diviner lunar radiometer observations of cold traps in the moon s south polar region diviner lunar radiometer experiment surface temperature maps reveal the existence of widespread surface and near surface cryogenic regions that extend beyond the boundaries of persistent shadow the lunar crater observation and sensing satellite lcross struck one of the coldest of these regions where subsurface temperatures are estimated to be 38 kelvin large areas of the lunar polar regions are currently cold enough to cold trap water ice as well as a range of both more volatile and less volatile species the diverse mixture of water and high volatility compounds detected in the lcross ejecta plume is strong evidence for the impact delivery and cold trapping of volatiles derived from primitive outer solar system bodies

the importance of secondary cratering to age constraints on planetary surfaces small craters less than one kilometer diameter can be primary craters produced by impact of interplanetary debris or they can be secondary craters produced by fallback of high velocity ejecta blocks from much larger but infrequent primary impacts the prevalent assumption over recent decades has been that primaries are most abundant so most small craters are independent random events and can be used for dating however recent results from europa and mars support the early theory that distant secondaries globally dominate the number of small lunar craters this would invalidate part of production functions that have been widely used for age dating crater excavation results in higher mean ejection velocities for smaller fragments resulting in a steeper size frequency distribution for secondary craters than is produced by the same size frequency distribution of interplanetary debris this review also discusses how small craters can sometimes be used to derive meaningful age constraints

a simple analytical model of the nocturnal low level jet over the great plains of the united states abstracta simple analytical model including both diurnal thermal forcing over sloping terrain the holton mechanism and diurnally varying boundary layer friction the blackadar mechanism is developed to account for the observed amplitude and phase of the low level jet llj over the great plains and to understand better the role of each mechanism the present model indicates that for the pure holton mechanism time independent friction coefficient the maximum southerly wind speed occurs depending on the assumed friction coefficient between sunset and midnight local standard time which is earlier than the observed after midnight maximum for the pure blackadar mechanism time independent thermal forcing the present model shows that generally occurs later closer to sunrise than observed and has a strong latitudinal dependence for both mechanisms combined the present model indicates that occurs near to the observed time which lies between the time obtained in the pure holton mechanism and

radar imagery of mercury s putative polar ice 1999 2005 arecibo results abstract we present an updated survey of mercury s putative polar ice deposits based on high resolution 1 5 km imaging with the upgraded arecibo s band radar during 1999 2005 the north pole has now been imaged over a full range of longitude aspects making it possible to distinguish ice free areas from radar shadowed areas and thus better map the distribution of radar bright ice the new imagery of the south pole though derived from only a single pair of dates in 2005 improves on the pre upgrade arecibo imagery and reveals many additional ice features some medium size craters located within 3 of the north pole show near complete ice coverage over their floors central peaks and southern interior rim walls and little or no ice on their northern rim walls while one large 90 km crater at 85 n shows a sharp ice cutoff line running across its central floor all of this is consistent with the estimated polar extent of permanent shading from direct sunlight some craters show ice in regions that though permanently shaded should be too warm to maintain unprotected surface ice owing to indirect heating by reflected and reradiated sunlight however the ice distribution in these craters is in good agreement with models invoking insulation by a thin dust mantle comparisons with goldstone x band radar imagery indicate a wavelength dependence that could be consistent with such a dust mantle more than a dozen small ice features have been found at latitudes between 67 and 75 all of this low latitude ice is probably sheltered in or under steep pole facing crater rim walls although since most is located in the mariner unimaged hemisphere confirmation must await imaging by the messenger orbiter these low latitude features are concentrated toward the cold longitudes possibly indicating a thermal segregation effect governed by indirect heating the radar imagery places the corrected locations of the north and south poles at 7 w 88 35 n and 90 w 88 7 s respectively on the original mariner based maps

mercury radar imaging evidence for polar ice the first unambiguous full disk radar mapping of mercury at 3 5 centimeter wavelength with the goldstone 70 meter antenna transmitting and 26 antennas of the very large array receiving has provided evidence for the presence of polar ice the radar experiments conducted on 8 and 23 august 1991 were designed to image the half of mercury not photographed by mariner 10 the orbital geometry allowed viewing beyond the north pole of mercury a highly reflective region was clearly visible on the north pole during both experiments this polar region has areas in which the circular polarization ratio pt was 1 0 to 1 4 values 0 1 are typical for terrestrial planets such high values of have hitherto been observed in radar observations only from icy regions of mars and icy outer planet satellites

the morphology of craters on mercury results from messenger flybys topographic data measured from the mercury laser altimeter mla and the mercury dual imaging system mdis aboard the messenger spacecraft were used for investigations of the relationship between depth and diameter for impact craters on mercury results using data from the messenger flybys of the innermost planet indicate that most of the craters measured with mla are shallower than those previously measured by using mariner 10 images mdis images of these same mla measured craters show that they have been modified the use of shadow measurement techniques which were found to be accurate relative to the mla results indicate that both small bowl shaped and large complex craters that are fresh possess depth to diameter ratios that are in good agreement with those measured from mariner 10 images the preliminary data also show that the depths of modified craters are shallower relative to fresh ones and might provide quantitative estimates of crater in filling by subsequent volcanic or impact processes the diameter that defines the transition from simple to complex craters on mercury based on messenger data is consistent with that reported from mariner 10 data

some insights into the characteristics and dynamics of the chilean low level coastal jet abstract the characteristics and dynamics of the chilean low level coastal jet cllcj are examined here through diagnosing real time mesoscale model forecasts in support of the variability of the american monsoon system vamos ocean cloud atmosphere land study vocals and additional sensitivity simulations the forecasted surface winds over the southeast pacific compare favorably with available observations according to the forecasts and sensitivity simulations the southeast pacific high pressure system seph plays a primary role in driving the cllcj the andes significantly intensify the cllcj mainly through interacting with the seph and anchoring a baroclinic zone along the chilean coast the land sea differential heating also enhances the cllcj by strengthening the coastal baroclinic zone based on the location of the seph center the cllcj can be separated into two types a strong forcing jet with the seph close to the central chilean coastline and a weak forcing jet with the seph centered fa

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

mercury full disk radar images and the detection and stability of ice at the north pole the first full disk radar images of mercury were obtained on august 8 and 23 1991 these images were constructed using the very large array vla in socorro new mexico to receive and map radar flux at 3 5 cm x band which was continuously transmitted from the 70 m jet propulsion laboratory deep space network antenna at goldstone california approximately 77 of the surface was imaged at resolutions as good as 150 km about half of the hemisphere photographed by mariner 10 was imaged as well as most of the hemisphere which has not previously been photographed at the time of the observations the north pole was visible and the feature with the highest same sense ss circular reflectivity in the images is near the nominal polar position the peak ss reflectivity of this feature was 7 9 and the circular polarization ratio throughout much of the feature is 1 our best estimate of the size of the feature is that its diameter is 350 km we interpret the feature to be indicative of the presence of ices because of the signal strength and polarization characteristics the ices must be very clean and were thus probably deposited in a relatively short time period the most likely place to find these ices is in any permanently shadowed areas in the polar regions which would be very cold in comparison to absolute reflectivities of other icy bodies and regions in the solar system the reflectivity of the north polar feature is slightly depressed this is probably because the ices do not fill an observational resolution cell i e there is incomplete areal coverage or are covered by a layer of dust or soil which absorbs some of the incoming and outgoing radar energy or both a covering layer would also protect any ices from erosion by energetic sources other prominent features on the unphotographed hemisphere correspond to positions where atmospheric sodium enhancements have been measured from earth this may indicate that these locations are large basins similar to the caloris basin where an atmospheric potassium enhancement has been measured which may be the result of increased degassing in the disrupted surface and near surface direct comparison of the radar echoes from our features with those from the caloris basin are hard to make as caloris was not imaged by us in a favorable geometry features on the photographed hemisphere are smaller and mostly associated with craters and crater complexes most notably the kuiper crater and its environs

stratigraphic and geochemical evidence for the depositional environment of the early archaean isua supracrustal belt southern west greenland the highly deformed c 3800 ma isua supracrustal belt is a fragment of a more extensive early archaean sedimentary and volcanic succession intruded by and tectonically intercalated with tonalitic and granitic amftsoq gneisses in the period 3800 3600 ma the supracrustal rocks recrystallised under amphibolite facies conditions between 3800 and 3600 ma in the late archaean and locally at c 1800 ma layered sequences of rock of sedimentary and probable volcanic origin form over 50 of the belt bodies of high mg al basic rocks and ultramafic rocks were intruded into the layered sequences prior to isoclinal folding and intrusion of amitsoq gneisses the layered rocks which are 1 km thick are divided into two sequences that are in faulted contact with each other the way up of these sequences has been determined from facing directions of locally preserved graded layering in felsic metasediments at several localities the overall upwards change in sedimentary succession is interpreted as showing change from dominantly basic to dominantly felsic volcanism which provided the major clastic component of the sediments clastic sedimentation took place against a background of chemical sedimentation shown by interlayers of banded iron formation metachert and calc silicate rocks throughout the sequences the felsic rocks locally preserve graded bedding and possible conglomerate structures indicating deposition from turbidite flows and possibly as debris flows nodules in the felsic rocks contain structures interpreted as fiamme there is an irregular enrichment in k2o na2o in many of the felsic rocks at constant sio2 and al2o3 content interpreted as owing to alteration of original andesitic to dacitic volcanic rocks banded iron formations locally contain conglomeratic structures suggesting sedimentary reworking possibly under shallow water conditions lithological and geochemical characters of the clastic components of the supracrustal sequences are consistent with derivation from felsic and basic volcanic rocks and do not require a continental source

new evidence for surface water ice in small scale cold traps and in three large craters at the north polar region of mercury from the mercury laser altimeter the mercury laser altimeter mla measured surface reflectance rs at 1064 nm on mercury most water ice deposits have anomalously low rs values indicative of an insulating layer beneath which ice is buried previous detections of surface water ice without an insulating layer were limited to seven possible craters here we map rs in three additional permanently shadowed craters that host radar bright deposits each crater has a mean rs value 0 3 suggesting that water ice is exposed at the surface without an overlying insulating layer we also identify small scale cold traps 0 3 and permanent shadows have biannual maximum surface temperatures 100 k we suggest that a substantial amount of mercury s water ice is not confined to large craters but exists within micro cold traps within rough patches and inter crater terrain

setting and origin for problematic rocks from the 3 7 ga isua greenstone belt southern west greenland earth s oldest coarse clastic sediments abstract whether or not coarse detrital sedimentary rocks occur within the 3 7 ga isua greenstone belt igb southern west greenland has been debated for some time repeated regional metamorphic deformational and metasomatic events have obscured most protolith lithologies leading to misunderstandings about the stratigraphy and environments of deposition rocks here interpreted as meta conglomerate crop out in a fault bounded structural domain that is lower in strain relative to adjacent domains the meta conglomerate has a strike length of 1 km and is 10 m thick bed thickness ranges from 10 cm to more than 1 m and beds may be either framework or matrix supported a poorly sorted and variably rounded polymict assemblage of framework clasts consisting of meta chert bif and a variety of mafic volcanic rock fragments are set into a matrix of biotite quartz garnet schist clast compositions indicate reworking of adjacent stratigraphic units a lack of structural similarity in framework clasts range of grain sizes range of rounding and polymict composition demand a primary sedimentary origin for the deposit inferred depositional processes include traction and debris flow which would be consistent with subaerial or shallow subaqueous environments although the limited extent of the meta conglomerate warrants interpretational caution

numerical simulations of the island induced circulations over the island of hawaii during harp abstract the fifth generation pennsylvania state university ncar mesoscale model mm5 land surface model lsm is used to simulate the diurnal island scale circulations over the island of hawaii during the hawaiian rainband project harp 11 july 24 august 1990 the model is initialized with the ncep ncar reanalysis data the diurnal variations of the land sea thermal contrast at the land surface and the planetary boundary layer at hilo hawaii are well simulated the main discrepancy occurs on the leeside areas of mountains or ridges below the trade wind inversion 2 km where the simulated afternoon land sea thermal contrast at the surface is 1 3 c lower than observed mainly due to the misrepresentation of lava rocks by the bare ground category in the u s geological survey usgs data and stronger than observed simulated sea breezes bringing in relatively cool maritime air the flow deceleration and splitting of the incoming trade wind flow and the evolution of the diurnal circulation cells on the

the nature of lunar volatiles as revealed by mini rf observations of the lcross impact site 1 on 9 october 2009 the lunar crater observation and sensing satellite lcross impacted cabeus crater located near the south pole of the moon prior to that impact the mini rf instruments on isro s chandrayaan 1 and nasa s lunar reconnaissance orbiter lro obtained s band 12 6 cm synthetic aperture radar images of the impact site at 150 and 30 m resolution respectively these observations show that the floor of cabeus has a circular polarization ratio cpr comparable to or less than the average of nearby terrain in the southern lunar highlands furthermore 2 of the pixels in cabeus crater have cpr values greater than unity this observation is not consistent with the presence of thick deposits of nearly pure water ice within a few meters of the lunar surface but it does not rule out the presence of small 10 cm discrete pieces of ice mixed in with the regolith in addition mini rf on lro acquired a postimpact s band image of the region surrounding the lcross impact site providing important geologic context for the site registering the lro image to a near infrared nir image taken by the lcross shepherding spacecraft we find that the impactor landed in the ray of a fresh radar bright 1 km crater however the difference between preimpact and postimpact images is not above the speckle noise this implies that the size of the lcross impact crater is less than mini rf s resolution 30 m and or that the impact did not excavate more decimeter size blocks than were already present at the impact site

the low level jet off the west coast of subtropical south america structure and variability abstract the subtropical anticyclone over the southeast pacific drives low level southerly flow along the west coast of south america in turn the alongshore flow induces coastal upwelling that supports a wealth of fishery resources within this region satellite data marine reports and coastal observations indicate the existence of a southerly coastal jet i e a maximum of wind speed off central chile 26 36 s the mean features and variability of this southerly jet is documented in this work using 4 yr of satellite derived sea surface winds complemented by satellite derived cloud amount fields and atmospheric reanalysis furthermore analysis of in situ data and model results of a well defined jet event during october 2000 allows a preliminary description of the jet s three dimensional structure and a comparison with the northerly jet off the coast of california southerly jet events off central chile occur year round but they are more frequent during spring summer over 60 of the time the

the migration of volatiles on the surfaces of mercury and the moon radar observations of mercury have provided the startling discovery of the probable existence of substantial deposits of ices in permanently shaded polar regions butler et al 1993 harmon et al 1994 this has renewed the old argument about the existence of such deposits in the polar regions of the moon it is most likely necessary for volatiles to be able to migrate to the polar regions of these bodies in order to build up such deposits this paper presents the results of the extension of a monte carlo simulation of the migration of molecules on the surface of mercury by butler et al 1993 the results of the simulations show that for typical conditions on mercury 5 15 of all h 2 o which is placed randomly on the surface migrates to stable permanently shaded polar regions for the moon the numbers are 20 50 the numbers for the migration of co 2 are 2 for mercury and 13 for the moon these percentages are similar to those previously calculated and support the idea of ice deposits in the polar regions of both mercury and the moon

craters hosting radar bright deposits in mercury s north polar region areas of persistent shadow determined from messenger images 1 radar bright features near mercury s poles were discovered in earth based radar images and proposed to be water ice present in permanently shadowed areas images from messenger s one year primary orbital mission provide the first nearly complete view of mercury s north polar region as well as multiple images of the surface under a range of illumination conditions we find that radar bright features near mercury s north pole are associated with locations persistently shadowed in messenger images within 10 of the pole almost all craters larger than 10 km in diameter host radar bright deposits there are several craters located near mercury s north pole with sufficiently large diameters to enable long lived water ice to be thermally stable at the surface within regions of permanent shadow craters located farther south also host radar bright deposits and show a preference for cold pole longitudes thermal models suggest that a thin insulating layer is required to cover these deposits if the radar bright material consists predominantly of long lived water ice many small 10 km diameter and low latitude extending southward to 66 n craters host radar bright material and water ice may not be thermally stable in these craters for 1 gy even beneath an insulating layer the correlation of radar bright features with persistently shadowed areas is consistent with the deposits being composed of water ice and future thermal modeling of small and low latitude craters has the potential to further constrain the nature source and timing of emplacement of the radar bright material

on the role of sloping terrain in the forcing of the great plains low level jet abstract the summertime great plains low level jet llj has been the subject of numerous investigations during the past several decades characteristics of the llj include nighttime development of a pronounced wind maximum of typically 15 20 m s 1 at levels 300 800 m above the surface and a clockwise rotation of the wind maximum during the course of the night maximum frequency of occurrence of the llj is found in the southern great plains theories proposed to explain the diurnal wind maximum of the great plains llj include inertial oscillation of the ageostrophic wind the diurnal oscillation of the horizontal pressure field associated with heating and cooling of the sloping terrain and the western boundary current interpretations a simple equation system and output from the 12 km horizontal resolution weather research and forecasting nonhydrostatic mesoscale model nam for july 2008 are used to provide evidence as to the importance of the great plains topography in driving the llj summertime heati

a three dimensional numerical investigation of a carolina coastal low level jet during gale iop 2 abstract the pennsylvania state university ncar mesoscale model is used to examine the structure and dynamics of three low level jets lljs observed during the second intensive observation period of the genesis of atlantic lows experiment 1 a piedmont llj along the east slope of the appalachians 2 a coastal llj the focus of this study along the carolina coastline and 3 an llj to the rein of a cold frontal system positioned over the gulf stream geostrophic forcing was important for the formation of the lljs shallow local baroclinity near the top of the cold dome associated with the cold air dammed to the east of the appalachian mountains forced the piedmont llj an analysis of the model momentum tendencies reveals that the coastal llj developed and was maintained by strong geostrophic forcing associated with the coastal baroclinic zone and its strength was modulated by strong inertial accelerations significant horizontal structure in the coastal llj developed during the daytime as a result of

the new york bight jet climatology and dynamical evolution abstract this paper describes the southerly new york bight nyb jet 11 17 m s 1 that develops primarily during the warm season just above the surface offshore east of the northern new jersey coast and south of long island the nyb observations from two offshore buoys are used to develop a 9 yr climatology of 134 jet events from 1997 to 2006 there is a seasonal maximum 2 5 events per month during june and july with a skew toward the spring months the wind directions for the jet trace out a nearly elliptical orbit for the 24 h period around the time of jet maximum at 2300 utc 1900 eastern daylight time edt on average composites reveal that the nyb jet occurs on days with southwesterly synoptic flow and the jet is part of a larger scale 200 300 km wind enhancement offshore of the mid atlantic and northeast u s coasts during the early evening hours high resolution observations surface mesonet aircraft soundings and a terminal doppler weather radar and weather research and forecastin

glaciation on mercury accumulation and flow of ice in permanently shadowed circum polar crater interiors abstract radar bright deposits that coincide with regions in permanent shadow typically found within impact craters at and near the poles of mercury have been interpreted as being composed of water ice we investigate the dynamic properties of these solid water ice deposits glaciers with the goal of constraining their movement flow rates possible deformation and related structures and deposits as an end member we treat the extreme case of maximum ice accumulation where these deposits fill the crater to the shadow line an event we would only expect following maximum accumulation conditions such as a large cometary impact or a comet shower we find that given the extremely cold conditions and the limited thickness of glaciers even under the most favorable accumulation conditions glaciation is cold based ice flow velocities are very low 4 10 8 m yr and with the exception of a sublimation lag deposit glaciation is unlikely to leave any significant impact on the terrain an important accelerator of ice flow is found to be the contribution of lateral heat conduction from the surrounding extremely hot surface terrain 225 k average with up to 450 k maximums which for 55 km craters yields velocities of 10 3 m yr while for smaller 10 km craters velocities may exceed 1 m yr enough to leave a detectable ice deformation imprint such as drop moraines however given that the observed deposits are substantially below their maximum fill capacities these estimates are unlikely to be attained

how thick are mercury s polar water ice deposits an estimate is made of the thickness of the radar bright deposits in craters near to mercury s north pole to construct an objective set of craters for this measurement an automated crater finding algorithm is developed and applied to a digital elevation model based on data from the mercury laser altimeter onboard the messenger spacecraft this produces a catalogue of 663 craters with diameters exceeding 4 km northwards of latitude 55 a subset of 12 larger well sampled and fresh polar craters are selected to search for correlations between topography and radar same sense backscatter cross section it is found that the typical excess height associated with the radar bright regions within these fresh polar craters is 50 35 m this puts an approximate upper limit on the total polar water ice deposits on mercury of 3 1015 kg

areas of permanent shadow in mercury s south polar region ascertained by messenger orbital imaging 1 radar bright features near mercury s poles have been postulated to be deposits of water ice trapped in cold permanently shadowed interiors of impact craters from its orbit about mercury messenger repeatedly imaged the planet s south polar region over one mercury solar day providing a complete view of the terrain near the south pole and enabling the identification of areas of permanent shadow larger in horizontal extent than approximately 4 km in mercury s south polar region all radar bright features correspond to areas of permanent shadow application of previous thermal models suggests that the radar bright deposits in mercury s south polar cold traps are in locations consistent with a composition dominated by water ice provided that some manner of insulation such as a thin layer of regolith covers many of the deposits

the thermal stability of water ice at the poles of mercury recent radar observations of mercury have revealed the presence of anomalous radar reflectivity and polarization features near its north and south poles thermal model calculations show that despite mercury s proximity to the sun the temperatures of flat low reflectivity surfaces at mercury s poles are not expected to exceed 167 kelvin the locations of the anomalous polar radar features appear to be correlated with the locations of large high latitude impact craters maximum surface temperatures in the permanently shadowed regions of these craters are expected to be significantly colder as low as 60 kelvin in the largest craters these results are consistent with the presence of water ice because at temperatures lower than 112 kelvin water ice should be stable to evaporation over time scales of billions of years

linear theory of the sea breeze in a thermal wind this article investigates the linear dynamics of the sea breeze in an along shore thermal wind shear the present analysis shows that the sea breeze circulation is tilted towards the slanted isentropes associated with the thermal wind at a critical value of the thermal wind shear the tilt of the sea breeze circulation becomes equal to the slope of the background isentropes the present analysis also shows a spatial shift between the heating pattern and the sea breeze circulation the present linear theory is then applied to interpret measurements made in the vicinity of new york city where there is a warm season synoptic southwesterly jet it is compared with observations and past numerical simulations agreement is found with respect to the enhanced along coast wind that follows the tilted isentropes the order of magnitude of the isentrope tilt and the clockwise rotating wind hodograph showing the jet maximum peaking at 1800 solar time there is a disagreement between theory and observations on the phase lag between the jet maximum and the cross shore pressure gradient maximum however this disagreement can reasonably be attributed to either the angle made by the synoptic jet to the coastline and or the presence of friction the inland spatial shift of the breeze indicated by the theory might also be indirectly confirmed by the coastal inlan dw ind observations of al arger diurnal amplitude for a stronger synoptic jet copyright c 2011 royal meteorological society

earliest part of earth s stratigraphic record a reappraisal of the 3 7 ga isua greenland supracrustal sequence investigations of the isua supracrustal rocks in west greenland allow us to identify the protoliths and alteration history for most isua rocks the protoliths consisted of alternating basalt and banded iron formation this sequence was invaded by dunitic sills metamorphosed and later intruded by felsic gneisses pervasive carbonation and k metasomatism produced a sequence of lithologies mimicking those found in modern platform deposits however the protoliths could have originated in a purely oceanic environment with no sialic detrital components the isua sequence probably consists of several tectonic panels some of which are cut by 3810 ma felsic intrusive rocks

barrier jets during tamex abstract a barrier jet is frequently found along the northwestern coast of taiwan in the prefrontal southwesterly flow regime during the taiwan area mesoscale experiment tamex it has a maximum wind speed of 14 m s 1 at approximately 1 km above the surface with a vertical wind shear approximately 10 10 3 s 1 below and 4 10 3 s 1 above that altitude during tamex the southwesterly monsoon flow strengthens over taiwan when the low level pressure trough surface front moves toward the southeastern china coast the barrier jet is a result of the stably stratified airflow past an island obstacle under a small froude number o 1 flow regime during the occurrence of a barrier jet a windward pressure ridge is observed along the southwestern coast due to island blocking in low levels the incoming southwesterly flow decelerates off the southwestern coast and moves around the island along the western coast the deflected airflow accelerates northward with a large cross contour wind component down the p

hollows on mercury materials and mechanisms involved in their formation recent images of the surface of mercury have revealed an unusual and intriguing landform sub kilometre scale shallow flat floored steep sided rimless depressions typically surrounded by bright deposits and generally occurring in impact craters these hollows appear to form by the loss of a moderately volatile substance from the planet s surface and their fresh morphology and lack of superposed craters suggest that this process has continued until relatively recently and may be on going hypotheses to explain the volatile loss have included sublimation and space weathering and it has been suggested that hollow forming volatiles are endogenic and are exposed at the surface during impact cratering however detailed verification of these hypotheses has hitherto been lacking in this study we have conducted a comprehensive survey of all messenger images obtained up to the end of its fourth solar day in orbit in order to identify hollowed areas we have studied how their location relates to both exogenic processes insolation impact cratering and solar wind and endogenic processes explosive volcanism and flood lavas on local and regional scales we find that there is a weak correlation between hollow formation and insolation intensity suggesting formation may occur by an insolation related process such as sublimation the vast majority of hollow formation is in localised or regional low reflectance material within impact craters suggesting that this low reflectance material is a volatile bearing unit present below the surface that becomes exposed as a result of impacts in many cases hollow occurrence is consistent with formation in volatile bearing material exhumed and exposed during crater formation while in other cases volatiles may have accessed the surface later through re exposure and possibly in association with explosive volcanism hollows occur at the surface of thick flood lavas only where a lower reflectance substrate has been exhumed from beneath them indicating that this form of flood volcanism on mercury lacks significant concentrations of hollow forming volatiles

sedimentology of archean greenstone belts signatures of tectonic evolution abstract stratigraphic styles in archean greenstone belts are compared to those of modern and phanerozoic depositional basins in order to test the conformity of tectonic style through time six lithological associations in greenstone belts are recognized 1 mafic ultramafic volcanic 2 calc alkaline volcanic 3 bimodal volcanic 4 quartz arenite iron formation or carbonate 5 conglomerate wacke and 6 conglomerate arenite examples of the associations are described from the kaapvaal superior and zimbabwe provinces and the pilbara block each association differs only slightly between the four regions thereby emphasizing a common tectonostratigraphic theme sedimentary rocks are a minor component of the mafic ultramafic volcanic association they were deposited in two types of volcanic basin environments one similar to barred lagoons and bays around oceanic volcanic islands and the other similar to sediment starved platforms adjacent to coalesced volcanoes in inter arc intra arc and back are basins in contrast sedimentary rocks in the calc alkaline volcanic association comprise thick wedges of epiclastic and volcaniclastic detritus deposited in elongate sedimentary basins and thick wedges of pyroclastic and volcaniclastic detritus deposited adjacent to volcanic centers sedimentary facies were identical to those of forearc trench and marine volcanoplutonic arc settings chemogenic lithofacies in both volcanic associations were deposited in shallow to deep marine waters although shallow water profiles were selectively preserved in some terrains sedimentary rocks of the bimodal volcanic association are thick wedges of siliciclastic and volcaniclastic deposits interbedded with subaerial to submarine erupted flows of komatiite basalt and rhyolite depositional environments ranged from braid plain and braid delta to coastal marine and submarine fan starved basin deposits include banded iron formation and sulfidic black shale the association is identical to that of cratonic extensional basins in arc continent and intracontinental rifts sedimentary rocks of the quartz arenite iron formation or carbonate association onlap weathered basement or bimodal volcanic association rocks depositional environments were either transitional from fluvial to siliciclastic and carbonate marginal marine to offshore pelagic hemipelagic or from inshore intrabasinal clastic and volcaniclastic to offshore pelagic hemipelagic siliciclastic deposits are supermature two tectonic sites are represented those with siliciclastic facies represent continent adjacent syn to post rift stable shelves and those dominated by banded iron formation with volcaniclastic deposits represent arc adjacent post rift stable shelves sedimentary rocks of the conglomerate wacke association are represented by thick wedges of siliciclastic or volcaniclastic sandstone with minor volcanic components these were deposited in braid plain braid delta and submarine fan environments within elongate sedimentary basins coastal plain and pelagic basin facies are also present siliciclastic detritus was derived from syndepositional magmatic and metasedimentary thrust belts two stratigraphic styles are preserved one that records a flysch like stage of deep to marginal marine environments and the other that records a molasse like stage of marginal marine to fluvial environments the association is identical to that of compressional foreland basins of arc continent collisional and compressional arc tectonic affinities the conglomerate arenite association is preserved in elongate structural basins that transgress crustal components and all other supracrustal units it is dominated by thick wedges of siliciclastic sandstone although bimodal volcanic and volcaniclastic rocks can also be present depositional environments ranged from talus and alluvial fan and braid plain to either lacustrine or coastal marine local basin margins often show lateral offsets from source terrains and vertically skewed facies patterns longitudinal facies geometries are typical the association is similar to that of strike slip collisional graben in hinterland tectonic escape and terrane accretion orogens the examples show that despite all the ramifications of secular geophysical geothermal and geochemical global change the stratigraphic style of sedimentary rocks in archean greenstone belts can be matched with modern tectonic analogues thereby emphasizing the conformity of stratigraphic style through time the inseparable link between stratigraphic and tectonic styles implies that the tectonic style of greenstone belts was not temporally unique major differences exist with regards to the chemical composition of certain magmatic and sedimentary products but these are compensated for by their constant stratigraphic function in terms of depositional processes depositional environments and tectonic sites

imaging mercury s polar deposits during messenger s low altitude campaign images obtained during messenger s low altitude campaign in the final year of the mission provide the highest spatial resolution views of mercury s polar deposits images for distinct areas of permanent shadow within 35 north polar craters were successfully captured during the campaign all of these regions of permanent shadow were found to have low reflectance surfaces with well defined boundaries additionally brightness variations across the deposits correlate with variations in the biannual maximum surface temperature across the permanently shadowed regions supporting the conclusion that multiple volatile organic compounds are contained in mercury s polar deposits in addition to water ice a recent large impact event or ongoing bombardment by micrometeoroids could deliver water as well as many volatile organic compounds to mercury either scenario is consistent with the distinctive reflectance properties and well defined boundaries of mercury s polar deposits and the presence of volatiles in all available cold traps

near surface ice on mercury and the moon a topographic thermal model abstract a thermal model that can be easily adapted to craters of arbitrary shape is developed and applied to high latitude impact craters on mercury and the moon chao meng fu crater at 87 5 l on mercury an unnamed bowl shaped crater at 86 7 l on mercury and peary crater at 88 6 l on the moon for an assumed input topography and grid of surface elements the model computes for each element the irradiation from direct insolation and reflected and emitted radiation from other elements taking into account shadowing by the walls of the crater partial obscuration of the solar disk near the poles and the diurnal orbital and seasonal cycles temperatures are computed over the surface grid as functions of depth and time from the surface to a specified depth and over the pertinent astronomical cycles including the effects of direct and indirect surface irradiation infrared radiation heat conduction and interior heating vapor fluxes and ice recession times are computed as functions of ice depth over the surface grid temperatures profiles vapor fluxes and ice recession times were computed for flat surfaces not associated with craters near the poles of mercury and the moon it was found that water ice could have existed throughout geologic time within the maximum radar detection depth of recent observation of mercury j k harmon and m a slade 1992 science 258 640 643 poleward of 87 88 l on mercury and poleward of 73 l on the moon for chao meng fu crater it was found that 40 of the crater floor is permanently shadowed from direct solar insolation while the remainder of the crater floor is periodically illuminated by a partially obscured sun temperatures at the upper levels of the south wall can slightly exceed 550 k surface temperatures in the permanently shadowed region of the crater floor are under 130 k which could have allowed water ice to exist throughout geologic time within the radar detection depth of recent observation of mercury for the small bowl shaped crater on mercury it was found that most of the crater is permanently shadowed from direct solar radiation except for a narrow semicircular band bordering the north rim however temperatures in the permanently shadowed region periodically reach a maximum near 315 k due to efficient heating of the small crater by thermal emission and reflection from the small sunlit region which periodically reaches temperatures exceeding 630 k water ice could not have existed throughout geologic time anywhere in this crater within the radar detection depth for peary crater on the moon the entire crater floor is permanently shadowed from direct solar insolation with maximum temperatures under 120 k the upper level of the north wall periodically reaches a maximum temperature near 310 k the low temperatures on the crater floor would have allowed water ice to exist near the surface throughout geologic time provided that the moon s obliquity was always as low as it is at present

the surface roughness of mercury from the mercury laser altimeter investigating the effects of volcanism tectonism and impact cratering surface roughness is a statistical measure of change in surface height over a given spatial horizontal scale after the effect of broad scale slope has been removed and can be used to understand how geologic processes produce and modify a planet s topographic character at different scales the statistical measure of surface roughness employed in this study of mercury was the root mean square rms deviation and was calculated from 45 90 n at horizontal baselines of 0 5 250 km with detrended topographic data from individual mercury laser altimeter tracks as seen in previous studies the surface roughness of mercury has a bimodal spatial distribution with the cratered terrain dominated by the intercrater plains possessing higher surface roughness than the smooth plains the measured surface roughness for both geologic units is controlled by a trade off between impact craters generating higher surface roughness values and flood mode volcanism decreasing surface roughness the topography of the two terrain types has self affine like behavior at baselines from 0 5 1 5 km the smooth plains collectively have a hurst exponent of 0 88 0 01 whereas the cratered terrains have a hurst exponent of 0 95 0 01 subtle variations in the surface roughness of the smooth plains can be attributed to differences in regional differences in the spatial density of tectonic landforms the northern rise a 1 000 km wide region of elevated topography centered at 65 n 40 e is not distinguishable in surface roughness measurements over baselines of 0 5 250 km

high resolution radar imaging of mercury s north pole abstract the recently upgraded arecibo s band 12 6 cm radar was used to make delay doppler images of mercury s north polar region where earlier observations had shown strong echoes from putative ice deposits in craters the image resolution of 1 5 3 km is a substantial improvement over the 15 km resolution of the older arecibo images j k harmon et al 1994 nature 369 213 215 the new observations confirm all the original polar features and reveal many additional features including several at latitudes as low as 72 75 n and several from craters less than 10 km in diameter all of the new features located on the mariner imaged side of the planet can be matched with known craters or other shaded areas we find the north pole to be located 65 km from the original mariner based pole and 15 km from the new mariner based pole of m s robinson et al 1999 j geophys res 104 30 847 30 852 the improved resolution reveals fine structure in the radar features and their respective host craters including radar shadowing highlighting by central peaks and rim walls rim terracing and preferential concentration of radar bright deposits in shaded southern floor areas the radar features high brightness circular polarization inversion c 1 25 and confinement to regions permanently shaded from direct sunlight are all consistent with volume scattering from a cold trapped volatile such as clean water ice the sizes and locations of most of the features show good agreement with the thermal model of a r vasavada d a paige and s e wood 1999 icarus 141 179 193 for insulated buried water ice although the problems of explaining radar features in small craters and the rapid burial required at lower latitudes suggest that other factors may be suppressing ice loss after emplacement

the marine atmospheric boundary layer jet in the coastal ocean dynamics experiment the vertical and horizontal structure of the atmospheric boundary layer near the northern california coast was investigated during spring upwelling conditions as part of the 1981 coastal ocean dynamics experiment two daytime aircraft flights were devised to measure mean and turbulent quantities for 25 km tracks along and across the continental shelf from 30 to 1200 m altitude the pacific high offshore and an inland thermal low characterized the synoptic situations and equatorward winds resulted which produced intense ocean upwelling the wind profile was found to be jet shaped maximum wind speeds were 25 m s 1 and 16 m s 1 at 400 and 100 m respectively in the two flights above and below the heights of the jet speed maxima the wind speed decreased rapidly sharp density inversions existed at the levels of the peak wind speeds in one flight the inversion also sloped down toward the coast turbulence was effectively confined below the inversions strong zonal temperature gradients above the inversion between the hot land and cool marine air caused a thermal wind for which the wind speed decreased with height below the inversion turbulent stress divergence was large and effective in transferring the horizontal momentum of the wind to the sea slowing the wind there was also a small thermal wind below the inversion but opposite to the one above owing to the well mixed air temperature following the sea surface temperature which was cold at the coast and relatively warmer offshore owing to the upwelling these effects explain the jet shaped wind profile the mean momentum equations show that an acceleration toward the coast can balance the pressure gradient coriolis and turbulent stress divergence forces and there were some observations to support this complete balance was not obtained for the turbulent kinetic energy budget inferred dissipation rates were too large

the age and pb loss behaviour of zircons from the isua supracrustal belt as determined by ion microprobe ion microprobe uthpb analyses of zircons from a conglomeratic metavolcanic unit in the isua supracrustal belt of west greenland show that their magmatic age is3807 1ma and failed to detect any older zircon cores or xenocrysts low u areas within zircons at a 30 m scale lost only small amounts of radiogenic pb and only in the recent past whereas high u areas within grains lost much greater proportions of their pb both recently and as early as the archaean some areas in the zircons have concordant upb and thpb ages the ion probe results agree with earlier determinations for the isua supracrustals and clarify minor discrepancies between previous multigrain and single crystal analyses

radar mapping of mercury full disk images and polar anomalies a random code technique has been used at arecibo to obtain delay doppler radar images of the full disk of mercury anomalously bright features were found at the north and south poles the north polar feature is oblong 4 by 8 and offset from the pole the smaller south polar feature is mostly confined to the floor of the crater chao meng fu the polar locations and radar properties of these features indicate that they may be produced by volume scattering in ice the images also reveal a variety of more subdued reflectivity features ranging in size from hundreds to thousands of kilometers some of these appear to have an impact origin

a case study of the interaction of the summertime coastal jet with the california topography coast parallel low level jets are commonplace in the marine boundary layer off the west coast of the united states during summer a field study was conducted in early summer of 1997 to document the forcing of boundary layer winds in the near coastal environment off california on 8 june 1997 the wyoming king air collected data along a 350 km stretch of coastal margin from cape mendocino to san francisco in order to examine the interaction between the coastal topography and the low level jet during the course of the flight 32 soundings were conducted the maximum speed of the coastal jet was found near the top of the marine boundary layer at altitudes from 200 to 600 m analysis of the data revealed a westward increase in the height of the marine boundary layer and maximum jet wind speeds strongest jet winds were observed southwest of cape mendocino with a maximum speed of 28 m s21 the coastal jet was characterized by a broad horizontal extent wind maxima were found at distances approximately 30 km to more than 100 km offshore hydraulic features such as jumps and expansion fans have previously been observed downwind of coastal capes and points along the california coast the flow upwind of cape mendocino and point arena was found to be supercritical but the king air data showed that accelerations associated with possible expansion fan phenomena were minimal it is proposed that the sloping inversion at the top of the marine boundary layer and attendant coastal jet are fundamentally the result of a geostrophic adjustment process arising because of the horizontal temperature contrast between the cool ocean and warm continent this view emphasizes that the coastal jet is a ubiquitous large scale feature of the summertime coastal environment terrain induced wind speed variations associated with expansion fans and hydraulic jumps only modulate the primary jet structure

regolith properties in the south polar region of the moon from 70 cm radar polarimetry abstract the south polar region of the moon contains areas permanently shadowed from solar illumination which may provide cold traps for volatiles such as water ice previous radar studies have emphasized the search for diagnostic polarization signatures of thick ice in areas close to the pole but near surface regolith properties and regional geology are also important to upcoming orbital studies of the shadowed terrain to study regional regolith variations we collected 70 cm wavelength 450 m resolution dual circular polarization radar data for latitudes 60 90 s using the arecibo and greenbank telescopes the circular polarization ratio c is sensitive to differences in rock abundance at the surface and up to tens of m below the surface depending upon the regolith loss tangent we observe significant variations in c attributed to changes in the surface and subsurface rock population across the south polar highlands concentric haloes of low polarization ratio surrounding hausen moretus and other young craters represent rock poor ejecta layers values of c up to 1 occur in the floors and near rim deposits of eratosthenian and copernican craters consistent with abundant rocky ejecta and or fractured impact melt enhanced c values also correspond to areas mapped as orientale derived plains forming material wilhelms d e howard k a wilshire h g 1979 usgs map i 1162 and similar polarization properties characterize the permanently shadowed floors of craters faustini and shoemaker small areas of very high 1 5 circular polarization ratio occur on shadowed and seasonally sunlit terrain and appear to be associated with small craters we suggest that regolith in low lying areas near the south pole is characterized by a significant impact melt component from orientale which provides a source for excavation of the block rich ejecta around small craters observed in this and earlier radar studies the lower portion of the interior wall of shackleton crater permanently shadowed from the sun but visible from earth is not significantly different in 70 cm scattering properties from diurnally seasonally sunlit areas of craters with similar morphology

comparison of central pit craters on mars mercury ganymede and the saturnian satellites we report on the first results of a large scale comparison study of central pit craters throughout the solar system focused on mars mercury ganymede rhea dione and tethys we have identified 10 more central pit craters on rhea dione and tethys than have previously been reported we see a general trend that the median ratio of the pit to crater diameter dp dc decreases with increasing gravity and decreasing volatile content of the crust floor pits are more common on volatile rich bodies while summit pits become more common as crustal volatile content decreases uplifted bedrock from below the crater floor occurs in the central peak upon which summit pits are found and in rims around floor pits which may or may not break the surface peaks on which summit pits are found on mars and mercury share similar characteristics to those of nonpitted central peaks indicating that some normal central peaks undergo an additional process to create summit pits martian floor pits do not appear to be the result of a central peak collapse as the median ratio of the peak to crater diameter dpk dc is about twice as high for central peaks summit pits than dp dc values for floor pits median dpk dc is twice as high for mars as for mercury reflecting differing crustal strength between the two bodies results indicate that a complicated interplay of crustal volatiles target strength surface gravity and impactor energy along with both uplift and collapse are involved in central pit formation multiple formation models may be required to explain the range of central pits seen throughout the solar system

the summertime low level jet and marine boundary layer structure along the california coast abstract this paper examines the strong summertime northerly low level jet llj that frequently exists along the california coast the persistent synoptic scale pressure distribution north pacific high to the west thermal low to the east and baroclinity created by the juxtaposition of the heated continent and the cool marine layer produce the mean structure of this llj strong diurnal thermal forcing coupled with topographic influences on the flow modulate the jet structure position and intensity a mesoscale model is used to examine many of the complex facets of the llj flow dynamics several sensitivity studies in addition to a control experiment aid in this investigation principal findings of this study include the following the pronounced east west slope of the marine planetary boundary layer mpbl is not due primarily to colder sst values along the coast dynamically forced low level coastal divergence coupled with synoptic scale divergence appears to be dominant in determining mpbl i

bright and dark polar deposits on mercury evidence for surface volatiles measurements of surface reflectance of permanently shadowed areas near mercury s north pole reveal regions of anomalously dark and bright deposits at 1064 nanometer wavelength these reflectance anomalies are concentrated on poleward facing slopes and are spatially collocated with areas of high radar backscatter postulated to be the result of near surface water ice correlation of observed reflectance with modeled temperatures indicates that the optically bright regions are consistent with surface water ice whereas dark regions are consistent with a surface layer of complex organic material that likely overlies buried ice and provides thermal insulation impacts of comets or volatile rich asteroids could have provided both dark and bright deposits

investigating mercury s south polar deposits arecibo radar observations and high resolution determination of illumination conditions there is strong evidence that mercury s polar deposits are water ice hosted in permanently shadowed regions in this study we present new arecibo radar observations of mercury s south pole which reveal numerous radar bright deposits and substantially increase the radar imaging coverage we also use images from messenger s full mission to determine the illumination conditions of mercury s south polar region at the same spatial resolution as the north polar region enabling comparisons between the two poles the area of radar bright deposits in mercury s south is roughly double that found in the north consistent with the larger permanently shadowed area in the older cratered terrain at the south relative to the younger smooth plains at the north radar bright features are strongly associated with regions of permanent shadow at both poles consistent with water ice being the dominant component of the deposits however both of mercury s polar regions show that roughly 50 of permanently shadowed regions lack radar bright deposits despite some of these locations having thermal environments that are conducive to the presence of water ice the observed uneven distribution of water ice among mercury s polar cold traps may suggest that the source of mercury s water ice was not a steady regular process but rather that the source was an episodic event such as a recent large impact on the innermost planet

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

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

the thickness of radar bright deposits in mercury s northern hemisphere from individual mercury laser altimeter tracks the discovery of mercury s radar bright deposits has expanded our understanding of volatiles in the solar system key to deciphering the history and origin of the radar bright deposits is an estimate of the volume of radar bright material that in turn requires a measure of the average thickness of the deposits in this study we investigate changes in topography across radar bright deposits hosted in flat floored complex craters using individual edited mercury laser altimeter mla tracks we compare the difference in heights of radar bright regions and non radar bright regions of the crater floor and the difference of similarly sized and located regions in non radar bright craters and show that the two populations cannot be distinguished the similarity of topography in these two sets of craters allows an upper limit of 15 m to be placed on the thickness of the radar bright deposits

an upper limit for ice in shackleton crater as revealed by lro mini rf orbital radar 1 although diverse measurements have indicated h oh or h2o species in the lunar polar regions pinpointing its location form and abundance in specific reservoirs has proven elusive here we report on the first orbital radar measurements of shackleton crater near the lunar south pole mini rf observations indicate a patchy heterogeneous enhancement in cpr circular polarization ratio on the crater walls whose strength decreases with depth toward the crater floor a result that is most consistent with a roughness effect due to less mature regolith present on the crater wall slopes however the results do not rule out a modest ice contribution and an upper limit of 5 10 wt h2o ice up to 30 vol present in the uppermost meter of regolith is also consistent with the observations

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

numerical simulations of the boundary layer jet off the southeastern coast of china abstracta strong coastal boundary layer jet cblj 8 m s 1 off the southeastern coast of china around 28 n 122 e is found from the july 2006 11 hourly model data simulated by the advanced research weather research and forecasting model wrf arw with a 9 km horizontal grid the southerly cblj has a jet core at the 925 hpa level located along the western periphery of the west pacific subtropical high wpsh the cblj is mainly contributed by large scale enhancement by diurnal forcing and orographic effects by the coastal terrain along the southeastern china coast and the terrain of taiwan although the geostrophic winds offshore are faster in the afternoon due to the larger east west pressure gradient caused by land surface heating over the china plain the cblj has a nocturnal 0200 lst maximum in the afternoon hours easterly ageostrophic winds driven by differential land sea thermal heating develop at low levels after sunset with the disappearance of land surface heating the ageostrophic win

recognizable primary volcanic and sedimentary features in a low strain domain of the highly deformed oldest known 3 7 3 8 gyr greenstone belt isua west greenland a low strain domain has been identified in the metamorphosed mostly highly deformed volcanic and sedimentary rocks of the early archaean isua supracrustal belt this domain contains well preserved volcanic and sedimentary features including basaltic pillow lavas pillow breccia heterogeneous volcanic breccia amygdules in metabasalt and polymict conglomerate dominated by recrystallized chert and volcanic clasts the low strain domain is bounded by highly deformed rocks mostly derived from basalt chert and banded iron formation these discoveries demonstrate that some primary features have escaped the pervasive metasomatism dominant in other parts of the belt and furthermore strengthen the characterization of the isua supracrustals as a typical greenstone belt

no evidence for thick deposits of ice at the lunar south pole the rim of the shackleton crater at the lunar south pole is a candidate crash site for nasa s lcross probe lunar crater observation and sensing satellite due to launch in 2008 the plume of debris kicked up by the crash is to be analysed in the hope that it will reveal the water thought to be there suggestions of lunar ice date from 1996 when data from the clementine spacecraft gave some indications of the presence of ice on crater walls at the south pole now using high resolution radar imagery the radar scattering parameter thought indicative of thick ice deposits has been found also to match radar echoes from the rock strewn walls and ejecta of young impact craters at all lunar latitudes there is no evidence for thick ice though there could be grains of water ice spread more thinly through the lunar soil shackleton crater at the moon s south pole has been suggested as a possible site of concentrated deposits of water ice on the basis of modelling of bi static radar polarization properties and interpretations of earlier earth based radar images1 2 this suggestion and parallel assumptions about other topographic cold traps is a significant element in planning for future lunar landings hydrogen enhancements have been identified in the polar regions3 but these data do not identify the host species or its local distribution the earlier earth based radar data lack the resolution and coverage for detailed studies of the relationship between radar scattering properties cold traps in permanently shadowed areas and local terrain features such as the walls and ejecta of small craters here we present new 20 m resolution 13 cm wavelength radar images that show no evidence for concentrated deposits of water ice in shackleton crater or elsewhere at the south pole the polarization properties normally associated with reflections from icy surfaces in the solar system4 5 6 were found at all the observed latitudes and are strongly correlated with the rock strewn walls and ejecta of young craters including the inner wall of shackleton there is no correlation between the polarization properties and the degree of solar illumination if the hydrogen enhancement observed by the lunar prospector orbiter3 indicates the presence of water ice then our data are consistent with the ice being present only as disseminated grains in the lunar regolith

burial rate of mercury s polar volatile deposits 1 delay doppler images of mercury s polar regions showing enhanced radar backscatter have been interpreted as evidence for water ice in the polar craters and are consistent with pure water ice covered by about 20 cm of regolith in this paper we assume that the volatile at the hermean poles is water ice and that it was initially deposited at one time in a clean layer we constrain the time of such an impact by determining the rate of regolith emplacement the rate of burial of ice deposits in polar craters on mercury is estimated to be 0 43 cm myr if the ice deposits in hermean polar craters are both clean and buried by 20 cm of regolith they must be relatively recently emplaced 50 myr ago the predicted h concentration in the uppermost meter of regolith is calculated as a function of both time since emplacement of the ice and initial thickness of the ice layer the combination of neutron data and radar data can provide additional insight into the size and age of ice deposits at mercury

thermally driven diurnally periodic wind signals off the east coast of china abstractthe characteristics of thermally driven diurnally periodic wind signals off the east coast of china are studied using hourly model data for the period june 2006 11 simulated with a mesoscale model analysis of these model data indicates low level diurnally periodic wind signals propagate eastward off the southeast coast whereas diurnal wind variations off the northeast coast are nearly in phase it is found that a simple 2d linear land sea breeze model with friction can capture this main difference in propagation character with respect to latitude idealized simulations using a simplified version of the mesoscale model that includes surface heating and terrain are found to explain certain features not captured by the present linear theory such as the absolute time phase and cross coast location of the maximum amplitude of the diurnally periodic winds

images of surface volatiles in mercury s polar craters acquired by the messenger spacecraft images acquired by nasa s messenger spacecraft have revealed the morphology of frozen volatiles in mercury s permanently shadowed polar craters and provide insight into the mode of emplacement and evolution of the polar deposits the images show extensive spatially continuous regions with distinctive reflectance properties a site within prokofiev crater identified as containing widespread surface water ice exhibits a cratered texture that resembles the neighboring sunlit surface except for its uniformly higher reflectance indicating that the surficial ice was emplaced after formation of the underlying craters in areas where water ice is inferred to be present but covered by a thin layer of dark organic rich volatile material regions with uniformly lower reflectance extend to the edges of the shadowed areas and terminate with sharp boundaries the sharp boundaries indicate that the volatile deposits at mercury s poles are geologically young relative to the time scale for lateral mixing by impacts and either are restored at the surface through an ongoing process or were delivered to the planet recently

a revised control network for mercury an improved control net for mercury has been completed by utilizing images acquired during the three mariner 10 flybys in 1974 1975 relative positional errors within the net are 1 km on average and absolute locations are estimated to be better than 25 km the analytical triangulation resulted in new values for focal lengths camera a 1493 6 mm camera b 1500 1 mm w0 329 548 and camera orientation angles for 811 images acquired during all three flybys of mercury

topography of the northern hemisphere of mercury from messenger laser altimetry laser altimetry by the messenger spacecraft has yielded a topographic model of the northern hemisphere of mercury the dynamic range of elevations is considerably smaller than those of mars or the moon the most prominent feature is an extensive lowland at high northern latitudes that hosts the volcanic northern plains within this lowland is a broad topographic rise that experienced uplift after plains emplacement the interior of the 1500 km diameter caloris impact basin has been modified so that part of the basin floor now stands higher than the rim the elevated portion of the floor of caloris appears to be part of a quasi linear rise that extends for approximately half the planetary circumference at mid latitudes collectively these features imply that long wavelength changes to mercury s topography occurred after the earliest phases of the planet s geological history

microfossil like objects from the archaean of greenland a cautionary note recent reports1 4 have described yeast like microfossils isuasphaera isua pflug2 in 3 800 myr old5 metaquartzites from the isua supracrustal belt of south west greenland a biogenic interpretation of these objects is inconsistent with the tectonic history of the isua region6 8 with the petrology of the metaquartzites and with the morphology of the microstructures themselves the putative microfossils are indistinguishable from limonite stained fluid inclusions microstructures which are demonstrably inorganic and post depositional in origin as such we contend here that these objects should not be regarded as evidence of early archaean life forms

planetary science constant illumination at the lunar north pole thinking of a property on the moon the northern rim of peary crater could be the place to be an illumination map of the moon s north pole based on images obtained by the clementine spacecraft reveals areas around the peary crater that are in permanent sunlight these are prime locations for lunar outposts as well as abundant solar energy temperatures are relatively benign and nearby regions in permanent shadow may conveniently contain water ice images returned by the spacecraft clementine have been used to produce a quantitative illumination map of the north pole of the moon revealing the percentage of time that points on the surface are illuminated during the lunar day we have used this map to identify areas that are constantly illuminated during a lunar day in summer and which may therefore be in permanent sunlight all are located on the northern rim of peary crater close to the north pole permanently sunlit areas represent prime locations for lunar outpost sites as they have abundant solar energy are relatively benign thermally when compared with equatorial regions and are close to permanently shadowed regions that may contain water ice

characterization of the morphometry of impact craters hosting polar deposits in mercury s north polar region 1 earth based radar images of mercury show radar bright material inside impact craters near the planet s poles a previous study indicated that the polar deposit hosting craters pdcs at mercury s north pole are shallower than craters that lack such deposits we use data acquired by the mercury laser altimeter on the messenger spacecraft during 11 months of orbital observations to revisit the depths of craters at high northern latitudes on mercury we measured the depth and diameter of 537 craters located poleward of 45 n evaluated the slopes of the northern and southern walls of 30 pdcs and assessed the floor roughness of 94 craters including nine pdcs we find that the pdcs appear to have a fresher crater morphology than the non pdcs and that the radar bright material has no detectable influence on crater depths wall slopes or floor roughness the statistical similarity of crater depth diameter relations for the pdc and non pdc populations places an upper limit on the thickness of the radar bright material 170 m for a crater 11 km in diameter that can be refined by future detailed analysis results of the current study are consistent with the view that the radar bright material constitutes a relatively thin layer emplaced preferentially in comparatively young craters

constraining the thickness of polar ice deposits on mercury using the mercury laser altimeter and small craters in permanently shadowed regions abstract radar bright deposits at the poles of mercury are located in permanently shadowed regions which provide thermally stable environments for hosting and retaining water ice on the surface or in the near subsurface for geologic timescales while the areal distribution of these radar bright deposits is well characterized their thickness and thus their total mass and volume remain poorly constrained here we derive thickness estimates for selected water ice deposits using small simple craters visible within the permanently shadowed radar bright deposits we examine two endmember scenarios in case i these craters predate the emplacement of the ice and in case ii these craters postdate the emplacement of the ice in case i we find the difference between estimated depths of the original unfilled craters and the measured depths of the craters to find the estimated infill of material the average estimated infilled material for 9 craters assumed to be overlain with water ice is 41 14 30 m where 1 standard error of the mean is reported as uncertainty reported uncertainties are for statistical errors only additional systematic uncertainty may stem from georeferencing the images and topographic datasets from the radial accuracy of the altimeter measurements or from assumptions in our models including 1 ice is flat in the bowl shaped crater and 2 there is negligible ice at the crater rims in case ii we derive crater excavation depths to investigate the thickness of the ice layer that may have been penetrated by the impact while the absence of excavated regolith associated with the small craters observed suggests that impacts generally do not penetrate through the ice deposit the spatial resolution and complex illumination geometry of images may limit the observations therefore it is not possible to conclude whether the small craters in this study penetrate through the ice deposit and thus case ii does not provide a constraint on the ice thickness for mercury s polar deposits we argue that case i of the small craters predating the emplacement of the ice deposits is more likely given other geologic evidence that suggests that these ice deposits are relatively young using the ice thickness estimates from case i to calculate the total amount of water ice currently contained in mercury s polar deposits results in a value of 10 14 10 15 kg this is equivalent to 100 1000 km 3 ice in volume this volume of water ice is consistent with delivery via micrometeorite bombardment jupiter family comets or potentially a single impactor

radar mapping of mercury s polar anomalies ground based radar observations of mercury have revealed unusually strong highly depolarized echoes from the north1 2 and south2 poles these anomalous echoes have been cited as evidence of polar ice deposits1 5 thermal studies3 5 suggest that the permanently shaded floors of large polar craters are cold enough to preserve water ice in a stable state over aeons in spite of mercury s proximity to the sun here we present high resolution radar maps of mercury s polar regions derived from delay doppler measurements we have resolved the north and south polar anomalies into numerous crater sized features and we have been able to identify the source craters for many of these features after making small corrections to the pole positions on the mariner 10 images the coincidence with crater locations together with other properties of the radar features are consistent with the polar ice hypothesis

comparison of areas in shadow from imaging and altimetry in the north polar region of mercury and implications for polar ice deposits earth based radar observations and results from the messenger mission have provided strong evidence that permanently shadowed regions near mercury s poles host deposits of water ice messenger s complete orbital image and topographic datasets enable mercury s surface to be observed and modeled under an extensive range of illumination conditions the shadowed regions of mercury s north polar region from 65 n to 90 n were mapped by analyzing mercury dual imaging system mdis images and by modeling illumination with mercury laser altimeter mla topographic data the two independent methods produced strong agreement in identifying shadowed areas all large radar bright deposits those hosted within impact craters 6 km in diameter collocate with regions of shadow identified by both methods however only 46 of the persistently shadowed areas determined from images and 43 of the permanently shadowed areas derived from altimetry host radar bright materials some sizable regions of shadow that do not host radar bright deposits experience thermal conditions similar to those that do the shadowed craters that lack radar bright materials show a relation with longitude that is not related to the thermal environment suggesting that the earth based radar observations of these locations may have been limited by viewing geometry but it is also possible that water ice in these locations is insulated by anomalously thick lag deposits or that these shadowed regions do not host water ice