venus express virtis observations of middle and lower cloud variability and implications for dynamics 1 we present an analysis of venus express visible and infrared thermal imaging spectrometer virtis data carried out to characterize the morphological geographical and evolutionary trends of the middle and lower cloud features that are observed in the atmosphere of venus as variations in brightness temperatures in specific near infrared wavelengths in this preliminary study we analyze only data collected over the span of 11 orbits the mean radiance as a function of latitude is consistent with previous ground based observations indicating that the overall global distribution of mean cloud cover is stable at least on a 10 to 20 year time scale in contrast with the consistent level of radiance at high latitudes a significant amount of variability to the radiance exists at lower latitudes consistent with significant convective activity in the lower and middle cloud decks the morphology of the holes tends from highly variable orientations of features with aspect ratios of nearly one at low latitudes to very large aspect ratios and zonally oriented features at higher latitudes the peak radiance of the holes appears not to demonstrate a latitudinal tendency there is evidence of more variability to the morphology and radiance of features at lower latitudes to investigate the evolution of the holes we examine a sequence of images taken over a 5 h span of a single orbit if this limited amount of data is representative then the typical e folding time scale for the evolution of a hole is about 1 day

the transport mechanisms of clay and fine silt in the north irish sea abstract the north irish sea represents an area of reworked sediments of very variable mechanical composition a particle size distribution study of these sediments however reveals an underlying correlation between the proportion of m material and the sand mode further throughout the range of samples examined this finer material has a very similar inherant particle size distribution and mineralogical composition the suggestion is made that this size grade is transported as flocs independently of the sand particles and this is supported from the study of flocs formed experimentally from a selection of the samples

local scouring at grade control structures in alluvial mountain rivers 1 scour holes below 73 grade control structures check dams and bed sills in six mountain rivers located in the eastern italian alps have been surveyed the most likely formative water discharge is used to evaluate jet thickness at each structure which along with drop height appears to determine scour hole dimensions as shown by the consistent trends observed for nondimensional plots of both maximum scour depth and length versus the respective drop ratio sediment differences regarding size and lithology apparently play a minor role in determining scour hole dimension measured maximum scour depths are well predicted by a semiempirical equation developed through laboratory results showing an average relative error of 0 13 scour hole geometry is described by several ratios that are thought to represent approximately invariant characteristics a new energy based normalization for scour hole dimensions is proposed as the most suited to evaluate the role of jet geometry and aeration upon scouring efficiency it is noteworthy that the ratio between the maximum scour depth and the total energy available at a drop tends toward an asymptotic value around unity for increasing drop heights

interference processes on scouring at bed sills the local scouring downstream of bed sills forming a sequence for bed stabilization in steep channels has been investigated in a laboratory flume the initial bed slopes ranged from 0 078 to 0 148 the bed alluvium was characterised by a non uniform grain size distribution the results show that when the ratio between the critical water depth hc and the sill spacing l rises above a characteristic value the scouring dynamics become heavily affected by the presence of the downstream sill associated with the onset of a form of interference which renders the scouring process less effective the difference with an undisturbed case is demonstrated self affinity of scour holes is confirmed and the scour length appears to be the reference parameter from which the scour depth might be evaluated copyright 2003 john wiley sons ltd

accumulation of late pleistocene and holocene biogenic sands and gravels on the continental shelf between northern scotland and western france abstract the paper reviews 51 radiocarbon ages for calcareous biogenic material from the top few centimetres of sands and gravels on the continental shelf between northern scotland and western france the majority of the ages fall within the past 5000 years while sea level was almost at its present height some dates represent the first half of the holocene and others date back to the late pleistocene they show that these sands and gravels have a high preservation potential under present conditions despite the evidence of bioerosion disturbance by storm waves and transport of material by currents the surface samples are well mixed and are classified as present day deposits underlying sediments young upwards where deposition is permitted but are condensed where thickening is virtually disallowed

alluvial channel geometry theory and applications the downstream hydraulic geometry of alluvial channels in terms of bank full width average flow depth mean flow velocity and friction slope is examined from a three dimensional stability analysis of noncohesive particles under two dimensional flows four governing equations flow rate resistance to flow secondary flow and particle mobility are solved to analytically define the downstream hydraulic geometry of noncohesive alluvial channels as a function of water discharge sediment size shields number and streamline deviation angle the exponents of hydraulic geometry relationships change with relative submergence four exponent diagrams illustrate the good agreement with several empirical regime equations found in the literature the analytical formulations were tested with a comprehensive data set consisting of 835 field channels and 45 laboratory channels the data set covers a wide range of flow conditions from meandering to braided sand bed and gravel bed rivers with flow depths and channe

effects of gravity waves on the day night difference of the general circulation in the venusian lower thermosphere 1 we investigated generation mechanisms of the local time variation of the wind velocity in the venusian mesosphere and thermosphere which has been suggested from recent ground based co millimeter submillimeter and co2 10 m observations using our general circulation model our model considers the momentum transport caused by gravity waves with the gravity wave parameterization developed by medvedev and klaassen 2000 our results show that atmospheric circulation distinctly changes from the dayside to the nightside the subsolar to antisolar ssas wind is predominant in the dayside on the other hand the retrograde superrotating zonal rsz wind is superposed on the ssas wind in the nightside these characteristics are consistent with the previous observations the westward momentum which drives the rsz wind in the nightside at an altitude of 110 km is supplied by gravity waves in the 115 130 km altitude region the downward flow that originates in the ssas wind transports the westward momentum downward in the nightside

variable winds on venus mapped in three dimensions 1 we present zonal and meridional wind measurements at three altitude levels within the cloud layers of venus from cloud tracking using images taken with the virtis instrument on board venus express at low latitudes zonal winds in the southern hemisphere are nearly constant with latitude with westward velocities of 105 ms 1 at cloud tops altitude 66 km and 60 70 ms 1 at the cloud base altitude 47 km at high latitudes zonal wind speeds decrease linearly with latitude with no detectable vertical wind shear values lower than 15 ms 1 indicating the possibility of a vertically coherent vortex structure meridional winds at the cloud tops are poleward with peak speed of 10 ms 1 at 55 s but below the cloud tops and averaged over the south hemisphere are found to be smaller than 5 ms 1 we also report the detection at subpolar latitudes of wind variability due to the solar tide

venus express mission 1 venus express is well and healthy and has now been providing exciting new data from venus our nearby twin planet for over 2 years many of the new results are presented and discussed in the subsequent papers in this special section the overall scientific objective of venus express is to carry out a detailed study of the atmosphere of venus including the interaction of the upper atmosphere with the solar wind and the interaction of the lowest part of the atmosphere with the surface of the planet in addition the plasma environment and magnetic fields as well as some aspects of the surface of the planet are addressed for the first time investigations make systematic use of the transparent infrared spectral windows in order to probe the atmosphere in four dimensions three spatial dimensions plus time the spacecraft design is taken from mars express with some modifications necessary owing to the specific environment around venus the payload is composed of three spectrometers a camera a magnetometer an instrument for detecting energetic particles and a radio science package the orbit is polar and highly elliptic with a pericenter altitude of about 200 km over the northern polar region and an apocenter altitude of 66 000 km presently the coverage of the southern hemisphere is very good but important gaps still do exist the coverage of the northern hemisphere is much less dense venus express is a part of the european space agency s program for the exploration of the inner solar system which includes missions to study the sun mercury venus the moon mars and comets and asteroids

characterization of mesoscale gravity waves in the upper and lower clouds of venus from vex virtis images 1 images obtained from the visible and infrared thermal imaging spectrometer virtis m instrument onboard venus express present visible trains of alternating bands of cloud brightness in two different layers at the upper cloud tops 66 km altitude observed in the dayside hemisphere using reflected ultraviolet light 380 nm and in the lower cloud 47 km altitude observed in the nightside hemisphere using thermal radiation 1 74 m the waves are nearly zonal with the bands perpendicular to latitude circles have wavelengths of 60 150 km propagate westward with low phase velocities relative to the zonal flow and are confined in wave packets of 400 to 1800 km in length the waves in the lower cloud observed in the infrared are widely distributed around the planet and their appearance varies widely throughout the virtis data set the locations of both types of waves seem not correlated with latitude local times surface topography or the structure of the wind in both cases the characteristics of the waves correspond to gravity waves propagating in confined stable layers of the atmosphere we examine the properties of these waves in terms of a linear model and perform a simple analysis to discuss the vertical stability of the atmosphere within venus clouds

the rise of hydrological science off earth summary it has been a long lasting interest to understand the laws that underlie water movement on earth with the purpose to control it and make use of it it is now recognized that water is not exclusive to the earth but rather is a major constituent of the matter in the universe and may be a proxy for life in other planets as well in this paper we reflect on the need to expand the boundaries of the current water sciences from the description of mere terrestrial hydrological processes to a comprehensive inclusion of the physical laws and processes pertaining to water dynamics off earth are we at the edge of a new scope of hydrology

south polar features on venus similar to those near the north pole venus has no seasons slow rotation and a very massive atmosphere which is mainly carbon dioxide with clouds primarily of sulphuric acid droplets infrared observations by previous missions to venus revealed a bright dipole feature surrounded by a cold collar at its north pole the polar dipole is a double eye feature at the centre of a vast vortex that rotates around the pole and is possibly associated with rapid downwelling the polar cold collar is a wide shallow river of cold air that circulates around the polar vortex one outstanding question has been whether the global circulation was symmetric such that a dipole feature existed at the south pole here we report observations of venus south polar region where we have seen clouds with morphology much like those around the north pole but rotating somewhat faster than the northern dipole the vortex may extend down to the lower cloud layers that lie at about 50 km height and perhaps deeper the spectroscopic properties of the clouds around the south pole are compatible with a sulphuric acid composition

images from galileo of the venus cloud deck images of venus taken at 418 violet and 986 near infrared nir nanometers show that the morphology and motions of large scale features change with depth in the cloud deck poleward meridional velocities seen in both spectral regions are much reduced in the nir in the south polar region the markings in the two wavelength bands are strongly anticorrelated the images follow the changing state of the upper cloud layer downwind of the subsolar point and the zonal flow field shows a longitudinal periodicity that may be coupled to the formation of large scale planetary waves no optical lightning was detected

statistical analysis of mineral diversity and distribution earth s mineralogy is unique abstract earth s mineralogical diversity arises from both deterministic processes and frozen accidents we apply statistical methods and comprehensive mineralogical databases to investigate chance versus necessity in mineral diversity distribution relationships hundreds of mineral species including most common rock forming minerals distinguish an earth like planet from other terrestrial bodies however most of earth s 5000 mineral species are rare known from only a few localities we demonstrate that in spite of deterministic physical chemical and biological factors that control most of our planet s mineral diversity earth s mineralogy is unique in the cosmos

effect of sill spacing and sediment size grading on scouring at grade control structures sequences of arti cial steps are sometimes used to reproduce the natural step pool morphology of high gradient streams the depth length and shape of the scour holes in gravel bed rivers can be predicted reasonably using recently developed formulae however the properties of the scour holes can sometimes be affected by the distance between structures this effect is called geometrical interference and leads to a reduction of the scour hole compared to its potential size geometrical interference may occur in sequences of arti cial steps in high gradient torrents where structures are sometimes built at distances of a few tens of metres apart but may also apply to natural step pool systems in this paper a series of tests have been conducted to determine the effect of bed sill spacing and sediment grading on the potential erosion by jets forming over the sills a new formula is derived applicable to high gradient streams slope 0 04 which can be applied to the special case of scour holes developed by interfering sills sediment size gradation not accounted for in previous formulae is found to have a signi cant effect on the scour dimensions and is included in the new predictive formula copyright 2004 john wiley sons ltd

mapping zonal winds at venus s cloud tops from ground based doppler velocimetry abstract the most significant aspect of the general circulation of the atmosphere of venus is its retrograde super rotation a complete characterization of this dynamical phenomenon is crucial for understanding its driving mechanisms here we report on ground based doppler velocimetry measurements of the zonal winds based on high resolution spectra from the uv visual echelle spectrograph uves instrument at eso s very large telescope under the assumption of predominantly zonal flow this method allows the simultaneous direct measurement of the zonal velocity across a range of latitudes and local times in the day side the technique based on long slit spectroscopy combined with the high spatial resolution provided by the vlt has provided the first ground based characterization of the latitudinal profile of zonal wind in the atmosphere of venus the first zonal wind field map in the visible as well as new constraints on wind variations with local time we measured mean zonal wind amplitudes between 106 21 and 127 14 m s at latitudes between 18 n and 34 s with the zonal wind being approximately uniform in 2 6 wide latitude bands 0 3 arcsec at disk center the zonal wind profile retrieved is consistent with previous spacecraft measurements based on cloud tracking but with non negligible variability in local time longitude and in latitude near 50 the presence of moderate jets is apparent in both hemispheres with the southern jet being stronger by 10 m s small scale wind variations with local time are also present at low and mid latitudes

high resolution cloud feature tracking on venus by galileo abstract the venus cloud deck was monitored in february 1990 for 16 hours at 400 nanometers wavelength by the galileo imaging system with a spatial resolution of about 15 km and with image time separations as small as 10 minutes velocities are deduced by following the motion of small cloud features in spite of the high temporal frequencies capable of being detected no dynamical phenomena are apparent in the velocity data except the already well known solar tides possibly altered by the slow 4 day wave and the hadley circulation there is no evidence to a level of approximately 4 m s 1 of eddy or wavelike activity the dominant size of sub global scale albedo features is 200 500 km and their contrast is approximately 5 at low latitudes there are patches of blotchy cell like structures but at most locations the markings are streaky the patterns are similar to those discovered by mariner 10 and pioneer venus m j s belton et al 1976 j atmos sci 33 1383 1393 w b rossow et al 1980 j geophys res 85 8107 8128 scaling arguments are presented to argue that the mesoscale blotchy cell like cloud patterns are caused by local dynamics driven in a shallow layer by differential absorption of sunlight it is also argued that mesoscale albedo features are either streaky or cell like simply depending on whether the horizontal shear of the large scale flow exceeds a certain critical value

the structure of venus middle atmosphere and ionosphere esa s venus express probe has been in orbit since april 2006 eight research papers in this issue present new results from the mission covering the atmosphere polar features interactions with the solar wind and the controversial matter of venusian lightning hakan svedham et al open the section with a review of the similarities and mostly differences between venus and its twin the earth andrew ingersoll considers the latest results and also how the project teams plan to make the most of the probe s remaining six years of life radio sounding results from the first venus express radio science vera occultation season are reported which determine the fine structure in temperatures at upper cloud deck altitudes detect a distinct day night temperature difference in the southern middle atmosphere and track day to day changes in venus ionosphere the atmosphere and ionosphere of venus have been studied in the past by spacecraft with remote sensing1 2 3 4 or in situ techniques3 4 these early missions however have left us with questions about for example the atmospheric structure in the transition region from the upper troposphere to the lower mesosphere 50 90 km and the remarkably variable structure of the ionosphere observations become increasingly difficult within and below the global cloud deck 50 km altitude where strong absorption greatly limits the available investigative spectrum to a few infrared windows and the radio range here we report radio sounding results from the first venus express radio science5 vera occultation season we determine the fine structure in temperatures at upper cloud deck altitudes detect a distinct day night temperature difference in the southern middle atmosphere and track day to day changes in venus ionosphere

influence of venus topography on the zonal wind and uv albedo at cloud top level the role of stationary gravity waves based on the analysis of uv images at 365 nm of venus cloud top altitude 67 2 km collected with vmc venus monitoring camera on board venus express vex it is found that the zonal wind speed south of the equator from 5 s to 15 s shows a conspicuous variation from 101 to 83 m s with geographic longitude of venus correlated with the underlying relief of aphrodite terra we interpret this pattern as the result of stationary gravity waves produced at ground level by the up lift of air when the horizontal wind encounters a mountain slope these waves can propagate up to the cloud top level break there and transfer their momentum to the zonal flow such upward propagation of gravity waves and influence on the wind speed vertical profile was shown to play an important role in the middle atmosphere of the earth by lindzen 1981 but is not reproduced in the current gcm of venus atmosphere from lmd in the equatorial regions the uv albedo at 365 nm varies also with longitude we argue that this variation may be simply explained by the divergence of the horizontal wind field in the longitude region from 60 to 10 where the horizontal wind speed is increasing in magnitude stretch it triggers air upwelling which brings the uv absorber at cloud top level and decreases the albedo and vice versa when the wind is decreasing in magnitude compression this picture is fully consistent with the classical view of venus meridional circulation with upwelling at equator revealed by horizontal air motions away from equator the longitude effect is only an additional but important modulation of this effect this interpretation is comforted by a recent map of cloud top h2o fedorova et al 2015 showing that near the equator the lower uv albedo longitude region is correlated with increased h2o we argue that h2o enhancement is the sign of upwelling suggesting that the uv absorber is also brought to cloud top by upwelling

a study of the possibility of sprites in the atmospheres of other planets 1 sprites are a spectacular type of transient luminous events which occur above thunderstorms immediately after lightning they have shapes of giant jellyfish carrots or columns and last tens of milliseconds in earth s atmosphere sprites mostly emit in red and blue wavelengths from excited n2 and n2 and span a vertical range between 50 and 90 km above the surface the emission spectra morphology and occurrence heights of sprites reflect the properties of the planetary atmosphere they inhabit and are related to the intensity of the initiating parent lightning this paper presents results of theoretical calculations of the expected occurrence heights of sprites above lightning discharges in the co2 atmosphere of venus the n2 atmosphere of titan and the h2 he atmosphere of jupiter the expected emission features are presented and the potential of detecting sprites in planetary atmospheres by orbiting spacecraft is discussed

scour downstream of grade control structures a theoretical investigation of local scour downstream of gradecontrol structures based on twodimensional jet diffusion and particle stability is experimentally verified turbulent jet diffusion red

affinity and similarity of local scour holes at bed sills 1 excessive erosion of gravel bed rivers represents a hazard which is often controlled by the construction of bed sills shape and volume of equilibrium local scour holes at bed sills in high gradient streams were investigated by analyzing steady flow experimental data scour profiles were normalized by scaling the depths and the longitudinal distance from the upstream sill with the maximum dimensions of the scour hole results exhibited a universal geometrical affinity of the scour geometrical similarity was also found to occur but only in a limited range of physical conditions evidence on the scaling nature of the scour hole shapes has important implications on the prediction of the eroded volume in turn a correct evaluation of the eroded volume is necessary for the optimization of the design of the intersill distance prediction formulae are proposed which link the eroded volume to the geometrical hydraulic and sediment properties

limb imaging of the venus o2 visible nightglow with the venus monitoring camera 1 we investigated the venus o2 visible nightglow with imagery from the venus monitoring camera on venus express drawing from data collected between april 2007 and january 2011 we study the global distribution of this emission discovered in the late 1970s by the venera 9 and 10 missions the inferred limb viewing intensities are on the order of 150 kr at the lower latitudes and seem to drop somewhat toward the poles the emission is generally stable although there are episodes when the intensities rise up to 500 kr we compare a set of venus monitoring camera observations with coincident measurements of the o2 nightglow at 1 27 m made with the visible and infrared thermal imaging spectrometer also on venus express from the evidence gathered in this and past works we suggest a direct correlation between the instantaneous emissions from the two o2 nightglow systems possible implications regarding the uncertain origin of the atomic oxygen green line at 557 7 nm are noted

venus as a more earth like planet venus is earth s near twin in mass and radius and our nearest planetary neighbour yet conditions there are very different in many respects its atmosphere mostly composed of carbon dioxide has a surface temperature and pressure far higher than those of earth only traces of water are found although it is likely that there was much more present in the past possibly forming earth like oceans here we discuss how the first year of observations by venus express brings into focus the evolutionary paths by which the climates of two similar planets diverged from common beginnings to such extremes these include a co2 driven greenhouse effect erosion of the atmosphere by solar particles and radiation surface atmosphere interactions and atmospheric circulation regimes defined by differing planetary rotation rates

atmospheric structure and dynamics as the cause of ultraviolet markings in the clouds of venus details about the atmosphere on venus are gradually emerging from the once apparently impenetrable global cloud cover simultaneous imaging in the ultraviolet and infrared by venus express provides a new view of the ultraviolet patterns seen in the cloud tops the picture that emerges is one of dark low latitudes dominated by convective mixing in the sulphuric acid clouds bringing unknown ultraviolet absorbers up from the lower atmosphere the cloud top morphology revealed in the southern hemisphere by venus express resembles that found earlier by pioneer venus and venera 15 in the north suggesting global symmetry between the two hemispheres when seen in ultraviolet light venus has contrast features that arise from the non uniform distribution of unknown absorbers within the sulphuric acid clouds this paper reports multi wavelength imaging that reveals that the dark low latitudes are dominated by convective mixing that brings the ultraviolet absorbers up from depth the bright and uniform mid latitude clouds reside in the cold collar which suppresses vertical mixing in low and middle latitudes the visible cloud top is located at a constant altitude of 72 1 km in both the ultraviolet dark and bright regions indicating that the brightness variations result from compositional differences caused by the colder environment when seen in ultraviolet light venus has contrast features that arise from the non uniform distribution of unknown absorbers within the sulphuric acid clouds1 2 3 and seem to trace dynamical activity in the middle atmosphere4 it has long been unclear whether the global pattern arises from differences in cloud top altitude which was earlier3 estimated to be 66 72 km compositional variations or temperature contrasts here we report multi wavelength imaging that reveals that the dark low latitudes are dominated by convective mixing which brings the ultraviolet absorbers up from depth the bright and uniform mid latitude clouds reside in the cold collar an annulus of cold air characterized by 30 k lower temperatures with a positive lapse rate which suppresses vertical mixing and cuts off the supply of ultraviolet absorbers from below in low and middle latitudes the visible cloud top is located at a remarkably constant altitude of 72 1 km in both the ultraviolet dark and bright regions indicating that the brightness variations result from compositional differences caused by the colder environment rather than by elevation changes the cloud top descends to 64 km in the eye of the hemispheric vortex which appears as a depression in the upper cloud deck the ultraviolet dark circular streaks enclose the vortex eye and are dynamically connected to it

venus s southern polar vortex reveals precessing circulation initial images of venus s south pole by the venus express mission have shown the presence of a bright highly variable vortex similar to that at the planet s north pole using high resolution infrared measurements of polar winds from the venus express visible and infrared thermal imaging spectrometer virtis instrument we show the vortex to have a constantly varying internal structure with a center of rotation displaced from the geographic south pole by 3 degrees of latitude and that drifts around the pole with a period of 5 to 10 earth days this is indicative of a nonsymmetric and varying precession of the polar atmospheric circulation with respect to the planetary axis

effects of air entrainment on plunge pool scour plunge pool scour depths are normally assumed to be dependent on unit flow q and head drop h with a surprising variation among authors concerning the importance of h it is hypothesized by the writer that this process may be linked to plunge pool air entrainment tests are carried out using a hydraulic model on which q h and the air water ratio in the plunge pool could each be varied separately scour depths are found to depend only on q and with the apparent effects of h recorded in the past being possibly due to associated variations of with h equations are developed explaining the results in terms of forces on the particles of bed material these are shown to apply to a wider body of model test data and also to prototype data particular areas of relevant future research are also identified it is proposed that any future plunge pool scour studies should recognize air entrainment as a significant variable

flow resistance estimation in mountain rivers examination of the flow resistance of high gradient gravel and boulder bed rivers using data collected in british mountain rivers with slopes of 0 4 4 shows that there are differences in resistance variation between mountain and lowland rivers and that between site variations do not necessarily reflect at a site variations comparison of data with the familiar resistance equation relating the dracy weisbach friction factor to the logarithm of relative submergence shows that the equation tends to overestimate the resistance in uniform flow the equation also tends to underestimate the rate of change of resistance at a site as discharge varies with high gradients the influences of nonuniform channel profile sediment size distribution channel slope and sediment transport are reviewed but the data do not allow any quantification of these effects instead an empirical approach based on the available data is presented allowing the friction factor to be calculated from the relative submergence with an error of up to n25 to n35 a summary of the field data is included

zonal winds in the middle atmosphere of venus from pioneer venus radio occultation data abstract pioneer venus radio occultation data for four seasons between december 1978 and october 1981 are used to construct meridional cross sections of temperature and zonal wind velocity for the middle atmosphere of venus in the altitude range of 40 80 km and in the latitude range of 1 5 85 wind speeds are derived assuming cyclostrophic balance the wind field contains as many as three jets first a prominent one above the clouds situated between 50 and 55 latitude with a maximum speed of 140 m s 1 a second with a speed of 95 m s 1 centered at 70 and at 60 km altitude and a possible third jet at 15 and 65 km altitude with a speed of 100 m s 1 the notable midlatitude jet is associated with the cold polar collar wind speeds above 70 km generally decrease with height because of the warm pole at these levels however within the jet the speed is 100 m s 1 at 83 km the jets may be barotropically unstable and inertial instability may occur above the clouds on the equatorial side of the main

sunlight refraction in the mesosphere of venus during the transit on june 8th 2004 abstract many observers in the past gave detailed descriptions of the telescopic aspect of venus during its extremely rare transits across the solar disk in particular at the ingress and egress the portion of the planet s disk outside the solar photosphere has been repeatedly perceived as outlined by a thin bright arc aureole those historical visual observations allowed inferring the existence of venus atmosphere the bright arc being correctly ascribed to the refraction of light by the outer layers of a dense atmosphere on june 8th 2004 fast photometry based on electronic imaging devices allowed the first quantitative analysis of the phenomenon several observers used a variety of acquisition systems to image the event ranging from amateur sized to professional telescopes and cameras thus collecting for the first time a large amount of quantitative information on this atmospheric phenomenon in this paper after reviewing some elements brought by the historical records we give a detailed report of the ground based observations of the 2004 transit besides confirming the historical descriptions we perform the first photometric analysis of the aureole using various acquisition systems the spatially resolved data provide measurements of the aureole flux as a function of the planetocentric latitude along the limb a new differential refraction model of solar disk through the upper atmosphere allows us to relate the variable photometry to the latitudinal dependency of scale height with temperature in the south polar region as well as the latitudinal variation of the cloud top layer altitude we compare our measurements to recent analysis of the venus express virtis m vmc and spicav soir thermal field and aerosol distribution our results can be used a starting point for new more optimized experiments during the 2012 transit event

box cores from the equatorial pacific 14c sedimentation rates and benthic mixing abstract carbon 14 determinations on box cores of calcareous ooze from the western and eastern equatorial pacific suggest that patterns of mixed layer ages sedimentation rates and mixed layer thicknesses are controlled by gradients of carbonate dissolution and fertility and by small scale redeposition processes mixed layer ages range from 3000 to 7000 years with a mode between 4000 and 5000 years sedimentation rates range from 0 8 to 2 4 cm 1000 years mixed layer depths calculated according to the box model of mixing range from 7 cm to 16 cm observed thicknesses are about one fourth smaller than calculated ones

assessing the long term variability of venus winds at cloud level from virtis venus express abstract the venus express vex mission has been in orbit to venus for more than 4 years now the visible and infrared thermal imaging spectrometer virtis instrument onboard vex observes venus in two channels visible and infrared obtaining spectra and multi wavelength images of the planet that can be used to sample the atmosphere at different altitudes day side images in the ultraviolet range 380 nm are used to study the dynamics of the upper cloud at 66 72 km while night side images in the near infrared 1 74 m map the opacity of the lower cloud deck at 44 48 km here we present a long term analysis of the global atmospheric dynamics at these levels using a large selection of orbits from the virtis m dataset covering 860 earth days that extends our previous work sanchez lavega a et al 2008 geophys res lett 35 l13204 and allows studying the variability of the global circulation at the two altitude levels the atmospheric superrotation is evident with equatorial to mid latitudes westward velocities of 100 and 60 m s 1 in the upper and lower cloud layers these zonal velocities are almost constant in latitude from the equator to 50 s from 50 s to 90 s the zonal winds at both cloud layers decrease steadily to zero at the pole individual cloud tracked winds have errors of 3 10 m s 1 with a mean of 5 m s 1 and the standard deviations for a given latitude of our zonal and meridional winds are 9 m s 1 the zonal winds in the upper cloud change with the local time in a way that can be interpreted in terms of a solar tide the zonal winds in the lower cloud are stable at mid latitudes to the tropics and present variability at subpolar latitudes apparently linked to the activity of the south polar vortex while the upper cloud presents a net meridional motion consistent with the upper branch of a hadley cell with peak velocity v 10 m s 1 at 50 s the lower cloud meridional motions are less organized with some cloud features moving with intense northwards and southwards motions up to v 15 m s 1 but on average with almost null global meridional motions at all latitudes we also examine the long term behavior of the winds at these two vertical layers by comparing our extended wind tracked data with results from previous missions

a reanalysis of venus winds at two cloud levels from galileo ssi images abstract the global circulation of the venus atmosphere is characterized at cloud level by a zonal super rotation studied over the years with data from a battery of spacecrafts orbiters balloons and probes among them the galileo spacecraft monitored the venus atmosphere in a flyby in february 1990 in its route toward jupiter since the flyby was almost equatorial published analysis of zonal winds obtained from displacements of cloud elements on images obtained by the ssi camera belton m j s and 20 colleagues 1991 science 253 1531 1536 stop at latitudes 50 north and south in this paper we present new results on venus winds based on a reanalysis of an extended set of images obtained at two wavelengths 418 nm violet and 986 nm near infrared that sense different altitude levels in the upper cloud our main result is that we have been able to extend the zonal wind profile up to the polar latitudes 70 n and 70 s at 418 nm and 70 n at 986 nm binned and smoothed profiles are given in tabular form we show that the zonal winds drop in their velocity poleward of latitudes 45 n and 50 s where an intense meridional wind shear develops at the two cloud levels our data confirm the magnitude of this shear retrieved previously from radio occultation data but disagrees with it in the latitudinal location of the sheared region the new wind data can be used to recalibrate the zonal winds retrieved from the previous measurements of the temperature field and the cyclostrophic balance assumption the meridional profiles of the zonal winds at the two cloud levels are used to assess the vertical wind shear in the upper cloud layer as a function of latitude and locate the most unstable region

first ever in situ observations of venus polar upper atmosphere density using the tracking data of the venus express atmospheric drag experiment vexade on its highly elliptical 24 h orbit around venus the venus express vex spacecraft briefly reaches a periapsis altitude of nominally 250 km recently however dedicated and intense radio tracking campaigns have taken place in august 2008 october 2009 february and april 2010 for which the periapsis altitude was lowered to the 186 176 km altitude range in order to be able to probe the upper atmosphere of venus above the north pole for the first time ever in situ as the spacecraft experiences atmospheric drag its trajectory is measurably perturbed during the periapsis pass allowing us to infer total atmospheric mass density at the periapsis altitude a precise orbit determination pod of the vex motion is performed through an iterative least squares fitting process to the doppler tracking data acquired by the vex radioscience experiment vera the drag acceleration is modelled using an initial atmospheric density model vts3 model hedin a e niemann h b kasprzak w t seiff a 1983 j geophys res 88 73 83 a scale factor of the drag acceleration is estimated for each periapsis pass which scales hedin s density model in order to best fit the radio tracking data reliable density scale factors have been obtained for 10 passes mainly from the second october 2009 and third april 2010 vexade campaigns which indicate a lower density by a factor of about 1 8 than hedin s model predicts these first ever in situ polar density measurements at solar minimum have allowed us to construct a diffusive equilibrium density model for venus thermosphere constrained in the lower thermosphere primarily by spicav soir measurements and above 175 km by the vexade drag measurements muller wodarg et al in preparation the preliminary results of the vexade campaigns show that it is possible to obtain with the pod technique reliable estimates of venus upper atmosphere densities at an altitude of around 175 km future vexade campaigns will benefit from the planned further lowering of vex pericenter altitude to below 170 km 2011 elsevier inc

sediment mixing and stratigraphic disorder revealed by the age structure of tellina shells in great barrier reef sediment radiocarbon calibrated amino acid racemization ages of 250 individually dated tellina shells from two sediment cores are used to quantify molluscan time averaging with increasing burial depth in the shallow water carbonate lagoon of rib reef central great barrier reef australia the top 20 cm of sediment contain a distinct essentially modern assemblage with a median age of only 5 yr sediment between 20 and 125 cm are age homogeneous and significantly older than the surface sediment median age 189 yr shell age distributions within layers indicate that the top 125 cm of lagoonal sediment is thoroughly mixed on a subcentennial scale shell size is an important correlate of shell half life and an important determinant of the inferred age of sedimentary layers these results illustrate the importance of bioturbation in these environments indicate that age estimates in this depositional setting are sensitive to specimen choice and document a size dependent bias in death assemblage formation

biological pumping upwards of the coarse fraction of deep sea sediments abstract in a restricted part of an area intensively sampled by box coring approximately 50 samples from a 2 4 km rectangle a stiff muddy glacial gravel till is encountered at a depth of 30 40 cm x radiographs of the upper 15 to 20 cm of the cores reveal gravel in overlying foraminiferal mud only from the area where there is the deeper till layer the localization strongly suggests that the material in the top of the cores has its source in the deeper layer i postulate that burrowing organisms move gravel upward by pushing aside the particles that are too large to be eaten because the strength of the enclosing mud decreases upwards the gravel particles move preferentially upward the upward decrease in shear strength of he sediment is rapid at an interface occurring 4 cm below the surface on average thus hydrostatic pressures of 20 to 200 g cm2 exerted by vermiform burrowing animals act within an environment of asymmetrical sediment property permitting an asymmetrical response to the uniformly directed body pressure this asymmetrical response a pumping mechanism affecting material that does not pass through the gut is contrasted with the mixing of finer sediments that are eaten and excreted documented by many other workers dimensional arguments suggest the flux of material is related to the ratio of biological mixing rate to sedimentation rate the mechanism is also applicable to maintenance of mn nodules and their nuclei at the surface if macrofossils have behaved like gravel some s ell beds may have been generated and some stratigraphic anomalies caused by this means

scouring at bed sills as a response to flash floods the temporal development of clear water local scour depth at bed sills in uniform gravel beds is considered experiments are presented on the development of scour holes under unsteady hydraulic conditions with the triangular shaped hydrographs tested being of different durations and different rates of flow variation based on the experimental results and a theoretical framework a method is given for the definition and prediction of the scouring process under unsteady flows in terms of a dimensionless temporal parameter a flash flood is here defined as an event for which the scour doesn t attain its potential magnitude i e the equilibrium value for the peak hydrograph flow rate this flood nature is dependent on both the characteristics of the flood event itself and the characteristics of the stream a quantitative measure of what constitutes a flash flood is given in terms of the identified temporal parameter results show that the ratio between the final scour depth and the potential scour depth

effect of flood recession on scouring at bed sills the effect of the flood recession time on the local scour depth at bed sills in gravel deposits is examined experiments were carried out to study the development of scour holes under time varying hydraulic conditions with no upstream sediment feed triangular shaped hydrographs having recession times up to three times the duration of the rising limb were used traditionally the peak water discharge in any flood event is used as a design value in estimating the final depth of scour formed by a flood this approach is overly conservative when the flow hydrograph is steep i e during the occurrence of flash floods the actual reduction of the scour depth from this estimated value is dependent on both the characteristics of the flood event and the characteristics of the stream the results show that the maximum potential scour depth can be achieved only for hydrographs with long recession times while the rate of this process can be estimated as a function of the ratio between a characteristic flood time and the steady state temporal scale of scour development a method is proposed for the prediction of the scouring process under unsteady flows in terms of two dimensionless temporal parameters results obtained for clear water boundary conditions can be extended to sediment supply tests if specific supply input conditions hold

a dynamic upper atmosphere of venus as revealed by virtis on venus express esa s venus express probe has been in orbit since april 2006 eight research papers in this issue present new results from the mission covering the atmosphere polar features interactions with the solar wind and the controversial matter of venusian lightning hakan svedham et al open the section with a review of the similarities and mostly differences between venus and its twin the earth andrew ingersoll considers the latest results and also how the project teams plan to make the most of the probe s remaining six years of life observations of infrared emission from co2 o2 and no established that photochemical and dynamic activity controls the structure of the upper atmosphere of venus but were unable to identify the altitude of the emission but it is reported here that day side co2 emission extends from 90 120 km altitude with a peak at 115 km night side o2 emission peaks at 96 km and is visible over the range 95 100 km the upper atmosphere of a planet is a transition region in which energy is transferred between the deeper atmosphere and outer space molecular emissions from the upper atmosphere 90 120 km altitude of venus can be used to investigate the energetics and to trace the circulation of this hitherto little studied region previous spacecraft1 and ground based2 3 4 observations of infrared emission from co2 o2 and no have established that photochemical and dynamic activity controls the structure of the upper atmosphere of venus these data however have left unresolved the precise altitude of the emission1 owing to a lack of data and of an adequate observing geometry5 6 here we report measurements of day side co2 non local thermodynamic equilibrium emission at 4 3 m extending from 90 to 120 km altitude and of night side o2 emission extending from 95 to 100 km the co2 emission peak occurs at 115 km and varies with solar zenith angle over a range of 10 km this confirms previous modelling7 and permits the beginning of a systematic study of the variability of the emission the o2 peak emission happens at 96 km 1 km which is consistent with three body recombination of oxygen atoms transported from the day side by a global thermospheric sub solar to anti solar circulation as previously predicted8

modelling time varying scouring at bed sills in this paper a modelling approach is presented to predict local scour under time varying flow conditions the approach is validated using experimental data of unsteady scour at bed sills the mode

high rayleigh number compressible convection in venus atmosphere penetration entrainment and turbulence numerical simulations of two dimensional nonlinear fully compressible convection at the subsolar point in the clouds of venus are presented one moderate rayleigh number case raq 6 8 106 and two high rayleigh number raq 1 1 109 cases are considered cloud level convection is characterized by cold narrow downwellings that deeply penetrate the underlying stable layer and that entrain warmer air from the overlying stable layer the convection layer depth as determined from the horizontally averaged static stability spans 9 km 47 56 km altitude and 14 km 46 60 km altitude for the moderate rayleigh number and high rayleigh number simulations respectively in the high rayleigh number cases convective penetration extends over a scale height from the bottom of the convection layer down to 38 km altitude strong convective entrainment completely erodes the overlying stable layer in the high raq cases and incorporates it into the convection layer the timescale for entrainment of the overlying stable layer is roughly 1 day and may explain why cellular features are predominantly found near and downwind of the subsolar point the high rayleigh number simulations are convectively turbulent and exhibit a spectral energy cascade of k 3 where k is the horizontal wavenumber our results suggest that cellular features in the subsolar region are observed at the cloud tops because convection may extend to much higher altitudes there downward penetrative convection may also be responsible for turbulence observed in venus atmosphere at 45 km altitude

saturn s latitudinal c2h2 and c2h6 abundance profiles from cassini cirs and ground based observations abstract hydrocarbons in the upper atmosphere of saturn are known from voyager ground based and early cassini results to vary in emission intensity with latitude of particular interest is the marked increase in hydrocarbon line intensity near the south pole during southern summer as the increased line intensity cannot be simply explained by the increased temperatures observed in that region since the variations between c2h2 and c2h6 emission in the south pole region are different in order to measure the latitudinal variations of hydrocarbons in saturn s southern hemisphere we have used 3 cm 1 resolution cassini cirs data from 2006 and combined this with measurements from the ground in october 2006 at nasa s irtf using celeste an infrared high resolution cryogenic grating spectrometer these two data sets have been used to infer the molecular abundances of c2h2 and c2h6 across the southern hemisphere in the 1 10 mbar altitude region we find that the latitudinal acetylene profile follows the yearly average mean daily insolation except at the southern pole where it peaks in abundance near the equator 5 s the c2h2 abundance at the 1 2 mbar level is 1 6 0 19 10 7 and it decreases by a factor of 2 7 from the equator toward the pole however at the pole 87 s the c2h2 abundance jumps to 1 8 0 3 10 7 approximately the equatorial value the c2h6 abundance near the equator at the 2 mbar level is 0 7 0 1 10 5 and stays approximately constant until mid latitudes where it increases gradually toward the pole attaining a value of 1 4 0 4 10 5 there the increase in ethane toward the pole with the corresponding decrease in acetylene is consistent with southern hemisphere meridional winds greathouse t k lacy j h bezard b moses j i griffith c a richter m j 2005 icarus 177 18 31 the localized increase in acetylene at the pole provides evidence that there is dynamical transport of hydrocarbons from the equator to the southern pole

direct wind measurements from november 2007 in venus upper atmosphere using ground based heterodyne spectroscopy of co2 at 10 μm wavelength abstract between november 23 and 28 2007 the cologne tuneable heterodyne infrared spectrometer this was installed at the mcmath pierce solar telescope kitt peak arizona usa to determine zonal wind velocities and to estimate the subsolar to antisolar flow we investigate dynamics in the upper atmosphere of venus by measuring the doppler shift of fully resolved non lte co 2 emission lines at 959 3917 cm 1 10 423 m which probe a narrow altitude region in venus atmosphere around 110 10 km 1 bar the results show no significant zonal wind velocity at the equator an increase with latitude up to 43 13 m s at a latitude of 33 n was observed this confirms the deduction of a minor influence of venus superrotation at an altitude of 110 km from previous measurements in may 2007 sornig et al 2008 the specific observing geometry enables estimating the maximum cross terminator velocity of the subsolar to antisolar flow at 72 47 m s

local scour by a deeply submerged horizontal circular jet this study investigates local scour caused by a deeply submerged circular jet both a wall jet and an offset jet were used in the experiments with uniform cohesionless sediments making up the bed experiments conducted in both air and water show that the densimetric froude number f i do is the main characteristic scouring parameter in the correlation of the maximum equilibrium scour dimensions for an offset jet the offset distance iy which is the vertical distance between the undisturbed bed level and the center of the jet also affects the scour hole dimensions a higher iy causes the formation of a smaller scour hole because most of the energy is diffused into the flow instead of being used to erode the sediment for the same f i do value the size of the scour hole is consistently smaller for tests conducted in water than in air the reason is attributed to the formation of a sediment ridge at the downstream end of the scour hole due to the density difference between air and water the ridge height is markedly different in the two flow media

vortex circulation on venus dynamical similarities with terrestrial hurricanes 1 some dynamical and morphological similarities exist between the vortex organization of the atmosphere in the northern and southern hemispheres of venus and the tropical cyclones hurricanes on earth an s shape feature detected in the center of the vortices on venus from pioneer venus orbiter and venus express observations has also been seen in tropical cyclones this feature can be simulated with an idealized nonlinear and non divergent barotropic model and like in the vortices on venus and in tropical cyclones it is found to be transient given the challenges in measuring the deep atmospheric circulation of venus the morphological similarities provide clues toward understanding the processes involved in the maintenance of venus atmospheric super rotation

last millennia sedimentary record on a micro tidal low accumulation prodelta tet nw mediterranean statistical sequential analysis was performed on a series of sediment cores collected from the tet prodelta in the gulf of lions northwestern mediterranean sea between october 2003 and october 2004 seabed changes during that period were correlated to hydrodynamic conditions waves and currents and river discharge low sediment supply prevents full preservation of new sediment strata on this low accumulation prodelta located on a microtidal storm dominated inner shelf severe meteorological events caused a rapid succession of erosion and deposition phases for example the december 2003 flood and storm produced a flood layer deposit that persisted for 2 months with only slight transformations due to early diagenesis and or bioturbation until a new storm event eroded this layer a typical sedimentary sequence was observed for the secular deposits composed of a 10 cm thick sandy layer overlaying siltyclayey layers these characteristic features were used to analyse the last millennia sedimentary record of the tet prodelta the low preservation of freshly deposited sediments and variable sedimentation rates during the last millennia period yield a sedimentary sequence formed by the outcropping of muddy prodeltaic units intersected by heterogeneous siltysandy units similar to those formed under present day hydrodynamic conditions no flood layer was found related to catastrophic flooding of the last century in the sedimentary record the little ice age 1550 1850 ad probably favoured the formation of a well developed muddy prodelta in the mouth of the tet river later on the decrease of sediment supply by rivers due to climate change and or human activities damming irrigation and the increase of the number of high energy storms reaching the coast induced a coarsening of the top sediment layer on this prodelta this modern change of the substrate is also observed in the composition of benthic biota found in the substrate

cloud level winds from the venus express monitoring camera imaging abstract six years of continuous monitoring of venus by european space agency s venus express orbiter provides an opportunity to study dynamics of the atmosphere our neighbor planet venus monitoring camera vmc on board the orbiter has acquired the longest and the most complete so far set of ultra violet images of venus these images enable a study the cloud level circulation by tracking motion of the cloud features the highly elliptical polar orbit of venus express provides optimal conditions for observations of the southern hemisphere at varying spatial resolution out of the 2300 orbits of venus express over which the images used in the study cover about 10 venus years out of these we tracked cloud features in images obtained in 127 orbits by a manual cloud tracking technique and by a digital correlation method in 576 orbits total number of wind vectors derived in this work is 45 600 for the manual tracking and 391 600 for the digital method this allowed us to determine the mean circulation its long term and diurnal trends orbit to orbit variations and periodicities we also present the first results of tracking features in the vmc near ir images in low latitudes the mean zonal wind at cloud tops 67 2 km following rossow w b del genio a t eichler t 1990 j atmos sci 47 2053 2084 is about 90 m s with a maximum of about 100 m s at 40 50 s poleward of 50 s the average zonal wind speed decreases with latitude the corresponding atmospheric rotation period at cloud tops has a maximum of about 5 days at equator decreases to approximately 3 days in middle latitudes and stays almost constant poleward from 50 s the mean poleward meridional wind slowly increases from zero value at the equator to about 10 m s at 50 s and then decreases to zero at the pole the error of an individual measurement is 7 5 30 m s wind speeds of 70 80 m s were derived from near ir images at low latitudes the vmc observations indicate a long term trend for the zonal wind speed at low latitudes to increase from 85 m s in the beginning of the mission to 110 m s by the middle of 2012 vmc uv observations also showed significant short term variations of the mean flow the velocity difference between consecutive orbits in the region of mid latitude jet could reach 30 m s that likely indicates vacillation of the mean flow between jet like regime and quasi solid body rotation at mid latitudes fourier analysis revealed periodicities in the zonal circulation at low latitudes within the equatorial region up to 35 s the zonal wind show an oscillation with a period of 4 1 5 days 4 83 days on average that is close to the super rotation period at the equator the wave amplitude is 4 17 m s and decreases with latitude a feature of the kelvin wave the vmc observations showed a clear diurnal signature a minimum in the zonal speed was found close to the noon 11 14 h and maxima in the morning 8 9 h and in the evening 16 17 h the meridional component peaks in the early afternoon 13 15 h at around 50 s latitude the minimum of the meridional component is located at low latitudes in the morning 8 11 h the horizontal divergence of the mean cloud motions associated with the diurnal pattern suggests upwelling motions in the morning at low latitudes and downwelling flow in the afternoon in the cold collar region

venus upper atmospheric dynamical structure from ground based observations shortly before and after venus inferior conjunction 2009 abstract investigations on the dynamical structure of venus upper atmosphere were carried out by infrared heterodyne doppler wind measurements shortly before and after the venusian inferior conjunction on march 27 2009 the cologne tuneable heterodyne infrared spectrometer this has been installed at the mcmath pierce solar telescope on kitt peak arizona usa to detect non local thermodynamical equilibrium non lte emission lines of co2 at a wavelength of 10 5 m these solar induced emission lines originate at a pressure level of 1 bar corresponding to an altitude level of 110 10 km from the frequency position of the spectral lines we directly derived doppler winds without any additional information the high spatial resolution with a field of view of 1 6 arcsec compared to an apparent diameter of venus of 57 arcsec allowed to collect information at different latitudes of the illuminated planet line of sight wind velocities between 189 11 m s and 41 14 m s were detected along the illuminated evening western limb in march and along the bright morning eastern limb in april single observations at the evening and morning terminator do not show a systematic difference of wind velocities the measured wind is uniform at low and mid latitudes in march a lower mean value of 134 1 m s was found compared to april where we retrieved a value of 141 1 m s poleward of a latitude of 50 we observed a strong decrease in wind speed down to 41 14 m s in addition to the pure line of sight wind velocities we used the observing geometry for additional interpretations regarding a global flow from the subsolar point to the antisolar point ss as flow and a global retrograde superrotational zonal wind rsz the estimations indicate a dominating ss as flow with a maximum wind velocity at the terminator of 138 1 m s at low and mid latitudes no indication of a global rsz component was found corresponding wind values for the latter yield wind velocities in the zonal direction between 20 m s retrograde direction and 20 m s prograde direction at different latitudes an inversion of the wind direction is in disagreement with a global rsz behavior the comprehensive dataset was used to investigate short term wind variabilities and changes up to 58 m s within few days were found we included a detailed comparison of concurrent single position observations with sub millimeter measurements clancy r t sandor b j moriarty schieven g 2012 icarus 217 794 812 suggesting a cross terminator gradient at certain latitudes a detailed interpretation of the observed time dependent behavior by global circulation models including wave activities will be addressed in future work

radiocarbon dating of irish sea sediments abstract radiocarbon dating has been carried out on three cores from areas of muddy sediments in the n irish sea to estimate rates of sediment accumulation 14c age profiles of the two eastern basin cores revealed a near constant age from the sediment surface to the base of the core 12 500 1000 years bp the 14c age profile of the western basin core revealed a zone of apparent mixing to a depth of 55 cm underlain by a zone of constant sedimentation rate 0 018 cm y 1 to 160 cm these data are discussed in relation both to previously reported sedimentological studies of the area and to the authorised discharges of low level radioactive waste from the sellafield nuclear fuel reprocessing plant

glacial incisions indicating middle and upper pieistocene ice limits off britain from the recognition that major incisions formed at lowland or tidewater ice sheet margins during each of the last three glacial stages it is assumed that a standard quaternary stratigraphy is applicable to the deposits geophysically profiled on the continental shelf off britain ice limits for each glacial stadial can be mapped from the geographical distribution of the incisions during the next glacial stage major incisions will be downcut on the present continental shelf or coastal lowlands to some 350 m below the ambient surface this will have important environmental consequences regarding the long term burial of hazardous wastes

structure of the venus neutral atmosphere as observed by the radio science experiment vera on venus express 1 the european space agency venus express radio science experiment vera obtained 118 radio occultation measurements of the venusian atmosphere between july 2006 and june 2007 southern latitudes are uniformly sampled measurements in the northern hemisphere are concentrated near the pole radial profiles of neutral number density derived from the occultations cover the altitude range 40 90 km which are converted to profiles of temperature t and pressure p versus height h profiles of static stability are found to be latitude dependent and nearly adiabatic in the middle cloud region below the clouds the stability decreases at high latitudes at an altitude of 65 km the vera t p h profiles generally lie between the venus international reference atmosphere vira and vira 2 models the retrieved temperatures at any given pressure level typically are within 5 k of those derived from the pioneer venus orbiter radio occultation experiments a large equator to pole temperature contrast of 30 k is found at the 1 bar 1000 hpa level the vera observations reveal a distinct cold collar region in the southern hemisphere complementing that in the north at the latitudes of the cold collars the tropopause altitude increases relative to higher and lower latitudes by 7 km while the temperature drops roughly 60 k the observations indicate the existence of a wave number 2 structure poleward of 75 latitude at altitudes of 62 km

venus atmospheric circulation known and unknown 1 after a pause of more than two decades venus atmosphere is being explored again since april 2006 european space agency s venus express has been acquiring data exploiting the near infrared windows that allow us to peer into the deep night side atmosphere in june 2007 nasa s messenger mission will fly past venus on its way to mercury collecting useful data for a few weeks instruments and experiments on venus express are expected to provide a more comprehensive set of atmospheric observations over three and perhaps more venus days venus express observations are already providing clues about the processes that maintain the rapid circulation of venus atmosphere the early observations show not only that the global circulation is organized into two hemispheric vortices centered over respective poles but also that the vortex organization extends deep into the atmosphere the limited galileo nims near infrared observations in 1989 had revealed the deep circulation in the equatorial regions but because of the spacecraft flyby trajectory could not observe the high latitudes to elucidate the polar circulation and its organization the long hiatus in systematic venus observations has provided an opportunity to perform some new analysis of the previous pioneer venus observations this paper presents a synopsis of the circulation measurements at high latitudes and an analysis of the solar thermal tides seen in the cloud motions and suggests some limitations of previous estimates of transport of angular momentum by eddies

vertical structure of the venus cloud top from the vera and virtis observations onboard venus express abstract we investigate the venus cloud top structure by joint analysis of the data from visual and thermal infrared imaging spectrometer virtis and the atmospheric temperature sounding by the radio science experiment vera onboard venus express the cloud top altitude and aerosol scale height are derived by fitting virtis spectra at 4 5 m with temperature profiles taken from the vera radio occultation our study shows gradual descent of the cloud top from 67 2 1 9 km in low latitudes to 62 8 4 1 km at the pole and decrease of the aerosol scale height from 3 8 1 6 km to 1 7 2 4 km these changes correlate with the mesospheric temperature field in the cold collar and high latitudes the cloud top position remarkably coincides with the sharp minima in temperature inversions suggesting importance of radiative cooling in their maintenance this behaviour is consistent with the earlier observations spectral trend of the cloud top altitude derived from a comparison with the earlier observations in 1 6 27 m wavelength range is qualitatively consistent with sulphuric acid composition of the upper cloud and suggests that particle size increases from equator to pole

local scour due to submerged horizontal jet the phenomena of local scour and sediment transport due to a horizontal jet issuing from a sluice and flowing over a rigid apron then on to an erodible bed have been investigated based on experimental data the scour characteristics have been correlated through the development of empirical expressions for the time to reach equilibrium stage the locations of maximum scour depth and peak of dune and the variation of maximum scour depth with time similarity criteria for the predication of development of the scour hole and sediment transport have also been developed and apart from the flow parameters and sediment properties the jet diffusion characteristics play an important role in these processes the empirical relationships developed in this study highlight the necessity of an individual assessment when developing the similarity criteria for a particular flow situation

high latitude gravity waves at the venus cloud tops as observed by the venus monitoring camera on board venus express high resolution images of venus northern hemisphere obtained with the venus monitoring camera vmc vex allow studying small scale dynamical phenomena at the cloud tops 62 70 km altitude including features like wave trains a systematic visual search of these waves was performed more than 1500 orbits were analyzed and wave patterns were observed in more than 300 images four types of waves were identified in vmc images on the base of their morphology long medium short and irregular type waves with the aim to characterize the wave types and their possible excitation source we retrieved wave properties such as location latitude and longitude local time solar zenith angle packet length and width orientation and wavelength of each wave the long type waves appear as long and narrow straight features extending more than a few hundreds kilometers and with wavelengths between 7 and 17 km medium type waves exhibit irregular wavefronts extending more than 100 km and with wavelengths in the range 8 21 km short wave packets have a width of several tens of kilometers and extend to few hundreds kilometers and are characterized by smaller wavelengths 3 16 km irregular wave fields appear to be the result of wave interference the waves are often identified in all vmc filters and are mostly found in the cold collar region at high latitudes 60 80 n and are concentrated above ishtar terra a continental size highland that includes the highest mountain belts of the planet the high speed of the venus express spacecraft close to the pericentre does not allow to measure phase speed of waves due to the short temporal interval between image pairs the lack of information on phase velocities does not allow us to establish with absolute confidence the nature of these waves however by comparing the morphology and properties of the wave features observed in vmc images to those seen by previous observations it is reasonable to assume that the waves studied here are gravity waves

scour downstream of an apron due to submerged horizontal jets the results of an experimental investigation on scour of noncohesive sediment beds uniform and nonuniform sediments downstream of an apron due to a submerged horizontal jet issuing from a sluice opening are presented attempts are made to explain the similarity existing in the scour process and profiles including dune in the downstream of the scour hole the scour profiles at different times follow a particular geometrical similarity and can be expressed by the combination of two polynomials using experimental scour depth at different times the time variation of scour depth is scaled by an exponential law where time scale increases linearly with densimetric froude number the equilibrium scour depth related to the sediment size relative to the sluice opening decreases with increase in sediment size and sluice opening on the other hand the equilibrium scour depth increases with increase in densimetric froude number the variation of equilibrium scour depth with tailwater depth indicates a critical tailwater depth corresponding to a minimum equilibrium scour depth the effect of sediment gradation on scour depth is pronounced for nonuniform sediments which reduce scour depth significantly due to formation of an armor layer and therefore prompted study of the reduction of scour depth by a launching apron placed downstream of the rigid apron the results show that the average reduction of scour depth by placing a launching apron was 39 having a maximum of 57 3 and a minimum of 16 2 the characteristic parameters affecting maximum equilibrium scour depth are identified based on the physical reasoning and dimensional analysis equation of maximum equilibrium scour depth obtained empirically agrees well with the experimental data

evolution of scouring process downstream of grade control structures under steady and unsteady flows for many incised channels one of the most common strategies is to install some hard structures such as grade control structures gcss in the riverbed to resist further incision in this study a series of experiments including both steady and unsteady flow conditions were conducted to investigate the scouring process downstream of a gcs three distinct phases including the initial developing and equilibrium phases during the evolution of scour holes were identified in addition a semi empirical method was proposed to predict the equilibrium scour hole profile for the scour countermeasure design in general the comparisons between the experimental and simulated results are reasonably consistent as the studies on temporal variation of the scour depth at gcss caused by floods are limited the effect of flood hydrograph shapes on the scour downstream of gcss without upstream sediment supply was also investigated experimentally in this study based on the dimensional analysis and the concept of superposition a methodology is proposed to simulate the time evolution of the maximum scour depth downstream of a gcs for steady flows moreover the proposed scheme predicts reasonably well the temporal variations of the maximum scour depth for unsteady flows with both single and multiple peak copyright 2012 john wiley sons ltd

venus cloud top winds from tracking uv features in venus monitoring camera images 1 to date dynamical observations of the venus clouds have delivered mainly either only short term or long term averaged results with the venus monitoring camera vmc it finally became possible to investigate the global dynamics with a relatively high resolution in space and time on a long term basis our findings from manual cloud feature wind tracking in vmc uv image sequences so far show that the details of the mesospheric dynamics of venus appear to be highly variable although the general rotation of the atmosphere remained relatively stable since mariner 10 more than 30 years ago by now there are indications of short term variations in the general circulation pattern of the venus atmosphere at cloud top level in some cases significant variations in the zonal wind properties occur on a timescale of days in other cases we see rather stable conditions over one atmospheric revolution or longer at cloud top level it remains an interesting question whether the irregularly observed midlatitude jets are indeed variable or simply become shielded from view by higher h2so4 haze layers for varying time intervals winds at latitudes higher than 60 s are still difficult to obtain track because of low contrast and scarcity of features but increasing data is being collected over all it was possible to extend latitudinal coverage of the cloud top winds with vmc observations thermal tides seem to be present in the data but final confirmation still depends on synthesis of visible and infrared thermal imaging spectrometer and vmc observations on night and dayside although poorly resolved meridional wind speed measurements agree mainly with previous observations and with the presence of a hadley cell spanning between equatorial region and about 45 s latitude

fine particle retention and deposition in regions of cyclonic tidal current rotation abstract benthic sediments in continental shelf seas control a variety of biogeochemical processes yet their composition especially that of fine sediment remains difficult to predict mechanisms for mud or fine sediment deposition and retention are not fully understood using sediment data and a hydrodynamic model of the northwest european shelf seas a relationship is shown to exist between fine benthic sediment composition and regions of cyclonic tidal current rotation the reduced thickness of cyclonic tidal benthic boundary layers compared with the anticyclonic case promotes deposition of fine sediment and trapping of resuspended material adding the effects of the benthic boundary layer thickness as influenced by ellipticity or not sheds some light on the limitations of approaches only focusing on bed shear stress and sediment pathways to predict the location of mud deposits a tidal boundary layer predictor that includes ellipticity alongside tidal current magnitude and depth was shown to spatially agree with maps of mud deposits

transport and accumulation of actinide elements in the near shore environment field and modelling studies nuclear facilities in coastal locations often discharge low level liquid wastes into the sea and the radioisotopes in these discharges are of interest both in assessing possible environmental impacts and as tracers for coastal processes the distributions of a range of artificial radionuclides derived from the authorized discharges from british nuclear fuels bnfl sellafield have been determined in the sediments of an intertidal salt marsh in the esk estuary cumbria uk where published discharge histories exist for 137cs 238pu 239 240pu and 241am the sediment core profile distributions of these radionuclides have been compared with the releases from sellafield and consistent values of the accumulation rate 0 226 0 007 g cm 2 yr 1 are obtained a quantitative model has been developed describing association of radionuclides with suspended particulate material which is then accumulated and mixed in an offshore mud patch before resuspension and deposition in the salt marsh the model has been used to describe radionuclide distributions observed in both the mud patch and the salt marsh and to identify isotopes for which post depositional remobilization or solution transport from the discharge point are important the behaviour of the commonly studied isotopes 137cs 238pu 239 240pu and 241am is similar to that observed at this and other nearby locations the activation product isotope 236u is enhanced in these sediments over the natural baseline by four to eight orders of magnitude and the results suggest that sellafield derived uranium is comparably mobile to 137cs in these sediments although the processes governing the behaviour of these two elements may be different in situ production of 241am by decay of its 241pu parent has generated only 17 of the current sediment inventory of this isotope insufficient to account for the increase over the last 20 25 years and suggesting that the input material for these sediments is preferentially enriched in am relative to pu during transport from the offshore mud patch the discharge history of 244cm which is unknown has also been reconstructed from the sediment profile and the model

altimetry of the venus cloud tops from the venus express observations 1 simultaneous observations of venus by visible and infrared thermal imaging spectrometer and venus monitoring camera onboard the venus express spacecraft are used to map the cloud top altitude and to relate it to the ultraviolet uv markings the cloud top altitude is retrieved from the depth of co2 absorption band at 1 6 m in low and middle latitudes the cloud top is located at 74 1 km it decreases poleward of 50 and reaches 63 69 km in the polar regions this depression coincides with the eye of the planetary vortex at the same latitude and hour angle cloud top can experience fast variations of about 1 km in tens of hours while larger long term variations of several kilometers have been observed only at high latitudes uv markings correlate with the cloud altimetry however the difference between adjacent uv dark and bright regions does not exceed several hundred meters surprisingly co2 absorption bands are often weaker in the dark uv features indicating that these clouds may be a few hundred meters higher or have a larger scale height than neighboring clouds ultraviolet dark spiral arms which are often seen at about 70 correspond to higher altitudes or to the regions with strong latitudinal gradient of the cloud top altitude cloud altimetry in the polar region reveals the structure that correlates with the thermal emission maps but is invisible in uv images this implies that the uv optically thick polar hood is transparent in the near ir

time scale for local scour at bridge piers the temporal development of clear water local scour depth at cylindrical bridge piers in uniform sand beds is considered new data are presented and used to quantify the influence of flow duration on the depth of local scour an equilibrium time scale t is defined the data show that both t and the equilibrium scour depth dse are subject to similar influences of flow and sediment parameters as might be expected because they are inherently interdependent a method is given for determination of the time for development of dse for a given pier sediment and approach flow velocity and the concomitant estimation of the scour depth at any stage during development of the equilibrium scour hole the results show that the scour depth after 10 of the time to equilibrium is between about 50 and 80 of the equilibrium scour depth depending on the approach flow velocity of local scour d se is rapidly attained in live bed conditions but rather more slowly in clear water conditions fig 1 clear water scour occurs for mean flow velocities up to the threshold velocity for bed sediment entrainment i e v vc while live bed scour occurs for v vc the maximum equilibrium scour depth dse max occurs at v vc in armored cobble or cohesive sediment bed streams multiple flood events may be required before the maximum clear water scour is reached this may take many years the equilibrium scour depth in live bed con ditions fluctuates due to the effects of bed form migration the dashed lines in fig 1 represent the temporal average scour depth under live bed conditions the diagram also shows the time taken te for the equilibrium scour depth to develop the equilibrium time te is the focus of this paper it increases rapidly with flow velocity under clear water conditions but then decreases rapidly for live bed scour existing equations for depth of local scour at bridge piers give the equilibrium depth and are therefore conservative re garding temporal effects for the live bed conditions that typ ically pertain in floods equilibrium scour depths are appro priate however where clear water scour conditions exist the equilibrium depth of scour may be overly conservative peak flood flows may last only a number of hours or a few days in the field and short floods have insufficient time to generate equilibrium depths for example bridge piers situated on the floodplain may be wet for periods of less than one day during a flood typically clear water conditions pertain at such sites the actual scour may be only a small fraction of the equilib rium scour depth which could take weeks to fully develop johnson and mccuen 1991 developed an analytical model to simulate the temporal process of local scour at piers the model was applied to a hypothetical bridge pier using a gen erated sequence of flood flows over a 75 year period the in dividual storms being of 24 h duration at the end of the 75 year period the scour depth was still increasing

morphology and dynamics of the upper cloud layer of venus esa s venus express probe has been in orbit since april 2006 eight research papers in this issue present new results from the mission covering the atmosphere polar features interactions with the solar wind and the controversial matter of venusian lightning hakan svedham et al open the section with a review of the similarities and mostly differences between venus and its twin the earth andrew ingersoll considers the latest results and also how the project teams plan to make the most of the probe s remaining six years of life venus is completely covered by a thick cloud layer with the cloud tops in fast retrograde rotation global and small scale properties of these clouds and their temporal and latitudinal variations are investigated and the wind velocities are derived the southern polar region is highly variable and can change dramatically on time scales as short as one day perhaps arising from the injection of so2 into the mesosphere venus is completely covered by a thick cloud layer of which the upper part is composed of sulphuric acid and some unknown aerosols1 the cloud tops are in fast retrograde rotation super rotation but the factors responsible for this super rotation are unknown2 here we report observations of venus with the venus monitoring camera3 on board the venus express spacecraft we investigate both global and small scale properties of the clouds their temporal and latitudinal variations and derive wind velocities the southern polar region is highly variable and can change dramatically on timescales as short as one day perhaps arising from the injection of so2 into the mesosphere the convective cells in the vicinity of the subsolar point are much smaller than previously inferred4 5 6 which we interpret as indicating that they are confined to the upper cloud layer contrary to previous conclusions7 8 but consistent with more recent study9

fine bed material in pools of natural gravel bed channels natural gravel bed channels commonly contain a fine mode of sand and fine gravel that fills voids of the bed framework of coarser gravel if the supply of fine bed material exceeds the storage capacity of framework voids excess fine material forms surficial patches which can be voluminous in pools during low flow data collected in 34 natural channels in northern california and southern oregon indicate the following 1 fine material on the bed surface can be readily winnowed and transported at high particle velocities much of it in intermittent suspension fine material can dominate the bed material load in gravel bed channels but its abundance on the bed surface is limited by its increasing mobility as hiding places among prominent particles are filled 2 fine material in pools is typically replaced many times per year 3 the proportion v of residual pool volume filled with fine bed material correlates with annual sediment yield in channels whose parent material produces abundant sandy sediment 4 temporal and spatial changes in v appear to correspond to variations in the balance between sediment inputs and water discharge these results suggest that v can be used to monitor and evaluate the supply of excess fine material in gravel bed channels and that samples of fine material in pools can characterize the fine mobile mode of bed material load the sediment load of a stream channel the amount supplied and transported over a period of time can be difficult to evaluate contributions from hillslopes can be quantified with erosion surveys and sediment budgeting but uncertainty in routing makes it difficult to assess the load at any point in a channel network and direct measurement of transport rates is notoriously difficult bed material typically furnishes the bulk of the annual bed load especially in more distal channels but the active volume that contributes to the load is highly variable and difficult to evaluate it may be easier to detect variations in load by examining the mobility of the bed surface of gravel bed channels bed material in gravel bed channels characteristically includes a wide range of particle size and the bed can become

stream bed stabilization using boulder check dams that mimic step pool morphology features in northern italy during the last 10 years the check dams made of boulders have been fully employed for torrent management particularly for high gradient stream stabilization the analysis of this typology is shown in relation to three aspects building features field of use and design according to geomorphologic principles the maso di spinelle torrent located in the province of trento italy north italian alps is an example where a sequence of low check dams made of boulders have been used for bed stabilization the design criteria are taken from the step pool morphology features and the results are encouraging for further applications the artificial step pool grade control structures in the maso di spinelle torrent have been successfully tested by floods events with return periods of about 7 10 and 20 25 years

hydrodynamic processes and their impacts on the mud deposit in the southern yellow sea abstract the sedimentation processes of mud deposits on the continental shelves of the yellow sea ys are investigated using a combined data analysis and hydrodynamic modeling approach in order to identify the dominant factors that contribute significantly to the formation of these deposits the data analysis makes extensive use of existing data especially recently collected deep core data while the hydrodynamic and sediment transport processes are studied using a 3d hydrodynamics model that incorporates the effects of tides waves and wind the average deposit rate of the central yellow sea mud cs is estimated to be 3 6 107 t a 1 based on high resolution chirp sonar profiles combined with core data available sedimentological mineralogical geochemical and fluid flow data all indicate that the fine sediments discharged from huanghe river and changjiang river as well as the resuspended sediments from the old huanghe delta are the main sources for the mud deposits in the southern yellow sea sys this study confirms that tidal current flow is indeed the main agent for transporting the fine sediment to the mud patch in the central sys but wave effect is also significant as it is responsible for maintaining suspension concentration and causing sediment resuspension the wave influence is particularly notable around the old huanghe delta in winter storms as during these storm periods current circulation mainly caused by the asian monsoon can transport a large quantity of fine sediments from the old huanghe delta to the central sys under the present hydrodynamic conditions the modeling results showed that approximately 16 1 33 108 t a 1 of the huanghe river derived sediment is transported out of bohai strait of which around 44 5 72 107 t a 1 will finally be transported to the south yellow sea the corresponding values without accounting for the wave effects are 9 8 and 2 6 respectively it is noted that the deposition rate in the cs mud area over the past 12 kyr is virtually constant despite the significant rise in sea level and associated changes in the tidal current fields and wave distributions in the yellow sea the reason for this is believed to be that the weaker currents and waves during a lower water period is compensated by the shorter distance the suspended sediments have to travel from the paleo huanghe river to the cs mud area thus maintaining a nearly constant deposition rate in the cs mud area

a warm layer in venus cryosphere and high altitude measurements of hf hcl h2o and hdo esa s venus express probe has been in orbit since april 2006 eight research papers in this issue present new results from the mission covering the atmosphere polar features interactions with the solar wind and the controversial matter of venusian lightning hakan svedham et al open the section with a review of the similarities and mostly differences between venus and its twin the earth andrew ingersoll considers the latest results and also how the project teams plan to make the most of the probe s remaining six years of life venus mesosphere is a transition region between the retrograde super rotation at the top of the thick clouds and the solar antisolar circulation in the thermosphere the mesospheric distributions of hf hcl h2o and hdo are reported and an unexpected extensive layer of warm air at altitudes 90 120 km on the nightside is found venus has thick clouds of h2so4 aerosol particles extending from altitudes of 40 to 60 km the 60 100 km region the mesosphere is a transition region between the 4 day retrograde superrotation at the top of the thick clouds and the solar antisolar circulation in the thermosphere above 100 km which has upwelling over the subsolar point and transport to the nightside1 2 the mesosphere has a light haze of variable optical thickness with co so2 hcl hf h2o and hdo as the most important minor gaseous constituents but the vertical distribution of the haze and molecules is poorly known because previous descent probes began their measurements at or below 60 km here we report the detection of an extensive layer of warm air at altitudes 90 120 km on the night side that we interpret as the result of adiabatic heating during air subsidence such a strong temperature inversion was not expected because the night side of venus was otherwise so cold that it was named the cryosphere above 100 km we also measured the mesospheric distributions of hf hcl h2o and hdo hcl is less abundant than reported 40 years ago3 hdo h2o is enhanced by a factor of 2 5 with respect to the lower atmosphere and there is a general depletion of h2o around 80 90 km for which we have no explanation

cloud tracked winds from pioneer venus ocpp images abstract analysis of ultraviolet image sequences obtained from the pioneer venus orbiter cloud photopolarimeter and covering five 80 day periods from 1979 1985 provides the first climatological description of the cloud top circulation on venus the average zonal winds can be characterized as a 5 day retrograde rotation of the whole cloud level atmosphere with weak jets at middle to high latitudes both the midlatitude and equatorial zonal winds vary by about 5 8 m s 1 over time spans of 1 6 years the average meridional circulation is poleward in both hemispheres up to at least 60 latitude consistent with the presence of a thermally direct hadley circulation associated with the clouds the strength of the hadley circulation also varies with time four wave modes are clearly identified a diurnal solar tide a semi diurnal solar tide a 4 day equatorial wave and a 5 day midlatitude wave the semidiurnal tide appears to have an amplitude of about 5 m s 1 and to be approximately constant with time

evidence of recent sedimentation in the eastern irish sea the recent sedimentation history of the eastern irish sea has been investigated by radiocarbon dating age versus depth profiles of the shells of the gastropod turritella communis risso indicate that sedimentation has been taking place at two sites at a relatively slow but constant rate 0 02 0 08 cm a 1 for the past 3000 4000 years at a third site sedimentation appears to have been more variable and more rapid 0 3 cm a 1 dating t communis shells provides a more reliable indicator of the sediment accumulation rate than dating the bulk sediment carbonate fraction the latter is predominantly of marine origin but has been reworked and unlike the shells is subject to the intense mixing by bioturbation which characterizes the muddy sediments of this area bulk sediment carbonate ages are much greater than those of t communis at equivalent depths 10 300 15 300 yrs and 130 3800 yrs respectively and the profiles are more variable leading to difficulties in interpretation

effects of upstream weir slope on local scour at submerged weirs abstractthe variation of upstream slope of a submerged weir could significantly alter the local flow pattern and sediment transport this paper presents an experimental investigation into local sco