variable winds on venus mapped in three dimensions 1 we present zonal and meridional wind measurements at three altitude levels within the cloud layers of venus from cloud tracking using images taken with the virtis instrument on board venus express at low latitudes zonal winds in the southern hemisphere are nearly constant with latitude with westward velocities of 105 ms 1 at cloud tops altitude 66 km and 60 70 ms 1 at the cloud base altitude 47 km at high latitudes zonal wind speeds decrease linearly with latitude with no detectable vertical wind shear values lower than 15 ms 1 indicating the possibility of a vertically coherent vortex structure meridional winds at the cloud tops are poleward with peak speed of 10 ms 1 at 55 s but below the cloud tops and averaged over the south hemisphere are found to be smaller than 5 ms 1 we also report the detection at subpolar latitudes of wind variability due to the solar tide

long term variation in the cloud tracked zonal velocities at the cloud top of venus deduced from venus express vmc images 1 we present observational evidence of the variation of the cloud tracked zonal velocity by 20 m s 1 with a timescale of a few hundred days in the southern low latitude region based on an analysis of cloud images taken by the venus monitoring camera on board venus express a spectral analysis suggests that the variation has a periodicity with a period of about 255 days although cloud features are not always passive tracers the periodical variation of the dynamical state is a robust feature superposed on this long term variation of the zonal velocity kelvin wave like disturbances tend to be observed in periods of relatively slow background velocity while rossby wave like disturbances tend to be observed in periods of fast background velocity since the momentum deposition by these waves can accelerate and decelerate the mean flow these waves may contribute to the suggested long term oscillation

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

planetary scale waves and the cyclic nature of cloud top dynamics on venus abstract pioneer venus ocpp ultraviolet images spanning eight years have been analyzed objectively to derive quantitative information on the properties of planetary scale wave modes at the venus cloud tops we infer propagation characteristics for longitudinal wavenumber 1 by fourier analyzing time series of longitudinal mean normalized image brightness the dominant equatorial mode during 1979 80 was the 4 day periodicity associated with zonal motion of the y feature the difference between this and the 4 7 day equatorial rotation period derived from the tracking of small cloud features implies that the y is a propagating wave with a prograde phase speed of about 15 ms 1 relative to the wind simultaneous time series of cloud tracked wind fluctuations also exhibit a 4 day periodicity lending support to the wave interpretation the prograde propagation and equatorial confinement of the wave and the absence of analogous meridional wind fluctuations identify it as a kelvin wave zonal winds peak near the

the fully developed superrotation simulated by a general circulation model of a venus like atmosphere abstract formation and maintenance of the fully developed superrotation in the venus atmosphere are investigated by using a center for climate system research national institute for environmental study ccsr nies venus like atmospheric general circulation model under the condition that zonally uniform solar heating is used the meridional circulation is dominated by a single cell in a whole atmosphere and the superrotation with velocities faster than 100 m s 1 is formed near 60 km altitude the meridional circulation effectively pumps up angular momentum from the lower to the middle atmosphere then the angular momentum is transported by poleward flows of the meridional circulation and a part of the transported momentum is returned back to the low latitudinal regions by waves as a result the simulated superrotation is formed by the gierasch mechanism equatorward angular momentum flux required in the gierasch mechanism is caused by not only barotropic waves but also various waves rossby mixed ross

superrotation of venus atmosphere analyzed with a full general circulation model 1 a general circulation model gcm has been developed for the venus atmosphere from the surface up to 100 km altitude based on the gcm developed for earth at our laboratory key features of this new gcm include topography diurnal cycle dependence of the specific heat on temperature and a consistent radiative transfer module based on net exchange rate matrices this allows a consistent computation of the temperature field in contrast to previous gcms of venus atmosphere that used simplified temperature forcing the circulation is analyzed after 350 venus days 111 earth years superrotation is obtained above roughly 40 km altitude below the zonal wind remains very small compared to observed values which is a major pending question the meridional circulation consists of equator to pole cells the dominant one being located within the cloud layers the modeled temperature structure is globally consistent with observations though discrepancies persist in the stability of the lowest layers and equator pole temperature contrast within the clouds 10 k in the model compared to the observed 40 k in agreement with observational data a convective layer is found between the base of the clouds around 47 km and the middle of the clouds 55 60 km altitude the transport of angular momentum is analyzed and comparison between the reference simulation and a simulation without diurnal cycle illustrates the role played by thermal tides in the equatorial region without diurnal cycle the gierasch rossow williams mechanism controls angular momentum transport the diurnal tides add a significant downward transport of momentum in the equatorial region causing low latitude momentum accumulation

influence of venus topography on the zonal wind and uv albedo at cloud top level the role of stationary gravity waves based on the analysis of uv images at 365 nm of venus cloud top altitude 67 2 km collected with vmc venus monitoring camera on board venus express vex it is found that the zonal wind speed south of the equator from 5 s to 15 s shows a conspicuous variation from 101 to 83 m s with geographic longitude of venus correlated with the underlying relief of aphrodite terra we interpret this pattern as the result of stationary gravity waves produced at ground level by the up lift of air when the horizontal wind encounters a mountain slope these waves can propagate up to the cloud top level break there and transfer their momentum to the zonal flow such upward propagation of gravity waves and influence on the wind speed vertical profile was shown to play an important role in the middle atmosphere of the earth by lindzen 1981 but is not reproduced in the current gcm of venus atmosphere from lmd in the equatorial regions the uv albedo at 365 nm varies also with longitude we argue that this variation may be simply explained by the divergence of the horizontal wind field in the longitude region from 60 to 10 where the horizontal wind speed is increasing in magnitude stretch it triggers air upwelling which brings the uv absorber at cloud top level and decreases the albedo and vice versa when the wind is decreasing in magnitude compression this picture is fully consistent with the classical view of venus meridional circulation with upwelling at equator revealed by horizontal air motions away from equator the longitude effect is only an additional but important modulation of this effect this interpretation is comforted by a recent map of cloud top h2o fedorova et al 2015 showing that near the equator the lower uv albedo longitude region is correlated with increased h2o we argue that h2o enhancement is the sign of upwelling suggesting that the uv absorber is also brought to cloud top by upwelling

atmospheric structure and dynamics as the cause of ultraviolet markings in the clouds of venus details about the atmosphere on venus are gradually emerging from the once apparently impenetrable global cloud cover simultaneous imaging in the ultraviolet and infrared by venus express provides a new view of the ultraviolet patterns seen in the cloud tops the picture that emerges is one of dark low latitudes dominated by convective mixing in the sulphuric acid clouds bringing unknown ultraviolet absorbers up from the lower atmosphere the cloud top morphology revealed in the southern hemisphere by venus express resembles that found earlier by pioneer venus and venera 15 in the north suggesting global symmetry between the two hemispheres when seen in ultraviolet light venus has contrast features that arise from the non uniform distribution of unknown absorbers within the sulphuric acid clouds this paper reports multi wavelength imaging that reveals that the dark low latitudes are dominated by convective mixing that brings the ultraviolet absorbers up from depth the bright and uniform mid latitude clouds reside in the cold collar which suppresses vertical mixing in low and middle latitudes the visible cloud top is located at a constant altitude of 72 1 km in both the ultraviolet dark and bright regions indicating that the brightness variations result from compositional differences caused by the colder environment when seen in ultraviolet light venus has contrast features that arise from the non uniform distribution of unknown absorbers within the sulphuric acid clouds1 2 3 and seem to trace dynamical activity in the middle atmosphere4 it has long been unclear whether the global pattern arises from differences in cloud top altitude which was earlier3 estimated to be 66 72 km compositional variations or temperature contrasts here we report multi wavelength imaging that reveals that the dark low latitudes are dominated by convective mixing which brings the ultraviolet absorbers up from depth the bright and uniform mid latitude clouds reside in the cold collar an annulus of cold air characterized by 30 k lower temperatures with a positive lapse rate which suppresses vertical mixing and cuts off the supply of ultraviolet absorbers from below in low and middle latitudes the visible cloud top is located at a remarkably constant altitude of 72 1 km in both the ultraviolet dark and bright regions indicating that the brightness variations result from compositional differences caused by the colder environment rather than by elevation changes the cloud top descends to 64 km in the eye of the hemispheric vortex which appears as a depression in the upper cloud deck the ultraviolet dark circular streaks enclose the vortex eye and are dynamically connected to it

thermal tides in the atmosphere of venus comparison of model results with observations a linearized primitive equation lpe model is developed to study thermal tides in the atmosphere of venus the lpe model describes diurnal and semidiurnal oscillations of a cyclostrophically balanced atmosphere in which zonal velocity varies with altitude and latitude the numerical algorithm follows staniforth and daley the solar thermal forcing is increased algebraically in time to separate the forced tidal response from free atmospheric oscillations parameters of the basic state and forcing agree with pioneer venus observations results of the model are compared with the solar fixed component of brightness temperature variations measured by taylor et al and elson using data from the pioneer venus orbiter infrared radiometer oir the comparison is made by convolving the computed model radiances with the weighting functions of the oir channels agreement between lpe model results and oir observations is excellent two interesting features of the oir data are accounted for namely the slow variation of phase with altitude and the dominance of the semidiurnal oscillation over the diurnal oscillation success of the lpe model opens the way for calculating tidal transports of heat and momentum and assessing the role of tides in maintaining the venus super rotation

a post new horizons global climate model of pluto including the n 2 ch 4 and co cycles abstract we have built a new 3d global climate model gcm to simulate pluto as observed by new horizons in 2015 all key processes are parametrized on the basis of theoretical equations including atmospheric dynamics and transport turbulence radiative transfer molecular conduction as well as phases changes for n 2 ch 2 and co pluto s climate and ice cycles are found to be very sensitive to model parameters and initial states nevertheless a reference simulation is designed by running a fast reduced version of the gcm with simplified atmospheric transport for 40 000 earth years to initialize the surface ice distribution and sub surface temperatures from which a 28 earth year full gcm simulation is performed assuming a topographic depression in a sputnik planum sp like crater on the anti charon hemisphere a realistic pluto is obtained with most n 2 and co ices accumulated in the crater methane frost covering both hemispheres except for the equatorial regions and a surface pressure near 1 1 pa in 2015 with an increase between 1988 and 2015 as reported from stellar occultations temperature profiles are in qualitative agreement with the observations in particular a cold atmospheric layer is obtained in the lowest kilometers above sputnik planum as observed by new horizons s rex experiment it is shown to result from the combined effect of the topographic depression and n 2 daytime sublimation in the reference simulation with surface n 2 ice exclusively present in sputnik planum the global circulation is only forced by radiative heating gradients and remains relatively weak surface winds are locally induced by topography slopes and by n 2 condensation and sublimation around sputnik planum however the circulation can be more intense depending on the exact distribution of surface n 2 frost this is illustrated in an alternative simulation with n 2 condensing in the south polar regions and n 2 frost covering latitudes between 35 n and 48 n a global condensation flow is then created inducing strong surface winds everywhere a prograde jet in the southern high latitudes and an equatorial superrotation likely forced by barotropic instabilities in the southern jet using realistic parameters the gcm predict atmospheric concentrations of co and ch 4 in good agreement with the observations n 2 and co do not condense in the atmosphere but ch 4 ice clouds can form during daytime at low altitude near the regions covered by n 2 ice assuming that nucleation is efficient enough this global climate model can be used to study many aspects of the pluto environment for instance organic hazes are included in the gcm and analysed in a companion paper bertrand and forget icarus this issue

constraints on mantle plumes on venus implications for volatile history abstract the analysis of venus gravity field and topography suggests the presence of a small number of deep mantle plumes 9 this study predicts the number of plumes formed at the core mantle boundary their characteristics and the production of partial melt from adiabatic decompression numerical simulations are performed using a 3d spherical code that includes large viscosity variations and internal heating this study investigates the effect of several parameters including the core mantle boundary temperature the amount of internal heating and the mantle viscosity the smallest number of plumes is achieved when no internal heating is present however scaling earth s radiogenic heating to venus suggests a value of 16 tw cases with internal heating produce more realistic lid thickness and partial melting but produce either too many plumes or no plumes if a high mantle temperature precludes the formation of a hot thermal boundary layer mantle viscosity must be reduced to at least 10 20 pa s in order to include significant internal heating and still produce hot plumes in all cases that predict melting melting occurs throughout the upper mantle only cases with high core temperature 1700 k produce dry melting over time the upper mantle may have lost significant volatiles depending on the water content of the lower mantle deep plumes may contribute to present day atmospheric water via volcanic outgassing assuming 50 ppm water in mantle 10 plumes with a buoyancy flux of 500 kg s continuously erupting for 4 myr will outgas an amount of water on the order of that in the lower atmosphere a higher level of internal heating than achieved to date as well as relatively low mantle viscosity may be required to achieve simulations with 10 plumes and a thinner lid alternatively if the mantle is heating up due to the stagnant lid the effect is equivalent to having lower rates of internal heating a temperature increase of 110 k byr is equivalent to 13 tw this value along with the internal heating of 3 tw used in this study may represent the approximate heat budget of venus mantle

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

a reanalysis of venus winds at two cloud levels from galileo ssi images abstract the global circulation of the venus atmosphere is characterized at cloud level by a zonal super rotation studied over the years with data from a battery of spacecrafts orbiters balloons and probes among them the galileo spacecraft monitored the venus atmosphere in a flyby in february 1990 in its route toward jupiter since the flyby was almost equatorial published analysis of zonal winds obtained from displacements of cloud elements on images obtained by the ssi camera belton m j s and 20 colleagues 1991 science 253 1531 1536 stop at latitudes 50 north and south in this paper we present new results on venus winds based on a reanalysis of an extended set of images obtained at two wavelengths 418 nm violet and 986 nm near infrared that sense different altitude levels in the upper cloud our main result is that we have been able to extend the zonal wind profile up to the polar latitudes 70 n and 70 s at 418 nm and 70 n at 986 nm binned and smoothed profiles are given in tabular form we show that the zonal winds drop in their velocity poleward of latitudes 45 n and 50 s where an intense meridional wind shear develops at the two cloud levels our data confirm the magnitude of this shear retrieved previously from radio occultation data but disagrees with it in the latitudinal location of the sheared region the new wind data can be used to recalibrate the zonal winds retrieved from the previous measurements of the temperature field and the cyclostrophic balance assumption the meridional profiles of the zonal winds at the two cloud levels are used to assess the vertical wind shear in the upper cloud layer as a function of latitude and locate the most unstable region

zonal winds near venus cloud top level a model study of the interaction between the zonal mean circulation and the semidiurnal tide abstract a primitive equation wave mean flow interaction model designed by j r holton and used originally to study earth s middle atmosphere has been adapted to venus in order to clarify our understanding of the interaction between the semidiurnal tide and the thermally driven mean meridional circulation near the cloud top level with or without the tide the model produces midlatitude jets whose structure is insensitive to vertical shear of the background angular velocity above and below the cloud top level but it is sensitive to background angular velocity at the cloud top level when this background angular velocity is close to that of venus the latitudes and speeds of these jets are similar to the latitudes and speeds of jets at the venus cloud top level as inferred from observed temperatures and the cyclostrophic balance condition in agreement with the hypothesis of fels and lindzen the model tide accelerates the equatorial zonal wind near the cloud top level and decelerates it at higher levels the tidal vertical wavelength maximum amplitude dissipative decay length and zonal flow accelerations are sensitive functions of background angular velocity in agreement with elementary gravity wave theory in the equatorial cloud top region tidal acceleration is comparable in magnitude to the decelerative effects of vertical advection and the model s rayleigh friction damping for sufficiently rapid initial zonal flow near the cloud top level the area weighted global mean cloud top level zonal wind increases with time over a 50 day model run as a result of tidal acceleration agreement between the model tide and the observed tide or the tide determined in the more detailed calculations of pechmann and ingersoll is best when the background angular velocity at the jet level is about 30 larger than that observed

superrotation in a venus general circulation model a superrotating atmosphere with equatorial winds of 35 ms 1 is simulated using a simplified venus general circulation model gcm the equatorial superrotation in the model atmosphere is maintained by barotropic instabilities in the midlatitude jets which transport angular momentum toward the equator the midlatitude jets are maintained by the mean meridional circulation and the momentum transporting waves are qualitatively similar to observed midlatitude waves an equatorial kelvin wave is also present in the atmosphere the gcm is forced by linearized cooling and friction parameterizations with hyperdiffusion and a polar fourier filter to maintain numerical stability atmospheric superrotation is a robust feature of the model and is spontaneously produced without specific tuning a strong meridional circulation develops in the form of a single hadley cell extending from the equator to the pole in both hemispheres and from the surface to 50 km altitude the zonal jets produced by this circulation reach 45 ms 1 at 60 km with peak winds of 35 ms 1 at the equator a warm pole and cold collar are also found in the gcm caused by adiabatic warming in the mean meridional circulation wave frequencies and zonal wind speeds are smaller than in observations by cloud tracking but are consistent with a doppler shifting by wind speeds in the generating region of each wave magnitudes of polar temperature anomalies are smaller than the observed features suggesting dynamical processes alone may not be sufficient to maintain the large observed temperature contrasts at the magnitudes and periods found in this gcm

an approximate analytical method for calculating tides in the atmosphere of venus abstract we describe a semianalytical method for calculating solar tides in an atmosphere whose zonal mean velocity need not be close to solid body rotation but which varies slowly in the vertical direction the scheme is closely related to the asymptotic methods developed earlier by others for use in work on terrestrial equatorial waves and leads to a simple and intuitively appealing formulation of the nonseparable tidal problem as a set of uncoupled ordinary differential equations the manner in which the meridional structure of the mean state affects the vertical and horizontal tidal structure is especially transparent the method has been used recently to explain a number of observed features of the venus semidiurnal tide the sensitivity of these tidal fields to the structure of the zonal mean wind is briefly discussed and the eliasson palm flux divergence calculated

continuous 60 year stable isotopic and earth alkali element records in a modern laminated tufa jaruga river krka croatia implications for climate reconstruction abstract a continuous 60 year record 1938 1998 of stable isotope compositions of carbon and oxygen as well as trace metal mg sr ba concentrations in a laminated calcite crust precipitated in a short artificial tunnel on a non equilibrium groundwater fed karstic river is presented chemical and isotopic records have been compared to hydrometeorological data available for the last 48 years an attempt is made to relate isotopic and geochemical variations in the crust to environmental parameters such as temperature precipitation and changes in vegetation cover as well as to postdepositional recrystallisation of the older crust material isotopic composition of the crust is largely influenced by non equilibrium precipitation which favours the incorporation of isotopically depleted c and o into the carbonate furthermore because of the complicated hydrological situation there is no observable correlation between the stable oxygen isotope composition of water and temperature the result is that the 18 o isotopic thermometers overestimate the measured precipitation temperatures temperatures calculated from mg ca ratios of water and the carbonate match the 18 o palaeotemperatures within 2 4 c in the older part of the crust precipitated before the onset of industrial pollution of the river it was demonstrated that the application of mg palaeothermometry in natural systems where the mg ca ratio of water is influenced not only by temperature but also by other environmental parameters such as precipitation surface runoff groundwater retention time and anthropogenic influences is subject to a large uncertainty up to 10 c

maintenance of strong rotational winds in venus middle atmosphere by thermal tides the cloud level atmosphere of venus takes little more than 4 days to complete one rotation whereas the solid planet below has a 243 day period computer simulations of the circulation of the venus middle atmosphere between 40 and 85 kilometers as driven by solar radiation absorbed in the clouds reproduce i the observed cloud level rotation rate ii strong vertical shears above and below the cloud tops and iii midlatitude jets and strong poleward flow on the day side simulated circulations converge to yield nearly the same zonal winds when initialized with both stronger or weaker rotation rates these results support the hypothesis that the observed cloud top rotation rate is maintained by statistical balance between fluxes of momentum by thermal tides and momentum advection by mean meridional circulation

effects of topography on the spin up of a venus atmospheric model 1 we study how topography affects the spin up from rest of a model of the atmosphere of venus the simulations are performed with the epic model using its isentropic terrain following hybrid vertical coordinate and are forced with the newtonian cooling profile used to achieve superrotation in a venus model with no topography by lee et al 2005 we are able to reproduce their results with our model which was developed independently and uses a different vertical coordinate both groups use a horizontal resolution of 5 which is dictated by the need for reasonable computer runtime and is not a claim of numerical convergence we find that the addition of topography substantially changes both the evolution and end state of the model s spin up the magnitude of the superrotation is diminished from 55 ms 1 to 35 ms 1 and it reaches steady state faster in a few years instead of a few decades a large stationary eddy associated with ishtar terra forms that has a local horizontal temperature anomaly of order 2 k at the 0 7 bar level such a feature may be observable in high resolution infrared images

origin of some conjugate or x fault structures cross cutting faults of the type illustrated by john castagna tle may 1995 are common in normal fault systems and can occur on a range of scales and in a variety of tectonic settings intersecting faults which produce the characteristic x in cross section are generally termed conjugate faults or hourglass structures john s article prompted several letters tle december 1995 explaining how such fault geometries may arise

multispectral surface emissivity from virtis on venus express abstract the surface composition of venus is mostly inaccessible to remote observation due to the dense cloud cover there are five spectral windows that show measurable thermal emission from the surface at night the virtis spectrometer on venus express observed three of these windows over much of the southern hemisphere of venus we use these data along with magellan altimetry to map surface emissivity the data are initially processed to correct for instrumental straylight from the dayside of venus and to improve wavelength registration these corrected data are then inverted to emissivity at 1020 1100 and 1180 nm wavelength using lookup tables created by an atmospheric radiative transfer model as in earlier studies we find residual trends of surface emissivity with respect to the magellan altimetry that is used in the model to determine surface temperature and thickness of the atmosphere a new observation is that these trends vary significantly from region to region indicating some lateral variability of atmospheric parameters most likely near surface atmospheric temperature the trends are consistent over hundreds to thousands of km thus it is possible to correct for them heuristically in two regions studied in this paper there are significant deviations from the background emissivity which are associated with some geologic features the high noise in 1100 and 1180 nm maps derived from virtis data result in large uncertainties of spectral shape the virtis instrument was not designed for this task and future observations could provide high signal to noise ratio maps in at least 5 distinct bands diagnostic of major rock types and minerals

the role of porosity in thermal inertia variations on basaltic lavas abstract thermal inertia is inversely proportional to porosity for hawaiian basalts extreme porosities 80 are required if the observed low thermal inertias on the martian shield volcanoes are the result of pristine lava flow surface properties such volcanic surfaces are anticipated to have a short lifetime in the martian environment and an aeolian origin appears to be the most likely interpretation of the thermal measurements on mars

venus topography and kilometer scale slopes during the first 8 months of the magellan mission the radar altimeter has made some three million measurements of the surface of venus covering the latitude range from 85 n to 80 s methods involving range correlation doppler filtering multi burst summation and range migration are used to focus the observations and to achieve high surface resolution results are presented as maps of the global distribution of topography meter scale roughness and power reflection coefficient the results are similar to those reported in previous experiments surface heights exhibit a unimodal distribution with more than 80 of the surface lying within 1 km of the 6051 84 km mean radius but the higher resolution of the magellan altimeter has disclosed several surprisingly steep features e g the southwest face of the maxwell montes the southern face of the danu montes and the chasmata to the east of thetis regio where average kilometer scale slopes of greater than 30 are not uncommon this conclusion is corroborated by close inspection of synthetic aperture radar imagery

structure of the venus neutral atmosphere as observed by the radio science experiment vera on venus express 1 the european space agency venus express radio science experiment vera obtained 118 radio occultation measurements of the venusian atmosphere between july 2006 and june 2007 southern latitudes are uniformly sampled measurements in the northern hemisphere are concentrated near the pole radial profiles of neutral number density derived from the occultations cover the altitude range 40 90 km which are converted to profiles of temperature t and pressure p versus height h profiles of static stability are found to be latitude dependent and nearly adiabatic in the middle cloud region below the clouds the stability decreases at high latitudes at an altitude of 65 km the vera t p h profiles generally lie between the venus international reference atmosphere vira and vira 2 models the retrieved temperatures at any given pressure level typically are within 5 k of those derived from the pioneer venus orbiter radio occultation experiments a large equator to pole temperature contrast of 30 k is found at the 1 bar 1000 hpa level the vera observations reveal a distinct cold collar region in the southern hemisphere complementing that in the north at the latitudes of the cold collars the tropopause altitude increases relative to higher and lower latitudes by 7 km while the temperature drops roughly 60 k the observations indicate the existence of a wave number 2 structure poleward of 75 latitude at altitudes of 62 km

venus atmospheric circulation known and unknown 1 after a pause of more than two decades venus atmosphere is being explored again since april 2006 european space agency s venus express has been acquiring data exploiting the near infrared windows that allow us to peer into the deep night side atmosphere in june 2007 nasa s messenger mission will fly past venus on its way to mercury collecting useful data for a few weeks instruments and experiments on venus express are expected to provide a more comprehensive set of atmospheric observations over three and perhaps more venus days venus express observations are already providing clues about the processes that maintain the rapid circulation of venus atmosphere the early observations show not only that the global circulation is organized into two hemispheric vortices centered over respective poles but also that the vortex organization extends deep into the atmosphere the limited galileo nims near infrared observations in 1989 had revealed the deep circulation in the equatorial regions but because of the spacecraft flyby trajectory could not observe the high latitudes to elucidate the polar circulation and its organization the long hiatus in systematic venus observations has provided an opportunity to perform some new analysis of the previous pioneer venus observations this paper presents a synopsis of the circulation measurements at high latitudes and an analysis of the solar thermal tides seen in the cloud motions and suggests some limitations of previous estimates of transport of angular momentum by eddies

quantification of middle and lower cloud variability and mesoscale dynamics from venus express virtis observations at 1 74 μm abstract we present an analysis of virtis m ir observations of 1 74 m emission from the nightside of venus the 1 74 m window in the near infrared spectrum of venus is an ideal proxy for investigating the evolution of middle and lower cloud deck opacity of venus because it exhibits good signal to noise due to its brightness good contrast between bright and dark regions and few additional sources of extinction beside the clouds themselves we have analyzed the data from the first 407 orbits equivalent to 407 earth days of the venus express mission to determine the magnitude of variability in the 1 74 m radiance we have also performed an analysis of the evolution of individual features over a span of roughly 5 6 h on two successive orbits of venus express we find that the overall 1 74 m brightness of venus has been increasing through the first 407 days of the mission indicating a gradual diminishing of the cloud coverage and or thickness and that the lower latitudes exhibited more variability and more brightening than higher latitudes we find that individual features evolve with a time scale of about 30 h consistent with our previous analysis analysis of the evolution and motion of the clouds can be used to estimate the mesoscale dynamics within the clouds of venus we find that advection alone cannot explain the observed evolution of the features the measured vorticity and divergence in the vicinity of the features are consistent with evolution under the influence of significant vertical motions likely driven by a radiative dynamical feedback we measure a zonal wind speed of around 65 m s and a meridional wind speed around 2 5 m s by tracking the motion of the central region of the features but we also find that the measured wind speeds depend strongly on the points chosen for the wind speed analysis

zonal superrotation above venus cloud base induced by the semidiurnal tide and the mean meridional circulation abstract we have calculated the equilibrium zonal wind structure resulting from the interaction of the semidiurnal tide and the mean meridional circulation driven by the zonally averaged solar heating above the venus cloud base the results show that the tidal mechanism proposed by fels and lindzen can account for a substantial fraction and possibly all of the increase of the equatorial wind speed above the cloud base above the cloud tops tidal deceleration may be too small to produce the zonal wind decrease with height inferred from thermal data tidal forcing does not explain the superrotation below the clouds and additional eddy sources are needed to account for the zonal wind structure at mid and high latitudes

zonal winds near venus cloud top level an analytic model of the equatorial wind speed abstract it is proposed that the equatorial wind speed near venus cloud top level is maintained by a balance between the pumping effect of the semidiurnal tide and vertical advection by the hadley circulation both integrated across the thermal driving region a consequence of this hypothesis is that the maximum equatorial zonal wind speed is proportional to nh where n is buoyancy frequency and h is a measure of the thickness of the driving region the proportionality constant is a weakly increasing function of the heating rate and a decreasing function of h where is an inverse length characterizing the mean zonal wind shear the equilibrium solution considered is shown to be stable for the class of solutions investigated there is a threshold value of heating rate below which there is no equilibrium satisfying the hypothesized balance but this result depends on the assumption that the shape of the zonal wind profile is invariant with thermal forcing amplitude

a new subgrid scale orographic drag parametrization its formulation and testing a scheme for the representation of subgrid scale orography sso in numerical weather prediction and climate models is presented the new scheme arose in part from a desire to represent nonlinear low level mountain drag effects not currently parametrized an important feature of the scheme is that it deals explicitly with a low level flow which is blocked when the effective height of the subgrid scale orography is sufficiently high in this new scheme it is assumed that for this blocked flow separation occurs at the mountain flanks resulting in a form drag this drag is parametrized on model levels which are intersected by the sso and provides a dynamically based replacement for envelope orography the upper part of the low level flow goes over the orography and generates gravity waves at the model resolutions considered t106 and t213 it is assumed that the length scales characteristic of the sso are sufficiently small for the coriolis force to be neglected the various parameters of the scheme are adjusted using an off line procedure in which the scheme is used to estimate the mountain drag and the momentum profiles above the pyrenees and these estimates are validated with the pyrex data forecasts using t106 and t213 resolutions with this new scheme and with mean orography show that the forecast mountain drag consistently reproduces the drag measured during pyrex whenever the flow component normal to the ridge is large isentropic flow diagnostics further show that the new scheme has a realistic impact on the flow dynamics reinforcing the low level wake observed in mesoscale analyses of the flow with this new scheme and a mean orography the ecmwf model outperformed in forecast skill a version of the model which had an envelope orography and the old gravity wave drag scheme while no longer suffering any disadvantages of envelope orography the proposed low level drag parametrization should also be relevant at model horizontal resolutions much higher than t213

venus upper atmospheric dynamical structure from ground based observations shortly before and after venus inferior conjunction 2009 abstract investigations on the dynamical structure of venus upper atmosphere were carried out by infrared heterodyne doppler wind measurements shortly before and after the venusian inferior conjunction on march 27 2009 the cologne tuneable heterodyne infrared spectrometer this has been installed at the mcmath pierce solar telescope on kitt peak arizona usa to detect non local thermodynamical equilibrium non lte emission lines of co2 at a wavelength of 10 5 m these solar induced emission lines originate at a pressure level of 1 bar corresponding to an altitude level of 110 10 km from the frequency position of the spectral lines we directly derived doppler winds without any additional information the high spatial resolution with a field of view of 1 6 arcsec compared to an apparent diameter of venus of 57 arcsec allowed to collect information at different latitudes of the illuminated planet line of sight wind velocities between 189 11 m s and 41 14 m s were detected along the illuminated evening western limb in march and along the bright morning eastern limb in april single observations at the evening and morning terminator do not show a systematic difference of wind velocities the measured wind is uniform at low and mid latitudes in march a lower mean value of 134 1 m s was found compared to april where we retrieved a value of 141 1 m s poleward of a latitude of 50 we observed a strong decrease in wind speed down to 41 14 m s in addition to the pure line of sight wind velocities we used the observing geometry for additional interpretations regarding a global flow from the subsolar point to the antisolar point ss as flow and a global retrograde superrotational zonal wind rsz the estimations indicate a dominating ss as flow with a maximum wind velocity at the terminator of 138 1 m s at low and mid latitudes no indication of a global rsz component was found corresponding wind values for the latter yield wind velocities in the zonal direction between 20 m s retrograde direction and 20 m s prograde direction at different latitudes an inversion of the wind direction is in disagreement with a global rsz behavior the comprehensive dataset was used to investigate short term wind variabilities and changes up to 58 m s within few days were found we included a detailed comparison of concurrent single position observations with sub millimeter measurements clancy r t sandor b j moriarty schieven g 2012 icarus 217 794 812 suggesting a cross terminator gradient at certain latitudes a detailed interpretation of the observed time dependent behavior by global circulation models including wave activities will be addressed in future work