possible dust devils vortices on mars this paper presents the results of a study of local vortices and dust devils on mars as observed by viking landers 1 and 2 it is found that these vortices are most common during martian spring and summer as occurs on earth seven of the vortices involve wind speeds that may raise dust from the martian surface there is no indication that these possible dust devils contribute to the planet wide spread of major dust storms however it appears that they may help in maintaining the atmospheric dust content the data indicate that there is no preference in rotation direction at least to core diameters of 300 m corresponding to a region of influence of about 3 km diameter

a boundary layer model for mars comparison with viking lander and entry data abstract a one dimensional boundary layer model for mars is described and its results are compared with viking data the model equations are similar to earth boundary layer models in that they include contributions from coriolis pressure gradient and frictional forces for momentum and radiation sensible heat flux convergence and advection for heat turbulent fluxes are computed from the level 2 second order closure theory of mellor and yamada with similarity relations employed for boundary conditions the pressure gradient force can be specified or computed from a simple slope model radiative heating is due to the absorption of solar and infrared radiation by co2 gas and suspended dust particles ground temperatures are computed by solving a surface heat budget using an accurate treatment of conduction into the martian soil the data used for comparison were obtained by the viking 1 and 2 landers for early northern summer at each site these data include a single profile of wind and temperature be

a survey of martian dust devil activity using mars global surveyor mars orbiter camera images 1 a survey of dust devils using the mars global surveyor mgs mars orbiter camera moc wide and narrow angle wa and na images has been undertaken the survey comprises two parts 1 sampling of nine broad regions from september 1997 to july 2001 and 2 a focused seasonal monitoring of variability in the amazonis region an active dust devil site from march 2001 to april 2004 for part 1 dust devils were identified in na and wa images and dust devil tracks were identified in na images great spatial variability in dust devil occurrence is highlighted with amazonis planitia being the most active region examined other active regions included cimmerium sinai and solis numerous dust devil tracks but very few dust devils were observed in casius this may suggest dust devils here occur at local times other than that of the mgs orbit 2 pm alternatively variations in surface properties may affect the ability of dust devils to leave visible tracks the seasonal campaign within amazonis shows a relatively smooth variation of dust devil activity with season peaking in mid northern summer and falling to zero in southern spring and summer this pattern of activity correlates well with the boundary layer maximum depth and hence the vigor of convection global maps of boundary layer depth and surface temperature do not predict that amazonis should be especially active potentially suggesting a role for mesoscale circulations measurement of observed dust devils yields heights of up to 8 km and widths in excess of 0 5 km

a wave tank experiment on the erosional mechanism at a cliff base a laboratory experiment using a two dimensional wave tank was designed to investigate the mechanism of erosion at a cliff base by waves armed with rock fragments the experiment was performed under constant wave conditions by systematically changing the amount of beach sand at the foot of steep model cliffs of the same slope and strength cliff erosion occurred when the beach material at the cliff beach junction was moved by waves turbulence created by bores rushing up on the beach mobilized the sand and exerted a mechanical shearing force on the cliff face using the sand as an abrasive the analysis of results indicated that the effect of the abrasive doubled when the cliff beach junction was located above still water level swl as compared to when it was below swl the assailing force of the sediment laden water masses was proportional to the square of the bore speed immediately in front of the cliff face the factor of proportionality is related to the quantity of beach sand entrapped in the turbulent fluid

initial results from radio occultation measurements with the mars reconnaissance orbiter a nocturnal mixed layer in the tropics and comparisons with polar profiles from the mars climate sounder abstract the mars reconnaissance orbiter mro performs radio occultation ro measurements on selected orbits generally once per day we have retrieved atmospheric profiles from two subsets of data yielding a variety of new results that illustrate the scientific value of the observations one set of measurements sounded the tropics in northern summer at a local time 1 h before sunrise some of these profiles contain an unexpected layer of neutral stability with a depth of 4 km and a pressure at its upper boundary of 160 pa the mixed layer is bounded above by a temperature inversion and below by another strong inversion adjacent to the surface this type of structure is observed near gale crater in the tharsis region and at a few other locations whereas profiles in amazonis planitia and elysium planitia show no sign of a detached mixed layer with an overlying inversion we supplemented the measurements with numerical simulations by the nasa ames mars general circulation model which demonstrate that water ice clouds can generate this distinctive type of temperature structure through their influence on radiative transfer at infrared wavelengths in particular the simulations predict the presence of a nocturnal cloud layer in the tharsis region at a pressure of 150 pa 10 km above the surface and the nighttime radiative cooling at cloud level is sufficient to produce a temperature inversion above the cloud as well as convective instability below the cloud consistent with the observations the second set of measurements sounded mid to high northern latitudes in spring when carefully coordinated observations by the mro mars climate sounder mcs are also available the differences between the ro and mcs temperature profiles are generally consistent with the expected performance of the two instruments within this set of 21 comparisons the average temperature difference is less than 1 k where the aerosol opacities are smaller than 10 3 km 1 at pressures of 10 50 pa whereas it increases to 2 k where the aerosol opacities exceed this threshold at pressures of 50 300 pa the standard deviation of the temperature difference is 2 k independent of pressure the second set of ro measurements also provides unique information about the stability of the annual co 2 cycle and the dynamics near the edge of the seasonal co 2 ice cap

structure and dynamics of the convective boundary layer on mars as inferred from large eddy simulations and remote sensing measurements the structure of the martian convective boundary layer bl is decribed by means of a novel approach involving both modelling and data analysis mars express radio occultation ro temperature profiles are compared to large eddy simulations less performed with the martian mesoscale model the model combines the martian radiative transfer soil and surface layer schemes designed at laboratoire de meteorologie dynamique lmd with the most recent version of the weather research and forecast wrf fully compressible non hydrostatic dynamical core the key roles of the vertical resolution and to lesser extent of the domain horizontal extent have been investigated to ensure the robustness of the les results the dramatic regional variations of the bl depth are quantitatively reproduced by the martian les intense bl dynamics are found to underlie the measured depths up to 9 km vertical speed up to 20 m s 1 heat flux up to 2 7 k m s 1 and turbulent kinetic energy up to 26 m2 s 2 under specific conditions both the model and the measurements show a distinctive positive correlation between surface topography and bl depth our interpretation is that in the tenuous co2 martian near surface environment the daytime bl is to first order controlled by the infrared radiative heating fairly independent of elevation which implies a simple correlation between the bl potential temperature and the inverse pressure pressure effect no prominent pressure effect is in action on earth where sensible heat flux dominates the bl energy budget both ro observations and numerical simulations confirm the terrain following behaviour of near surface temperature on mars induced by the dominant radiative influence the contribution of the martian sensible heat flux is not negligible and results in a given isotherm in the bl being comparatively closer to the ground at higher surface elevation the strong radiative control of the martian convective bl implies a generalised formulation for the bl dimensionless quantities based on this formulation and the variety of simulated bl depths by the les new similarity relationships for the martian convective bl in quasi steady midday conditions are derived rigorous comparisons between the martian and terrestrial bl and fast computations of the mean martian bl turbulent statistics are now made possible by such similarity laws copyright 2010 royal meteorological society

dust devil track survey at elysium planitia mars implications for the insight landing sites abstract the insight interior exploration using seismic investigations geodesy and heat transport robotic lander is scheduled to land in elysium planitia on mars in september 2016 insight will perform the first comprehensive surface based geophysical investigation including seismic measurements knowledge about encounter rates of dust devils with the insight lander are important for two main reasons 1 dust devils will affect the scientific measurements i e wind induced seismic noise and 2 the power supply of the insight lander and instruments is provided by solar arrays and previous landers and rovers on mars were affected by a steady decline in electrical power output due to atmospheric dust deposition on the solar panels long term science operations were only made possible by dust clearing events of the solar arrays caused by wind gusts and dust devils in this study we analyzed dust devil tracks ddts at the final insight landing site region in elysium planitia formation of ddts is caused by the removal of a layer of dust by passing dust devils hence in principle the same process as clearing of dust from solar panels we mapped the number size width and length and orientation of ddts in repeat observations using high resolution imaging science experiment hirise images covering the exact same surface area acquired within a relatively short time span l s 200 consistent with the seasonal reversal in direction of the hadley circulation ddt formation rates vary between 0 002 and 0 08 ddt km 2 sol 1 ddt area formation rates using the measured ddt widths lengths and formation rates are in the range of 0 0003 0 00006 km 2 km 2 sol 1 implying that a given spot on the surface may be cleared of dust only once between 3000 and 16 000 sols i e every 5 24 mars years measured ddt formation rates were used to find a scaling factor to the seasonal dda index and then integrated over the year to estimate a mean annual ddt formation rate of 0 046 ddt km 2 sol 1 this translates into a solar panel clearing recurrence interval estimate of 11 mars years using the mean annual ddt formation rate and the mean ddt width and length from all measured ddts due to several uncertainties this solar panel clearing recurrence interval for the insight landing should be seen as an upper limit estimate

decadal scale coastal cliff retreat in southern and central california abstract airborne lidar data collected in 1998 and 2009 2010 were used to measure coastal cliff erosion and retreat between the mexico california border and bodega head california cliff erosion was detected along 44 of the 595 km of shoreline evaluated while the remaining cliffs were relatively stable the mean cliff top retreat rate was 0 12 m yr while mean retreat averaged over the entire cliff face was 0 04 m yr the maximum cliff top and face retreat rates were 4 2 and 3 8 m yr respectively historical 1930s to 1998 and recent retreat rates were significantly inversely correlated for areas with large historical or recent cliff retreat such that locations with elevated historical retreat had low levels of recent retreat and locations with elevated recent retreat were preceded by low rates of historical retreat the strength of this inverse correlation increased with cliff change magnitudes up to r2 of 0 91 for cliff top retreat rates 2 9 m yr mean recent retreat rates were 52 83 lower than mean historical retreat rates although beaches can protect cliffs against wave driven erosion cliffs fronted by beaches retreated 49 more than cliffs without beaches on average unarmored cliff faces retreated 0 05 m yr between 1998 and 2009 2010 about three times faster than artificially armored cliffs alongshore metrics of wave cliff impact precipitation and cliff hardness were generally not well correlated with recent cliff changes a cliff hazard metric is used to detect cliff steepening and areas prone to future cliff top failures

alongshore variability in wave energy transfer to coastal cliffs abstract the alongshore distribution of wave energy is believed to be an important control on the spatial variability of coastal erosion there is however a lack of field data quantifying the alongshore variability in wave energy on rock coasts whereby the relative control of coastline geometry versus foreshore characteristics on wave energy delivery remains unclear a number of studies have identified high frequency cliff top ground shaking to be generated by wave impacts at the cliff toe during high tides ht to capture the variability of wave cliff impact energy along coast we installed an array of cliff top seismometers along a 1 km stretch of coastline in north yorkshire uk our aim is to constrain how wave energy transfer to the cliff toe varies and to examine the relative energy transfer around typical coastline features including a bay and headlands whilst the greatest ht ground motion energy is recorded at a headland and the lowest at the centre of the bay 5 of that observed at the headland we identify no systematic alongshore variation in the ht ground motion energy that can be related to coastline morphology we also note considerable variation between features of similar form the total ht ground motion energy at one headland is only 49 of the next headland 1 km alongshore between neighbouring sites within the bay separated by only 100 m we observe up to an order of magnitude difference in ground motion energy transfer our results demonstrate the importance of the foreshore in driving the variations in energy delivery that we observe local alterations in water depth and foreshore topography control the alongshore distribution of wave energy available to generate cliff ht ground motions importantly this apparently local effect overrides the influence of macroscale coastal planform morphology which has previously been assumed to be the dominant control the results show that foreshore characteristics that hold influence over wave energy transfer vary significantly over short 100 m distances and so we expect erosion controlled by wave impacts to vary over similar scales

coastline retreat via progressive failure of rocky coastal cliffs despite much research on the myriad processes that erode rocky coastal cliffs accurately predicting the nature location and timing of coastline retreat remains challenging and is confounded by the apparently episodic nature of cliff failure the dominant drivers of coastal erosion marine and subaerial forcing are anticipated to increase in the future so understanding their present and combined efficacy is fundamental to improving predictions of coastline retreat we captured change using repeat laser scanning across 2 7 104 m2 of near vertical rock cliffs on the uk north sea coast over 7 yr to determine the controls on the rates patterns and mechanisms of erosion for the first time we document that progressive upward propagation of failure dictates the mode and defines the rate at which marine erosion of the toe can accrue retreat of coastline above this is a failure mechanism not conventionally considered in cliff stability models propagation of instability and failure operates at these sites at 10 yr time scales and is moderated by local rock mass strength and the time dependence of rock fracture we suggest that once initiated failure propagation can operate ostensibly independently to external environmental forcing and so may not be tightly coupled to prevailing subaerial and oceanographic conditions our observations apply to coasts of both uniform and complex lithology where failure geometry is defined by rock mass strength and structure and not intact rock strength alone and where retreat occurs via any mode other than full cliff collapse

the martian daytime convective boundary layer results from radio occultation measurements and a mesoscale model abstract we investigate the behavior of the martian daytime convective boundary layer cbl through a combination of data analysis and modeling this study relies on two subsets of mars express radio occultation ro measurements that sounded the atmosphere in northern spring of successive mars years only the first year of observations has been examined previously hinson et al 2008 the second year provides complementary spatial coverage and greatly increases the total number of observations analysis of the ro profiles yields basic characteristics of the cbl such as its depth d and the average potential temperature of the mixed layer m we also combine ro retrievals of surface pressure with surface temperatures from infrared sounding to characterize the surface forcing expressing the result as a potential temperature s these observations are at local times in early afternoon for s and late afternoon for m and d when each parameter is near its diurnal maximum we use measurements at mid to low latitudes which sample a wide range of s 227 294 k to determine the response of the lower atmosphere to spatial variations in surface forcing the depth of the cbl ranges from less than 3 km in the midlatitude topographic basins to more than 9 km above elevated terrain in the tropics the dependence of m on s is linear with a characteristic slope of about 0 7 in both years we gain further insight by performing a simulation with the oregon state university mars mesoscale model in a region centered on isidis planitia which includes two potential landing sites for the mars 2020 rover as expected from previous modeling of much smaller craters the arc of steep topography along the western and southern margins of isidis produces a distinctive diurnally varying mesoscale circulation the simulation captures key features of the observations such as the wide variations in m and d by 34 k and 9 km respectively that occur within this region the model also accounts for peculiar features of ro profiles on the rim of isidis where the wind field strongly influences the depth and diurnal evolution of the cbl detailed comparisons with the observations validate the general performance of the model and confirm several aspects of the simulated wind field

a new process response coastal recession model of soft rock cliffs abstract the development of cliff erosion predictive models is limited by the complex interactions between environmental processes and material properties over a range of temporal and spatial scales current models incorporate a stochastic representation of cliff behavior based on assumptions regarding the magnitude and frequency of events in a probabilistic framework the new model presented here has been developed to incorporate the behavioral and mechanical characteristics of coastal cliffs which are dominated geologically by overconsolidated clays tills and an associated protective colluvial wedge this model is capable of providing precise and stable responses to some of the inherent uncertainties in cliff recession processes including those caused by different failure mechanisms e g colluvium generation groundwater and erosive tidal cycles material strength is incorporated using the unconfined compressive strength of the material that composes the cliff unlike previous models a calibration parameter is restricted to account for uncertainties linked to marine processes the mechanisms of cliffline retreat have been identified as slump and topple landslides once cliff material has fallen colluvium formation at the cliff foot is incorporated into the model using three different procedures according to the geomechanical characteristics of the debris the model is validated through profile evolution assessment at various locations of coastline retreat on the holderness coast uk higher groundwater content also produces an increase in the number and size of the slope failures the results represent an important step forward in linking material properties to the processes of cliff recession

radio occultation measurements and mgcm simulations of kelvin waves on mars we have derived new results concerning thermal tides on mars from a combination of radio occultation measurements and numerical simulations by a mars general circulation model mgcm this investigation exploits a set of concurrent observations by mars express mex and mars global surveyor mgs in mid 2004 when the season on mars was midspring in the northern hemisphere the mex occultations sampled the atmosphere near the evening terminator at latitudes ranging from 54 n to 15 s the mgs occultations provided complementary coverage near the morning terminator at latitudes of 35 n and 71 s the geopotential field derived from these measurements contains distinctive modulation caused by solar asynchronous thermal tides through careful analysis of the combined observations we characterized two prominent wave modes obtaining direct solutions for some properties such as the amplitude and phase as well as constraints on others such as the period zonal wave number and meridional structure we supplemented these observations with mgcm simulations after evaluating the performance of the mgcm against the measurements we used the validated simulation to deduce the identity of the two tidal modes and to explore their behavior one mode is a semidiurnal kelvin wave with a zonal wave number of 2 sk2 while the other is a diurnal kelvin wave with a zonal wave number of 1 dk1 both modes are known to be close to resonance in the martian atmosphere our observations of the sk2 are more complete and less ambiguous than any previous measurement the well known dk1 is the dominant solar asynchronous tide in the martian atmosphere and our results confirm and extend previous observations by diverse instruments

retreat rates modalities and agents responsible for erosion along the coastal chalk cliffs of upper normandy the contribution of terrestrial laser scanning in order to follow all the changes affecting the coastal chalk cliff face in upper normandy and improve knowledge about cliff erosion repeated terrestrial laser scanning tls surveys were carried out frequently between 2010 and 2013 every 4 5 months they were conducted at two sites with similar lithostratigraphic characteristics but different exposures to marine actions the former being an abandoned cliff and the latter an active cliff they provide a quantification of the production of debris with centimeter precision from 0 01 to 0 04 m these surveys provided three major outcomes 1 cliff retreat rates were measured at high spatial resolution with retreat values unsurprisingly 3 4 times higher for an active cliff than for an abandoned cliff this result highlights that marine actions should be seen as not only a transport agent but also a particularly effective erosion agent 2 a significant proportion of debris fall production about 25 in the total active cliff retreat was identified and 3 one of the modalities of retreat was visualized as the creation of a basal notch which propagates instability towards the upper part of the cliff face later this instability generates rock falls coming from the whole cliff face

the depth of the convective boundary layer on mars abstract we are using observations obtained with mars express to explore the structure and dynamics of the martian lower atmosphere we consider a series of radio occultation experiments conducted in may august 2004 when the season on mars was midspring of the northern hemisphere the measurements are widely distributed in latitude and longitude but the local time remained within a narrow range 17 0 17 2 h most of the atmospheric profiles retrieved from these data contain a distinct well mixed convective boundary layer cbl we have accurately determined the depth of the cbl and its spatial variations at fixed local time through analysis of these profiles the cbl extends to a height of 3 10 km above the surface at the season and locations of these measurements its depth at fixed local time is clearly correlated with variations in surface elevation on planetary scales with a weaker dependence on spatial variations in surface temperature in general the cbl is deep 8 10 km where the surface elevation is high as in tharsis montes and syrtis major and shallow 4 6 km where the surface elevation is low as in amazonis and utopia this variability results from the combined effects of conditions near the surface and in the atmosphere above the cbl convection arises from solar heating of the ground and the impact of this heat source on thermal structure is largest where the surface pressure and atmospheric density are smallest at high surface elevations the vertical extent of the cbl is in turn constrained by the static stability of the overlying atmosphere these results greatly reduce the long standing uncertainty concerning the depth of the cbl

coastal knickpoints and the competition between fluvial and wave driven erosion on rocky coastlines abstract active margin coastlines are distinguished by rock erosion that acts in two different directions waves erode the coast horizontally or landwards a process that creates sea cliffs and rivers and streams erode the landscape vertically via channel incision the relative rates of each process exert a dominant control on coastline morphology using a model of river channel incision and sea cliff retreat we explore how terrestrial and marine erosion compete to shape coastal topography and specifically what conditions encourage the development of coastal knickpoints i e a river or stream channels that end at a raised sea cliff edge we then compare results to actual landscapes model results and observations show that coastal knickpoint development is strongly dependent on drainage basin area where knickpoints typically occur in drainage basins smaller than 5 105 6 106 m2 as well as channel geometry and sea cliff retreat rate in our study area coastal knickpoints with persistent flow waterfalls are uncommon and form only within a small morphological window when 1 drainage basin area is large enough to sustain steady stream discharge but not large enough to out compete sea cliff formation 2 sea cliff retreat is rapid and 3 channel concavity is low so that channel slopes at the coast are high this particular geomorphic combination can sustain sea cliff formation even when streams tap into larger drainage basins with greater discharge and more stream power and provides an initial explanation of why persistent coastal waterfalls are along many coastlines relatively rare features

sea stack formation and the role of abrasion on beach mantled headlands sea stacks are common and striking coastal landforms but few details are known about how how quickly and under what conditions they form we present numerical and analytical models of sea stack formation due to preferential erosion along a pre existing headland to address these basic questions on sediment rich rocky coasts as sea cliffs erode and retreat they produce beach sediment that is distributed by alongshore sediment transport and controls future sea cliff retreat rates depending on their width beaches can encourage or discourage sea cliff erosion by acting either as an abrasive tool or a protective cover that dissipates wave energy seaward of the cliff along the flanks of rocky headlands where pocket beaches are often curved and narrow due to wave field variability abrasion can accelerate alongshore directed sea cliff erosion eventually abrasion induced preferential erosion can cut a channel through a headland separating it from the mainland to become a sea stack under a symmetrical wave climate i e equal influence of waves approaching the coastline from the right and from the left numerical and analytical model results suggest that sea stack formation time and plan view size are proportional to preferential erosion intensity caused by for example abrasion and or local rock weakness from joints faults or fractures and initial headland aspect ratio and that sea stack formation is discouraged when the sediment input from sea cliff retreat is too high i e sea cliffs retreat quickly or are sand rich when initial headland aspect ratio is too small and the headland is rounded much wider in the alongshore direction at its base than at its seaward apex the headland is less conducive to sea stack formation on top of these geomorphic and morphologic controls a highly asymmetrical wave climate decreases sea stack size and discourages stack formation through rock sediment interactions copyright 2014 john wiley sons ltd

lithological controls on soft cliff planshape evolution under high and low sediment availability this paper addresses a series of geomorphic questions relating to large scale 1 km long term 100 1 000 years coastal planshape evolution previous research on soft cliff coasts has recognised the role of protective fronting beach volumes on reducing rates of cliff toe retreat however it is the maintenance of this critical threshold that ultimately determines two contrasting modes of shoreline behaviour mode a in which there is little beach sediment and shoreline evolution is controlled by material strength and mode b when ample beach sediment means that shoreline evolution is controlled by longshore sediment transport here we use a numerical model scape to investigate temporal and spatial changes in beach volume on a broader range of feedbacks than considered in previous models the transition between mode a and mode b coasts is defined by relative sediment inputs to outputs and used to explore how these contrasting modes control the evolution of an initial linear frontage exhibiting longshore changes in cliff lithology material resistance and the proportion of beach grade material in the eroded bedrock under mode a relative changes in material resistance result in long term heterogeneous rates of retreat which result in the development of persistent headland and embayment features however under mode b feedbacks between coastal planshape longshore sediment transport beach volume and wave energy result in steady state retreat rates regardless of longshore variations in resistance results are compared and contrasted to previous simulations and site specific examples and a conceptual model of mode a and mode b interactions presented copyright 2015 john wiley sons ltd

mars orbiter camera observations of martian dust devils and their tracks september 1997 to january 2006 and evaluation of theoretical vortex models 1 a multiyear planet wide survey of martian dust devils was conducted using observations from mars global surveyor mars orbiter camera acquired through 21 january 2006 a total of 223 350 images were surveyed and 11 456 dust devils were seen in 0 4 of the images 11 5 in the southern and 88 5 in the northern hemisphere dust devils were observed at latitudes from 71 9 s to 62 2 n over a range of surface albedos am 0 11 0 22 and elevations from hellas 8750 m to arsia mons 17 250 m the light and dark toned streaks created by dust devils were observed from 80 s to 80 n and changed on timescales as short as 1 month at mid to high latitudes seasonal changes in streak patterns contribute to the seasonal wave of darkening observed telescopically from earth dust devils were observed in all seasons in both hemispheres with the exception of ls 202 8 281 5 in the north peak activity occurred during midsummer in each hemisphere five regions in amazonis syria claritas meridiani and gusev were monitored regularly amazonis had the largest dust devils and was the most active planet wide with annual activity occurring from ls 8 5 197 interannual variability resulted from dust storms and planet encircling dust hazes which were observed to initiate and abate dust devil activity there was no evidence suggesting dust devils cause or lead to initiation of dust storms model derived tangential wind speeds of large vortices were 20 m s 1 at 20 m above the surface dust flux calculations suggest that dust devils are a contributor to the background dust opacity observed through northern spring and summer

an analysis of the effect of topography on the martian hadley cells previous work with mars general circulation models mgcms has shown that the north south slope in martian topography causes asymmetries in the hadley cells at equinox and in the annual average to quantitatively solve for the latitude of the dividing streamline and poleward boundaries of the cells the hadley cell model of lindzen and hou was modified to include topography the model was thermally forced by newtonian relaxation to an equilibrium temperature profile calculated with daily averaged solar forcing at constant season two sets of equilibrium temperatures were considered that either contained the effects of convection or did not when convective effects were allowed the presence of the slope component shifted the dividing streamline upslope qualitatively similar to a change in season in lindzen and hou s original flat model the modified model also confirmed that the geometrical effects of the slope are much smaller than the thermal effects of the slope on the radiative convective equilibrium temperature aloft the results are compared to a simple mgcm forced by newtonian relaxation to the same equilibrium temperature profiles and the two models agree except at the winter pole near solstice the simple mgcm results for radiative convective forcing also show an asymmetry between the strengths of the hadley cells at the northern summer and northern winter solstices the hadley cell weakens with increasing slope steepness at northern summer solstice but has little effect on the strength at northern winter solstice

simulation of surface meteorology at the pathfinder and vl1 sites using a mars mesoscale model 1 the fifth generation penn state ncar mesoscale model mm5 has been adapted to study circulations in the martian atmosphere the nasa ames mars general circulation model gcm provides initial and boundary conditions the meteorology of this mars mm5 the osu mmm5 is compared with pathfinder and viking lander 1 vl1 data for late northern summer the mmm5 uses an equator crossing semiglobal polar stereographic mother domain significantly reducing the boundary reflections inherent in martian mesoscale simulations using two way nests simultaneous simulations of two regions are performed 1 chryse planitia mars pathfinder mpf vl1 and 2 the central chasmas of valles marineris simulations are hydrostatic and dry the mmm5 uses the same atmospheric radiation package as the gcm but a much enhanced near surface vertical resolution and a different planetary boundary layer pbl scheme model topography thermal inertia and surface albedo maps have all been developed using the most recent data from the mars global surveyor mgs mars orbiter laser altimeter mola and thermal emission spectrometer tes experiments the diurnal cycles of surface air temperature surface pressure and surface wind all show improvement in comparison with the gcm for certain regions the local surface pressure tidal amplitudes are strongly dependent on the resolution of the model and or the topography vl1 and mpf are in such a region the diurnal cycles of wind are complex and for many locations the near surface winds are dominated by slope flows of multiple scales comparison with data indicates that resolving these slope flows is very important for simulating the diurnal wind cycle at specific locations these slope flows dramatically influence the diurnal surface pressure cycle

a sporadic third layer in the ionosphere of mars the daytime martian ionosphere has been observed as a two layer structure with electron densities that peak at altitudes between about 110 and 130 kilometers the mars express orbiter radio science experiment on the european mars express spacecraft observed in 10 out of 120 electron density profiles a third ionospheric layer at altitude ranges of 65 to 110 kilometers where electron densities on average peaked at 0 8 10 10 per cubic meter such a layer has been predicted to be permanent and continuous its origin has been attributed to ablation of meteors and charge exchange of magnesium and iron our observations imply that this layer is present sporadically and locally

active dust devils in gusev crater mars observations from the mars exploration rover spirit 1 a full dust devil season was observed from spirit from 10 march 2005 sol 421 first active dust devil observed to 12 december 2005 sol 691 last dust devil seen this corresponds to the period ls 173 2 to 339 5 or the southern spring and summer on mars thermal emission spectrometer data suggest a correlation between high surface temperatures and a positive thermal gradient with active dust devils in gusev and that spirit landed in the waning stages of a dust devil season as temperatures decreased 533 active dust devils were observed enabling new characterizations they ranged in diameter from 2 to 276 m with most in the range of 10 20 m in diameter and occurred from about 0930 to 1630 hours local true solar time with the maximum forming around 1300 hours and a peak occurrence in southern late spring ls 250 horizontal speeds of the dust devils ranged from 1 to 21 m s while vertical wind speeds within the dust devils ranged from 0 2 to 8 8 m s these data when combined with estimates of the dust content within the dust devils yield dust fluxes of 3 95 10 9 to 4 59 4 kg m2 s analysis of the dust devil frequency distribution over the inferred dust devil zone within gusev crater yields 50 active dust devils km2 sol suggesting a dust loading into the atmosphere of 19 kg km2 sol this value is less than one tenth the estimates by cantor et al 2001 for regional dust storms on mars

estuarine shore platforms in whanganui inlet south island new zealand abstract whanganui inlet is a low mesotidal environment where wave energy at the shoreline is limited due to a small fetch a narrow entrance and tidal flat accretion to intertidal elevations wave energy is therefore only an erosive force at high tide and under storm conditions despite this low energy environment extensive shore platforms occur within the inlet they are sub horizontal and range in width from 4 1 to 185 2 m with an average of 44 9 m all the platforms are formed in sandstone of low resistance mean n type schmidt hammer rebound value of 17 8 and have their seaward edges buried by intertidal sediment flats the majority of platforms occur at around mhwn level corresponding to the elevation of those flats where wave energy is highest opposite the inlet s entrance and at those sites with the largest fetch platforms develop to 0 5 1 0 m below msl a higher platform level is also found at mhws elevations however it appears to be relict with active erosion of its seaward edge occurring and therefore is most likely related to a higher mid holocene sea level apart from the location of the lowest platforms little correspondence is found between platform morphology and wave energy platform evolution appears to be intrinsically linked to the intertidal sediment flats which determine the degree of surface saturation of the bedrock and hence the number of wetting and drying cycles the platforms may undergo as the seaward edge is buried platform development is primarily through retreat of the landward cliff this process can however be complicated by the migration of intertidal water channels onto the seaward edge of the platforms or relative sea level fall which may rejuvenate landward retreat of the low tide cliff

high resolution thermal inertia mapping of mars sites of exobiological interest we have mapped thermal inertia at high resolution for selected regions of mars that are of potential biological relevance using observations made by the mars global surveyor thermal emission spectrometer thermal inertia is a direct indicator of physical properties of the surface at the decimeter to meter scale our goal is to understand the geological processes by which the sites formed and their subsequent evolution their current state and their safety and science potential as landing sites for future lander rover and sample return spacecraft missions the thermal inertia values at 3 km scale for the sites considered span the entire range of values measured at mars thermal inertias range from low values indicative of substantial aeolian mantling up to high values suggesting surfaces covered predominantly with bedrock exposed rocks or blocks or well indurated crusts the highest thermal inertias correlate strongly with local morphology while areas with intermediate and low thermal inertias generally show no such correlation this suggests that selection of future landing sites will be plagued by a choice of a well mantled site that is safe but less interesting scientifically versus an unmantled site that is more interesting scientifically but less safe

beach and sea cliff dynamics as a driver of long term rocky coastline evolution and stability we investigate rocky coastline evolution over millennial time scales using exploratory analytical and numerical models based on interactions between beaches and sea cliffs in the models wave driven sea cliff retreat is a nonlinear function of beach width where cliff retreat is maximized by sediment abrasion and minimized by either a lack of beach sediment or too much sediment which prevents waves from reaching the sea cliff as sea cliffs retreat beach sediment is produced and distributed alongshore by wave driven sediment transport and local beach widths determine future cliff retreat rates numerical experiments indicate that through such interactions rocky coastlines can reach an equilibrium configuration where headlands and embayments remain stable through time even in the absence of alongshore variations in sea cliff lithology furthermore the equilibrium coastline configuration or the alongshore proportion of rocky headland to cliff backed pocket beach can be predicted analytically initial tests suggest that predictions match well qualitatively with actual landscapes

recent acceleration in coastal cliff retreat rates on the south coast of great britain rising sea levels and increased storminess are expected to accelerate the erosion of soft cliff coastlines threatening coastal infrastructure and livelihoods to develop predictive models of future coastal change we need fundamentally to know how rapidly coasts have been eroding in the past and to understand the driving mechanisms of coastal change direct observations of cliff retreat rarely extend beyond 150 y during which humans have significantly modified the coastal system cliff retreat rates are unknown in prior centuries and millennia in this study we derived retreat rates of chalk cliffs on the south coast of great britain over millennial time scales by coupling high precision cosmogenic radionuclide geochronology and rigorous numerical modeling measured 10be concentrations on rocky coastal platforms were compared with simulations of coastal evolution using a monte carlo approach to determine the most likely history of cliff retreat the 10be concentrations are consistent with retreat rates of chalk cliffs that were relatively slow 2 6 cm y 1 until a few hundred years ago historical observations reveal that retreat rates have subsequently accelerated by an order of magnitude 22 32 cm y 1 we suggest that acceleration is the result of thinning of cliff front beaches exacerbated by regional storminess and anthropogenic modification of the coast

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

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

mars pathfinder convective vortices frequency of occurrence 1 the frequency of occurrence of small scale convective vortices at the mars pathfinder lander location exhibits a diurnal variation similar to terrestrial dust devil observations the 79 vortices detected via their pressure signatures during the 83 sol mission when combined with an assessment of the incompleteness of data temporal coverage implies that at least two vortices passed by the lander site each sol if the vortices are dust laden as inferred from lander imaging then the observed vortex frequency is capable of maintaining the observed atmospheric dust load against sedimentation loss the time of sol variation in vortex occurrence provided by pathfinder when combined with orbiter imaging of dust devils at a very limited time of sol offers a potential means of quantifying the effect of these small scale vortices upon the atmospheric dust cycle

dust devils on mars observed by the high resolution stereo camera fourteen active dust devils were observed by the high resolution stereo camera hrsc on mars express which enable the first analysis of the forward speed of dust devils on mars determined from orbit results show speeds on the order of 20 m s which compares favorably with values of the wind profiles estimated from the martian climate database for higher altitudes smaller dust devils of 1 km height and very small diameters were found moving only at 1 5 to 6 0 m s in agreement with surface wind speeds

the mars regional atmospheric modeling system model description and selected simulations the mars regional atmospheric modeling system mrams is introduced and selected model results are presented and compared with landed meteorological data when possible mrams is descended from a nonhydrostatic earth mesoscale and cloud scale model that is widely used for forecasting weather and simulating atmospheric systems over complex terrain mesoscale models such as mrams are ideal tools for making use of the high resolution data sets arriving from mars global surveyor experiments simulation of the mars pathfinder mpf landing site at lsd 142 using 1 2 degree mars orbiter laser altimeter mola derived topography and thermal emission spectrometer thermal inertia is shown to be in good agreement with observed near surface temperature pressure and wind direction simulations of topographically induced thermal circulations and mountain induced gravity waves are shown to be consistent with theory and earlier studies that tie large amplitude mountain waves to strong winds capable of producing dust streaks and local dust lifting events a large eddy simulation of the convective boundary layer provides estimates of vertical profiles of heat flux momentum flux turbulent kinetic energy and vertical velocity variance the model results suggest that the martian atmosphere is roughly two to three times more turbulent than the terrestrial atmosphere during the afternoon but fluxes are roughly an order of magnitude smaller due to the lower density dust devillike circulations are also predicted in the large eddy simulation finally a simulation that examines atmosphere surface interactions near big crater is discussed predicted surface wind stress patterns are consistent with aeolian processes inferred through mars orbiter camera imagery of big crater located near the mpf landing site c 2001 academic press

martian and terrestrial dust devils test of a scaling theory using pathfinder data the mars pathfinder meteorological station recorded wind pressure and temperature fluctuations that have been interpreted as dust devils warm core vortices that form at the bottom of connective plumes we apply a scaling theory renno et al 1998 developed to explain terrestrial dust devil observations to test the validity of this interpretation and to provide a simple physical interpretation of the general characteristics of martian dust devils the theory is based on the thermodynamics of heat engines and predicts the central pressure and the wind speed of the connective vortices our findings are as follows for the best documented candidate event sol 25 observed wind and pressure fluctuations are consistent with those predicted by the model and hence strengthen the interpretation of this case as a dust devil a number of other candidates less well documented however also are consistent with passage of a dust devil over or near the lander temperature fluctuations observed on other sols permit dust devils an order of magnitude larger than the ones measured by the meteorology package the strongest dust devils predicted by our theory have a central pressure deficit of about 50 pa and wind speed of about 60 m s 1 the strongest dust devils are capable of lofting dust and hence support the interpretation of selected pathfinder images as showing the passage of dust devils within sight of the lander

thermal structure of the atmospheric boundary layer on mars based on mini tes observations this paper presents and discusses the vertical profiles of the potential temperature in the martian boundary layer the profiles were remotely sensed from on board the spirit mars exploration rover during the first 702 sols of its operation in 2004 2005 the rover carried the miniature thermal emission spectrometer mini tes which allowed it to retrieve temperature profiles up to a level 2 km above the ground surface the data analyzed here permit a reconstruction of the diurnal and seasonal structure of the lower part of the martian convective boundary layer an evaluation of the boundary layer depth and a computation of the temperature heat flux

the opportunity rover s athena science investigation at meridiani planum mars the mars exploration rover opportunity has investigated the landing site in eagle crater and the nearby plains within meridiani planum the soils consist of fine grained basaltic sand and a surface lag of hematite rich spherules spherule fragments and other granules wind ripples are common underlying the thin soil layer and exposed within small impact craters and troughs are flat lying sedimentary rocks these rocks are finely laminated are rich in sulfur and contain abundant sulfate salts small scale cross lamination in some locations provides evidence for deposition in flowing liquid water we interpret the rocks to be a mixture of chemical and siliciclastic sediments formed by episodic inundation by shallow surface water followed by evaporation exposure and desiccation hematite rich spherules are embedded in the rock and eroding from them we interpret these spherules to be concretions formed by postdepositional diagenesis again involving liquid water

pressure wave generated by the mount st helens eruption histories of the air pressure wave radiated from the eruption of mount st helens on may 18 1980 were calculated for two models of the eruption cloud expansion the first considered the wave radiated from an accelerated plane surface while the second examined the wave radiated from an expanding hemisphere two histories of eruption cloud motion based on photographs were used peak positive overpressures were about the same for these cloud motion histories of expansion into a hemisphere was assumed if an accelerated planar source model was used the peak positive pressures have again about the same value in east and west direction but values are about half in the north and south direction observed peak overpressures at microbarograph stations are somewhat higher than the calculated with the most marked departures at the greater surface ranges these observed overpressures may have been about half the correct values however microbarograph records show a weaker rarefaction than calculated histories or none at all this can be explained in part by a lack of areal motion coherence in the slowing eruption cloud it is also possible the net ash cloud volume increased considerably after its vertical growth ceased and weakened the negative phase as well as lengthening the positive phase

the unsteady nature of sea cliff retreat due to mechanical abrasion failure and comminution feedbacks sea cliff retreat is often linked to large waves heavy precipitation and seismic events but the specific operative mechanics have not been well constrained in particular what is the role of mechanical abrasion by beach sediments in cliff platform evolution and how does it relate to the episodic nature of cliff retreat observed at certain locations here we present a simple numerical model of sea cliff retreat that incorporates mechanical abrasion of a basal notch threshold controlled failure of the cantilevered block and a feedback mechanism wherein retreat is dependent on the rate of sediment comminution within the surf zone using shore platform and cliff characteristics found in two coastal settings the central california coast and the english north sea coast the model produces retreat rates comparable to those observed via field measurements the highest retreat rates coincide with the steepest shore platforms and increasing wave height steeper platforms promote wave access to the cliff toe and correspondingly the receding cliff face produces additional accommodation space for the platform beach preserving the erosive efficacy of the beach sediments when exposed to energetic wave forcing the slope of the inner platform segment controls retreat rates for concave platforms whereas the slope of the outer platform segment exerts greater control for convex platforms platform beaches approached a long term dynamic equilibrium on the concave profiles leading to more consistent and steady retreat platform beaches were ephemeral on convex profiles mirroring observed sand wave ord migration on the holderness coast uk these findings agree with previous field observations and support mechanical abrasion as a viable cause of temporal heterogeneity in cliff retreat rate for both coastlines

the spirit rover s athena science investigation at gusev crater mars the mars exploration rover spirit and its athena science payload have been used to investigate a landing site in gusev crater gusev is hypothesized to be the site of a former lake but no clear evidence for lacustrine sedimentation has been found to date instead the dominant lithology is basalt and the dominant geologic processes are impact events and eolian transport many rocks exhibit coatings and other characteristics that may be evidence for minor aqueous alteration any lacustrine sediments that may exist at this location within gusev apparently have been buried by lavas that have undergone subsequent impact disruption

a multiannual record of gravity wave activity in mars s lower atmosphere from on planet observations by the mars climate sounder abstract gravity waves in mars s atmosphere strongly affect the general circulation as well as middle atmospheric cloud formation but the climatology and sources of gravity waves in the lower atmosphere remain poorly understood at earth the statistical variance in satellite observations of thermal emission above the instrumental noise floor has been used to enable measurement of gravity wave activity at a global scale here is presented an analysis of variance in calibrated radiance at 15 4 m 635 665 cm 1 from off nadir and nadir observations by the mars climate sounder mcs on board mars reconnaissance orbiter mro a major expansion in the observational data available for validating models of martian gravity wave activity these observations are sensitive to gravity waves at 20 30 km altitude with wavelength properties h 10 100 km z 5 km that make them likely to affect the dynamics of the middle and upper atmosphere we find that 1 strong moderately intermittent gravity wave activity is scattered over the tropical volcanoes and throughout the middle to high latitudes of both hemispheres during fall and winter 2 gravity wave activity noticeably departs from climatology during regional and global dust storms and 3 strong intermittent variance is observed at night in parts of the southern tropics during its fall winter but frequent co 2 ice clouds prevents unambiguous attribution to gw activity the spatial distribution of wave activity is consistent with topographic sources being dominant but contributions from boundary layer convection and other convective processes are possible

shore platform development around lord howe island southwest pacific this paper describes the morphology of near horizontal basalt and calcarenite shore platforms around lord howe island as well as the lithological and process environment in which they occur the morphology of platforms around the island is highly varied for instance they occur at a wide range of elevations between low tide level and several metres above the highest tides and their width ranges between just a few metres to over 100 m however common to most platforms is that they have near horizontal surfaces that terminate abruptly in a steep scarp at their seaward edge correlations indicate that the variability in platform elevation and width is attributable to variability in key parameters of erosion such as rock resistance and shoreline water depth whereas wider platforms occur in rocks of lesser resistance platform elevation is shown to increase both as rock resistance and the depth of water at the shoreline increases wave exposure has a significant control on platform width in some instances but an over arching relationship was not detected most platforms around the island appear to have developed over the holocene and a conceptual model is proposed to account for the varied morphology of platforms that have developed over this period resistant plunging cliffs occur along about 18 of the rocky coastline of lord howe island and represent the starting point for the model where cliffs have yielded to wave erosion platforms have been initiated at an elevation controlled predominantly by rock resistance and shoreline water depth at lord howe island narrow platforms up to about 20 m wide in exposed locations generally occur about 4 to 6 m above high tide level and have apparently been subject to very infrequent erosion shore platforms about 20 to 40 m wide have generally formed in less resistant rocks are somewhat lower at about 2 to 3 m above high tide level and have been subject to more frequent erosion over the holocene most basalt platforms around the island fall within these first two categories but there are some instances of platforms about 50 m wide these platforms have formed in rocks of comparatively low resistance and are relatively low in elevation occurring close to the level of high tide an interesting feature of some of these wide platforms is that unlike the morphology of narrower platforms raised ramparts sometimes occur on their outer edge

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

traveling waves in the martian atmosphere from mgs tes nadir data abstract we have characterized the annual behavior of martian atmospheric traveling waves in the mgs tes data set from the first two martian years of mapping there is a high degree of repeatability between the two years they are dominated by strong low zonal wavenumber waves with high amplitudes near the polar jets strongest in late northern fall and early northern winter the m 1 waves have amplitudes up to about 20 k are vertically extended and occasionally extend even into the tropics periods for m 1 range from 2 5 to 30 sols much weaker waves were identified in the south with amplitudes less than about 3 5 k traveling waves with m 2 and m 3 are also seen but their amplitudes are typically limited to less than 4 k and are generally more confined near the surface in the north they are more evident in fall and spring rather than winter solstice which is clearly dominated by m 1 waves some evidence of storm tracks has been identified in the data with accentuated weather related temperature perturbations near longitudes 200 to 320 e for both the southern and northern hemispheres near latitude 65 at the surface some evidence was also found for a sharpening of longitudinal gradients into what may be frontal systems ep flux divergences show the waves extracting energy from the zonal mean winds when the m 1 waves were strongest decelerations of the zonal jet of order 30 m s sol were measured above 1 scale height the waves extract energy from the jet predominately through barotropic processes but their character is overall mixed barotropic baroclinic inertial instabilities may exist at altitude on the equatorward flanks of the polar jets and marginal stability extends through to the tropics this may explain the coordination of the tropical behavior of the waves with that centered along the polar jet consistent with the ideas expressed in wilson et al 2002 geophys res lett 29 1684 and similar to those in barnes et al 1993 j geophys res 98 3125 3148 throughout the year there exist large regions with the meridional gradient of pv less than zero but they are strongest near winter solstice poleward of the winter jet the regions of instability reach the surface equatorward they do not these regions satisfying a necessary criterion for instability likely explain the genesis of the waves and perhaps also their bimodal character between surface faster waves and altitude slow m 1 waves

planetary boundary layer and slope winds on venus few constraints are available to characterize the deep atmosphere of venus though this region is crucial to understand the interactions between surface and atmosphere on venus based on simulations performed with the ipsl venus global climate model the possible structure and characteristics of venus planetary boundary layer pbl are investigated the vertical profile of the potential temperature in the deepest 10 km above the surface and its diurnal variations are controlled by radiative and dynamical processes the model predicts a diurnal cycle for the pbl activity with a stable nocturnal pbl while convective activity develops during daytime the diurnal convective pbl is strongly correlated with surface solar flux and is maximum around noon and in low latitude regions it typically reaches less than 2 km above the surface but its vertical extension is much higher over high elevations and more precisely over the western flanks of elevated terrains this correlation is explained by the impact of surface winds which undergo a diurnal cycle with downward katabatic winds at night and upward anabatic winds during the day along the slopes of high elevation terrains the convergence of these daytime anabatic winds induces upward vertical winds that are responsible for the correlation between height of the convective boundary layer and topography

sea cliff retreat and shore platform widening steady state equilibrium we challenge the notion of steady state equilibrium in the context of progressive cliff retreat on micro tidal coasts ocean waves break at or close to the abrupt seaward edge of near horizontal shore platforms and then rapidly lose height due to turbulence and friction conceptual models assume that wave height decays exponentially with distance from the platform edge and that the platform edge does not erode under stable sea level these assumptions combine to a steady state view of holocene cliff retreat we argue that this model is not generally applicable recent data show that 1 exponential decay in wave height is not the most appropriate conceptual model of wave decay 2 by solely considering wave energy at gravity wave frequencies the steady state model neglects a possible formative role for infragravity waves here we draw attention to possible mechanisms through which infragravity waves may drive cliff retreat over much greater distances and longer timescales than imaginable under the established conceptual model copyright 2013 john wiley sons ltd

impact of gravity waves on the middle atmosphere of mars a non orographic gravity wave parameterization based on global climate modeling and mcs observations the impact of gravity waves gw on diurnal tides and the global circulation in the middle upper atmosphere of mars is investigated using a general circulation model gcm we have implemented a stochastic parameterization of non orographic gw into the laboratoire de meteorologie dynamique lmd mars gcm lmd mgcm following an innovative approach the source is assumed to be located above typical convective cells urn x wiley jgre media jgre21298 jgre21298 math 0001250 pa and the effect of gw on the circulation and predicted thermal structure above 1 pa urn x wiley jgre media jgre21298 jgre21298 math 000250 km is analyzed we focus on the comparison between model simulations and observations by the mars climate sounder mcs on board mars reconnaissance orbiter during martian year 29 mcs data provide the only systematic measurements of the martian mesosphere up to 80 km to date the primary effect of gw is to damp the thermal tides by reducing the diurnal oscillation of the meridional and zonal winds the gw drag reaches magnitudes of the order of 1 m s sol above 10 urn x wiley jgre media jgre21298 jgre21298 math 0003 pa in the northern hemisphere winter solstice and produces major changes in the zonal wind field from tens to hundreds of m s while the impact on the temperature field is relatively moderate 10 20 k it suggests that gw induced alteration of the meridional flow is the main responsible for the simulated temperature variation the results also show that with the gw scheme included the maximum day night temperature difference due to the diurnal tide is around 10 k and the peak of the tide is shifted toward lower altitudes in better agreement with mcs observations

equilibrium responses of cliffed coasts to changes in the rate of sea level rise abstract basic formulae have long been used to predict the effects of sea level rise on coastal recession for instance the geometric bruun rule and its modifications has often been applied to sandy coasts both low lying and steep however the behavior of rocky coasts whether strongly or poorly lithified should be significantly different than that of sandy coasts given that rocky coast evolution depends upon the irreversible breakdown of rock whereas sandy and depositional systems are controlled by the transport and related transport gradients of mobile sediment here we investigate the basis of a modeled relationship which suggests with a number of caveats that the equilibrium soft rock cliff recession rate can be estimated by the square root of the relative change in sea level rise rate although this relationship was derived using the numerical model scape soft cliff and platform erosion which simulates a broad soft rock cliffed coastal system driven by stochastic environmental forces here we show that a simplified modeling approach also reproduces the relationship we then extend this approach to develop a general theoretical framework within which it is possible to consider the potential responses of the different types of cliffed coasts to changes in the rate of sea level rise although a wide variety of processes affect different coastal settings this framework demonstrates how the strength and the nature of feedbacks within cliffed system control their response to sea level rise this suggests that cliffed environments controlled by different processes can still respond in similar ways to changes in the rate of sea level rise most rocky coasts would be expected to respond as a damped or negative feedback system between the extremes of a no feedback system that is unresponsive to sea level rise rate and an instant response system characterized by a linear response similar to the bruun rule this framework suggests that a potential inverse feedback case could also exist in which increased rates of sea level rise reduce the rate of coastal recession in almost all cases it is apparent that cliffed coast response to sea level rise depends not only upon the total elevation change of sea level but on the rate of the sea level rise these theoretical investigations and the classifications presented provide a framework to understand the behavior of systems affected by a wide array of processes and provide expectations that can be tested using more complex models of cliffed coast evolution in a variety of environments whether sandy or rocky hard or soft

simulation of the atmospheric thermal circulation of a martian volcano using a mesoscale numerical model mesoscale 100 km atmospheric phenomena are ubiquitous on mars as revealed by mars orbiter camera images numerical models provide an important means of investigating martian atmospheric dynamics for which data availability is limited but the resolution of general circulation models which are traditionally used for such research is not sufficient to resolve mesoscale phenomena to provide better understanding of these relatively small scale phenomena mesoscale models have recently been introduced here we simulate the mesoscale spiral dust cloud observed over the caldera of the volcano arsia mons by using the mars regional atmospheric modelling system our simulation uses a hierarchy of nested models with grid sizes ranging from 240 km to 3 km and reveals that the dust cloud is an indicator of a greater but optically thin thermal circulation that reaches heights of up to 30 km and transports dust horizontally over thousands of kilometres

dust devils on mars columnar cone shaped and funnel shaped clouds rising 1 to 6 kilometers above the surface of mars have been identified in viking orbiter images they are interpreted as dust devils confirming predictions of their occurrence on mars and giving evidence of a specific form of dust entrainment

the global topography of mars and implications for surface evolution elevations measured by the mars orbiter laser altimeter have yielded a high accuracy global map of the topography of mars dominant features include the low northern hemisphere the tharsis province and the hellas impact basin the northern hemisphere depression is primarily a long wavelength effect that has been shaped by an internal mechanism the topography of tharsis consists of two broad rises material excavated from hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary the present topography has three major drainage centers with the northern lowlands being the largest the two polar cap volumes yield an upper limit of the present surface water inventory of 3 2 to 4 7 million cubic kilometers

initial results from radio occultation measurements with mars global surveyor a series of radio occultation experiments conducted with mars global surveyor in early 1998 has yielded 88 vertical profiles of the neutral atmosphere the measurements cover latitudes of 29 n to 64 s and local times from 0600 through midnight to 1800 during early summer in the southern hemisphere ls 264 308 retrieved profiles of pressure and temperature versus radius and geopotential extend from the surface to the 10 pa pressure level near surface uncertainties in temperature and pressure are about 1 k and 2 pa respectively far smaller than in previous radio occultation measurements at mars the profiles resolve the radiative convective boundary layer adjacent to the surface and also reveal gravity waves particularly at northern and equatorial latitudes which appear to be breaking in some cases distinctive meridional gradients of pressure and temperature indicate the presence of a low altitude westerly jet at latitudes of 15 30 s at southern summer solstice this jet appears in predictions of general circulation models in connection with the strong seasonal cross equatorial hadley circulation the pressure gradient at 2 km altitude implies a wind speed of 33 m s 1 stronger than predicted which may help explain the occurrence of numerous local dust storms within this latitude band in late southern spring these measurements also characterize the response of the atmosphere to stationary thermal forcing at midsouthern latitudes where high terrain south of tharsis and low terrain in hellas planitia produce large zonal temperature variations in the lowest scale height above the surface pressure measured at constant geopotential decreases at an average rate of 0 13 per degree ls due primarily to condensation of co2 at the north pole

convective instability in the martian middle atmosphere dry convective instabilities in mars s middle atmosphere are detected and mapped using temperature retrievals from mars climate sounder observations spanning 1 5 martian years the instabilities are moderately frequent in the winter extratropics the frequency and strength of middle atmospheric convective instability in the northern extratropics is significantly higher in my 28 than in my 29 this may have coupled with changes to the northern hemisphere mid latitude and tropical middle atmospheric temperatures and contributed to the development of the 2007 global dust storm we interpret these instabilities to be the result of gravity waves saturating within regions of low stability created by the thermal tides gravity wave saturation in the winter extratropics has been proposed to provide the momentum lacking in general circulation models to produce the strong dynamically maintained temperature maximum at 1 2 pa over the winter pole so these observations could be a partial control on modeling experiments