orbital forcing of the martian polar layered deposits since the first images of polar regions on mars revealed alternating bright and dark layers there has been speculation that their formation might be tied to the planet s orbital climate forcing1 2 3 4 but uncertainties in the deposition timescale exceed two orders of magnitude estimates based on assumptions of dust deposition ice formation and sublimation and their variations with orbital forcing suggest a deposition rate of 10 3 to 10 2 cm yr 1 refs 5 6 whereas estimates based on cratering rate result in values as high as 0 1 to 0 2 cm yr 1 ref 7 here we use a combination of high resolution images of the polar layered terrains8 high resolution topography9 and revised calculations of the orbital and rotational parameters of mars to show that a correlation exists between ice layer radiance as a function of depth obtained from photometric data of the images of the layered terrains and the insolation variations in summer at the martian north pole similar to what has been shown for palaeoclimate studies of the earth10 11 12 for the best fit between the radiance profile and the simulated insolation parameters we obtain an average deposition rate of 0 05 cm yr 1 for the top 250 m of deposits on the ice cap of the north pole of mars

quasi periodic climate changes on mars a review abstract we critically review our present understanding of the impact of quasi periodic variations in axial obliquity and direction and orbital eccentricity on the climate of mars and the relationship between these climatic changes and the occurrence of polar layered terrain emphasis is placed on the behavior of the seasonal cycles of dust water and carbon dioxide at the present epoch as constrained by ground based and spacecraft observations and the modification of these cycles by the astronomical variations we also consider the relationship between these modifications and the formation of layered terrain and discuss critical measurements and calculations that can help to resolve some of the present uncentainties the present seasonal cycle of water is controlled by regolith adsorption and desorption sublimation and condensation onto the permanent polar caps and atmospheric transport an enhanced meridional transport at times of global dust storms may be responsible for the occurence of a more extensive permanent cap and a larger annual average water vapor abundance in the northern hemisphere than in the southern hemisphere on the longer time scales of the astronomical variations 105 106 years exchange of water between the atmosphere and high latitude subsurface permafrost may also play an important role in the water cycle in addition to the factors mentioned above the current seasonal cycle of carbon dioxide is dominated by exchange between the atmosphere and seasonal carbon dioxide ice deposits on longer time scales adsorption and desorption of the subpolar regolith may help to modulate the atmospheric pressure a key point of uncertainty is the depth of the regolith and its possible blockage by water permafrost and therefore its ability to cause large changes in atmospheric pressure also it is unclear whether the perennial south cap always retains a co2 cover at the present epoch although there is a limited amount of evidence that it is sometimes absent injection of dust into the atmosphere occurs throughout the martian year but it is greatest at times close to orbital perihelion and summer solstice in the southern hemisphere the dust cycle influences the h2o and co2 cycles most strongly by contributing dust particles to the polar ice deposits which significantly lower their albedo and therefore impact their stability key areas of uncertainty include the fraction of airborne dust deposited in the polar regions where the laminae beside and the physical processes responsible for the growth and especially the decay of global dust storms at times of low obliquity permanent co2 caps form the atmospheric pressure drops sharply dust storm activity is severely curtailed or eliminated and water is deposited onto the permanent caps at the expense of the regolith and permafrost reservoirs during periods of high obliquity no perennial co2 polar caps occur water is pumped out of the polar regions and dust loading increases over its present value if the regolith is capable of significantly elevating the atmospheric pressure eccentricity variations and axial precession are particularly effective in modulating the climate at times of intermediate axial obliquity for conditions of low eccentricity and intermediate axial obliquity hemispherical asymmetries tend to be eliminated dust loading decreases somewhat and more water is sublimated from both polar caps than fro the north cap for the present epoch the layered nature of the polar laminae are due to a depth dependent susceptibility to erosion which in turn is due to astronomically induced modulations in the amounts and relative proportions of airborne dust and water ice deposited in the polar regions key questions include the proportion of dust and water ice in the laminae and its variation within individual layers the relative importance of older laminae and lower latitude material as sources of new laminae and the factors responsible for the great youth of the laminated terrain e g do troughs within the laminae propagate laterally thus burying craters

postscript summary of the coventry groundwater investigation and implications for the future abstract the broader implications of the coventry groundwater investigation are discussed in this postscript the complex interbedded sandstone and mudstone sequence under coventry is seriously polluted by chlorinated hydrocarbon solvents investigations in such terrain will require much greater expenditure than was available for this project if they are to describe the distribution and movement of pollutants in enough detail to evaluate quantitatively options for aquifer clean up it is not realistic to consider clean up of coventry s groundwater at the present time because of the lack of detailed knowledge it is probable at least for the present that clean up is not feasible because of hydrogeological constraints arising from the extreme variability of permeability in the system and an absence of operational techniques for clean up stronger more pro active protection of groundwater is needed a major recommendation for future investigations is a procedure to avoid open boreholes which can allow pollution to penetrate deeper into the aquifer and may confuse the results of sampling

martian north polar cap summer water cycle abstract a key outstanding question in martian science is are the polar caps gaining or losing mass and what are the implications for past current and future climate to address this question we use observations from the compact reconnaissance imaging spectrometer for mars crism of the north polar cap during late summer for multiple martian years to monitor the summertime water cycle in order to place quantitative limits on the amount of water ice deposited and sublimed in late summer we establish here for the first time the summer cycle of water ice absorption band signatures on the north polar cap we show that in a key region in the interior of the north polar cap the absorption band depths grow until l s 120 when they begin to shrink until they are obscured at the end of summer by the north polar hood this behavior is transferable over the entire north polar cap where in late summer regions flip from being net sublimating into net condensation mode this transition or mode flip happens earlier for regions closer to the pole and later for regions close to the periphery of the cap the observations and calculations presented herein estimate that on average a water ice layer 70 microns thick is deposited during the l s 135 164 period this is far larger than the results of deposition on the south pole during summer where an average layer 0 6 6 microns deep has been estimated by brown et al 2014 earth planet sci lett 406 102 109

interannual observations and quantification of summertime h2o ice deposition on the martian co2 ice south polar cap abstract the spectral signature of water ice was observed on martian south polar cap in 2004 by the observatoire pour l mineralogie l eau les glaces et l activite omega bibring et al 2004 three years later the omega instrument was used to discover water ice deposited during southern summer on the polar cap langevin et al 2007 however temporal and spatial variations of these water ice signatures have remained unexplored and the origins of these water deposits remains an important scientific question to investigate this question we have used observations from the compact reconnaissance imaging spectrometer for mars crism instrument on the mars reconnaissance orbiter mro spacecraft of the southern cap during austral summer over four martian years to search for variations in the amount of water ice we report below that for each year we have observed the cap the magnitude of the h2o ice signature on the southern cap has risen steadily throughout summer particularly on the west end of the cap the spatial extent of deposition is in disagreement with the current best simulations of deposition of water ice on the south polar cap montmessin et al 2007 this increase in water ice signatures is most likely caused by deposition of atmospheric h2o ice and a set of unusual conditions makes the quantification of this transport flux using crism close to ideal we calculate a minimum apparent amount of deposition corresponding to a thin h2o ice layer of 0 2 mm with 70 porosity this amount of h2o ice deposition is 0 6 6 of the total martian atmospheric water budget we compare our minimum apparent quantification with previous estimates this deposition process may also have implications for the formation and stability of the southern co2 ice cap and therefore play a significant role in the climate budget of modern day mars

chaotic obliquity and the nature of the martian climate recent calculations of the martian obliquity suggest that it varies chaotically on timescales longer than about 107 years and varies between about 0 and 60 we examine the seasonal water behavior at obliquities between 40 and 60 up to several tens of centimeters of water may sublime from the polar caps each year and possibly move to the equator where it is more stable co2 frost and co2 h2o clathrate hydrate are stable in the polar deposits below a few tens of meters depth so that the polar cap could contain a significant co2 reservoir if co2 is present it could be left over from the early history of mars also it could be released into the atmosphere during periods of high obliquity causing occasional periods of more clement climate

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

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

zonally symmetric response to atmospheric tidal forcing in the dusty martian atmosphere abstract we have computed a steady state zonally symmetric response of an atmospheric circulation to the combined efffects of the very large zonal mean diabatic heating and thermotidal forcing thought to exist in the dusty martian atmosphere during one of its episodic global dust storms the zonal mean components of the tidal flux convergences of momentum and heat are computed using an existing classical atmospheric tidal model constrained by the surface pressure observations at the two viking lander sites on mars the zonally symmetric response to the computed tidal flux convergences and to the zonal mean heating of the airborne dust is then computed by a nearly inviscid two dimensional 2 d model previously used to study the mars hadley circulation tidally induced easterly forces at southern summer solstice can extend the core of the descending branch of the zonally symmetric circulation from 50 to 55 n which is consistent with viking lander 2 surface pressure observations but not far enough polewa

a martian general circulation experiment with large topography abstract a three layer general circulation model used to simulate the martian atmosphere is described and results are presented the model assumes a dust free pure c02 atmosphere and allows for a diurnally varying convective boundary layer smoothed martian topography and albedo variations are incorporated the simulation described is for the period near southern winter solstice season of the viking landings the zonally averaged circulation mass heat and momentum balances and properties of stationary and transient waves are described in some detail and are compared with results of previous simulations of the martian general circulation with related features of the earth s general circulation and with observed characteristics of the martian atmosphere the principal conclusions are the following 1 the simulated zonally averaged circulation is not very sensitive to differences between this model and the earlier general circulation model of leovy and mintz 1969 and compares reasonably well wi

the spatial and seasonal distribution of martian clouds and some meteorological implications the spatial and seasonal distributions of martian atmospheric clouds organized according to simple morphologic criteria exhibit distinct patterns when interpreted self consistently using analogies to terrestrial cloud forms and martian temperature wind direction and water vapor measurements patterns of cloud occurrence provide some loose constraints on global scale near surface wind speed static stability and humidity we have examined all mariner 9 and viking orbiter images for this study we concentrate primarily on the larger viking data set whenever observations are possible relatively high near surface winds appear to follow the seasonal cap edges during early fall late winter and spring moderate to high winds are also inferred in mid latitudes for mid southern winter and in low latitudes mainly in the steeply sloping areas of tharsis near the solstices at other times lower winds are suspected hemispheric asymmetries are traced to differences in atmospheric hydration state and to global dust storm related effects on the atmospheric temperature structure and the north polar cap recession schedule cloud occurrence data suggest that the near surface daytime static stability is low in the northern hemisphere during summer and at low latitudes during mid northern spring relatively high static stability is deduced near the winter poles and globally during the dust storm season in spite of low atmospheric temperatures the correspondingly low absolute humidity apparently precludes the formation of thick water ice clouds at high latitudes in mid to late autumn and winter in both hemispheres and in southern mid latitudes during early winter during northern spring and summer saturation conditions seem to be easily achieved at mid latitudes and condensate clouds are abundant the situation is complicated by atmospheric dust in southern spring and summer low latitudes generally appear to be farther from saturation than mid latitudes and clouds generally form more easily in the northern hemisphere than in the south during corresponding seasons

alteration and breakdown of xenotime y and monazite ce in granitic rocks of the western carpathians slovakia abstract in the granitic rocks of the western carpathians xenotime y occurs both as a late stage magmatic mineral and as a secondary post magmatic phase magmatic xenotime occurs with monazite and displays minor compositional zonation involving si th and u the source of elements for the formation of secondary xenotime y in the granitic rocks results from leaching of p and y ree mainly from zircon and apatite both xenotime y and monazite ce are unstable during fluid activated overprinting low temperature alteration of monazite in s type granites leads to the formation of apatite enriched in the britholite component but low to medium grades of metamorphism result in the formation of apatite and lree enriched epidote partly allanite as a corona enclosing the monazite ce core xenotime y shows a similar alteration pattern but with different ree distributions within the products at greenschist amphibolite facies rims of secondary y rich apatite and y rich epidote form around xenotime y in low ca granites however apatite is missing from this alteration assemblage as xenotime y breaks down directly to y enriched epidote the relative mobilities of the heavy and light ree are different during breakdown of monazite and xenotime the fluid responsible for the breakdown of monazite and xenotime contains elements released from alteration of anorthite ca and biotite si al and f

the martian hadley circulation comparison of viscous model predictions to observations abstract the predictions of an analytical steady thermally forced viscous model for the zonally averaged global circulation of the martian atmosphere are compared to observations of atmospheric temperatures and eolian feature directions the temperature of the winter polar atmosphere is a sensitive indicator of the value of the mean eddy diffusivity v of the atmosphere for global dust storm season the observed large warming of the atmosphere over the winter north pole during the 1977b storm as well as the distribution and azimuths of type i b dust streaks can be well reproduced if v 10 7 10 8 cm 2 sec 1 observed northeasterly surface winds at high northern latitudes could be produced by plausible fluxes of co 2 from the northern polar cap the thermal structure at southern latitudes during this storm is satisfactorily produced but a major discrepancy exists between observations and predictions of the temperature structure at middle northern latitudes by comparing these results with those from previous inviscid models of the zonal mean circulation on mars we suggest v 10 7 cm 2 sec 1 at heights above 30 km and v 10 7 cm 2 sec 1 at lower altitudes may yield a meridional circulation which produces the dynamical warming necessary to account for the observed thermal structure at 0 6 mbar at all latitudes for late southern summer when the dust content of the atmosphere has decreased to levels characteristic of much of the martian year the lack of dynamical warming of the winter pole implies v 10 6 cm 2 sec 1 in addition the predicted surface wind azimuths at this season agree well with the observed azimuths of type i d dust streaks which are observed to form at this season the observed latitudinal concentration of the streaks is not explained by the model and may require additional processes which have not been included

the role of sublimation for the formation of the northern ice cap results from the mars orbiter laser altimeter abstract the evolutionary history of the martian ice caps is practically unknown and the caps are key to understanding the climatic history of mars sublimation and ice flow are two hypotheses that have recently been suggested to explain the observed form of the northern ice cap here we present a sublimation model and compare the shape of the cap obtained from this model with mars orbiter laser altimeter mola observations of the north polar region this model can reproduce the shape of the cap and individual troughs sublimation is an important process as are flow and wind erosion we were able to constrain the time scales of sublimation only to about two orders of magnitude 1 100 million years this estimate depends on many unknown parameters such as friction velocity and wind speed over the ice caps these can be determined only by direct measurement over the surface

new martian paradigms several interrelated paradigms concerning the nature and the evolution of mars are discussed these include an impact origin of the northern lowland mars as a water rich planet former oceans in the northern lowlands a warm wet climate on early mars and the possibility of ancient life on mars locations on mars suggested for the search of possible ancient life include the heavily cratered terrain dissected by valley networks possible lacustrine deposits in valles marineris the oxidizing layer below the surface sites along the fringes of the hypothetical northern circumpolar ocean and in evaporite deposits

variability of mars north polar water ice cap i analysis of mariner 9 and viking orbiter imaging data abstract previous studies interpreted differences in ice coverage between mariner 9 and viking orbiter observations of mars north residual polar cap as evidence of interannual variability of ice deposition on the cap however these investigators did not consider the possibility that there could be significant changes in the ice coverage within the northern residual cap over the course of the summer season our more comprehensive analysis of mariner 9 and viking orbiter imaging data shows that the appearance of the residual cap does not show large scale variance on an interannual basis rather we find evidence that regions that were dark at the beginning of summer look bright by the end of summer and that this seasonal variation of the cap repeats from year to year our results suggest that this brightening was due to the deposition of newly formed water ice on the surface we find that newly formed ice deposits in the summer season have the same red to violet band image ratios as permanently bright deposits within the residual cap we believe the newly formed ice accumulates in a continuous layer to constrain the minimum amount of deposited ice we used observed albedo data in conjunction with calculations using mie theory for single scattering and a delta eddington approximation of radiative transfer for multiple scattering the brightening could have been produced by a minimum of 1 a 35 m thick layer of 50 m sized ice particles with 10 dust or 2 a 14 m thick layer of 10 m sized ice particles with 50 dust

the effects of martian orbital variations upon the sublimation and relaxation of north polar troughs and scarps abstract the north polar layered deposits pld of mars are climatologically significant because they represent the largest actively exchanging reservoir of martian water the kilometer scale topography of the north pld is dominated by troughs and scarps which exhibit highly correlated surface slopes and total depths the most widespread theories of pld evolution presume that the asymmetrical nature of north pld troughs characterized by equatorward facing slopes that are generally steeper than poleward facing slopes is the result of preferential h 2 o sublimation from equatorward facing trough walls however our orbitally modulated simulations indicate that there is no long term sublimation advantage of equatorward facing trough walls because of the effects of obliquity upon the slope dependence of sublimation rate in contrast we propose that viscous relaxation of subsurface water is consistent with the slope and depth distributions of north pld troughs and scarps the results of our finite element simulations suggest that a mere 2 k difference in the subsurface temperatures of opposing trough walls is sufficient to produce the observed slope disparity due to the slower rate of uplift of colder poleward facing trough walls both our sublimation and relaxation simulations indicate that present day north pld troughs have formed since 5 ma and are not sites of long term deposition additionally our results imply that glacial flow may govern the large scale evolution of the north pld especially at high obliquity

classification of wind streaks on mars abstract a classification of martian wind streaks has been developed to assist in investigations of eolian transport and related meteorological phenomena on mars streaks can be grouped by their albedo contrast with their surroundings and by the presence of either topographic obstacles or sediment deposits at their points of origin the vast majority of wind streaks can be included in three categories 1 bright streaks with no source deposit interpreted to be formed by preferential deposition of dust from suspension 2 dark streaks with no source deposit interpreted to be formed by preferential erosion of bright dust and its removal in suspension 3 dark streaks associated with deposits of sediment interpreted to be formed by deposition of dark material moved by saltation the orientations of the different streak types are distinctive and reflect both global flow patterns and slope controlled winds the wind directions derived from streaks and the geographical distribution of the features show a strong north south asymmetry consistent with the fact that perihelion and hence maximum wind activity occurs near southern summer solstice

waxing and waning of the perennial north polar h2o ice cap of mars over obliquity cycles abstract the perennial north polar h2o ice cap of mars is investigated with the dynamic thermodynamic ice sheet model sicopolis computational results for flow velocities ice temperatures and surface accumulation ablation rates are presented for the steady state with present conditions as well as for transient scenarios over idealized obliquity cycles with periods of 1 3 myr and 125 kyr the transient simulations lead to a stop and go type dynamics with a cold and almost stagnant modern ice cap and a warmer flowing ice cap for past large obliquity periods the most likely scenario for the present ice cap comprises an ice volume of 1 2 million km3 a maximum thickness of 3 km the absence of pronounced local isostasy h2o ice accumulation rates of the order of tenth mm water equivalent w e per earth year yr flow velocities of the order of mm yr and an ice base far below pressure melting

investigation of water vapor on mars with pfs sw of mars express abstract new insight into the seasonal diurnal and spatial distribution of water vapor on mars has been obtained from analyzing the spectra of the short wavelength channel sw of the planetary fourier spectrometer pfs onboard mars express the processed dataset recorded between january 2004 and april 2005 covers the seasons from l s 331 of mars year 26 to l s 196 of the following year in this period the mean column density around vernal equinox was 8 2 pr m the maximum values during northern summer were about 65 pr m located around 75 n latitude with a longitudinally inhomogeneous distribution regarding the atmospheric transport the majority of polar water vapor remains in the north polar region while only about a quarter is transported southward geographically there are two water vapor maxima visible over arabia terra and the tharsis plateau that are most likely caused both by atmosphere ground interaction and by atmospheric circulation a comparison with other instruments generally shows a good agreement only the spicam results are systematically lower compared to the results from the pfs long wavelength channel the results of this work are slightly higher a strong discrepancy is visible northward of about 50 n during the northern summer that is possibly explained by a non uniform vertical h 2 o mixing in particular a confinement of the water to the lower few kilometers yields a much better agreement between the retrieved column densities of the two pfs channels

measurements of the atmospheric water vapor on mars by the imager for mars pathfinder the imager for mars pathfinder imp was the first instrument to measure the atmospheric water on mars from its surface it took the images of the sun through the martian atmosphere in five narrowband filters two in the 0 94 m h2o band and three in the continuum around it the observations were carried out in the mornings and in the evenings when the sun was between 3 and 8 above the horizon the absorption due to the atmospheric water vapor did not exceed 2 an average column density of 6 4 precipitated microns pr m was derived from the imp data the dependence of the observed h2o transmittance on sun elevation tentatively implies that the water vapor is not uniformly mixed in the atmosphere but is rather confined to a layer 1 3 km thick near the surface imp observations also indicate a horizontal inhomogeneity of the layer but show no significant morning to evening variations of the water vapor amount

on the orbital forcing of martian water and co2 cycles a general circulation model study with simplified volatile schemes 1 variations in the martian water and co2 cycles with changes in orbital and rotational parameters are examined using the geophysical fluid dynamics laboratory mars general circulation model the model allows for arbitrary specification of obliquity eccentricity and argument of perihelion as well as the position and thickness of surface ice exchange of co2 between the surface and atmosphere is modeled generating seasonal cycles of surface ice and surface pressure water is allowed to exchange between the surface and atmosphere cloud formation is treated and both cloud and vapor are transported by modeled winds and diffusion exchange of water and co2 with the subsurface is not allowed and radiative effects of water vapor and clouds are not treated the seasonal cycle of co2 is found to become more extreme at high obliquity as suggested by simple heat balance models maximum pressures remain largely the same but the minima decrease substantially as more co2 condenses in the more extensive polar night vapor and cloud abundances increase dramatically with obliquity the stable location for surface ice moves equatorward with increasing obliquity such that by 45 obliquity water ice is stable in the tropics only ice is not spatially uniform but rather found preferentially in regions of high thermal inertia or high topography eccentricity and argument of perihelion can provide a second order modification to the distribution of surface ice by altering the temporal distribution of insolation at the poles further model simulations reveal the robustness of these distributions for a variety of initial conditions our findings shed light on the nature of near surface ice rich deposits at midlatitudes and low latitudes on mars

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

possible precipitation of ice at low latitudes of mars during periods of high obliquity most of the old cratered highlands of mars are dissected by branching river valleys that appear to have been cut by running water1 2 yet liquid water is unstable everywhere on the martian surface in the equatorial region where most of the valleys are observed even ice is unstable3 4 it has been suggested therefore that mars had an early denser atmosphere with sufficient greenhouse warming to allow the existence of liquid water5 here we suggest instead that during periods of very high obliquities ice could accumulate at low latitudes as a result of sustained sublimation of ice from the poles and transport of the water vapour equatorwards at low latitudes the water vapour would saturate the atmosphere and condense onto the surface where it would accumulate until lower obliquities prevailed the mechanism is efficient only at the very high obliquities that occurred before formation of tharsis very early in the planet s history but limited equatorial ice accumulation could also have occurred at the highest obliquities during the rest of the planet s history partial melting of the ice could have provided runoff to form the channels or replenish the groundwater system

assessing the impact of groundwater abstractions on river flows abstract groundwater abstractions affect the water balance in catchments of rivers in hydraulic continuity with groundwater and may lead to reductions in river baseflow the environment agency issues licences for groundwater abstractions and takes into account the risk of such adverse impacts when deciding whether to grant licences and what conditions to associate with each licence assessing the impact of a particular licence is a difficult task but analytical solutions to idealizations of the complex river aquifer interaction can help guide such judgements this paper presents a brief review of available analytical solutions and discusses their applicability to real groundwater systems the most useful analytical solutions developed by theis hantush and stang have been incorporated into a spreadsheet and a new methodology has been made available to support environment agency hydrogeologists working in abstraction licensing this offers a consistent approach to making an initial evaluation of the impact of groundwater abstraction on river flow that may be applied across the diverse hydrogeological systems found throughout the environment agency regions of england and wales the use of analytical solutions in this methodology inevitably represents a significant simplification of what is generally a very complex issue and the limitations of the new methodology are emphasized

viking era diurnal water ice clouds 1 water ice clouds during the viking era are mapped as a function of season latitude longitude and time of day in the springtime hemisphere where data are available clouds are observed to decrease from morning to midday they are observed to increase in extent from midday to afternoon possibly due to increased atmospheric temperatures causing uplifting of dust which then acts as cloud condensation nuclei during the summer hemisphere clouds are observed to decrease in extent throughout the day indicating sufficient warming to prevent water reaching the condensation level the hadley cell upwelling branch is seen throughout the year via cloud belts in both the northern aphelion cloud belt and southern hemispheres in their respective springs and summers clouds extending equatorward of 60 n in late northern summer and early northern autumn are seen primarily over the acidalia planitia longitudinal sector and may indicate the southernmost extent of the north polar hood or clouds associated with storms water ice clouds associated with topographic features are seen including olympus mons the tharsis volcanoes and the northern rim of hellas basin there is little evidence for interannual variability in the prominent cloud features e g the aphelion cloud belt since they are present in both martian years examined though the detailed structure does change

thermal and albedo mapping of the polar regions of mars using viking thermal mapper observations 1 north polar region we present the first maps of the apparent thermal inertia and albedo of the south polar region of mars the observations used to create these maps were acquired by the infrared thermal mapper irtm instruments on the two viking orbiters over a 30 day period in 1977 during the martian late southern summer season the maps cover the region from 60 s to the south pole at a spatial resolution of 1 of latitude thus completing the initial thermal mapping of the entire planet the analysis and interpretation of these maps is aided by the results of a one dimensional radiative convective model which is used to calculate diurnal variations in surface and atmospheric temperatures and brightness temperatures at the top of the atmosphere for a range of assumptions concerning dust optical properties and dust optical depths the maps show that apparent thermal inertias of bare ground regions decrease systematically from 60 s to the south pole in unfrosted regions close to the south pole apparent thermal inertias are among the lowest observed anywhere on the planet on the south residual cap apparent thermal inertias are very high due to the presence of co2 frost in most other regions of mars best fit apparent albedos based on thermal emission measurements are generally in good agreement with actual surface albedos based on broadband solar reflectance measurements however in the frost free region poleward of 75 s best fit apparent albedos are significantly higher than measured lambert albedos implying that measured brightness temperatures in this area are up to 15 k colder than would be expected for surfaces with the same measured albedos during this season the one dimensional atmospheric model calculations also predict anomalously cold brightness temperatures close to the pole during late summer and after considering a number of alternatives it is concluded that the net surface cooling due to atmospheric dust is the best explanation for this phenomenon the observed systematic decrease in apparent thermal inertia from 60 s to the south pole during this season is also consistent with the predictions of atmospheric model calculations the region of lowest apparent thermal inertia close to the pole which includes the south polar layered deposits is interpreted to be mantled by a continuous layer of aeolian material that must be at least a few millimeters thick the low thermal inertias mapped in the south polar region imply an absence of surface water ice deposits which is consistent with viking mars atmospheric water detector mawd measurements which show low atmospheric water vapor abundances throughout the summer season however these observations do not necessarily imply a complete absence of water thermal model calculations that can reproduce observed diurnal temperature variations in the south polar region show that annual maximum subsurface temperatures at depths ranging from 4 to 20 cm are cold enough to permit the stability of ground ice deposits even if they are in excellent diffusive contact with the atmosphere therefore the presence of near surface ground ice in the south polar region is not inconsistent with the viking irtm and mawd observations

groundwater chemistry in southeast suffolk u k and its relation to quaternary geology abstract east anglia has a complex pleistocene geological history having been affected both by major changes in the level of the adjacent north sea and by glacial processes the resulting geology has a profound effect on the distribution of water chemistry in the chalk aquifer which underlies the pleistocene deposits a detailed study of the chemistry of the chalk groundwater including strontium fluoride and iodide as well as major elements has shown that this chemistry results from three phases of saline intrusion early pleistocene to modern and at least two periods of freshwater flushing climatic changes and erosional history were important in controlling flushing periods

the seasonal behavior of water ice clouds in the tharsis and valles marineris regions of mars mars orbiter camera observations abstract the mars global surveyor mars orbiter camera was used to obtain global maps of the martian surface with equatorial resolution of 7 5 km pixel in two wavelength ranges blue 400 450 nm and red 575 625 nm the maps used were acquired between march 15 1999 ls 110 and july 31 2001 ls 205 corresponding to approximately one and a quarter martian years using the global maps cloud area in km2 has been measured daily for water ice clouds topographically corresponding to olympus mons ascraeus mons pavonis mons arsia mons alba patera the western valles marineris canyon system and for other small surface features in the region seasonal trends in cloud activity have been established for the three tharsis volcanoes olympus mons and alba patera olympus ascraeus and pavonis mons show cloud activity from about ls 0 220 with a peak in cloud area near ls 100 one of our most interesting observational results is that alba patera shows a double peaked feature in the cloud area with peaks at ls 60 and 140 and a minimum near ls 100 arsia mons shows nearly continuous cloud activity the altitudes of several of these clouds have been determined from the locations of the visual cloud tops and optical depths were measured for a number of them using the disort code of stamnes et al 1988 appl opt 27 2502 2509 several aspects of the observations e g cloud heights effects of increased dust on cloud activity are similar to simulations in richardson et al 2002 j geophys res 107 5064 a search for short period variations in the cloud areas revealed only indirect evidence for the diurnal cloud variability in the afternoon hours unambiguous evidence for other periodicities was not found

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

distribution and state of h2o in the high latitude shallow subsurface of mars abstract a quantitative model of the state distribution and migration of water in the shallow martian regolith is presented reported results are confined to the region of the planet greater than 40 lat the calculations take into account 1 expected thermal variations at all depths latitudes and times resulting from seasonal and astronomically induced insolation variations 2 variations in atmospheric ph2o and pco2 resulting from polar insolation variations and regolith adsorptive equilibria 3 feedback effects related to latent heat and albedo variations resulting from condensation of atmospheric constituents 4 two possible regolith mineralogies 5 variable total h2o content of the regolith 6 kinetics of h2o transport through the martian atmosphere and regolith and 7 equilibrium phase partitioning of h2o between the condensed adsorbed and vapor phases results suggest that the adsorptive capacity of the regolith is important in controlling the state and distribution of high latitude h2o unweathered mafic silicates favor the development of shallow ground ice at all temperate and polar latitudes while heavily weathered clay like regolith materials leads to a deeper ground ice interface and far more extensive quantities of adsorbed h2o the capacity of the high latitude regolith for storage of h2o and the total mass of h2o exchanged between the atmosphere polar cap and subsurface over an obliquity cycle is found to be relatively independent of mineralogy the maximum exchanged volume is found to be 3 0 104 km3 of ice per cycle implications for the history of the polar caps and the origin of the layered terrain are discussed results also suggest that seasonal thermal waves act to force adsorbed h2o into the solid phase over a wide variety of latitude obliquity conditions seasonal phase cycling of regolith h2o is most common at high latitudes and obliquities such phase behavior is highly dependent on regolith mineralogy in a highly weathered regolith adsorbed h2o is annually forced into the solid phase at all latitudes 40 at obliquities greater than approximately 25 seasonal adsorption freezing cycles which are predicted here may produce geomorphologic signatures not unlike those produced by terrestrial freeze thaw cycles

the evolution of lacustrine environments on mars is mars only hydrologically dormant abstract this study surveys the evolution of martian impact crater paleolakes through time by establishing their age comparing their locations and describing the formation of lacustrine sedimentary structures and features over time we explore their meaning in terms of global climate changes but also on local and regional scales we observe a co location between recent impact crater paleolakes and regions where gcm modeling shows that mars is currently experiencing days above triple point and below boiling point of water some source areas show morphologies that could be consistent with ancient glacier features in the argyre basin darwin crater region in locations that are also consistent with gcm models of past snow precipitation on mars we propose that at least for some paleolakes our results are best explained by recent and abundant aqueous activity on mars with some meteorological contribution these results are supported by other recent findings on martian meteorite ages by the analysis of new mgs data showing recent volcanic and fluvial activity and by climate modeling they point toward the possibility that mars currently is only hydrologically dormant and that there is a potential for hydrological activity to be generated again in the future following changes in the planet s orbital parameters

distribution of the ices exposed near the south pole of mars using thermal emission imaging system themis temperature measurements 1 understanding the present and past water cycle on mars requires an accurate knowledge of the distribution and amount of h2o available near the surface in this article we present a map of the distribution of the surface material exposed between 87 s and 70 s in the summer e g co2 and h2o ices dust based on temperature measurements made by thermal emission imaging system themis our compositional map 100 m per pixel is in good agreement with spectral mapping returned by observatoire pour la mineralogie l eau la glace et l activite omega and compact reconnaissance imaging spectrometer for mars crism exposed water ice covers a total surface area of approximately 40 000 km2 a large fraction of the water ice is exposed at the periphery of the co2 cap an approximately 25 000 km2 large patch centered at 83 5 s and 345 e is discovered and represents the largest exposure of water ice in the southern hemisphere it is not located on the south polar layered deposits but on the surrounding mantled terrains themis vis moc and hirise images indicate that the surface roughness of exposed water ice terrains is typically lower than that of the surrounding dust polygonal patterns are observed on the water ice but not exclusively there is a strong correlation between the surface albedo the composition of the exposed material and the timing of the initial seasonal co2 frost deposition and final removal these exposed water ice outcrops are not stable in the present environment and lose a vertical layer of tens to hundreds of micrometer a year to the atmosphere the spike of water vapor above the south pole during the southern summer occurs while the water ice is still covered by a layer of seasonal co2 frost indicating that the sublimation of the exposed water ice is not the main contributor of vapor for the southern atmosphere as water ice is not stable it may indicate the past location of part of the co2 perennial cap that has been eroded

mars the cloud effect on the blue clearing in the syrtis major region we conducted imaging observations of mars in march 1997 and april 1999 these apparitions were around its northern summer oppositions mars showed highly developed clouds that formed the aphelion cloud belt comparing the diurnal variations of the apparent contrasts of syrtis major to the adjacent bright areas with those of the optical depths of the aphelion clouds over those regions we conclude that the time when those regions are subject to the morning clouds is around 0900 martian local time mlt and that the diurnal variation of the degree of blue clearing strongly depends on the difference between the optical depth of h2o ice clouds over syrtis major and that over the adjacent bright area moreover our simple linear regression analyses of the degree of blue clearing to the optical depths of h2o ice clouds suggest that the key region in which the h2o ice cloud optical depth determines the degree of blue clearing is syrtis major

topographic control of hydrogen deposits at low latitudes to midlatitudes of mars 1 correlations between the longitudinal wave number two distribution of water equivalent hydrogen weh at low latitudes to midlatitudes of mars with variations in topography surface albedo thermal inertia regional dust storms and atmospheric water vapor are explored to provide guidance in determining the mechanisms that recharge or maintain these weh reservoirs the closest match is with low thermal inertia coupled with orographic control of the present day atmospheric circulation dynamics the engine for the simulated longitudinal two wave pattern maxima in arabia and tharsis is relatively cold nighttime surface temperatures and large amplitude temperature inversions that concentrate water ice over these regions geologically recent precipitated water ice by itself is insufficient to account for the observed distribution of weh retention of precipitate by hydratable minerals is necessary while current research cannot presently identify the hydration mechanism for the weh distribution whether it be from a past obliquity present climate conditions or some convolution of both this research suggests that current climatic conditions can sustain if not emplace the observed longitudinally constrained distribution of equatorial weh

a mesoscale model study of summertime atmospheric circulations in the north polar region of mars 1 the oregon state university mars mm5 was used in a comprehensive high resolution study of northern polar summertime circulations three simulations ls 120 ls 135 and ls 150 characterize the changing circulation the atmosphere is dry and model dynamics are hydrostatic a modified tes thermal inertia map provides a realistic simulation of the polar thermal environment the highest resolution nest 18 km resolves complex flows near the cap zonal mean easterlies 10 m s and zonal mean katabatic winds 5 m s near the surface are relatively steady during this study katabatic flows are shallow 300 m the easterlies are deeper 1 5 km transient eddies are very important within the first scale height they are excited by mechanisms and at locations that change dramatically during this short study period at ls 120 they form along the residual cap edge with a zonal wave number one structure producing strong excursion winds 10 15 m s that blow consistently across the cap by ls 135 strong eddies are seen to form on the northern slopes of alba patera and tharsis these eddies are quite suggestive of the large annular cloud structures seen in hubble space telescope and mars orbital camera imagery at this location and season and can traverse the high latitudes to reach the residual cap before dissipating eddies in the earlier two simulations appear to be primarily excited by energetic flows near the surface by ls 150 an early fall polar jet causes strong winter like baroclinic eddies to develop the transient eddies found in this study are probably important in the water cycle of the northern residual cap

the mars observer laser altimeter investigation the primary objective of the mars observer laser altimeter mola investigation is to determine globally the topography of mars at a level suitable for addressing problems in geology and geophysics secondary objectives are to characterize the 1064 nm wavelength surface reflectivity of mars to contribute to analyses of global surface mineralogy and seasonal albedo changes to assist in addressing problems in atmospheric circulation and to provide geodetic control and topographic context for the assessment of possible future mars landing sites the principal components of mola are a diode pumped neodymium doped yttrium aluminum garnet laser transmitter that emits 1064 nm wavelength laser pulses a 0 5 m diameter telescope a silicon avalanche photodiode detector and a time interval unit with 10 ns resolution mola will provide measurements of the topography of mars within approximately 160 m footprints and a center to center along track foot print spacing of 300 m along the mars observer subspacecraft ground track the elevation measurements will be quantized with 1 5 m vertical resolution before correction for orbit and pointing induced errors mola profiles will be assembled into a global 0 2 deg x 0 2 deg grid that will be referenced to mars center of mass with an absolute accuracy of approximately 30 m other data products will include a global grid of topographic gradients corrected individual profiles and a global 0 2 deg x 0 2 deg grid of 1064 nm surface reflectivity

the distribution and behavior of martian ground ice during past and present epochs mars undergoes significant oscillations in its orbit which will have a pronounced effect on its climate and in particular on the behavior of subsurface water ice we explore and map the behavior of ice in the martian near surface regolith over the past 1 m y using a diffusion and condensation model presented in an earlier paper with two primary modifications to include orbitally induced variations in insolation and atmospheric water abundance we find that the past behavior of ground ice differs significantly from that at the present epoch primarily the result of high amplitude oscillations in obliquity presently 25 in midlatitude and equatorial regions ground ice will condense from atmospheric water during times of higher obliquity filling the top few meters of the regolith with significant amounts of ice at an obliquity of 32 ground ice becomes stable globally during times of lower obliquity ground ice will sublime and diffuse back into the atmosphere dessicating the regolith to a depth of about 1 to 2 m equatorward of 60 to 70 latitude in the high latitude regions these oscillations are considerably subdued below this depth of cyclic saturation and dessication a long term stability of ice exists in some geographic regions we present a map of the distribution of ice expected at the present epoch cyclic exchange of water between the global regolith and polar regions will have significant implications for surface geology and the polar layered deposits

viking era water ice clouds we have spatially and temporally mapped water ice clouds on mars for 1 25 martian years using the viking infrared thermal mapper irtm data our technique compares brightness temperatures in the 11 and 20 m irtm channels utilizing the 11 m water ice absorption feature a complication arises because of the surface nonunit and wavelength dependent emissivities we developed a technique for removal of this effect using a surface thermal model we calculated brightness temperatures and their differences for the irtm channels resulting from the surface emissivity effect alone these were then subtracted from the measured brightness temperatures yielding brightness temperature differences dominated by atmospheric effects the ability to identify water ice clouds in the infrared provides potential new information about particle size and physical processes by comparing these clouds to those seen in visible wavelengths we found that water ice clouds were more widespread and frequent during the viking period than had been previously recognized with the northern spring and summer being the cloudiest periods on mars we interpret some of the identified cloudy zones as the southern and northern solstice season upwelling branches of the hadley cell although these were shifted 15 20 southward from model predictions additionally the transition between the two branches occurred later in time than in the model predictions we observed the extension of the north polar hood below 60 n in longitudes 120 200 we did not find evidence for a south polar hood north of 60 s nor any evidence for interannual variability within our limited data set

hydrochemical evolution of the east midlands triassic sandstone aquifer england a detailed hydrogeochemical interpretation has been made of the red bed sherwood sandstone triassic aquifer of the east midlands of england on which a radiocarbon model has been used to establish a chronology of groundwaters along the flow line groundwater evolution is dominated by carbonate and sulphate mineral solution and precipitation and by redox reactions cation exchange reactions are negligible and the hydrogeochemistry has evolved in the absence of residual saline water three distinct zones are recognised 1 i recent groundwater mainly 100 y oxidising dominated by congruent dissolution of dolomite and by inputs from atmospheric and anthropogenic sources 2 ii groundwater age 103 104 y predominantly reducing dominated by incongruent dissolution of dolomite 3 iii groundwater age 104 y reducing conditions approach to isotopic and chemical equilibrium in the carbonate system dominance of gypsum dissolution the minor and trace element variation can be interpreted in relation to the principal geochemical reactions and recharge history na cl f and b are controlled by atmospheric inputs sr2 and mn2 trends can be explained by carbonate and sulphate mineral dissolution ba2 is derived from carbonates but controlled by barite equilibrium fe so42 no3 and u are strongly influenced by redox reactions the concentrations of transition metals and other elements remain very low only li and k are considered to represent additions by reaction of silicate minerals the extent of direct anthropogenic influence is probably limited to enhanced so4 no32 and possibly cu zn and pb in zone i

lineations on the white accumulation areas of the residual northern ice cap of mars their relation to the accublation and ice flow hypothesis abstract mars orbiter camera moc images of the whiter areas of the residual north polar cap p c thomas et al 2000 nature404 161 164 show a gentle hummocky pitted surface that has been popularly called cottage cheese terrain the pits are 1 or 2 m deep and tens of meters across they are typically joined in roughly linear strings or long depressions and these features are referred to here as lineations the lineations tend to have one or occasionally two preferred directions we have examined the moc imagery for the north cap and using high resolution images that have good wide angle context images were able to determine the lineation angles for 31 sites scattered over most of the ice cap we propose a process that will produce linear features in the white areas then relate the orientation of the lineations over much of the north cap to these processes and the inferred ice flow direction there is first order agreement between the measured sign of the lineation angles and those predicted assuming ice flow higher accumulations and velocities are predicted in the catchment for ice that flows into chasma boreale this comes from the indications that katabatic winds are concentrated in this catchment

global patterns in cloud forms on mars abstract mariner 9 images and all viking orbiter images through july 1979 were searched for cloud forms a computer accessible catalog was assembled consisting of a classification of cloud type lee wav wave for example and properties directionality wavelength for example lee wave directionality shows a pattern and seasonal variation at high latitudes which is consistent with predictions of theoretical modeling fog and haze occurrence shows no obvious correlation with water abundance or any other simple causal factor lee waves are rare at equatorial latitudes plumes probably dust occur preferentially at locations where strong boundary layer convection is expected

modeling the martian seasonal water cycle ever since the observations of percival lowell the annual cycle of martian water has been a fascinating topic in planetary exploration observations by the viking orbiter supplemented by earth based microwave and infrared observations have given us a reasonable picture of this cycle we are now also able to model the cycle using our mars climate model a simplified atmospheric general circulation model designed specifically for this purpose we find that a thin adsorbing layer of the martian regolith plays a fundamental role in the water cycle limiting the lower atmospheric relative humidity and preventing the formation of widespread ice deposits at low latitudes we are thus able to estimate a large scale average value of the specific soil surface area of this regolith water which evaporates from the permanent north polar ice cap during summer is returned by a process of repeated evaporation and precipitation on the retreating seasonal cap the following spring so that the global inventory of water outside the polar caps ranges within narrow limits there is a small net annual deposition of water ice at the south polar cap which is always at dry ice temperatures if ice on the residual south polar cap is exposed during the summer it rapidly sublimes generating vapor amounts similar to those observed in northern summer recovery to normal dry conditions in the southern atmosphere occurs very rapidly in the next year such an event could explain the otherwise anomalous earth based pre viking observations of a wet southern summer if southern ice deposits at lower latitudes are exposed the vapor can be transferred irreversibly through the strong hadley cell to the north polar cap we therefore speculate that the asymmetry of mars current orbit is responsible for the asymmetry of the present water distribution with extensive permanent water ice deposits located only in the colder aphelion summer northern hemisphere