below with 1 newtonian cooling to climatological temperatures and salinities at the lower boundary 2 convective adjustment which occurs whenever the density of the second layer is unstable with respect to climatology and 3 mass entrainment in areas of strong upwelling when the deep ocean ventilates through the bottom surface the sensitivity of this model to changes in its internal mixed layer and external e g a newtonian coupling coefficient parameters is investigated and compared to the results from a control experiment we find that the model is not overly sensitive to changes in most of the parameters that were tested albeit these results may depend to some extent on the choice of the control experiment

a review of sea ice and ocean modeling relevant to the labrador and newfoundland shelves numerical and analytical models of sea ice and ocean circulation are reviewed from a viewpoint of their application to the labrador and newfoundland shelves seasonal variabilities of sea ice and ocean circulation have not been reported in numerical models the difficulty comes from the importance of both stratification and bottom topography sea ice should be included for seasonal cycle calculations individual mechanisms of variabilities with time scales ranging from a day to a month have been studied extensively using various models so that the coupling of these models will make it possible to test the predictability of sea ice and ocean circulation the data collected during limex 87 and 89 provide verification of the models

rapid changes in the east asian monsoon during the last interglacial in the bohai sea coastal zone china the bohai sea coastal zone of china faces the pacific ocean to the east and the eurasian continent to the west hence this region is influenced by both the ocean and continental landmasses the bohai sea coastal zone has significant monsoon climate characteristics and a strong sensitivity to climate change the miaodao stratigraphical section mds contains historical information about climate features in the region especially the high frequency variations during the last interglacial sea level changes and the evolution of the east asian monsoon by analyzing the ages of various sedimentary facies in combination with proxy paleoclimatic indices i e grain 63 mu m fraction average grain size mz clay silt sand content sc d magnetic susceptibility and the ratios na2o al2o3 and al2o3 tofe sio2 in the fifth segments of the mds from the last interglacial mds5 we conclude that subsections 5a 5c and 5e were controlled by summer monsoons whereas subsections 5b and 5d were formed when winter monsoons prevailed these results were similar to oxygen isotope analyses from previous studies including the spectral mapping project specmap and the north greenland ice core project northgrip five and a half comparable oscillations in proxy indices that were dated to ca 116 1 118 3 121 2 122 7 125 9 and 128 7 ka occurred within the mds 5e subsection when winter monsoon winds strengthened this millennial scale climate variability during the eemian period may have reached up to ten and a half oscillations with a quasi periodicity of approximately a 1 470 year cycle during the late glacial period this rapid period of climate change has been recorded in northern and central europe central asia and in east asia the climate influencing mechanism was probably initiated by changes in solar activity and driven by the east asian monsoon and sea level oscillations

kiloyear scale climate events and evolution during the last interglacial mu us desert china the fifth segment of the milanggouwan stratigraphical section mgs 5 in the mu us desert provides high resolution geological information on environmental variations during the last interglacial the analysis of grain content 50 mu m organic content sio2 al2o3 tofe and sio2 al2o3 tofe ratios in the mgs 5 suggest that there were 17 kiloyear scale climate fluctuations in the last interglacial including 9 warm events w1 w9 and 8 cold events c1 c8 dominated by the east asian summer monsoon and winter monsoon respectively the analysis also suggests that the eemian interglacial was unstable with 3 warm events w7 w9 and 2 cold events c7 c8 indicating that climate fluctuations affected the east asian monsoon in the mu us desert during the last interglacial the change cycles and the nature of the kiloyear scale climate events have a close temporal relationship with the greenland ice core oxygen isotope data suggesting that the climate forming mechanism was affected by polar weather north atlantic sea ice range of the eurasian ice front and movement of the arctic frontal all of which affect the intensity of the siberian mongolian high pressure region through the movement of the cold air mass c 2012 elsevier ltd and inqua all rights reserved

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

holocene water level changes inferred from a section of fluvio lacustrine sediments in the southeastern mu us desert china abstract a natural exposure of fluvio lacustrine sediments the dsgl section on the left bank of salawusu river located at the southeastern margin of the mu us desert in north china was studied in order to reconstruct holocene water level changes a chronology was established based on 11 ams 14c dates and variations in the lithology and grain size c m variations were used to assess the forcing factors of local hydrological changes during the holocene a lake swamp environment with high hydrodynamic energy occurred from 9 6 to 9 2 ka cal yr bp which was succeeded by a full lake environment at around 9 6 ka cal yr bp however an interval of sand deposits and peat sediments from 9 2 to 8 6 ka cal yr bp indicates unstable hydrodynamic conditions the salawusu paleo lake reached its maximum level between 8 4 and 6 5 ka cal yr bp and gradually shrank thereafter after 1 2 ka cal yr bp a shallow lake environment returned indicating a humid phase which may be correlative with the relatively warm and moist medieval warm period mwp after 0 68 ka cal yr bp broadly coeval with the little ice age lia a fluvial environment appeared the variations in water level were mainly triggered by the east asian monsoon however site specific factors may have also have been important

delayed advective oscillation of the atlantic thermohaline circulation a simple dynamic model is proposed to illustrate the multidecadal oscillation of the atlantic ocean thermohaline circulation the proposed oscillation relies on alternating actions of positive and negative feedbacks which are operated by a slow adjustment of the ocean circulation and the associated time delay in the advective flux response to a change in meridional density gradient the key element of the oscillation is the time delay which is conceptually related to the basin crossing time of long rossby waves in the highlatitude north atlantic for a sufficiently long time delay the solution becomes unstable in some regions of model parameter space and oscillates with a period of approximately 2 times the delay time

temporal variations of titan s middle atmospheric temperatures from 2004 to 2009 observed by cassini cirs we use five and one half years of limb and nadir viewing temperature mapping observations by the composite infrared radiometer spectrometer cirs on the cassini saturn orbiter taken between july 2004 and december 2009 ls from 293 to 4 northern mid winter to just after northern spring equinox to monitor temperature changes in the upper stratosphere and lower mesosphere of titan the largest changes are in the northern winter polar stratopause which has declined in temperature by over 20 k between 2005 and 2009 throughout the rest of the mid to upper stratosphere and lower mesosphere temperature changes are less than 5 k in the southern hemisphere temperatures in the middle stratosphere near 1 mbar increased by 1 2 k from 2004 through early 2007 then declined by 2 4 k throughout 2008 and 2009 with the changes being larger at more polar latitudes middle stratospheric temperatures at mid northern latitudes show a small 1 2 k increase from 2005 through 2009 at north polar latitudes within the polar vortex temperatures in the middle stratosphere show a 4 k increase during 2007 followed by a comparable decrease in temperatures in 2008 and into early 2009 the observed temperature changes in the north polar region are consistent with a weakening of the subsidence within the descending branch of the middle atmosphere meridional circulation

the two titan stellar occultations of 14 november 2003 1 we report the observation of two stellar occultations by titan on 14 november 2003 using stations in the indian ocean southern africa spain and northern and southern americas these occultations probed altitudes between 550 and 250 km 1 to 250 bar in titan s upper stratosphere the light curves reveal a sharp inversion layer near 515 6 km altitude 1 5 bar pressure level where the temperature increases by 15 k in only 6 km this layer is close to an inversion layer observed fourteen months later by the huygens hasi instrument during the entry of the probe in titan s atmosphere on 14 january 2005 fulchignoni et al 2005 central flashes observed during the first occultation provide constraints on the zonal wind regime at 250 km with a strong northern jet 200 m s 1 around the latitude 55 n wind velocities of 150 m s 1 near the equator and progressively weaker winds as more southern latitudes are probed the haze distribution around titan s limb at 250 km altitude is close to that predicted by the global circulation model of rannou et al 2004 in the southern hemisphere but a clearing north of 40 n is necessary to explain our data this contrasts with rannou et al s 2004 model which predicts a very thick polar hood over titan s northern polar regions simultaneous observations of the flashes at various wavelengths provide a dependence of q with q 1 8 0 5 between 0 51 and 2 2 m for the tangential optical depth of the hazes at 250 km altitude

time dependent adjustment in a simple model of the mid depth meridional overturning cell abstracta recently proposed reduced gravity model of the warm water branch of the middepth meridional overturning circulation in a rectangular basin with a circumpolar connection is extended to include time dependence the model describes the balance between gain of warm water through northward ekman advection across the circumpolar current loss of warm water through eddy fluxes southward across the current net gain or loss of warm water through diabatic processes north of the current and changes in the thickness of the warm water layer the steady solutions are the same as those found previously when the previous parameterization of diabatic fluxes is used time dependent solutions are considered for the approach of the solution to a new equilibrium when the forcing or parameters are abruptly changed and then held fixed an initial adjustment occurs through a combination of boundary and equatorial adjustment followed by planetary wave propagation the longer term adjustment to equilibrium consists p

stochastically driven multidecadal variability of the atlantic meridional overturning circulation in ccsm3 the atlantic meridional overturning circulation amoc in the last 250 years of the 700 year long present day control integration of the community climate system model version 3 with t85 atmospheric resolution exhibits a red noise like irregular multi decadal variability with a persistence longer than 10 years which markedly contrasts with the preceding 300 years of very regular and stronger amoc variability with 20 year periodicity the red noise like multi decadal amoc variability is primarily forced by the surface fluxes associated with stochastic changes in the north atlantic oscillation nao that intensify and shift northward the deep convection in the labrador sea however the persistence of the amoc and the associated oceanic anomalies that are directly forced by the nao forcing does not exceed about 5 years the additional persistence originates from anomalous horizontal advection and vertical mixing which generate density anomalies on the continental shelf along the eastern boundary of the subpolar gyre these anomalies are subsequently advected by the mean boundary current into the northern part of the labrador sea convection region reinforcing the density changes directly forced by the nao as no evidence was found of a clear two way coupling with the atmosphere the multi decadal amoc variability in the last 250 years of the integration is an ocean only response to stochastic nao forcing with a delayed positive feedback caused by the changes in the horizontal ocean circulation

the evolution of titan s mid latitude clouds spectra from cassini s visual and infrared mapping spectrometer reveal that the horizontal structure height and optical depth of titan s clouds are highly dynamic vigorous cloud centers are seen to rise from the middle to the upper troposphere within 30 minutes and dissipate within the next hour their development indicates that titan s clouds evolve convectively dissipate through rain and over the next several hours waft downwind to achieve their great longitude extents these and other characteristics suggest that temperate clouds originate from circulation induced convergence in addition to a forcing at the surface associated with saturn s tides geology and or surface composition

millennial and orbital scale climate variability in southeastern united states and in the subtropical atlantic during marine isotope stage 5 evidence from pollen and isotopes in odp site 1059 abstract we present directly correlative high resolution pollen and isotopic data from marine isotope stage mis 5 from a marine core taken on the continental margin off the southeastern united states 31 40 n 75 24 w 2985 m these data provide the first chronostratigraphically controlled pollen data for the last interglacial from this region comparison of the pollen and benthic isotope stratigraphies demonstrate that vegetation and climate development in southeastern united states did not always coincide with global ice volume changes deglacial terrestrial climate amelioration which was nearly synchronous with ice decay peaked slightly before the ice volume minimum in mis 5e cooling in the latter part of the last interglacial began at c27 prior to ice growth vegetation and climate were not stable during mis 5e suborbital climate oscillations persisted throughout mis 5 both onshore and in the subtropical atlantic offshore the largest correlative suborbital oscillations in the pinus pine and quercus oak forests of coastal georgia and south carolina and sea surface variability correspond to stadial interstadials documented in greenland ice cores however coupled oscillations also occur more frequently

small scale composition and haze layering in titan s polar vortex abstract fine scale layering of haze and composition in titan s stratosphere and mesosphere was investigated using visible uv images from cassini s imaging science sub system iss and ir spectra from cassini s composite infra red spectrometer cirs both iss and cirs independently show fine layered structures in haze and composition respectively in the 150 450 km altitude range with a preferred vertical wavelength of around 50 km layers are most pronounced around the north polar winter vortex although some weaker layers do exist at more southerly latitudes the amplitude of composition layers in each trace gas profile is proportional to the relative enrichment of that species in the winter polar vortex compared to equatorial latitudes as enrichment is caused by polar subsidence this suggests a dynamical origin we propose that the polar layers are caused by cross latitude advection across the vortex boundary this is analogous to processes that lead to ozone laminae formation around earth s polar vortices

a model study of wind and buoyancy driven coastal circulation a two level model with a flat bottom on a plane is employed to examine wind and buoyancy driven coastal circulation on the western boundary of the ocean the model of the ocean interior receives wind stress through the surface ekman layer which is purely determined from wind stress buoyancy flux is given to the upper level momentum equations are linear and geostrophy in cross shore momentum is assumed density equations retain horizontal and vertical advection terms as well as horizontal diffusion this cost effective three dimensional model is capable of a case study of a seasonal time scale simulation with various parameters varied oceanic responses to wind stress and buoyancy flux occur only along the coast to right of the forcing area facing offshore a barotropic component merging to the western boundary is responsible for elimination of the undercurrent in the wind driven flow in most cases the widths of the barotropic and baroclinic components are proportional to horizontal viscosity 1 3 and horizontal diffusion 1 2 respectively thus the undercurrent exists with a small diffusion coefficient a wind driven current in a stratified system is insensitive to bottom friction while a homogeneous system is sensitive to the friction a buoyancy flux produces a baroclinic eddylike feature in the forcing area plus a baroclinic coastal flow a significant barotropic component is produced by bottom friction in the buoyancy driven case increasing reducing the upper lower level flow model sensitivity to assumed interactions between the ekman layer and upper level and vertical finite difference scheme is examined the flow field is insensitive to the assumptions and scheme while vertical stratification is sensitive

titan s middle atmospheric temperatures and dynamics observed by the cassini composite infrared spectrometer the composite infrared radiometer spectrometer cirs instrument on the nasa cassini saturn orbiter has been acquiring thermal emission spectra from the atmosphere of titan since orbit insertion in 2004 observation sequences for measuring stratospheric temperatures have been obtained using both a nadir mapping mode and a limb viewing mode the limb observations give better vertical resolution and give information from higher altitudes while the nadir observations provide more complete longitude coverage because the scale height of titan s atmosphere is large enough so that emission from a grazing ray is influenced by horizontal temperature variations in the atmosphere we have developed a twodimensional temperature retrieval algorithm for reducing the limb spectra which solves simultaneously for meridional and vertical temperature variations the analyzed nadir mapping data have sampled nearly all longitudes at latitudes from about 90 st o 60 n providing temperatures between pressure levels of about 5 to 0 2 mbar the limb data covers latitudes between about 75 s and 85 n and yields temperatures between about 1 and 0 005 mbar at a small number of longitudes the retrieved temperatures are consistent with early results from nadir observations flasar f m and 44 colleagues 2005 science 308 975 978 between 0 5 and 5 mbar where both results are valid with the warmest temperatures at the equator and much stronger meridional temperature gradients in the northern winter hemisphere than in the southern at higher altitudes not probed by nadir viewing the limb data reveal that the stratopause is nearly 20 k warmer in the northern polar regions than at the equator and southern hemisphere and that the altitude of the stratopause shifts from 0 1 mbar 300 km near the equator to 0 01 mbar 400 km poleward of about 40 n when the gradient wind equation is used to construct a zonal mean wind the reversal in sign of the temperature leads to capping of the winter westerly flow the core of the resulting jet is about 190 m s 1 in magnitude spans between 30 n and 60 n and peaks near 0 1 mbar estimates of the radiative heating associated with the radiative disequilibrium lead to a meridional overturning timescale of about three earth years

interdecadal variability and oceanic thermohaline adjustment changes in the strength of the thermohaline overturning circulation are associated by geostrophy with changes in the east west pressure difference across an ocean basin the tropical polar density contrast and the east west pressure difference are connected by an adjustment process in flat bottomed ocean models the adjustment is associated with viscous baroclinic kelvin wave propagation weak high latitude stratification leads to the adjustment having an interdecadal timescale we reexamine model interdecadal oscillations in the context of the adjustment process for both constant flux and mixed surface boundary conditions under constant surface flux interdecadal oscillations are associated with the passage of a viscous kelvin wave around the model domain we carry out experiments suppressing wave propagation along each of the model boundaries suppressing wave propagation along either the tropical or eastern boundary does not eliminate the oscillation but increases both its period and amplitude suppressing wave propagation along either the polar or the western boundary eliminates the oscillation our results suggest the oscillations can be self sustained by perturbations to the western boundary current arising from the southward boundary wave propagation mixed boundary condition oscillations are characterized by the eastward cross basin movement of salinity dominated density anomalies and the westward return of these anomalies along the northern boundary we suggest the latter is associated with viscous kelvin wave propagation under both types of boundary conditions the strength of the thermohaline overturning and the tropical polar density contrast vary out of phase we show how the phase relationship is related to the boundary wave propagation box models and zonally averaged models assume that the east west and north south pressure gradients vary in phase and are proportional to one another we suggest this assumption is valid only on timescales long compared to the adjustment timescale the importance of boundary regions indicates an urgent need to examine the robustness of interdecadal variability in models as the resolution is increased and as the representation of the coastal shelf slope wave guide is improved

signal propagation related to the north atlantic overturning 1 changes of the meridional overturning circulation moc due to surface heat flux variability related to the north atlantic oscillation nao are analyzed in various ocean models i e eddying and non eddying cases a prime signature of the forcing is variability of the winter time convection in the labrador sea the associated changes in the strength of the moc near the subpolar front 45 n are closely related to the nao index leading moc anomalies by about 2 3 years in both the eddying and non eddying simulation further south the speed of the meridional signal propagation depends on model resolution with lower resolution non eddying case 4 3 resolution the moc signal propagates equatorward with a mean speed of about 0 6 cm s similar as spreading rates of passive tracer anomalies eddy permitting experiments 1 3 show a significantly faster propagation with speeds corresponding to boundary waves thus leading to an almost in phase variation of the moc transport over the subtropical to subpolar north atlantic

global and temporal variations in hydrocarbons and nitriles in titan s stratosphere for northern winter observed by cassini cirs mid infrared spectra measured by cassini s composite infrared spectrometer cirs between july 2004 and january 2007 ls 293 328 have been used to determine stratospheric temperature and abundances of c2h2 c 3h4 c 4h2 h cn and hc3n over 65 000 nadir spectra with spectral resolutions of 0 5 and 2 5 cm 1 were used to probe spatial and temporal composition variations in titan s stratosphere cassini s 180 orbital transfer in mid 2006 allowed low emission angle observations of the north polar region for the first time in the mission and allowed us to probe the full latitude range we present the first measurements of composition variations within the polar vortex which display increasing abundances right up to 90 n the lack of a homogeneous abundance latitude variation within the vortex indicates limited horizontal mixing and suggests that subsidence is greatest at the vortex core contrary to numerical model predictions and tropospheric cloud observations we do not see any evidence for a secondary circulation cell near the south pole which suggests a single hadley type circulation in the stratosphere at this epoch this difference can be reconciled if the secondary cell is restricted to altitudes below 100 km where there is no sensitivity in our data temporal variations in composition were observed in the south with volatile species becoming less abundant as the season progressed the observed variations are compared to numerical model predictions and observations from voyager

paleo monsoon activities of mu us desert china since 150 ka b p a study of the stratigraphic sequences of the milanggouwan section salawusu river area abstract the interbeddings of the aeolian sand dune facies and the fluvio lacustrine and paleosol facies in the milanggouwan stratigraphic section have been examined by a series of geological methods including grain size magnetic susceptibility sporo pollen and fossil analyses along with various dating methods the results showed a basic difference in depositional environments between the sand dune facies and the fluvio lacustrine and paleosol facies at least 27 cycles of alternate depositions of the aeolian dune sands and the fluvio lacustrine facies and or paleosols from 150 ka b p have been discovered in the mu us desert these cycles reflect the climatic variations that were induced by the growth and decline and confrontation between the winter monsoon and the summer monsoon of east asia in the past 150 ka the sporo pollen and magnetic susceptibility analyses suggest a great increase of rainfall 40 120 and temperature 2 6 c during the prevailing summer monsoon periods this is the only sedimentary profile that represents the climatic variations of millennial scale in the desert areas of north china for the late quaternary the high resolution results on paleo monsoon variations from the section may indicate sensitive reactions of the margin desert to climatic changes

loess particle size data indicative of stable winter monsoons during the last interglacial in the western part of the chinese loess plateau abstract particle size data from the western part of the chinese loess plateau do not support the last interglacial correlation suggested by the data from the central part of the loess plateau between the high dust influx events in the loess plateau and the cool events in the high northern latitudes the lack of marked oscillations in the particle size of the last interglacial paleosol s1 in the western part of the plateau is interpreted as an indication of stable winter monsoons it is thus inferred that the teleconnection between the northern high latitudes and the chinese loess plateau evident in the last glacial might not have existed during the last interglacial it is argued that the western part of the plateau is a better place to establish synchroneity between parent material eolian deposition and s1 paleosol formation 6 8 m thick under such cooler and drier conditions however to assume synchroneity between parent material eolian deposition and s1 paleosol formation only 2 5 m thick under the warmer and moister interglacial conditions in the central part of the plateau is a questionable practice thus the high resolution correlation with the data from the north atlantic area remains problematic

millennial scale climatic oscillations during the last interglaciation in central china repeated southward excursions of north atlantic polar water during the last interglaciation 18 o stage 5 130 74 ka are recorded by planktonic foraminifera and ice rafted detritus in north atlantic sediment cores and greenland ice sheet cores display quasi synchronous fluctuations comparable high frequency variations in the east asian winter monsoon climate are discernible in three loess paleosol profiles in central china that span the last interglaciation peak values of the 40 m quartz fraction and bulk sediment samples from the s1 last interglacial accretionary paleosol complex reflect major dust flux events when winter monsoon winds strengthened frequent oscillations of the dust flux and nine significant dust events are recorded six events falling between ca 110 and 70 ka are correlated with cold peaks c19 24 identified in north atlantic cores two comparable dust peaks occur within paleosol s1ss3 substage 5e the older of these dating to ca 121 ka may correlate with a brief cold event recently recognized in high resolution marine and terrestrial climate proxy records

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

mapping the zonal structure of titan s northern polar vortex abstract saturn exhibits an obliquity of 26 7 such that the largest moon titan experiences seasonal variations including the formation of a polar vortex in the winter hemisphere titan s polar vortex is characterised by cold stratospheric temperatures due to the lack of insolation over the winter pole and an increase in trace gas abundance as a result of complex organic chemistry in the upper atmosphere combined with polar subsidence meridional variations in temperature and gas abundance across the vortex have previously been investigated but there has not yet been any in depth study of the zonal variations in the temperature or composition of the northern vortex here we present the first comprehensive two dimensional seasonal mapping of titan s northern winter vortex using 18 nadir mapping sequences observed by the composite infrared spectrometer cirs instrument on board cassini we investigate the evolution of the vortex over almost half a titan year from late winter through to mid summer ls 326 86 2007 2017 we find the stratospheric symmetry axis to be tilted from the solid body rotation axis by around 3 5 although our results for the azimuthal orientation of the tilt are inconclusive we find that the northern vortex appears to remain zonally uniform in both temperature and composition at all times a comparison with vortices observed on earth mars and venus shows that large scale wave mechanisms that are important on other terrestrial planets are not as significant in titan s atmosphere this allows the northern vortex to be more symmetrical and persist longer throughout the annual cycle compared to other terrestrial planets

simulating the one dimensional structure of titan s upper atmosphere 1 formulation of the titan global ionosphere thermosphere model and benchmark simulations 1 we employ a newly developed navier stokes model the titan global ionosphere thermosphere model t gitm to address the one dimensional 1 d coupled composition dynamics and energetics of titan s upper atmosphere our main goals are to delineate the details of this new theoretical tool and to present benchmark calibration simulations compared against the ion neutral mass spectrometer inms neutral density measurements first we outline the key physical routines contained in t gitm and their computational formulation then we compare a series of model simulations against recent 1 d work by cui et al 2008 strobel 2008 2009 and yelle et al 2008 in order to provide a fiducial for calibrating this new model in paper 2 and a future paper we explore the uncertainties in our knowledge of titan s atmosphere between 500 km and 1000 km in order to determine how the present measurements constrain our theoretical understanding of atmospheric structures and processes

mapping of titan results from the first titan radar passes the first two swaths collected by cassini s titan radar mapper were obtained in october of 2004 ta and february of 2005 t3 the ta swath provides evidence for cryovolcanic processes the possible occurrence of fluvial channels and lakes and some tectonic activity the t3 swath has extensive areas of dunes and two large impact craters we interpret the brightness variations in much of the swaths to result from roughness variations caused by fracturing and erosion of titan s icy surface with additional contributions from a combination of volume scattering and compositional variations despite the small amount of titan mapped to date the significant differences between the terrains of the two swaths suggest that titan is geologically complex the overall scarcity of impact craters provides evidence that the surface imaged to date is relatively young with resurfacing by cryovolcanism fluvial erosion aeolian erosion and likely atmospheric deposition of materials future radar swaths will help to further define the nature of and extent to which internal and external processes have shaped titan s surface

vertical profiles of hcn hc3n and c2h2 in titan s atmosphere derived from cassini cirs data mid infrared limb spectra in the range 600 1400 cm 1 taken with the composite infrared spectrometer cirs on board the cassini spacecraft were used to determine vertical profiles of hcn hc3n c2h2 and temperature in titan s atmosphere both high 0 5 cm 1 and low 13 5 cm 1 spectral resolution data were used the 0 5 cm 1 data gave profiles at four latitudes and the 13 5 cm 1 data gave almost complete latitudinal coverage of the atmosphere both datasets were found to be consistent with each other high temperatures in the upper stratosphere and mesosphere were observed at titan s northern winter pole and were attributed to adiabatic heating in the subsiding branch of a meridional circulation cell on the other hand the lower stratosphere was much colder in the north than at the equator which can be explained by the lack of solar radiation and increased ir emission from volatile enriched air hc3n had a vertical profile consistent with previous ground based observations at southern and equatorial latitudes but was massively enriched near the north pole this can also be explained in terms of subsidence at the winter pole a boundary observed at 60 n between enriched and un enriched air is consistent with a confining polar vortex at 60 na nd hc 3n s short lifetime in the far north layers were observed in the hc3n profile that were reminiscent of haze layers observed by cassini s imaging cameras hcn was also enriched over the north pole which gives further evidence for subsidence however the atmospheric cross section obtained from 13 5 cm 1 data indicated a hcn enriched layer at 200 250 km extending into the southern hemisphere this could be interpreted as advection of polar enriched air towards the south by a meridional circulation cell this is observed for hcn but not for hc3n due to hcn s longer photochemical lifetime c2h2 appears to have a uniform abundance with altitude and is not significantly enriched in the north this is consistent with observations from previous cirs analysis that show increased abundances of nitriles and hydrocarbons but not c2h2 towards the north pole

the variability of the atlantic meridional overturning circulation the north atlantic oscillation and the el nino southern oscillation in the bergen climate model abstract the link between the interannual to interdecadal variability of the atlantic meridional overturning circulation amoc and the atmospheric forcing is investigated using 200 yr of a control simulation of the bergen climate model where the mean circulation cell is rather realistic as is also the location of deep convection in the northern north atlantic the amoc variability has a slightly red frequency spectrum and is primarily forced by the atmosphere the maximum value of the amoc is mostly sensitive to the deep convection in the irminger sea which it lags by about 5 yr the latter is mostly forced by a succession of atmospheric patterns that induce anomalous northerly winds over the area the impact of the north atlantic oscillation on deep convection in the labrador and greenland seas is represented realistically but its influence on the amoc is limited to the interannual time scale and is primarily associated with wind forcing the tropical pacific shows a strong variability in the model

eemian climatic and hydrographical instability on a marine shelf in northern denmark abstract benthic foraminifera and stable isotope data from the last interglaciation eemian substage 5e from a borehole at skagen denmark provide evidence for major environmental and hydrographic changes during this period during the first millennium of the eemian water masses covering northern denmark became gradually warmer temperate conditions prevailed during most of the interglaciation but these were interrupted by two periods with decreased water temperatures the first cooling event s 1 was not very distinct at skagen but the second event s 2 seen in both the foraminiferal and oxygen isotope record represents a large shift to subarctic conditions carbon isotopes indicate a change in ocean circulation during both events no comparable climate variations are seen within the holocene record at the site the final cooling of the water masses associated with the substage 5e 5d boundary occurred within a few hundred years these last interglacial climatic changes were probably caused by variations in strength and or position of the north atlantic drift possibly as a result of varying vigor of the atlantic conveyor in addition minor variations in the fossil assemblages also indicate fluctuations in the inflow of atlantic water to the skagerrak kattegat area during the warm intervals of substage 5e

a two level wind and buoyancy driven thermocline model abstract a simple two level model is designed to simulate the thermocline equations applicable for large scale steady oceanic flow the model serves two functions first it replaces problems with the interpretation of slablike dynamics e g luyten et al 1983 by using continuously horizontally varying buoyancy but at the cost of reducing the vertical resolution drastically the equations used are geostrophy plus a small linear drag to close a stommel like western boundary layer mass conservation and buoyancy conservation with a small but necessary horizontal diffusion inclusion of vertical diffusion has little effect the ocean is driven by an ekman layer whose functions are to provide a given surface input of mass through ekman pumping and buoyancy through a specified buoyancy in the ekman layer i e to maintain the same boundary conditions as in classical thermocline studies sidewall conditions are not well understood and are almost certainly over specified in this formulation s

timing duration and transitions of the last interglacial asian monsoon thorium 230 ages and oxygen isotope ratios of stalagmites from dongge cave china characterize the asian monsoon and low latitude precipitation over the past 160 000 years numerous abrupt changes in 18o 16o values result from changes in tropical and subtropical precipitation driven by insolation and millennial scale circulation shifts the last interglacial monsoon lasted 9 7 1 1 thousand years beginning with an abrupt less than 200 years drop in 18o 16o values 129 3 0 9 thousand years ago and ending with an abrupt less than 300 years rise in 18o 16o values 119 6 0 6 thousand years ago the start coincides with insolation rise and measures of full interglacial conditions indicating that insolation triggered the final rise to full interglacial conditions

on the robustness of the interdecadal modes of the thermohaline circulation ocean models in box geometry forced by constant surface fluxes of density have been found to spontaneously generate interdecadal oscillations of the thermohaline circulation this paper analyzes the sensitivity of these oscillations to various physical effects including the presence of mesoscale turbulence various thermal surface boundary conditions and the presence of wind forcing or bottom topography the role of unstable long baroclinic waves is also reexamined in an attempt to understand the oscillation period in idealized geometry it is found that the low frequency variability of the thermohaline circulation under quasi constant surface fluxes is a robust feature of the large scale circulation it is not strongly affected by energetic mesoscale turbulence the oscillation period is relatively invariant with respect to varying resolution and momentum and tracer horizontal mixing coefficients although it loses some regularity as shorter and longer periods of variability emerge when the mesoscale activity increases in strength with smaller mixing coefficients the oscillations are also retained as the ocean model is coupled to an interactive atmospheric energy balance model the thermohaline modes are robust to a range of exchange coefficients that widens with the amplitude of the mean circulation the presence of an additional wind forced component generally weakens the oscillation and depending on the relative strength of thermodynamic and dynamic forcings the oscillation may be completely killed a simple interpretation is given highlighting the role of upward ekman pumping in damping density anomalies finally the interaction of these baroclinic modes with bottom topography depends strongly on the relative directions of the mean topographic features and the mean currents and baroclinic waves but usually results in a damping influence

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr