transient features in a titan sea as northern summer solstice nears on saturn s moon titan dynamic processes on its surface are expected recent observations by the cassini spacecraft reveal transient bright features in or on a titan sea that are consistent with an ephemeral phenomenon such as waves

cassini imaging of titan s high latitude lakes clouds and south polar surface changes 1 cassini s imaging science subsystem iss has been observing titan since april 2004 compiling a nearly global surface map and monitoring the surface and atmosphere for activity early images of the south polar region revealed numerous dark surface features and contemporaneous convective cloud systems suggesting the presence of hydrocarbon lakes similar to those later detected at titan s north pole intriguingly repeated south polar imaging by iss revealed differences consistent with ponding of hydrocarbon liquids on the surface due to precipitation from a large storm more recent iss images of high northern latitudes illustrate the full extents 500 000 km2 of hydrocarbon seas sections of which have been observed by cassini s radar these observations demonstrate dynamic processes at work on titan and that the poles harbor liquid hydrocarbon reservoirs the extents of which differ from pole to pole and which may be coupled to seasonally varying circulation

active shoreline of ontario lacus titan a morphological study of the lake and its surroundings of more than 400 filled lakes now identified on titan the first and largest reported in the southern latitudes is ontario lacus which is dark in both infrared and microwave here we describe recent observations including synthetic aperture radar sar images by cassini s radar instrument 2 cm and show morphological evidence for active material transport and erosion ontario lacus lies in a shallow depression with greater relief on the southwestern shore and a gently sloping possibly wave generated beach to the northeast the lake has a closed internal drainage system fed by earth like rivers deltas and alluvial fans evidence for active shoreline processes including the wave modified lakefront and deltaic deposition indicates that ontario is a dynamic feature undergoing typical terrestrial forms of littoral modification

shoreline features of titan s ontario lacus from cassini vims observations we analyze observations of titan s south polar lake ontario lacus obtained by cassini s visual and infrared mapping spectrometer during the 38th flyby of titan t38 2007 december 5 these near closest approach observations have the highest signal to noise the finest spatial resolution and the least atmospheric influence of any near infrared lake observation to date we use the large spatially flat and low albedo interior of ontario lacus as a calibration target allowing us to derive an analytical atmospheric correction for emission angle the dark lake interior is surrounded by two separate annuli that follow the lake interior s contours the inner annulus is uniformly dark but not so much as the interior lake and is generally 5 10 kilometers wide at the lake s southeastern margin we propose that it represents wet lakebed sediments exposed by either tidal sloshing of the lake or seasonal methane loss leading to lower lake volume the exterior annulus is bright and shows a spectrum consistent with a relatively low water ice content relative to the rest of titan it may represent fine grained condensate deposits from a past era of higher lake level together the annuli seem to indicate that the lake level for ontario lacus has changed over time this hypothesis can be tested with observations scheduled for future titan flybys

bathymetry and absorptivity of titan s ontario lacus ontario lacus is the largest and best characterized lake in titan s south polar region in june and july 2009 the cassini radar acquired its first synthetic aperture radar sar images of the area together with closest approach altimetry acquired in december 2008 these observations provide a unique opportunity to study the lake s nearshore bathymetry and complex refractive properties average radar backscatter is observed to decrease exponentially with distance from the local shoreline this behavior is consistent with attenuation through a deepening layer of liquid and if local topography is known can be used to derive absorptive dielectric properties accordingly we estimate nearshore topography from a radar altimetry profile that intersects the shoreline on the east and west sides of the lake we then analyze sar backscatter in these regions to determine the imaginary component of the liquid s complex index of refraction the derived value 6 1 1 3 1 7 10 4 corresponds to a loss tangent of tan 9 2 2 0 2 5 10 4 and is consistent with a composition dominated by liquid hydrocarbons this value can be used to test compositional models once the microwave optical properties of candidate materials have been measured in areas that do not intersect altimetry profiles relative slopes can be calculated assuming the index of refraction is constant throughout the liquid accordingly we construct a coarse bathymetry map for the nearshore region by measuring bathymetric slopes for eleven additional areas around the lake these slopes vary by a factor of 5 and correlate well with observed shoreline morphologies

nature distribution and origin of titan s undifferentiated plains abstract the undifferentiated plains on titan first mapped by lopes et al lopes r m c et al 2010 icarus 205 540 588 are vast expanses of terrains that appear radar dark and fairly uniform in cassini synthetic aperture radar sar images as a result these terrains are often referred to as blandlands while the interpretation of several other geologic units on titan such as dunes lakes and well preserved impact craters has been relatively straightforward the origin of the undifferentiated plains has remained elusive sar images show that these blandlands are mostly found at mid latitudes and appear relatively featureless at radar wavelengths with no major topographic features their gradational boundaries and paucity of recognizable features in sar data make geologic interpretation particularly challenging we have mapped the distribution of these terrains using sar swaths up to flyby t92 july 2013 which cover 50 of titan s surface we compared sar images with other data sets where available including topography derived from the sartopo method and stereo dems the response from radar radiometry hyperspectral imaging data from cassini s visual and infrared mapping spectrometer vims and near infrared imaging from the imaging science subsystem iss we examined and evaluated different formation mechanisms including i cryovolcanic origin consisting of overlapping flows of low relief or ii sedimentary origins resulting from fluvial lacustrine or aeolian deposition or accumulation of photolysis products created in the atmosphere our analysis indicates that the undifferentiated plains unit is consistent with a composition predominantly containing organic rather than icy materials and formed by depositional and or sedimentary processes we conclude that aeolian processes played a major part in the formation of the undifferentiated plains however other processes fluvial deposition of photolysis products are likely to have contributed possibly in differing proportions depending on location

a numerical study of tides in titan s northern seas kraken and ligeia maria abstract the tidal response of titan s two largest northern seas ligeia mare and kraken mare is studied by means of a two dimensional depth averaged shallow water model slim http www climate be slim kraken mare is formed of two basins the northern one being assumed to be linked by a single strait trevize fretum to ligeia mare the tidal motions tend to be independent of each other in each basin i e ligeia mare kraken 1 and kraken 2 which results in sharp transitions in the straits our results are overall rather similar to those of tokano et al 2014 suggesting that a 2d model such as slim is adequate for modelling titan s tides and since it is presumably less computationally demanding may be better for sensitivity studies for instance the maximum tidal range in kraken and ligeia maria respectively are 0 29 m and 0 14 m which is within the range predicted by lorenz et al 2014 although smaller by 0 07 m and larger by 0 04 m than the estimates of tokano et al 2014 but it occurs at the same location the tidal currents are faster by about one order of magnitude in the straits linking those maria than in the basins themselves with a maximum of 0 36 m s in the strait linking kraken 1 and kraken 2 seldon fretum a decomposition of the tidal history into different harmonic components is carried out except in specific areas such as the straits and the amphidromic point s the main tidal component has a period of 1 titan day we also briefly studied the eigenmodes of the northern seas whose period is close to the tidal period such modes are very local indeed their magnitude is significant with respect to the magnitude of the modes elsewhere in the seas in small bay s or near the islands of kraken 2 and ligeia mare they are not excited by the tides as they do not appear in the tidal motion a sensitivity analysis to poorly constrained parameters bottom friction coefficient depth of trevize fretum and attenuation factor the latter is briefly discussed with respect to the values of the love numbers found in the literature is also conducted the model parameters are seen to have a significant impact on the liquid exchanges between the basins and consequently on the tidal range and phase fluid velocity and location of amphidromic point s

numerical simulation of tides and oceanic angular momentum of titan s hydrocarbon seas abstract tides and tidal currents in titan s hydrocarbon seas are numerically simulated by a 3 dimensional ocean circulation model using a bathymetry map constrained by cassini these predictions are used to calculate the tidally induced variations of the oceanic angular momentum of the seas the tides behave as a quasi standing wave with anti nodes at the northern and southern shores the tidal currents in kraken mare are mainly oriented along the major axis of the sea and are dominated by fast hydraulic currents through a narrow strait the axial oceanic angular momentum primarily changes due to redistribution of liquids in kraken mare and maximizes when there is ebb at the northern shore and flood at the southern shore on the other hand variations of the equatorial oceanic angular momentum are contributed by both tides and tidal currents the oceanic torque between sea and sea bottom is minor compared to its atmospheric counterpart i e the mountain torque between atmosphere and mountains

transient surface liquid in titan s polar regions from cassini cassini radar images of titan s south polar region acquired during southern summer contain lake features which disappear between observations these features show a tenfold increases in backscatter cross section between images acquired one year apart which is inconsistent with common scattering models without invoking temporal variability the morphologic boundaries are transient further supporting changes in lake level these observations are consistent with the exposure of diffusely scattering lakebeds that were previously hidden by an attenuating liquid medium we use a two layer model to explain backscatter variations and estimate a drop in liquid depth of approximately 1 m per year on larger scales we observe shoreline recession between iss and radar images of ontario lacus the largest lake in titan s south polar region the recession occurring between june 2005 and july 2009 is inversely proportional to slopes estimated from altimetric profiles and the exponential decay of near shore backscatter consistent with a uniform reduction of 4 1 3 m in lake depth of the potential explanations for observed surface changes we favor evaporation and infiltration the disappearance of dark features and the recession of ontario s shoreline represents volatile transport in an active methane based hydrologic cycle observed loss rates are compared and shown to be consistent with available global circulation models to date no unambiguous changes in lake level have been observed between repeat images in the north polar region although further investigation is warranted these observations constrain volatile flux rates in titan s hydrologic system and demonstrate that the surface plays an active role in its evolution constraining these seasonal changes represents the first step toward our understanding of longer climate cycles that may determine liquid distribution on titan over orbital time periods

evidence of titan s climate history from evaporite distribution abstract water ice poor 5 m bright material on saturn s moon titan has previously been geomorphologically identified as evaporitic here we present a global distribution of the occurrences of the 5 m bright spectral unit identified with cassini s visual infrared mapping spectrometer vims and examined with radar when possible we explore the possibility that each of these occurrences are evaporite deposits the 5 m bright material covers 1 of titan s surface and is not limited to the poles the only regions with extensive long lived surface liquid we find the greatest areal concentration to be in the equatorial basins tui regio and hotei regio our interpretations based on the correlation between 5 m bright material and lakebeds imply that there was enough liquid present at some time to create the observed 5 m bright material we address the climate implications surrounding a lack of evaporitic material at the south polar basins if the south pole basins were filled at some point in the past then where is the evaporite

temporal variations of titan s surface with cassini vims abstract we analyze cassini vims data of several areas on titan s surface looking for variations with time three of these locations are near the equator 10 30 s namely hotei regio tui regio and sotra patera in some cases changes in brightness and or in appearance were reported therein we also investigate a portion of the undifferentiated plains areas relatively homogeneous and dark in radar observations located near 20 25 n this is a follow up on a previous paper in which we had inferred surface albedos for some distinct regions of interest rois identified within the hotei tui and sotra areas through a principal component analysis pca and radiative transfer rt modeling solomonidou 2014 j geophys res 119 1729 1747 we apply the same methods here to a larger dataset looking for variations of the surface albedo with time and using the huygens landing site as the ground truth for calibration purposes as expected the undifferentiated plains remain unchanged from january 2010 to june 2012 our analysis of hotei regio data from march 2005 to march 2009 also does not show any significant surface albedo variations within uncertainties we note however that our rt retrievals are not optimal in this case because of the use of a plane parallel code and the unfavorable geometry of the associated datasets conversely tui regio and sotra patera show surface albedo fluctuations with time with pronounced trends for darkening and for brightening respectively the tui regio spectrum exhibits a surface albedo decrease from march 2005 to february 2009 at 0 94 1 08 2 03 and 5 m wavelengths while the spectrum shape remains the same over that time on the contrary the sotra patera area became at least two times brighter within a year april 2005 february 2006 at 1 58 m 2 03 m and 5 m we also retrieved surface albedo spectra for three reference regions surrounding hotei tui and sotra and for three additional regions we use as test cases that correspond to dune fields during the time periods explored here we find that as expected and contrary to tui regio and sotra patera the test cases did not show any significant changes in surface albedo we therefore suggest that temporal variations of surface albedo exist for some areas on titan but that their origin may differ from one region to the other they could be due to diverse past and or ongoing formation processes endogenic and or exogenic possibly cryovolcanic as discussed here

composition seasonal change and bathymetry of ligeia mare titan derived from its microwave thermal emission for the last decade the passive radiometer incorporated in the cassini radar has recorded the 2 2 cm wavelength thermal emission from titan s seas in this paper we analyze the radiometry observations collected from february 2007 to january 2015 over one of these seas ligeia mare with the goal of providing constraints on its composition bathymetry and dynamics in light of the depth profile obtained by mastrogiuseppe et al 2014 and of a two layer model we find that the dielectric constant of the sea liquid is 1 8 and its loss tangent is inline image both results point to a composition dominated by liquid methane rather than ethane a high methane concentration suggests that ligeia mare is primarily fed by methane rich precipitation and or ethane has been removed from it e g by crustal interaction our result on the dielectric constant of the seafloor is less constraining inline image but we favor a scenario where the floor of ligeia mare is covered by a sludge of compacted and possibly nitrile rich organic material formed by the deposition of photochemical haze or by rain washing of the nearby shores we use these results to produce a low resolution bathymetry map of the sea we also estimate the temperature variation of the bulk sea between february 2007 and july 2013 to be 2 k which provides a constraint on its net evaporative cooling currently being explored in ocean circulation models lastly we suggest a lag in the summer warming of the northern polar terrains

on the application of a boussinesq model to river flows including shocks serr 1d is a 4th order finite volume 1d boussinesq model including wave breaking energy dissipation through extra diffusive like terms this model has been primarily conceived to compute wave propagation in coastal areas and has been validated for breaking and non breaking waves propagating over uneven bathymetries cienfuegos et al 2005 2006a b 2007 the present paper aims at investigating the ability of serr 1d to simulate challenging fluvial hydraulic applications such as sudden gate operation in open channels generating short waves dam break flows and a steady hydraulic jump over a bump the performance of the absorbing generating boundary condition implemented in serr 1d is first analysed in the context of fluvial applications where relatively short waves must be evacuated from the computational domain without producing spurious reflection next by comparing numerical results to analytical and experimental dam break test cases we show that the model is able to reproduce the overall features of these flows but that additional care should be paid to the representation of energy dissipation and front speed in order to accurately represent bore dynamics

estimates of fluvial erosion on titan from sinuosity of lake shorelines 1 titan has few impact craters suggesting that its surface is geologically young titan s surface also has abundant landforms interpreted to be fluvial networks here we evaluate whether fluvial erosion has caused significant resurfacing by estimating the cumulative erosion around the margins of polar lakes a scarcity of detailed topographic data makes it difficult to measure fluvial incision on titan but images of drowned fluvial features around the lake margins where elevated levels of hydrocarbon liquids appear to have partly flooded fluvial valleys offer a constraint on the topography we mapped the shorelines of several lakes to obtain topographic contours that trace the fluvially dissected topography we then used a numerical landscape evolution model to calibrate a relationship between contour sinuosity which reflects the extent of fluvial valley incision and cumulative erosion we confirmed this relationship by analyzing a partially dissected surface adjacent to the minnesota river usa comparison of the mapped titan contours with the sinuosity erosion relationship suggests that cumulative fluvial erosion around the margins of titan s polar lakes including ligeia mare kraken mare and punga mare in the north and ontario lacus in the south ranges from 4 to 31 of the initial relief additional model simulations show that this amount of fluvial erosion does not render craters invisible at the resolution of currently available imagery suggesting that fluvial erosion is not the only major resurfacing mechanism operating in titan s polar regions

observation of undertow and turbulence in a laboratory surf zone abstract undertow and turbulence in the surf zone have been studied in a wave flume for a spilling breaker and a plunging breaker fluid velocities across a 1 on 35 sloped false bottom were measured using a fiber optic laser doppler anemometer and wave decay and set up were measured using a capacitance wave gage the characteristics of mean flow and turbulence in spilling versus plunging breakers were studied the mean flow is the organized wave induced flow defined as the phase average of the instantaneous velocity while the turbulence is taken as the deviations from the phase average it was found that under the plunging breaker turbulence levels are much higher and vertical variations of undertow and turbulence intensity are much smaller in comparison with the spilling breaker it was also found that turbulent kinetic energy is transported seaward under the spilling breaker and landward under the plunging breaker by the mean flow the study indicates that there are fundamental differences in the dynamics of turbulence between spilling and plunging breakers which can be related to the processes of wave breaking and turbulence production it is suggested that the types of beach profile produced by storm and swell waves may be the results of different relationships between mean flow and turbulence in these waves

dispersive and nonhydrostatic pressure effects at the front of surge undular bores and shocks generated by dam break flows or tsunamis are examined considering nonhydrostatic pressure and dispersive effects in one and two horizontal dimensional space the fully nonlinear boussinesq type equations based on a weakly nonhydrostatic pressure assumption are chosen as the governing equations the equation set is solved by a fourth order accurate finite volume method with an approximate riemann solver several typical benchmark problems such as dam break flows and tsunami wave fission are tested in one and two horizontal dimensional space the computed results by the boussinesq type model are at least as accurate as the results by the hydrostatic shallow water equations this is particularly evident near the steep front of the wave where frequency dispersion can play an important role the magnitude of this nonhydrostatic pressure and dispersive effect near the front is quantified and the engineering implications of neglecting these physics as would be done through the use of a hydrostatic model are discussed

strontium isotopes and rubidium in the ganga brahmaputra river system weathering in the himalaya fluxes to the bay of bengal and contributions to the evolution of oceanic87sr 86sr the concentrations of rb and sr and87sr 86sr isotopic ratios have been measured in the dissolved load of the ganga brahmaputra g b river system the ganga was sampled extensively from its source at gangotri in the higher himalaya to patna on the alluvial plains the brahmaputra was sampled in its stretch in assam in india the average sr concentration in the ganga at patna is 1 2 mol l and that in the brahmaputra at goalpara is 0 73 mol l the mean87sr 86sr ratios are 0 7239 and 0 7192 respectively the87sr 86sr in the ganga source waters the alaknanda the bhagirathi and their tributaries range between 0 7300 and 0 7986 considerably higher than the global average runoff value of 0 7119 the high87sr 86sr in the ganga source waters result from the intense weathering of precambrian granites and gneisses enriched in radiogenic sr the sr isotope systematics of the ganga waters is dominated by silicate weathering whereas carbonate weathering plays a significant role in their major ion chemistry the g b system transports about 910 million moles of dissolved sr annually to the bay of bengal with an average87sr 86sr of 0 7213 the sr transported by the g b system is about 2 7 of the global dissolved sr flux to the oceans via rivers model calculations reveal that the g b system has contributed significantly to the sr isotope evolution of seawater during the past 20 ma the flux of rb through the g b system is 24 million moles per year this is about 5 of the global river supply of rb to the oceans nearly twice the contribution of water via the g b system to the oceans our study suggests that the marine geochemistries of sr and rb and possibly u may have been influenced considerably by the himalayan orogeny

hydrocarbon lakes on titan distribution and interaction with a porous regolith from 10 to more than 100 000 km 2 the size and location of lakes provide constraints on parameters associated with subsurface transport using porous media properties inferred from huygens probe observations timescales for flow into and out of observed lakes are shown to be in the tens of years similar to seasonal cycles derived timescales are compared to the time between collocated sar observations in order to considertheroleofsubsurfacetransportintitan shydrologic cycle citation hayes a et al 2008 hydrocarbon lakes on titan distribution and interaction with a porous regolith geophys res lett 35 l09204 doi 10 1029 2008gl033409

the run up of nonbreaking and breaking solitary waves abstract the run up of nonbreaking and breaking solitary waves on plane impermeable beaches is investigated with a lagrangian finite element boussinesq wave model wave breaking is parameterized with an artificial viscosity diffusion term in the momentum equation and bottom friction is modelled with a term quadratic in the horizontal fluid velocity comparisons are presented with laboratory data of maximum run up shoreline motion and spatial profiles of near shore free surface elevation for both steep 20 and gradual 2 88 slopes for the steep slope only waves which do not break on run up are considered and excellent agreement is obtained with the laboratory data for the gradual slope wave shoaling breaking bore formation and subsequent collapse at the shoreline are predicted well by the model although the breaking algorithm does not attempt to model the details of the turbulent flow in the breaking region the backwash bore is also modelled reasonably well although it persists longer in the numerical computations than in the laboratory data it is shown that the inclusion of nonhydrostatic effects reduces the tendency of waves to break and improves the agreement of the numerical results with the laboratory run up data this allows higher amplitude waves to be modelled and larger propagation distances to be treated without the need to limit the wave steepness with artificial dissipation

controls over the strontium isotope composition of river water abstract strontium concentrations and isotope ratios have been measured in river and ground waters from the ganges orinoco and amazon river basins when compared with major element concentrations the data set has allowed a detailed examination of the controls over the strontium isotope systematics of riverine input to the oceans in the following environments 1 1 typical drainage basins containing limestones evaporites shales and alumino silicate metamorphic and igneous rocks 2 2 shield terrains containing no chemical or biogenic sediments and 3 3 the floodplains that constitute the largest areas of many large rivers the strontium concentration and isotope composition of river waters are largely defined by mixing of strontium derived from limestones and evaporites with strontium derived from silicate rocks the strontium isotope composition of the limestone endmember generally lies within the phanerozoic seawater range which buffers the 87 sr 86 sr ratios of major rivers a major exception is provided by the rivers draining the himalayas where widescale regional metamorphism appears to have led to an enrichment in limestones of radiogenic strontium derived from coexisting silicate rocks the strontium isotope systematics of rivers draining shield areas are controlled by the intense transportlimited nature of the weathering reactions and thereby limits variations in the strontium flux from these terrains floodplains are only a minor source of dissolved strontium to river waters and precipitation of soil salts in some floodplains can reduce the riverine flux of dissolved strontium to the oceans the most effective mechanisms for altering the isotope ratio and flux of riverine strontium to the oceans are increased glaciation and large scale regional metamorphism of the type produced during continental collision both mechanisms provide a means for increasing the 87 sr 86 sr ratio of the global riverine flux

a large cloud outburst at titan s south pole images of titan acquired over five nights in october 2004 using the adaptive optics system at the keck observatory show dramatic increases in tropospheric cloud activity at the south pole compared with all other images of titan clouds to date during this time titan s south polar clouds brightened to more than 18 times their typical values the cassini ta flyby of titan occurred as this storm was rapidly dissipating we find that the brightness of this cloud outburst is consistent with the dramatic transient brightening of titan observed in atmospheric windows on two nights in 1995 by griffith et al griffith c a owen t miller g a geballe t 1998 nature 395 6702 575 578 if we scale the brightness of the cloud by projecting it onto the equator while apparently infrequent the fact that large cloud events have been observed in different seasons of titan s year indicates that these large storms might be a year round phenomenon on titan we propose possible mechanisms to explain these occasional short term increases in titan s cloud activity

comparison of titan s north polar lakes with terrestrial analogs 1 the discovery of hydrocarbon lakes in the polar regions of titan offers a unique opportunity to compare terrestrial lakes with those in an extraterrestrial setting we selected 114 terrestrial lakes formed by different processes as analogs for comparison with the 190 titanian lakes that we had mapped in our previous study using the shuttle radar topography mission srtm c band backscatter data and the srtm water body data swbd we carried out an assessment of manual mapping versus existing automated mapping techniques and found the automated techniques to produce as good representations of the lake shorelines as the manual mapping in the terrestrial dataset we then calculated and compared terrestrial and titanian shoreline statistical parameters including fractal dimension shoreline development index and an elongation index we found different lake generation mechanisms on earth produce statistically different shorelines however we cannot identify any one mechanism or set of mechanisms to be responsible for forming the depressions enclosing the lakes on titan on the basis of our statistical analyses

geomorphological significance of ontario lacus on titan integrated interpretation of cassini vims iss and radar data and comparison with the etosha pan namibia abstract ontario lacus is the largest lake of the whole southern hemisphere of titan saturn s major moon it has been imaged twice by each of the cassini imaging systems imaging science subsystem iss in 2004 and 2005 visual and infrared mapping spectrometer vims in 2007 and 2009 and radar in 2009 and 2010 we compile a geomorphological map and derive a hydrogeological interpretation of ontario lacus based on a joint analysis of iss vims and radar sar datasets along with the t49 altimetric profile acquired in december 2008 the morphologies observed on ontario lacus are compared to landforms of a semi arid terrestrial analog which resembles titan s lakes the etosha pan located in the owambo basin namibia the etosha pan is a flat floored depression formed by dissolution under semi arid conditions of a surface evaporitic layer calcretes controlled by groundwater vertical motions we infer that ontario lacus is an extremely flat and shallow depression lying in an alluvial plain surrounded by small mountain ranges under climatic conditions similar to those of terrestrial semi arid regions channels are seen in the southern part of ontario lacus in vims and radar data acquired at a 2 years time interval their constancy in location with time implies that the southern portion of the depression is probably not fully covered by a liquid layer at the time of the observations and that they most probably run on the floor of the depression a shallow layer of surface liquids corresponding to the darkest portions of the radar images would thus cover about 53 of the surface area of the depression of which almost 70 is located in its northern part these liquid covered parts of the depression where liquid ethane was previously identified are interpreted as topographic lows where the alkanofer raises above the depression floor the rest of the depression and mostly its southern part is interpreted as a flat and smooth exposed floor likely composed of a thick and liquid saturated coating of photon absorbing materials in the infrared this hypothesis could explain its dark appearance both in the infrared and radar data and the persistence of channels seen on the depression floor over the time shorelines are observed on the border of ontario lacus suggesting past high stand levels of the alkanofer table the analogy with the etosha pan suggests that ontario lacus depression developed at the expense of a soluble layer covering the region dissolution of this layer would be controlled by vertical motions of the alkanofer table over the time during flooding events liquid hydrocarbons covering the depression floor would dissolve the surface layer increasing progressively the diameter of the depression on geological timescales during drought episodes liquid hydrocarbons of the underground alkanofer would evaporate leading to crystallization of evaporites in the pores and at the surface of the substratum and to the formation of the regional soluble layer the presence of specific landforms lunette dunes or evaporites is compatible with such evaporitic regional settings alternatively but not exclusively the surface soluble layer might have formed by accumulation on the ground of soluble compounds formed in the atmosphere

titan s magic islands transient features in a hydrocarbon sea abstract the region of titan s hydrocarbon sea ligeia mare where transient bright features were previously discovered was anomalously bright in the first of two more recent cassini radar observations but not the second another transient bright feature in a different region of ligeia mare was also discovered in the first of the new observations here we present all the high resolution observations of the regions containing these transient features and the quantitative constraints that we derived from them we argue that these features are unlikely to be sar image artifacts or permanent geophysical structures and thus their appearance is the result of ephemeral phenomena on titan we find that the transient features are more consistent with floating and or suspended solids bubbles and waves than tides sea level change or seafloor change and based on the frequency of these phenomena in terrestrial settings we consider waves to be the most probable hypothesis these transient features are the first instance of active processes in titan s lakes and seas to be confirmed by multiple detections and demonstrate that titan s seas are not stagnant but rather dynamic environments

are tropical cyclones possible over titan s polar seas abstract while extratropical cyclones cannot be expected in titan s barotropic troposphere tropical cyclones which gain their energy from the latent heat of sea evaporation cannot be entirely dismissed over titan s polar hydrocarbon seas the most essential condition for the genesis of tropical cyclones on titan is a methane rich composition of the polar seas the most likely season for titan s hypothetical tropical cyclones is around the northern summer solstice when the sea surface gets warmer and the relative vorticity of the near surface air increases by seasonal convergence and equatorial wave activity a tropical cyclone would manifest itself as an anti clockwise swirling vortex right over one of the northern seas kraken mare ligeia mare punga mare and increase the surface wind over the seas by an order of magnitude on the other hand tropical cyclones are unlikely to emerge over titan s few tropical lakes for dynamic reasons such as negligible coriolis parameter and large vertical wind shear

laboratory measurements of cryogenic liquid alkane microwave absorptivity and implications for the composition of ligeia mare titan the complex dielectric constants of liquids methane and ethane were measured at 90 k and 14 1 ghz close to the frequency of the cassini radar the liquid ethane loss tangent is far greater than that of liquid methane facilitating discrimination by remote sensing the results suggest a methane dominated composition for the northern sea ligeia mare on the basis of a recent loss tangent determination using cassini radar altimetry this contrasts a previous far higher loss tangent for the southern lake ontario lacus which is inconsistent with simple mixtures of methane and ethane the apparent nonequilibrium methane to ethane ratio of ligeia mare can be explained by poor admixture of periodically cycled methane with a deeper ethane rich alkanofer system consistent with obliquity driven volatile cycling sequestration of ethane from the hydrocarbon cycle by incorporation into crustal clathrate hydrates or periodic flushing of ligeia mare into adjacent kraken mare by fresh rainfall

himalayan tectonics weathering processes and the strontium isotope record in marine limestones the time evolution of the isotopic composition of seawater strontium the ratio of strontium 87 to strontium 86 over the last 500 million years has the form of an asymmetric trough the values are highest in the cambrian and recent 0 7091 and lowest in the jurassic 0 7067 superimposed on this trend are a number of smaller oscillations consideration of the geochemical cycle of strontium and the dynamics of weathering shows that only himalayan style continental collisions can influence the isotope ratio on the scale observed the contemporary himalayan orogeny is by far the largest since the late precambrian pan african event that produced the high in the cambrian

organic sedimentary deposits in titan s dry lakebeds probable evaporite we report the discovery of organic sedimentary deposits at the bottom of dry lakebeds near titan s north pole in observations from the cassini visual and infrared mapping spectrometer vims we show evidence that the deposits are evaporitic making titan just the third known planetary body with evaporitic processes after earth and mars and is the first that uses a solvent other than water

edge detection applied to cassini images reveals no measurable displacement of ontario lacus margin between 2005 and 2010 1 ontario lacus is thus far the largest flat floored topographic depression of titan s southern hemisphere interpreted as a permanent or ephemeral lake from 2005 to 2010 it was imaged several times and at various wavelengths by iss vims and radar instruments onboard cassini s spacecraft we analyze the position and uncertainty of ontario lacus margin in all these images using an edge detection method based on image derivation we find that given the range of uncertainties in contour locations derived from images no measurable displacement of ontario lacus margin can be detected between 2005 and 2010 at the actual image spatial resolutions the discrepancy between this result and previous ones is attributable to differences in 1 the basics behind the methods used 2 the actual spatial resolutions and contrasts of the available images due to differential atmospheric scattering effects at different wavelengths and 3 the geomorphological interpretation of contours derived from images acquired at different wavelengths this lack of measurable displacement in the images suggests that the imaged contour corresponds either 1 to the border of a surface liquid body provided that potential changes in its extent over five terrestrial years were not sufficiently large to be measured or 2 to the stationary topographic border between ontario lacus depression and the surrounding alluvial plain potential displacements of ontario lacus margin between 2005 and 2010 are thus below the actual resolution of currently available images or have to be sought for within the extent of the topographic depression rather than along its borders

nonhydrostatic granular flow over 3 d terrain new boussinesq type gravity waves understanding granular mass flow is a basic step in the prediction and control of natural or man made disasters related to avalanches on the earth savage and hutter 1989 pioneered the mathematical modeling of these geophysical flows introducing saint venant type mass and momentum depth averaged hydrostatic equations using the continuum mechanics approach however denlinger and iverson 2004 found that vertical accelerations in granular mass flows are of the same order as the gravity acceleration requiring the consideration of nonhydrostatic modeling of granular mass flows although free surface water flow simulations based on nonhydrostatic depth averaged models are commonly used since the works of boussinesq 1872 1877 they have not yet been applied to the modeling of debris flow can granular mass flow be described by boussinesq type gravity waves this is a fundamental question to which an answer is required given the potential to expand the successful boussinesq type water theory to granular flow over 3 d terrain this issue is explored in this work by generalizing the basic boussinesq type theory used in civil and coastal engineering for more than a century to an arbitrary granular mass flow using the continuum mechanics approach using simple test cases it is demonstrated that the above question can be answered in the affirmative way thereby opening a new framework for the physical and mathematical modeling of granular mass flow in geophysics whereby the effect of vertical motion is mathematically included without the need of ad hoc assumptions

an efficient solver for nearshore flows based on the waf method abstract we describe an efficient and robust flow solver for the integration of the classic nonlinear shallow water equations nswe on a beach of arbitrary topography on the basis of the shock capturing weighted average flux waf method a numerical code is implemented which employs a space splitting technique to integrate the nswe over a horizontally two dimensional domain 2dh special care is put in handling the moving shoreline and a new efficient formulation of the shoreline boundary conditions is presented this is based on the hydrodynamic equivalent of the cavitation condition used in gas dynamics model capabilities are illustrated by means of a number of tests both 1dh and 2dh these reveal that though primarily conceived for modelling nearshore hydrodynamics the solver can be successfully adopted even for studying the run up of large tsunami waves

morphological evidence that titan s southern hemisphere basins are paleoseas abstract cassini has shown that modern liquid bodies are largely restricted to north polar latitudes 55 with a comparatively small volume of liquid in the southern hemisphere this dichotomy has previously been attributed to saturn s current orbital configuration but if correct the configuration is transient and southern depositional basins equivalent in volume to the northern seas are required in the south polar region we have identified four dry broad depressions equivalent in area to the northern seas morphologic and topographic data suggest that they represent paleoseas that were filled during an earlier epoch more favorable to the accumulation of southern liquids all four basins are characterized by topographically low sar dark plains along with dissected margins that mark putative paleo shorelines these characteristics imply that these depressions represent depositional basins topographically the basins have a combined volume that is 3 times greater than the northern seas sufficiently large to contain all of the northern liquids a lack of evidence for 5 m bright material interpreted as evaporite challenges our interpretations in the absence of efficient removal or burial mechanisms the long time scale over which fluids migrate however suggests that any deposits have ample time to be altered removed

nonhydrostatic dam break flows i physical equations and numerical schemes abstractmodeling of dam break flows is frequently required in civil and environmental engineering because of the risk associated with this catastrophic flow typically model predictions are conducted using the saint venant hydrostatic theory which can lead to unrealistic predictions the prediction of the amplitude of nonhydrostatic waves generated during dam break flows is an important engineering problem given the risk of overtopping of flow in manmade canals or the increasing of flooding areas in natural watercourses the weakly nondispersive and fully nonlinear serre equations are a suitable choice for modeling these flows but there is a lack of a systematic assessment of this system of equations for dam break flow modeling reported in the literature in this paper the serre equations are applied to dam break flows over horizontal rigid bottoms whereas in the second part of this research the nonhydrostatic dam break waves over erodible beds are considered here a high resolution finite volume m

wave transformation and swash oscillation on gentle and steep slopes the numerical model developed previously for coastal structures is slightly modified and applied to predict the wave transformation in the surf and swash zones on gentle slopes as well as the wave reflection and swash oscillation on relatively steep beaches the numerical model is one dimensional in the cross shore direction and is based on the finite amplitude shallow water equations including the effect of bottom friction which are solved in the time domain for the incident wave train specified as input at the seaward boundary of the computation located outside the breakpoint the slight modification is related to the effect of the time averaged current on the seaward boundary condition and improves the agreement between the computed and measured mean water levels on gentle slopes the modified numerical model is compared with available small scale test data for monochromatic waves spilling on gentle slopes as well as for monochromatic waves plunging and surging on a relatively steep slope additional comparisons are made with small scale tests conducted using transient monochromatic and grouped waves on a 1 8 smooth slope with and without an idealized nearshore bar at the toe of the 1 8 slope as a whole the numerical model is shown to be capable of predicting both time varying and time averaged hydrodynamic quantities in the surf and swash zones on gentle as well as steep slopes

large catchment area recharges titan s ontario lacus abstract we seek to address the question of what processes are at work to fill ontario lacus while other deeper south polar basins remain empty our hydrological analysis indicates that ontario lacus has a catchment area spanning 5 5 of titan s surface and a large catchment area to lake surface area ratio this large catchment area translates into large volumes of liquid making their way to ontario lacus after rainfall the areal extent of the catchment extends to at least southern mid latitudes 40 s mass conservation calculations indicate that runoff alone might completely fill ontario lacus within less than half a titan year 1 titan year 29 5 earth years assuming no infiltration cassini visual and infrared mapping spectrometer vims observations of clouds over the southern mid and high latitudes are consistent with precipitation feeding ontario s large catchment area this far flung rain may be keeping ontario lacus filled making it a liquid hydrocarbon oasis in the relatively dry south polar region

geochemistry and water dynamics application to short time scale flood phenomena in a small mediterranean catchment we report major trace elements and sr isotope data for water samples taken regularly during a four day long september flood of a mediterranean river the vene herault s france the objective is to combine all these data into a dynamic model that describes the origin s and movements of waters and their loads this river drains the runoff from a small mainly carbonate partly karstified watershed with miocene and jurassic lithologies the watershed is also impacted by both agricultural and urban activities both the dissolved and the particulate loads were analyzed concentrations of the dissolved components show major remobilization of almost all elements during the first few hours of the flood water treatment plants and aerosol scavenging followed by a sharp concentration decrease some major species return to their previous summer values ca hco3 while others reach low background levels na k cl s04 some trace elements rb sr cs show similar behaviour but ba appears somewhat unaffected trace element concentrations and ratios define two main periods three in the suspended particulate matter ratios do not allow distinguishing between the three main sources for the dissolved load in the first period miocene jurassic water treatment plants but clearly show the jurassic karst influence later on the 87sr 86sr of the suspended particulate matter is more variable and more radiogenic than in the dissolved phase variations in concentration ratios and sr isotope composition in particulates indicate the large and variable contribution of miocene silicates with some carbonate however there is a need for another component with rb sr higher than bedrocks internal or external to the watershed possibly due to differential erosion dissolved ca and mg fluxes during the flood were calculated at 0 26 ton and 0 029 ton km2 respectively even though the carbonate nature of the watershed restricts variability in sr isotope composition in the dissolved load we distinguish several endmembers seawater marine rain miocene marls jurassic limestones water treatment plants and possibly another attributable to fertilizers combined with major and trace element variations sr isotope fluctuations indicate time varying proportions of different water endmembers at the outflow and suggest a general dynamic model based on pca principal component analysis a 3d representation allows to visualize the geochemical evolution of the vene waters in particular sr isotopes clearly indicate that the inflow of karstic waters during the flood was not continuous but occurred as a series of marked oscillations between flowing waters with chemical signature of miocene lithologies and increasing flushes of deeper waters that interacted with jurassic lithologies

shoreline retreat at titan s ontario lacus and arrakis planitia from cassini imaging science subsystem observations recent observations by cassini s imaging science subsystem reveal that part of the shoreline of titan s ontario lacus has retreated by several kilometers and may indicate that the dark area that appeared at arrakis planitia 80 s 120 w in late 2004 has subsequently faded these changes provide constraints on aspects of titan s methane cycle as well as on the properties of titan s surface materials

dam break wave front celerity this work is concerned with the role that friction and inertia effects can play on the magnitude of dam break wave front celerity classic analytical solutions are presented a large collection of experimental data is used covering a wide range of different initial conditions fixed bed or mobile bed five types of bed material dry or wet bed downstream and with or without bed step to overcome the limitations of analytical solutions a numerical model is used the model is based on the shallow water approach with contact load dominated sediment transport and it makes use of developments recently made in the study of sheet flows the analytical and numerical results are compared with experimental data it was found that the celerity is mainly dictated by the friction coefficient by the sediment inertia by the initial downstream water depth and by the initial bed step height for good data fitting the friction coefficient must be influenced by the type of bed fixed or mobile in the latter the coefficient must vary with the bed material characteristics the dissimilarities between the experimental analytical and numerical results are interpreted

finite volume model for shallow water flooding of arbitrary topography a model based on the finite volume method is developed for unsteady two dimensional shallow water flow over arbitrary topography with moving lateral boundaries caused by flooding or recession the model uses roe s approximate riemann solver to compute fluxes while the monotone upstream scheme for conservation laws and predictor corrector time stepping are used to provide a second order accurate solution that is free from spurious oscillations a robust novel procedure is presented to efficiently and accurately simulate the movement of a wet dry boundary without diffusing it in addition a new technique is introduced to prevent numerical truncation errors due to the pressure and bed slope terms from artificially accelerating quiescent water over an arbitrary bed model predictions compare favorably with analytical solutions experimental data and other numerical solutions for one and two dimensional problems

a boussinesq model for waves breaking in shallow water abstract a simple description of wave breaking in shallow water is incorporated in the boussinesq equations by using the concept of surface rollers the roller is considered as a volume of water being carried by the wave with the wave celerity the effect of the roller is included in the vertical distribution of the horizontal velocity which leads to an additional convective momentum term the breaking criterion is related to the local slope of water surface and the thickness of the roller is determined from simple geometrical considerations although the model is simple it is capable of representing a variety of processes such as the initiation and cessation of wave breaking the evolution of wave profiles before during and after wave breaking the initial conversion of potential energy into forward momentum flux and the associated horizontal shift between the break point and the point where the setup in mean water level is initiated results are presented for regular and irregular wave trains and comparison with measurements shows good agreement