wrinkle ridge assemblages on the terrestrial planets the wrinkle ridge assemblage is a group of associated features that have been observed on the moon mars and mercury members of the wrinkle ridge assemblage are classified as either arches or ridges based on morphology and ridges are subdivided into first second or third order ridges on the basis of dimensions the ridge assemblages described in this study are known to occur in mare basalts on the moon and smooth plains units that may be volcanic in origin on mars and mercury the structures that occur in the continental flood basalts of the columbia plateau in the northwestern united states are morphologically and dimensionally similar to features in the ridge assemblages on the terrestrial planets the anticlinal ridges of the columbia plateau and many first order ridges on the moon mars and mercury are interpreted to be folds with reverse or thrust faulting developed as a result of buckling flexure fracture or buckling as a consequence of reverse or thrust faulting fracture flexure estimates of the unit shortening across first order ridges using simple geometric forms to approximate the ridge morphology are lower than those determined for the anticlines of the columbia plateau where displacements are the results of folding and reverse to thrust faulting evidence of layer parallel extension that often accompanies folds developed by fracture flexure mechanisms i e drape or fault bend folds is not found in the anticlinal ridges of the columbia plateau and has only been observed in one ridge on the moon a kinematic model involving buckling followed by reverse to thrust faulting flexure fracture is favored for the origin of the anticlinal ridges of the columbia plateau and many of the first order ridges on the moon mars and mercury

a new look at greenland flow distortion and its impact on barrier flow tip jets and coastal oceanography 1 a new diagnostic that partitions the occurrence of high speed surface wind events by wind direction is described that allows for a more complete view of the atmospheric flow distortion arising from greenland s high topography this flow distortion has previously been shown to result in the frequent occurrence of high speed surface wind events in the vicinity of cape farewell greenland s southernmost point as well along its southeast coast this new diagnostic is able to distinguish between easterly and westerly cape farewell tip jets in addition it clearly identifies the 2 locations along the southeast coast of greenland where barrier flow is enhanced and confirms previous work that indicated that these locations are collocated with regions of steep coastal topography it also results in the identification of new regions the northeast and southwest coasts of greenland as well as the southeast coast of iceland where tip jets and barrier flow also develop along the northeast coast these high speed wind events are proposed to be associated with the formation of the north east water polynya as well as contributing to the southward advection of sea ice along the southwest coast the high speed wind events which result in a reversal of the wind direction may contribute to the enhanced oceanic eddy activity observed to occur in this region

air sea interaction associated with a greenland reverse tip jet 1 greenland lies in close proximity to the north atlantic storm track and as such can be a point of strong orographic interaction with atmospheric flow for several years now it has been known that the interaction of synoptic scale cyclones with greenland s orography can spawn localized high wind speed events known as tip jets off its southernmost point climatologies of these events have shown that tip jets can have either a westerly normal or easterly reverse sense in this paper we present the first simulation of a reverse tip jet presenting an examination of the air sea interaction that occurs during this event the strength of this interaction demonstrates the potential influence that these events can have on the region s surface and abyssal oceanic circulation

influence of the icelandic low latitude on the frequency of greenland tip jet events implications for irminger sea convection 1 the occurrence of greenland tip jet events has been reported as the dominant factor controlling the formation of intermediate water in the irminger sea it has been suggested that the frequency of these events is correlated with the north atlantic oscillation to examine this process in more detail we separate the north atlantic oscillation into icelandic low and azores high components and carry out a regression fit of the frequency of tip jet events between 1961 and 2005 our findings suggest that the frequency of greenland tip jet events is highly dependent on the latitude of the icelandic low and the 2 year time lagged february icelandic low latitude with r 2 0 48 we find that the winds near the southern tip of greenland are predominately westerly during years when the iceland low is located above 63n latitude these conditions also correspond to colder air temperatures in the labrador and irminger seas implying larger oceanic heat losses due to the greenland tip jet events and hence stronger convective overturning in the irminger sea

open ocean convection in the irminger sea open ocean deep convection is known to occur in a very few locations in the present climate convection is important for the ventilation of the oceans and for the operation of the meridional overturning circulation using data from ships and profiling floats we present evidence for the occurrence of convection in the irminger sea of the north atlantic south east of greenland confirmation of this convective site in the north atlantic will influence our understanding of the connection of the atmosphere to the ocean depths and of the mechanisms of climate variability

variability of sea ice simulations assessed with rgps kinematics 1 sea ice drift and deformation from coupled ice ocean models are compared with high resolution ice motion from the radarsat geophysical processor system rgps in contrast to buoy drift the density and extent of the rgps coverage allows a more extensive assessment and understanding of model simulations at spatial scales from 10 km to near basin scales and from days to seasonal timescales this work illustrates the strengths of the rgps data set as a basis for examining model ice drift and its gradients as it is not our intent to assess relative performance we have selected four models with a range of attributes and grid resolution model fields are examined in terms of ice drift export deformation deformation related ice production and spatial deformation patterns even though the models are capable of reproducing large scale drift patterns variability among model behavior is high when compared to the rgps kinematics the characteristics shared by the models are 1 ice drift along coastal alaska and siberia is slower 2 the skill in explaining the time series of regional divergence of the ice cover is poor and 3 the deformation related volume production is consistently lower attribution of some of these features to specific causes is beyond our current scope because of the complex interplay between model processes parameters and forcing the present work suggests that high resolution ice drift observations like those from the rgps would be essential for future model developments improvements intercomparisons and especially for evaluation of the small scale behavior of models with finer grid spacing

surprising return of deep convection to the subpolar north atlantic ocean in winter 2007 2008 in the process of open ocean convection in the subpolar north atlantic ocean surface water sinks to depth as a distinct water mass the characteristics of which affect the meridional overturning circulation and oceanic heat flux in addition carbon is sequestered from the atmosphere in the process in recent years this convection has been shallow or non existent which could be construed as a consequence of a warmer climate here we document the return of deep convection to the subpolar gyre in both the labrador and irminger seas in the winter of 2007 2008 we use profiling float data from the argo programme to document deep mixing analysis of a variety of in situ satellite and reanalysis data shows that contrary to expectations the transition to a convective state took place abruptly without going through a phase of preconditioning changes in hemispheric air temperature storm tracks the flux of fresh water to the labrador sea and the distribution of pack ice all contributed to an enhanced flux of heat from the sea to the air making the surface water sufficiently cold and dense to initiate deep convection given this complexity we conclude that it will be difficult to predict when deep mixing may occur again

on the spatial distribution of high winds off southeast greenland 1 the spatial distribution of barrier winds along southeast greenland has been investigated through idealized modeling of unidirectional flow towards an isolated mountain the regions of enhanced surface wind speed seen in previous studies are reproduced and shown to be primarily the result of promontories in the orography along the southeast coast the maxima disappear in experiments without the promontories two mechanisms are proposed to explain these enhancements firstly a reduction in pressure experienced by the flow as it passes a promontory results in an acceleration akin to that of easterly tip jets at cape farewell secondly mountain waves observed along the southeast coast are accompanied by strong low level downslope winds in the lee of the promontories both mechanisms contribute to the simulated wind speed maxima

assimilating synthetic cryosat sea ice thickness in a coupled ice ocean model 1 simulated cryosat ice thickness measurements have been assimilated into a coupled ice ocean model to examine the impact in arctic ocean prediction systems the model system is based on the hybrid coordinate ocean model hycom and the evp ice rheology and the data assimilation method is the ensemble kalman filter enkf it is shown how ocean salinity surface temperature and ice concentration fields are affected by the ice thickness assimilation and how these fields are improved relative to a free run experiment of the model the ice thickness assimilation primarily affects the surface properties of the ocean by running two different assimilation experiments it is shown how the choice of stochastic forcing is crucial to the performance of the assimilation specifically it is shown how stochastic wind forcing is important to correctly describe model prediction errors which are important for the data assimilation step the assimilation experiments illustrate how the ice thickness observations can have a strong impact on the ice thickness estimates of the model system the manner in which the enkf forcing is set up is crucial but with the correct setup the assimilation of ice thickness measurements could have a beneficial effect on the modeled ice thickness and ocean fields

grabens basin tectonics and the maximum total expansion of the moon the presence of grabens and wrinkle ridges indicates that stresses sufficient to deform or fault crustal rocks have existed for at least part of lunar history these structures have been explained as due to global expansion and contraction basin subsidence or both even if the extension implied by all lunar grabens were due to global expansion the total radius increase permissible after terminal bombardment would be much less than that predicted by the most conservative models of lunar thermal evolution the obvious areal association of most grabens and wrinkle ridges with impact basins suggests that a genetic relationship exists also but it is necessary to develop either kinematic or dynamic models to determine if basin subsidence alone can account for these structures kinematic models are the most useful because fewer assumptions regarding material properties are needed than for dynamic models for both types the grabens and wrinkle ridges provide the data that must be predicted by the models considerations of geometry kinematics and mechanics suggest that the simple grabens on the moon are reliable indicators of crustal extension two end member kinematic models of postimpact basin modification are derived one assuming that subsidence is accomplished entirely by an increase in radius of curvature of the basin floor the other assuming that subsidence is accomplished without any change in radius of curvature of the basin floor any combination of the two also would be possible both models predict enough extension to account completely for basin related grabens and thus they indicate that virtually all of the extension implied by lunar grabens can be provided by modest amounts of basin subsidence in addition both models also predict total radial and hoop shortening of the basin floor of about the correct magnitude to explain wrinkle ridges if these features are structures resulting from compression consequently almost all extension and shortening of the lunar crust implied by grabens and wrinkle ridges can be explained by basin subsidence alone significant global expansion after 3 9 b y is unlikely and significant global contraction is unnecessary

the shallow structure of the martian lithosphere in the vicinity of the ridged plains wrinkle ridges in the smooth plains of the coprates and lunae planum regions of mars form linear or concentric patterns with a regular spacing of 25 50 km the authors test the hypothesis that the periodic development of deformation was a consequence of unstable horizontal compression that occurred prior to probable ridge related faulting of a strength stratified lithosphere which consists of a mechanically strong surface plains unit that successively overlies a weak megaregolith and a strong lithospheric basement results show that a range of models with both rigid and deformable megaregolith basement interface conditions yield solutions which can explain the ridge spacing within the constraint provided by the estimated thickness of the smooth plains materials in models that incorporate viscous and plastic rheologies uniform and exponentially varying vertical strength distributions and the presence or absence of interfacial slip at the base of the surface plains unit the ridge spacing is primarily controlled by the power law exponent of the lithosphere the megaregolith plains unit thickness ratio and the plains unit megaregolith strength contrast deformable basement models with a viscous rheology 1 le n approx le 3 can explain the ridge spacing if the megaregolith was thicker than and approximately 1 3 orders of magnitude weaker than themore plains unit similar models with a perfectly plastic n yields infinity rheology require plains unit thicknesses greater than 5 km which exceeds most observational estimates ridge spacing in the combined viscous and plastic models can be consistent with either a dry water rich or ice rich megaregolith at the time of ridge formation less

landscapes soils and mound histories of the upper indus valley pakistan new insights on the holocene environments near ancient harappa abstract the site of harappa in central pakistan has been the primary source of information on indus valley cultural and natural landscapes in the upper indus basin while the site has been excavated for over 100 years little was known of the pre occupation history and environments responsible for the culture s emergence in the third millennium bc recent geoarcheological investigations of sites sharing the same landform as harappa the bari doab along the ancient beas river have synthesized sediment soil and cultural stratigraphies that place harappa in the context of a regional landscape history two key sites lahoma lal tibba and chak purbane syal illustrate that larger floodplains of the indus system stabilized sometime in the early holocene when soil development exceeded rates of alluviation the site of harappa was revisited to procure radiocarbon dates beneath initial occupation horizons the stratigraphy and dates established the pleistocene holocene interface and confirmed coeval trends of diminished early holocene floodplain accretion and sustained soil formation pedogenesis continued at least to the beginning of the fifth millennium bp when occupation began to intensify along the beas and elsewhere in the upper indus site formation sequences at lahoma lal tibba and chak purbane syal mirror those of harappa proper albeit on a smaller scale

magnitude of a catastrophic flood event at kasei valles mars kasei valles compose an enormous outflow channel system on mars the upper part of the channel system is typically less than 1 km deep and descends from echus chasma about 1 km over a distance of 1000 km it then splits into north and south channels on the basis of a stereomodel of viking images we have measured the geometry of a steep constricted reach of the north channel that drops 900 m in only 100 km a late stage flood is hypothesized to have scoured the channel if we assume that channel striations indicate water levels then the flood had a minimum cross sectional area of 3 12 x 10 7 m 2 the putative flood had a width of 83 km an average depth of 374 m and maximum depth of 1280 m these channel measurements suggest that flood velocities ranged from 32 to 75 m s 1 and that discharge was greater than 1 km 3 s 1 values larger than those calculated for any other flood event on mars or earth the flood maintained supercritical flow and caused intense erosion in this area scouring a 350 m deep megapothole the source of the flood water may have been a temporary lake in echus chasma a deep canyon formed in association with tectonism at valles marineris

wrinkle ridges of arcadia planitia mars wrinkle ridges of arcadia planitia were examined to determine their morphology spatial distribution and the amount of crustal shortening and strain they accommodate ridges trend generally northward but their orientation and distribution are strongly controlled by the relief of the underlying knobby material ridges begin or end at inselbergs of older terrain and are associated with buried craters arcadia planitia ridges have an average width of 3425 m and accommodate an average folding shortening of 3 m and a faulting shortening of 55 m mean total shortening is 57 m three east west transects were constructed at 20 25 and 28 n to estimate regional shortening and strain average total shortening across the transects is about 900 m corresponding to a regional compressive strain of 0 06 the total shortening and compression across arcadia planitia are less than in lunae planum faults associated with the arcadia ridges are inferred to have a westward dip compared with an eastward dip for lunae planum ridges the generally levels of compression and symmetric orientation of the ridges suggest a regionally organized stress system differences in the shortening and strain between lunae planum and arcadia planitia may reflect the effects of local lithology or azimuthal variations in the stress field

winter atmospheric buoyancy forcing and oceanic response during strong wind events around southeastern greenland in the regional arctic system model rasm for 1990 2010 abstractstrong mesoscale tip jets and barrier winds that occur along the southeastern greenland coast have the potential to impact deep convection in the irminger sea the self organizing map som training algorithm was used to identify 12 wind patterns that represent the range of winter november march ndjfm wind regimes identified in the fully coupled regional arctic system model rasm during 1990 2010 for all wind patterns the ocean loses buoyancy primarily through the turbulent sensible and latent heat fluxes haline contributions to buoyancy change were found to be insignificant compared to the thermal contributions patterns with westerly winds at the cape farewell area had the largest buoyancy loss over the irminger and labrador seas due to large turbulent fluxes from strong winds and the advection of anomalously cold dry air over the warmer ocean similar to observations rasm simulated typical ocean mixed layer depths mld of approximately 400 m throughout the irminger basin with indi

multi event analysis of the westerly greenland tip jet based upon 45 winters in era 40 the westerly greenland tip jet is an intense narrow and intermittent wind phenomenon located southeast of cape farewell that occurs frequently during the winter season using the era 40 reanalysis dataset a catalogue of 586 objectively detected westerly tip jet events is compiled for the winters 1957 2002 and an analysis is undertaken of the character of the jet and its accompanying atmospheric features it is shown that the tip jet frequency exhibits a significant positive correlation with both the nao index and the latitude of the icelandic low the peak wind speed and accompanying heat fluxes of the jet have values up to 30 m s 1 and 600 w m 2 respectively and are sustained for less than one day the air parcels constituting the tip jet are shown based upon a trajectory model and the era 40 dataset to have a continental origin and to exhibit a characteristic deflection and acceleration around southern greenland the events are almost invariably accompanied both by a notable coherence of the lower level tip jet with an overlying upper level jet stream and by a surface cyclone located to the lee of greenland it is also shown that the cyclone originates upstream of and is advected to the lee of greenland and thereby it both precedes in time and contributes dynamically to the formation of the tip jet on this basis it is suggested that the tip jet arises from the interplay of the synoptic scale flow evolution and the perturbing effects of greenland s topography upon the flow copyright 2009 royal meteorological society

atmospheric conditions associated with oceanic convection in the south east labrador sea 1 it has been speculated that low level reverse tip jets caused by the interaction of synoptic scale atmospheric flow and greenland are an important mechanism for forcing open ocean convection in the south east labrador sea here float data and meteorological reanalysis fields from the winter of 1996 1997 in combination with a simple mixed layer ocean model are used to show that although relatively deep ocean convection did occur during this winter the primary forcing mechanism was cold air outbreaks from the labrador coast rather than the smaller scale reverse tip jets during this winter the north atlantic oscillation nao was in a weak positive phase similar treatments of the winters of 1994 1995 strong positive nao and 1995 1996 strong negative nao suggest that the result is robust regardless of the state of the nao

deep convection in the irminger sea forced by the greenland tip jet open ocean deep convection one of the processes by which deep waters of the world s oceans are formed is restricted to a small number of locations for example the mediterranean and labrador seas recently the southwest irminger sea has been suggested as an additional location for open ocean deep convection the deep water formed in the irminger sea has the characteristic temperature and salinity of the water mass that fills the mid depth north atlantic ocean which had been believed to be formed entirely in the labrador basin here we show that the most likely cause of the convection in the irminger sea is a low level atmospheric jet known as the greenland tip jet which forms periodically in the lee of cape farewell greenland and is associated with elevated heat flux and strong wind stress curl using a history of tip jet events derived from meteorological land station data and a regional oceanic numerical model we demonstrate that deep convection can occur in this region when the north atlantic oscillation index is high which is consistent with observations this mechanism of convection in the irminger sea differs significantly from those known to operate in the labrador and mediterranean seas

modeling crater topography and albedo from monoscopic viking orbiter images 1 methodology a new photoclinometric technique for extraction of topographic data from single planetary images is presented that overcomes many previous limitations of photoclinometry the procedure fully compensates for oblique viewing geometry prevalent in spacecraft images albedo variations have been one of the most serious obstacles in the application of photoclinometry to planetary surfaces this problem is overcome in the topographic solution by simultaneously utilizing brightness data from a pair of profiles both segments are assumed to have the same topographic and albedo variations along their lengths profile directions are chosen where the orientation of downslope or upslope is obvious thus resolving a major ambiguity in photoclinometry this requirement is particularly easy to satisfy for craters and not very difficult for many irregular features an additional procedure is presented that eliminates even the requirement of topographic symmetry along the pair of profiles if two profiles have the same relief but their shapes are very different another method can be used in an iterative process to derive topographic profiles however this procedure does require that the albedo not vary along the profiles test results indicate that both procedures have an accuracy and precision of approximately 2 for slopes of typical bowl shaped craters which translates to approximately 5 for depths

strong downslope wind events in ammassalik southeast greenland abstractammassalik in southeast greenland is known for strong wind events that can reach hurricane intensity and cause severe destruction in the local town yet these winds and their impact on the nearby fjord and shelf region have not been studied in detail here data from two meteorological stations and the european centre for medium range weather forecasts interim re analysis era interim are used to identify and characterize these strong downslope wind events which are especially pronounced at a major east greenland fjord sermilik fjord within ammassalik their local and regional characteristics their dynamics and their impacts on the regional sea ice cover and air sea fluxes are described based on a composite of the events it is concluded that wind events last for approximately a day and seven to eight events occur each winter downslope wind events are associated with a deep synoptic scale cyclone between iceland and greenland during the events cold dry air is advected down the ice sheet

mesoscale structure of cape farewell tip jets abstractcape farewell greenland s southernmost point is characterized by a number of low level jets that are the result of topographic flow distortion associated with passing extratropical cyclones the heavy seas associated with these wind events are a hazard to maritime traffic in the region in addition the air sea heat flux associated with these weather systems plays an important role in the climate system by contributing to the forcing of the lower limb of the atlantic meridional overturning circulation in this paper the north american regional reanalysis will be used to generate a higher resolution climatology of these mesoscale jets as compared to previous studies through the use of a diagnostic that partitions the occurrence frequency of high speed wind events by wind direction the author shows that there are four different types of cape farewell tips jets that are characterized as having either northwesterly southwesterly northeasterly or southeasterly wind direction all four types hav

winter mixed layer development in the central irminger sea the effect of strong intermittent wind events abstract the impact of the greenland tip jet on the wintertime mixed layer of the southwest irminger sea is investigated using in situ moored profiler data and a variety of atmospheric datasets the mixed layer was observed to reach 400 m in the spring of 2003 and 300 m in the spring of 2004 both of these winters were mild and characterized by a low north atlantic oscillation nao index a typical tip jet event is associated with a low pressure system that is advected by upper level steering currents into the region east of cape farewell and interacts with the high topography of southern greenland heat flux time series for the mooring site were constructed that include the enhancing influence of the tip jet events this was used to force a one dimensional mixed layer model which was able to reproduce the observed envelope of mixed layer deepening in both winters the deeper mixed layer of the first winter was largely due to a higher number of robust tip jet events which in turn was caused by the stee

impact craters on regional plains on venus age relations with wrinkle ridges and implications for the geological evolution of venus 1 a global assessment of impact craters on venus 30 km in diameter shows that 146 craters are completely or partially superposed on the regional plains that dominate the surface and typically are deformed by wrinkle ridges in this study we found that 10 of these craters are deformed by wrinkle ridges pre wr 93 craters are superposed on wrinkle ridges post wr and 43 craters were found to be ambiguous cases we compared our findings with the results of a similar study by mcgill 2004 done for craters of all sizes but for 1 3 of the surface of venus we found that the percentage of pre wr craters found by mcgill 2004 among the unambiguous cases 15 is close to our percentage 10 but we are in disagreement on the classification of a significant number of specific craters and in this analysis we describe the major reason for the disagreements we then summarize published data on the crater densities for different plains on venus we assess monte carlo modeling of volcanic resurfacing which competed with the ongoing formation of impact craters on the basis of these data and analyses we conclude that the mean age of the regional plains is close to the mean global surface age of venus and that the potential time span of regional plains emplacement was relatively short we interpret our results as evidence that wrinkle ridging on venus was a distinct tectonic phase that occurred rather early in post regional plains time probably within the first 10 although the exact duration remains uncertain regional and global stratigraphic relationships strongly support the hypothesis that wrinkle ridging on venus predominantly occurred during a specific phase of history the geologic record of wrinkle ridging and post plains tectonic evolution of volcanic plains on the moon and mars show interesting similarities to those of venus

tip jets and barrier winds a quikscat climatology of high wind speed events around greenland the high topography of greenland results in a number of orographically induced high wind speed flows along its coast that are of interest from both a severe weather and climate perspective here the surface wind field dataset from the nasa jpl seawinds scatterometer on board the quick scatterometer quikscat satellite is used to develop a wintertime climatology of these flows the high spatial resolution and the twice daily sampling of the seawinds instrument allows for a much more detailed view of the surface winds around greenland than has been previously possible three phenomena stand out as the most distinctive features of the surface wind field during the winter months the previously identified tip jets and reverse tip jets as well as the hitherto unrecognized barrier flows along its southeast coast in the vicinity of the denmark strait peak surface wind speeds associated with these phenomena can be as large as 50 m s 1 with winds over 25 m s 1 occurring approximately 10 15 of the time at each location a compositing technique is used to show that each type of flow is the result of an interaction between a synoptic scale parent cyclone and the high topography of greenland in keeping with previous work it is argued that tip jets are caused by a combination of conservation of the bernoulli function during orographic descent and acceleration due to flow splitting as stable air passes around cape farewell while barrier winds are a geostrophic response to stable air being forced against high topography it is proposed that reverse tip jets occur when barrier winds reach the end of the topographic barrier and move from a geostrophic to a gradient wind balance becoming supergeostrophic as a result of their anticyclonic curvature

complexities in the climate of the subpolar north atlantic a case study from the winter of 2007 as a result of its high topography greenland significantly distorts the atmospheric flow affecting local as well as remote weather systems and via air sea interaction processes the coupled climate system during february and march 2007 a field campaign was carried out to investigate this as part of the international greenland flow distortion experiment gfdex the observational programme occurred during anomalous conditions relative to the climatological mean that favoured the formation of barrier flow along the southeastern coast of greenland and easterly tip jets at cape farewell greenland s southernmost point while inhibiting the formation of westerly tip jets in the same region the north atlantic oscillation nao index was positive indicating a deep icelandic low however there was a southeastward shift in the low s centre and a more zonally oriented storm track that we propose to be the result of the concurrent positive phase of the east atlantic ea teleconnection unlike the usual situation for an nao positive state there was also a warming in the lower troposphere over the labrador sea that we argue was the result of a relatively weak canadian polar trough over the eastern canadian arctic it is shown that consideration of the strength of the canadian polar trough in conjunction with information on the phases of the nao and ea provides for a qualitatively better representation of the state of the atmosphere over the subpolar north atlantic during the winter of 2007 and by inference in general than is possible via the nao alone

comparison of wintertime mesoscale winds over the ocean around southeastern greenland in wrf and era interim strong mesoscale tip jets and barrier winds that occur over the ocean near southern greenland have the potential for impacting deep convection in the ocean the self organizing map som training algorithm was used to identify and classify the range of 10 m wind patterns present during ten winters 1997 2007 ndjfm in the ecmwf interim reanalysis era i and from a regional simulation using the weather research and forecasting wrf model at 50 km into a som the som is used to identify differences in the manifestation of westerly tip jets easterly tip jets and barrier flow the north atlantic oscillation nao index is well correlated with the type of tip jet present at cape farewell but the nao was not well correlated with the absence or presence of barrier flow wrf simulated patterns with strong barrier parallel flow more frequently than era i and wrf also had faster coastal winds than era i during all types of strong wind events the difference in coastal winds is likely related to model resolution and the resulting ability of each model to simulate strong mesoscale winds that are driven by greenland s steep terrain

thick shell tectonics on one plate planets applications to mars a theory for stress distributions in thick lithospheric shells on one plate planets is developed based on the zero frequency equations of a self gravitating elastic spherical shell overlying a strengthless fluid stress distributions in lithospheres are reviewed for both the compensated and flexural modes in the former case surface stresses only depend on surface topography while for the latter case it is shown for long wavelengths that stress trajectories are mainly dependent on the lithospheric lateral density distribution and not on elastic properties computational analyses are carried out for mars and it is found that isostatically compensated models correctly predict the graben structure in the immediate tharsis region and a flexural loading model is satisfactory in explaining the graben in the regions surrounding tharsis a three stage model is hypothesized for the evolution of tharsis isostasy with north south graben formation on tharsis followed by flexural loading and radial graben formation on the perimeter of tharsis followed by a last stage of loading with little or no regional deformation this model is consistent with the martian lithosphere monotonically thickening over geologic time

origin of planetary wrinkle ridges based on the study of terrestrial analogs wrinkle ridges linear asymmetric topographic highs are common physiographic features on the moon mars and mercury we describe here some terrestrial features of similar morphology and scale that have formed under compressional stress systems similar to planetary wrinkle ridges all of the terrestrial analogs are produced by the anticlinal folding of rocks above reverse faults that shallow and typically break the surface characteristics common to both terrestrial and planetary ridges include 1 a linear asymmetric antiformal shape 2 tension cracks and grabens along the hinges of the antiform 3 overlapping en echelon lobes 4 reversals of the sense of asymmetry along strike 5 occurrence in compressional environments and 6 similarity to features produced during compression of various materials in laboratory scale models these similarities strongly suggest that planetary wrinkle ridges result from deformation associated with shallow thrust faults that either break or come close to the surface kinematic models capable of explaining the development of wrinkle ridges include 1 anticlinal folding of rocks over a buried thrust fault that may subsequently propagate to the surface and 2 fault bend folding of upper plate rocks over the surface flattening bend of a thrust fault

the impact of polar mesoscale storms on northeast atlantic ocean circulation every year thousands of mesoscale storms termed polar lows cross the climatically sensitive subpolar north atlantic ocean high resolution numerical simulations of the ocean circulation taking into account the effect of these storms on deep water formation suggest that polar lows significantly affect the global ocean circulation

an easterly tip jet off cape farewell greenland ii simulations and dynamics an easterly tip jet that occurred on 21 february 2007 off cape farewell greenland is examined in part i of this article aircraft observations were described now in part ii numerical simulations and an analysis of the dynamical forcing mechanisms are presented the simulations make use of a limited area 12 km resolution configuration of the met office s unified model sea surface temperatures and sea ice concentrations have been replaced using the operational sea surface temperature and sea ice analysis ostia product addressing a boundary layer temperature bias while roughness lengths over sea ice have been updated addressing a wind speed bias these modifications ensured a reasonably accurate simulation generally within 1 2 k and 2 3 m s 1 when compared with dropsonde observations a momentum budget analysis along a curved locus through the core of the jet has been derived off southeast greenland the easterly tip jet was in cross jet geostrophic balance but was being accelerated downstream by an along jet pressure gradient over the curved part of the locus as the jet rounded cape farewell a cross jet residual suggests that the jet was unbalanced at the height of the jet core this residual decreases with height so that an approximate gradient wind balance applies in the upper part of the jet the anticyclonic curvature characteristic of easterly tip jets was caused by a dramatic decrease in the cross jet pressure gradient force at the end of the barrier after which the jet aligned with the synoptic scale isobars and returned to approximate geostrophic balance the momentum budget is shown to be robust and applicable to other cases copyright 2009 royal meteorological society

tectonic history of the syria planum province of mars we attribute most of the development of extensive fractures in the tharsis region to discrete tectonic provinces within the region rather than to tharsis as a single entity one of these provinces is in syria planum faults and collapse structures in the syria planum tectonic province on mars are grouped into 13 sets based on relative age areal distribution and morphology according to superposition and fault crosscutting relations and crater counts we designate six distinct episodes of tectonic activity in the following chronologic order stage i is an early to late noachian deformation forming mostly east west structures fault set ia some large volcanoes also formed faults were produced possibly by flexural uplift also arcuate north trending grabens set ib indicate that faulting is transitional to the next stage stage ii is late noachian to early hesperian radial faulting centered in syria planum possibly due to isostatic uplift in late noachian set iia to early hesperian set iib time stage iii is early to late hesperian faulting tangential to syria planum that was related to local centers of uplift sets iii1 iii3 on the periphery of syria planum stage iv is a late hesperian graben formation that was circumferential to syria planum set iva caused either by collapse associated with eruption of magma or by flexure of the lithosphere due to volcanic loading in association with volcanism minor faulting occurred producing an oval pattern of faults in southwest syria planum set ivbl and a radial pattern south of the planum set ivb2 that apparently rejuvenated buried stage ii faults stage v is a late hesperian to early amazonian development of grabens and troughs of noctis labyrinthus and western valles marineris set v that was probably instigated by local uplift exposure of groundwater or ground ice zones may have produced further collapse and trough enlargement stage vi is early amazonian northwest trending faulting in noctis fossae set vil perhaps due to tharsis monies centered tectonism and north northwest normal faulting along the eastern side of the claritas rise set vi2 that was due to tectonic subsidence the duration of tectonic activity in the syria planum province was perhaps 2 3 b y photoclinometric topographic profiles across 132 grabens and fault scarps show that syria planum grabens have widths average of 2 5 km and most range from 1 to 6 km similar to lunar grabens but the martian grabens have slightly higher side walls average about 132 m and gentler wall slopes average of 9 and range of 2 25 than lunar grabens 93 m high and 18 slopes scarp degradation on mars has progressed through quakes impact shaking and dry slope processes the lower slopes may be due to mars higher gravity estimates of the amount of extension for individual grabens range from 20 to 350 m most estimates of the thickness of the faulted layer range from 0 5 to 4 5 km average is 1 5 km this thickness range corresponds closely to the 0 8 to 3 6 km range in depth for pits troughs and canyons in noctis labyrinthus and along the walls of valles marineris we propose that the predominant 1 to 1 5 km values obtained for both the thickness of the faulted layer and the depths of the pits troughs and theater heads of the canyons reflect the initial depth to the water table in this region as governed by the depth to the base of ground ice maximum depths for these features may indicate lowered groundwater table depths and the base of ejecta material

wind driven recirculations and exchange in the labrador and irminger seas it is demonstrated that recently observed cyclonic recirculation gyres in the irminger and labrador seas may be forced by the strong cyclonic wind stress curl that develops each winter seaward of the east coast of greenland idealized analytical and numerical models forced with such variable winds over a sloping bottom reproduce the essential aspects of the observed gyres strength location and horizontal and vertical length scales the communication between the forcing region in the irminger sea and the recirculation to the west is achieved by baroclinic topographic rossby wave propagation along potential vorticity contours the circulation is characterized as a time dependent stratified topographic beta plume for weak stratification as found in the subpolar north atlantic the recirculation strength exhibits only weak seasonal variability consistent with the observations even though the forcing is active only during the winter baroclinic rossby waves that develop when the wind forcing ceases in springtime interact with the bottom to provide a source of cyclonic vorticity that maintains the circulation until the wind strengthens again in the following winter

wrinkle ridges in lunae planum mars implications for shortening and strain photoclinometric data for lunae planum wrinkle ridges indicate average relief of approximately 130 m and distinct elevation discontinuities across the ridge of 55 m modeling ridges as the result of thrust faulting and associated upper plate folding indicates shortening across individual ridges of approximately 131 m 90 faulting total shortening at 20 degree n across lunae planue is approximately 1 840 m corresponding to a regional compressive strain of 0 29 strain appears uniform across lunae planum although it is accommodated by larger and few structures in the west than in the east

gale force winds over the irminger sea to the east of cape farewell greenland 1 high wind events that occur over the irminger sea to the east of cape farewell greenland are of interest as a result of the significant hazard they represent to maritime activity as well as their potential role in forcing deep ocean convection in the region in this paper the ncep reanalysis is used to develop a climatology of gale force wind events over the irminger sea in addition to the previously identified tip jet events that are characterized by strong westerly flow we show that there also exist reverse tip jet events that are characterized by strong easterly flow both types of events are associated with deep extra tropical cyclones that are undergoing an interaction with the high topography of southern greenland we also show that the frequency of both types of events is highest in the winter months and is modulated by the phase of the north atlantic oscillation nao

clues to the lithospheric structure of mars from wrinkle ridge sets and localization instability 1 wrinkle ridges are a manifestation of horizontal shortening in planetary lithospheres for which deformation is localized on faults that underlie individual ridges in ridged plains of mars such as solis planum or lunae planum wrinkle ridges are spaced 40 km apart whereas in the martian northern lowlands where ridges are identified only in mars observed laser altimeter mola altimetric data the ridge spacing is at least 80 km we attribute ridge spacing to an instability of the lithosphere under horizontal compression the localization instability which results in periodically spaced faults montesi and zuber 2003a links the difference of ridge spacing in the northern lowlands and in the highland ridged plains to the difference of crustal thickness via the depth of the brittle ductile transition bdt in solis and lunae plana where the crust is 50 to 60 km thick the crust may be ductile at depth limiting faulting to the bdt of crustal rocks in the lowlands the crust is only about 30 km thick and may be brittle throughout thus the depth of faulting may be controlled by the bdt of mantle rocks which is roughly a factor of two deeper than that of crustal rocks the geotherm can be identical in both regions at 12 3 k km 1 although differences of a few k km 1 can be accommodated within this model the heat flux implied by this geotherm is similar to the heat produced by radiogenic decay 3 gyr ago our analysis provides a rheological explanation for the difference in spacing between ridges in the highlands and the lowlands in contrast to the suggestion of head et al 2002 who proposed that alternating lowlands ridges are buried by sediments in addition finite element models that use the lithospheric structure deduced from ridge spacing show that modest gradients of crustal thickness or heat flux across a ridged plains favor the formation of faults dipping toward high elevation areas as may be the case in solis planum golombek et al 2001

the oceanic response to mesoscale atmospheric forcing the response of the oceanic circulation to mesoscale atmospheric forcing is studied by comparing integrations of a global sea ice ocean model with high resolution european centre for medium range weather forecasts analysis data 0 4 to those with the same forcing coarse grained to a resolution typically employed in climate models and atmospheric reanalyses 1 8 it is shown that the representation of mesoscale features in atmospheric forcing fields leads to an increase in the strength of the wind driven gyres in the north atlantic and north pacific regions of about 5 10 of its mean value an increase of similar magnitude is found for the atlantic meridional overturning circulation from the results of this study it is argued that small scale atmospheric phenomena such as fronts mesoscale cyclones and topographic jets play an important role in driving the mean oceanic circulation

beta regio venus evidence for uplift rifting and volcanism due to a mantle plume abstract geophysical data have led to the interpretation that beta regio a 2000 25000 km wide topographic rise with associated rifting and volcanism formed due to the rise of a hot mantle diapir interpreted to be caused by a mantle plume we have tested this hypothesis through detailed geologic mapping of the v 17 quadrangle which includes a significant part of the beta regio rise and reconnaissance mapping of the remaining parts of this region our analysis documents signatures of an early stage of uplift in the formation of the agrona linea fracture belts before the emplacement of regional plains and their deformation by wrinkle ridging we see evidence that the theia rift associated volcanism occurred during the first part of post regional plains time and cannot exclude that it continued into later time we also see evidence that devana chasma rifting was active during the first and the second parts of post regional plains time these data are consistent with uplift rifting and volcanism associated with a mantle diapir geophysical modeling shows that diapiric upwelling may continue at the present time together these data suggest that the duration of mantle diapir activity was as long as several hundred million years the regional plains north of beta rise and the area east and west of it were little affected by the beta forming plume but the broader area at least 4000 km across whose center northern part includes beta regio could have experienced earlier uplift as morphologically recorded in formation of tessera transitional terrain