vortex encounter rates with fixed barometer stations comparison with visual dust devil counts and large eddy simulations abstracta phenomenological model is developed wherein vortices are introduced at random into a virtual arena with specified distributions of diameter core pressure drop longevity and translation speed and the pressure history at a fixed station is generated using an analytic model of vortex structure only a subset of the vortices present are detected as temporary pressure drops and the observed peak pressure drop distribution has a shallower slope than the vortex core pressure drops field studies indicate a detection rate of about two vortex events per day under favorable conditions for a threshold of 0 2 mb 1 mb 1 hpa this encounter rate and the observed falloff of events with increasing pressure drop can be reproduced in the model with approximately 300 vortices per square kilometer per day rather more than the highest visual dust devil counts of approximately 100 devils per square kilometer per day this difference can be reconciled if dust lifting typically only occurs in the field above a

early mis 3 occupation of mochena borago rockshelter southwest ethiopian highlands implications for late pleistocene archaeology paleoenvironments and modern human dispersals abstract between 70 and 50 ka bp anatomically modern humans dispersed across and out of africa to eventually populate all inhabitable continents knowledge of paleoenvironments and human behavioral patterns in africa prior to and during these dispersals is crucial for understanding how and why hunter gatherers were able to adapt rapidly to the new environments they encountered however few well dated sites from this time period are known from the horn of africa one of the purported staging areas for population movements into southern arabia and asia excavations at mochena borago rockshelter situated on the western slopes of a dormant volcano where the sw ethiopian highlands meet the ethiopian rift have yielded the first securely dated archaeological sequence for later periods of the dispersal three major lithostratigraphic groups incorporating occupational episodes have yielded charcoal radiocarbon ages 53 38 ka calbp deeper deposits have been tested but remain undated archaeological assemblages consist mainly of obsidian flaked stone artifacts manufactured from small minimally prepared single to multi platform flake cores radially prepared cores are rare and blade cores are absent small unifacial to bifacial points from non radial cores dominate the earliest shaped tool assemblages and backed pieces first appear by 45 ka calbp by 43 ka calbp scrapers and backed pieces are predominant rather than points however there is little evidence for technological change other than the appearance of bipolar technology mochena borago s archaeological sequence thus cannot be neatly classified as middle stone age later stone age or transitional and calls into question some of the principles by which archaeologists have attempted to classify african toolmaking traditions

characterization of the last deglacial transition in tropical east africa insights from lake albert abstract new biomarker analyses from lake albert east africa spanning 15 9 ka show the most extreme abrupt multi stage climate and environmental shifts during the last deglacial transition of anywhere in africa records of hydroclimate expressed in compound specific d values from terrestrial leaf waxes and a tex86 paleotemperature record support multiple stages of pronounced drying and cooling from 13 8 to 11 5 ka and demonstrate the dynamic behavior of the low latitude tropics during the deglaciation the vegetation response illustrated by compound specific 13c values and fossil pollen records was an expansion of c4 grassland when the region was cool and arid these results advance our understanding of a spatially and temporally complex regional response to global climate forcing suggesting weakening of the indian ocean monsoon at the end of the pleistocene that coincides with a minor decrease in the rate of the atlantic meridional overturning circulation amoc and during a time of stepwise cooling in the northern high latitudes

dust devil speeds directions of motion and general characteristics observed by the mars express high resolution stereo camera abstract a total of 205 dust devils were detected in 23 high resolution stereo camera hrsc images taken between january 2004 and july 2006 with the esa mars express orbiter in which average dust devil heights were 660 m and average diameters were 230 m for the first time dust devil velocities were directly measured from orbit and range from 1 to 59 m s the observed dust devil directions of motion are consistent with data derived from a general circulation model gcm in some respects hrsc dust devil properties agree favorably with data from the nasa mars exploration rover spirit dust devil analyses the spatial distribution of the active dust devils detected by hrsc supports the conjecture that the ascending branch of the hadley circulation is responsible for the increase in dust devil activity especially observed during southern summer between 50 and 60 s latitude combining the dust lifting rate of 19 kg km2 sol derived from the spirit observations with the fewer in number but larger in size dust devils from various other locations observed by hrsc we suggest that dust devils make a significant contribution to the dust entrainment into the atmosphere and to the martian dust cycle

a survey of martian dust devil activity using mars global surveyor mars orbiter camera images 1 a survey of dust devils using the mars global surveyor mgs mars orbiter camera moc wide and narrow angle wa and na images has been undertaken the survey comprises two parts 1 sampling of nine broad regions from september 1997 to july 2001 and 2 a focused seasonal monitoring of variability in the amazonis region an active dust devil site from march 2001 to april 2004 for part 1 dust devils were identified in na and wa images and dust devil tracks were identified in na images great spatial variability in dust devil occurrence is highlighted with amazonis planitia being the most active region examined other active regions included cimmerium sinai and solis numerous dust devil tracks but very few dust devils were observed in casius this may suggest dust devils here occur at local times other than that of the mgs orbit 2 pm alternatively variations in surface properties may affect the ability of dust devils to leave visible tracks the seasonal campaign within amazonis shows a relatively smooth variation of dust devil activity with season peaking in mid northern summer and falling to zero in southern spring and summer this pattern of activity correlates well with the boundary layer maximum depth and hence the vigor of convection global maps of boundary layer depth and surface temperature do not predict that amazonis should be especially active potentially suggesting a role for mesoscale circulations measurement of observed dust devils yields heights of up to 8 km and widths in excess of 0 5 km

orbital monitoring of martian surface changes abstract a history of martian surface changes is documented by a sequence of global mosaics made up of mars global surveyor mars orbiter camera daily color images from 1999 to 2006 together with a single mosaic from the mars reconnaissance orbiter mars color imager in 2009 these observations show that changes in the global albedo patterns of mars take place by a combination of dust storms and strong winds many of the observed surface changes took place along the tracks of seasonally repeating winter dust storms cataloged by wang and richardson 2015 these storms tend to sweep dust towards the equator progressively shifting albedo boundaries and continuing surface changes that began before the arrival of mgs the largest and most conspicuous changes took place during the global dust storm of 2001 my 25 which blanketed syrtis major stripped dust from the tharsis region and injected dust into solis planum high wind speeds but low wind stresses are predicted in syrtis tharsis and solis by the nasa ames gcm frequent changes in these regions show that dust accumulations are quickly removed by stronger winds that are not predicted by the gcm but may result from smaller scale influences such as unresolved topography

environmental change and human occupation of southern ethiopia and northern kenya during the last 20 000 years abstract our understanding of the impact of climate driven environmental change on prehistoric human populations is hampered by the scarcity of continuous paleoenvironmental records in the vicinity of archaeological sites here we compare a continuous paleoclimatic record of the last 20 ka before present from the chew bahir basin southwest ethiopia with the available archaeological record of human presence in the region the correlation of this record with orbitally driven insolation variations suggests a complex nonlinear response of the environment to climate forcing reflected in several long term and short term transitions between wet and dry conditions resulting in abrupt changes between favorable and unfavorable living conditions for humans correlating the archaeological record in the surrounding region of the chew bahir basin presumably including montane and lake marginal refugia for human populations with our climate record suggests a complex interplay between humans and their environment during the last 20 ka the result may contribute to our understanding of how a dynamic environment may have impacted the adaptation and dispersal of early humans in eastern africa

analytical and numerical studies of the beta effect in tropical cyclone motion part i zero mean flow abstract the effect on tropical cyclone motion is studied using an analytical as well as a numerical model in a nondivergent barotropic framework the analytical model and the linear version of the numerical model give essentially the same result the linear effect causes a westward stretching of the model vortex but no significant movement of the vortex center an east west asymmetry in the meridional wind field is also created it is the inclusion of the nonlinear term that produces the northwestward movement of the vortex previously found by other investigators e g kitade 1981 this northwestward movement increases with both the maximum wind speed and the radius of maximum wind in a constant shape vortex a wind maximum is also found to the northeast of the vortex which appears to be consistent with the observational findings of shea and gray this asymmetry plays an important role in the vortex motion

structure and dynamics of the convective boundary layer on mars as inferred from large eddy simulations and remote sensing measurements the structure of the martian convective boundary layer bl is decribed by means of a novel approach involving both modelling and data analysis mars express radio occultation ro temperature profiles are compared to large eddy simulations less performed with the martian mesoscale model the model combines the martian radiative transfer soil and surface layer schemes designed at laboratoire de meteorologie dynamique lmd with the most recent version of the weather research and forecast wrf fully compressible non hydrostatic dynamical core the key roles of the vertical resolution and to lesser extent of the domain horizontal extent have been investigated to ensure the robustness of the les results the dramatic regional variations of the bl depth are quantitatively reproduced by the martian les intense bl dynamics are found to underlie the measured depths up to 9 km vertical speed up to 20 m s 1 heat flux up to 2 7 k m s 1 and turbulent kinetic energy up to 26 m2 s 2 under specific conditions both the model and the measurements show a distinctive positive correlation between surface topography and bl depth our interpretation is that in the tenuous co2 martian near surface environment the daytime bl is to first order controlled by the infrared radiative heating fairly independent of elevation which implies a simple correlation between the bl potential temperature and the inverse pressure pressure effect no prominent pressure effect is in action on earth where sensible heat flux dominates the bl energy budget both ro observations and numerical simulations confirm the terrain following behaviour of near surface temperature on mars induced by the dominant radiative influence the contribution of the martian sensible heat flux is not negligible and results in a given isotherm in the bl being comparatively closer to the ground at higher surface elevation the strong radiative control of the martian convective bl implies a generalised formulation for the bl dimensionless quantities based on this formulation and the variety of simulated bl depths by the les new similarity relationships for the martian convective bl in quasi steady midday conditions are derived rigorous comparisons between the martian and terrestrial bl and fast computations of the mean martian bl turbulent statistics are now made possible by such similarity laws copyright 2010 royal meteorological society

dust devil track survey at elysium planitia mars implications for the insight landing sites abstract the insight interior exploration using seismic investigations geodesy and heat transport robotic lander is scheduled to land in elysium planitia on mars in september 2016 insight will perform the first comprehensive surface based geophysical investigation including seismic measurements knowledge about encounter rates of dust devils with the insight lander are important for two main reasons 1 dust devils will affect the scientific measurements i e wind induced seismic noise and 2 the power supply of the insight lander and instruments is provided by solar arrays and previous landers and rovers on mars were affected by a steady decline in electrical power output due to atmospheric dust deposition on the solar panels long term science operations were only made possible by dust clearing events of the solar arrays caused by wind gusts and dust devils in this study we analyzed dust devil tracks ddts at the final insight landing site region in elysium planitia formation of ddts is caused by the removal of a layer of dust by passing dust devils hence in principle the same process as clearing of dust from solar panels we mapped the number size width and length and orientation of ddts in repeat observations using high resolution imaging science experiment hirise images covering the exact same surface area acquired within a relatively short time span l s 200 consistent with the seasonal reversal in direction of the hadley circulation ddt formation rates vary between 0 002 and 0 08 ddt km 2 sol 1 ddt area formation rates using the measured ddt widths lengths and formation rates are in the range of 0 0003 0 00006 km 2 km 2 sol 1 implying that a given spot on the surface may be cleared of dust only once between 3000 and 16 000 sols i e every 5 24 mars years measured ddt formation rates were used to find a scaling factor to the seasonal dda index and then integrated over the year to estimate a mean annual ddt formation rate of 0 046 ddt km 2 sol 1 this translates into a solar panel clearing recurrence interval estimate of 11 mars years using the mean annual ddt formation rate and the mean ddt width and length from all measured ddts due to several uncertainties this solar panel clearing recurrence interval for the insight landing should be seen as an upper limit estimate

ice dynamical constraints on the existence and impact of subglacial volcanism on west antarctic ice sheet stability 1 subglacial volcanism in west antarctica may play a crucial role in the dynamics and stability of the west antarctic ice sheet wais evidence supporting the existence of an individual subglacial volcanic center mt casertz in the upper catchments of whillans and kamb ice stream wis and kis comes from a comparison of ice sheet modeling results with measured ice velocities lubrication of an area which otherwise should be frozen to its bed is best explained by basal melt water generated in the vicinity of mt casertz the estimated melt water production of mt casertz corresponds to 8 of the total melt water production in the two catchments this would be sufficient to offset basal freezing in the dormant kis relubricating its bed and potentially causing a restart near future volcanic activity changes are speculative but would have far reaching implications on the dynamics and stability of the wais requiring further investigation

measurements of martian dust devil winds with hirise 1 we report wind measurements within martian dust devils observed in plan view from the high resolution imaging science experiment hirise orbiting mars the central color swath of the hirise instrument has three separate charge coupled devices ccds and color filters that observe the surface in rapid cadence active features such as dust devils appear in motion when observed by this region of the instrument our image animations reveal clear circulatory motion within dust devils that is separate from their translational motion across the martian surface both manual and automated tracking of dust devil clouds reveal tangential winds that approach 20 30 m s 1 in some cases these winds are sufficient to induce a 1 decrease in atmospheric pressure within the dust devil core relative to ambient facilitating dust lifting by reducing the threshold wind speed for particle elevation finally radial velocity profiles constructed from our automated measurements test the rankine vortex model for dust devil structure our profiles successfully reveal the solid body rotation component in the interior but fail to conclusively illuminate the profile in the outer regions of the vortex one profile provides evidence for a velocity decrease as a function of r 1 2 instead of r 1 suggestive of surface friction effects however other profiles do not support this observation or do not contain enough measurements to produce meaningful insights

lowland forest collapse and early human impacts at the end of the african humid period at lake edward equatorial east africa in africa the early holocene was characterized by wetter warmer conditions than today followed by rapid aridification at 5 2 ka however a lack of lowland vegetation records has prevented a detailed evaluation of forest response to holocene climate change additionally although modern vegetation communities are linked to human disturbance few studies have addressed how prehistoric human activities helped engineer the character of modern african ecosystems understanding the architecture of lowland and highland forests is important to prevent further degradation from climate land use change we present an 11 000 yr fossil pollen record from lake edward uganda we show that guineo congolian forests dominated the highlands and lowlands in equatorial east africa in the early holocene highlighting the importance of rainfall and temperature in controlling forest communities these forests remained until 5 2 ka when the climate became drier the lacustrine ecosystem response to aridification was abrupt however forest decreased gradually replaced by deciduous woodlands woodlands dominated until after an arid period at 2 ka however forest did not recover increased disturbance indicators and grasses suggest that the arrival of iron age people resulted in the modern fire tolerant vegetation although late holocene climate played a role in vegetation opening the modern ecosystem architecture in east africa is linked to early human activities

ultra high resolution multivariate record and multiscale causal analysis of pridoli late silurian implications for global stratigraphy turnover events and climate biota interactions abstract the upper silurian and especially pridoli epoch is a critical interval for the understanding the evolution of earth s biota since it witnessed series of powerful extinction events global reorganizations of paleocommunities and expansion of new clades which assumed dominance in the subsequent devonian period the stratigraphic record of the eastern part of the silurian baltic basin represents an excellent candidate for the fine scale analysis of paleoecological and paleoceanographic dynamics therefore we presenting here stratigraphic record of the milaiciai 103 core south western lithuania of conodonts brachiopods 13ccarb 18ocarb and a series of various geochemical and geophysical proxies most of which were sampled at a very high resolution 11 ka spanning uppermost ludlow pridoli and the lowermost devonian the analysis revealed that the pridoli was characterized by four distinct long term dynamic states here named i normal pridoli i ii silal negative carbon isotopic excursion and extinction event iii normal pridoli ii and iv klonk positive stable carbon isotopic event and excursion the most significant change in most variables is detected approximately in the middle of the pridoli at the beginning of the delotaxis detorta zone at the recovery after silal event of conodonts and at the onset of collapse of brachiopod communities the analysis of dynamic complexity revealed the strong evidence for the presence of 405 ka metronome milankovitch cycles in the record of 13ccarb which constrains the duration of the pridoli epoch to 4 3 0 2 ma the recurrence plot analyses revealed deterministic coordination between 13ccarband conodont paleocommunity dynamics at all scales finally lead lag analysis using conditional joint recurrence revealed that conodont dynamics as a rule were driven by perturbations in the carbon cycle although silal event interval shown opposite pattern thus confirming the unusual nature of this previously unrecognized coordinated climatic and biotic event

mesoscale linear streaks on mars environments of dust entrainment abstract variable surface albedo features on mars are likely caused by the entrainment and deposition of dust by the wind most discrete markings are associated with topographic forms or with regional slopes that serve to alter the effective wind shear stress on the surface some of the largest variable features here termed mesoscale linear streaks are up to 400 km in length and repeatedly occur in one of the smoothest regions of mars amazonis planitia their orientations and apparent season of variability as observed by viking and mars orbiter cameras indicate linear streak formation by enhanced surface wind stresses during regional or local dust storms and during the initial stages of global dust storms they provide an example of the ability of large scale winds without significant local enhancement to initiate dust motion on mars the sizes and spacing of the linear streaks may be controlled by boundary layer rolls the repetitive formation of these streaks over a span of more than 11 mars years gives one measure of the stability of mars eolian processes

large eddy simulation of stable atmospheric boundary layers with a revised stochastic subgrid model simulations of stable atmospheric boundary layers have been conducted at various stabilities with a revised stochastic backscatter model based on mason and thomson s theoretical and numerical results compared to the previous results of mason and derbyshire there is more turbulence and a deeper boundary layer as was expected from the tendency of the parametrization change to increase the surface stress scatterplots of various local non dimensional quantities against the gradient richardson number are presented which indicate a high degree of collapse to a single local scaling curve agreement of the non dimensional gradients with the surface layer observations is greatly improved by the inclusion of backscatter

abrupt or gradual change point analysis of the late pleistocene holocene climate record from chew bahir southern ethiopia we used a change point analysis on a late pleistocene holocene lake sediment record from the chew bahir basin in the southern ethiopian rift to determine the amplitude and duration of past climate transitions the most dramatic changes occurred over 240 yr from similar to 15 700 to 15 460 yr during the onset of the african humid period ahp and over 990 yr from similar to 4875 to 3885 yr during its protracted termination the ahp was interrupted by a distinct dry period coinciding with the high latitude younger dryas stadial which had an abrupt onset less than similar to 100 yr at similar to 13 260 yr and lasted until similar to 11 730 yr wet dry wet transitions prior to the ahp may reflect the high latitude dansgaard oeschger cycles as indicated by cross correlation of the potassium record with the northgrip ice core record between similar to 45 20 ka these findings may contribute to the debates regarding the amplitude and duration and mechanisms of past climate transitions and their possible influence on the development of early modern human cultures

abrupt onset and termination of the african humid period rapid climate responses to gradual insolation forcing a detailed ca 100 yr resolution and well dated 18 ams 14 c dates to 23 cal ka bp record of latest pleistocene holocene variations in terrigenous eolian sediment deposition at odp site 658c off cap blanc mauritania documents very abrupt large scale changes in subtropical north african climate the terrigenous record exhibits a well defined period of low influx between 14 8 and 5 5 cal ka bp associated with the african humid period when the sahara was nearly completely vegetated and supported numerous perennial lakes an arid interval corresponding to the younger dryas chronozone punctuates this humid period the african humid period has been attributed to a strengthening of the african monsoon due to gradual orbital increases in summer season insolation however the onset and termination of this humid period were very abrupt occurring within decades to centuries both transitions occurred when summer season insolation crossed a nearly identical threshold value which was 4 2 greater than present these abrupt climate responses to gradual insolation forcing require strongly non linear feedback processes and current coupled climate model studies invoke vegetation and ocean temperature feedbacks as candidate mechanisms for the non linear climate sensitivity the african monsoon climate system is thus a low latitude corollary to the bi stable behavior of high latitude deep ocean thermohaline circulation which is similarly capable of rapid and large amplitude climate transitions

wet phases in the sahara sahel region and human migration patterns in north africa the carbon isotopic composition of individual plant leaf waxes a proxy for c3 vs c4 vegetation in a marine sediment core collected from beneath the plume of sahara derived dust in northwest africa reveals three periods during the past 192 000 years when the central sahara sahel contained c3 plants likely trees indicating substantially wetter conditions than at present our data suggest that variability in the strength of atlantic meridional overturning circulation amoc is a main control on vegetation distribution in central north africa and we note expansions of c3 vegetation during the african humid period early holocene and within marine isotope stage mis 3 50 45 ka and mis 5 120 110 ka the wet periods within mis 3 and 5 coincide with major human migration events out of sub saharan africa our results thus suggest that changes in amoc influenced north african climate and at times contributed to amenable conditions in the central sahara sahel allowing humans to cross this otherwise inhospitable region

radio occultation measurements and mgcm simulations of kelvin waves on mars we have derived new results concerning thermal tides on mars from a combination of radio occultation measurements and numerical simulations by a mars general circulation model mgcm this investigation exploits a set of concurrent observations by mars express mex and mars global surveyor mgs in mid 2004 when the season on mars was midspring in the northern hemisphere the mex occultations sampled the atmosphere near the evening terminator at latitudes ranging from 54 n to 15 s the mgs occultations provided complementary coverage near the morning terminator at latitudes of 35 n and 71 s the geopotential field derived from these measurements contains distinctive modulation caused by solar asynchronous thermal tides through careful analysis of the combined observations we characterized two prominent wave modes obtaining direct solutions for some properties such as the amplitude and phase as well as constraints on others such as the period zonal wave number and meridional structure we supplemented these observations with mgcm simulations after evaluating the performance of the mgcm against the measurements we used the validated simulation to deduce the identity of the two tidal modes and to explore their behavior one mode is a semidiurnal kelvin wave with a zonal wave number of 2 sk2 while the other is a diurnal kelvin wave with a zonal wave number of 1 dk1 both modes are known to be close to resonance in the martian atmosphere our observations of the sk2 are more complete and less ambiguous than any previous measurement the well known dk1 is the dominant solar asynchronous tide in the martian atmosphere and our results confirm and extend previous observations by diverse instruments

the depth of the convective boundary layer on mars abstract we are using observations obtained with mars express to explore the structure and dynamics of the martian lower atmosphere we consider a series of radio occultation experiments conducted in may august 2004 when the season on mars was midspring of the northern hemisphere the measurements are widely distributed in latitude and longitude but the local time remained within a narrow range 17 0 17 2 h most of the atmospheric profiles retrieved from these data contain a distinct well mixed convective boundary layer cbl we have accurately determined the depth of the cbl and its spatial variations at fixed local time through analysis of these profiles the cbl extends to a height of 3 10 km above the surface at the season and locations of these measurements its depth at fixed local time is clearly correlated with variations in surface elevation on planetary scales with a weaker dependence on spatial variations in surface temperature in general the cbl is deep 8 10 km where the surface elevation is high as in tharsis montes and syrtis major and shallow 4 6 km where the surface elevation is low as in amazonis and utopia this variability results from the combined effects of conditions near the surface and in the atmosphere above the cbl convection arises from solar heating of the ground and the impact of this heat source on thermal structure is largest where the surface pressure and atmospheric density are smallest at high surface elevations the vertical extent of the cbl is in turn constrained by the static stability of the overlying atmosphere these results greatly reduce the long standing uncertainty concerning the depth of the cbl

mars orbiter camera observations of martian dust devils and their tracks september 1997 to january 2006 and evaluation of theoretical vortex models 1 a multiyear planet wide survey of martian dust devils was conducted using observations from mars global surveyor mars orbiter camera acquired through 21 january 2006 a total of 223 350 images were surveyed and 11 456 dust devils were seen in 0 4 of the images 11 5 in the southern and 88 5 in the northern hemisphere dust devils were observed at latitudes from 71 9 s to 62 2 n over a range of surface albedos am 0 11 0 22 and elevations from hellas 8750 m to arsia mons 17 250 m the light and dark toned streaks created by dust devils were observed from 80 s to 80 n and changed on timescales as short as 1 month at mid to high latitudes seasonal changes in streak patterns contribute to the seasonal wave of darkening observed telescopically from earth dust devils were observed in all seasons in both hemispheres with the exception of ls 202 8 281 5 in the north peak activity occurred during midsummer in each hemisphere five regions in amazonis syria claritas meridiani and gusev were monitored regularly amazonis had the largest dust devils and was the most active planet wide with annual activity occurring from ls 8 5 197 interannual variability resulted from dust storms and planet encircling dust hazes which were observed to initiate and abate dust devil activity there was no evidence suggesting dust devils cause or lead to initiation of dust storms model derived tangential wind speeds of large vortices were 20 m s 1 at 20 m above the surface dust flux calculations suggest that dust devils are a contributor to the background dust opacity observed through northern spring and summer

context camera investigation on board the mars reconnaissance orbiter 1 the context camera ctx on the mars reconnaissance orbiter mro is a facility instrument i e government furnished equipment operated by a science team not responsible for design and fabrication designed built and operated by malin space science systems and the mro mars color imager team marci ctx will 1 provide context images for data acquired by other mro instruments 2 observe features of interest to nasa s mars exploration program e g candidate landing sites and 3 conduct a scientific investigation led by the marci team of geologic geomorphic and meteorological processes on mars ctx consists of a digital electronics assembly a 350 mm f 3 25 schmidt type telescope of catadioptric optical design with a 5 7 field of view providing a 30 km wide swath from 290 km altitude and a 5000 element ccd with a band pass of 500 700 nm and 7 m pixels giving 6 m pixel spatial resolution from mro s nearly circular nearly polar mapping orbit raw data are transferred to the mro spacecraft flight computer for processing e g data compression before transmission to earth the ground data system and operations are based on 9 years of mars global surveyor mars orbiter camera on orbit experience ctx has been allocated 12 of the total mro data return or about 3 terabits for the nominal mission this data volume would cover 9 of mars at 6 m pixel but overlapping images for stereo mosaics and observation of changes and meteorological events will reduce this area ctx acquired its first instrument checkout images of mars on 24 march 2006

martian aeolian features and deposits comparisons with general circulation model results the development of a general circulation model gcm of mars atmosphere allows questions to be addressed concerning the relationships between near surface winds and the distribution of wind related features and deposits predictions of wind surface stress as a function of season and dust optical depth are used to investigate the distribution and orientation of wind streaks yardangs and rock abundance on the surface the occurrence and orientation of bright streaks are well accounted for by the gcm results suggest that bright streaks form during southern hemisphere summer by hadley cell circulation in which dust is raised in the southern hemisphere carried northward at high altitudes then deposited in the wake of craters and other topographic obstacles by the descending hadley cell the reduction in the number of bright streaks southward from 30 n is interpreted to reflect the depletion of dust by near surface winds blowing to the south although the winds responsible for the formation of the dark streaks are not well reproduced in all areas by gcm simulations a band of high wind surface stresses in the southern subtropics corresponding to the latitude band where most of the dark streaks are found are predicted at the height of the dust storm season southern hemisphere summer yardang orientations do not match the gcm simulations for any season their orientation is attributed to either structural control in the rocks such as joint patterns or to a change in wind patterns from the time when the yardangs formed the global distribution of rocks on the surface is correlated well with predicted wind stress particularly during dust storm season the rocky areas are sites of strong winds suggesting that fine material is swept away by the wind leaving rocks and coarser material behind

nanodiamond rich layer across three continents consistent with major cosmic impact at 12 800 cal bp abstracta major cosmic impact event has been proposed at the onset of the younger dryas yd cooling episode at 12 800 150 years before present forming the yd boundary ydb layer distributed over 50 million km2 on four continents in 24 dated stratigraphic sections in 10 countries of the northern hemisphere the ydb layer contains a clearly defined abundance peak in nanodiamonds nds a major cosmic impact proxy observed nd polytypes include cubic diamonds lonsdaleite like crystals and diamond like carbon nanoparticles called n diamond and i carbon the nd abundances in bulk ydb sediments ranged up to 500 ppb mean 200 ppb and that in carbon spherules up to 3700 ppb mean 750 ppb 138 of 205 sediment samples 67 contained no detectable nds isotopic evidence indicates that ydb nds were produced from terrestrial carbon as with other impact diamonds and were not derived from the impactor itself the ydb layer is also marked by abundance peaks in other impact related proxies including

late holocene forest contraction and fragmentation in central africa during the warmer holocene period two major climatic crises affected the central african rainforests the first crisis around 4000 cal yr bp caused the contraction of the forest in favor of savanna expansion at its northern and southern periphery the second crisis around 2500 cal yr bp resulted in major perturbation at the forest core leading to forest disturbance and fragmentation with a rapid expansion of pioneer type vegetation and a marked erosional phase the major driver of these two climatic crises appears to be rapid sea surface temperature variations in the equatorial eastern atlantic which modified the regional atmospheric circulation the change between ca 2500 to 2000 cal yr bp led to a large increase in thunderstorm activity which explains the phase of forest fragmentation ultimately climatic data obtained recently show that the present day major rise in thunderstorms and lightning activity in central africa could result from some kind of solar influence and hence the phase of forest fragmentation between ca 2500 to 2000 cal yr bp may provide a model for the present day global warming related environmental changes in this region

origin and provenance of spherules and magnetic grains at the younger dryas boundary abstract one or more bolide impacts are hypothesized to have triggered the younger dryas cooling at 12 9 ka in support of this hypothesis varying peak abundances of magnetic grains with iridium and magnetic microspherules have been reported at the younger dryas boundary ydb we show that bulk sediment and or magnetic grains microspherules collected from the ydb sites in arizona michigan new mexico new jersey and ohio have 187os 188os ratios 1 0 similar to average upper continental crust 1 3 indicating a terrestrial origin of osmium os in these samples in contrast bulk sediments from ydb sites in belgium and pennsylvania exhibit 187os 188os ratios 1 0 and at face value suggest mixing with extraterrestrial os with 187os 188os of 0 13 however the os concentration in bulk sample and magnetic grains from belgium is 2 8 pg g and 15 pg g respectively much lower than that in average upper continental crust 31 pg g indicating no meteoritic contribution the ydb site in pennsylvania is remarkable in yielding 2 to 5 mm diameter spherules containing minerals such as suessite fe ni silicide that form at temperatures in excess of 2000 c gross texture mineralogy and age of the spherules appear consistent with their formation as ejecta from an impact 12 9 ka ago the 187os 188os ratios of the spherules and their leachates are often low but os in these objects is likely terrestrially derived the rare earth element patterns and sr and nd isotopes of the spherules indicate that their source lies in 1 5 ga quebecia terrain in the grenville province of northeastern north america

the horizontal motion of dust devils on mars derived from crism and ctx hirise observations abstract we derived the horizontal motion speed and direction of dust devils from time delayed mars reconnaissance orbiter mro coordinated image data sets of the compact reconnaissance imaging spectrometer for mars crism to the context camera ctx and or the high resolution imaging science experiment hirise acquired between 2008 and 2011 in total 47 dust devils were observed in 15 regions with diameters ranging from 15 to 280 m with an average diameter of 100 m and heights from 40 to 4400 m horizontal speeds of 44 dust devils range from 4 to 25 ms 1 with average speeds of 12 ms 1 the majority of dust devils were observed in the northern hemisphere 79 mainly in amazonis planitia 67 5 from the northern hemisphere dust devils seasonal occurrence of dust devils in the northern hemisphere is predominant in early and mid spring 76 we compared our measured dust devil horizontal speeds and directions of motion to the monthly climatologies wind speed and direction released in the mars climate database mcd derived from general circulation model gcm predictions there is a broad agreement between dust devil horizontal speeds and mcd wind speed predictions within the planetary boundary layer pbl as well as dust devil directions of motion and mcd predicted wind directions occurring within the pbl comparisons between dust devil horizontal speeds and mcd near surface wind speed predictions at 10 m height above the surface do not correlate well dust devils move about a factor of 2 faster than mcd near surface wind predictions the largest offsets between dust devil motion and mcd predictions were related to three dust devils occurring near the phoenix landing site when the lander was still active the offsets could be explained by a regional weather front passing over the phoenix landing site in general the good agreement between dust devil horizontal speeds and directions of motion and ambient wind speeds and directions predicted within the pbl through gcm show that dust devils on mars move with ambient winds in the pbl hence faster than near surface winds

convective vortices and dust devils at the msl landing site annual variability two hundred fifty two transient drops in atmospheric pressure likely caused by passing convective vortices were detected by the rover environmental monitoring station instrument during the first martian year of the mars science laboratory msl landed mission these events resembled the vortex signatures detected by the previous mars landers pathfinder and phoenix however the msl observations contained fewer pressure drops greater than 1 5 pa and none greater than 3 0 pa apparently these vortices were generally not lifting dust as only one probable dust devil has been observed visually by msl the obvious explanation for this is the smaller number of strong vortices with large central pressure drops since according to arvidson et al 2014 ample dust seems to be present on the surface the annual variation in the number of detected convective vortices followed approximately the variation in dust devil activity dda predicted by the marswrf numerical climate model this result does not prove however that the amount of dust lifted by dust devils would depend linearly on dda as is assumed in several numerical models of the martian atmosphere since dust devils are only the most intense fraction of all convective vortices on mars and the amount of dust that can be lifted by a dust devil depends on its central pressure drop sol to sol variations in the number of vortices were usually small however on 1 martian solar day a sudden increase in vortex activity related to a dust storm front was detected

quantifying the distribution of nanodiamonds in pre younger dryas to recent age deposits along bull creek oklahoma panhandle usa high levels of nanodiamonds nds have been used to support the transformative hypothesis that an extraterrestrial et event comet explosion triggered younger dryas changes in temperature flora and fauna assemblages and human adaptations firestone rb et al 2007 proc natl acad sci usa 104 41 16016 16021 we evaluate this hypothesis by establishing the distribution of nds within the bull creek drainage of the beaver river basin in the oklahoma panhandle the earlier report of an abundance spike of nds in the bull creek i younger dryas boundary soil is confirmed although no pure cubic diamonds were identified the lack of hexagonal nds suggests bull creek i is not near any impact site potential hexagonal nds at bull creek were found to be more consistent with graphene graphane an additional nd spike is found in deposits of late holocene through the modern age indicating nds are not unique to the younger dryas boundary nd distributions do not correlate with depositional environment pedogenesis climate perturbations periods of surface stability or cultural activity

martian dust devil statistics from high resolution large eddy simulations dust devils are one of the key elements in the martian atmospheric circulation in order to examine their statistics we conducted high resolution up to 5 m and wide domain about 20 20 km2 large eddy simulations of the martian daytime convective layer large numbers of dust devils developed spontaneously in the simulations which enabled us to represent a quantitative consideration of martian dust devil frequency distributions we clarify the distributions of size and intensity a topic of debate and conclude that the maximum vertical vorticity of an individual dust devil has an exponential distribution while the radius and circulation have power law distributions a grid refinement experiment shows that the rate parameter of the vorticity distribution and the exponent of the circulation distribution are robust the mode of the size distribution depends on the resolution and it is suggested that the mode is less than 5 m

atmospheric imaging results from the mars exploration rovers spirit and opportunity a visible atmospheric optical depth of 0 9 was measured by the spirit rover at gusev crater and by the opportunity rover at meridiani planum optical depth decreased by about 0 6 to 0 7 per sol through both 90 sol primary missions the vertical distribution of atmospheric dust at gusev crater was consistent with uniform mixing with a measured scale height of 11 56 0 62 kilometers the dust s cross section weighted mean radius was 1 47 0 21 micrometers mm at gusev and 1 52 0 18 mm at meridiani comparison of visible optical depths with 9 mm optical depths shows a visible to infrared optical depth ratio of 2 0 0 2 for comparison with previous monitoring of infrared optical depths

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

tipping points early warning and wishful thinking 1 the causes for and possible predictions of rapid climate changes are poorly understood the most pronounced changes observed beside the glacial terminations are the dansgaard oeschger events present day general circulation climate models simulating glacial conditions are not capable of reproducing these rapid shifts it is thus not known if they are due to bifurcations in the structural stability of the climate or if they are induced by stochastic fluctuations by analyzing a high resolution ice core record we exclude the bifurcation scenario which strongly suggests that they are noise induced and thus have very limited predictability

suspect cubic diamond impact proxy and a suspect lonsdaleite identification the presence of nanometer sized diamonds in purported younger dryas yd boundary dated sediments carbon spherules and greenland ice was cited as evidence of a yd impact event 1 although cubic and hexagonal lonsdaleite diamond have been found in shocked metamorphosed meteorites and are associated with terrestrial impact structures cubic diamonds are well known to occur in terrestrial deposits that have no associations with impact processes for example submicron and smaller cubic diamond crystals have been found recently in carbonaceous spherules isolated in upper soils from various german and belgian sites 2 lacking links to impact structures these diamonds are evidently not products of impact

classifying past climate change in the chew bahir basin southern ethiopia using recurrence quantification analysis the chew bahir drilling project cbdp aims to test possible linkages between climate and evolution in africa through the analysis of sediment cores that have recorded environmental changes in the chew bahir basin in this statistical project we consider the chew bahir palaeolake to be a dynamical system consisting of interactions between its different components such as the waterbody the sediment beneath lake and the organisms living within and around the lake recurrence is a common feature of such dynamical systems with recurring patterns in the state of the system reflecting typical influences identifying and defining these influences contributes significantly to our understanding of the dynamics of the system different recurring changes in precipitation evaporation and wind speed in the chew bahir basin could result in similar but not identical conditions in the lake e g depth and area of the lake alkalinity and salinity of the lake water species assemblages in the water body and diagenesis in the sediments recurrence plots rps are graphic displays of such recurring states within a system measures of complexity were subsequently introduced to complement the visual inspection of recurrence plots and provide quantitative descriptions for use in recurrence quantification analysis rqa we present and discuss herein results from an rqa on the environmental record from six short 17 m sediment cores collected during the cbdp spanning the last 45 kyrs the different types of variability and transitions in these records were classified to improve our understanding of the response of the biosphere to climate change and especially the response of humans in the area

the mars regional atmospheric modeling system model description and selected simulations the mars regional atmospheric modeling system mrams is introduced and selected model results are presented and compared with landed meteorological data when possible mrams is descended from a nonhydrostatic earth mesoscale and cloud scale model that is widely used for forecasting weather and simulating atmospheric systems over complex terrain mesoscale models such as mrams are ideal tools for making use of the high resolution data sets arriving from mars global surveyor experiments simulation of the mars pathfinder mpf landing site at lsd 142 using 1 2 degree mars orbiter laser altimeter mola derived topography and thermal emission spectrometer thermal inertia is shown to be in good agreement with observed near surface temperature pressure and wind direction simulations of topographically induced thermal circulations and mountain induced gravity waves are shown to be consistent with theory and earlier studies that tie large amplitude mountain waves to strong winds capable of producing dust streaks and local dust lifting events a large eddy simulation of the convective boundary layer provides estimates of vertical profiles of heat flux momentum flux turbulent kinetic energy and vertical velocity variance the model results suggest that the martian atmosphere is roughly two to three times more turbulent than the terrestrial atmosphere during the afternoon but fluxes are roughly an order of magnitude smaller due to the lower density dust devillike circulations are also predicted in the large eddy simulation finally a simulation that examines atmosphere surface interactions near big crater is discussed predicted surface wind stress patterns are consistent with aeolian processes inferred through mars orbiter camera imagery of big crater located near the mpf landing site c 2001 academic press

comprehensive analysis of nanodiamond evidence relating to the younger dryas impact hypothesis during the end of the last glacial period in the northern hemisphere near 12 9k cal a bp deglacial warming of the bolling allerod interstadial ceased abruptly and the climate returned to glacial conditions for an interval of about 1300 years known as the younger dryas stadial the younger dryas impact hypothesis proposes that the onset of the younger dryas climate reversal pleistocene megafaunal extinctions and disappearance of the clovis paleoindian lithic technology were coeval and caused by continent wide catastrophic effects of impact bolide events in north america while there are no known impact structures dated to the younger dryas onset physical evidence of the impact bolide events is argued to be present in sediments spanning several continents at stratigraphic levels inferred to date to the bolling allerod younger dryas boundary ydb reports of nanometer to submicron sized diamonds in ydb sediments in particular the rare 2h hexagonal polytype of diamond lonsdaleite have been presented as strong evidence for shock processing of crustal materials we review the available data on diamonds in sediments and provide new data we find no evidence for lonsdaleite in ydb sediments and find no evidence of a spike in nanodiamond concentration at the ydb layer to support the impact hypothesis

apparent thermal inertia and the surface heterogeneity of mars abstract thermal inertia derivation techniques generally assume that surface properties are uniform at horizontal scales below the footprint of the observing instrument and to depths of several decimeters consequently surfaces with horizontal or vertical heterogeneity may yield apparent thermal inertia which varies with time of day and season to investigate these temporal variations we processed three mars years of mars global surveyor thermal emission spectrometer observations and produced global nightside and dayside seasonal maps of apparent thermal inertia these maps show broad regions with diurnal and seasonal differences up to 200 j m 2 k 1 s 1 2 at mid latitudes 60 s to 60 n and 600 j m 2 k 1 s 1 2 or greater in the polar regions we compared the seasonal mapping results with modeled apparent thermal inertia and created new maps of surface heterogeneity at 5 resolution delineating regions that have thermal characteristics consistent with horizontal mixtures or layers of two materials the thermal behavior of most regions on mars appears to be dominated by layering with upper layers of higher thermal inertia e g duricrusts or desert pavements over fines prevailing in mid latitudes and upper layers of lower thermal inertia e g dust covered rock soils with an ice table at shallow depths prevailing in polar regions less common are regions dominated by horizontal mixtures such as those containing differing proportions of rocks sand dust and duricrust or surfaces with divergent local slopes other regions show thermal behavior that is more complex and not well represented by two component surface models these results have important implications for mars surface geology climate modeling landing site selection and other endeavors that employ thermal inertia as a tool for characterizing surface properties

dust devils on mars observed by the high resolution stereo camera fourteen active dust devils were observed by the high resolution stereo camera hrsc on mars express which enable the first analysis of the forward speed of dust devils on mars determined from orbit results show speeds on the order of 20 m s which compares favorably with values of the wind profiles estimated from the martian climate database for higher altitudes smaller dust devils of 1 km height and very small diameters were found moving only at 1 5 to 6 0 m s in agreement with surface wind speeds

thermal structure of the atmospheric boundary layer on mars based on mini tes observations this paper presents and discusses the vertical profiles of the potential temperature in the martian boundary layer the profiles were remotely sensed from on board the spirit mars exploration rover during the first 702 sols of its operation in 2004 2005 the rover carried the miniature thermal emission spectrometer mini tes which allowed it to retrieve temperature profiles up to a level 2 km above the ground surface the data analyzed here permit a reconstruction of the diurnal and seasonal structure of the lower part of the martian convective boundary layer an evaluation of the boundary layer depth and a computation of the temperature heat flux

unveiling non stationary coupling between amazon and ocean during recent extreme events the interplay between extreme events in the amazon s precipitation and the anomaly in the temperature of the surrounding oceans is not fully understood especially its causal relations in this paper we investigate the climatic interaction between these regions from 1999 until 2012 using modern tools of complex system science we identify the time scale of the coupling quantitatively and unveil the non stationary influence of the ocean s temperature the findings show consistently the distinctions between the coupling in the recent major extreme events in amazonia such as the two droughts that happened in 2005 and 2010 and the three floods during 1999 2009 and 2012 interestingly the results also reveal the influence over the anomalous precipitation of southwest amazon has become increasingly lagged the analysis can shed light on the underlying dynamics of the climate network system and consequently can improve predictions of extreme rainfall events

evidence from central mexico supporting the younger dryas extraterrestrial impact hypothesis we report the discovery in lake cuitzeo in central mexico of a black carbon rich lacustrine layer containing nanodiamonds microspherules and other unusual materials that date to the early younger dryas and are interpreted to result from an extraterrestrial impact these proxies were found in a 27 m long core as part of an interdisciplinary effort to extract a paleoclimate record back through the previous interglacial our attention focused early on an anomalous 10 cm thick carbon rich layer at a depth of 2 8 m that dates to 12 9 ka and coincides with a suite of anomalous coeval environmental and biotic changes independently recognized in other regional lake sequences collectively these changes have produced the most distinctive boundary layer in the late quaternary record this layer contains a diverse abundant assemblage of impact related markers including nanodiamonds carbon spherules and magnetic spherules with rapid melting quenching textures all reaching synchronous peaks immediately beneath a layer containing the largest peak of charcoal in the core analyses by multiple methods demonstrate the presence of three allotropes of nanodiamond n diamond i carbon and hexagonal nanodiamond lonsdaleite in order of estimated relative abundance this nanodiamond rich layer is consistent with the younger dryas boundary layer found at numerous sites across north america greenland and western europe we have examined multiple hypotheses to account for these observations and find the evidence cannot be explained by any known terrestrial mechanism it is however consistent with the younger dryas boundary impact hypothesis postulating a major extraterrestrial impact involving multiple airburst s and and or ground impact s at 12 9 ka

the origin evolution and trajectory of large dust storms on mars during mars years 24 30 1999 2011 abstract mars daily global maps mdgm derived from the mars global surveyor mgs mars orbiter camera moc and mars reconnaissance orbiter mro mars color imager marci are used to study the distribution and evolution of large dust storms over the period from mars years 24 30 1999 2001 large storms are defined here as discrete dust events visible in image sequences extending over at least 5 sols mars days and where the dust covers areas beyond the origination region a total of 65 large dust storms meeting these criteria are identified during the observational period and all are observed during the l s 135 30 seasonal window dust storms originating in the northern and southern hemispheres appear to form two distinct families all but two of the storms originating in the northern hemisphere are observed in two seasonal windows at l s 180 240 and l s 305 350 while all but two of those originating in the southern hemisphere are observed during l s 135 245 none of the large dust storms originating in the northern hemisphere are observed to develop to global scale but some of them develop into large regional storms with peak area 1 10 7 km 2 and duration on the order of several weeks in comparison large dust storms originating in the southern hemisphere are typically much smaller except notably in the two cases that expanded to global scale the 2001 and 2007 global storms distinct locations of preferred storm origination emerge from the dust storm image sequences including acidalia utopia arcadia and hellas a route trajectory graph for the observed sequences is provided the routes are highly asymmetric between the two hemispheres in the south for non global dust storms the main routes are primarily oriented eastwest whereas in the north the routes are primarily north south and zonally concentrated into meridional channels in a few impressive cases storms originating in the northern hemisphere are observed to flush through acidalia and utopia across the equator and then branch in the low and mid southern latitudes the origin of the 2007 global dust storm is ambiguous from the imaging data immediately prior to the global storm a dust storm sequence from chryse is identified this storm s connection to the explosive expansion observed to start from noachis west hellas is unclear due to image coverage this paper further identifies and describes three different styles of dust storm development which we refer to as consecutive dust storms sequential activation and merging the evolution of a given dust storm sequence can exhibit different combinations of these growth styles at different stages of development dust storm sequences can overlap in time which makes them good candidate to grow into larger scale

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

martian dust storms 1999 mars orbiter camera observations the mars orbiter camera on board the mars global surveyor from march 9 1999 ls 107 where ls is the areocentric longitude of the sun measured in degrees from mars northern spring equinox to december 31 1999 ls 274 has obtained 7 5 km pixel 1 daily global maps of the martian surface in two wavelength bands blue 400 450 nm and red 575 625 nm visual inspection of these maps during the 1999 dust storm season has resulted in the detection of 783 dust storms ranging in size from local 102 km2 to regional 1 6 106 km2 no global storms were observed the difference in the numbers of dust storms occurring in the two hemispheres north 343 south 440 was not statistically significant fifty percent of the regional size dust storms formed as a result of the merger of two or more smaller local storms the regional storms from ls 207 to ls 223 were observed to move from the northern hemisphere into the southern hemisphere between 30 w and 50 w longitude this cross equatorial transport of dust suggests the location of the low lying southward flowing branch of the hadley circulation observations show that dust storms occur in several regions on mars at the two polar cap edges at the base of high elevation regions in the northern hemisphere near the polar hood during northern fall and at mid latitudes in both hemispheres specific regions such as solis planum and hesperia which were regions of significant dust activity in the past showed almost no dust storm activity in 1999 suggesting that regional dust sources are variable over a 20 year time frame one region of exceptional activity not noted previously was the arcadia amazonis border however other regions such as near elysium mons acidalia chryse hellas noachis argyre cimmeria and sirenum again were active dust storm regions relative dust opacities were modeled for 117 red wavelength events and ranged from 0 54 diffuse haze to 2 13 concentrated local events from the dust opacities we estimated the north polar sedimentation rate to be 6 0 10 10 4 g cm 2 yr 1 a factor of 40 smaller than previous estimates from the two 1977 global dust storms pollack et al 1979 along with the global dust mass loading 2 6 4 0 10 4 g cm 2 and cross equatorial dust mass loading 3 6 10 4 g cm 2 the 1999 cross equatorial mass dust loading suggests that the southern hemisphere subtropical latitudes require at least 2 3 martian years to replenish their dust sources before global storms can form

comparing modern and pleistocene enso like influences in nw argentina using nonlinear time series analysis methods higher variability in rainfall and river discharge could be of major importance in landslide generation in the northwestern argentine andes annual layered varved deposits of a landslide dammed lake in the santa maria basin 26 s 66 w with an age of 30 000 14c years provide an archive of precipitation variability during this time the comparison of these data with present day rainfall observations tests the hypothesis that increased rainfall variability played a major role in landslide generation a potential cause of such variability is the el nino southern oscillation enso the causal link between enso and local rainfall is quantified by using a new method of nonlinear data analysis the quantitative analysis of cross recurrence plots crp this method seeks similarities in the dynamics of two different processes such as an ocean atmosphere oscillation and local rainfall our analysis reveals significant similarities in the statistics of both modern and palaeo precipitation data the similarities in the data suggest that an enso like influence on local rainfall was present at around 30 000 14c years ago increased rainfall which was inferred from a lake balance modeling in a previous study together with enso like cyclicities could help to explain the clustering of landslides at around 30 000 14c years ago

shock synthesized hexagonal diamonds in younger dryas boundary sediments the long standing controversy regarding the late pleistocene megafaunal extinctions in north america has been invigorated by a hypothesis implicating a cosmic impact at the llerod younger dryas boundary or ydb 12 900 100 cal bp or 10 900 100 14c years abrupt ecosystem disruption caused by this event may have triggered the megafaunal extinctions along with reductions in other animal populations including humans the hypothesis remains controversial due to absence of shocked minerals tektites and impact craters here we report the presence of shock synthesized hexagonal nanodiamonds lonsdaleite in ydb sediments dating to 12 950 50 cal bp at arlington canyon santa rosa island california lonsdaleite is known on earth only in meteorites and impact craters and its presence strongly supports a cosmic impact event further strengthened by its co occurrence with other nanometer sized diamond polymorphs n diamonds and cubics these shock synthesized diamonds are also associated with proxies indicating major biomass burning charcoal carbon spherules and soot this biomass burning at the younger dryas yd onset is regional in extent based on evidence from adjacent santa barbara basin and coeval with broader continent wide biomass burning biomass burning also coincides with abrupt sediment mass wasting and ecological disruption and the last known occurrence of pygmy mammoths mammuthus exilis on the channel islands correlating with broader animal extinctions throughout north america the only previously known co occurrence of nanodiamonds soot and extinction is the cretaceous tertiary k t impact layer these data are consistent with abrupt ecosystem change and megafaunal extinction possibly triggered by a cosmic impact over north america at 12 900 100 cal bp

observational evidence of a suppressed planetary boundary layer in northern gale crater mars as seen by the navcam instrument onboard the mars science laboratory rover abstract the navigation cameras navcam of the mars science laboratory rover curiosity have been used to examine two aspects of the planetary boundary layer vertical dust distribution and dust devil frequency the vertical distribution of dust may be obtained by using observations of the distant crater rim to derive a line of sight optical depth within gale crater and comparing this optical depth to column optical depths obtained using mastcam observations of the solar disc the line of sight method consistently produces lower extinctions within the crater compared to the bulk atmosphere this suggests a relatively stable atmosphere in which dust may settle out leaving the air within the crater clearer than air above and explains the correlation in observed column opacity between the floor of gale crater and the higher elevation meridiani planum in the case of dust devils despite an extensive campaign only one optically thick vortex 1 5 0 5 10 3 was observed compared to 149 pressure events 0 5 pa observed in rems pressure data correcting for temporal coverage by rems and geographic coverage by navcam still suggests 104 vortices should have been viewable suggesting that most vortices are dustless additionally the most intense pressure excursions observed on other landing sites pressure drop 2 5 pa are lacking from the observations by the rems instrument taken together these observations are consistent with pre landing circulation modeling of the crater showing a suppressed shallow boundary layer they are further consistent with geological observations of dust that suggests the northern portion of the crater is a sink for dust in the current era

kilometer scale roughness of mars results from mola data analysis the mars orbiter laser altimeter mola data are used to characterize the kilometer scale surface roughness of mars the median absolute value of the differential slope at a given baseline is proposed as a data derived measure of the surface roughness at this scale study of the scale dependence of roughness for the smoothest terrains gives an independent estimate of 20 cm for mola ranging accuracy the baseline lengths from 0 6 to 20 km are used and kilometer scale roughness is mapped for the entire surface the maps show that different geological units have distinctive roughness characteristics scale dependence of roughness for a number of geological units is presented and discussed the southern polar cap is rougher than the northern at kilometer and subkilometer scale which suggests differences in the sublimation condensation balance the vastitas borealis formation has a distinctive 3 km scale background surface topography which suggests a nonvolcanic origin for its upper layer young volcanic plains in amazonis planitia and the eastern part of elysium planitia are very similar to each other in their roughness characteristics and differ from other volcanic plains on mars which suggests a distinctive eruption style there are systematic latitudinal variations of roughness in both the southern highlands and the northern lowlands terrains at high latitude are smoother at short baselines the characteristic vertical scale related to this difference is several meters processes that could be responsible for formation of this trend include creep of ice rich near surface material at high latitudes treatment of the surface with repetitive deposition and sublimation of seasonal frost climate controlled deposition and or cementation of dust at high latitudes and repetitive sublimation and accumulation of subsurface ice at low latitudes with climate variations all mechanisms of origin could operate more effectively under different climate conditions relevant morphological observations favor mechanisms involving deposition of smooth blankets at high latitudes

dust devil height and spacing with relation to the martian planetary boundary layer thickness abstract in most remote and unmonitored places little is known about the characteristics of daytime turbulent activity few processes render the optically transparent atmospheres of earth and mars visible put more plainly without clever instruments it is difficult to see the unseen to address this we present a pilot study of images of martian dust devils dds testing the hypothesis that dd height and spacing correlates with the thickness of the planetary boundary layer pbl h the survey includes context camera ctx images from a 580 590 km 2 area 196 208 e 30 40 n in northern amazonis planitia spanning 3 6 mars years my from l s 134 55 my 28 13 november 2006 to l s 358 5 my 31 28 july 2013 dd activity follows a repeatable seasonal pattern similar to that found in previous surveys with a distinct on season during local summer beginning shortly before the northern spring equinox l s 0 and lasting until just after the northern fall equinox l s 180 dd heights measured from shadow lengths varied considerably with median values peaking at local midsummer modeled pbl heights constrained by those measured from radio occultation data follow a similar seasonal trend and correlation of the two suggests that the martian pbl thickness is approximately 5 times the median dd height these results compare favorably to the limited terrestrial data available dd spacing was measured using nearest neighbor statistics following the assumption that because convection cell widths have been measured to be 1 2 0 2 h willis g e deardorff j w 1979 j geophys res 84 c1 295 302 a preference for dd formation at vertices of convection cells intersections could be used to estimate the pbl height during local spring and summer the dd average nearest neighbor ann ranged from 1 to 2 h indicating that dd spacing does indeed correlate with pbl height however this result is complicated by two factors 1 convection cell spacing estimates indicate that the observed dd distributions undersample the possible grid of cell vertices in each ctx image and 2 comparison of the ann with a random distribution shows that the most closely spaced dd distributions exhibit some clustering we propose that this clustering demonstrates that many of the observed dds are located along convection cell walls in addition to cell vertices

abrupt change in tropical african climate linked to the bipolar seesaw over the past 55 000 years 1 the tropics play a major role in global climate dynamics and are vulnerable to future climate change we present a record of east african climate since 55 ka preserved in lake malawi sediments that indicates rapid shifts between discrete climate modes related to abrupt warming d o events observed in greenland although the timing of the malawi events cannot be determined exactly our age model implies that they occur prior to their greenland counterparts consistent with southward excursions of the intertropical convergence zone during greenland stadials the magnitude of each of the events recorded in malawi sediments corresponds to the scale of the subsequent greenland warming this suggests that a tropical component of climate sets a template for abrupt high northern latitude climate fluctuations associated with the bipolar seesaw

a global perspective on last glacial maximum to holocene climate change while the abrupt climate events of the last deglaciation are well defined in ice core records from the polar regions of both hemispheres their manifestation elsewhere is less well constrained here we compile 104 high resolution paleoclimate records to characterize the timing and spatial pattern of climate change during the last deglaciation this compilation indicates relatively concurrent timing of the last glacial maximum lgm peak glacial conditions and the altithermal peak interglacial conditions in the northern 22 1 4 3 ka and 8 0 3 2 ka and southern 22 3 3 6 ka and 7 4 3 7 ka hemispheres suggesting the hemispheres were synchronized by greenhouse gases local insolation and or northern hemisphere induced ocean circulation changes the magnitude of the glacialeinterglacial temperature change increases with latitude reflecting the polar amplification of climate change with a likely minimum global mean cooling of ww4 9 c during the lgm relative to the altithermal empirical orthogonal function eof analysis of 71 records spanning 19e11 ka indicates that two modes explain 72 of deglacial climate variability eof1 61 of variance shows a globally near uniform pattern with its principal component pc1 strongly correlated with changes in atmospheric co2 e of2 11 of variance exhibits a bipolar seesaw pattern between the hemispheres with its principal component pc2 resembling changes in atlantic meridional overturning circulation strength eof analysis of 90 records from 15 to 11 ka indicates that northern and southern modes of climate variability characterize the younger dryas bolling allerod interval these modes dominate at the higher latitudes of each hemisphere and exhibit a complex interaction in the tropics the magnitude of the younger dryas climate anomaly cooler drier increases with latitude in the northern hemisphere with an opposite pattern warmer wetter in the southern hemisphere reflecting a general bipolar seesaw climate response global mean temperature decreased by w0 6 c during the younger dryas therefore our analysis supports the paradigm that while the younger dryas was a period of global climate change it was not a major global cooling event but rather a manifestation of the bipolar seesaw driven by a reduction in atlantic meridional overturning circulation strength

towards an understanding of climate proxy formation in the chew bahir basin southern ethiopian rift abstract deciphering paleoclimate from lake sediments is a challenge due to the complex relationship between climate parameters and sediment composition here we show the links between potassium k concentrations in the sediments of the chew bahir basin in the southern ethiopian rift and fluctuations in the catchment precipitation evaporation balance our micro x ray fluorescence and x ray diffraction results suggest that the most likely process linking climate with potassium concentrations is the authigenic illitization of smectites during episodes of higher alkalinity and salinity in the closed basin lake due to a drier climate whole rock and clay size fraction analyses suggest that illitization of the chew bahir clay minerals with increasing evaporation is enhanced by octahedral al to mg substitution in the clay minerals with the resulting layer charge increase facilitating potassium fixation linking mineralogy with geochemistry shows the links between hydroclimatic control process and formation of the chew bahir k patterns in the context of well known and widely documented eastern african climate fluctuations over the last 45 000 years these results indicate characteristic mineral alteration patterns associated with orbitally controlled wet dry cycles such as the african humid period 15 5 ka or high latitude controlled climate events such as the younger dryas 12 8 11 6 ka chronozone determining the impact of authigenic mineral alteration on the chew bahir records enables the interpretation of the previously established xrf derived aridity proxy k and provides a better paleohydrological understanding of complex climate proxy formation

climatic change recorded in the sediments of the chew bahir basin southern ethiopia during the last 45 000 years abstract east african paleoenvironments are highly variable marked by extreme fluctuations in moisture availability which has far reaching implications for the origin evolution and dispersal of homo sapiens in and beyond the region this paper presents results from a pilot core from the chew bahir basin in southern ethiopia that records the climatic history of the past 45 ka with emphasis on the african humid period ahp 15 5 ka calbp geochemical physical and biological indicators show that chew bahir responded to climatic fluctuations on millennial to centennial timescales and to the precessional cycle since the last glacial maximum potassium content of the sediment appears to be a reliable proxy for aridity showing that chew bahir reacted to the insolation controlled humidity increase of the ahp with a remarkably abrupt onset and a gradual termination framing a sharply defined arid phase 12 8 11 6 ka calbp corresponding to the younger dryas chronozone the chew bahir record correlates well with low and high latitude paleoclimate records demonstrating that the site responded to regional and global climate changes

dust devils on mars columnar cone shaped and funnel shaped clouds rising 1 to 6 kilometers above the surface of mars have been identified in viking orbiter images they are interpreted as dust devils confirming predictions of their occurrence on mars and giving evidence of a specific form of dust entrainment

reply to blaauw et al boslough daulton gill et al and hardiman et al younger dryas impact proxies in lake cuitzeo mexico blaauw et al 1 take issue with our age depth model for the cuitzeo core they state that no offset for our accelerator mass spectrometry ams 14c dates was quantified that our identification of the cieneguillas tephra is doubtful that we used an outdated calibration model and they object to our rejection of six ams dates in the anomalous zone

initial results from radio occultation measurements with mars global surveyor a series of radio occultation experiments conducted with mars global surveyor in early 1998 has yielded 88 vertical profiles of the neutral atmosphere the measurements cover latitudes of 29 n to 64 s and local times from 0600 through midnight to 1800 during early summer in the southern hemisphere ls 264 308 retrieved profiles of pressure and temperature versus radius and geopotential extend from the surface to the 10 pa pressure level near surface uncertainties in temperature and pressure are about 1 k and 2 pa respectively far smaller than in previous radio occultation measurements at mars the profiles resolve the radiative convective boundary layer adjacent to the surface and also reveal gravity waves particularly at northern and equatorial latitudes which appear to be breaking in some cases distinctive meridional gradients of pressure and temperature indicate the presence of a low altitude westerly jet at latitudes of 15 30 s at southern summer solstice this jet appears in predictions of general circulation models in connection with the strong seasonal cross equatorial hadley circulation the pressure gradient at 2 km altitude implies a wind speed of 33 m s 1 stronger than predicted which may help explain the occurrence of numerous local dust storms within this latitude band in late southern spring these measurements also characterize the response of the atmosphere to stationary thermal forcing at midsouthern latitudes where high terrain south of tharsis and low terrain in hellas planitia produce large zonal temperature variations in the lowest scale height above the surface pressure measured at constant geopotential decreases at an average rate of 0 13 per degree ls due primarily to condensation of co2 at the north pole

radio science investigations with mars observer mars observer radio science investigations focus on two major areas of study the gravity field and the atmosphere of mars measurement accuracies expressed as an equivalent spacecraft velocity are expected to be of the order of 100 m s for both types of investigations from use of an improved radio transponder for two way spacecraft tracking and a highly stable on board oscillator for atmospheric occultation measurements planned gravity investigations include a combination of classical and modern elements a spherical harmonic or equivalent field model of degree and order in the range 30 50 will be obtained while interpretation will be in terms of internal stress and density models for the planet using the topography to be obtained from the mars observer laser altimeter atmospheric investigations will emphasize precision measurement of the thermal structure and dynamics in the polar regions which are regularly accessible as a result of the highly inclined orbit studies based on the measurements will include polar processes cycling of the atmosphere between the poles traveling baroclinic disturbances small scale waves and turbulence the planetary boundary layer and possibly the variability and altitude of the ionosphere as the radio occultation is insensitive to dust in the atmosphere per se and measures only the resulting change in thermal structure it is expected that the radio technique can contribute to understanding of dust storm phenomena mutual observations of the atmosphere by means of radio occultation and by the pressure modulator infrared radiometer and the thermal emission spectrometer are expected to strengthen the reliability and accuracy of all three investigations

the high resolution imaging science experiment hirise during mro s primary science phase psp the high resolution imaging science experiment hirise on the mars reconnaissance orbiter mro acquired 8 terapixels of data in 9137 images of mars between october 2006 and december 2008 covering 0 55 of the surface images are typically 5 6 km wide with 3 color coverage over the central 20 of the swath and their scales usually range from 25 to 60 cm pixel nine hundred and sixty stereo pairs were acquired and more than 50 digital terrain models dtms completed these data have led to some of the most significant science results new methods to measure and correct distortions due to pointing jitter facilitate topographic and change detection studies at sub meter scales recent results address noachian bedrock stratigraphy fluvially deposited fans in craters and in or near valles marineris groundwater flow in fractures and porous media quasi periodic layering in polar and non polar deposits tectonic history of west candor chasma geometry of clay rich deposits near and within mawrth vallis dynamics of flood lavas in the cerberus palus region evidence for pyroclastic deposits columnar jointing in lava flows recent collapse pits evidence for water in well preserved impact craters newly discovered large rayed craters and glacial and periglacial processes of particular interest are ongoing processes such as those driven by the wind impact cratering avalanches of dust and or frost relatively bright deposits on steep gullied slopes and the dynamic seasonal processes over polar regions hirise has acquired hundreds of large images of past present and potential future landing sites and has contributed to scientific and engineering studies of those sites warming the focal plane electronics prior to imaging has mitigated an instrument anomaly that produces bad data under cold operating conditions