polar vortices on earth and mars a comparative study of the climatology and variability from reanalyses polar vortices on mars provide case studies to aid understanding of geophysical vortex dynamics and may help to resolve long standing issues regarding polar vortices on earth due to the recent development of the first publicly available martian reanalysis dataset macda for the first time we are able to characterise thoroughly the structure and evolution of the martian polar vortices and hence perform a systematic comparison with the polar vortices on earth the winter atmospheric circulations of the two planets are compared with a specific focus on the structure and evolution of the polar vortices the martian residual meridional overturning circulation is found to be very similar to the stratospheric residual circulation on earth during winter while on earth this residual circulation is very different from the eulerian circulation on mars it is found to be very similar unlike on earth it is found that the martian polar vortices are annular and that the northern hemisphere vortex is far stronger than its southern counterpart while winter hemisphere differences in vortex strength are also reported on earth the contrast is not as large distinctions between the two planets are also apparent in terms of the climatological vertical structure of the vortices in that the martian polar vortices are observed to decrease in size at higher altitudes whereas on earth the opposite is observed finally it is found that the martian vortices are less variable through the winter than on earth especially in terms of the vortex geometry during one particular major regional dust storm on mars martian year 26 an equatorward displacement of the vortex is observed sharing some qualitative characteristics of sudden stratospheric warmings on earth

the simulation of a fair weather marine boundary layer in gate using a three dimensional model a detailed three dimensional model has been used to simulate a cumulus topped tropical oceanic boundary layer a particularly dense set of observational data from surface based and airborne instrumentation collected during one day of the garp atlantic tropical experiment gate has been used enabling comprehensive initial and boundary conditions to be specified this also permits detailed comparisons to be drawn between the model and observations the model is found to reproduce the structure of the observed undisturbed boundary layer quite realistically the clouds developed in the model are similar to those observed in both amount and physical size and the modelled turbulent fluxes in the subcloud layer agree well with observations also the evolution of the modelled boundary layer is similar to that in which the observations were made the model confirms that the major effects of the turbulent mixing are to warm the subcloud layer but to moisten and cool the cloud layer the limited scale of the model 2 km x 2 km x 2 km does however lead to systematic differences between measured and modelled variances the model s turbulent kinetic energy balance for the coupled cloud subcloud layers is presented although reliable measurements are only available in the subcloud layer they confirm that the model s values are qualitatively correct except when very close to the bottom boundary the model s temperature and humidity profiles are strongly affected by mixing occurring across cloud base throughout much of the subcloud layer this is reflected in the shape of the v profile which displays a characteristic minimum midway through the subcloud layer when scaled using cloudbase parameters the resulting profiles are similar to those obtained in more unstable conditions over land

the turbulent kinetic energy budget for shallow cumulus convection turbulence kinetic energy tke budgets derived from large eddy simulations of the cumulus capped boundary layer are analysed using recently developed similarity ideas the budgets for the main part of the cumulus layer and the overlying inversion and the cloud base transition zone are considered separately the terms in the budget can be scaled using the similarity theory developed by grant and brown 1999 below the inversion tke is produced by buoyancy with the transport of tke representing a loss of tke in the inversion layer the transport of tke from the underlying cloud layer is the dominant production term although negatively buoyant downdraughts are present in the upper part of the inversion and contribute to the production of tke the terms in the tke budget in the transition zone between the subcloud and cloud layers scale with mixed layer scales but for the buoyancy production term there is a region in which both mixed layer and cloud layer scalings are valid using the mass flux approximation in conjunction with the scaling results it is shown that it is possible to obtain a parametrization of the cumulus mass flux profile

double and single itczs with and without clouds abstracta major bias in tropical precipitation over the pacific in climate simulations stems from the models tendency to produce two strong distinct intertropical convergence zones itczs too often several mechanisms have been proposed that may contribute to the emergence of two itczs but current theories cannot fully explain the bias this problem is tackled by investigating how the interaction between atmospheric cloud radiative effects acres and the large scale circulation influences the itcz position in an atmospheric general circulation model simulations are performed in an idealized aqua planet setup and the longwave and the shortwave acres are turned off individually or jointly the low level moist static energy mse is shown to be a good predictor of the itcz position therefore a mechanism is proposed that explains the changes in mse and thus itcz position due to acres consistently across simulations the mechanism implies that the itcz moves equatorward if the hadley circulation strengt

a comparison of shear and buoyancy driven planetary boundary layer flows abstract planetary boundary layer pbl flows are known to exhibit fundamental differences depending on the relative combination of wind shear and buoyancy forces these differences are not unexpected in that shear instabilities occur locally while buoyancy force sets up vigorous thermals which result in nonlocal transport of heat and momentum at the same time these two forces can act together to modify the flow field in this study four large eddy simulations less spanning the shear and buoyancy flow regimes were generated two correspond to the extreme cases of shear and buoyancy driven pbls while the other two represent intermediate pbls where both forces are important the extreme cases are used to highlight and quantify the basic differences between shear and convective pbls in 1 flow structures 2 overall statistics and 3 turbulent kinetic energy tke budget distributions results from the two intermediate les cases are used to develop and verify a velocity scaling and a tke budget mode

possible effects of breaking gravity waves on the circulation of the middle atmosphere of mars a simplified quasi geostrophic beta plane dynamical model of the zonal mean flow is used to investigate the possible effects of breaking internal gravity waves on the circulation in the middle atmospheric region 10 100 km altitude of mars the gravity wave parameterization employed is basically the saturation parameterization of lindzen 1981 which has been utilized in several terrestrial modeling studies numerical simulations are performed for a range of plausible values of the gravity wave parameters and for different representations of the mean flow thermal forcing with a focus on the effects of topographically forced stationary gravity waves on the winter hemisphere circulation the results of the model simulations show that breaking gravity waves of intermediate horizontal scales 100 1000 km wavelengths could act to close off the winter westerly circumpolar jet in the 40 80 km altitude region and induce strong high latitude warming at these levels the latter could explain recent thermal measurements indicating that martian winter polar latitudes may be very warm far above radiative equilibrium in this middle atmospheric region deming et al 1986 for the most plausible range of parameter values breaking gravity waves do not induce much warming below 40 km consistent with available data showing that winter high latitudes are normally very cold at lower levels several dust storm cases indicate that breaking gravity waves possibly could act to induce a very large polar warming at relatively low altitudes such as was observed during the 1977 winter solstice dust storm however quite large gravity wave amplitudes and or relatively long horizontal wavelengths are required for such strong low level effects thermal forcing associated with dust heating might be a source for such anomalous gravity wave activity during a global dust storm summer simulations indicate that breaking gravity waves might alter the mean flow at somewhat higher levels than in the winter hemisphere as a consequence of the presence of westerlies in the lower atmosphere this could explain the presence of a warm summer pole in the recent 50 80 km thermal measurements of deming et al several aspects of the results relating to the middle atmospheric circulation and the polar warming phenomenon are discussed the possible importance of breaking gravity waves for constituent transports in the middle atmosphere of mars is also briefly considered

mars atmospheric dynamics as simulated by the nasa ames general circulation model 3 winter quasi stationary eddies a set of simulations with the nasa ames mars general circulation model gcm has been analyzed to define the basic properties and dynamics of quasi stationary eddy circulations in the winter hemisphere these circulations differing substantially from those in low latitudes and the summer hemisphere extend from the surface to the model top at 47 km typically the largest geopotential and wind perturbations are found at the highest model level near the surface the eddies are of largest amplitude in lower latitudes but above 5 10 km the amplitudes are a maximum in middle and high latitudes the vertical structure of the eddies is nearly equivalent barotropic the phase variation in latitude is also relatively small zonal wavenumbers 1 and 2 dominate the stationary circulations with wave 3 being of significance only at low levels below 10 km the quasi stationary eddies differ substantially in northern and southern winters and undergo considerable changes with increasing dustiness in northern winter the southern winter eddy circulation is dominated by zonal wavenumber 1 while the northern eddies have a strong wavenumber 2 component at low levels of dust loading at high dust levels wavenumber 1 becomes dominant this change may be at least partly the result of the dusty zonal mean state becoming more responsive to wave 1 forcing the standing eddies in a gcm simulation for ls 0 exhibit considerable similarity in basic structure and amplitude to those revealed by an recent analysis of viking irtm data banfield et al 1996 though there are differences in the phases of the eddy patterns

sublimation and transport of water from the north residual polar cap on mars several features of the viking mars atmospheric water detection observations have suggested that the residual north polar cap on mars is a major source of atmospheric water during northern summer and that the water it supplies to the atmosphere is transported equatorward to low northern latitudes by summer s end we have explored the role of the north residual cap in the current martian water cycle by constructing models to assess the ability of the cap to supply water to the atmosphere and the ability of the atmosphere to transport it out of the polar regions from our sublimation model we conclude that the residual cap can sublime the 7 1014 g of water that appears in the atmosphere after ls 80 provided surface winds are high 10 m s the cap emissivity is low 0 9 or the exposed soil in polar regions contains ice that is accessible to the atmosphere in our view these requirements seem unlikely and we are drawn to the conclusion that other sources of water exist this conclusion is further supported by the results of two dimensional transport simulations which show that most of the water sublimed from the cap remains at high latitudes the polar circulation simply lacks the intensity and scale to move water very far from the cap a weak circulation places additional constraints on cap sublimation rates since abundant clouds and significant ice deposits would form just equatorward of the cap edge according to the model if the cap is allowed to sublime 7 1014 g of water such predictions are inconsistent with available data we suggest that the nature of the additional source is water desorbing from the nonpolar regolith

numerical simulation of the stratus to cumulus transition in the subtropical marine boundary layer part i boundary layer structure abstract a stratus to cumulus transition sct that resembles observations occurred in lagrangian numerical simulations of the subtropical marine boundary layer over the northeastern pacific ocean southwest of california the lagrangian approach involves translating the domain along the climatological boundary layer trajectory at a rate equal to the observed surface wind speed the sst is increased at a corresponding rate the simulations did not include drizzle the diurnal cycle divergence changes or mesoscale circulations and thus demonstrate that these processes are not essential for an sct a 2d numerical cloud model that can explicitly represent large convective eddies is used turbulence at scales smaller than the large eddies is parameterized using a third moment turbulence closure this type of model requires no cloud regime specific input and is computationally economical for multiday simulations the results suggest that there are four stages in the transition from the stratus topped boundary

estimation of entrainment rate in simple models of convective clouds a method for estimating lateral entrainment rate in clouds is suggested linking its magnitude to buoyant production of vertical kinetic energy within a cloud updraught in single column model studies the formulation captures the high values of entrainment seen in shallow convection and the values an order of magnitude lower in cases of deep convection as suggested by observational studies and large eddy model simulations together with a realistic vertical variation comparison is made with other recent attempts to parametrize entrainment

linear baroclinic instability in the martian atmosphere abstract the linear baroclinic instability of zonal mean flows like those in the wintertime martian atmosphere under both relatively nondusty and highly dusty conditions is examined using a spherical quasi geostrophic model the basic states are idealized but based closely upon mariner 9 and viking observations zonal wavenumbers 3 and 4 are found to be most unstable and phase speeds are 10 20 m s 1 in middle latitudes generally consistent with observations as well as with previous results obtained with simpler models growth rates are not greatly reduced by the rapid martian radiative relaxation though the growth at higher wavenumbers is significantly inhibited by ekman friction even with this dissipation minimum e folding times of 2 days are obtained for a dust storm basic state characterized by enhanced static stability growth rates are substantially decreased but the most unstable wavenumber is essentially not altered this behavior differs from that found in simple models but is consistent wi

winter polar warmings and the meridional transport on mars simulated with a general circulation model abstract winter polar warmings in the middle atmosphere of mars occur due to the adiabatic heating associated with the downward branch of the cross equatorial meridional circulation thus they are the manifestation of the global meridional transport rather than of local radiative effects we report on a series of numerical experiments with a recently developed general circulation model of the martian atmosphere to examine the relative roles of the mechanical and thermal forcing in the meridional transport the experiments were focused on answering the question of whether the martian circulation is consistent with the thermally driven nearly inviscid hadley cell as was pointed out by some previous studies or it is forced mainly by zonally asymmetric eddies it is demonstrated that under realistic conditions in the middle atmosphere the meridional transport is maintained primarily by dissipating large scale planetary waves and solar tides this mechanism is similar to the extratropical pump in the middle atmosphere on earth only in the run with artificially weak zonal disturbances was the circulation reminiscent of thermally induced hadley cells in the experiment with an imposed dust storm the modified atmospheric refraction changes the vertical propagation of the eddies as the result the eliassen palm fluxes convergence increases in high winter latitudes of the middle atmosphere the meridional transport gets stronger and the polar temperature rises additional numerical experiments demonstrated that insufficient model resolution increased numerical dissipation and especially neglect of non lte effects for the 15 m co2 band could weaken the meridional transport and the magnitude of polar warmings in gcms

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

entrainment and detrainment in cumulus clouds abstract vertical redistribution of air and its properties inside convective clouds can be studied by standard thermodynamic analyses paluch and saturation point diagrams if the clouds are nonprecipitating and ice free it is shown from such analysis that the linear patterns often seen in these diagrams can result from continued lateral entrainment the observations are consistent with the hypothesis that buoyancy sorting is an important factor in determining cloud composition this yields a simple graphical means for estimating the thermodynamic properties of in cloud air at any pressure field observations of detrained fluxes near cumulus clouds reveal the existence of rather thin detrainment layers which can occur anywhere over the cloud layer these observations are shown to be consistent with the conclusion of bretherton and smolarkiewicz that detrainment is governed by vertical gradients of cloud buoyancy this allows prediction of detrainment regions from cloud base temperature and pressure an

racoro continental boundary layer cloud investigations 3 separation of parameterization biases in single column model cam5 simulations of shallow cumulus climatically important low level clouds are commonly misrepresented in climate models the fast physics system testbed and research faster project has constructed case studies from the atmospheric radiation measurement climate research facility s southern great plain site during the racoro aircraft campaign to facilitate research on model representation of boundary layer clouds this paper focuses on using the single column community atmosphere model version 5 scam5 simulations of a multi day continental shallow cumulus case to identify specific parameterization causes of low cloud biases consistent model biases among the simulations driven by a set of alternative forcings suggest that uncertainty in the forcing plays only a relatively minor role in depth analysis reveals that the model s shallow cumulus convection scheme tends to significantly under produce clouds during the times when shallow cumuli exist in the observations while the deep convective and stratiform cloud schemes significantly over produce low level clouds throughout the day the links between model biases and the underlying assumptions of the shallow cumulus scheme are further diagnosed with the aid of large eddy simulations and aircraft measurements and by suppressing the triggering of the deep convection scheme it is found that the weak boundary layer turbulence simulated is directly responsible for the weak cumulus activity and the simulated boundary layer stratiform clouds increased vertical and temporal resolutions are shown to lead to stronger boundary layer turbulence and reduction of low cloud biases

mixing mechanisms in cumulus congestus clouds part ii numerical simulations abstract the entrainment mechanisms of deep convective clouds in south africa are simulated by using both axially and slab symmetric cumulus models having very high spatial and temporal resolutions the simulated clouds on three different days show a structured organization with small scale features such as in cloud downdrafts the mixing processes are examined by analyzing the time variation of dynamic and thermodynamic quantities along computed parcel trajectories the calculations indicate that most of the entrainment occurs at the cloud top evaporative cooling and perturbation pressure cause downdrafts that transport highly diluted air from the cloud top down to lower levels the penetrative downdrafts are mainly located near the edges of the cloud in the presence of wind shear the downshear portion of the clouds becomes cooler and more diluted and it is associated with stronger downdrafts compared to the upshear side the asymmetric organization is attributed to turbulent exchange of horizontal mo

observations of wind shear over the southern ocean 1 the thermodynamic structure of the lower troposphere over the southern ocean is analyzed by employing over 16 years of high resolution upper air soundings from macquarie island 54 62 s 158 85 e the soundings are analyzed to develop an understanding of the structure of the boundary layer and wind shear occurring through the lower levels over this region and to compare this to european centre for medium range weather forecasts ecmwf model level reanalysis data for the year of tropical convection yotc a multiple layered structure is commonly observed in the high resolution soundings and is also observed in yotc but with a lower frequency the climatological mean and variability of a number of variables are calculated for both data sets which reveals that yotc performs well but has weaknesses in modeling the observed moisture and wind fields particularly evident in wind shear profiles a distinction between a number of boundary layer types is made and the frequency with which they occur is quantified for both data sets this highlights important differences between the observations in the macquarie island soundings and the reanalysis product proxy cloud fields are constructed for the two data sets and these suggest that clouds are commonly observed in a region between the top of the boundary layer and a secondary temperature inversion i e a buffer layer in the words of russell et al 1998 the peak relative frequency of observing these clouds lies roughly around 912 5 hpa for both data sets an examination of the wind shear across the cloud boundaries finds wind shear over cloud base occurs more frequently than cloud top suggesting that the cloud fields are not embedded in a well mixed boundary layer

wind turning across the marine atmospheric boundary layer the directional wind turning across the boundary layer in short range forecasts made as part of the recent era 40 reanalysis project is compared with radiosonde data from oceanic stations in the north atlantic significant errors are identified particularly in cases of warm advection in which it is found that the observed wind turning is systematically underestimated similar problems are found in the higher resolution operational forecasts and also in forecasts made with the independent met office model furthermore comparisons of forecast wind direction with scatterometer data give consistent results over the north atlantic and indicate that the same problems are present over other oceans a large fraction of the cases with the largest errors are shown to have stable boundary layers in these cases the modelled boundary layers are typically too deep and sensitivity tests have shown that more realistic structures are obtained by switching to a stable boundary layer parametrization based on monin obukhov similarity some possible problems with the convective boundary layer parametrization in highly baroclinic conditions are also identified copyright 2005 royal meteorological society

tropical intraseasonal variability in version 3 of the gfdl atmosphere model abstracttropical intraseasonal variability is examined in version 3 of the geophysical fluid dynamics laboratory atmosphere model am3 in contrast to its predecessor am2 am3 uses a new treatment of deep and shallow cumulus convection and mesoscale clouds the am3 cumulus parameterization is a mass flux based scheme but also unlike that in am2 incorporates subgrid scale vertical velocities these play a key role in cumulus microphysical processes the am3 convection scheme allows multiphase water substance produced in deep cumuli to be transported directly into mesoscale clouds which strongly influence large scale moisture and radiation fields the authors examine four am3 simulations using a control model and three versions with different modifications to the deep convection scheme in the control am3 using a convective closure based on cape relaxation both mjo and kelvin waves are weak relative to those in observations by modifying the convective closure and trigger assumptions to inhibit deep c

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

aircraft observations of the ekman layer during the joint air sea interaction experiment results are presented from an observational study of the mid latitude atmospheric boundary layer over the sea the data were obtained mainly by instrumented aircraft as part of the joint air sea interaction experiment jasin the eight occasions chosen for study are characterized by small surface buoyancy fluxes and the conditions are well described as near neutral and barotropic in the absence of low level inversions a well mixed ekman layer is observed on each occasion but is limited to a depth of approximately 0 2u f accurate measurements of horizontal gradients including pressure together with improved wind observations and turbulent flux measurements enabled each of the terms of the momentum balance to be evaluated throughout the depth of this layer these terms were found to balance quite closely were well described by ekman scaling and were consistent with the requirements of the measured turbulent kinetic energy balance the latter suggests that the main shear production terms are dissipated locally and that little is exported to upper levels in the ekman layer to enable significant deepening by entrainment although only a slight increase in instability appears to be needed to alter this balance conditions in which such boundary layer structure might be observed are suggested values of various coefficients used in schemes for relating surface fluxes to mean quantities cd ce cg a b are derived and compared with previous measurements spectral analysis reveals that most of the turbulent transport is confined to a distinct high wavenumber region whose characteristics vary as a function of ekman layer depth and stability parameters this is superimposed on larger scale fluctuations which do not vary appreciably within the ekman layer and which therefore dominate the variances in the upper regions as the intensity of the smaller scale turbulence decreases strongly with height finally further implications of this interpretation are discussed with particular reference to the heat and water vapour balance these imply that removal of water vapour from the ekman layer is accomplished by transfer related to cloud activity marking a significant change in the mechanism of turbulent transport at the top of this layer the relationship between these and similar results obtained concurrently by different methods is also discussed

numerical simulations and a conceptual model of the stratocumulus to trade cumulus transition abstract a two dimensional eddy resolving model is used to study the transition from the stratocumulus topped boundary layer to the trade cumulus boundary layer the 10 day simulations use an idealized lagrangian trajectory representative of summertime climatological conditions in the subtropical northeastern pacific the sea surface temperature is increased steadily at 1 5 k day 1 reflecting the southwestward advection of the subtropical marine boundary layer by the trade winds while the free tropospheric temperature remains unchanged results from simulations with both a fixed diurnally averaged shortwave radiative forcing and a diurnally varying shortwave forcing are presented a two stage model for the boundary layer evolution consistent with these simulations is proposed in the first stage decoupling is induced by increased latent heat fluxes in the deepening boundary layer after decoupling cloud cover remains high but the cloudiness regime changes from a single stratocumulus layer to sporadic

atmospheric tidal forcing of the zonal mean circulation the martian dusty atmosphere abstract classical atmospheric tidal theory has been used to compute the bilinear tidal zonal mean forcing per unit mass of the zonal mean meridional and zonal winds together with the tidal zonal mean heating per unit mass for the dusty martian atmosphere the convergences of the tidal eliassen palm ep flux have been computed for both clear and dusty atmospheric conditions including the special case of a dusty corridor in the summer southern subtropics that is meant to simulate the early stages of a planetary scale martian dust storm the calculation of the tidal ep zonal forcing differs from hamilton in that more realistic thermotidal forcings and basic state temperatures are used the zonal mean convergences of the tidal fluxes of heat and momentum are large during a martian great dust storm and should alter significantly the zonal mean circulation and its residual component driven by the zonal mean heating in particular the tidal forcing of the meridional wind which is an order of magnitude gr

a moist pbl parameterization for large scale models and its application to subtropical cloud topped marine boundary layers abstract a new general purpose boundary layer parameterization that permits realistic treatment of stratocumulus capped boundary layers scbls with coarse vertical resolution is described it combines a 1 5 order turbulent closure model with an entrainment closure at the boundary layer top three different implementations of the entrainment closure in which the boundary layer height is respectively prognosed reconstructed from thermodynamic values at the grid points or restricted to lie on a flux level of the host model grid are tested in a single column modeling framework at both fine and coarse vertical resolution the first two approaches permit a stratocumulus top and base to lie between grid levels and evolve continuously with time but are more complicated to implement in a three dimensional model the model performs very well in cases of dry convection whatever the inversion implementation and the vertical resolution with 15 mb or better vertical resolution all approaches properly simulate

a modeling case study of mixed phase clouds over the southern ocean and tasmania abstract the cloud structure associated with two frontal passages over the southern ocean and tasmania is investigated the first event during august 2006 is characterized by large quantities of supercooled liquid water and little ice the second case during october 2007 is more mixed phase the weather research and forecasting model wrfv2 2 1 is evaluated using remote sensed and in situ observations within the post frontal air mass the thompson microphysics module is used to describe in cloud processes where ice is initiated using the cooper parameterization at temperatures lower than 8 c or at ice supersaturations greater than 8 the evaluated cases are then used to numerically investigate the prevalence of supercooled and mixed phase clouds over tasmania and the ocean to the west the simulations produce marine stratocumulus like clouds with maximum heights of between 3 and 5 km these are capped by weak temperature and strong moisture inversions when the inversion is at temperatures warmer

subsiding shells around shallow cumulus clouds abstract in this study large eddy simulations les are used to gain more knowledge on the shell of subsiding air that is frequently observed around cumulus clouds first a detailed comparison between observational and numerical results is presented to better validate les as a tool for studies of microscale phenomena it is found that horizontal cloud profiles of vertical velocity humidity and temperature are in good agreement with observations they show features similar to the observations including the presence of the shell of descending air around the cloud second the availability of the complete 3d dataset in les has been exploited to examine the role of lateral mixing in the exchange of cloud and environmental air the origin of the subsiding shell is examined by analyzing the individual terms of the vertical momentum equation buoyancy is found to be the driving force for this shell and it is counteracted by the pressure gradient force this shows that evaporative cooling at the cloud edge

numerical simulations of interactions between gravity waves and deep moist convection abstract this study uses a numerical model to simulate deep convection both in the tropics over the ocean and the midlatitudes over land the vertical grid that was used extends into the stratosphere allowing for the simultaneous examination of the convection and the vertically propagating gravity waves that it generates a large number of trajectories are used to evaluate the behavior of tracers in the troposphere and it is found that the tracers can be segregated into different types based upon their position in a diagram of normalized vertical velocity versus displacement conditional sampling is also used to identify updrafts in the troposphere and calculate their contribution to the kinetic energy budget of the troposphere in addition fourier analysis is used to characterize the waves in the stratosphere it was found that the waves simulated in this study have similarities to those observed and simulated by other researchers finally this study examines the wave energy flux as a means to provid

marine atmospheric boundary layer height over the eastern pacific data analysis and model evaluation the atmospheric boundary layer abl height h is a crucial parameter for the treatment of the abl in weather and climate models about 1000 soundings from 11 cruises between 1995 and 2001 over the eastern pacific have been analyzed to document the large meridional zonal seasonal and interannual variations of h in particular its latitudinal distribution in august has three minima near the equator in the intertropical convergence zone itcz and over the subtropical stratus stratocumulus region near the west coast of california and mexico the seasonal peak of h in the itcz zone between 5 68 and 11 28n occurs in the spring february or april while it occurs in august between the equator and 5 68n comparison of these data with the 10 yr monthly output of the community climate system model ccsm2 reveals that overall the model underestimates h particularly north of 208n in august and september directly applying the radiosonde data to the ccsm2 formulation for computing h shows that at the original vertical resolution with the lowest five layers below 2 1 km the ccsm2 formulation would significantly underestimate h in particular the correlation coefficient between the computed and observed h values is only 0 06 for cloudy cases if the model resolution were doubled below 2 1 km however the performance of the model formulation would be significantly improved with a correlation coefficient of 0 78 for cloudy cases

parametrization of momentum transport by convection ii tests in single column and general circulation models diagnostics derived from cloud resolving model simulations in part i of this study relating to the vertical transport of horizontal momentum by convection are used to develop a parametrization of convective momentum transports for deep convection based upon the mass flux convection scheme discussed by gregory and rowntree the importance of cloud pressure gradients to the flow within the cloud is emphasised and a simple method of representing their effect is suggested the scheme is able to reproduce the fluxes derived from the cloud resolving model studies where cloud organization by the flow is unimportant inclusion of the parametrization in a version of the meteorological office unified model demonstrates that convective momentum transports play a large role in the momentum balance of the atmosphere generally simulation of the mean atmospheric circulation by the unified model is improved by the inclusion of such transports

dynamical modeling of a planetary wave mechanism for a martian polar warming abstract a dynamical mechanism for the martian atmospheric polar warming observed by the viking irtm during the 1977 winter solstice dust storm and a similar one possibly observed by mariner 9 in 1971 is proposed and investigated using a simplified nonlinear model the model is of a type previously used to successfully simulate the essential aspects of terrestrial sudden stratospheric warmings the dynamical mechanism is in part very similar fundamentally to that responsible for these warmings involving planetary scale waves a number of numerical experiments have been conducted to assess the basic viability of such a mechanism for the martian polar warming and to examine its sensitivity to several factors these experiments demonstrate that a planetary wave mechanism can produce a polar warming with the magnitude and suddenness of that observed a planetary wave mechanism must primarily involve wavenumber 1 as wavenumber 2 is too strongly vertically trapped to produce a warming like that observed the necessary wave forcing in the present model can be topographic mechanical or thermal and nonstationary and is relatively large but certainly plausible the strong radiative damping in the mars atmosphere acts to substantially inhibit a warming through its effects on both the zonal flow and the wave dissipation plays a greater role relative to transience in a model martian warming of the type studied here than in a sudden stratospheric warming increasing radiative damping during a warming due to higher temperatures and greater dust loading may play a role in yielding a relatively rapid cooling phase for the mars warming event the residual mean meridional circulation during a model warming entails strong poleward and downward flow into high northern latitudes throughout a very deep region this probably indicates similar transport of atmospheric dust as well as water such transports are of considerable potential significance for both the dust and water cycles on mars

a new parameterization for shallow cumulus convection and its application to marine subtropical cloud topped boundary layers part i description and 1d results abstract a new parameterization of shallow cumulus convection is presented the parameterization consists of a mass flux scheme based on a buoyancy sorting entrainment detrainment plume model the mass flux scheme is coupled to a 1 5 order turbulence closure model with an entrainment closure for convective boundary layers model performance is verified using single column model simulations at relatively high vertical resolution of pure trade cumulus convection and a cumulus to stratocumulus transition mixing rates cloud cover and vertical flux profiles as deduced from previously published large eddy simulation studies are well reproduced by the parameterization the model is used to demonstrate that height variations of lateral mixing rates can be successfully captured by a simple implementation of a buoyancy sorting mechanism in the updraft cloud model a companion paper describes the implementation of the scheme in a mesoscale model

planetary scale wave structure in the martian atmosphere abstract wave like perturbations are found in the mariner 9 iris atmospheric temperature data during late northern hemisphere winter in a latitude band between 45 n and 65 n the nature of the data base prevents a unique separation of spatial and temporal behavior but fourier analysis of the data constrains the waves to discrete combinations of planetary wavenumber and period one major spectral component possesses a meridional amplitude cross section with a maximum near the 1 mbar level at 60 n and is strongly correlated with the circumpolar jet observed in thermal winds calculated from the mean meridional temperature cross section this feature is consistent with the low wavenumber baroclinic waves observed in viking lander data and the vertical structure reflects the behavior anticipated for a vertically penetrating quasi geostrophic disturbance other possible origins for the wave cannotbe ruled out however among these is a stationary wave forced by wavenumber 2 topographic relief

characteristics of the marine boundary layers during two lagrangian measurement periods 2 turbulence structure characteristics of turbulence mixing in remote marine boundary layers are analyzed using aircraft measurements from six flights during the two intensive lagrangian measurement periods of ace1 the southern hemisphere aerosol characterization experiment the six cases studied here represent a variety of boundary layer conditions in the region south of tasmania australia our study indicated that 1 lagrangian a la had stronger turbulence mixing and entrainment compared to lagrangian b lb due to greater shear generation of turbulence kinetic energy tke 2 strong mesoscale variation in boundary layer turbulence and thus turbulence mixing existed in the ace1 region during lb due to variations in sea surface temperature sst 3 stable thermal stratification in the boundary layer was found during the last flight of each lagrangian consequently tke decreased rapidly with height resulting in small or near zero entrainment rate in spite of strong shear forcing at the surface and in the boundary layer and 4 the buffer layer which lies above the boundary layer and below the main inversion had weak and intermittent turbulence mostly associated with cloud bands and cumulus evidence of entrainment was found in the buffer layer however it is difficult to quantify by flux measurements due to the weak and intermittent nature of the turbulence field

a new parameterization for shallow cumulus convection and its application to marine subtropical cloud topped boundary layers part ii regional simulations of marine boundary layer clouds abstract the impact of physical parameterizations on simulations of cloud topped marine boundary layers is investigated using the fifth generation pennsylvania state university ncar mesoscale model mm5 three month mm5 simulations of the northeast and southeast pacific during june august 1987 are boundary forced with time varying ecmwf analyses runs with four planetary boundary layer pbl parameterizations already implemented in mm5 are compared with runs using new parameterizations of boundary layer turbulence and shallow cumulus convection shcu described in a companion paper numerous modifications to the mm5 that allow it to be used as a regional climate model are described the simulated 3 month mean shortwave cloud radiative forcing swcf and vertical structure of cloud topped boundary layers in the northeast pacific are sensitive to the pbl shallow convection schemes all four current mm5 pbl schemes the blackadar medium range forecast mrf burk thompson and gayno seaman schemes produc

modeling entrainment and finescale mixing in cumulus clouds abstract a model used to study entrainment and mixing of thermodynamic properties in the stratus topped boundary layer has been extended to represent these processes in cumulus clouds the new model called the explicit mixing parcel model empm depicts finescale internal structure of a rising thermal in a cumulus cloud using a 1d domain the empm links the conventional parcel model which has no internal structure and multidimensional cloud models which resolve cloud scale structure produced by large eddies in the empm the internal structure evolves as a consequence of a sequence of discrete entrainment events and an explicit representation of turbulent mixing based on kerstein s linear eddy model in this version of the empm subgrid scale eddy diffusion is found to be adequate for representing the effects of the smallest turbulent eddies in addition a simple parameterization is used to determine the local condensation or evaporation rates if the grid size is reduced so that the kolmogorov

patterns of tropical pacific convection anomalies and associated extratropical wave trains in amip5 in this paper the performance of 18 coupled model intercomparison project phase 5 cmip5 models forced by observational ssts in simulating the tropical pacific convective variation and the atmospheric responses in the extratropics are assessed the multi model ensemble mean results of 18 cmip5 models show that five major patterns of tropical pacific convection anomaly in winter can indeed be well reproduced however the simulation of the corresponding extratropical responses for each pattern exists some deficiency except for the la nina pattern compared with observations we defined an optimized subset of well performing models access1 0 canam4 ccsm4 cmcc cm hadgem2 a mpi esm mr in tropical pacific deep convection according to the ranking of model skill score these models exhibit approximately identical convection anomaly patterns in both amplitude and spatial structure to the observation which potentially might improve the representation of extratropical teleconnections with the tropical pacific especially for the cp el nino cpen ep el nino epen and western cp w cp patterns both evident atmospheric anomalies of cpen and epen patterns over the na e sector and the northeastward propagating wave trains of w cp pattern can be quite well simulated in the high skilled models

characteristics of the marine atmospheric boundary layer over the southern ocean in response to the synoptic forcing the characteristics of the marine atmospheric boundary layer mabl in relation to synoptic meteorology over the southern ocean are examined using upper air soundings and surface precipitation at macquarie island 54 62 s 158 85 e with a primary focus on the post cold frontal environment where large cloud and radiative biases are presented in a multitude of climate models thermodynamic profiles from the european centre for medium range weather forecasts era interim reanalyses are compared with the observations to evaluate their representation of the mabl characteristics observations confirm that boundary layer clouds over the southern ocean commonly reside within a shallow mabl under the influence of frequent midlatitude cyclones and fronts the evaluation of mabl height shows that for both observations and reanalysis the inversion is higher northward of the low center and under postcold front conditions under cold frontal passages however the main inversions are not well represented by era interim which is featured by an underestimate of the mabl height by 22 significant differences are found in the moisture profiles within the mabl between the observations and era interim soundings within the context of cold frontal passages the moisture in the era interim is found to be too confined to the surface layer which is consistent with the shallower mabl represented by the era interim analysis of the surface precipitation shows that era interim overestimates the amount of precipitation over macquarie island in the vicinity of cyclone cores but underestimates the precipitation not immediately associated with cold fronts leading to an overall underestimate of the annual precipitation by 11

a comprehensive mass flux scheme for cumulus parameterization in large scale models abstract observational studies indicate that a mass flux approach may provide a realistic framework for cumulus parameterization in large scale models but this approach through the introduction of a spectral cloud ensemble leads normally to rather complex schemes in this paper the question is addressed whether much simpler schemes can already provide realistic values of the thermal forcing by convection under various synoptic conditions this is done through verifying such a scheme first on data from field experiments for periods of tropical penetrative convection gate marshall islands tradewind cumuli atex bomex and extratropical organized convection sesame 79 and then in a nwp model the scheme considers a population of clouds where the cloud ensemble is described by a one dimensional bulk model as earlier applied by yanai et al in a diagnostic study of tropical convection cumulus scale downdrafts are included various types of convection are represented i e penetrative convection in c

radio science investigations with mars observer mars observer radio science investigations focus on two major areas of study the gravity field and the atmosphere of mars measurement accuracies expressed as an equivalent spacecraft velocity are expected to be of the order of 100 m s for both types of investigations from use of an improved radio transponder for two way spacecraft tracking and a highly stable on board oscillator for atmospheric occultation measurements planned gravity investigations include a combination of classical and modern elements a spherical harmonic or equivalent field model of degree and order in the range 30 50 will be obtained while interpretation will be in terms of internal stress and density models for the planet using the topography to be obtained from the mars observer laser altimeter atmospheric investigations will emphasize precision measurement of the thermal structure and dynamics in the polar regions which are regularly accessible as a result of the highly inclined orbit studies based on the measurements will include polar processes cycling of the atmosphere between the poles traveling baroclinic disturbances small scale waves and turbulence the planetary boundary layer and possibly the variability and altitude of the ionosphere as the radio occultation is insensitive to dust in the atmosphere per se and measures only the resulting change in thermal structure it is expected that the radio technique can contribute to understanding of dust storm phenomena mutual observations of the atmosphere by means of radio occultation and by the pressure modulator infrared radiometer and the thermal emission spectrometer are expected to strengthen the reliability and accuracy of all three investigations