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

the shape of mars and the topographic signature of the hemispheric dichotomy reanalysis of occultation data from the mariner 9 and viking orbiter spacecraft to determine the shape of mars indicated that the hemispheric dichotomy is not a fundamental feature of the shape of the planet it is a consequence of an approximately 3 kilometer offset between mars9s center of mass and center of figure and the boundary along most of its length consists of broad gradual surface slopes over distances of thousands of kilometers this result was supported by analysis of high spatial resolution earth based radar topographic profiles any successful model for the origin of the dichotomy must explain a planet with an ellipsoidal shape and a long wavelength gradual topographic transition between the northern and southern hemispheres

multifrequency full waveform sonic logging in the screened interval of a large diameter production well abstracta set of field experiments using multiple transmitter center frequencies was completed to test the application potential of low frequency full waveform sonic logging in large diameter production wells wireline logs were acquired in a simple open drillhole and a high yield large diameter production well completed with wire wound sand screens at an aquifer storage and recovery site in perth western australia phase shift transform methods were applied to obtain phase velocity dispersion images for frequencies of up to 4 khz a 3d representation of phase velocity dispersion was developed to assist in the analysis of possible connections between low frequency wave propagation modes and the distribution of hydraulic properties for sandstone intervals in the test well the highest hydraulic conductivity intervals were typically correlated with the lowest phase velocities the main characteristics of dispersion images obtained from the sand screened well were highly comparable with those obtained at t

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

estimating phase velocity and attenuation of guided waves in acoustic logging data in acoustic logging the guided waves which propagate along the borehole are affected by the properties of the formation for acoustic logging tools with many receivers array processing methods can be used to calculate the phase velocity and attenuation of these waves this information is crucial in estimating formation properties like permeability transverse isotropy and s wave velocity

wave analysis in the atmosphere of venus below 100 km altitude simulated by the lmd venus gcm a new simulation of venus atmospheric circulation obtained with the lmd venus gcm is described and the simulated wave activity is analysed agreement with observed features of the temperature structure static stability and zonal wind field is good such as the presence of a cold polar collar diurnal and semi diurnal tides at the resolution used 96 longitudes 96 latitudes a fully developed superrotation is obtained both when the simulation is initialised from rest and from an atmosphere already in superrotation though winds are still weak below the clouds roughly half the observed values the atmospheric waves play a crucial role in the angular momentum budget of the venus s atmospheric circulation in the upper cloud the vertical angular momentum is transported by the diurnal and semi diurnal tides above the cloud base approximately 1 bar equatorward transport of angular momentum is done by polar barotropic and mid to high latitude baroclinic waves present in the cloud region with frequencies between 5 and 20 cycles per venus day periods between 6 and 23 earth days in the middle cloud just above the convective layer a kelvin type wave period around 7 3 ed is present at the equator as well as a low latitude rossby gravity type wave period around 16 ed below the clouds large scale mid to high latitude gravity waves develop and play a significant role in the angular momentum balance

sources and occurrence of c12c22n alkane distributions with even carbon number preference in sedimentary environments abstract the occurrence of c12 c22n alkanes with a strong even carbon number preference is reported in recent and miocene sediments encompassing marine and freshwater systems deposited under oxic and anoxic conditions it is therefore shown that these n alkanes can be found in a wider type of sedimentary environment than those previously described the occurrence in some cases of a parallel distribution of c14 c20n alk 1 enes is also illustrated a variety of biological sources including both marine and freshwater bacteria as well as fungi and yeast species is suggested to account for such distributions

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

western boundary currents in the atmosphere of mars western boundary currents wbcs are an intensification of north south flow adjacent to an eastward facing meridional boundary although most familiar in the oceans where the gulf stream is the best known example wbcs also occur in the earth s troposphere the main example being the east african jet1 which is thought to play an important role in the asiatic monsoon here we identify boundary currents in a different geophysical context a numerical simulation of the atmosphere of mars in our simulation wbcs exist in association with significant cross equatorial flow and the presence of equatorial martian topography which has vertical scale far exceeding terrestrial relief2 the intensity and width of these currents depend on model parameters notably the surface drag from a comparison of our results with other martian models we suggest that wbcs have already been simulated although they were not previously identified as such3 the available observational evidence appears to be consistent with the presence of martian wbcs which may be important in the generation of global and great dust storms

absorption and scattering properties of the martian dust in the solar wavelengths a new wavelength dependent model of the single scattering properties of the martian dust is presented the model encompasses the solar wavelengths 0 3 to 4 3 m at 0 02 m resolution and does not assume a particular mineralogical composition of the particles we use the particle size distribution shape and single scattering properties at viking lander wavelengths presented by pollack et al 1995 we expand the wavelength range of the aerosol model by assuming that the atmospheric dust complex index of refraction is the same as that of dust particles in the bright surface geologic units the new wavelength dependent model is compared to observations taken by the viking orbiter infrared thermal mapper solar channel instrument during two dust storms the model accurately matches afternoon observations and some morning observations some of the early morning observations are much brighter than the model results the increased reflectance can be ascribed to the formation of a water ice shell around the dust particles thus creating the water ice clouds which colburn et al 1989 among others have predicted

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

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

organic markers as source discriminants and sediment transport indicators in south san francisco bay california sediment samples from nearshore sites in south san francisco bay and from streams flowing into that section of the bay have been characterized in terms of their content of biogenic and anthropogenic molecular marker compounds the distributions input sources and applicability of these compounds in determining sediment movement are discussed by means of inspection and multivariate analysis the compounds were grouped according to probable input sources and the sampling stations according to the relative importance of source contributions a suite of polycyclic aromatic hydrocarbons pahs dominated by pyrene fluoranthene and phenanthrene typical of estuarine environments worldwide and suites of mature sterane and hopane biomarkers were found to be most suitable as background markers for the bay a homologous series of long chain n aldehydes c12 c32 with a strong even over odd carbon number dominance in the higher molecular weight range and the ubiquitous n alkanes n c24 c34 with a strong odd over even carbon number dominance were utilized as terrigenous markers several ratios of these terrigenous and bay markers were calculated for each station these ratios and the statistical indicators from the multivariate analysis point toward a strong terrigenous signal in the terminus of south bay and indicate net directional movement of recently introduced sediment where nontidal currents had been considered to be minimal or nonexistent and tidal currents had been assumed to be dominant

possible pingo fields in the utopia basin mars geological and climatical implications abstract the presence of pingos on mars has been hypothesized since the period of the viking mission in fact a diverse range of pingo like features has been found at various martian sites including elysium chryse and utopia planitiae in the northern lowlands due to the morphology and the geological setting some of those features were interpreted in different ways creating some controversies as happened in athabasca valles this reflects the complexity of interpreting these features by remote sensing and multiple plausible interpretations of the same feature with the objective of identifying new possible pingos or rootless cones on mars we selected a study area in utopia planitia 10 55 n 210 260 w where the presence of both features is possible due to its geological history volcanic and hydrological we analyzed more than 2100 mars orbiter camera moc narrow angle images in addition to viking thermal emission imaging system themis and high resolution stereo camera hrsc images together with mars orbiter laser altimeter mola derived digital elevation models dems with a geographic information system gis we found in 94 moc narrow angle images dome cone and ring shaped features we analyzed them from morphological and morphometrical points of view in order to compare them with relevant features on mars and earth we tested different possible origins for those features following the approach of multiple working hypotheses we conclude that the dome cone and ring shaped features could be pingos which is in agreement with their geological settings regarding the driving heat source for the formation of the purported pingos we propose the existence of a heat source possibly a magma chamber underneath the surface of the utopia basin together with possible climatic shifts the past activities of the heat source may have caused melting of ground ice the pingo growth due to freezing of the water would have occurred during the following cold climatic conditions

organic geochemical correlation of oklahoma crude oils using r and q mode factor analysis for the past several decades there has been a significant amount of crude oil exploration and production throughout the state of oklahoma publications with respect to biological marker compound distributions and stable isotopic compositions of oklahoma crude oils their potential genetic relationships and possible sources have however been very limited in this study a detailed organic geochemical investigation of 46 crude oils from throughout the state of oklahoma is presented in addition to assessing similarities and differences of the oils with respect to reservoir ages and geologic provinces an attempt was made to establish possible genetic relationships on the basis of combined r and q mode factor analysis of source related geochemical parameters while the oils from throughout the state were found to be remarkably similar in chemical and stable isotopic composition four genetic families of oils have been delineated based on this statistical approach the possible effects of thermal alteration migration and multiple sources i e mixing of the oil groups are discussed

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

effects of in situ permeability on the propagation of stoneley tube waves in a borehole we investigated the theoretical relationship between propagation characteristics of stoneley tube waves in a borehole and in situ permeability by using a modified formulation of a borehole model with a formation that behaves as a biot porous medium we found that stoneley wave attenuation and phase velocity dispersion increased with increasing permeability and porosity and decreased with increasing frequency in rocks with low to medium permeabilities less than 100 md variations in formation velocity and attentuation were major contributors to variations in stoneley wave properties at normal logging frequencies however in high permeability rocks greater than 100 md coupling between the borehole and pore fluids associated with in situ permeability was more important than lithological changes in controlling stoneley wave properties pore fluid viscosity had an effect on stoneley wave propagation equal but opposite to permeability and hence must he taken into account we compared our theoretical

solar locked and geographical atmospheric structures inferred from a venus general circulation model with radiative transfer abstract solar locked and geographical atmospheric structures of daily averaged wind and temperature on venus were investigated using an atmospheric general circulation model with venusian topography and a two stream radiative code and were compared with wind fields obtained from the akatsuki ultraviolet imager the horizontal wind fields simulated around the subsolar region are similar to the observed ones at the cloud top mid latitude jets of 120 m s 1 and an equatorial fast flow of 90 m s 1 are formed around the cloud top a poleward flow of 8 m s 1 is formed above the cloud layer where solar heating is strong around the cloud top a poleward flow of 1 m s 1 is confined within the equatorward flank of the jet core whereas an indirect circulation is formed in the jet core by the eddy heat fluxes owing to the thermal tide and baroclinic waves in solar fixed coordinates the subsolar to antisolar circulation is predominant around the cloud top thus differences are significant between the zonal and dayside averages of the meridional wind and its related fluxes within the cloud layer this suggests the zonal mean meridional wind of the hadley circulation eddy momentum and heat fluxes from the one side hemisphere must be estimated carefully in the experiment including topography a near surface subrotation is formed in latitudinal zones over high land and mountains a weakly stable layer is formed at 10 20 km at low latitudes and the zonal wind is weakened at the cloud top over the aphrodite terra regional stationary modification of the atmospheric structure due to topographical waves appears in the cloud layer

the martian zonal mean circulation angular momentum and potential vorticity structure in gcm simulations abstract analysis of simulations performed with the nasa ames mars gcm shows that under dusty conditions the northern hemisphere winter solstice circulation becomes characterized by a zonally averaged state in which the potential vorticity at upper levels is very small outside of high latitudes the available observational data in particular the 15 m observations obtained by the viking irtm during the 1977 winter solstice global dust storm provide evidence for changes in the martian circulation that are basically like those found in the gcm in the mars gcm simulations for dusty solstice conditions an extremely intense and approximately angular momentum conserving hadley circulation is responsible for creating the low potential vorticity configuration this can be contrasted with the venus titan numerical simulations discussed by allison et al in which quasi barotropic eddies appear to be largely responsible for the existence of low potential vorticity in lower and midlatitudes at a near equinox seaso

unusual distributions of long chain n alkanes and n alkenes in antarctic soil abstract hydrocarbons in soil samples from the mcmurdo dry valleys of southern victoria land antarctica were studied to examine their features and to elucidate source materials normal alkanes and n alkenes were found at concentrations ranging from 13 to 2200 and from 1 1 to 5000 ng g of dry soil respectively unexpectedly the major hydrocarbons were all odd carbon numbered long chain n alkanes with maximum concentrations n c 23 n c 25 or n c 27 this may be due to the erosion of sedimentary materials containing vascular plant debris formed during the pre and inter glaciation periods of antarctica miocene pliocene and microbial debris such as fungi and microalgae normal alkenes maximize at n c 23 1 carbon chain length number of double bonds n c 25 1 n c 27 1 or n c 29 2 which could be derived from cyanobacteria and microalgae that lived in the past in the antarctic cold desert and or organic debris of wind transported cyanobacterial mats

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

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

organic geochemical studies of a recent inner great barrier reef sediment ii factor analysis of sedimentary organic materials in input source determinations abstract the abundance of bound monocarboxylic acids at seven sites in a tropical carbonate inner great barrier reef sediment depth profile has been analysed to determine input source variations bound components were chosen as after deposition they are degraded less than the free ones factor analysis of acid components reduces the large initial data matrix of acid abundances at each depth into a smaller number of hypothetical factors which can be interpreted in terms of input sources the factors are consistent with six inputs one of higher plant derived material three which are related to previously defined bacterial chemotypes and two microbial or invertebrate inputs three of these inputs higher plant detritus bacteria defined by a high concentration of 18 1 7 and bacteria identified by the presence of branched acids as major components are consistent with inputs previously identified in the surface sediment using biological markers

solar related variations of the cloud top circulation above aphrodite terra from vmc venus express wind fields winds derived by a digital tracking technique from uv 365 nm images captured by the venus monitoring camera onboard the venus express spacecraft from 2006 through 2013 were used to study the atmospheric circulation at cloud top level 70 2 km this data set allows variations of the wind speed with both latitude and longitude to be studied and establishes their correlation with surface topography as well as local time dependence both zonal and meridional wind components show some correlation with topography the minimum zonal wind speed was found at noon above ovda regio 10 s 93 e the highest region of aphrodite terra one of the largest highlands in the equatorial region the area of slow zonal wind extends to at least 30 s and shifts in the direction of superrotation in the afternoon and with increasing latitude poleward the observed deceleration of cloud top wind was recently attributed to the interaction of the gravity mountain waves generated by aphrodite terra with the atmospheric circulation the present study was performed for different local time over the mountainous longitudes the deceleration pattern in the zonal wind field is mainly conserved within a few hours around noon systematic longitude shift is observed in the afternoon in the direction of the evening terminator another area of perturbation of both zonal and meridional wind components is observed in the equatorial region around lt 13 14 h and may be explained by the solar tide

hydrocarbon geochemistry of hydrothermally generated petroleum from escanaba trough offshore californi u s a abstract in 1986 three samples of sulfide rich sediments impregnated with hydrothermally derived asphaltic petroleum were recovered in a dredge and by submersible from escanaba trough the sediment covered southern end of the gorda ridge spreading axis offshore northern california the molecular distributions of hydrocarbons in the two pyrrhotite rich samples recovered by submersible are similar and compare well the hydrocarbon composition of the first pyrrhotite rich samples containing petroleum discovered at a 1985 dredge site about 30 km to the south of the site of the submersible dive in contrast the 1986 dredge sample composed of a polymetallic assemblage of sulfides containes petroleum in which the distribution of hydrocarbons indicates a slightly higher of maturity relative to the other samples the observation that petroleum of variable composition occurs with metallic sulfides at two and probably more distinct site indicates that petroleum generation may be a common process in the hydrothermally active escanaba trough

unusual normal alkane distributions in offshore new zealand sediments the occurrence of unique even carbon dominated normal alkanes in sediment extracts was confirmed in sediments from the eastern continental shelf offshore of north island new zealand in hawke bay the range in carbon chain lengths was from n c16 to least n c36 extending distributions well beyond the previously reported 24 carbons stable isotope analysis of individual alkanes suggest an independent origin for the odd and even n alkanes it is suggested that sedimentary even number n alkane predominances are more widespread than previously thought but go unrecognized due to substantial overprinting by terrestrial derived odd carbon number n alkanes

organic geochemistry of marine sediments in antarctic region marine lipids in mcmurdo sound abstract the compositions of resolvable lipid components from four sediment cores 0 90 cm of mcmurdo sound ross sea have been examined the various lipid components occur in the following order of abundance sterols fatty acids n alcohols n alkanes pah the data indicate that the organic matter is mainly derived from recycled kerogen mixed with modern marine input the distribution of lipids and lignin analyses indicate that there is little recognizable higher plant debris in the sediments the sediments contain unaltered biogenic triterpenoids and there is no evidence for natural and or anthropogenic petroleum influx in the region aeolian transport of organic carbon from the continents appears to be negligible the dominance of labile alkenes c 25 compounds and hopenes and the presence of unsaturated fatty acids down to a depth of 90 cm reflect a very early diagenetic stage the persistent cold climate has probably helped in the better preservation of these labile lipids in the water column and in the young sediments diploptene 17 h 21 h hop 22 29 ene appeats to originate from autochthonous marine productivity in mcmurdo sound

improved general circulation models of the martian atmosphere from the surface to above 80 km we describe a set of two new generation general circulation models of the martian atmosphere derived from the models we originally developed in the early 1990s the two new models share the same physical parameterizations but use two complementary numerical methods to solve the atmospheric dynamic equations the vertical resolution near the surface has been refined and the vertical domain has been extended to above 80 km these changes are accompanied by the inclusion of state of the art parameterizations to better simulate the dynamical and physical processes near the surface boundary layer scheme subgrid scale topography parameterization etc and at high altitude gravity wave drag in addition radiative transfer calculations and the representation of polar processes have been significantly improved we present some examples of zonal mean fields from simulations using the model at several seasons one relatively novel aspect previously introduced by wilson 1997 is that around northern winter solstice the strong pole to pole diabatic forcing creates a quasi global angular momentum conserving hadley cell which has no terrestrial equivalent within such a cell the coriolis forces accelerate the winter meridional flow toward the pole and induce a strong warming of the middle polar atmosphere down to 25 km this winter polar warming had been observed but not properly modeled until recently in fact thermal inversions are generally predicted above one and often both poles around 60 70 km however the mars middle atmosphere above 40 km is found to be very model sensitive and thus difficult to simulate accurately in the absence of observations

thermal inertia mapping of mars from 60 s to 60 n twenty micrometer brightness temperatures are used to derive the thermal inertia for 81 of the martian surface between latitudes 60 these data were acquired by the two viking infrared thermal mappers in 1977 and 1978 following the two global dust storms of 1977 the spatial resolution used is 2 in latitude by 2 in longitude and the total range in derived inertia is 1 to 15 10 3 cal cm 2 sec 12 k 1 the distribution of thermal inertia is strongly bimodal with all values of thermal inertia less than 4 10 3 cal cm 2 sec 12 k 1 being associated with three disjoint bright regions mostly in the northern hemisphere sufficient dust is raised in global storms to provide fine material adequate to produce these low inertia areas but the specific deposition mechanism has not been defined at the low resolution used no complete exposures of clean rock were found there is some tendency for darker material to be associated with higher thermal inertia although the trend is far from one to one the distribution of high and low inertia areas is sufficiently nonrandom to produce a variation in whole disk brightness temperature with central meridian longitude this variation and the change in surface kinetic temperature associated with dust storms are factors in establishing the whole disk brightness temperature at radio and infrared wavelengths and will be important for those who use mars as a calibration source

the mean rotation rate of venus from 29 years of earth based radar observations abstract we measured the length of the venus sidereal day lod from earth based radar observations collected from 1988 to 2017 using offsets in surface feature longitudes from a prediction based on a 243 0185d period derived from analysis of magellan mission images over a 487 day interval we derive a mean lod over 29 years of 243 0212 0 0006d our result is consistent with earlier estimates but with smaller uncertainties including those based on offsets between venus express infrared mapping data and magellan topography that suggest a mean lod of 243 0228 0 002d over a 16 year interval we cannot detect subtle short term oscillations in rate but the derived value provides an excellent fit to observational data over a 29 year period that can be used for future landing site planning

modeling of low frequency stoneley wave propagation in an irregular borehole a fast modeling method is formulated for low frequency stoneley wave propagation in an irregular borehole this fast modeling method provides synthetic waveforms which include the effects of two borehole irregularities diameter changes washout and formation property changes the essential physics of the low frequency stoneley waves are captured with a simple 1 d model a mass balance boundary condition and a propagator matrix are used to express stoneley wave interactions with the borehole irregularities the accuracy of the proposed method was confirmed through comparison with existing finite difference and boundary integral modeling methods that yielded cross correlations greater than 0 98 comparison of synthetic records calculated for an actual borehole with field records showed qualitative agreement in the major reflections because of the washout zones but showed some disagreements in the reflections caused by the fractures since the synthetic records include only information relating to the borehole geometry and the elastic properties of formation the reflection caused by the fracture will appear only in the field record these results suggest the possibility of distinguishing stoneley wave reflections caused by fractures from those caused by borehole irregularities further the fast computational speed of this method over 300 times faster than either boundary integral or finite difference methods makes it quite suitable for field application

aerial seismology using balloon based barometers seismology on venus has long eluded planetary scientists due to extreme temperature and pressure conditions on its surface which most electronics cannot withstand for mission durations required for ground based seismic studies we show that infrasonic low frequency pressure fluctuations generated as a result of ground motion produced by an artificial seismic source known as a seismic hammer and recorded using sensitive microbarometers deployed on a tethered balloon are able to replicate the frequency content of ground motion we also show that weak artificial seismic activity thus produced may be geolocated by using multiple airborne barometers the success of this technique paves the way for balloon based aero seismology leading to a potentially revolutionary method to perform seismic studies from a remote airborne station on the earth and solar system objects with substantial atmospheres such as venus and titan

alleviation of a systematic westerly bias in general circulation and numerical weather prediction models through an orographic gravity wave drag parametrization systematic westerly biases in the northern hemisphere wintertime flow of the meteorological office 15 layer operational model and 11 layer general circulation model are described evidence that the failure to parametrize subgrid scale orographic gravity wave drag may account for such biases is presented this evidence is taken from aircraft studies surface pressure drag measurements and studies of the zonally averaged momentum budget a parametrization scheme is described in which the surface stress is proportional to the near surface wind speed and static stability and to the variance of subgrid scale orography the stress is absorbed in the vertical by considering the influence of such gravity wave activity on static stability and vertical wind shear a richardson number dependent wave breaking formulation is devised and the vertical stress profile determined by a saturation hypothesis whereby the breaking waves are maintained at marginal stability it is shown that wave breaking preferentially occurs in the boundary layer and in the lower stratosphere results from a simple zonally symmetric model show how the adjustment to thermal wind balance with a wave drag in the stratosphere warms polar regions by adiabatic descent and decelerates the mean westerlies in the troposphere the influence of the parametrization scheme on integrations of the 11 layer model is described and found to be generally beneficial in a discussion of the reasons why this problem has only recently emerged it is suggested that the satisfactory northern hemisphere winter circulations of previous coarser general circulation models were due to a compensation implied by underestimating both the surface drag and the horizontal flux of momentum by explicitly resolved large scale eddies

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

orographic control of storm zones on mars low pressure cyclones and their accompanying frontal systems in the middle latitudes of the earth s troposphere develop travel eastwards and decay preferentially within latitudinally and longitudinally confined geographical regions known as storm zones1 these zones can be readily identified in the circulation statistics of terrestrial weather systems2 mars like the earth is a rapidly rotating solid planet and has a seasonally varying shallow atmosphere large scale orography and in a broadly defined context continental structures3 although there are also important differences between the two planets travelling weather systems do exist on mars3 this raises the question of whether storm zones also occur there and if so by what mechanisms here we report the results of numerical simulations of global atmospheric circulation patterns on mars we find that storm zones can exist during the northern winter and that continental scale orography rather than surface thermal contrasts is the main factor determining the development of these zones storm zones on mars should play an important role in the martian climate cycle4 5 by influencing the transport of for example heat momentum water vapour and atmospheric dust3 6 8 towards the poles

co2 ice clouds in the upper atmosphere of mars recent sept 1996 sept 1997 observations of mars submillimeter co lines from the james clerk maxwell telescope jcmt on mauna kea hawaii have revealed surprisingly cold temperatures as typical of the mars atmosphere over the 50 80 km altitude region measurements of these j 2 3 and j 3 4 rotational transitions of mars atmospheric 12co provide unique seasonal coverage of global averaged dayside temperatures within this poorly observed mesophere of mars at solar longitudes ls of 8 90 150 and 187 in 1996 97 the mean atmospheric temperature for the 70 80 km 2 0 0 3 bars altitude region is observed to be at or below 120 k which is only 10 15 k above the vapor saturation temperature for the co2 mars atmosphere consequently local co2 saturation conditions at these altitudes would be likely to exist and in fact were observed during the 3 am descent entry of the pathfinder spacecraft on july 4 1997 we argue that the blue wave clouds imaged from the pathfinder lander 35 100 minutes prior to sunrise on sol 39 are evidence of such co2 ice formation within the 60 100 km altitude region and that the 4 3 m co2 lines of solar scattered flux in mariner 6 and 7 infrared limb spectra of mars are a direct spectral identification of co2 ice cloud formation in the dayside mars mesosphere simple considerations of these pathfinder and mariner 6 and 7 observations suggest 0 1 0 3 m cloud particle radii and particle number densities of the order 10 cm 3 on the basis of a variety of such day and night time measurements we assert that the mesosphere of mars does not exhibit extreme 25 k diurnal temperature variations as maintained by the pathfinder meteorology team and that it is often substantially colder 20 k than determined from the viking descent measurements in 1976 due to temporal variations in dust loading of this region

rotation period of venus estimated from venus express virtis images and magellan altimetry abstract the 1 02 m wavelength thermal emission of the nightside of venus is strongly anti correlated to the elevation of the surface the virtis instrument on venus express has mapped this emission and therefore gives evidence for the orientation of venus between 2006 and 2008 the magellan mission provided a global altimetry data set recorded between 1990 and 1992 comparison of these two data sets reveals a deviation in longitude indicating that the rotation of the planet is not fully described by the orientation model recommended by the iau this deviation is sufficiently large to affect estimates of surface emissivity from infrared imaging a revised period of rotation of venus of 243 023 0 002 d aligns the two data sets this period of rotation agrees with pre magellan estimates but is significantly different from the commonly accepted value of 243 0185 0 0001 d estimated from magellan radar images it is possible that this discrepancy stems from a length of day variation with the value of 243 023 0 002 d representing the average of the rotation period over 16 years

geochemical controls on sediment reactivity and buffering processes in a heterogeneous aquifer the injection and recovery of oxic water into deep anoxic aquifers may help to alleviate short and longterm imbalance between freshwater supply and demand the extent and structure of physical and geochemical heterogeneity of the aquifer will impact the water quality evolution during injection storage and recovery water sediment interactions within the most permeable parts of the aquifer where the bulk of the injectant will penetrate may dominate however water quality may also be impacted by interactions within the finer grained less permeable but potentially highly reactive media in this study the heterogeneity of the reductive capacity of an aquifer selected for water reuse projects was characterised the amount type and reactivity of the sedimentary reductants present determined and the relationship between reductive capacity and sedimentary lithologies quantified the average potential reductive capacities prctot based on total organic c and pyrite concentrations of the sediment were quantified for sands 382 lmol o2 g 1 clays 1522 lmol o2 g

possible origin of n alkanes with a remarkable even to odd predominance in recent marine sediments abstract n alkane distributions with a remarkable even to odd predominance c16 c24 were found in marine surface sediments the previously proposed diagenetic reduction of the corresponding n fatty acids could not be considered as a source for these n alkane based on a comparison of compositional features of n alkane n fatty acid and n alcohol distributions carbon isotope analyses and other geochemical parameters the data indicate that the even predominant n alkanes were derived directly from marine bacteria

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

the vertical structure of limb hazes in the martian atmosphere abstract profiles of scattered light above the planetary limb from over 100 viking orbiter images are used to constrain the temporal and spatial behavior of earosols suspended in the martian atmosphere the data cover a wide range of seasons locations and viewing geometry providing information about the aerosol optical properties and vertical distribution the vertical resolution of the data is about 1 5 km with an absolute elevation accuracy of 1 to 4 km viking orbiter camera colibration algorithms provided reflectance accuracies to 7 absolute allowing meaningful radiometric analysis the typical atmospheric column contains one or more discrete optically thin ice like haze layers between 30 and 90 km elevation depending on season whose composition is inferred to be water ice below the detached hazes there is a continuous haze extending to the surface the continuous haze is rarely observed above 50 km and is much redder in color than the detached hazes above implying a composition that has a strong dust component the aerosol distribution exhibits a strong seasonal control inferred to be driven by the variable solar flux around the orbit of mars

borehole seismic profiling and tube wave applications in a dam site investigation continuous single channel reflection profiling has been carried out in pvc lined boreholes primarily with the aim of ascertaining the position of an old subsurface gas storage tunnel on a proposed dam site tube wave reflection patterns thus generated have been interpreted in terms of sediment rigidity and shear wave velocity and these results could be compared with some independent data it is interesting to note that within the well section penetrating tertiary clays the velocity of the hydraulic transients apparently was not affected by the pvc casing which might be explained by a tight coupling between casing and clay wall in such situations tube waves turn out a straightforward tool for the determination of shear wave velocity and the derivation of dynamic elastic moduli of unconsolidated sediments further applications of the study of the distribution of seismic velocities on the dam site dealt with the consolidation history of the clays a level of abnormally low p wave velocities has been detected and interpreted as a gas charged horizon which by its coincidence with the base level of clay diapirs might be considered to have contributed to clay flowage in past geological times data about maximum past burial depth derived from shear wave velocities more turned out to be in agreement with results from consolidation testing less

fracture detection in oil based drilling mud using a combination of borehole image and sonic logs abstract the deeply buried 5 5 7 1 km lower cretaceous bashijiqike sandstones are important fractured reservoirs in the kuqa depression in these high temperature high pressure drilling environments oil based muds are used to limit drilling risks and improve efficiency making facture detection using resistivity based image logs difficult the maximum horizontal stress sh max trends close to north south 0 10 based on orientations of the drilling induced fractures and borehole breakouts core descriptions thin sections and image logs used to describe the fractures in the bashijiqike sandstone reservoirs show that opening mode natural fractures are common and the fractures range from fully open to sealed by calcite and clay minerals the open fractures are dominantly steeply dipping or vertical and primarily strike north south locally horizontal fractures or fractures with low angle dip are detected we compare fracture visibility on image logs acquired in the same ks 2 2 12 key well in oil based mud and water based mud fmi hd logs successfully detect large 0 1 mm aperture vertical fractures in oil based mud better than obmi image logs and the two imaging tools have a similar ability in detecting the high dip angle fractures since the ubi tool is not affected by oil based muds most of the fractures can be picked out on ubi images minor negative deviations of bulk density could be observed in fractured zones and the presence of fractures obviously causes an increase in sonic transit time full waveforms from dsi tools combined with electrical image logs detect fractured zones both the velocity and amplitude of the sonic waves are sensitive to fractures and the fractured zones could be identified according to the attenuation of stoneley waves the combination of cores image logs and full wave sonic logs offers comprehensive detection of fractures in oil based mud environments

prediction of source rock characteristics based on terpane biomarkers in crude oils a multivariate statistical approach abstract the distributions of eight tricyclic and eight pentacyclic terpanes were determined for 216 crude oils located worldwide with subsequent simultaneous rq mode factor analysis and stepwise discriminate analysis for the purpose of predicting source rock features or depositional environments five categories of source rocks are evident nearshore marine i e paralic deltaic deeper water marine lacustrine phosphaticrich source beds and ordovician age source rocks the first two factors of the rq mode factor analysis describe 45 percent of the variation in the data set the tricyclic terpanes appear to be twice as significant as pentacyclic terpanes in determining the variation among samples lacustrine oils are characterized by greater relative abundances of c 21 diterpane and gammacerane nearshore marine sources by c 19 and c 20 diterpanes and oleanane deeper water marine facies by c 24 and c 25 tricyclic and c 31 plus c 32 extended hopanes and ordovician age oils by c 27 and c 29 pentacyclic terpanes although thermal maturity trends can be observed in factor space the trends do not necessarily obscure the source rock interpretations also since bacterial degradation of crude oils rarely affects tricyclic terpanes biodegraded oils can be used in predicting source rock features the precision to which source rock depositional environments are determined might be increased with the addition of other biomarker e g steranes and stable isotope data using multivariate statistical techniques

thermal structure and dust loading of the martian atmosphere during late southern summer mariner 9 revisited the temperature structure and dust loading of the martian atmosphere are investigated using thermal emission spectra recorded by the mariner 9 infrared interferometer spectrometer iris the analysis is restricted to a subset of the iris data consisting of approximately 2400 spectra in a 12 day period extending from ls 343 to ls 348 corresponding to late southern summer on mars simultaneous retrieval of the vertical distribution of both atmospheric temperature and dust optical depth is accomplished through an iterative procedure which is performed on each spectrum the inclusion of dust opacity in the retrieval algorithm causes the retrieved temperatures to change by more than 20 k in some atmospheric layers the largest column integrated 9 m dust optical depths 0 4 occur over the equatorial regions the highest atmospheric temperatures 260 k are found at low altitudes near the subsolar latitude 6 s while the coldest temperatures 150 k are found at levels near 1 0 mbar over the winter pole a comparison of temperature maps for 1400 lt and 0200 lt indicates diurnal temperature variations as large as 80 k at low altitudes near the subsolar latitude whereas diurnal temperature changes at pressures less than 1 0 mbar are typically about 10 k both dayside and night side temperatures above about 0 1 mbar 40 km are warmer over the winter north polar region than over the equator or the summer south polar region this thermal structure suggests the existence of a net zonally averaged meridional circulation with rising motion at low latitudes poleward flow at altitudes above 40 km and subsidence over the poles because a meridional circulation transports atmospheric constituents as well as heat it has significant implications for the net flux of dust and water into the polar regions

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

atmospheric mountain wave generation on venus and its influence on the solid planet s rotation rate the akatsuki spacecraft observed a 10 000 km long meridional structure at the top of the cloud deck of venus that appeared stationary with respect to the surface and was interpreted as a gravity wave additionally over four venus solar days of observations other such waves were observed to appear in the afternoon over equatorial highland regions this indicates a direct influence of the solid planet on the whole venusian atmosphere despite dissimilar rotation rates of 243 and 4 days respectively how such gravity waves might be generated on venus is not understood here we use general circulation model simulations of the venusian atmosphere to show that the observations are consistent with stationary gravity waves over topographic highs or mountain waves that are generated in the afternoon in equatorial regions by the diurnal cycle of near surface atmospheric stability we find that these mountain waves substantially contribute to the total atmospheric torque that acts on the planet s surface we estimate that mountain waves along with the thermal tide and baroclinic waves can produce a change in the rotation rate of the solid body of about 2 minutes per solar day this interplay between the solid planet and atmosphere may explain some of the difference in rotation rates equivalent to a change in the length of day of about 7 minutes measured by spacecraft over the past 40 years

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

a statistical approach to the interpretation of aliphatic hydrocarbon distributions in marine sediments abstract q mode factor analysis was used to quantitate the distribution of the major aliphatic hydrocarbon n alkanes pristane phytane systems in sediments from a variety of marine environments the compositions of the pure end members of the systems were obtained from factor scores and the distribution of the systems within each sample was obtained from factor loadings all the data from the diverse environments sampled estuarine san francisco bay fresh water san francisco peninsula polar marine antarctica and geothermal marine gorda ridge sediments were reduced to three major systems a terrestrial system mostly high molecular weight aliphatics with odd numbered carbon predominance a mature system mostly low molecular weight aliphatics without predominance and a system containing mostly high molecular weight aliphatics with even numbered carbon predominance with this statistical approach it is possible to assign the percentage contribution from various sources to the observed distribution of aliphatic hydrocarbons in each sediment sample

topographical and local time dependence of large stationary gravity waves observed at the cloud top of venus the existence of large stationary gravity waves was discovered during akatsuki s first observation sequence in 2015 in this study the further detection of large stationary gravity waves in brightness temperature images over a 1 5 year period is reported the waves periodically appeared mostly above four specific highland regions in the low latitudes when these regions were in the local afternoon the wave amplitudes attenuated after the wave locations passed beyond the evening terminator and the locations of the waves tended to slowly drift eastward over their lifetimes the appearances of stationary waves depend not only on surface topography but also on latitude and local time suggesting that solar heating during the daytime and atmospheric structure affected by solar heating may control the excitation and propagation of stationary waves

mesoscale modeling of venus bow shape waves abstract the akatsuki instrument lir measured an unprecedented wave feature at the top of venusian cloud layer stationary bow shape waves of thousands of kilometers large lasting several earth days have been observed over the main equatorial mountains here we use for the first time a mesoscale model of the venus s atmosphere with high resolution topography and fully coupled interactive radiative transfer computations mountain waves resolved by the model form large scale bow shape waves with an amplitude of about 1 5 k and a size up to several decades of latitude similar to the ones measured by the akatsuki spacecraft the maximum amplitude of the waves appears in the afternoon due to an increase of the near surface stability propagating vertically the waves encounter two regions of low static stability the mixed layer between approximately 18 and 30 km and the convective layer between 50 and 55 km some part of the wave energy can pass through these regions via wave tunneling these two layers act as wave filter especially the deep atmosphere layer the encounter with these layers generates trapped lee waves propagating horizontally no stationary waves is resolved at cloud top over the polar regions because of strong circumpolar transient waves and a thicker deep atmosphere mixed layer that filters most of the mountain waves

borehole stoneley wave propagation across permeable structures this study investigates the propagation of borehole stoneley waves across permeable structures by modeling the structure as a zone intersecting the borehole a simple 1d theory is formulated to treat the interaction of the stoneley wave with the structure this is possible because the stoneley wave is a guided wave with no geometric spreading as it propagates along the borehole the interaction occurs because the zone and the surrounding formation possess different stoneley wavenumbers given appropriate representations of the wavenumber the theory can be applied to treat a variety of structures including a fluid filled fracture of special interest are the cases of permeable porous zones and fracture zones the results show that while stoneley wave reflections are generated strong stoneley wave attenuation is produced across a very permeable zone this result is particularly important in explaining the observed strong stoneley wave attenuation at major fractures where it has been difficult to explain the attenuation in terms of the single planar fracture theory in addition by using a simple and sufficiently accurate theory to model the effects of the permeable zone a fast and efficient method is developed to characterize the fluid transport properties of a permeable fracture zone

a numerical investigation of head waves and leaky modes in fluid filled boreholes although synthetic borehole seismograms can be computed for a wide range of borehole conditions the physical nature of shear and compressional head waves in fluid filled boreholes is poorly understood this paper presents a series of numerical experiments designed to explain the physical mechanisms controlling head wave propagation in boreholes these calculations demonstrate the existence of compressional normal modes equivalent to shear normal modes or pseudo rayleigh waves with sequential cutoff frequencies spaced between the cutoff frequencies for the shear normal modes major contributions to head wave spectra occur in discrete peaks at frequencies just below mode cutoff for both compressional and shear modes this result is confirmed by calculations with synthetic waveforms at frequencies corresponding to mode cutoff and by branch cut integrals designed to yield independent spectra for the compressional mode for soft formations where shear velocity falls below acoustic velocity in the borehole

acoustic waves in sand screened deepwater completions comparison of experiments and modeling real timecompletionmonitoringwithacousticwaveshas been proposed recently as a method to monitor permeability changes along completions typical deepwater completions containadditionallayersofsandscreen gravelsand andperforatedcasing whichmakethemquitedifferentfromafluidfilled open borehole monitoring changes in flow properties across the completion is crucial because impairment of permeabilityinanyoftheselayerscouldcausereducedwellproductivity in contrast to an open hole model a sand screened completion supports two tube waves related to an inner fluid column and a gravel suspension in the annulus to study effects of screen and sand permeability on tube wave signatures weconstructsimplenumericalmodelsofvariouscompletionscenariosusingporoelasticdescriptionsofscreenand sand models generally predict that a fast tube wave does not attenuate at either low or high permeability but experiences resonant attenuation at intermediate frequencies in contrast a slow tube wave attenuates completely above a certain permeabilityvalue modelsprovideaqualitativeandsometimes a semiquantitative description for signatures of the fast tube wave however theyareunabletoexplainwhytheslowtube wave is observed in experiments with high permeabilities of sandandscreen wespeculatethatabettermodelofcomplex sandscreensisrequiredtomatchexperimentaldata

the parametrization of drag induced by stratified flow over anisotropic orography a new parametrization of drag arising from the flow over unresolved topography ut in a general circulation model gcm is presented it is comprised of three principle components a parametrization of the source spectrum and drag associated with freely propagating hydrostatic gravity waves in the absence of rotation a parametrization of the drag associated with low level wave breaking and a parametrization of low level drag associated with upstream blocking and lee vortex dynamics novel features of the scheme include a new procedure for defining the ut in each gcm grid cell which takes account of the gcm resolution and includes only the scales represented by the parametrization scheme a new method of representing the azimuthal distribution of vertical momentum flux by two waves whose direction and magnitude systematically vary with the flow direction and with the anisotropy of the ut in each gcm grid cell and a new application of form drag in the lowest levels which can change the direction of the low level flow so that it is more parallel to unresolved two dimensional topographic ridges the new scheme is tested in the canadian centre for climate modelling and analysis third generation atmospheric gcm at horizontal resolutions of t47 and t63 five year seasonal means of present day climate show that the new scheme improves mean sea level pressures or mass distribution and improves the tropospheric circulation when compared with the gravity wave drag scheme used currently in the gcm the benefits are most pronounced during northern hemisphere winter it is also found that representing the azimuthal distribution of the momentum flux of the freely propagating gravity wave field with two waves rather than just one allows 30 50 more gravity wave momentum flux up into the middle atmosphere depending on the season the additional momentum flux into the middle atmosphere is expected to have a beneficial impact on gcms that employ a more realistic representation of the stratosphere

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

sonic logging of compressional wave velocities in a very slow formation borehole sonic waveforms are commonly acquired to produce logs of subsurface compressional and shear wave velocities to this purpose modern borehole sonic tools are usually equipped with various types of acoustic sources i e monopole and dipole sources while the dipole source has been specifically developed for measuring shear wave velocities we found that the dipole source has an advantage over the monopole source when determining compressional wave velocities in a very slow formation consisting of unconsolidated sands with a porosity of about 35 and a shear wave velocity of about 465 m s in this formation the recorded compressional refracted waves suffer from interference with another wavefield component identified as a leaky p wave which hampers the determination of compressional wave velocities in the sands for the dipole source separation of the compressional refracted wave from the recorded waveforms is accomplished through bandpass filtering since the wavefield components appear as two

the speed of a tube wave the low frequency tube wave speed is given explicitly for a variety of borehole environments the presence of a logging tool the effects of casing and bore eccentricity are considered the results are all relatively simple and indicate that the speed decreases in the presence of a tool or borehole eccentricity the speed increases in the presence of casing as long as the casing shear modulus exceeds that of the formation

solstitial temperature inversions in the martian middle atmosphere observational clues and 2 d modeling abstract the possible existence of stable warming at middle altitudes in the martian atmosphere was first examined by j r barnes j geophys res 95 1401 1990 in one dimensional modeling of the effect of breaking gravity waves on the general circulation this work was motivated by infrared observations of d deming m j mumma f espenak t kostius and d zipoy icarus 66 366 1986 which suggested temperatures far from radiative equilibrium above polar regions at solstice new observational evidence was obtained from heterodyne measurements of the j 2 1 12 co and 13 co transitions made during the 1988 opposition at this date corresponding to southern summer solstice these lines were mapped as a function of the position on the martian disk with the iram 30 m telescope wind velocities near 50 km altitude and vertical thermal profiles were derived from the doppler shift and the line profiles respectively at various locations on mars the northern winter hemisphere profiles indicate the presence of a warm layer in the 40 60 km altitude range with a relative warming of 5 k compared to smoothly decreasing temperature profiles such as those found in the southern hemisphere this may be interpreted in terms of a temperature inversion in the northern middle atmosphere such a phenomenon may be similar to the stable inversion layers observed in the terrestrial mesosphere which are believed to be a response to the gravity wave activity we show that a zonally averaged model of the martian middle atmosphere using the parametrization of gravity waves effects propounded by r s lindzen j geophys res 86 9707 1981 is able to produce both a plausible zonal wind field consistent with the measurements of e lellouch j j goldstein s w bougher g paubert and j rosenqvist astrophys j 383 401 1991 and a thermal field in good agreement with the observations the 2 d modeling further indicates that weak equatorial thermal inversions may occur due to the penetration of the summer hemisphere retrograde jet into the winter hemisphere

atmospheric thermal structure and cloud features in the southern hemisphere of venus as retrieved from virtis vex radiation measurements thermal structure and cloud features in the atmosphere of venus are investigated using spectroscopic nightside measurements recorded by the visible and infrared thermal imaging spectrometer virtis aboard esa s venus express mission in the moderate resolution infrared mapping channel m ir 1 5 m new methodical approaches and retrieval results for the northern hemisphere have been recently described by haus et al haus r kappel d arnold g 2013 planet space sci 89 77 101 http dx doi org 10 1016 j pss 2013 09 020 now southern hemisphere maps of mesospheric temperature and cloud parameter fields are presented that cover variations with altitude latitude local time and mission time measurements from the entire usable data archive are utilized comprising radiation spectra recorded during eight venus solar days between april 2006 and october 2008 zonal averages of retrieved temperature altitude profiles in both hemispheres are very similar and give evidence of global n s axial symmetry of atmospheric temperature structure cold collar and warmer polar vortex regions exhibit the strongest temperature variability with standard deviations up to 8 5 k at 75 s and 63 km altitude compared with about 1 0 k at low and mid latitudes above 75 km the mesospheric temperature field strongly depends on local time at altitudes above about 75 km the atmosphere is warmer in the second half of night while the dawn side at lower altitudes is usually colder than the dusk side by about 8 k local minimum temperature of 220 k occurs at 03 00 h local time at 65 km and 60 s temperature standard deviation at polar latitudes is particularly large near midnight temperature variability with solar longitude is forced by solar thermal tides with a dominating diurnal component the influence of observed cloud parameter changes on retrieved mesospheric zonal average temperature structure is moderate and does not exceed 2 3 k at altitudes between 60 and 75 km the mesospheric thermal structure was essentially stable with julian date between 2006 and 2008 global n s axial symmetry is also observed in cloud structures cloud top altitude at 1 m slowly decreases from 71 km at the equator to 70 km at 45 50 and rapidly drops poleward of 50 it reaches 61 km over both poles average particle size in the vertical cloud column increases from mid latitudes toward the poles and also toward the equator resulting in minimum and maximum zonal average cloud opacities of about 32 and 42 and a planetary average of 36 5 at 1 m zonal averages of cloud features are similar at different solar days but variations with local time are very complex and inseparably associated with the superrotation of the clouds

new dust opacity mapping from viking infrared thermal mapper data global dust opacity mapping for mars has been carried forward using the approach described by martin 1986 for viking ir thermal mapper data new maps are presented for the period from the beginning of viking observations until ls 210 in 1979 1 36 mars years this range includes the second and more extensive planet encircling dust storm observed by viking known as storm 1977b improvements in approach result in greater time resolution and smaller noise than the earlier work a strong local storm event filled the hellas basin at ls 170 prior to the 1977a storm dust is retained in equatorial regions following the 1977b storm far longer than in mid latitudes minor dust events appear to raise the opacity in northern high latitudes during northern spring additional mapping with high time resolution has been done for the periods of time near the major storm origins in order to search for clues to the mechanism of storm initiation the first evidence of the start of the 1977b storm is pushed back to ls 274 2 preceding signs of the storm in images by about 15 hours

core concept to improve weather and climate models researchers are chasing atmospheric gravity waves on september 3 2018 an unpowered experimental sailplane made history by flying into the stratosphere after leaving from el calafate a town near the southern patagonian ice field in argentina glider pilots jim payne and tim gardner surfed on enormous airborne waves emanating from the andes mountains they achieved a world record height of 23 203 meters higher than a lockheed u 2 spy plane s cruising altitude no other unpowered aircraft has ever achieved such elevation it was a feat made possible by not just human ingenuity but also the incredible strength of a phenomenon known as atmospheric gravity waves atmospheric gravity waves seen here over the indian ocean via the moderate resolution imaging spectroradiometer housed in nasa s terra satellite emerge when parcels of air are forced upward image credit jacques descloitres modis rapid response team nasa gsfc unlike the similarly named and perhaps more famous cosmic gravitational waves which are ripples in the fabric of space time atmospheric gravity waves are a wholly terrestrial occurrence they emerge when parcels of air are forced upward for instance by a tall mountain range moving from a dense atmospheric layer to a thinner one the heavier blobs of air then succumb to the force of gravity and fall back down resulting in a periodic oscillation that can carry energy and momentum over vast distances they are the smallest atmospheric waves that researchers study generally between a few hundred meters and a few hundred kilometers in size but their cumulative effects can be dramatic the actions of atmospheric gravity waves bring energy from the troposphere the lowest atmospheric layer which ends at an altitude of about 10 kilometers out past the edge of space 500 or more kilometers above earth s surface they play important roles in daily weather as well as long term climate fluctuations decelerating powerful jet streams and affecting the circulating