intraseasonal variability of the saharan heat low and its link with midlatitudes abstract the saharan heat low shl is thought to be a key feature of the west african monsoon and its variations during the summer season have not yet been systematically assessed to characterize the intraseasonal variations of the shl real and complex empirical orthogonal function analyses were applied to the 850 hpa potential temperature field over northern africa and the mediterranean using ncep department of energy doe atmospheric model intercomparison project amip ii reanalysis results a robust quasi propagative mode was highlighted over north africa and the mediterranean this mode consists of two phases the west phase corresponds to a maximum temperature over the coast of morocco mauritania propagating southwestward and a minimum between libya and sicily propagating southeastward the east phase corresponds to the opposite temperature structure which propagates as in the west phase a lag composite analysis revealed that this shl mode was preceded by large scale midlatitude intrase

continental scale salt tectonics on mars and the origin of valles marineris and associated outflow channels a synthesis of deformation patterns within and around the thaumasia plateau mars points to a new interpretation for regional deformation and the origin of valles marineris and associated outflow channels the morphology of the thaumasia plateau is typical of thin skinned deformation akin to a mega slide in which extensional deformation in syria planum and noctis labyrinthus connects via lateral zones of transtension and strike slip claritas fossae and valles marineris to a broad zone of compressional uplift and shortening defined by truncated craters and thrust faults along the coprates rise and thaumasia highlands however the low regional slope 1 results in gravitational body forces that are too small to deform the basaltic lava flows conventionally thought to compose the flanks of the tharsis volcanic province instead we conclude that geothermal heating and topographic loading of extensive buried deposits of salts and or mixtures of salts ice and basaltic debris would allow for weak detachments and large scale gravity spreading we propose that the generally linear chasmata of valles marineris reflect extension collapse and excavation along fractures radial to tharsis either forming or reactivated as part of one lateral margin of the thaumasia gravity spreading system the other dextral lateral margin is a massive splay of extensional faults forming the claritas fossae which resembles a trailing extensional imbricate fan the compressional mountain belt defined by the coprates rise and thaumasia highlands forms the toe of the mega slide topographic observations and previous structural analyses reveal evidence for a failed volcanic plume below syria planum that could have provided further thermal energy and topographic potential for initiating regional deformation either intrusively through inflation or extrusively through lava flow and or ash fall emplacement higher heat flow during noachian time or geothermal heating due to burial by tharsis derived volcanic rocks would have contributed to flow of salt deposits as well as formation of groundwater from melting ice and dewatering of hydrous salts we further propose that connection of overpressured groundwater from aquifers near the base of the detachment through the cryosphere to the martian surface created the outflow channels of echus coprates and juventae chasmata at relatively uniform source elevations along the northern margin of the mega slide where regional groundwater flow would have been directed toward the surface our hypothesis provides a unifying framework to explain perplexing relationships between the rise of the tharsis volcanic province deformation of the thaumasia plateau and the formation of valles marineris and associated outflow channels

global climatic anomalies associated with extremes in the southern oscillation abstract composite temperature and precipitation anomalies during various stages of an event in the southern oscillation so have been computed for several hundred stations across the globe large regions of coherent significant signals are shown to exist for both extremes of the so with warm event signals generally opposite to those during cold events in addition during the year preceding the development of an event in the so year 1 climatic anomalies tend to be opposite to those during the following year year 0 this confirms that the biennial tendency of the so over the pacific indian ocean sectors is also present in more remote regions with climatic signals related to the so many of the signals are consistent enough from event to event to be useful for extended range forecasting purposes

diagenetic layers in the upper walls of valles marineris mars evidence for drastic climate change since the mid hesperian a packet of relatively resistant layers totaling 400 m thickness is present at the tops of the chasma walls throughout valles marineris the packet consists of an upper dark layer 50 m thick a central bright layer 250 m thick and a lower dark layer 100 m thick the packet appears continuous and of nearly constant thickness and depth below ground surface over the whole valles system 4000 km e w 800 km n s independent of elevation 3 10 km and age of plateau surface noachian through upper hesperian the packet continues undisturbed beneath the boundary between surface units of noachian and hesperian ages and continues undisturbed beneath impact craters transected by chasma walls these attributes are not consistent with layer formation by volcanic or sedimentary deposition and are consistent with layer formation in situ i e by diagenesis during or after upper hesperian time diagenesis seems to require the action of aqueous solutions in the near subsurface which are not now stable in the valles marineris area to permit the stability of aqueous solutions mars must have had a fairly dense atmosphere 1 bar co2 when the layers formed obliquity variations appear to be incapable of producing such a massive atmosphere so late in mars history

salt tectonics and collapse of hebes chasma valles marineris mars a photogeologic and physical modeling study indicates that hebes chasma mars formed by collapse of the megaregolith local heating facilitated drainage of 10 5 km 3 of brines and entrained particulates through fractures in the chasma floor and into a regional aquifer a megaregolith rich in salts and water is implied by massive low gradient allochthonous flows that terminate in deep pits and troughs by emergent diapirs and by arching of hebes mensa these structures are consistent with plastic and viscous deformation but inconsistent with collapse of basalt flows and or tephra spectral measurements confirm that hydrated sulfate salts are spatially associated with allochthonous flows from depth and light toned deposits collapse features and flows are present in many other chasmata in valles marineris suggesting that widespread salt tectonics and dissolution may have shaped the region

spectral and geological study of the sulfate rich region of west candor chasma mars sulfates have been discovered by the omega spectrometer in different locations of the planet mars they are strongly correlated to light toned layered deposits in the equatorial regions west candor chasma is the canyon with the thickest stack of layers and one with the largest area covered by sulfates a detailed study coupling mineralogy derived from omega spectral data and geology derived from hrsc imager and other datasets leads to some straightforward issues the monohydrated sulfate kieserite is found mainly over heavily eroded scarps of light toned material it likely corresponds to a mineral present in the initial rock formed either during formation and diagenesis of sediments or during hydrothermal alteration at depth because it is typically found on outcrops that are eroded and steep polyhydrated sulfates that match any ca na fe or mg sulfates with more than one water molecule are preferentially present on less eroded and darker outcrops than outcrops of kieserite these variations can be the result of a diversity in the composition and or of the rehydration of kieserite on surfaces with longer exposure the latter possibility of rehydration in the current or recent atmosphere suggests the low surface temperatures preserve sulfates from desiccation and also can rehydrate part of them strong signatures of iron oxides are present on sulfate rich scarps and at the base of layered deposits scarps they are correlated with tes gray hematite signature and might correspond to iron oxides present in the rock as sand size grains or possibly larger concretions that are eroded and transported down by gravity at the base of the scarp pyroxenes are present mainly on sand dunes in the low lying terrains pyroxene is strongly depleted or absent in the layered deposits when mixed with kieserite local observations favor a spatial mixing with dunes over layered deposits sulfates such as those detected in the studied area require the presence of liquid water to form by precipitation either in an intermittent lacustrine environment or by hydrothermal fluid circulation both possibilities require the presence of sulfur rich groundwater to explain fluid circulation the elevation of the uppermost sulfate signatures suggests the presence of aquifers up to 2 5 km above datum only 1 km below the plateau surface

new models for the origin of valles marineris closed depressions current models for the formation of the abundant large closed depressions of valles marineris have serious shortcomings purely tectonic mechanisms are inconsistent with the morphology of many depressions and removal of large quantities of ground ice from the canyon walls is inconsistent with the observed strength of the walls accordingly we offer some alternatives one possibility involves decay of ice rich bodies occupying partially sediment choked ancient graben that predated the overlying cratered and ridged plains other possibilities involve the removal of massive equatorial carbonate deposits storing much of the planet s co2 inventory generated during greenhouse conditions on early mars solution by carbonic acid derived from the atmosphere analogous to terrestrial karst requires extensive recycling of the available water supply solution by various groundwater acids possibly derived from the tharsis magmas requires less water especially if only the smaller closed depressions are due to carbonate decay alternatively volume loss due to decarbonation of carbonate during early high heat flow or a later tharsis related heat pulse can produce extensive collapse especially if the carbonates have high silica content

formation of martian outflow channels by catastrophic dewatering of evaporite deposits geological mapping based on topographic analysis of mars orbiter laser altimeter mola data together with photointerpretation of mars orbiter camera moc images and thermodynamic and heat flow considerations frame a new hypothesis for the formation of martian outflow channels through catastrophic dewatering of evaporite deposits mola transects across valles marineris show that the valley is located at the crest of a 3 km high topographic bulge on the flank of the much larger tharsis rise interpretation of moc images showing layered deposits within valles marineris as unconformably underlying hesperian age lava flows means that these thick deposits thought to contain hydrous sulfates were heated by an increased geothermal gradient due to development of tharis increased temperatures adequate to dehydrate hydrous evaporites would trigger significant volumetric expansion and catastrophically release tremendous amounts of overpressured water

prediction of tropical atlantic sea surface temperatures using linear inverse modeling the predictability of tropical atlantic sea surface temperature on seasonal to interannual timescales by linear inverse modeling is quantified the authors find that predictability of caribbean sea and north tropical atlantic sea surface temperature anomalies sstas is enhanced when one uses global tropical sstas as predictors compared with using only tropical atlantic predictors this predictability advantage does not carry over into the equatorial and south tropical atlantic indeed persistence is a competitive predictor in those regions to help resolve the issue of whether or not the dipole structure found by applying empirical orthogonal function analysis to tropical atlantic ssts is an artifact of the technique or a physically real structure the authors combine empirically derived normal modes and their adjoints to form influence functions maps highlighting the geographical areas to which the north tropical atlantic and the south tropical atlantic ssts are most sensitive at specified lead times when the analysis is confined to the atlantic basin the 6 month influence functions in the north and south tropical atlantic tend to be of the opposite sign and evolve into clear dipoles within 6 months when the analysis is performed on global tropical ssts the 6 month influence functions are connected

studies of el nino and interdecadal variability in tropical sea surface temperatures using a nonnormal filter abstract a dynamically based filter is used to separate tropical sea surface temperatures ssts into three components the evolving el nino signal the global tropical trend and the background the components thus isolated are not independent on the contrary this procedure allows us to see the importance of the interdecadal signal to the predictability of el nino the data filtered in this way reveal el nino signals in the equatorial indian ocean and in the north tropical atlantic ocean that are remarkably similar a signature of el nino in the south tropical atlantic leads nino 3 4 sst anomalies by about 9 months the time series of a global tropical trend is found to have a very smooth parabolic structure in unfiltered data this trend conspires with el nino to obscure a meridional tropical atlantic dipole which is significant in the filtered background sst data

a ten year data set for fetch and depth limited wave growth abstract this paper presents the key results from a ten year data set for lake ijssel and lake sloten in the netherlands containing information on wind storm surges and waves supplemented with swan 40 51 wave model results the wind speeds u 10 effective fetches x and water depths d for the data set ranged from 0 24 m s 1 0 8 25 km and 1 2 6 m respectively for locations with non sloping bottoms the range in non dimensional fetch x g x u 10 2 was about 25 80 000 while the range in dimensionless depth d g d u 10 2 was about 0 03 1 7 land water wind speed differences were much smaller than the roughness differences would suggest part of this seems due to thermal stability effects which even play a role during near gale force winds for storm surges a spectral response analysis showed that lake ijssel has several resonant peaks at time scales of order 1 h as for the waves wave steepnesses and dimensionless wave heights h g h m0 u 10 2 agreed reasonably well with parametric growth curves although there is no single curve to which the present data fit best for all cases for strongly depth limited waves the extreme values of d 0 03 and h m0 d 0 44 at the 1 7 m deep lake sloten were very close to the extremes found in lake george australia for the 5 m deep lake ijssel values of h m0 d were higher than the depth limited asymptotes of parametric wave growth curves the wave model test cases of this study demonstrated that swan underestimates h m0 for depth limited waves and that spectral details enhanced peak secondary humps were not well reproduced from h m0 d 0 2 0 3 on swan also underestimated the quick wave response within 0 3 1 h to sudden wind increases for the remaining cases the new van der westhuysen a j zijlema m and battjes j a 2007 nonlinear saturation based whitecapping dissipation in swan for deep and shallow water coast eng 54 151 170 swan physics yielded better results than the standard physics of komen g j hasselmann s hasselmann k 1984 on the existence of a fully developed wind sea spectrum j phys oceanogr 14 1271 1285 except for persistent overestimations that were found for short fetches the present data set contains many interesting cases for detailed model validation and for further studies into the evolution of wind waves in shallow lakes

ancient volcanism and its implication for thermal evolution of mars abstract volcanism plays an important role in the formation and thermal evolution of the crusts of all terrestrial planets martian volcanoes have been extensively studied and it has been suggested that the volcanism on mars that created the visible volcanic features was initiated in the noachian 3 8 ga and continued to the late amazonian 4 0 ga volcanoes are preserved in the heavily cratered southern highlands most of these are central volcanoes with diameters ranging from 50 to 100 km and heights of 2 3 km most of them are spatially adjacent to and temporally continuous with the tharsis and circum hellas volcanic provinces suggesting that these two volcanic provinces have experienced more extensive and longer duration volcanism than previously thought these edifices are heavily cut by radial channels suggesting that an early phase of aqueous erosion occurred and ended prior to the emplacement of the encircling hesperian lava fields

the light toned stratified sedimentary rock exposures in western juventae chasma mars in context abstract juventae chasma an isolated depression northeast of the valles marineris trough system hosts four mounds of light toned layered materials these are erosional remnants interpreted to consist of sedimentary rocks the geological setting of juventae chasma is a complex amalgamation of terrains and surfaces of different morphologies ages and structures most previous published studies assumed or interpreted that the light toned mound forming materials were deposited in the chasm after it opened or began to open here we use detailed observations of the geologic setting the nature of chasm wall rocks and the distribution and nature of the contacts of the light toned materials with adjacent geologic materials to argue that the light toned mounds in juventae chasma are more likely remnants of light toned materials that existed in the subsurface before the chasm opened up the rock cut by the chasm was not a monolithic unit e g lava flows and might have included both light toned and dark toned sedimentary rocks bearing a range of diagenetic properties the light toned materials were deposited as clasts precipitates or both within craters or depressions that were filled buried lithified and then exposed when juventae chasma formed because the sedimentary rock types and stratal package properties differ from one mound to the next the buried craters or depressions could have existed at different times and provide sedimentary records of different environments that existed at different times during the planet s early history noachian period upon exposure these materials as well as chasm wall rocks and chaotic terrain blocks underwent differential erosion as a function of rock physical properties to produce the geomorphic expressions observed today

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

seasonal and intraseasonal variability of large scale barotropic modes abstract the barotropic instability of time dependent observed basic states that are periodic with a period of 1 yr covering the complete annual cycle is analyzed using floquet theory the time dependent basic state is constructed from observed monthly averaged 300 mb streamfunction fields linearly interpolated between the different months the propagator over the 1 yr period is constructed and its eigenvalues and some of the fastest growing eigenvectors termed finite time normal modes ftnms are calculated the fast growing ftnms are large scale modes with generally largest amplitudes in the northern hemisphere they exhibit intraseasonal variability in their structures as well as longer period variations and their amplification rates vary with time the fastest growing ftnm has its largest growth rate in early northern winter and its amplification has maximum cumulative effect in boreal spring when the equatorward penetration of this disturbance is also the largest the other fast growing ftnms

on the dependence of sea surface roughness on wave development abstract the aerodynamic roughness of the sea surface z0 is investigated using data from lake ontario from the north sea near the dutch coast and from an exposed site in the atlantic ocean off the coast of nova scotia scaling z0 by rms wave height gives consistent results for all three datasets except where wave heights in the atlantic ocean are dominated by swell the normalized roughness depends strongly on wave age younger waves traveling slower than the wind are rougher than mature waves alternatively the roughness may be normalized using the friction velocity u of the wind stress again young waves are rougher than mature waves this contradicts some recent deductions in the literature but the contradiction arises from attempts to describe z0 in laboratory tanks and in the field with a single simple parameterization here it is demonstrated that laboratory waves are inappropriate for direct comparison with field data being much smoother than their field equivalents in the open ocea

the southern oscillation part ii associations with changes in the middle troposphere in the northern winter abstract we have investigated the relationship between the extremes of the southern oscillation and the following quantities at 700 mb in winter 1948 1949 to 1978 1979 eddy transfer of sensible heat temperature geopotential height and geostrophic wind in the phase of the southern oscillation when pressures are high over the tropical south indian ocean and low over the tropical south pacific ocean in contrast with the opposite pressure distribution the zonal mean poleward flux of sensible heat in the quasistationary waves tends to be higher in middle latitudes the temperatures and heights tend to be lower between 30 and 60 n with the maximum difference at 45 n the geostrophic wind tends to be stronger south of 45 n and weaker to the north and the transfer of sensible heat by the transient waves tends to be stronger south of 45 s and weaker to the north in this extreme of the southern oscillation the zonal mean geostrophic wind on both hemispheres is stronger in the subtropics and weaker at high

barotropic rossby wave dynamics of zonally varying upper level flows during northern winter abstract the evolution of linear rossby waves on representative zonally varying upper tropospheric flows is examined structures associated with maximum perturbation energy growth over both short and long time intervals are obtained sensitivity is determined with respect to the background flow the manner in which the background flow is maintained and vertical level the background flows considered are a 26 winter 250 mb climatology obtained from the national meteorological center 13 winter 300 250 and 150 mb climatologies obtained from the european centre for medium range weather forecasts flows representative of warm and cold enso events and nearby free steady solutions of the nonlinear barotropic vorticity equation the principal finding is that no matter which of the above background flows is used no matter how the perturbation problem is formulated no matter whether modal or nonmodal evolution is considered the growth of free perturbations in a linear barotropic model is too weak to expla

direct measurements of wind stress over the surf zone field data of the wind stress over surf zone waves are presented from an open ocean beach on the east australian coast two ultrasonic anemometers were deployed at nominal heights of 5 and 10 m above the water surface in the intertidal and inner surf zones with concurrent measurements of water levels and offshore wave parameters following a rigorous quality control procedure the wind stress was determined by the eddy correlation technique a constant stress layer was observed between 5 and 10 m elevation considering near neutral conditions only the wind drag coefficients were found to systematically change with the wind angle of approach relative to the shoreline and are much smaller for longshore wind than during onshore wind the concept of an apparent wave steepness changing with wind direction is suggested to explain this behavior the drag coefficients over the surf zone during onshore wind and near neutral conditions were determined to be almost twice the values expected at the same wind speed and open ocean conditions the observed charnock coefficient was similarly an order of magnitude larger than open ocean values a wave celerity of the order of that expected in the inner surf zone is required to explain the observed large roughness and drag coefficients using existing wave age dependent parameterizations this suggests that the slower wave celerity in the surf zone is an important contributor to the increased wind stress in addition to the sawtooth wave shape key points a new field data set of the wind stress over surf zone waves is presented concept of an apparent wave steepness is proposed to explain drag observations surf zone drag coefficients were almost twice the values outside the surf

on the effect of sea drops on the atmospheric boundary layer 1 one of the possible mechanisms responsible for the reduction of the sea surface drag at high winds is explored the mechanism is based on the direct effect of sea drops as heavy particles on the turbulent mixing if assumed that sea drops are ejected upward from the sea surface no significant effect can be found a more realistic picture presumes that the spume drops resulting from a mechanical tearing of wave crests are ejected horizontally at altitudes of breaking crests a model of the spume drops generation is proposed the spume drops being torn off from breaking crests and sprayed inside the airflow significantly affect the surface drag at highest model wind speeds 60 80 m s the model actually predicts an effect of the slippery surface when the drag coefficient is reduced in about 10 times a comparison with available observations is given

opaline silica in young deposits on mars high spatial and spectral resolution reflectance data acquired by the mars reconnaissance orbiter compact reconnaissance imaging spectrometer for mars crism instrument reveal the presence of h 2o and sioh bearing phases on the martian surface the spectra are most consistent with opaline silica and glass altered to various degrees confirming predictions based on geochernicall experiments and models that amorphous silica should be a common weathering product of the basaltic martian crust these materials are associated with hydrated fe sulfates including h 3o bearing jarosite and are found in finely stratified deposits exposed on the floor of and on the plains surrounding the valles marineris canyon system stratigraphic relationships place the formation age of these deposits in the late hesperian or possibly the amazonian implying that aqueous alteration continued to be an important and regionally extensive process on mars during that time

impact of swell on the marine atmospheric boundary layer a model that describes the impact of swell on the marine atmospheric boundary layer is proposed the model is based on the two layer approximation of the boundary layer the near surface inner region and the outer region above the swell induced momentum and energy fluxes are confined within the inner region swell loses energy to the atmosphere and enhances the turbulent kinetic energy in the inner region the transfer of momentum results in acceleration or deceleration of the airflow near the surface following wind swell accelerates the flow which for a very low wind results in a swell driven wind opposite wind swell decelerates the airflow which for a steep swell could cause the reverse airflow the sea drag in the case of opposite wind swell is considerably enhanced as compared with the following wind swell case cross wind swell causes the rotation of the wind velocity vector with height which leads to the deviation of the turbulent stress vector from the wind velocity vector the impact of swell becomes more pronounced when the wind speed decreases or when the swell phase velocity increases in fact it is the wave age of the swell that characterizes the swell impact because the dimensionless wave induced fluxes of energy and momentum are proportional to the wave age parameter both fluxes are also proportional to the swell slope so that the swell impact is stronger for a steeper swell the model reproduces qualitatively and quantitatively the main experimental findings for the ocean swell the impact of swell on the sea drag is very pronounced for opposite wind swell is less pronounced for cross wind swell and is only at low wind speeds

influence of the scar geometry on landslide dynamics and deposits application to martian landslides received 24 january 2011 revised 23 june 2011 accepted 30 june 2011 published 4 october 2011 1 landslides dynamics prediction remains difficult in spite of a considerable number of studies the runout distance is widely used in analysis of landslide dynamics and in the calibration of the rheological parameters involved in numerical modeling however the unknown impact of the significant uncertainty in the shape of the initial released mass on the runoutdistanceandontheoverallshapeofthedepositraisesquestionsabouttherelevanceof these approaches the impact of the initial scar geometry on flow and distribution of the deposits is studied here using satellite data and numerical modeling of theoretical landslides and martian landslides informed by geomorphological analysis by varying the initial scar geometry from spoon shaped to steep wall geometry our results show that the runout distance is a very robust parameter that is only slightly affected by the change in the geometry of the initial scar on the contrary the lateral extent of the deposit is shown to be controlled by the scar geometry providing unique insights into the initial landsliding conditionsonmarsandmakesitpossibletoaccuratelyrecoverthevolumeinitiallyinvolved an essential ingredient for volume balance calculation a feedback analysis of valles marineris landslides can be drawn showing good agreement between numerical results and geomorphological analysis the geometry of the initial scar inferred from numerical modeling is strongly correlated with the regional tectonic history in valles marineris area

the dependence of sea surface roughness on the height and steepness of the waves it is proposed that the sea surface roughness zo can be predicted from the height and steepness of the waves zo hs a hs lp b where hs and lp are the significant wave height and peak wavelength for the combined sea and swell spectrum best estimates for the coefficients are a 1200 b 4 5 the proposed formula is shown to predict well the magnitude and behavior of the drag coefficient as observed in wave tanks lakes and the open ocean thus reconciling observations that previously had appeared disparate indeed the formula suggests that changes in roughness due to limited duration or fetch are of order 10 or less thus all deep water pure windseas regardless of fetch or duration extract momentum from the air at a rate similar to that predicted for a fully developed sea this is confirmed using published field data for a wide range of conditions over lakes and coastal seas only for field data corresponding to extremely young waves u10 cp 3 were there appreciable differences between the predicted and observed roughness values the latter being larger on average significant changes in roughness may be caused by shoaling or by swell a large increase in roughness is predicted for shoaling waves if the depth is less than about 0 2lp the presence of swell in the open ocean acts on average to significantly decrease the effective wave steepness and hence the mean roughness compared to that for a pure windsea thus the predicted open ocean roughness is at most wind speeds significantly less than is observed for pure wind waves on lakes only at high wind speeds such that the windsea dominates the swell do the mean open ocean values reach those for a fully developed sea

the formation of a giant collapse caprock sinkhole on the barda negra plateau basalts argentina magnetic mineralogical and morphostructural evidences the 1 5 km wide 40 m deep crater like structure in the 10 ma old barda negra basaltic plateau in central argentina was discovered in the early 2000s based on remote sensing surveys and on its morphological characteristics similar to those of the barringer crater in arizona the structure is described to be originated by an impact in this study we ran several field work campaigns and collected and analysed samples in order to find more evidences to endorse or reject this hypothesis we observe a circular depression not generally surrounded by raised rims in contrast to craters produced either by a meteorite impact or phreatomagmatic eruption maars mineralogical investigations of rocks and sediments do not show high pressure and temperature minerals such as coesite or stishovite or any remnants of an impactite or impact melt glass likewise no textural evidences for impact related fracturing or stress are observed a detailed geomorphological mapping indicates a successive crater development which invokes local stepwise subsidence magnetic mapping performed with the eu funded newton multisensor novel instrument shows a 2000 nt field anomaly associated to the edges of the crater and susceptibility measurements cast an important contrast between the basaltic rims and plateau and the crater interior therefore we propose a sink hole origin for the crater with a former collapse of the plateau basalts and a latter infill with sedimentary material this hypothesis is supported by the fact that the 40 to 85 m thick and 14 to 15 ma old carbonate bearing collon cura formation underneath the 100 to 150 m thick basaltic plateau lava sheet represents ideal rocks for dissolution and karst formation remote sensing data show other nearby sinkholes 20 km westward with extensions of 3 6 km and 100 m depth which are emplaced within a cogenetic neighboring basaltic plateau with a similar underlying lithology and the consistence of the magnetic model computed with this scheme and on measured rock remanence and susceptibilities of the structure and surroundings these giant collapse sinkholes up to 6 km in diameter within caprocks of very thick plateau basalts represent unique examples for planetary surface shaping processes which also occur on mars and comets in areas with ba salts or rigid caprocks

a case study of air sea interaction during swell conditions air sea interaction data from a situation with pronounced unidirectional swell have been analyzed measurements of turbulence at three levels 10 18 and 26 m above mean sea level together with directional wave buoy data from the site ostergarnsholm in the baltic sea were used the situation which lasted for 48 hours appeared in the aftermath of a gale the wind direction during the swell situation turned slowly within a 90 sector both during the gale phase and the swell phase the over water fetch was 150 km the wind speed during the swell phase was typically 4 m s 1 during the swell phase a wind maximum near or below the lowest wind speed measuring level 10 m was observed the net momentum flux was very small resulting in cd values 0 7 10 3 throughout the lowest 26 m covered by the tower measurements turbulence intensities in all three components remained high despite the low value of the kinematic momentum flux u w resulting in a reduction of the correlation coefficient for the longitudinal and vertical velocity from its typical value around 0 35 to between 0 2 and 0 and with some positive values at the higher measuring levels appearing abruptly at wave age c0 u10 equal to 1 2 turbulence spectra of the horizontal components were shown not to scale with height above the water surface in contrast to vertical velocity spectra for which such a variation was observed in the low frequency range in addition spectral peaks in the horizontal wind spectra were found at a frequency as low as 10 3 hz from a comparison with results from a previous study it was concluded that this turbulence is of the inactive kind being brought down from the upper parts of the boundary layer by pressure transport

breaking probabilities for dominant surface waves on water of finite constant depth this paper extends our previous study of the breaking probability of dominant deep water gravity surface waves into the finite water depth environment it reports a unified behavior of the mean breaking statistics once the effects of finite water depth are taken into account the shallow water wave data that form the basis of this study were acquired at a field experiment site at lake george new south wales australia the breaking events were detected through visual observation of videotaped records of the wave field in combination with acoustic signatures of the breaking waves from a collocated hydrophone following banner et al 2000 we argue that when constant finite depth bottom influence is operative nonlinear hydrodynamical effects associated with energy and momentum fluxes within deforming wave groups remain the primary determinant of breaking onset this underpins our proposed finite depth water parameterization for the environmental dependence of dominant wave breaking probability given by the average number of breakers passing a fixed point per dominant wave period the additional influence of bottom interaction with the wind drift current shear and wind forcing are also included in our finite constant depth formulation this is a natural extension of our recently proposed deep water dependence and reduces to it as the significant wave height becomes much smaller than the water depth in common with the deep water case we propose that there exists a threshold of the significant peak steepness below which negligible dominant wave breaking occurs the available data show encouraging agreement with our proposed dependence with a correlation coefficient approaching 0 9

the linear and nonlinear extratropical response of the atmosphere to tropical intraseasonal heating abstract this study examines the dynamical nature of the linear and nonlinear extratropical response of the atmosphere to tropical intraseasonal heating with various temporal and spatial structures a global two level model is used it is found that the midlatitude response is very sensitive to the phase speed of the forcing and to a lesser extent to its spatial scale for a narrow monopolar heating source traveling eastward uniformly with an around the world period of 40 days as in gcm simulations of the madden julian oscillation mjo the response is weak and explains very little of the extratropical variance for dipolar beating with zonal scale around 15 000 km k 2 3 and wave period of 40 days propagating slowly eastward within a confined longitudinal domain a good approximation of the outgoing longwave radiation fields associated with the real mjo the extratropical response is wavelike and well defined and stands significantly above the background variability the nonlinear wavetrains evolv

groundwater processes in hebes chasma mars we describe a conceptual model of groundwater processes at hebes chasma mars which can account for the distribution of hydrated minerals and their subsequent evolution at hebes chasma pressure gradients set up by the large central mound hebes mensa could cause groundwater to be sourced predominantly from beneath the central region if such water were present evaporation of upwelling groundwater would cause monohydrates to form at or near the surface through efflorescence and polyhydrates to form inside the central mound through subflorescence this crystallization could lead to an excess pore pressure causing large scale weakening and subsequent collapse that can reveal the interior polyhydrated deposits if evaporation is high compared to groundwater inflow then increased crystallization would promote the formation of collapse zones if evaporation is low compared to groundwater inflow then there would be a greater chance for water reaching the surface and the possible formation of karst landforms

candidate ice rich material within equatorial craters on mars 1 the floors and walls of many mid latitude 30 60 craters on mars appear to be mantled by relatively young material s with distinct morphology and erosional properties collectively this material fill is often interpreted as ice rich with emplacement and modification related to climatological processes here i document material and associated landforms within 38 craters between 4 13 s in the sinus sabaeus region that appear morphologically similar to material and landforms within mid latitude craters these equatorial mid latitude materials may also share a common composition and emplacement mechanism near surface ice is unstable at equatorial latitudes under present conditions suggesting that emplacement could have occurred under different climate conditions in the past high obliquity 35 45 general circulation model gcm simulations show surface ice accumulation in sinus sabaeus and tharsis where similar material and landforms have been documented these observations are consistent with the hypothesis that past obliquity driven climate change resulted in equatorward volatile migration on mars

the global atmospheric circulation response to tropical diabatic heating associated with the madden julian oscillation during northern winter abstractthe detailed dynamical mechanisms of the upper tropospheric circulation response to the madden julian oscillation mjo convection are examined by integrating a primitive equation model a series of initial value calculations with the climatological boreal winter background flow forced by the mjo like thermal forcing successfully capture the key aspects of the observed circulation response to the mjo convection this suggests that a large fraction of mjo related circulation anomalies are direct responses to tropical heating in both the tropics and extratropics and can be largely explained by linear dynamics it is found that mjo like dipole heatings not only intensify tropical upper tropospheric anomalies but also weaken them at certain regions because of the interaction between equatorial kelvin and rossby waves the rossby wave train primarily excited by horizontal divergence of upper level perturbation flow propagates northeastward and then heads back to the equator in this way rossby wave act

the dynamics of euro atlantic blocking onsets the mechanisms leading to euro atlantic blocking are investigated using 31 winters of 500 hpa geopotential height from nmc and ecmwf daily analyses and a 30 000 day perpetual winter run from a simple 3 level quasi geostropic model a composite analysis of the atmospheric flow during days preceding blocking events is carried out it indicates that euro atlantic blocking events have two simultaneous main precursors a high latitude retrograding wave number 1 pattern at planetary scale and an enhanced baroclinic wavetrain travelling across the north atlantic at synoptic scale these phenomena are identified both in observed and in simulated data the nonlinear interactions between small scale large scale and the mean flow during the establishment of the blocking anomaly are examined by a budget analysis of the quasi geostrophic potential vorticity equation these diagnostics demonstrate that wave wave interactions contribute to about 50 of the local amplification of the blocking anomaly while wave mean flow interactions contribute to propagation of the large and small scale anomalies and their phase locking finally the question is addressed as to whether the two precursors are necessary and sufficient conditions for blocking onsets by performing various sets of initial value experiments performed with the quasi geostrophic model these experiments show that the two precursors occur simultaneously but only the synoptic scale baroclinic wavetrain is necessary to trigger euro atlantic blocking

winds near the surface of waves observations and modeling abstractthe concept of a constant flux layer is usually employed for vertical profiling of the wind measured at some elevation near the ocean surface the surface waves however modify the balance

the critical role of non normality in partitioning tropical and extratropical contributions to pna growth abstractthe pacific north american pna teleconnection pattern has been linked both to tropical phenomena including the madden julian oscillation mjo and el nino southern oscillation enso an

wave follower field measurements of the wind input spectral function part ii parameterization of the wind input abstract nearly all of the momentum transferred from wind to waves comes about through wave induced pressure acting on the slopes of waves known as form drag direct field measurements of the wave induced pressure in airflow over water waves are difficult and consequently rare those that have been reported are for deep water conditions and conditions in which the level of forcing measured by the ratio of wind speed to the speed of the dominant spectral peak waves is quite weak u10 cp 3 the data reported here were obtained over a large shallow lake during the australian shallow water experiment auswex the propagation speeds of the dominant waves were limited by depth and the waves were correspondingly steep this wider range of forcing and concomitant wave steepness revealed some new aspects of the rate of wave amplification by wind the so called wind input source function in the energy balance equation for wind driven water waves it was found that the exponential growth rate parameter fra

organization of extratropical transients during el nino abstract four observed el nino southern oscillation enso events are studied to determine the mechanisms responsible for the anomalous extratropical atmospheric circulation during northern winter a parallel analysis of a gcm s response to el nino is performed in order to assess if similar mechanisms are operative in the model atmosphere the observed stationary wave anomalies over the pacific north american pna region are found to he similar during the four winters despite appreciable differences in sea surface temperatures the anomalous transient vorticity fluxes are remarkably robust over the north pacific during each event with an eastward extension of the climatological storm track leading to strong cyclonic forcing near 40 n 150 w this forcing is in phase with the seasonal mean aleutian trough anomaly suggesting the importance of eddy mean flow interactions by comparison the intersample variability of the gcm response over the pna region is found to exceed the observed inter el nino variabi

mineralogy of saline perennial cold springs on axel heiberg island nunavut canada and implications for spring deposits on mars abstract in recent years evidence for spring deposits on mars has been mounting it seems increasingly likely that groundwater upwelling and surfacing as springs may be responsible for some mineral deposits on mars surface in order to more easily detect and better understand potential spring deposits on mars it is pertinent that we gain a better understanding of the distribution of minerals at cold spring systems on earth here we report on the detailed mineralogy and distribution of precipitates in crusts and sediments of three non volcanic perennial saline cold spring systems associated with gypsum anhydrite diapirs on axel heiberg island canada wolf spring ws also known as lost hammer colour peak springs cp and gypsum hill springs gh at these sites permafrost frigid winter temperatures and arid atmospheric conditions approximate conditions of present day as well as past mars mineralogy of the three springs is dominated by halite nacl calcite caco 3 gypsum caso 4 2h 2 o thenardite na 2 so 4 mirabilite na 2 so 4 10h 2 o and elemental sulfur s minerals at ws are more sodium rich than at the other two sites and water salinity is much higher suggesting water flows through halite in the subsurface mirabilite is likely deposit at ws during winter months and dehydrates to thenardite during summer months elemental sulfur is typically associated with gypsum and may be related to microbial metabolism spring sediments are home to thriving microbial communities in winter and summer months and presumably year round if spring systems did exist on the surface of mars they may represent environments capable of supporting microbial life it is not known to what extent mineral crusts in cold saline spring systems on earth preserve evidence of microbial life or if they ever did on mars therefore studying terrestrial saline spring mineral deposits such as those on axel heiberg island may help us to better understand cold spring precipitation on mars and guide us in the search for minerals that may have been precipitated in spring systems and that may contain evidence of life additionally spectral data from europa indicates the presence of mirabilite while the depositional environment on europa differs from axel heiberg island the springs may still be a good mineralogical analogue given the precipitation of mirabilite by the upwelling of cold salty subsurface water in a cold semi arid desert environment

valles marineris landslides evidence for a strength limit to martian relief abstract unresolved controversies in martian geology surround the role of active tectonics and a wetter climate early in mars history and particularly the history and amount of liquid water at or near the surface among the various lines of evidence brought into such debates are the massive landslides along the walls of valles marineris which generally have been interpreted as resulting from marsquakes and therefore necessitating active tectonics under either wet or dry conditions we analyze valles marineris landslides using digital elevation data from the mars orbiter laser altimeter mola and find that a relief limit consistent with the intact strength of evaporites or other weak sedimentary rock defines an upper bound to the length and relief of unfailed slopes as would material with the strength properties of basalt lithology subjected to ground accelerations of about 0 2 g in contrast to prior interpretations of valles marineris landslides we propose an alternative complementary hypothesis that does not require significant pore water pressures or ground acceleration based on the close correspondence between back calculated material strength properties and values consistent with portions of the chasm walls at least locally being composed of relatively weak materials such as potentially frozen evaporites and or mixtures of ash fall or flow deposits ice hydrated salts and lava flows

the global response to tropical heating in the madden julian oscillation during the northern winter a life cycle of the madden julian oscillation mjo was constructed based on 21 years of outgoing long wave radiation data regression maps of ncep ncar reanalysis data for the northern winter show statistically significant upper tropospheric equatorial wave patterns linked to the tropical convection anomalies and extratropical wave patterns over the north pacific north america the atlantic the southern ocean and south america to assess the cause of the circulation anomalies a global primitive equation model was initialized with the observed three dimensional 3d winter climatological mean flow and forced with a time dependent heat source derived from the observed mjo anomalies a model mjo cycle was constructed from the global response to the heating and both the tropical and extratropical circulation anomalies generally matched the observations well the equatorial wave patterns are established in a few days while it takes approximately two weeks for the extratropical patterns to appear the model response is robust and insensitive to realistic changes in damping and basic state the model tropical anomalies are consistent with a forced equatorial rossby kelvin wave response to the tropical mjo heating although it is shifted westward by approximately 20 longitude relative to observations this may be due to a lack of damping processes cumulus friction in the regions of convective heating once this shift is accounted for the extratropical response is consistent with theories of rossby wave forcing and dispersion on the climatological flow and the pattern correlation between the observed and modelled extratropical flow is up to 0 85 the observed tropical and extratropical wave patterns account for a significant fraction of the intraseasonal circulation variance and this reproducibility as a response to tropical mjo convection has implications for global medium range weather prediction copyright 2004 royal meteorological society

modeling the collapse of hebes chasma valles marineris mars physical modeling and detailed mapping of hebes chasma provide new insights into the crustal composition and origin of the valles marineris region of equatorial mars hebes chasma is a 315 km long and 8 km deep closed depression containing distinctive landforms that include diapirs and extensive allochthonous flows that end in pits a central puzzle of hebes chasma is how and where 10 5 km 3 of missing material disappeared our physical models tested the hypothesis that the chasma formed by collapse and removal of material from below gravity driven collapse in the models reproduced all the chasma9s main landforms as subsidence evolved from early sagging of the upper surface to inward collapse and removal of material to emergence of diapirs and low gradient flows the models and geologic evidence suggest that hebes mensa arched upward diapirically and raised deep stratigraphy almost level with the chasma rim if the chasma indeed collapsed by subsurface drainage as occurred in the models the upper 8 10 km of deposits at hebes must have been solid to depths of 5 km but viscous at greater depths the materials removed could not have consisted mainly of basalt flows instead they probably were a mixture of hydrated and nonhydrated salts water ice liquid water and insoluble likely basaltic particles the proportions of these constituents are unknown but constrained because the material drained from the subsiding chasma and apparently contributed to the outburst floods released down neighboring echus chasma and kasei valles

simulating the atmospheric response to the 1985 87 el nino cycle abstract the atmospheric response to the evolution of global sea surface temperatures ssts from 1985 to 1987 is studied using the ncar community climate model ccm1 five separate 2 year integrations are performed and results are presented for the ensemble averaged response during the pre el nino 1985 86 winter and the mature el nino 1986 87 winter no skill is found in ccm1 s simulation for 1985 86 the simulation for the following winter when tropical pacific sst anomalies approached 2 c is more successful a large amplitude wave train extends poleward and eastward from the location of anomalous central pacific convection in ccm1 although the model s wave train is shifted 30 too far east compared to observations a linear barotropic stationary wave model is used to diagnose ccm1 s response during 1986 87 the eastward shifted pna response is easily excited by a dipole pattern of upper level forcing with convergence over the western tropical pacific and divergence over the central tropical pacifi

free barotropic rossby wave dynamics of the wintertime low frequency flow abstract in recent years much attention has been given to rossby wave propagation and dispersion on representative zonally and meridionally varying background flows in the atmosphere particular emphasis has been placed on the 300 mb flow as shaping the structure and evolution of extratropical low frequency eddies in this paper an attempt is made to check this hypothesis against the observed evolution of low pass filtered 300 mb streamfunction anomalies during the eight northern winters of 1985 93 the filter passes periods greater than 10 days the focus is on explaining the observed evolution of these low pass anomalies over 10 days this evolution is expected to be nonmodal that is a mix of several evolving normal modes rather than a single mode two questions are asked 1 given an initial anomaly to what extent can one explain the observed subsequent evolution with an unforced barotropic vorticity equation linearized about the climatological 300 mb flow and 2 in instances of anomaly growth to

zonal eddy dynamics of the north atlantic oscillation abstract this research is an attempt to understand the dynamical mechanisms that drive the wintertime north atlantic oscillation nao on monthly and longer timescales in an earlier work by deweaver and nigam the authors showed that momentum fluxes from stationary waves play a large role in maintaining the zonal mean zonal wind u perturbations associated with the nao in this paper a linear stationary wave model is used to show that zonal mean flow anomalies in turn play a large role in maintaining the nao stationary waves a strong two way coupling thus exists between u and the stationary waves in which each is both a source of and a response to the other when forced by zonal eddy coupling terms terms that represent the interaction between nao covariant zonal mean zonal wind anomalies and the climatological eddy flow together with heating and transient fluxes the model produces a realistic simulation of the observed stationary wave pattern zonal eddy coupling terms make the largest contribution

sulfates and iron oxides in ophir chasma mars based on omega and crism observations abstract we investigate the sulfate and iron oxide deposits in ophir chasma mars based on short wave infrared data from the compact reconnaissance imaging spectrometer for mars crism and from the observatoire pour la mineralogie l eau les glaces et l activite omega sulfates are detected mainly in two locations in the valley between ophir mensa and the southern wall of ophir chasma kieserite is found both within the slope of ophir mensa and superposed on the basaltic wall of the chasm here kieserite is unconformably overlain by polyhydrated sulfate deposits and iron oxides locally jarosite and unidentified phases with absorptions at 2 21 m or 2 23 m are detected which could be mixtures of jarosite and amorphous silica or other poorly crystalline phases the second large sulfate rich outcrop is found on the floor of the central valley although the same minerals are found here polyhydrated sulfates kieserite iron oxides and locally a possibly jarosite bearing phase this deposit is very distinct it is not layered almost horizontal and located at a much lower elevation of below 4250 m kieserite superposes polyhydrated sulfate rich deposits and iron oxides form lags the facies of sulfate formation remains unclear and could be different for the two locations a formation in a lake playa or under a glacier is consistent with the mineralogy of the central valley and its flat low lying topography this is not conceivable for the kieserite deposits observed south of ophir mensa these deposits are observed over several thousands of meters of elevation which would require a standing body of water several thousands of meters deep this would have lead to much more pervasive sulfate deposits than observed these deposits are therefore more consistent with evaporation of groundwater infiltrating into previously sulfate free light toned deposits the overlying polyhydrated sulfates and other mineral phases are observed in outcrops on ridges along the slopes of the southern chasm wall which are too exposed to be reached by groundwater here a water supply from the atmosphere by rain snow fog or frost is more conceivable

the generation of global rotational flow by steady idealized tropical divergence abstract tropical convective heating is balanced on the large scale by the adiabatic cooling of ascent the horizontal divergence of the wind above this heating may be viewed as driving the upper tropospheric rotational wind field a vorticity equation model is used to diagnose this relationship it is shown that because of the advection of vorticity by the divergent component of the flow the rossby wave source can be very different from the simple fd source often used in particular an equatorial region of divergence situated in easterly winds can lead to a rossby wave source in the subtropical westerlies where it is extremely effective this part of the source can be relatively insensitive to the longitudinal position of the equatorial divergence a divergence field which is asymmetric about the equator can lead to a quite symmetric rossby wave source for a steady frictionless flow the rossby wave source averaged over regions within closed streamfunction or absolute vorticity contours is under cert

origin of the south pacific convergence zone abstract the importance of the presence of south america and australia to the existence and orientation of the south pacific convergence zone spcz during january is explored using the ecmwf t21 model each of the continents is removed from the model and replaced with an ocean surface and the resulting precipitation and circulation associated with the spcz are then compared to a perpetual january control run results show that the presence of south america and the equatorial pacific upwelling zone does not appear to be crucial to the spcz but that the removal of australia destroys the southern monsoon and substantially weakens the western part of the spcz this suggests that the northwest southeast orientation of the spcz during southern summer is more dependent on interactions with the midlatitude westerlies over the south pacific than on the distribution of sea surface temperature and land over the southern hemisphere

enso signal in continental temperature and precipitation records warm events in the tropical pacific ocean associated with one extreme of the southern oscillation generally known as el nino southern oscillation or enso events are now known to be of global significance in perturbing the general circulation of the atmosphere1 8 it is also apparent that episodes of enhanced cold water upwelling cold events have an impact on large scale atmospheric circulation patterns9 11 here we examine the effect of warm and cold events on short term fluctuations of continental surface air temperature and precipitation throughout the northern hemisphere using a newly compiled set of high quality temperature and precipitation data12 13 the data were in the form of gridded anomalies from a 1951 70 reference mean for temperature and a 1921 60 reference mean for precipitation13 14

el nino la nina and the nonlinearity of their teleconnections the paradigm of an atmospheric system varying linearly with respect to extreme phases of the el nino southern oscillation is questioned it is argued that the global response to tropical pacific sea surface temperature forcing will be inherently nonlinear a physical basis for this intrinsic nonlinearity is the thermodynamic control on deep convection climate statistics for warm and cold events of the tropical pacific are analyzed separately for the northern winter periods during 1950 96 composite analysis of 500 mb heights reveal planetary scale teleconnection patterns as noted in earlier studies a new result is the evidence for an appreciable 358 longitude phase shift between the warm and cold event circulation composites and the two wave trains appear to have different tropical origins a large nonlinear component in north american surface climate anomalies is also found which is consistent with such a phase shift in teleconnections in the tropics rainfall anomalies also show evidence of nonlinear behavior the maximum rain anomalies along the equator are located east of the date line during warm events but west of the date line during cold events the interpretation of this behavior is complicated however by the fact that composite warm event sst anomalies are not the exact inverse of their cold event counterparts idealized atmospheric general circulation model agcm experiments are performed in order to test the question of whether the observed nonlinearity is an intrinsic property of the atmospheric system the model is forced with a composite sst anomaly that undergoes a realistic seasonally varying enso life cycle as described by e rasmusson and t carpenter both positive and negative phases of the sst anomaly are used and a 40 member ensemble of warm and cold event model simulations is conducted a nonlinear climate response in the agcm is found that closely resembles the observed composites including a shift in the equatorial positions of the maxmium rain responses and a phase shift of teleconnection patterns in the upper troposphere barotropic model experiments indicate that the inherent nonlinearity in the tropical rain response may itself be responsible for the phase shift in the extratropical teleconnection patterns

effects of wind trend and gustiness on the sea drag lake george study 1 the air sea coupling is usually parameterized in terms of the drag coefficient cd but the scatter of experimental data around such dependences is very significant and has not improved noticeably over some 30 years in the paper which is meant to be the first in a series a complex approach to the problem is suggested multiple mechanisms contributing into the sea drag are to be singled out studied separately evaluated and then reunited in a joint parameterization for cd dependences of the drag coefficient on the wind speed and sea state and effects of wind trends and gustiness are investigated in detail gustiness is found to be responsible for the most distant outliers our approach also combines an experimental lake george study with theoretical investigations conducted by means of the wowc wind over waves coupling model overall agreement of the model with measured wind stresses is quite good within 20 for the bulk of the data lower envelopes of the drag dependences are an important result of the paper they provide some lake george ideal relationships for the sea drag almost any deviation from such conditions causes the drag to increase it is suggested that decrease of the drag with respect to the ideal conditions which exhibits itself in a number of known open ocean data sets would be caused by a momentum flux back from the waves to the wind due to long waves outrunning the wind behavior of the charnock parameter in terms of wave age is also considered

a precipitation dipole in eastern north america 1 we have identified a dipole in annual precipitation across eastern north america ena east of 100 w between 30 n and 60 n this dipole appears to create spatially coherent opposing variations in precipitation with a separation of the two regions around 45 n annual average precipitation over ena appears to be stable and unimodal suggesting that the amount of overall precipitation variability is a small fraction of the mean and is largely determined by similar large scale processes analysis of regional average time series at interannual 3 7 year and decadal 10 16 year scales indicates that the dipole over the ena region is most clearly discernible at the decadal scale linear regression analysis between global sea surface temperatures ssts and precipitation over the two subregions in ena suggests that sst variations in several areas of the oceans tend to be associated with opposite precipitation anomalies in the two subregions of ena

a network of lava tubes as the origin of labyrinthus noctis and valles marineris on mars abstract the role of lava tube networks and lava channels is reassessed as the primordial stage of the volcano erosional processes that formed the labyrinthus noctis valles marineris system instead of a tectonic origin the combined use of ctx crism hirise imagery and mola profiles has provided valuable insight in the evolution of pit chains into fossae first and then chasmata later due to mass wasting processes caused by the erosional effect of the lava flows that draped valles marineris and other outflow channels although a quantitative evaluation of eruption rates is difficult even with digital terrain models dtms because of the mixing between new flows and paleoflows a comparison with elysium and other tharsis outflow channels suggests that the availability of lava supply is correlated to their widths the images of ubiquitous lava flows rather than sporadic light toned deposits strengthen the role of lava over that of water in the erosional processes that formed labyrinthus noctis and carved valles marineris like many other outflow channel on mars the erosional evolution of the outflow channels shows an increasing trend of age and a decreasing trend of depth from the sources on tharsis to the mouths at chryse planitia this finding coupled with the observation of lava flows mantling chryse planitia may have profound implications for the water inventories thought to have filled the lowlands with an ocean

numerical investigation of spectral evolution of wind waves part i wind input source function abstract this paper is dedicated to the investigation and calibration of the parameterized form for the wind input source term sin proposed earlier on the basis of field observations at lake george australia the main objective of this study was to obtain spectral forms for the wind input source function sin which incorporates the novel observation based features and at the same time satisfies the important physical constraint that the total integrated wind input must agree with independently observed magnitudes of the wind stress within this approach a new methodology a dynamic self adjusting routine was developed for correction of the wind input source function sin this correction involves a frequency dependent adjustment to the growth rate f based on extrapolations from field data the model results also show that light winds require higher rate adjustments of the wind input than strong winds

variation of the drag coefficient and its dependence on sea state using a gill propeller vane anemometer and resistance wave wires over a water column depth of 15 m simultaneous measurements of the momentum flux and sea surface wave spectra were acquired from the pisa mast 28 km offshore in the german bight during autumn and winter 1979 these data were analyzed to identify the relationship between wind stress and surface waves it was found that wind stresses for wind speeds above 15 m s were regularly higher than open ocean wind stresses as reported by smith 1980 and by large and pond 1981 for the same mean wind speed these results when described in terms of the drag coefficient compared closely with the results of sheppard et al 1972 who collected surface layer statistics over lough neagh northern ireland after modeling the surface waves of the north sea as a function of wave saturation or wave age it became evident that variations in the magnitude of the drag coefficient could be explained by coincident variations in the surface wave energy spectrum by applying the wave dependent roughness length model described by kitaigorodskii 1973 the north sea drag coefficient was predicted to be larger than drag coefficients reported from the open sea

periodic bedrock ridges on mars 1 evidence for sediment transport and erosion by wind is widespread over the surface of mars today and was likely a major geomorphic process for much of its geological past although martian surface features resembling aeolian dunes and ripples have been recognized since the mariner and viking missions such features have been interpreted previously as active indurated or exhumed sedimentary forms here we report evidence based on high resolution imaging science experiment images that show some megaripple forms are eroded into cohesive substrate rather than being composed of loose granular material or fossilized dunes exposure of stratigraphic continuity within layered cohesive material extending crest to trough through features with mean wavelengths of 18 to 51 m demonstrates the primarily erosional formation of what we term periodic bedrock ridges pbrs hence some surfaces on mars previously considered to be covered by wind deposited material are actually wind carved exposures that offer windows into martian history pbrs lack the distinctive streamlining associated with wind parallel yardangs and comparison of pbr orientation to yardangs megayardangs and active sedimentary dunes in the same vicinity confirm that these pbrs formed transverse to prevailing winds observed wavelengths of pbrs are comparable to those predicted by a simple model for erosional wavelengths of periodic transverse bed forms owing to the spacing of flow separations within the flow recognition of these transverse aeolian erosional forms brings up the question of how widespread martian pbrs are and how many have been misinterpreted as active or indurated fossilized sedimentary dunes