thickness of sets of cross strata and planar strata as a function of formative bed wave geometry and migration and aggradation rate cross strata and planar strata formed by the migration of ripples and dunes or low relief bed waves on upper stage plane beds respectively are the most common internal structures in fluvial sands and sandstones the thickness of cross sets or planar laminae at a given location is controlled by 1 aggradation rate relative to downstream migration rate of bed waves and 2 the succession of bed waves of varying height passing the location a quantitative understanding of this relationship is now appearing based on new theory and experimental studies with ripples dunes and upper stage plane beds in many cases the effects of control 1 can be ignored in such cases only the largest bed waves in a population form cross sets or planar laminae the ratio of mean cross set thickness mean height of formative bed waves is less than 0 4 and the ratio of mean cross set thickness mean height of all bed waves is less than 0 5 a simple quantitative model a modified form of the paola borgman model is presented for predicting the height distributions of bed waves ripples dunes low relief bed waves from the thickness distributions of cross sets or planar laminae if the aggradation rate is appreciable more of the smaller bed waves in a population can form cross sets or planar laminae and the preservation ratios increase to 1 in the case of supercritical climbing ripple cross strata in this case it is necessary to determine the angle of climb and length of the bed waves in order to use the model to predict bed wave height distributions

empirical assessment of theory for bankfull characteristics of alluvial channels we compiled a data set of 541 bankfull measurements of alluvial rivers see supporting information and used bayesian linear regression to examine empirical and theoretical support for the hypothesis that alluvial channels adjust to a predictable condition of basal shear stress as a function of sediment transport mode an empirical closure based on channel slope bankfull channel depth and median grain size is proposed and results in the scaling of bankfull shields stress with the inverse square root of particle reynolds number the empirical relationship is sufficient for purposes of quantifying paleohydraulic conditions in ancient alluvial channels however it is not currently appropriate for application to alluvial channels on extraterrestrial bodies because it depends on constant valued earth based coefficients

new bedform phase diagrams and discriminant functions for formative conditions of bedforms in open channel flows understanding of the formative conditions of fluvial bedforms is significant for both river management and geological studies diagrams showing bedform stability conditions have been widely used for the analyses of sedimentary structures however the use of discriminants to determine the boundaries of different bedforms regimes has not yet been explored in this study we use discriminant functions to describe formative conditions for a range of fluvial bedforms in a 3d dimensionless parametric space we do this by means of discriminant analysis using the mahalanobis distance we analyzed 3793 available laboratory and field data and used these to produce new bedform phase diagrams these diagrams employ three dimensionless parameters representing properties of flow hydraulics and sediment particles as their axes the discriminant functions for bedform regimes proposed herein are quadratic functions of three dimensionless parameters and are expressed as curved surfaces in 3d space these empirical functions can be used to estimate paleoflow velocities from sedimentary structures as an example of the reconstruction of hydraulic conditions we calculated the paleoflow velocity of the 2011 tohoku oki tsunami backwash flow from the sedimentary structures of the tsunami deposit in so doing we successfully reconstructed reasonable values of the paleoflow velocities

eddies and the annular modes of climate variability the dominant modes of month to month varia tion in the troposphere are realistically simulated in a gen eral circulation model whose lower boundary is prescribed with realistic topography and seasonally varying climato logical sea surface temperatures in both hemispheres these internal modes describe a nearly zonally symmetric north south shifting of the zonal jets as anomalous westerlies vac illate between high 50 60 a nd low 30 40 latitudes the eddy structures evolve with the jets and the corre sponding eddy momentum forcings support the shifts in jet position stationary synoptic wave variations mainly ac count for the total eddy forcings in the northern south ern hemisphere pronounced eddy variations occur over the north atlantic sector

models of the distribution and abundance of hydrogen at the lunar south pole 1 permanently shadowed locations at the lunar poles are potential sites for significant concentrations of cold trapped volatiles including water ice hydrogen enhancements are seen at the poles but the physical form abundance and distribution of this hydrogen remains controversial using a pixon based image reconstruction algorithm to effectively improve spatial resolution we derive maps of the lunar south polar water equivalent hydrogen concentration that are fully consistent with the orbital neutron measurements with abundances greater than 0 5 wt in some permanently shadowed locations this is much greater than the highest solar wind hydrogen abundance in returned lunar samples and may indicate ice between regolith grains if the hydrogen distribution is inhomogeneous within a permanently shadowed crater then even higher abundances are implied in shackleton crater for example the derived count rates are consistent with 10 of the crater floor area having 20 wt water equivalent hydrogen and the remainder at 0 25 wt

frozen dynamics of migrating bedforms here we show how a continuum granular flow model can replicate realistic self organizing subaqueous bedforms and we explore how a record of this dynamic topography is transferred into the substrate where it can be fossilized modeled bedform behavior is quantitatively compared to laboratory and field data sediment scouring and deposition by migrating bedforms produce sets of partially preserved bedforms recording nonlinear behavior at the sediment fluid interface model results show the importance of spatial and temporal variations in bedform size and migration rate to the generation of sets addition of net bed aggradation to modeled bedforms allows us to explore the preservation of topography under a wide range of depositional conditions we present new relationships among aggradation rate bedform migration rate and set thickness variability of set thickness is shown to be a product of the competition between bed aggradation and bedform migration rates these results show how using the entire distribution of set thickness for ancient strata can refine estimates of the formative paleoenvironmental conditions

valley formation and methane precipitation rates on titan branching valley networks near the landing site of the huygens probe on titan imply that fluid has eroded the surface the fluid was most likely methane which forms several percent of titan s atmosphere and can exist as a liquid at the surface the morphology of the valley networks and the nature of titan s surface environment are inconsistent with a primary valley formation process involving thermal chemical or seepage erosion the valleys were more likely eroded mechanically by surface runoff associated with methane precipitation if mechanical erosion did occur the flows must first have been able to mobilize any sediment accumulated in the valleys we develop a model that links precipitation open channel flow and sediment transport to calculate the minimum precipitation rate required to mobilize sediment and initiate erosion using data from two monitored watersheds in the alps we show that the model is able to predict precipitation rates in small drainage basins on earth the calculated precipitation rate is most sensitive to the sediment grain size for a grain diameter of 1 10 cm a range that brackets the median size observed at the huygens landing site the minimum precipitation rate required to mobilize sediment in the nearby branching networks is 0 5 15 mm hr 1 we show that this range is reasonable given the abundance of methane in titan s atmosphere these minimum precipitation rates can be compared with observations of tropospheric cloud activity and estimates of long term methane precipitation rates to further test the hypothesis that runoff eroded the valleys

stability of polar frosts in spherical bowl shaped craters on the moon mercury and mars following svitek martian water frost control of global distribution by small scale processes ph d thesis california institute of technology 1992 analytic solutions are presented for the effective albedo the effective emissivity and the radiative equilibrium temperature in the shadowed portions of a spherical bowl shaped crater the model assumes that the surface is a lambert scatterer with visual albedo and infrared emissivity each independent of wavelength across their respective spectral ranges absorption emission and multiple scattering from the walls of the crater are treated rigorously to all orders for airless bodies whose surfaces are in radiative equilibrium all shadowed portions of any individual crater have the same temperature whose value depends on four quantities the insolation product of the solar constant and the sine of the solar elevation angle the depth diameter ratio of the crater the visual albedo and the infrared emissivity as long as the crater is deep enough to have shadows the lowest temperatures are for the shallowest crater those with the smallest depth diameter ratio the model is applied first to the moon and mercury using a depth diameter ratio of 0 2 which is typical of the lunar highlands according to pike geophys res lett 1 291 294 1974 in impact and explosion cratering roddy et al eds pp 489 509 pergamon new york 1977 for mercury and the moon temperatures in shadows in polar craters are below 102 k so the sublimation rate of water ice calculated according to the model of watson et al j geophys res 66 3033 3015 1961 is less than 1 cm per byr the latitudinal extent of the cold zone on the moon is greater than that on mercury although temperatures at the poles of the two planets are similar the other application is to polar frosts on mars illuminated water frosts in radiative equilibrium grow rougher because the average temperature of a depression is greater than that of flat ground subliming co 2 frosts which are always at the same temperature grow rougher at low solar elevation angles because the heat flux absorbed by a depression is greater than that for a flat surface at high insolation rates high sun near perihelion the average heat flux to a depression is less than for a flat surface the latter evaporates faster which makes the average surface smoother and leads to a high average albedo this behavior helps explain the fact that the south co 2 cap which receives its greatest insolation near perihelion has a higher effective albedo and therefore can survive the summer whereas the north co 2 cap has a lower effective albedo and disappears each year around summer solstice

the clementine mission to the moon scientific overview in the course of 71 days in lunar orbit from 19 february to 3 may 1994 the clementine spacecraft acquired just under two million digital images of the moon at visible and infrared wavelengths these data are enabling the global mapping of the rock types of the lunar crust and the first detailed investigation of the geology of the lunar polar regions and the lunar far side in addition laser ranging measurements provided the first view of the global topographic figure of the moon the topography of many ancient impact basins has been measured and a global map of the thickness of the lunar crust has been derived from the topography and gravity

the southern oscillation index wave climate and beach rotation short embayed beaches bounded by headlands are a common feature along the southern and central coastline of new south wales australia many of these embayed beaches have experienced severe erosion at their southern end over the last decade previous studies have suggested that this erosion may be the result of an oscillatory medium term phenomenon known as beach rotation the present study was undertaken with the objectives of 1 establishing definitive links between the southern oscillation index soi wave climate and beach rotation and 2 determining the physical processes governing beach rotation data from two similar new south wales beaches were analysed using time series analysis techniques and image processing techniques using argus video images in this study the results indicate that the northern end of this type of beach accretes during el nino phases while the southern end erodes resulting in a net clockwise rotation of the beach the opposite occurs during la nina phases resulting in a net anti clockwise rotation of the beach the beach response at the northern and southern ends lags soi trend shifts by 3 and 17 months respectively waves are predominantly incident from the southeast during both el nino and la nina phases offshore wave height is positively correlated with the soi while offshore wave direction is negatively correlated with the soi on average the number of storms per year doubles from el nino to la nina based on these links between beach width fluctuations soi and incident wave conditions a conceptual model of beach rotation is presented the model describes the combinations of cross shore and longshore sediment transport and hydrodynamic processes that are expected to result in the observed clockwise and anti clockwise beach rotation during el nino and la nina phases respectively

spatial distribution of lunar polar hydrogen deposits after kaguya selene 1 although controversial in its physical form there is mounting evidence of hydrogen enhancements at the lunar poles the permanently shadowed locales are potential sites for significant concentrations of cold trapped volatiles including water ice we derive maps of the lunar hydrogen distribution near the poles by applying a pixon image reconstruction algorithm to the lunar prospector epithermal neutron data coupled with a new map of cold trap locations derived from the kaguya selene altimetry measurements the results presented in this article require the hydrogen to be concentrated into cold traps

integration of lunar polar remote sensing data sets evidence for ice at the lunar south pole in order to investigate the feasibility of ice deposits at the lunar south pole we have integrated all relevant lunar polar data sets these include illumination data arecibo ground based monostatic radar data newly processed clementine bistatic radar data and lunar prospector neutron spectrometer measurements the possibility that the lunar poles harbor ice deposits has important implications not only as a natural resource for future human lunar activity but also as a record of inner solar system volatiles e g comets and asteroids over the past billion years or more we find that the epithermal neutron flux anomalies measured by lunar prospector are coincident with permanently shadowed regions at the lunar south pole particularly those associated with shackleton crater furthermore these areas also correlate with the 0 circular polarization ratio cpr enhancements revealed by new processing of clementine bistatic radar echoes which in turn are colocated with areas of anomalous high cpr observed by arecibo observatory on the lower sun shadowed wall of shackleton crater estimates of the extent of high cpr from arecibo observatory and clementine bistatic radar data independently suggest that 10 km2 of ice may be present on the inner earth facing wall of shackleton crater none of the experiments that obtained the data presented here were ideally suited for definitively identifying ice in lunar polar regions by assessing the relative merits of all available data we find that it is plausible that ice does occur in cold traps at the lunar south pole and that future missions with instruments specifically designed to investigate these anomalies are worthy

lunar polar topography derived from clementine stereoimages clementine stereoimagery has been used to produce digital elevation models of the moon at a scale of 1 km pixel these models cover regions poleward of 60 in both hemispheres and reveal topography beyond that covered by the clementine laser altimeter or earth based radar by combining these polar terrain models with the current clementine laser altimeter data we have produced a global topographic map of the lunar surface several topographic features in the new polar topographic data set are described including three previously unrecognized pre nectarian impact basins several known basins have also been mapped including the southern extent of the south pole aitken basin and other previously suspected basins have been verified

comparison of methods to estimate sediment flux in ancient sediment routing systems abstract the need to predict accurately the volume timing and location of sediments that are transported from an erosional source region into a basin depocentre sink is important for many aspects of pure and applied sedimentological research in this study the results of three widely used methods to estimate sediment flux in ancient sediment routing systems are compared using rich input datasets from two systems eocene south pyrenean foreland basin spain and late pleistocene to holocene gulf of corinth rift basin greece for which mapped dated sediment volumes provide an independent reference value of sediment accumulation rates the three methods are 1 the empirical bqart model which uses values of drainage basin area relief temperature lithology and water discharge 2 empirical scaling relationships between characteristic geomorphological parameters of sediment routing system segments and 3 the fulcrum model which uses the palaeohydrological parameters of trunk river channels to estimate downsystem sediment discharge the bqart model and empirical geomorphological scaling relationships were originally developed using modern sediment routing systems and have subsequently been applied to ancient systems in contrast the fulcrum model uses hydrological scaling relationships from modern systems but was developed principally for application in ancient systems our comparative analysis quantifies the sensitivity of the three methods to their input parameters and identifies the data required to make plausible estimates of sediment flux for ancient sediment routing systems all three methods can generate estimates of sediment flux that are comparable with each other and are accurate to at least one order of magnitude relative to independent reference values the bqart model uses palaeoclimatic and palaeocatchment input data which are accurate for sub modern systems but may be highly uncertain in deep time systems corresponding estimates of sediment flux are most sensitive to the accuracy with which the palaeocatchment area is constrained and to palaeoclimatic parameters that reflect temperature and precipitation the fulcrum model uses palaeohydrological input data its sediment flux estimates are sensitive to palaeochannel dimensions and in particular the duration of bankfull discharge which is invariably difficult to constrain accurately in deep time sediment routing systems this uncertainty can give rise to large potential ranges of sediment flux estimates geomorphological scaling relationships offer comparable order of magnitude accuracy for both sub modern and deep time sediment routing systems in which geomorphological segments can be identified but when used on relatively small sediment routing systems the ranges of sediment volumes deposited can vary greatly limiting the utility of the technique we suggest that methods to estimate sediment flux should be chosen for a particular sediment routing system based on the types and uncertainty of available data where input parameter values are highly uncertain such as in deep time systems monte carlo simulation is an effective tool to calculate probability distributions of estimated sediment flux

mapping and characterization of non polar permanent shadows on the lunar surface abstract we present the first globally complete inventory of permanent shadows on the lunar surface that are detectable with the current global instrument datasets including discovery of regions with persistent shadows over geologic time periods as close to the equator as 58 of latitude these results were obtained through application of a ray tracing technique to the latest global topographic datasets from the lunar reconnaissance orbiter our analysis reveals that 13 361 km2 of surface in the northern hemisphere and 17 698 km2 in the southern hemisphere are permanently shadowed we present maps showing the locations of all the permanent shadows detectable using these datasets then turn our focus toward the permanent shadows farthest from the poles each permanent shadow on the equator side of 65 of latitude is shown in detail surface brightness temperature data derived from the diviner mid infrared radiometer on board the lunar reconnaissance orbiter have been analyzed for four of these locations and found to have mid day temperatures 75 120 k less than nearby comparison locations that experience direct daytime illumination in some cases the permanently shadowed locations have nighttime temperatures 10 25 k lower than surroundings the temperature results support our finding that these non polar craters are permanently shadowed the surface brightness temperature results also raise interesting questions about their ability to cold trap volatiles discovery of these non polar permanently shadowed regions increases possible locations of water resources and high priority exploration targets on the moon

evidence for water ice near the lunar poles improved versions of lunar prospector thermal and epithermal neutron data were studied to help discriminate between potential delivery and retention mechanisms for hydrogen on the moon improved spatial resolution at both poles shows that the largest concentrations of hydrogen overlay regions in permanent shade in the north these regions consist of a heavily cratered terrain containing many small less than 10 km diameter isolated craters these border circular areas of hydrogen abundance h that is only modestly enhanced above the average equatorial value but that falls within large flat bottomed and sunlit polar craters near the south pole h is enhanced within several 30 km scale craters that are in permanent shade but is only modestly enhanced within their sunlit neighbors we show that delivery by the solar wind cannot account for these observations because the diffusivity of hydrogen at the temperatures within both sunlit and permanently shaded craters near both poles is sufficiently low that a solar wind origin cannot explain their differences we conclude that a significant portion of the enhanced hydrogen near both poles is most likely in the form of water molecules

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

the clementine bistatic radar experiment during the clementine 1 mission a bistatic radar experiment measured the magnitude and polarization of the radar echo versus bistatic angle beta for selected lunar areas observations of the lunar south pole yield a same sense polarization enhancement around beta 0 analysis shows that the observed enhancement is localized to the permanently shadowed regions of the lunar south pole radar observations of periodically solar illuminated lunar surfaces including the north pole yielded no such enhancement a probable explanation for these differences is the presence of low loss volume scatterers such as water ice in the permanently shadowed region at the south pole

reconstructing random topography from preserved stratification one of the fundamental problems of interpreting the sedimentary record is reconstructing the original heights of palaeotopographical features such as bedforms or river channels this requires an understanding of the relationship between topography and set thickness but at present an exact theory exists only for periodic topography of uniform height the applicability of this simple theory is severely limited by the random variability characteristic of many sedimentary systems in this paper we develop an exact theory for the probability density function pdf of sets generated from topography of random height we focus on the limiting case of zero net deposition in order to provide a lower bound for the set thickness and derive an analytical set thickness pdf that is determined by one parameter of the pdf for topographical height this parameter measures the breadth of the tail of the topographical pdf the mean set thickness is 0 8225 for bedforms and 1 645 for river channels if the topographical height is gamma distributed the preservation ratio defined as mean thickness of preserved sets mean topographical height is 0 8225 r2 for bedforms and 1 645 r2 for river channels where r is the coefficient of variation standard deviation mean of the generating topography in a comparison with data from laboratory current ripples our analytical predictions compare well with observations of both mean set thickness and thickness distribution the preservation ratio for the ripples is about 0 5 whilst measured dune heights give a preservation ratio of about 0 12 depth data from two modern braided streams yield preservation ratios ranging from 0 4 to 0 75 as more data on the distributions of topographical height in modern environments become available calculations such as these should help provide reliable error bounds for quantitative topographical reconstruction

palaeozoic landscapes shaped by plant evolution fluvial landscapes diversified markedly over the 250 million years between the cambrian and pennsylvanian periods the diversification occurred in tandem with the evolution of vascular plants and expanding vegetation cover in the absence of widespread vegetation landscapes during the cambrian and ordovican periods were dominated by rivers with wide sand beds and aeolian tracts during the late silurian and devonian periods the appearance of vascular plants with root systems was associated with the development of channelled sand bed rivers meandering rivers and muddy floodplains the widespread expansion of trees by the early pennsylvanian marks the appearance of narrow fixed channels some representing anabranching systems and braided rivers with vegetated islands we conclude that the development of roots stabilized the banks of rivers and streams the subsequent appearance of woody debris led to log jams that promoted the rapid formation of new river channels our contention is supported by studies of modern fluvial systems and laboratory experiments in turn fluvial styles influenced plant evolution as new ecological settings developed along the fluvial systems we suggest that terrestrial plant and landscape evolution allowed colonization by an increasingly diverse array of organisms

seasonal variability of the global spectral wind wave climate our understanding of the seasonal variability in the global wind wave field is revisited here using a novel analysis that resolves the directional wave spectra empirical orthogonal function analysis was applied to modeled wave spectral data from a wavewatch iii hindcast across a sparse global grid to identify the main patterns of the climatological wave spectral variability at each grid point prior methods have focused on the variability of two modes of the wave field locally generated sea and the primary swell component our results also consider additional wave modes at each location enabling us to track the passage of the less dominant swell modes consistent with existing climatological knowledge the main modes of wave spectral variability at high latitudes are related to eastward propagating waves that disperse equatorward as swell following great circle paths however despite being the less energetic mode the northern hemisphere generated swell is found to propagate into the southern hemisphere further than the more energetic southern hemisphere swell which propagates northward in the equatorial zone a complex multimodal wave climate is found with the spectra variability modulated by remotely generated swell and higher frequency waves associated with the prevailing winds the evolution of these patterns throughout the year is clearly depicted overall our approach captures a more complete picture of the seasonal variability of the global wave field by accounting for all the wave modes observed in the spectra at each location together with their temporal variability

evolution of fixed channel alluvial plains in response to carboniferous vegetation the establishment of terrestrial plants during the palaeozoic era was one of the most significant changes to the earth system during the phanerozoic eon the continuing evolution and expansion of land plants irrevocably altered the alluvial landscape the broad unconfined and unconsolidated blankets of coarse sediment found at the start of the cambrian period were replaced by a diverse array of braided and meandering channel styles and stable floodplains by the end of the devonian period here we show that the first appearance of a sedimentary facies suite attributed to low energy organic rich river systems with multiple channels and stable alluvial islands known as anabranching or anastomosing rivers occurred during the carboniferous period our field studies and literature review demonstrate that the appearance of these rivers coincides with the continuing evolution of tree like plants we suggest that increased floodplain stability and new triggers for channel avulsion were provided by the increase in complexity and diversity of root assemblages density of floodplain forests and production of woody debris associated with expansion of arborescence we conclude that the expansion of tree habitats led to the crossing of a threshold in vegetative control of floodplain and river morphology during the carboniferous

subaqueous gravel dunes abstract gravel dunes are rarely reported owing to comparative rarity of occurrence and generic confusion with antidunes and classes of gravel bars a compilation of data from the literature for sediments with a median size greater than 2 mm shows that dunes have been developed in the laboratory in median grain sizes up to 28 6 mm for field conditions there are data for grain sizes up to 60 mm equilibrium and non equilibrium gravel dunes range in length from less than 0 6 m to greater than 100 m heights range from less than 0 1 m to 16 m height and length data for the steepest three dimensional 3 d gravel dunes are consistent with the h l function reported by ashley 1990 for equilibrium dunes developed in sand for a broad range of dune length 3 d gravel dunes are steeper than two dimensional 2 d dunes but for l 100 m and h 8 m there are too few data to draw any conclusion ashley s h l function does not apply to a broad range of 2 d gravel dunes a separate well defined function is proposed to describe the h l relationship for 2 d gravel dunes of maximum steepness there are few data on the hydrodynamic development of gravel dunes as a guide gravel dunes develop for a range of froude numbers up to 0 75 given that the nondimensional mean bed shear stress exceeds circa 0 1 dunes reach their maximum height at 0 25 and have reduced in height when 0 3 froude numbers of 0 84 and above lead to crestal flattening dune diminution and eventual replacement by antidunes or upper stage plane beds however owing to lag effects transitional bedforms have been recorded for froude numbers near the critical value of 1 the development of gravel dune steepness from lower stage plane bed through to upper stage plane bed is well described in only one case by dinehart 1992a fredsoe s 1975 function for equilibrium dune steepness applies reasonably well to dinehart s steepest dunes allen s 1984 bedform existence field based on and a characteristic grain size of the bed sediment has been extended from 5 mm to include bedstocks as coarse as 33 mm

migration calculations for water in the exosphere of the moon dusk dawn asymmetry heterogeneous trapping and d h fractionation water ice is trapped in permanently shadowed craters near the lunar poles where it is thought to have arrived from an exogenic or endogenic source via ballistic hops we use a model of the migration of water molecules in the lunar exosphere to investigate three problems 1 a strong continuous source would lead to an enhanced concentration of h2o at the morning terminator but not at the evening terminator hence spectral features observed at both terminators do not suggest that there is diurnal migration of volatiles 2 cold trapping after a comet impact leads to an unequal partitioning between the two hemispheres depending on the latitude of the impact but to nearly equal partitioning with respect to longitude 3 the d h fractionation as the water molecules migrate toward the poles is small hence the isotopic composition of ice deposits in the cold traps can be related to that of the source

a multimodal wave spectrum based approach for statistical downscaling of local wave climate abstractcharacterization of wave climate by bulk wave parameters is insufficient for many coastal studies including those focused on assessing coastal hazards and long term wave climate influences on coastal evolution this issue is particularly relevant for studies using statistical downscaling of atmospheric fields to local wave conditions which are often multimodal in large ocean basins e g pacific ocean swell may be generated in vastly different wave generation regions yielding complex wave spectra that are inadequately represented by a single set of bulk wave parameters furthermore the relationship between atmospheric systems and local wave conditions is complicated by variations in arrival time of wave groups from different parts of the basin here this study addresses these two challenges by improving upon the spatiotemporal definition of the atmospheric predictor used in the statistical downscaling of local wave climate the improved methodology separates the local wave spectrum into w

the south pole region of the moon as seen by clementine the clementine mission has provided the first comprehensive set of high resolution images of the south pole region of the moon within 5 of latitude of the pole an area of an estimated 30 000 square kilometers remained in shadow during a full lunar rotation and is a promising target for future exploration for ice deposits the schrodinger basin 320 kilometers in diameter centered at 75 s is one of the two youngest least modified great multiring impact basins on the moon a large maar type volcano localized along a graben within the schrodinger basin probably erupted between 1 and 2 billion years ago

a tenfold slowdown in river meander migration driven by plant life meandering rivers are diagnostic landforms of hydrologically active planets and their migration regulates the continental component of biogeochemical cycles that stabilize climate and allow for life on earth the rise of river meanders on earth has been linked to riverbank stabilization driven by the palaeozoic evolution of plant life about 440 million years ago here we provide a fundamental test for this hypothesis using a global analysis of active meander migrations that includes previously ignored unvegetated rivers from the arid interiors of modern continents when normalized by channel size unvegetated meanders universally migrate an order of magnitude faster than vegetated ones while providing irrefutable evidence that vegetation is not required for meander formation we demonstrate how profoundly vegetation transformed the pace of change for earth s landscapes and we at last offer a mechanistic explanation for the radically distinct stratigraphic records of barren and vegetated rivers we posit that the migration slowdown driven by the rise of land plants dramatically impacted biogeochemical fluxes and rendered earth s landscapes even more hospitable to life therefore the tenfold faster migration of unvegetated rivers may be key to deciphering the environments of barren worlds such as early earth and mars river meanders migrate much faster in barren than in vegetated landscapes according to global analyses of active meander migration of both unvegetated and vegetated rivers the difference in migration rates suggests that the rise of land plants had a significant influence on landscapes

alluvial facies evolution during the palaeozoic greening of the continents case studies conceptual models and modern analogues the palaeozoic greening of the continents the appearance and expansion of embryophytes land plants in terrestrial environments was arguably the most fundamental phanerozoic change to the earth system thirteen case studies of cambrian to devonian fluvial deposits from north america and europe are documented here to illustrate the evolution of fluvial style during this period during the cambro ordovician prior to the advent of terrestrial vegetation fluvial systems laid down relatively coarse sands with little mud resulting in self formed channels and an architecture dominated by broad sheets of trough cross beds sheet braided style similar deposits formed across a wide range of latitudes and passed basinward into sandy coastal deposits from the mid ordovician onwards an increase in floodplain mudstone corresponds broadly with the appearance of embryophytes which would have progressively enhanced upland weathering mud production and floodplain storage of fines during the late silurian small heterolithic channel bodies with lateral accretion sets provide the first evidence of meandering channels and floodplain mudstones contain more varied palaeosols especially calcretes which appear abundantly for the first time by the early devonian channel deposits comprise sandstone lenses channelled braided style probably due to the increased bank strength and cohesion and reduced potential for sediment sorting imparted by sand mud mixtures muddy coastal deposits are prominent by the upper devonian fluvial deposits commonly contain fossil trees and large mainstem meandering channels with lateral accretion sets indicating that rooted vegetation stabilized channels the advent of stable floodplains with levees crevasse splays and organic litter would have encouraged the diversification of terrestrial invertebrates which left alluvial ichnological signatures from the late silurian onwards

permanent shadow in simple craters near the lunar poles 1 an analysis of simple craters in the lunar polar regions has produced new values for the minimum amount of permanent shadow in these areas 7500 km2 and 6500 km2 for the north and south pole respectively these values were obtained by conducting illumination simulations of realistically shaped simple craters 20 km in diameter to investigate the size and latitudinal extent of permanently shadowed regions near the lunar poles craters as far as 20 from the pole still contain significant amounts of permanent shadow larger simple craters have slightly more relative permanent shadow than smaller craters seasonal effects are independent of crater size and latitude with a crater having 15 more of its interior shadowed during a lunar day in winter than in summer

life on land in the proterozoic evidence from the torridonian rocks of northwest scotland the stoer group and diabaig formation of the torridonian succession in northwest scotland are late mesoproterozoic to early neoproterozoic ca 1200 1000 ma features preserved on the top surfaces of fine to medium grained sandstone beds in a number of stratigraphically and geographically separated localities are attributable to microbially induced sedimentary structures these include wrinkle structures remnants of apparent microbial crusts and indications of original cohesiveness and pliancy in sand sized sediment the surfaces on which the microbial structures formed were exposed subaerially abundant deep desiccation cracks and locally pedogenic structures in alluvial interfluve and lacustrine margin settings and many of the structures developed in areas well away from the perennially wetted regions adjacent to shorelines and fluvial channels thus these features indicate that earth9s biosphere had adapted to and colonized land surfaces many hundreds of millions of years before the dawn of the phanerozoic

influence of the pacific south american modes on the global spectral wind wave climate in this study we analyse the influence of the pacific south american modes psa 1 and psa 2 on the global wind wave climate using wave data derived from a wavewatch iii global wave hindcast we apply an empirical orthogonal function analysis to daily averaged directional wave spectra to extract the two main patterns of interannual wave spectral variability these are related to changes in the wave spectral density levels variability in the wave heights and to rotations of the wave signal variability in wave direction the psa 1 mode is positively correlated with the wave height variability in the southeast pacific and negatively correlated in the indian ocean sector of the southern ocean the psa 2 mode presents a strong negative correlation with wave heights in the central south pacific moreover the psa modes are significantly correlated with changes in modelled wave direction in the south pacific region composite maps of wind anomalies during positive stages of psa 1 and psa 2 provide a compelling explanation for the observed correlation patterns the methodology applied in this study is also used to assess the influence of other climate modes on the global wind wave climate namely the southern annular mode arctic oscillation north atlantic oscillation el nino southern oscillation and the pacific north american mode while our results are consistent with previous studies we provide more clarity as to how different atmospheric modes influence the variability of specific components of the wave spectrum importantly we assess the how these climate modes would modulate the interannual variability of wave direction

variability of the winter wind waves and swell in the north atlantic and north pacific as revealed by the voluntary observing ship data this paper analyses secular changes and interannual variability in the wind wave swell and significant wave height swh characteristics over the north atlantic and north pacific on the basis of wind wave climatology derived from the visual wave observations of voluntary observing ship vos officers these data are available from the international comprehensive ocean atmosphere data set icoads collection of surface meteorological observations for 1958 2002 but require much more complicated preprocessing than standard meteorological variables such as sea level pressure temperature and wind visual vos data allow for separate analysis of changes in wind sea and swell as well as in significant wave height which has been derived from wind sea and swell estimates in both north atlantic and north pacific midlatitudes winter significant wave height shows a secular increase from 10 to 40 cm decade 1 during the last 45 yr however in the north atlantic the patterns of trend changes for wind sea and swell are quite different from each other showing opposite signs of changes in the northeast atlantic trend patterns of wind sea swell and swh in the north pacific are more consistent with each other qualitatively the same conclusions hold for the analysis of interannual variability whose leading modes demonstrate noticeable differences for wind sea and swell statistical analysis shows that variability in wind sea is closely associated with the local wind speed while swell changes can be driven by the variations in the cyclone counts implying the importance of forcing frequency for the resulting changes in significant wave height this mechanism of differences in variability patterns of wind sea and swell is likely more realistic than the northeastward propagation of swells from the regions from which the wind sea signal originates

low gradient single threaded rivers prior to greening of the continents the silurian age rise of land plants is hypothesized to have caused a global revolution in the mechanics of rivers in the absence of vegetation controlled bank stabilization effects pre silurian rivers are thought to be characterized by shallow multithreaded flows and steep river gradients this hypothesis however is at odds with the pancontinental scale of early neoproterozoic river systems that would have necessitated extraordinarily high mountains if such river gradients were commonplace at continental scale which is inconsistent with constraints on lithospheric thickness to reconcile these observations we generated estimates of paleogradients and morphologies of pre silurian rivers using a well developed quantitative framework based on the formation of river bars and dunes we combined data from previous work with original field measurements of the scale texture and structure of fluvial deposits in proterozoic age torridonian group scotland a type example of pancontinental prevegetation fluvial systems results showed that these rivers were low sloping gradients 10 5 to 10 4 relatively deep 4 to 15 m and had morphology similar to modern lowland rivers our results provide mechanistic evidence for the abundance of low gradient single threaded rivers in the proterozoic eon at a time well before the evolution and radiation of land plants despite the absence of muddy and vegetated floodplains single threaded rivers with stable floodplains appear to have been a persistent feature of our planet despite singular changes in its terrestrial biota

ocean waves and teleconnection patterns in the northern hemisphere abstractunderstanding long term ocean wave climate variability is important to assess climate change impacts on coastal and ocean physics and engineering teleconnection patterns can represent wave climate variability in the context of climate change the objective of this study is to identify how large scale spatial distributions of wave heights vary on a monthly basis and how they are influenced by various teleconnection patterns using reanalysis datasets the wave height climate responses to teleconnection patterns in the eastern part of the north pacific and north atlantic are more sensible than in the corresponding western parts the dominant spatial patterns of monthly averaged wave height variability in winter were obtained by empirical orthogonal function analysis the three dominant patterns in the north pacific and north atlantic are similar it is remarkable that one of the three dominant patterns a band shaped pattern exhibits a strong relation to the teleconnection pattern in each ocean t

topography of the lunar poles from radar interferometry a survey of cold trap locations detailed topographic maps of the lunar poles have been obtained by earth based radar interferometry with the 3 5 centimeter wavelength goldstone solar system radar the interferometer provided maps 300 kilometers by 1000 kilometers of both polar regions at 150 meter spatial resolution and 50 meter height resolution using ray tracing these digital elevation models were used to locate regions that are in permanent shadow from solar illumination and may harbor ice deposits estimates of the total extent of shadowed areas poleward of 87 5 degrees latitude are 1030 and 2550 square kilometers for the north and south poles respectively

thermal stability of ice on ceres with rough topography the dwarf planet ceres may have an ice rich crust and subsurface ice exposed by impacts or endogenic activity would be subject to sublimation we model surface and subsurface temperatures on ceres to assess lifetimes of water ice and other volatiles topographic shadowing allows a small but non negligible fraction 0 4 of ceres surface to be perennially below the 110 k criterion for 1 gyr of stability these areas are found above 60 latitude other molecules ch3oh nh3 so2 co2 may be cold trapped in smaller abundances a model for the transport gravitational escape and photoionization of h2o molecules suggests net accumulation in the cold traps buried ice is stable within a meter for 1 gyr at latitudes higher than 50 an illuminated polar cap of water ice would be stable within a few degrees of the poles only if it maintained a high albedo 0 5 at present obliquity if the obliquity exceeded 5 in the geologically recent past then a putative polar cap would have been erased at latitudes 0 30 ice is stable under solar illumination only briefly 10 100 yr unless it has high albedo and thermal inertia in which case lifetimes of 104 yr are possible finally a small hemispheric asymmetry exists due to the timing of ceres perihelion passage which would lead to a detectable enhancement of ice in the northern hemisphere if the orbital elements vary slowly relative to the ice accumulation rate our model results are potentially testable during the dawn science mission

near surface temperatures on mercury and the moon and the stability of polar ice deposits abstract in order to assess the thermal stability of polar ice deposits we present model calculated temperatures of flat surfaces and surfaces within bowl shaped and flat floored polar impact craters on mercury and the moon our model includes appropriate insolation cycles realistic crater shapes multiple scattering of sunlight and infrared radiation and depth and temperature dependent regolith thermophysical properties unshaded water ice deposits on the surface of either body are rapidly lost to thermal sublimation a subsurface water ice deposit is stable within 2 latitude of the moon s poles meter thick water ice deposits require billions of years to sublime if located in the permanently shaded portions of flat floored craters within 10 latitude of the poles of mercury and 13 latitude of the poles of the moon results for craters associated with radar features on mercury are consistent with the presence of stable water ice deposits if a thin regolith layer thermally insulates deposits at lower latitudes and within smaller craters a regolith cover would also reduce losses from diffusion ion sputtering impact vaporization and h ly and is implied independently by the radar observations permanently shaded areas near the moon s poles are generally colder than those near mercury s poles but the moon s obliquity history its orbit through earth s magnetospheric tail and its radar opaque regolith may limit the volume and radar detectability of ice deposits there

illumination conditions of the lunar polar regions using lola topography abstract we use high resolution altimetry data obtained by the lunar orbiter laser altimeter instrument onboard the lunar reconnaissance orbiter to characterize present illumination conditions in the polar regions of the moon compared to previous studies both the spatial and temporal extent of the simulations are increased significantly as well as the coverage fill ratio of the topographic maps used thanks to the 28 hz firing rate of the five beam instrument we determine the horizon elevation in a number of directions based on 240 m resolution polar digital elevation models reaching down to 75 latitude the illumination of both polar regions extending to 80 can be calculated for any geometry from those horizon longitudinal profiles we validated our modeling with recent lunar reconnaissance orbiter wide angle camera images we assessed the extent of permanently shadowed regions psrs defined as areas that never receive direct solar illumination and obtained total areas generally larger than previous studies 12 866 and 16 055 km2 in the north and south respectively we extended our direct illumination model to account for singly scattered light and found that every psr does receive some amount of scattered light during the year we conducted simulations over long periods several 18 6 years lunar precession cycles with a high temporal resolution 6 h and identified the most illuminated locations in the vicinity of both poles because of the importance of those sites for exploration and engineering considerations we characterized their illumination more precisely over the near future every year a location near the shackleton crater rim in the south polar region is sunlit continuously for 240 days and its longest continuous period in total darkness is about 1 5 days for some locations small height gains 10 m can dramatically improve their average illumination and reduce the night duration rendering some of those particularly attractive energy wise as possible sites for near continuous sources of solar power

galileo stereo topography of the lunar north polar region 1 estimates of the elevation of the lunar polar regions are uncertain to a few km galileo stereo images of the north polar region were used to derive a new topographic map partially filling the gap in clementine lidar topography northward of 80 and providing an independent constraint on lunar polar topography and solar illumination our galileo elevation model has an estimated vertical precision of 200 m and a measurement footprint of 9 km these new data show that the north polar region frontside is to within the margin of error consistent with radar derived estimates

illumination conditions at the lunar south pole recent remote sensing data strongly suggest that deposits of ice occur in permanently shadowed regions at the lunar poles clementine by providing the first contiguous coverage of the moon has enabled the production of an illumination map of the south pole this map shows the extent of the areas of permanent darkness during winter in this region as well as identifying places on the lunar surface that receive illumination for more than 50 of the lunar day the permanently dark areas are prime candidates for locations of ice deposits while regions that are illuminated for anomalous periods are possible sites for lunar bases in this paper we study in detail the illumination history during a lunar day of some of these sites while we find no area that receives permanent illumination we do find two areas only 10 km apart which collectively receive sunlight for over 98 of the time

statistics and dynamics of persistent anomalies abstract persistent anomalies with recurrent spatial patterns play an important role in the atmosphere s low frequency variability we establish a connection between statistical and dynamical methods of description and prediction of persistent anomalies this is done by computing and analyzing the empirical orthogonal functions eofs in a simple deterministic model on the one hand and in southern hemisphere geopotential heights on the other the dynamical model is governed by the fully nonlinear equivalent barotropic vorticity equation on the sphere with simplified forcing dissipation and topography model solutions exhibit persistent anomalies identifiable with blocked zonal and wave train anomalies in northern hemisphere atmospheric data flow structures similar to the patterns above occur as high variance eofs of this nonlinear model the southern hemisphere data we analyze consist in gridded daily maps of 500 mb heights from june 1972 to july 1983 two types of persistent anomalies appear in t

illumination conditions of the south pole of the moon derived using kaguya topography abstract we have used the kaguya laser altimeter derived topography to conduct a comprehensive study of the illumination conditions at the moon s south pole we have determined by comparing simulated and actual clementine images that the kaguya topography can be used to generate realistic illumination conditions we generated an average illumination map for the year 2020 for the lunar south pole region from this we identified the areas that receive the most illumination the place receiving the most illumination 86 of the year is located close to the rim of shackleton crater at 88 74 s 124 5 e however two other areas less than 10 km apart from each other are collectively lit for 94 of the year we found that sites exist near the south pole that are continuously lit for several months during summer we were also able to map the locations and durations of eclipse periods for these areas finally we analyzed the seasonal variations in lighting conditions from summer to winter for key areas near the south pole we conclude that areas exist near the south pole that have illumination conditions that make them ideal candidates as future outpost sites

lunar cold traps effects of double shielding abstract this paper deals with the problem of water permanence on the surface of the moon possible zones where water ice can survive are called cold traps k watson b c murray and h brown 1961 j geophys res 66 3033 3045 these are zones of the moon permanently obscured where the temperatures are low enough to preserve ice for billions of years in this work we developed a model for the topographic temperatures of complex craters whose shape was approximated by a capsized frustum of a circular right cone double shaded areas were simulated by embedding a small hemispherical crater in the shadowed part of the previous one their temperatures were calculated using the r r hodges jr 1980 proc lunar planet sci conf 11th 2463 2477 model first we verified that our results were in agreement with those of previous models our results confirm those obtained by j r salvail and f p fanale 1994 icarus 111 441 445 and in agreement with hodges 1980 we found that the lowest temperatures are reached by tycho like craters that are the larger and shallower among the examined cases when small craters are embedded in the shaded area of larger ones their temperatures are low enough to preserve other volatiles like co 2 hodges 1980 in particular if we consider double shaded areas in biot like craters the temperatures are lower than 103 k in a shell of almost 20 around the poles thus allowing the preservation of ices for geometrical reasons a hemispherical crater embedded in the bottom of a biot like crater cold remain in the shadowed area for latitude values lower than those reached by an analogous crater embedded in sosigene or tycho like craters therefore the latitudinal radius of polar frost caps could be greater than that predicted by previous models that did not consider double shaded areas however double shielding occurs in only a fraction of the secondary craters therefore in this case eventual deposits of ice would be of smaller dimensions compared with the case of primary shielding analysis of the clementine radar data s nozette c l lichtenberg p spudis r bonner w ort e malaret m robinson and e m shoemaker 1996 science 274 5292 5300 and the lunar prospector neutron spectrometer data seems to be consistent with the presence of water ice in very low concentrations across a significant number of craters thus confirming the old hypothesis of watson et al 1961

the pacific south american modes and tropical convection during the southern hemisphere winter abstract atmospheric circulation features and convection patterns associated with two leading low frequency modes in the southern hemisphere sh are examined in multiyear global reanalyses produced by ncep ncar and nasa dao the two leading modes referred to as the pacific south american psa modes are represented by the first two eof patterns the two patterns are in quadrature with each other and are dominated by wavenumber 3 in midlatitudes with large amplitudes in the pacific south american sector in the pacific anomalies in the subtropics and in the midlatitudes are opposite in phase taken together the two psa modes represent the intraseasonal oscillation in the sh with periods of roughly 40 days the evolution of the psa modes shows a coherent eastward propagation a composite analysis was conducted to study the evolution of tropical convection and the corresponding circulation changes associated with the psa modes outgoing longwave radiation olr anomaly composites during the mature phase

pervasive aqueous paleoflow features in the aeolis zephyria plana region mars abstract a survey of themis visible wavelength images in the aeolis zephyria plana region over the two western lobes of the equatorial medusae fossae formation mff shows 150 sinuous ridges having a variety of morphologies and contexts to systematize investigation we use a classification scheme including both individual ridge and ridge network types as well as associations with impact craters and fan shaped features the morphology of the ridges their location downslope from higher topography e g crater rims and scarps and their association with fan shaped forms indicate that most sinuous ridges formed through overland aqueous flow analysis of observations by individual ridge type leads to interpretation of most of these sinuous ridges as inverted fluvial channels or floodplains and a few as possible eskers with the origin of the remaining ridges under continuing investigation about 15 of the sinuous ridges are associated with impact craters but data analysis does not support a genetic relationship between the craters and the sinuous ridges instead analysis of one sinuous ridge network associated with a crater indicates that the water source for the network was atmospheric in origin namely precipitation runoff the broad areal distribution of these 150 ridges and the network morphologies in particular the branched and subparallel types suggest that an atmospheric water source is generally applicable to the population of sinuous ridges as a whole this concentration of sinuous ridges is the largest single population of such landforms on mars and among the youngest these ridges are situated at a paleoscarp between cerberus palus and the aeolis highlands suggesting that the precipitation that formed them was orographic in origin the ages of the equatorial mff units in which this population of sinuous ridges is found imply that this orographic rain and or snow fell during some period from the late hesperian through the middle amazonian

reevaluating dune scaling relations abstract in sand bedded rivers dunes dominate sediment transport and flow resistance dunes are also commonly preserved in fluvial deposits as cross stratified units that record their size shape and migration rates prediction of dune dimensions is therefore important for forecasting modern river channel dynamics as well as reconstructing past fluvial environments on earth and other planets predictions are often made by assuming that the formative flow depth h sets dune dimensions with height scaling as 1 6h and length as 5h yet there is a suite of other scaling relations that link dune dimensions to other variables like grain size transport stage and froude number here we present a new compilation of flow and dune dimension data to evaluate scaling relations the data reveal approximately two orders of magnitude variation in dune height and length at any given flow depth dune heights in shallow flows 2 5 m are often more symmetric have lower lee angles are relatively shorter in height than 1 6h and have a wider range of observed heights for a given depth none of the scaling relations predict the observations exceptionally well likely because of natural variability in dune dimensions and because they do not explicitly account for the apparent scaling break that occurs at 2 5 m we propose new simple depth scaling relations with added statistical uncertainty for the prediction of dune height and length from flow depth as well as flow depth from dune height we conclude that shallow and deep flow dunes exhibit different scaling due to a change in the dominant process controls as dunes get larger

space weathering effects on lunar cold trap deposits 1 both steady and episodic sources have been proposed as sources of hydrogen observed by lunar prospector in association with the regions of permanent shadow at the poles of the moon either source could supply significant quantities of water to the poles however space weathering processes affect the retention of water in the cold traps we investigate those effects by simulating the evolution of a column of regolith in the region of permanent shadow over time we determine the hydrogen concentration as a function of depth using a monte carlo model of discrete impacts and of delivery from the solar wind we treat the delivery sublimation sputtering and very small scale impacts as continual processes comparing the amount of water delivered to the poles to the amount remaining after space weathering we find a retention efficiency of 5 6 the retention efficiency of the polar cold traps is adequate for preserving volatile deposits over long periods of time the average hydrogen concentration in the regolith column is 4100 ppm in the top meter after 1 gyr this is a saturation level in the regolith increasing the amount of time deepens the enriched layer but does not lead to increased concentrations in 1 gyr about 1 6 m of the regolith is gardened therefore the top meter which is probed by the neutron spectroscopy technique has reached steady state in the simulations the 4100 ppm saturation level is about half of the amount of hydrogen inferred from the lunar prospector neutron data

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

evolution of alluvial mudrock forced by early land plants mudrocks are a primary archive of earth s history from the archean eon to recent times and their source to sink production and deposition play a central role in long term ocean chemistry and climate regulation using original and published stratigraphic data from all 704 of earth s known alluvial formations from the archean eon 3 5 billion years ago to the carboniferous period 0 3 billion years ago we prove contentions of an upsurge in the proportion of mud retained on land coeval with vegetation evolution we constrain the onset of the upsurge to the ordovician silurian and show that alluvium deposited after land plant evolution contains a proportion of mudrock that is on average 1 4 orders of magnitude greater than the proportion contained in alluvium from the preceding 90 of earth s history we attribute this shift to the ways in which vegetation revolutionized mud production and sediment flux from continental interiors

radon anomaly in the soil of taal volcano the philippines a likely precursor of the m 7 1 mindoro earthquake 1994 1 the soil gas 222rn concentration had been monitored almost continuously from june 1993 till november 1996 on taal volcano luzon island the philippines during this measurement period a singular mb 7 1 earthquake occurred on november 15 1994 between luzon and mindoro 48 km south of the volcano twenty two days before the earthquake an anomalous increase in soil gas radon peak to background ratio 6 was recorded unique in the whole time series the possible generation of this anomaly by typhoon teresa which struck luzon island a few days before was ruled out one year later when super typhoon angela the most powerful storm to hit the philippines in ten years crossed luzon island along almost the same track without triggering a similar disturbance in the radon signal consequently there is strong evidence that the taal radon anomaly originated in stress accumulation preceding the mindoro earthquake

the role of vegetation and large wood on the topographic characteristics of braided river systems riparian vegetation and large wood play a crucial role in shaping rivers on the one hand vegetation tends to increase bank stability reduce channel width and reduce the braiding index in gravel bed rivers conversely large wood tends to increase channel dynamics and promote avulsions the effects of vegetation and large wood have been rarely simulated together in flume experiments in this paper we present a series of experimental runs conducted in a large flume facility using cylindrical wooden dowels and alfalfa seedlings to represent logs and vegetation respectively in order to investigate their role on determining the topographical nature of braided river systems a terrestrial laser scanner was used to measure in detail the topography of the channels and bars and distribution of the elevations and second order structure functions were used to explore the topography that large wood and vegetation imposed on the braided pattern in the flumes results show that vegetation reduced the braiding index and produced wider and deeper channels the standard deviation of the bed elevations was higher than in flumes without vegetation large wood alone was not effective in changing the braiding index or the standard deviation of the elevations when vegetation and large wood acted together in the flume the braiding index reached a minimum value and the skewness of the distribution of elevation increased revealing shallower pools if compared with runs conducted with only vegetation

blocking over the south pacific and rossby wave propagation abstract atmospheric blocking events over the south pacific are investigated using a 39 yr record of 500 hpa height fields from the ncep ncar reanalysis dataset the analysis extends earlier work using a 16 yr record and confirms that the occurrence of blocking over the southeast pacific is strongly modulated by the enso cycle during austral spring and summer comparison of results at 500 hpa with the 300 hpa meridional wind component showed that blocking events are associated with large scale wave trains lying across the south pacific from the region of australia to southern south america similar wave trains are evident in both hemispheres in singular value decomposition analyses between 300 hpa meridional wind components and tropical pacific outgoing longwave radiation olr anomalies the hypothesis that the divergence associated with tropical olr anomalies forces an extratropical wave response that results in enhanced blocking over the southeast pacific was tested using a linearized barotropic vorti

paleozoic vegetation and the siluro devonian rise of fluvial lateral accretion sets a long standing hypothesis links the increased prominence of meandering rivers in the middle paleozoic to the colonization of terrestrial environments by vegetation this hypothesis is tested using a data set of cambrian to devonian fluvial literature and field examination of key stratigraphic units according to some researchers cambrian to mid silurian river systems were braided in planform with a sharp increase in the abundance of meandering rivers during the silurian devonian although meandering systems were largely identified on the basis of thick mudstones and organized channel deposits the data set record of lateral accretion sets appears to be a robust proxy for the abundance of meandering river point bars lateral accretion is first recorded from pridolian lochkovian strata but is noted in nearly 40 of fluvial case studies by the famennian this trend matches the known record of rooted vegetation suggesting that vegetation progressively stabilized river banks and promoted single thread channels however the presence of precambrian and extraterrestrial meandering systems indicates that vegetation is not essential for meandering and the lack of evidence for cambrian to silurian ludlow point bars is surprising if originally present they may largely have been destroyed by extreme floods chute cut offs in coarse grained meandering systems and eolian activity

polar hydrogen deposits on the moon neutron and gamma ray data measured using the lunar prospector spectrometers were analyzed to define the enhanced hydrogen deposits near both poles of the moon combining the new low altitude neutron data 30 15 km with previous high altitude 100 20 km neutron data and the results of several recent radar investigations sharply constrains the characteristics of each of the polar deposits the deposits at the north appear to be in the form of many small pockets or of generally distributed hydrogen that average to a 100 ppm weight fraction enhancement over that which exists in regolith at more equatorial latitudes those deposits in the permanently shaded craters near the south pole are consistent with a thick ferroan anorthosite regolith containing an enhancement of 1670 890 ppm hydrogen which if in the form of water ice amounts to 1 5 0 8 weight fraction of h sub 2 o neutron data alone cannot discriminate between hydrogen implanted in lunar soil from the solar wind hydrated minerals or h sub 2 o these craters appear to be surrounded by regolith that either contains small pockets of enhanced hydrogen or is soil that is uniformly impregnated with hydrogen enhanced on average by about 100 ppm above that contained in soils at more equatorial latitudes c more 2000 american geophysical union less

a novel method for estimating sandbody compaction in fluvial successions clastic sedimentary successions are subject to variable amounts of compaction which causes a decrease in both the thickness and porosity of sand rich depositional units methods for estimating the degree of sediment compaction are needed for characterizing changes in the geometry and petrophysical properties of depositional elements in relation to their burial history conventional methods for estimating compaction of rock successions through the application of several empirical equations return estimations whose uncertainties can be significant and integrative approaches that can produce reliable estimations are therefore desirable to this end a new method is proposed here for the estimation of the degree of compaction of sandbodies in ancient channelized fluvial successions for outcropping fluvial successions the compacted geometry of channel fill margins cut into non cohesive deposits can be measured whereas the decompacted angle of repose of the material originally forming the channel banks can be estimated experimentally sediment compaction can therefore be estimated by comparing the observed geometry of the uppermost part of a channel fill margin with the angle of repose of the non cohesive bank material the proposed method has been applied to three different sand prone fluvial successions seen in outcrop for the purposes of i illustrating the approach and ii testing it through a comparison of its estimations against results produced by a conventional method based on thin section observations the comparison demonstrates that the two methods yield similar results highlighting how the proposed approach can be readily applied to the assessment of compaction in clastic successions for scopes of both pure and applied geological research

dynamic single thread channels maintained by the interaction of flow and vegetation most rivers on earth today flow as a single channel in some cases with occasional islands and follow a more or less sinuous course however single thread channels have proven difficult to reproduce and study experimentally experimental self formed channels tend to widen and subdivide leading to a braided pattern cohesive sediment has been the main mechanism studied for stabilizing banks and producing a single thread channel we show how laboratory experiments using vegetation to stabilize banks can organize the flow and convert the planform morphology from braided to single thread our experimental strategy a repeated cycle of short periods of high water discharge alternating with longer periods of low discharge accompanied by plant seeding and growth leads to the evolution of a dynamic self maintaining single thread channel with well defined banks and floodplain by eliminating weak flow paths the vegetation corrals the water into a single dominant channel until the reduction in total wetted width leads to a new self organized state in which the flow removes vegetated area as fast as it is produced the new channel is deeper and has a broader distribution of depths than the braided one with channel size adjusted to carry almost all the flood flow the resulting system maintains a dynamic steady state via similar mechanisms to those that operate in meandering channels in the field specifically erosion at the outside of bends bend growth and bar development our methodology provides a basis for experimental development of self sustaining high amplitude meanders and has applications for river management and basic research purposes

variability and predictability of the north atlantic wave climate wave climate across the ocean basins can be described using satellite altimetry here we concentrate on the north atlantic region waves in the north atlantic are strongly seasonal and peak in the winter season the northeastern sector of the atlantic and adjoining shelf seas also exhibit exceptionally high interannual variability in the winter with monthly average significant wave height varying by up to a factor of 2 from one year to the next the strength and geographical distribution of variability is broadly consistent throughout the winter months december march a large fraction of these wave height anomalies is associated with a single pattern of pressure anomalies that resembles the north atlantic oscillation nao a predictor based on nao dependence is trained from relatively recent satellite data and then tested against earlier satellite and in situ data the predictor is successful in large areas of the north atlantic confirming a robust relationship between wave height anomalies and the nao over the last few decades a substantial rise up to 0 6 m in monthly mean wave heights on the northeastern atlantic during the latter part of the twentieth century is attributable to changes in the nao substantial residual anomalies in wave heights exist after the influence of the nao has been subtracted these are partly explained by a second pair of north atlantic patterns in wave height anomalies and sea level pressure anomalies this east atlantic pattern is particularly influential in midwinter and affects the southern part of the northeastern sector including the region of seven stones light vessel