a 160 k y old record of el nino southern oscillation in marine production and coastal runoff from santa barbara basin california usa a 160 k y old laminated sediment record from the santa barbara basin california analyzed using scanning electron microscope techniques provides a history of interannual variability of marine production and coastal runoff we used backscatter electron imagery to measure the components of the varve these include a terrigenous lamina formed by seasonal runoff from winter rains together with a diatomaceous lamina that records marine production during the spring and early summer spectral analysis of terrigenous and diatomaceous laminae thickness reveals significant periodicities of 3 1 and 8 4 yr in the terrigenous series these are indistinguishable within the frequency resolution of the spectra from significant periodicities of 3 5 and 7 6 yr in the diatomaceous series the 3 1 and 3 5 yr periodicities record el nino modulation of coastal runoff and marine production the 8 4 and 7 6 yr periodicities are consistent with modulation by strong to very strong el nino events this is supported by the results of cross spectral analysis of the terrigenous and diatomaceous records which reveal inverse or antiphase relationships at 3 5 and 7 6 yr our work adds to a body of evidence that suggests that el nino has been a persistent feature of late quaternary climate variability

el nino la nina and sahel precipitation during the middle holocene simulations with a synchronously coupled atmo sphere land ocean sea ice model indicate el nino la nina like events in the eastern tropical pacific ocean during the middle holocene 6 ka with similar intensities and frequencies as at present 0 ka july august september sahel precipitation shifts northward as expected from proxy data for present day interannual decadal variability of western sahel precipi tation is correlated with both pacific el nino la nina sea sur face temperature sst anomalies and the atlantic dipole teleconnections at 6 ka between sahel precipitation and el nino la nina sst anomalies are absent with tropical atlantic ssts asserting a dominant influence these results illustrate potential problems with using present day teleconnection patterns in interpreting past climate variability from proxy data

an 15 000 year record of el nino driven alluviation in southwestern ecuador debris flows have deposited inorganic laminae in an alpine lake that is 75 kilometers east of the pacific ocean in ecuador these storm induced events were dated by radiocarbon and the age of laminae that are less than 200 years old matches the historic record of el nino events from about 15 000 to about 7000 calendar years before the present the periodicity of clastic deposition is greater than or equal to 15 years thereafter there is a progressive increase in frequency to periodicities of 2 to 8 5 years this is the modern el nino periodicity which was established about 5000 calendar years before the present this may reflect the onset of a steeper zonal sea surface temperature gradient which was driven by enhanced trade winds

a high resolution proxy record of rainfall and enso since ad 1550 from layering in stalagmites from anjohibe cave madagascar two stalagmites from anjohibe cave have annual layers made up of inclusion rich calcite over inclusion free calcite or of darker aragonite over clear aragonite geochemical evidence indicates that the basal units are deposited slowly in the wet season and the upper units more rapidly in the dry season for the period with rainfall and temperature data ad 1951 1992 layer thickness correlates well with the southern oscillation index soi as well as rainfall water surplus and actual evapotranspiration aet at nearby majunga com parison of the layer record for one stalagmite with 1866 1994 soi data indicates that layer thickness correlates best with the frequency and intensity of warm low phase so el nino events not with average soi conditions in addition the 415 year layer thickness time series from that speleothem agrees remarkably well with historical records of el nino frequency with galapagos ecuador coral records of sea surface temperature in the eastern pacific and with accumulation

windblown sand on venus preliminary results of laboratory simulations abstract small particles and winds of sufficient strength to move them have been detected from venera and pioneer venus data and suggest the existence of aeolian processes on venus the venus wind tunnel vwt was fabricated in order to investigate the behavior of windblown particles in a simulated venusian environment preliminary results show that sand size material is readily entrained at the wind speeds detected on venus and that saltating grains achieve velocities closely matching those of the wind measurements of saltation threshold and particle flux for various particle sizes have been compared with theoretical models which were developed by extrapolation of findings from martian and terrestial simulations results are in general agreement with theory although certain discrepancies are apparent which may be attributed to experimental and or theoretical modeling procedures present findings enable a better understanding of venusian surface processes and suggest that aeolian processes are important in the geological evolution of venus

a comparative study of interior layered deposits on mars interior layered deposits ilds of the eastern valles marineris and adjacent chaos regions were analysed using high resolution imagery topography and spectral data in order to detect possible correlations we find that ilds are susceptible to erosion and weathering as proven by their shapes mesa buttes surface structures pitted fluted yardangs stair stepped morphologies at different scales and metre sized boulders and talus ilds bear hydrated sulphates consequently we conclude that aqueous conditions dominated during their formation subhorizontal layering and parallel bedding of the ilds could then indicate that deposition took place under low energy aquatic conditions their superposition on chaotic terrain suggests that they are younger than chaotic terrain and hence younger than late hesperian for the hydrated ilds which show polyhydrated on top of monohydrated sulphates we think that formation within an evaporative body is not conceivable and we assume instead that a conversion of sulphates by post formational humidity changes took place as hydrated ilds correlate well with rock fragmentation we suppose that volume changes due to water content are responsible for rock fragmentation despite the different ild settings the basic conditions during sedimentation and erosion of ilds could not have varied greatly because comparable mineralogies and morphologies are found among ilds

ocean wave dynamics and the time scale of enso abstract a reexamination of the coupled delayed action oscillator model of suarez and schopf for the el nino southern oscillation enso phenomenon is made by deriving it using a parameterized atmosphere and explicit linear ocean wave dynamics the derivation attempts to clarify the role of boundary reflections damping and scale sensitivity in determining the characteristic timescale of the model making the assumption that sst anomalies are related to thermocline perturbations in the central to eastern part of the basin and that wind anomalies are related to sst anomalies ocean wave dynamics are invoked to solve for the relationship between wind anomalies and the relevant thermocline displacement a perturbation to sst causes wind anomalies which drive kelvin waves eastward thereby increasing the sst perturbation the wind perturbations also generate rossby waves in the ocean which propagate westward eventually reflecting from the western boundary as kelvin waves the thermocline displacements of

a geologic evaluation of thermal properties for the elysium and aeolis quadrangles of mars thermal inertias with spatial resolutions as small as 2 by 5 km were combined in a regional study of the elysium and aeolis quadrangles of mars 30 n to 30 s 180 w to 225 w the range of thermal inertias obtained was 1 14 10 3 cal cm 2 s k 1 41 84 j m 2 s k 1 with the lowest values corresponding to the elysium rise and the highest values correlating with dark patches of aeolian material in the southern highlands the thermal properties obtained from the high spatial resolution measurements are essentially identical to the results obtained from data with much poorer spatial resolution indicating a regional homogeneity of surface properties at scales greater than 5 km aeolian features both dark patches and bright materials associated with topographic obstacles such as craters have higher thermal inertias than do their surroundings other surface features do not display distinctive thermal properties even when clearly resolved from their surroundings comparison of the thermal inertias with global data sets shows a pronounced inverse correlation with albedo consistent with globally observed trends and brightnesses at red green and violet wavelengths but no prominent correlation with elevation thermal inertias for individual geologic units within the two quadrangles appear to be more strongly controlled by the location of the terrain in either the northern plains or the southern highlands than by properties intrinsic to the unit

on the evolution of the southern oscillation abstract the evolution of the southern oscillation so is examined in the time domain by computing lagged cross correlations between sea level pressures at darwin and sea level or surface pressures at selected stations also in the northern hemisphere the historical and u s navy sea level pressure analyses are used all monthly time series are low pass filtered to retain periodicities greater than 20 months in order to highlight the interannual fluctuations which are primarily associated with the so a detailed analysis of the post 1941 period results in plotted maps of the phase lead or lag and magnitude of the maximum cross correlations with darwin in a manner analogous to a broadband coherence and phase spectrum the relationships within the so are further examined where possible back to 1882 using time series of running decadal cross covariances the dominant pattern reveals the two poles of the traditional standing oscillation or seesaw of the so with centers of opposite sign over indonesia

on the origin of gypsum in the mars north polar region 1 we describe the distribution and concentration of the largest martian gypsum deposit discovered to date by the mars express omega observatoire pour le mineralogie l eau les glaces et l activite imaging spectrometer its relationship to the late amazonian aged north polar dunes in which it is found and its likely origin gypsum has not been discovered anywhere within the north polar region outside of the olympia undae dune sea in the areas of highest gypsum a concentration 35 pure gypsum grains of a few tens of micrometers in size mixed with 65 millimeter sized gypsum grains containing dark spectrally featureless inclusions best fit the omega observations the gypsum rich dunes contain no significant average albedo temperature or morphological anomalies we propose that water emanating from nearby channels carved during melting of the polar layered deposits infiltrated the eastern end of the polar dune sea percolating through the dunes deposits of gypsum resulted from a combination of direct in situ alteration of sulfide and high calcium pyroxene bearing dunes and from formation of evaporitic gypsum crystals in the pore spaces of these dunes this gypsum deposit formed in a unique local environment and is disconnected from sulfate forming events elsewhere on mars which are thought to have occurred much earlier during the late noachian and hesperian by various means sulfates have not been discovered in any other collection of dunes on mars

quantitative compositional analysis of martian mafic regions using the mex omega reflectance data 2 petrological implications abstract the primary objectives of this paper are to determine the modal mineralogy of selected low albedo terrains of different ages ranging from noachian to amazonian exposed on the surface of mars this analysis is conducted using the spectral modeling of the observatoire pour la mineralogie l eau les glaces et l activite omega reflectance data results from this work are consistent with the major results of previous spectroscopic studies plagioclase 40 60 in volume and high calcium pyroxene 20 40 hcp are the dominant minerals of the most regions low calcium pyroxene 10 15 lcp and minor amounts of olivine are also present the oldest terrains are characterized by the largest amount of lcp and the lowest concentration of plagioclase these overall compositions are consistent with two pyroxene basalts the particle sizes are in the range of a few hundreds of micrometers which is in good agreement with the thermal inertia of the martian low albedo regions in the region around the nili fossae localized concentrations of olivine up to 40 with millimeter particle size similar to picritic basalts observed in situ by the spirit rover in the gusev crater are inferred chemical compositions are calculated for the first time from omega spectra they are quite consistent with gusev rocks and shergottite compositions but they appear to be significantly sio2 poorer than thermal emission spectrometer data a decreasing low calcium pyroxene abundance with the decreasing age of the low albedo regions is reported this may be indicative of decreasing degree of partial melting as thermal flux decreases with time we propose that the ancient noachian aged lcp rich terrains could have been formed from h2o bearing melts then dry basaltic volcanism occurred leading to decreasing lcp abundance with time due to decreasing degree of partial melting the olivine bearing material modeled in nili fossae resembles the composition of alh77005 and chassigny meteorites consistent with prior studies implications on the formation of the basaltic shergottites are discussed

initial results from the mini tes experiment in gusev crater from the spirit rover the miniature thermal emission spectrometer mini tes on spirit has studied the mineralogy and thermophysical properties at gusev crater undisturbed soil spectra show evidence for minor carbonates and bound water rocks are olivinerich basalts with varying degrees of dust and other coatings dark toned soils observed on disturbed surfaces may be derived from rocks and have derived mineralogy 5 to 10 of 45 pyroxene 20 ca rich pyroxene and 25 pigeonite 40 sodic to intermediate plagioclase and 15 olivine forsterite 45 5 to 10 two spectrally distinct coatings are observed on rocks a possible indicator of the interaction of water rock and airfall dust diurnal temperature data indicate particle sizes from 40 to 80 microm in hollows to approximately 0 5 to 3 mm in soils

aeolian processes and dune morphology in gale crater abstract datasets at resolutions many times greater than previously available were used to study aeolian features within gale crater high resolution thermal inertia data allowed for detailed particle size estimation with the data sufficient to resolve dunefields a wide range of grain sizes have now been identified in the gale crater dunefields ranging from medium to very coarse sand high resolution imaging science experiment hirise and themis vis data allowed for detailed analysis of the dune morphology and slip faces which shows that the dunes have responded to topographic influences on prevailing wind directions under a present day wind regime this result was corroborated by a regional mesoscale model for the crater under dust storm conditions the central mound and smaller scale crater floor topography has altered the prevailing wind regime and dune patterns aeolian activity has thus played and continues to play an important role in shaping many of the present surface features of gale crater the arrival of a future lander mission such as the mars science laboratory would be able to sample these surface features directly and add a wealth of data to the understanding of gale crater

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

volcanic sands of iceland diverse origins of aeolian sand deposits revealed at dyngjusandur and lambahraun the origin formation and evolution of volcanic sands are less well known than the formation of the much more common quartz rich sand sheets combining active volcanism and a cold climate iceland is covered for about 21 of its surface by sandy areas the sands were analyzed in detail at two sites and results reveal their diverse origins the first site is dyngjusandur located north of vatnajokull and the second site is the lambahraun area located south of langjokull at both sites the sand origin is determined from field observations wind directions from ventifacts chemical and mineralogical analyses of rocks and sands at dyngjusandur the sand is dominated by glass grains a situation typical of sand plains in iceland hyaloclastite ridges presently buried beneath vatnajokull are the dominant source of the sand and only large size plagioclase crystals 0 5 cm in sands seem to be derived from the lava flows hyaloclastite ridges were crushed by glaciers and mechanically eroded sediments were washed out by melt water onto flood plains the sand chemical composition is spatially homogeneous and similar to the average composition of neighboring sub aerial lava flows reflecting efficient mixing of distinct sources below the glacier the presence of sand north of dyngjujokull can be taken as a way to explore the average chemical composition of non exposed volcanic material beneath the glacier in the case of lambahraun prevailing winds indicate several potential sources of sand at the north of the sand sheet comparison of chemical and mineralogical analyses of sands and rock samples helped to refine the exact origin in contrast with the first site the sand is dominated by crystals and is chemically consistent with a mixture of material derived from the lava flows of eldborgir and skersli shield volcanoes analysis of the contact between the lava flows and the glacier reveals that basaltic sand grains formed as the result of recent advances of the glacier abrading the rocks the direct interaction of glacial and fluvio glacial activity with basaltic plains appears to be necessary to produce a large amount of sands in a relatively short period of time 4000years this site appears to be an excellent natural laboratory for further studies concerning the sand evolution and physical sorting processes in basaltic material which have important implications for understanding aeolian processes on mars copyright c 2011 john wiley sons ltd

surface textures and dynamics of the 2005 lava dome at shiveluch volcano kamchatka shiveluch is one of the largest and most active andesitic volcanoes of the kuril kamchatka arc it commonly alternates between vulcanian explosive eruptions and periods of dome growth and subsequent dome collapse driven block and ash flows the volcano was in an extended period of heightened activity for most of the period 2004 2010 we examined this activity in detail using thermal infrared tir remote sensing as part of the urgent request protocol urp program of the advanced spaceborne thermal emission and reflection radiometer aster instrument and confirmed the results with ground based photography and airborne tir camera data high spatial resolution tir images were collected during both daytime and nighttime satellite overpasses prior to and following the large explosive event eruption of 27 february 2005 and the dome growth that followed during a field campaign in august 2005 a helicopter overflight designed to acquire visible and tir data of the active dome was performed this was a nadir looking low altitude overflight and the first ever of shiveluch volcano involving non russian scientists the image data revealed an active crease structure in the center of the dome with a distinctly different crescent shaped high temperature 380 c zone roughly perpendicular to the crease in order to provide a time context and estimate extrusion rates the airborne data were compared to the spaceborne aster data and long distance ground based photography of the dome acquired by our russian colleagues the presence of a crease structure and the complex thermal pattern on the surface were both unexpected discoveries that reveal the way in which exogenous dome growth was occurring at the time this highly active period at shiveluch provides a unique example to better understand silicic lava dome growth using tir data the results also demonstrate a straightforward approach for fusing ground air and spaceborne image data which could be applied to other active domes around the world

contrasting eastern pacific and central pacific types of enso abstract surface observations and subsurface ocean assimilation datasets are examined to contrast two distinct types of el nino southern oscillation enso in the tropical pacific an eastern pacific ep type and a central pacific cp type an analysis method combining empirical orthogonal function eof analysis and linear regression is used to separate these two types correlation and composite analyses based on the principal components of the eof were performed to examine the structure evolution and teleconnection of these two enso types the ep type of enso is found to have its sst anomaly center located in the eastern equatorial pacific attached to the coast of south america this type of enso is associated with basinwide thermocline and surface wind variations and shows a strong teleconnection with the tropical indian ocean in contrast the cp type of enso has most of its surface wind sst and subsurface anomalies confined in the central pacific and tends to onset develop and decay in situ

low frequency changes in el nino southern oscillation abstract although there are indications from numerical models that el nino southern oscillation enso may be an internal mode of the coupled pacific ocean atmosphere system sensitive to climatic background parameters it has not yet been possible to find significant changes in enso variability between the little ice age and the present yet a number of authors have found qualitative indications in anecdotal and proxy records of shorter century scale variations in the return interval statistics for el nino episodes to objectively determine what nonstationarities exist we statistically examine the el nino occurrences since 1525 compiled by quinn et al we have stratified the return intervals both for strong events and for all events according to two null hypotheses 1 return intervals are stationary over periods of 200 500 years and 2 the intervals are stationary on a centenary time scale between epochs of contrasting solar variability two parameter weibull distributions are fit to subsamples of

el nino southern oscillation enso and decadal scale climate variability at 10 n in the eastern pacific from 1893 to 1994 a coral based reconstruction from clipperton atoll we have developed a 101 year 1893 1994 subseasonal oxygen 18o and carbon 13c isotopic time series from clipperton atoll in the eastern pacific using the coral porites lobata in agreement with linsley et al 1999 we find that seasonal and interannual coral 18o variability at clipperton results from variability in both water temperature and salinity three new coral time series demonstrate the reproducibility of a secular coral 18o trend of 0 35 since 1910 but show varying 13c trends strong decadal scale variability in the 18o record appears related to the pacific decadal oscillation pdo through postulated changes in the strengths of the equatorial counter current and north equatorial current interannual variability in this coral 18o record is directly related to the el nino southern oscillation enso and isolation of this frequency band indicates reduced enso variability in the eastern equatorial pacific in the period 1925 to 1940 in agreement with instrumental and other pacific coral records

spectroscopic study of the moses lake dune field washington determination of compositional distributions and source lithologies 1 source lithologies and transport histories of materials within the ephrata fan are investigated data were collected using a variety of remote sensing laboratory spectroscopic and field observations and techniques laboratory thermal emission spectra were collected of bedrock within the grand coulee dune samples and clast deposits factor analysis target transformation and end member recovery techniques were applied to the set of dune samples as well as a set of grain size fractions the dune sample spectra are composed of three components that represent basalt granodiorite and clay compositions the basalt and granodiorite components are similar to spectra of clast and bedrock samples from the grand coulee and the ephrata fan the clay component is similar to weathering surfaces located within the dune field the same components were recovered from the set of grain size fractions from a single dune sample demonstrating a relatively higher basalt concentration with grain sizes greater than 250 m thermal infrared multispectral scanner tims data display significant intradune compositional variation and no discernable interdune compositional variation indicating that the basalt and granodiorite components were likely deposited simultaneously and subsequently separated by wind based on grain size basalt and granodiorite bedrock units within the channeled scablands are source materials for the deposits within the ephrata fan and moses lake dune field the columbia river located 20 km west of the dune field is not a likely source of material

eastern pacific sea surface temperature since 1600 a d the δ18o record of climate variability in galapagos corals we measured stable oxygen isotope ratios and skeletal growth rates in the massive corals pavona clavus and p gigantea from the west coast of isabela island galapagos to assess interannual to decadal climate variability in the eastern pacific comparisons of instrumental data sets show that sea surface temperatures sst in the galapagos region are representative of a broad portion of the eastern equatorial pacific the site is especially well suited for long term studies of the el nino southern oscillation enso phenomenon as it lies within the eastern pacific center of action for thermal anomalies associated with enso the p gigantea isotope record is nearly monthly in resolution spans the period 1961 1982 and shows strong correlation with a galapagos instrumental sst record r 0 90 for annual averages cross spectral analysis shows that sst can explain greater than 80 of the variance in 18o at both the annual cycle and within the high frequency portion of the enso band 3 5 years the p clavus record is annual in resolution extends from 1587 to 1953 a d and was obtained from a 10 m diameter colony preserved within the urvina bay uplift because seawater 18o variations in the region are very small we interpret the urvina bay coral 18o record in terms of annual average sst the isotopic record appears to be a very good but not perfect indicator of enso events and shows good correspondence with the historical enso reconstruction of quinn et al 1987 a number of low 18o excursions that we observe during the 17th and 18th centuries very likely represent enso events that are missing from the historical tabulations most interannual 18o variations between 1607 and 1953 a d represent annual average temperature excursions of 1 to 2 5 c during the little ice age the annual 18o series correlates well with many north american tree ring records and shows low temperatures during the early 1600s and early 1800s and relatively warmer conditions during the 1700s unlike most northern hemisphere tree ring and instrumental records we see no evidence at this site for warming between 1880 and 1940 but rather observe a slight cooling 28 of the total variance the main enso mode is centered at 4 6 years and accounts for 12 of the total variance additional significant oscillations occur at periods of 3 3 6 8 11 17 22 and 34 years both annual growth rate and 18o show variance at periods equivalent to the solar and solar magnetic periods e g 11 and 22 years respectively in addition the amplitude of the 11 year 18o cycle generally varies with the amplitude of the solar cycle supporting previous suggestions that the solar cycle may modulate interannual to decadal climate variability in the tropics the dominant oscillatory modes both within the enso and interdecadal frequency bands shift to shorter periods from the early to middle 1700s and again from the middle to late 1800s this may reflect major reorganizations within the tropical ocean atmosphere system and suggests that tropical pacific climate variability is linked across timescales ranging from years to decades

variation in particle size distribution over a small dune the variation in particle size distribution for a sequence of sand samples collected from the surface of a small barchanoid dune along a sampling line parallel to the windflow is studied by means of the hyperbolic distribution the modal or typical value of the log size increases linearly with distance from the windward foot to the crest of the dune and falls off steeply on the lee side the spread of the log size distribution locally near the modal value is roughly constant on the windward side but decreases significantly down the slip face two other parameters of the four parameter hyperbolic distribution can be considered largely constant a comparison of the log size distributions for heavy and light mineral grains based on a selected set of the samples showed that heavy and light minerals follow different hyperbolic patterns however the difference in modal size of the distributions for the two types of minerals was virtually constant among the samples

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

dust transport and the question of desert loess formation although contemporary dust storms are frequent in arid and semi arid areas desert loess deposits are poorly developed much of the world s loess occurs in mid latitude areas which experienced glaciation during the pleistocene ocean core evidence indicates that dust transport from sub tropical deserts increased during cold stages of the pleistocene but loess formed only on certain desert margins for reasons which have not been fully explained this paper re examines the mechanisms of dust transport and deposition and the circumstances leading to the accumulation of thick loess typical loess is composed mainly of medium silt grains which are transported in short term suspension a few metres above the ground significant thicknesses of loess form only when dust is trapped within a limited area often relatively close to the source dust particles finer than 20 m are transported mainly in long term suspension over a greater height range and may be widely dispersed the availability of silt and the frequency magnitude and direction of dust transporting winds are important factors governing the potential for loess formation but the existence of a suitable dust trap is particularly important traps may be formed by topographic obstacles areas of moist ground or vegetated surfaces vegetation adjacent to glacial outwash plains and braided meltwater streams trapped dust in mid latitudes during the pleistocene dust blown during glacial periods from certain deserts notably in sinai soviet central asia and china accumulated as loess in neighbouring semi arid regions on the margins of other deserts loess formation was inhibited partly by the absence of vegetation traps during most of the holocene net dust deposition rates in all desert marginal areas have been too low for significant loess accumulation this is mainly due to a reduction in silt availability and a tendency towards landscape stability reported dust storm frequencies during the past 50 years over estimate the longer term holocene dust flux due to the effects of human activities much modern dust owes its origin to erosion of cultivated soils in semi arid areas and is finer than typical loess

high resolution investigations of transverse aeolian ridges on mars abstract transverse aeolian ridges tars are the most pervasive aeolian feature on mars their small size requires high resolution data for thorough analyses we have utilized mars reconnaissance orbiter mro context camera ctx and high resolution image stereo experiment hirise images along with mro compact reconnaissance imaging spectrometer for mars crism spectroscopic data to study tars in detail tar deposits along with related dark dune material and layered terrains have been mapped in six study areas in order to identify sediment pathways and determine whether tars are sourced locally or from global wind borne materials tar morphology and orientation were mapped in grids within each study area the results show that tars are probably locally sourced we constructed four hirise digital terrain models dtms to measure tar heights widths spacing areas symmetry and to calculate sediment volumes results show that tars have average heights of 1 5 m are very symmetrical and are similar in form to terrestrial megaripples orthorectified hirise images taken 3 years apart were analyzed for tar movement and none was found superposed craters on equatorial tars give ages of 2 ma suggesting that these are relatively ancient and generally inactive aeolian deposits crism data were analyzed over tar deposits dark dune material and light toned terrains although the surfaces were somewhat obscured by dust cover the results did not show any remarkable difference between tars and other deposits we conclude that tars may be sourced from local materials and form in a similar way to terrestrial megaripples

spatial resolution and the geologic interpretation of martian morphology implications for subsurface volatiles abstract viking orbiter images of mars provide global coverage of the major geologic and tectonic provinces on the planet however only a fraction of the orbiter images are useful for assessing the processes responsible for the generation or modification of surface landforms an example from acheron fossae illustrates that aeolian dunes visible at 9 m pixel resolution are indistinguishable at 57 m pixel resolution dunes in acheron fossae valleys lend support to an aeolian interpretation for lineated valley fill at this location this result provides an alternative hypothesis for the proposed ice rich interpretation of this terrain consequently it seems unlikely that images with a spatial resolution 50 m pixel can provide strong constraints on the relative importance of various geologic processes that have acted upon the surface a survey of the best viking orbiter images with

radar measurement of small scale surface texture syrtis major recent radar observations of syrtis major have shown it to be smooth and relatively homogeneous when sensed at centimeter wavelengths there is a gradual decrease in surface roughness east to west across the basin which correlates with an apparent decrease in small 1 km diameter crater density root mean square surface slopes range from more than 1 5 2 0 in the east to less than 0 5 along the western margin at 12 6 cm the surface appears somewhat rougher at 3 6 cm a 0 3 dependence is inferred radar reflectivity increases from about 5 to about 12 across syrtis major being greatest near the western margin high resolution 8 to 20 m pixel viking images suggest that an increasing amount of resurfacing has occurred in western syrtis major compared with the eastern parts the radar infrared and optical imaing evidence are consistent with resurfacing by geologically recent low viscosity lavas which were subsequently mantled by thin layers of aeolian material each data set may be taken as a unique source of scale dependent information on surface materials and properties from comparison of radar derived surface roughness with image derived crater density curves we conclude that processes other than cratering control the surface texture on 0 03 to 100 m surface scales

tropical pacific variability in the ncar climate system model a 300 yr simulation with the ncar climate system model csm version 1 captured only 60 of the observed enso signal and exaggerated the interannual variability of sst in the western tropical pacific here a simulation with a new version of the csm which significantly improves the spatial and temporal patterns of tropical pacific variability is described maximum sst variability is shifted to the central and eastern pacific a better simulation of the equatorial pacific thermocline structure results in nino 3 and nino 4 statistics com parable to the observed estimates for the last century the evolution of sst and subsurface temperature anomalies is in excellent agreement with observed events the majority of events evolve as a standing mode with weak sst anomalies occurring in the northern spring in the eastern tropical pacific and maximum anomalies covering the eastern tropical pacific ocean to the date line by the following northern winter at the same time subsurface temperature anomalies spread eastward and upward along the tropical thermocline the delayed oscillator and wyrtki s buildup hypothesis are consistent with aspects of the csm simulation on the equator a westerly wind stress anomaly in the central pacific forces off equatorial upwelling anomalies which propagate westward reaching the western boundary about one half year later this upwelling signal then propagates eastward along the equator arriving 2 months before cooling in the eastern pacific basin the tropical pacific atmospheric response to warm oceanic events also agrees with observational analyses with a negative southern oscillation pattern in sea level pressure wind stress anomalies and low level convergence to the west of the maximum sst anomalies and enhanced deep convection and precipitation in the central and eastern tropical pacific

quantitative compositional analysis of martian mafic regions using the mex omega reflectance data 1 methodology uncertainties and examples of application abstract the mars express observatoire pour la mineralogie l eau les glaces et l activite omega collected an unprecedented visible and near infrared hyperspectral dataset covering the low albedo regions of mars we investigate the ability to infer modal abundance of surfaces of these regions from a radiative transfer model developed by shkuratov et al shkuratov y starukhina l hoffmann h arnold g 1999 icarus 137 235 246 and adapted to basaltic surfaces by poulet and erard poulet f erard s 2004 j geophys res 109 e2 doi 10 1029 2003je002179 from omega measurements of mafic surfaces we develop several sensitivity tests to assess the extent to which the model can be applied to predict pyroxene composition high calcium phase and low calcium phase abundance of almost neutral components plagioclase in the near infrared wavelength as well as grain sizes by using a library of selected end members results of the sensitivity tests indicate that the scattering model can estimate both abundances and grain sizes of major basaltic materials of low albedo regions within uncertainties 5 to 15 vol the model is then applied to data from dissected cratered terrains located in terra meridiani the derived grain size including uncertainties is in the 50 500 m range this is consistent with the thermal inertia and albedo of this region which indicates a fine sand sized surface with little dust the abundances of plagioclase 43 57 and pyroxenes 35 45 10 including 11 5 of low calcium phase are in good agreement with previous basalt like compositions of low albedo regions from thermal infrared spectral measurements the method presented in this paper will provide a valuable tool for evaluating the modal mineralogy of other mafic regions of mars observed in the near infrared wavelength range

martian north polar hazes and surface ice results from the viking survey completion mission viking infrared observations of the martian north polar regions taken during the 1979 1980 viking survey completion mission have been used to determine the location and nature of the retreating polar cap edge and of an accompanying atmospheric ice haze the haze is composed of water ice and its visible opacity is approximately unity equivalent to 1 2 precipitable microns of water ice during the polar cap retreat aerocentric longitude ls 340 60 the haze is nearly always present and extends from at most a few degrees south of the polar cap edge to an undetermined distance over the cap interior the transition from ice free ground to a predominantly ice covered surface at the cap edge spans 5 10 of latitude the ability of the viking infrared observations to distinguish haze from surface condensate yields a more accurate seasonal regression for the polar cap than can be determined from visual images generally the infrared observations presented here yield a regression similar to those determined from earth based and or spacecraft visual data for the same and for previous northern springs however there are differences concerning details of the cap retreat the thermal data indicate that the martian seasonal polar cap did extend south of 60 n during this particular late winter and that the midspring resumption of the cap retreat occurs at ls 50

surface properties of the pettit wind streak on mars implications for sediment transport abstract pettit crater 12 n 174 w is associated with a complex wind streak consisting of both type i bright streak and type ii dark streak materials broadband albedo measurements of the streak indicate a minimum of 20 and a maximum of 32 with 27 on the surrounding plains the darkest materials have the highest thermal inertias which can be related to an effective grain diameter typical of medium sand most of the dark streak materials have thermal inertias representative of fine sand the material most easily set in motion by the wind on mars the bright portions of the streak have thermal inertias higher than that of the surrounding plains the bright streak values are representative of very fine sand differences between temperatures measured at 11 and 20 m indicate there is no difference in the areal abundance of unresolved high thermal inertia materials e g blocks bedrock between the pettit streak and the surrounding plains the dark streak material is consistent with models involving sand saltation and transport but the bright streak thermal inertia is not consistent with a volumetrically significant enhancement of unconsolidated dust in the streak

grain size variations on a longitudinal dune and a barchan dune abstract the grain size characteristics of the sand upon two dunes a 40 m high longitudinal dune in the central namib desert and a 6 0 m high barchan in the jafurah sand sea of saudi arabia vary with position on the dunes on the longitudinal dune median grain size decreases sorting improves and the grain size distributions are less skewed and more normalized toward the crest though sand at the windward toe is distinct elsewhere on the dune the changes in grain size characteristics are gradual an abrupt change in grain size and sorting near the crest as described by bagnold 1941 pp 226 229 is not well represented on this dune coarse grains remain as a lag on concave slope units and small particles are winnowed from the sand on the steepest windward slopes near the crest avalanching down slipfaces at the crest acts only as a supplementary grading mechanism on the barchan dune median grain size also decreases near the crest but sorting becomes poorer though the grain size distributions are more symmetric and more normalized the dune profile is a gaussian curve with a broad convex zone at the apex upon which topset beds had accreted prior to sampling grain size increases and sorting improves down the dune s slipface however this grading mechanism does not influence sand on the whole dune because variations in wind regime bring about different modes of dune accretion on both dunes height and morphology appear to influence significantly the grain size characteristics

el nino southern oscillation variability from the late cretaceous marca shale of california changes in the possible behavior of el nino southern oscillation enso with global warming have provoked interest in records of enso from past greenhouse climate states the latest cretaceous laminated marca shale of california permits a seasonal scale reconstruction of water column flux events and hence interannual paleoclimate variability the annual flux cycle resembles that of the modern gulf of california with diatoms characteristic of spring upwelling blooms followed by silt and clay and is consistent with the existence of a paleo north american monsoon that brought input of terrigenous sediment during summer storms and precipitation runoff variation is also indicated in the extent of water column oxygenation by differences in lamina preservation time series analysis of interannual variability in terrigenous sediment and diatom flux and in the degree of bioturbation indicates strong periodicities in the quasi biennial 2 1 2 8 yr and low frequency 4 1 6 3 yr bands both characteristic of enso forcing as well as decadal frequencies this evidence for robust late cretaceous enso variability does not support the theory of a permanent el nino in the sense of a continual el nino like state in periods of warmer climate

triton s streaks as windblown dust the encounter of the voyager 2 spacecraft with neptune s satellite triton revealed many dark about 10 20 darker than the adjacent frost surface streaks in triton s southern hemisphere1 resembling the streaks that are due to windblown dust on mars2 it seems therefore that dust transport by winds in triton s tenuous atmosphere is required the main question being the mechanism for raising dust from the surface or sub surface the two obvious candidates are geyser like eruptions and direct lofting by surface winds1 here we show that despite triton s tenuous 16 3 bar atmosphere3 low cohesion grains with diameters of 5 m may be carried into suspension by aeolian surface shear stress given expected geostrophic wind speeds4 of l0ms 1 the wind velocities needed to lift grains as cohesive as those found on earth however are implausibly high for erupting plumes we show that dust settling timescales and expected wind velocities yield streak length scales in good agreement with those observed both candidate mechanisms therefore seem to be consistent with present observations of triton

the spatial distribution of rocks on mars abstract the spatial distribution of rocks exposed at the surface of mars has been mapped using viking infrared thermal mapper irtm observations overall there are no regions on the surface of mars at a scale of 1 1 in latitude and longitude that are rock free the modal value of rock abundance is 6 areal coverage with no areas having more than 30 35 rock cover the model developed to determine rock abundance relates the thermal emission in each of the four surface sensing irtm bands to temperature contrasts within the field of view non unit thermal emissivity due to absorption bands in the surface materials and the absorption and scattering of the outgoing energy by atmospheric dust and water ice each of these effects produce characteristic spectral and diurnal signatures allowing them to be separated the temperature contrasts provide a means to determine both the abundance of exposed rocks and the fine component thermal intertia rock abundance alone does not produce the observed variation in bulk thermal inertia of the surface low inertia fine bright surfaces have fewer rocks exposed than do high inertia coarse dark surfaces rock abundance does not correlate well with the rms slope nor reflectivity determined from delay doppler radar measurements there is however a possible correlation between rms slope determined from continuous wave radar observations dual polarization radar measurements which provide the best radar measure of small scale roughness indicate that the tharsis volcanic region is very rough whereas thermal measurements indicate very few rocks and a covering of dust together these observations suggest an approximately 1 m thick mantle of fines covering a very rough subsurface this fine material may be an aeolian deposit of dust storm fallout valles marineris together with several major channels and chaotic terrains have high rock abundances as does the acidalia planitia basin this observed distribution may reflect the initial deposition of coarse material associated with channel formation syrtis major is unique in having a high inertia but a very low rock abundance together with low radar roughness these observations are consistent with mantling of rocks by sand the observed distribution of rocks and fines indicates that aeolian processes both erosional and depositional play a dominant role in shaping the present martian surface

present wind activity on mars relation to large latitudinally zoned sediment deposits the relation of present martian winds to large latitudinally zoned sediment deposits has been investigated using global wind streak data and mapping of large sand and dust deposits dune sand deposits occur primarily in three latitude belts north polar 74 85 degrees north low latitude 5 degrees north 20 degrees south and south polar 40 80 degrees south comparison with wind streak data shows the high latitude dunes to be in areas of seasonally reversing winds the present winds can form latitudinal dune belts from a variety of initial dune distributions including uniform distribution and a polar source the presence of dune sand within the polar layered deposits the erosional state of the deposits and the present surface wind flow away from the poles indicate that both polar dune concentrations have been derived from erosion of the layered deposits the low latitude dunes are topographically confined in canyons and craters they are probably subject to long term reversal of orientations with climate cycles

palaeoclimatic implications of a storm erosion record from late holocene lake sediments north island new zealand abstract a ca 2250 year storm history has been identified from a high resolution lake sediment record from the east coast of the north island new zealand this event based chronology identifies 340 storms in the pre european record the record is largely one of natural variability without human impacts layers of minerogenic sediment representing the products of individual storm events are clearly visible in lake cores these storm sediment pulses derived mainly from landslides record the frequency and magnitude of storms clusters of pulses identify six periods of high sedimentation and associated erosion before european settlement a d 1878 at least five of these are interpreted as periods of higher rainfall and probably warmer temperatures since historic records show that most large storms are derived from the subtropics tropics most of the storm periods correspond to warm climate intervals previously identified from new zealand and from southern hemisphere palaeoclimatic evidence the mapara 2 period ca 2090 1855 cal yr b p was the stormiest other periods were of shorter duration the mapara 2 period occurred at times of sustained warmth in the tasmanian and chilean tree ring records which might suggest hemispheric warming at this time one storm period burrell which occurred during the historical enso record was at a time of moderately high enso activity three earlier periods also appear to show responses to enso two storm periods correspond to previously proposed new zealand wide periods of increased erosion and sedimentation estimates of palaeo storm rainfalls from relationships between storm rainfall and sediment thickness of historical events suggest that storm pulses ca 12 mm thick represent palaeo storms of ca 450 mm rainfall

martian intracrater splotches occurrence morphology and colors abstract martian intracrater splotches and related streaks are studied with global data on their occurrence and regional data on color and morphology the fraction of craters with splotches is greatest at high latitudes splotch occurrence is not strongly correlated with surface properties such as albedo and thermal inertia except where these correlate with substantial sediment cover large numbers of splotches are or include dunes especially at high southern latitudes color data show that the dune and nondune materials in splotches are part of one related group of materials that may be of similar composition but varying particle sizes the color data also show that some streaks are simply material deflated from splotches and mixed with local plains material while other streaks are more complex and may involve erosion of thin surface layers by material blown from the splotches splotches appear to be trapped eolian sand but probably have been formed by a great variety of mechanisms a large percentage of craters with splotches show evidence of complex histories of sediment deposition and erosion many splotches may be lag deposits from erosion of regional sediment cover present sediment budgets in splotches are not known but there is some evidence for loss of material and no evidence for resupply from outside the craters

evidence for locally derived ultramafic intracrater materials in amazonis planitia mars 1 we studied a dark intracrater feature in amazonis planitia using visible thermal and spectral data from the mars global surveyor mgs thermal emission spectrometer tes mgs mars orbiter camera moc and 2001 mars odyssey thermal emission imaging system ody themis instruments visible and thermal data indicate that there are heterogeneities within the dark feature at meter to kilometer scales and suggest that it represents eroded terrain containing inactive ripple like bed forms possibly armored or indurated as well as loose possibly actively saltating sediment in addition part of the dark intracrater material may be covered with dust either as an optically thin few microns thick layer or as thicker discontinuous patches the thermal properties of the dark material are consistent with a mixture of sand rock and bedrock whereas the rest of the crater floor has thermal characteristics of fine 35 m particulates spectral data indicate that the crater floor is covered by a layer of dust that is spectrally and compositionally similar to the globally homogenized surface dust in other high albedo regions on mars the mineralogy of the dark materials is mafic dominated modally by pyroxene and olivine however unlike other lithologies common in low albedo regions i e surface types i and ii its derived bulk chemistry indicates that it is an ultramafic lithology with the lowest silica content detected on mars to date sheet silicates and glasses are not identified above detection limits and as such the materials do not display evidence for significant chemical weathering the geomorphology and visible distribution of the dark intracrater materials combined with the lack of an obvious source in the region outside the crater suggest they are the product of erosion of a local source

a 2100 year bp record of the pacific decadal oscillation el nino southern oscillation and quasi biennial oscillation in marine production and fluvial input from saanich inlet british columbia exceptional varved sediments of 2100 years bp recovered from saanich inlet have been analysed using high resolution scanning electron microscopy and spectral analysis techniques each varve may contain up to 22 well defined individual laminae which can be attributed to seasonal scale processes sediment flux comprises alternating diatom ooze diatomaceous mud deposited during spring through autumn and a silty clay deposited during winter the latter may be sporadically punctuated by clay rich laminae identification of some 2000 individual consecutive laminae based on fabric and diatom assemblage has allowed the construction of time series data for spectral analysis laminae types analysed include early spring thalassiosira spp late spring early summer skeletonema costatum multiple summer autumn chaetoceros spp diatom oozes and sporadically present clay rich winter flood deposits sub decadal periods have been identified and linked to the quasi biennial oscillation qbo and el nino southern oscillation enso and decadal periods to the pacific decadal oscillation pdo comparison of spectral analysis results with modern analogues suggests associations may exist between early spring thalassiosira spp laminae and stronger la nina events late spring early summer s costatum laminae and el nino events summer autumn chaetoceros spp multiple laminae and negative pacific northwest index pni regimes and sporadically present winter clay rich laminae and pni regimes the average period for an enso cycle was 3 6 years qbo 2 5 years and pdo 14 8 years spectral analysis of the more recent pni record shows similar significant periods of 13 2 3 7 and 2 6 years multi decadal periods recorded include 42 2 and 31 3 years which might suggest multiples of pdo

early holocene decadal scale ocean variability recorded in gulf of california laminated sediments scanning electron microscope examination of holocene laminated sediment from guaymas basin gulf of california resolves up to five depositional events per year each lamina sublamina of an early holocene section of continuously laminated sediment was recorded from backscattered electron imagery photomosaic analysis diatom mat laminae composed predominantly of thalassiothrix longissima are associated with early winter mixed diatom flora laminae mats are probably brought into the gulf with pacific water during the summer concentrated at the surface or at the pycnocline and then rapidly deposited in the early winter as water column stratification breaks down time series analysis of one 300 year section from piston core jpc56 revealed significant periodicities in the deposition of mat laminae at 50 years 11 years and 22 24 years an 50 year cycle in fish populations has been related to changing north pacific ocean atmosphere circulation these pacific wide changes in circulation affect the currents dominant at the mouth of the gulf when the california current is dominant fewer diatom mats are imported into the gulf and when the north equatorial pacific gyre is dominant more are imported the 11 year 22 to 24 year and 50 year cycles are all suggested to be influenced by solar cycles

eolian intracrater deposits on mars physical properties and global distribution abstract an investigation of martian intracrater materials has been made using their thermophysical properties as derived from viking irtm observations over one fourth of all craters larger than 25 km in diameter between 50 s and 50 n have localized deposits of coarse material on the floor which are associated with dark splotches seen visually assuming homogeneous unconsolidated materials the measured thermal inertias of these deposits i 0 003 10 3 to 0 026 10 3 cal cm 2 sec 1 2 k 1 imply effective grain sizes ranging from 0 1 mm to 1 cm with a modal value of 0 9 mm these deposits are coarser and darker than the surrounding terrains and the majority of the martian surface but are not compositionally distinct from materials with similar albedos they occur more frequently in the south in regions of relatively coarse material 0 2 to 2 mm and in relatively dark areas these features most likely formed by entrapment of marginally mobile material which can be transported into but not out of crater depressions by the wind very few have recognizable dune forms those that do have effective grain sizes less than 0 5 mm the majority of the splotch deposits are coarser than the dune forming materials found in the north polar region and inside extreme southern latitude craters and probably form low broad zibar dunes or lag deposits intracrater deposits are noticeably lacking from the interior of the large northern hemisphere low inertia region of arabia 10 s to 30 n 300 to 360 w interpreted to be a sink for suspended dust but do occur around the perimeter of this region this distribution suggests that the intracrater features have been buried in the interior of arabia and that the dust deposit is less extensive at the margins and may currently be expanding the occurrence of regional dust deposits in the north may be related to the maximum wind activity currently occurring in the southern hemisphere and suggests that the location of regional sinks may migrate with time as the solar insolation maximum migrates

a fossil coral perspective on western tropical pacific climate 350 ka 1 the nature of tropical climate variability 350 ka is addressed using 18o and sr ca records from a modern and a fossil coral from vanuatu southwestern tropical pacific ocean modern el nino events at vanuatu produce positive coral 18o and sr ca anomalies similar anomalies observed in the fossil coral records suggest that el nino was operative 350 kyr ago seasonal variations in coral sr ca a sea surface temperature sst proxy have the same amplitude in both corals whereas seasonal 18o variations are smaller in the fossil coral than in the modern coral this is consistent with displacement of the south pacific convergence zone toward the southwest during the boreal summer 350 ka mathematical modeling results preclude warmer sst and higher sss at vanuatu during this time but permit the surface ocean to be 2 c cooler and 0 2 psu fresher than today assessing the potential of variations in late quaternary seawater sr ca remains the largest obstacle to accurately reconstructing tropical sst using pristine fossil corals

north south asymmetry of eolian features in martian polar regions analysis based on crater related wind markers abstract a comparison of crater related wind markers in the north and south polar 40 90 latitude regions of mars has been made on the basis of comprehensive mapping from viking orbiter and mariner 9 images wind streaks show that present wind activity is most effective in both north and south in the southern spring and summer this asymmetry is consistent with the present asymmetry of climate the more massive intracrater dune fields are also oriented with the presently strongest winds this alignment may reflect a long term asymmetry in the effectiveness of northern and southern spring flow because reorientation times far exceed the period of cycles of hemispherical climate asymmetry 51 000 years streaks originating from dark crater splotches indicate that windflow away from the south pole is effective over a larger latitude range than it is in the north this difference may be partly responsible for the contrasting distribution of dune sand in the north and south polar regions

saltation threshold on earth mars and venus new formulations valid for wide ranges of particle diameter and density and gas density are presented for prediction of saltation threshold speed for small particles a low air density wind tunnel was used to extend the range of previous investigations and to separate the effects of reynolds number and interparticle forces of cohesion the new formulations are used to predict saltation threshold for atmospheric conditions on the surface of the earth mars and venus

wind streaks in tharsis and elysium implications for sediment transport by slope winds detailed maps of wind streaks in tharsis and elysium have been compiled from viking orbiter observations spanning one complete martian year the streak pattern is controlled by slope winds on the central volcanoes and on the flanks of the tharsis bulge while the global circulation dominates in elysium dust erosion by downslope winds occurs over much of tharsis and in the vicinity of elysium mons this process is effective even at the low atmospheric pressures found near the summits of the large volcanoes erosional streaks are largely absent in elysium planitia net deposition of dust might have occurred during the period of our observations surface properties such as slope thermal inertia and roughness may influence the efficiency of slope wind production sufficiently to account for the pronounced differences in streak types and patterns present in these two regions

the role of the asian australian monsoon system in the onset time of el nino events abstract based on the time of first occurrence of a significant sea surface temperature anomaly ssta in the nino 3 4 area 5 s 5 n 170 120 w two types of el nino episodes can be identified the spring sp type in which the ssta first increased to greater than 0 5 c in april or may and the summer su type in which this threshold is first reached in july or august composites of the sstas for these two types of events during the period 1950 97 show that the sp su event is generally a stronger weaker warm episode in terms of the ssta amplitude and longer shorter in terms of the period during which the ssta is greater than 0 5 c before the occurrence of both types of el nino episodes the zonal wind anomalies over the western equatorial pacific are always westerly the east asian winter monsoon is also strong the difference between the two types is mainly in the timing of the occurrence of the westerly anomalies for the sp su events these anomalies extend to the date line by january may

unsteady saltation on mars abstract saltation is an important process on mars as it contributes to dust raising bedform dynamics and aeolian abrasion lander measurements and mesoscale meteorological models suggest that winds in the martian atmosphere rarely exceed the fluid threshold value that is necessary to aerodynamically initiate saltation a fact in stark contrast to the existence of dunes and ripples on the planet many of which are in an active state of migration in an attempt to reconcile these observations we perform an unsteady simulation with a simple turbulence model to calculate the saltation transport rate sinusoidal wind variations are imposed on the saltation layer the numerical simulations verify that gusty transport is one of the main manifestations of martian sediment transport events a formula for the saltation transport rate is reported q m u u it p where u and u it are the friction velocity and impact threshold friction velocity the power p varies in the range of 0 7 1 8 on mars and 1 5 on earth depending on the period and amplitude of the gusty inflow wind our results show that the law of martian and terrestrial transport rate are not universal and hence one should be cautious when trying to extrapolate existing terrestrial results to mars

the particle size of martian aeolian dunes the effective particle size of unconsolidated materials on the martian surface can be determined from thermal inertia due to a pore size dependence of thermal conductivity at martian atmospheric pressures because dunes consist of a narrow range of well sorted unconsolidated particles they provide for a test of the relationship between particle size and thermal inertia calculated from midinfrared emission data for the martian surface we use two independent approaches first thermal inertia data indicate that martian dunes have an average particle size of about 500 100 m or medium to coarse sand second we determine expected dune particle sizes from grain trajectory calculations and the particle size transition from suspension to saltation on earth the transition occurs for a grain when the ratio of the terminal fall velocity to the wind friction speed u t is near unity for grains at u t this occurs at about 52 m terrestrial dune sands have a mean of 250 m and are composed entirely of grains 52 m the corresponding martian transition grain size is about 210 m suggesting that martian dunes should be significantly coarser than terrestrial dunes grain saltation path length as a function of particle size also shows that under martian conditions larger grains than on earth will become suspended both approaches indicate that martian dune sand should be coarser than terrestrial dune sand thus while terrestrial dune grains are in the fine to medium sand range the average martian dune sediments are probably medium to coarse sands these results closely match the grain sizes determined from thermal inertia models providing the first direct test of the validity of these models for actual martian surface materials

evidence for stronger el nino southern oscillation enso events in a mid holocene massive coral we present a 47 year long record of sea surface temperature sst derived from sr ca and u ca analysis of a massive porites coral which grew at 4150 calendar years before present b p in vanuatu southwest tropical pacific ocean mean sst is similar in both the modern instrumental record and paleorecord and both exhibit el nino southern oscillation enso frequency sst oscillations however several strong decadal frequency cooling events and a marked modulation of the seasonal sst cycle with power at both enso and decadal frequencies are observed in the paleorecord which are unprecedented in the modern record

historical changes in el nino and la nina characteristics in an ocean reanalysis 1 the variation of el nino southern oscillation enso events from the mid nineteenth century until the beginning of the twenty first century is explored using an ocean reanalysis a comparison of the reanalysis with three sea surface temperature reconstructions shows that the timing of events is similar in all four products however there are important differences in the strength and location of events the difference between the reconstructions is sometimes larger than the difference between the reanalysis and a given reconstruction these differences are larger in the first half of the record a period for which there are relatively sparse observations the reanalysis is used to explore decadal variability and trends in the frequency duration and propagation direction of enso events there is considerable decadal variability of these enso characteristics with the time between events ranging from several months to ten years and the duration of enso varying from 5 to 27 months as has been previously shown for the strength and location of enso there is little overall trend in the characteristics having a three dimensional representation of the ocean from the reanalysis allows exploration of subsurface changes during enso an analysis of subsurface anomalies shows that during enso events the subsurface anomalies are highly correlated with the strength of surface anomalies over the 140 year period overall there is no evidence that there are changes in the strength frequency duration location or direction of propagation of el nino and la nina anomalies caused by global warming during the period from 1871 to 2008

visual and infrared observations of wind streaks on mars abstract estimation of surface properties and physical setting of three common martian wind streak types bright dark and splotch related provides constraints on models of the formation and variability of streaks bright streaks form independently of surface properties other than local topography this is consistent with their formation being due to deposition of atmospheric dust in the lee of topographic features although they are widespread on mars dark streaks are noted as variable only in regions near 30 s latitude and elevations between 3 and 7 km and are associated with dark surfaces that have relatively high thermal inertias splotch related streaks occur at elevations between 0 and 6 km and in regions of relatively high thermal inertia splotch related streaks occur near the boundaries of thermally defined regions such as the south polar cap and other areas of either low or high thermal inertia these thermal conditions are responsible for the production of surface winds which form and modify these streaks the source of sidements which form splotch related streaks varies from dunes to well indurated stratified deposits regional studies of the various types in syrtis major syria planum claritas fossae oxia palus mesogea and pettit craters and noachis confirm that the correlations found at the global level occur at regional scales

the m3 project 2 global distributions of mafic mineral abundances on mars abstract a radiative transfer model was used to reproduce several millions of omega observatoire pour la mineralogie l eau les glaces et l activite spectra representative of igneous terrains of mars this task provided the modal composition and grain sizes at a planetary scale the lithology can be summarized in five mineral maps at km scale we found that the low albedo equatorial regions of the martian surface from 60 s to 30 n are globally dominated by plagioclase with average abundance 50 vol and pyroxenes with total averaged abundance close to 40 vol an evolution of the lcp lcp hcp ratio is observed with time at the global scale suggesting an evolution of the degree of partial melting throughout the martian eras olivine and martian dust are minor components of the modelled terrains the olivine distribution is quite different from the other minerals because it is found on localized areas with abundance reaching 20 vol a statistical approach to classify the pixels of the abundances maps using k means clustering highlighted seven distinct mineral assemblages on the surface this classification illustrates that diverse mineralogical units are found in the noachian and hesperian terrains which suggests the presence of various and complex magmatic processes at a global scale during the two oldest eras the chemical composition was derived from the modal composition maps the omega derived chemical composition is quite consistent with several distinctive geochemical characteristics previously considered as fingerprints of the martian surface a major discrepancy is in regards to the fe content that is significantly smaller than soil and rock analyses from grs and in situ measurements the discrepancy could be partly explained by the assumptions used for the spectral modelling or could also indicate surface alteration rinds

el nino events and their relation to the southern oscillation 1925 1986 relationships among sea surface temperatures ssts at the coast of peru and offshore river discharge in northern peru and sea level pressure at darwin australia during the period 1925 1986 are investigated using time series plots frequency distributions and a simple statistical analysis it is shown that ssts undergo a larger seasonal cycle offshore than at the coast exhibit more interannual variability during the warm than the cool season are positively skewed during much of the year and exhibit greatest month to month persistence during the cool season many but not all episodes of above normal coastal ssts are accompanied by enhanced river discharge in northern peru comparison of the darwin pressure and coastal sst records during the past 60 years shows that el nino events episodes of above normal ssts along the coast of peru have occurred both in advance of and subsequent to major negative swings of the southern oscillation and associated climatic changes in the central equatorial pacific in addition el nino events and negative swings of the southern oscillation have occurred separately hence el nino and the southern oscillation are more loosely coupled than other studies would imply

the generation of synthetic sea surface temperature data for the equatorial pacific ocean abstract synthetic monthly sst anomaly data are constructed using frequency domain analyses of significant principle components derived from reconstructed sst data in the equatorial pacific ocean the model provides insight into the dominant physical processes contained in each component and retains the relevant statistical properties of the original data such as the mean variance and autocorrelation thus numerous sets of synthetic sst anomaly data can be produced for the equatorial pacific that are statistically indistinguishable from the original sst anomaly data the spatial and temporal sst signatures of the biennial intradecadal and decadal pseudoperiodicities are reproduced including their frequency and duration of occurrence specifically the enso warm and cold event signatures recur in the synthetic data at peak return periods of 2 4 3 5 5 0 and 6 4 yr moreover the anticipated return period of an extreme enso event with a maximum sst anomaly magnitude of 1 7 c is approximately every

sand dune materials and polar layered deposits on mars abstract the relationship of dark sand dunes to the polar layered deposits of mars is investigated by mapping the colors and morphologic settings of the dunes in and near the polar deposits in the north polar region the dunes have restricted sources in the layered deposits that are associated with are arcuate scarps 10 50 km in length and

nature and origin of materials exposed in the oxia palus western arabia sinus meridiani region mars abstract mars observer will map physical elemental and mineralogical properties of surface materials a key to understanding the regional variations in crustal composition will be the extent to which in situ debris produced from bedrock can be separated from laterally mixed eolian sediments viking orbiter image and thermal data covering equatorial cratered terrain in western arabia eastern oxia and sinuses sabaeus and meridiani were evaluated to test whether local materials related to bedrock could be identified characterized and mapped crater obliteration models imply that kilometers of debris have been produced locally although obliteration rates for the past few billion years have been less than 8 10 3 m year fluvial and eolian landforms clearly indicate lateral transport and mixing of tens of meters of debris six sets of calibrated violet green and red viking images covering the study area were mosaicked and examined in combination with block abundance and fine component inertias from irtm data three major color thermal units can be discerned bright red dust storm deposits brown materials that are probably indurated and dark less red materials that are probably composed of lithic fragments in the medium sand size range the unit boundaries are independent of bedrock geology and erosional landforms the brightest red material apparently mixes with each of the darker units the presence of dark splotches streaks and dunes associated with large craters in oxia indicates that the dark less red material is also mobile the surficial units exposed over the 6 10 6 km 2 study area are therefore likely to represent mixed eolian deposits predominantly decoupled from the underlying bedrock unraveling the mixtures and assignment of components to local bedrock origins will be a major challenge for mars observer