origin of fine scale wind stress curl structures in the benguela and canary upwelling systems numerous studies have shown the primary importance of wind stress curl in coastal upwelling dynamics the main goal of this new analysis is to describe the quikscat surface wind stress curl at various scales in the benguela and canary upwelling systems the dominant spatial pattern is characterized by cyclonic curl near continental boundaries and anticyclonic curl offshore in association with equatorward alongshore upwelling favorable wind stress at a smaller scale we demonstrate the sensitivity of the quikscat wind stress curl to coastal processes related to sea surface temperature sst mesoscale fluctuations by presenting a linear relationship between the curl and crosswind sst gradients despite the spatial and temporal sensitivity of the underlying thermal coupling coefficient a local analysis of the fraction of the curl ascribed to sst variability shows that sst is a main driver of the wind stress curl variability and magnitude over the upwelling extension zone 100 300 km from the coast in both the canary and benguela systems closer to the shore the curl patterns derived from quikscat observations are only loosely related to sst wind interactions as a working hypothesis they can also be associated with the coastline geometry and orographic effects that are likely to play an important role in local cooling processes

the source of benguela ninos in the south atlantic ocean 1 the intermittent occurrence of anomalous warm events in the upwelling regions of the pacific el ninos has been intensively studied pacific ninos have striking effects on the local ecosystem hence on the fisheries and on rainfall similar dramatic events have been observed in the south atlantic off the coasts of angola and namibia and named benguela ninos they tend not to occur in unison with their pacific counterpart and may thus have unrelated forcing mechanisms using an ocean general circulation model forced by real winds and verified with satellite data it is shown that benguela ninos are generated by specific wind stress events in the west central equatorial atlantic and progress from there as subsurface temperature anomalies that eventually outcropped only at the south west african coast these results suggest that it now may be possible to predict the occurrence of these disruptive events with a lead time of 2 months

an analysis of sinuous ridges in the southern argyre planitia mars using hirise and ctx images and mola data 1 a suite of sinuous ridges with branching and braided morphologies forms an anastomosing network in southern argyre planitia mars several modes of origin have been proposed for the argyre ridges imagery from the high resolution imaging science experiment hirise and context camera ctx aboard mars reconnaissance orbiter mro and mars orbiter laser altimeter mola topographic data sets from mars global surveyor mgs are used to constrain processes involved in formation of the argyre ridges we find the characteristics of the ridges and associated layered deposits consistent with glaciofluvial lacustrine processes and conclude that the ridges are most likely eskers in particular variations in ridge height appear to be related to the surrounding surface slope ridge height increases with descending slopes and decreases with ascending slopes this characteristic is observed in terrestrial eskers and is related to subice flow processes the nature of some eroding beds in the ridges suggests induration if the argyre ridges are indeed eskers the southern argyre basin was once covered by the margin of a large thick stagnating or retreating ice deposit that extended for hundreds of kilometers or more during ridge formation water flowed on top within or beneath the ice deposit the continuity and preservation of the ridges suggests that flow was primarily at the base of the ice the dimensions up to hundreds of meters tall and several kilometers wide aspect ratio and extent hundreds of kilometers of the ridges as well as preliminary calculations of discharge suggest that a significant amount of water was available

origin and evolution of a cold based tropical mountain glacier on mars the pavonis mons fan shaped deposit 1 each of the large tharsis montes volcanoes in the equatorial region of mars has an unusual amazonian aged fan shaped deposit on its west northwestern flank on the basis of viking orbiter data the origin of these deposits has been variously ascribed to volcanic mass wasting tectonic and glacial processes using new mgs and odyssey data combined with recent developments in the study of cold based glaciers we reassess the geology and mode of origin for these deposits with particular emphasis on pavonis mons the deposits share three characteristic facies including 1 a ridged facies consisting of tens to 100 parallel concentric ridges around the margins of the deposits 2 a knobby facies composed of irregular hills and hummocks and 3 a smooth facies of broad lobate plains that superposes all other units within the deposits on the basis of morphology topography superposition relationships and close terrestrial analogs in the dry valleys of antarctica we interpret the pavonis fan shaped deposit as the depositional remains of a cold based glacier that formed on the northwestern flank in recent martian history we interpret the ridged facies as drop moraines formed around the margins of a retreating cold based glacier the knobby facies as a sublimation till derived from in situ down wasting of cold based glacial ice and the smooth facies as extant debris covered glacial ice in addition to the three main facies the fan shaped deposit at pavonis mons contains several unique features including arcuate scarps high relief flow like features and radial ridges which suggest that volcanism played a role during its formation using recent results from mars general circulation model simulations we outline a model of glacier formation involving atmospheric deposition of water ice on the northwestern flanks of the tharsis montes during periods of high mean obliquity reconstructed ice sheet profiles for each of the tharsis montes glaciers suggest that the ice sheets attained average thicknesses of 1 6 2 4 km values that are consistent with a cold based glacial origin analysis of crater size frequency distributions using new data indicates that the age of the glaciation lies within the late amazonian 10 200 ma thus our results suggest that multiple phases of tropical mountain glaciation occurred on mars within the past few hundred myr and that significant amounts of near surface equatorial ice may remain within the deposit today

role of ocean mesoscale structures in shaping the angola low pressure system and the southern africa rainfall southern african climate is under the influence of both tropical and subtropical systems which result in a complex region where important interactions co exist over a large spectrum of spatiotemporal scales the angola low al situated on boundary between tropical and subtropical southern africa has been diagnosed as a key driver of moisture distribution in the region on daily to seasonal time scales it has been demonstrated that the al pressure system is sensitive to the dynamics of the neighbouring oceans but to date no study has considered the model resolution of air sea interactions required to simulate this sensitivity using sensitivity experiments with a regional atmospheric model which differ only in the mesoscale sea surface temperature sst forcing characteristics either the full spectrum of sst variability or only its large scale components are included we first quantify the importance of sst gradients on the al strength and variability the results suggest that the mesoscale sst variability of the angola benguela frontal zone abfz plays a key role in al activity particularly during the late summer synoptic scale tropical lows which form the al are automatically detected and the results suggest more extreme events occur when the model is forced by mesoscale ssts everywhere and in the abfz area only the rainfall resulting from those events suggests that tropical low episodes are associated with nearly 15 of the total rain in angola and namibia the link between al dynamics and wet spells is also discussed with the former showing a different spatial pattern as well as frequency when the ocean is fully resolved

evolution of interannual warm and cold events in the southeast atlantic ocean extreme warm episodes in the southeast atlantic ocean known as benguela ninos have devastating envi ronmental impacts and have been shown to be remotely forced to place these extreme events into perspective the investigation is here extended to minor warm events as well as to cold episodes to this end different sets of observations have been combined with outputs from a numerical simulation of the tropical atlantic for the period 1982 99 it is shown that both warm and cold surface events develop regularly in the same specific region along the coast of angola and namibia some cold events compete in magnitude with major warm episodes local sea air heat flux exchanges do not seem to precondition the sea surface in the angola benguela region prior to the arrival of an event most warm and cold episodes are large scale events despite their limited surface signature they appear to be generated by wind anomalies in the western and central equatorial atlantic in the same way as benguela ninos seasonal fluctuations of the depth and shape of the tropical thermocline seem partly to control the way subsurface anomalies eventually impact the surface during austral summer surface anomalies create an identifiable pool centered near 158s whereas in winter they show an elongated pattern along the coast stretching toward the equator local upwelling or downwelling favorable wind regimes as well as local net heat fluxes may modulate the surface expression of events

the huygens hellas giant dike system on mars implications for late noachian early hesperian volcanic resurfacing and climatic evolution two narrow broadly arcuate low ridges extend for 600 700 km in western terra tyrrhena mars crosscut ancient noachian terrain and are associated with early hesperian plains which cover 30 of mars geological relationships suggest that the ridges represent near surface erosional remnants of subsurface dikes solidified magma filled cracks that were responsible for the volcanic emplacement of the plains ridge width and geometry are consistent with very high effusion rate flood basalt eruptions emplacement events that would form smooth featureless plains and input significant volcanic gas into the atmosphere geological relationships suggest that the ridges were exposed by erosion fluvial sublimation eolian and partial removal of a regional volatile rich dust layer

a mirror layer of temperature and salinity in the ocean using the newly available 13 year argo float data for the period 2004 2016 a three dimensional temperature salinity t s correlation field is constructed for the global upper ocean it is revealed that the layer averaged correlation between t and s time series has a significant peak 0 7 at a depth of approximately 300 m suggesting that the density compensated thermohaline covariation may lead to a maximum t s coupling in the vicinity of the pycnocline this argument is supported by subsequent findings that the spatial distributions of temperature and salinity have excellent consistencies in terms of both climatology and seasonality around this depth which we call a t s mirror layer since mass heat and salt are mainly transported by dynamic events and processes dominant currents and prevailing eddies in the pycnocline zone are found to determine the fundamental patterns of the global t s climatologies which are characterized by a unified pattern of six well defined warm salty pools with collocated centroids and a clear west preference our results also suggest that the climatological ocean circulations transport heat salt as a conveyor belt meanwhile heat and salt parcels are discretely transported by numerous migrating mesoscale eddies the combined effects of which lead to the formation of six well defined warm salty pools in the western subtropical oceans with a core depth of 300 m at the mirror layer

recurrent daily olr patterns in the southern africa southwest indian ocean region implications for south african rainfall and teleconnections a cluster analysis of daily outgoing longwave radiation olr anomalies from 1979 to 2002 over the southern africa southwest indian ocean swio region for the november to february season reveals seven robust and statistically well separated recurrent patterns of large scale organized convection among them are three regimes indicative of well defined tropical temperate interactions linking the hinterland parts of southern africa to the mid latitudes of the swio preferred transitions show a tendency for an eastward propagation of these systems analysis of daily rainfall records for south africa shows that six of the olr regimes are associated with spatially coherent and significant patterns of enhanced or reduced daily rainfall over the country atmospheric anomalies from the ncep doe ii reanalysis dataset show that the olr regimes are associated with either regional or near global adjustments of the atmospheric circulation the three regimes representative of tropical temperate interactions being in particular related to a well defined wave structure encompassing the subtropical and temperate latitudes featuring strong vertical anomalies and strong poleward export of momentum in the lee of the location of the cloud band the time series of olr regimes seasonal frequency are correlated to distinctive anomaly patterns in the global sea surface temperature field among which are shown to be those corresponding to el nino and la nina conditions the spatial signature of el nino southern oscillation s enso influence is related to the combination of an increased decreased frequency of these regimes it is shown in particular that the well known dipole in convection anomalies contrasting southern africa and the swio during enso events arises as an effect of seasonal averaging and is therefore not valid at the synoptic scale this study also provides a framework to better understand the observed non linearities between enso and the seasonal convection and rainfall anomalies over the region

plateaus and sinuous ridges as the fingerprints of lava flow inflation in the eastern tharsis plains of mars abstract the tharsis montes rift aprons are composed of outpourings of lava from chaotic terrains to the northeast and southwest flank of each volcano sinuous and branching channel networks that are present on the rift aprons suggest the possibility of fluvial processes in their development or erosion by rapidly emplaced lavas but the style of lava flow emplacement throughout rift apron development is not clearly understood to better characterize the style of lava emplacement and role of fluvial processes in rift apron development we conducted morphological mapping of the pavonis mons southwest rift apron and the eastern tharsis plains using images from the high resolution imaging science experiment hirise mars orbiter camera moc context camera ctx thermal emission imaging system themis and high resolution stereo camera hrsc along with the mars orbiter laser altimeter mola precision experiment data records pedrs and gridded data our approach was to 1 search for depositional fans at the slope break between the rift apron and adjacent low slope plains 2 determine if there is evidence that previously formed deposits might have been buried by plains units 3 characterize the tharsis plains morphologies east of pavonis mons and 4 assess their relationship to the rift apron units we have not identified topographically significant depositional fans nor did we observe evidence to suggest that plains units have buried older rift apron units flow features associated with the rift apron are observed to continue across the slope break onto the plains in this area the plains are composed of a variety of small fissures and low shield vents around which broad channel fed and tube fed flows have been identified we also find broad flat topped plateaus and sinuous ridges mixed among the channels tubes and vents flat topped plateaus and sinuous ridges are morphologies that are analogous to those observed on the coastal plain of hawai i where lava flows have advanced from the volcano s several degree flank onto the nearly zero degree coastal plain when local volumetric flow rates are low flow fronts tend to spread laterally and often thicken via endogenous growth or inflation of the sheet like flow units if flow advance is restricted by existing topography into narrow pathways inflation can be focused into sinuous elongate ridges the presence of plateaus and ridges emplaced from the rift zones across the plains to the east of pavonis mons and a lack of fan like features or evidence for their burial are consistent with rift apron lavas crossing a slope break with low local volumetric flow rates that led to inflation of sheet like and tube fed lava flows

the angola low relationship with southern african rainfall and enso the main states of the angola low al are identified using clustering analysis applied to daily anomalous patterns of 700 hpa wind vorticity over angola and adjacent countries from november to march for the 1980 81 2014 15 period at the daily timescale we examine the extent to which the main states of the al modulate daily rainfall over southern africa at the interannual timescale we assess both the relationship between the occurrence of these al states and el nino southern oscillation enso and the role of the al in explaining enso s failure in driving southern african rainfall at times three reanalyses are considered to account for uncertainties induced by the scarcity of data available for assimilation over southern africa three preferential states of the angola low are identified al state close to its seasonal climatology with slight zonal displacements anomalously weak al state and anomalously strong al state with meridional displacements these different states all significantly modulate daily southern african rainfall near climatological al state promotes wet rainfall anomalies over eastern subtropical southern africa and dry rainfall anomalies over its western part a slight westward shift in the near climatological position of the al leads to reversed zonal gradient in rainfall the remaining regimes significantly modulate the meridional gradient in southern african rainfall anomalously weak and anomalously northward al states promote wet rainfall anomalies over tropical southern africa and dry rainfall anomalies over subtropical southern africa the reverse prevails for anomalously southward al at the interannual timescale enso significantly modulates the seasonal occurrence of most al states in the three reanalyses anomalously weak and southward al states are more strongly correlated with regional rainfall than enso in all reanalyses suggesting that accounting for al variability may improve seasonal forecasts case study analysis of the major 1982 83 and 1997 98 el nino events suggests that the weak rainfall anomalies and strong seasonal al in 1997 98 may result from counteracting effects between enso and indian ocean coupled modes of variability

characterizing the synoptic expression of the angola low the angola low is a key feature of the southern africa wet season atmosphere that influences precipitation across the continent this paper uses era interim to show that the synoptic expression of the angola low is a combination of dry heat lows and moist tropical low pressure systems the angola heat low and angola tropical low composites are contrasted against similar lows observed in other continental tropical regions and found to be broadly comparable the implications that the distinction between dry and moist events has for the interannual relationship among the angola low precipitation and enso are examined the tropical lows exhibit unusual semistationary behavior by lingering in the angola region rather than traveling offshore this behavior is proposed to be caused by an integrated sea breeze anabatic wind that enhances inhibits cyclonic vorticity stretching and convection inland near the coast the combined effect of the heat lows and the anchored tropical lows creates the angola low in the climatological average by elucidating the mechanisms of the angola low this research improves the foundation of process based evaluation of southern africa present and future climate in cmip and amip models

dominant anomaly patterns in the near surface baroclinicity and accompanying anomalies in the atmosphere and oceans part i north atlantic basin abstract variability in the monthly mean flow and storm track in the north atlantic basin is examined with a focus on the near surface baroclinicity b bxi byj dominant patterns of anomalous b found from empirical orthogonal function eof analyses generally show patterns of shift and changes in the strength of b composited anomalies in the monthly mean wind at various pressure levels based on the signals in the eofs display robust accompanying anomalies in the mean flow up to 50 hpa in the winter and up to 100 hpa in other seasons anomalous eddy fields accompanying the anomalous bx patterns exhibit broadly speaking structures anticipated from linear theories of baroclinic instabilities and suggest a tendency for anomalous wave fluxes to accelerate decelerate the surface westerly accordingly atmospheric anomalies accompanying by anomalies have patterns different from those that accompany bx anomalies but are as large as those found for bx anomalies in the sea surface temperature sst found for

subtropical sst dipole events in the southern indian ocean sea surface temperature sst anomalies in the subtropical southern indian ocean show interannual dipole events that are seasonally phase locked to the austral summer a positive phase of the event is characterized by cold sst anomalies in the eastern part i e off australia and warm sst anomalies in the southwestern part south of madagascar such an event is found to produce above normal rainfall over many regions in south central africa the cooling of sst in the eastern part is mainly caused by the enhanced evaporation this is associated with stronger winds along the eastern edge of the subtropical high which is strengthened and shifted slightly to the south during the event on the other hand relative decrease in the seasonal latent heat loss due to reduced evaporation dominates the warming in the southwestern part evolution of such subtropical dipole events shows quite a contrast to that of the tropical dipole events discovered recently in the indian ocean

circulation anomalies associated with tropical temperate troughs in southern africa and the south west indian ocean daily rainfall variability over southern africa sa and the southwest indian ocean swio during the austral summer months has recently been described objectively for the first time using newly derived satellite products the principle mode of variability in all months is a dipole structure with bands of rainfall orientated northwest to southeast across the region these represent the location of cloud bands associated with tropical temperate troughs ttt this study objectively identifies major ttt events during november to february and on the basis of composites off ncep reanalysis data describes the associated atmospheric structure the two phases of the rainfall dipole are associated with markedly contrasting circulation patterns there are also pronounced intra seasonal variations in early summer the position of the temperate trough and ttt cloud band alternates between the swio and southwest atlantic in late summer the major ttt axis lies preferentially over the swio associated with an eastward displacement in the indian ocean high in all months positive events in which the ttt cloud band lies primarily over the swio are associated with large scale moisture flux anomalies in which convergent fluxes form a pronounced poleward flux along the cloud band this suggests that ttt events are a major mechanism of poleward transfer of energy and momentum moisture transport occurs along three principle paths 1 the northern or central indian ocean where anomalous fluxes extend eastward to the maritime continent 2 south equatorial africa and the equatorial atlantic 3 from the south within a cyclonic flow around the tropical temperate trough the relative importance of 2 is greatest in late summer thus synoptic scale ttt events over sa swio often result from large scale planetary circulation patterns hovmoeller plots show that ttt development coincides with enhanced tropical convection between 10 30 e itself exhibiting periodicity of around 5 days and often with convergence of eastward and westward propagating convection around 40 e harmonic analysis of 200 hpa geopotential anomalies show that ttt features are forced by a specific zonally asymmetric wave pattern with wave 5 dominant or significant in all months except february when quasi stationary waves 1 2 and 3 dominate these findings illustrate the importance of tropical and extratropical dynamics in understanding ttt events finally it is suggested that in november januar ttt rainfall over sa swio may be in phase with similar rainfall dipole structures observed in the south pacific and south atlantic convergence zones

impacts of sst anomalies in the agulhas current system on the regional climate variability abstractthe potential impact of the variability in the agulhas current system on the large scale atmospheric state in the southern hemisphere is examined using the monthly near surface baroclinicity as the key parameter for the period between september 1980 and august 2002 dominant patterns of anomalous near surface baroclinicity found from empirical orthogonal function eof analyses in the region that includes most of the agulhas current system show a wide variety of anomaly patterns some of which indicate spatial shifts in the position of the agulhas retroflection and or agulhas return current composited anomalies in various atmospheric fields sea surface temperature and the net surface heat flux at the air sea boundary based on the signals in the eofs suggest that sea surface temperature anomalies in the agulhas current system thermally force the atmosphere on the synoptic scale via modification of the near surface baroclinicity in march and april and possibly in january and february as well

long range high resolution stratigraphic correlation of rotliegend fluvial fan deposits in the central dutch offshore abstract the rotliegend feather edge area in the central part of the endorheic southern permian basin in the dutch offshore is characterized by a predominance of mud prone evaporite bearing playa and lake deposits with a subordinate amount of interbedded thin fluvial sheet sandstones the distribution and lateral facies changes of the sandstone bodies have been analyzed by generating a long range high resolution chronostratigraphic correlation framework the correlation technique of pattern matching of gr logs was applied supported by calculating spectral trend curves flooding events are the primary near synchronous correlation surfaces which can be traced up to and over 100 km the basin setting of the southern permian basin the studied sandstone depositional architecture logs and sedimentary characteristics core are analogous to the depositional setting of laterally amalgamated terminal lobes of dryland river systems in an endorheic basin such as the holocene altiplano basin in bolivia present day lake eyre australia and the miocene ebro basin spain the integrated approach has yielded a stratigraphic reservoir architecture framework in which the reservoir sandstones with net sand up to 10 m have been identified as amalgamated terminal splay sandstone sheets formed at the end of dryland river pathways alternating with lacustrine mudstone layers deposited during short duration high magnitude flooding in intermittent wet climate periods

extensive linear ridge networks in nili fossae and nilosyrtis mars implications for fluid flow in the ancient crust 1 we have undertaken high resolution mapping of the distribution physical characteristics orientation and stratigraphic occurrence of 4000 linear ridge segments in two study areas the nilosyrtis highlands and the nili fossae region covering 1 105 km2 ridges are typically hundreds of meters in length meters in width and up to tens of meters in height ridges form intersecting networks of anastomosing and bifurcating segments and consequently have variable orientations ridges are expressed in altered and brecciated basement materials on the floors and rims of impact craters deeply eroded by fluvial and other processes the ridge bearing basement is the lowest exposed stratigraphic unit and is overlain by a relatively unaltered mafic cap rock ridges are observed to terminate at the contact of these two units we interpret the ridges to represent a complex of fractures faults shear zones clastic and melt bearing dikes and pseudotachylytes that have been variably indurated by fluid percolation and mineralization the fluid conduits were hardened relative to the host rock and are expressed as ridges due to differential erosion the orientations of the exhumed ridges record the state of stress in the crust at the time of formation in nili fossae a significant population of ridges is aligned with the orientations of the nili fossae graben indicating that their emplacement may be related to crustal loading of the isidis basin after the impact event the association of ridges with the hydrated mineral bearing basement suggests that in the postimpact environment the fractures served as conduits of preferential fluid flow which were cemented by mineral precipitation

dike indicators in the hadriaca patera promethei terra region mars abstract the eastern hellas basin rim has been highly modified by a multitude of both volcanic and fluvial processes it is covered by a large part of the circum hellas volcanic province consisting of the volcanic plains of hesperia planum and western promethei terra as well as the two central volcanoes hadriaca and tyrrhena patera and their associated lava flows large outflow channels of dao niger harmakhis reull and teviot valles dissect the wrinkle ridged plains postdating the major volcanic events the origin of these outflow channels is still ambiguous as the mobilization mechanism for the underground volatile reservoirs has yet to be revealed due to the proximity of the volcanic structures many previous studies have suggested via models that the released ice or ground water was mobilized due to endogenic heating from magmatic activity in the region to find evidence of this we conducted a systematic search for any magmatic intrusions at 50 m pixel resolution this paper provides detailed mapping of several areas where we found features which we interpret to be dikes and shows the overall distribution of such structures in the eastern hellas rim region the hadriaca patera volcano flanks exhibit a concentric pattern of linear ridges and fractures indicative of a vast ring dike system the dikes occupy mostly the area near the summit and the hellas facing flank extending there for over 400 km away from the caldera a hadriaca radial dike swarm pattern is observed extending southwards from the volcano composed of isolated parallel linear ridge group outcrops and cut by the valles canyons an additional isolated dike ridge group exists south of lower reull valles possibly controlled by the tyrrhena patera volcano some 1300 km away all dikes within the study region are roughly late hesperian in age either predating the valles formation or being roughly concurrent with them in total 500 dike segments were identified with a combined length of 2500 km since 90 of the dikes are ridges they suggest that the entire region has undergone large scale erosion of at least a few tens of meters to expose the dikes the dike orientations were most probably controlled by the volcanic centers and possibly partly by a hellas concentric fracture pattern

volcanic geology of tyrrhena patera mars tyrrhena patera is a large low relief volcano located in the southern cratered highlands of mars on a proposed ring fracture of the hellas basin the volcano is composed of four or possibly five principal units the oldest and most areally extensive of which are suggested to be ash on the basis of their morphology and erosional characteristics lava flows are observed in a flank flow unit extending from the central caldera to the southwest and apparently cap the summit region models derived from the study of terrestrial pyroclastic flows have been applied to the deposits at tyrrhena patera and indicate that the distribution and lengths of the observed deposits are consistent with an origin by the emplacement of gravity driven ash flows generated by hydromagmatic or magmatic explosive eruptions the hydromagmatic case requires considerable quantities of water 7 5 1016 kg however at volumetric water flow rates determined by other investigators 105 m3 s and calculated from the regional slopes in the hesperia planum region 106 m3 s the amounts necessary could be supplied relatively rapidly in geologic time tyrrhena patera represents the earliest central vent volcanism identified on mars and may reflect a transition from the flood style eruptions which dominated early martian history a hydromagmatic origin for tyrrhena patera is in agreement with suggested climatic changes on mars and may explain the absence of this style of volcanism in later eras alternatively a magmatic origin for tyrrhena patera implies an evolution in the types of magmas produced on mars from hesperian to amazonian time during which the prominent shields in the tharsis region formed

interannual warm and cool events in the subtropical mid latitude south indian ocean region interannual warm and cool events in the subtropical mid latitude south indian ocean region that are not associated with extreme phases of the el nino southern oscillation are examined during these events there tend to be periods of significantly anomalous rainfall in large parts of southern africa typically the sea surface temperature sst anomalies become significant during the austral autumn of the first calendar year of the event and dissipate during the spring of the following year examination of cloud cover and near surface winds suggests that atmospheric forcing may contribute towards the sst anomalies via changes in insolation and wind driven upper ocean mixing and surface fluxes

modelling the precipitation response over southern africa to the 2009 2010 el nino using a stretched grid global atmospheric model the 2009 2010 el nino event was a moderately strong central pacific type enso and as such expected to lead to a substantial drought over southern africa during austral summer however many parts of the region experienced average to well above average rainfall during this season given that seasonal forecasting skill tends only to be good during enso seasons and many parts of the sub continent rely on rain fed agriculture understanding why the rainfall was so anomalous during this el nino event is important to this end a global stretched grid atmospheric general circulation model with relatively high horizontal resolution of 0 5 0 5 is applied over the region with observed and idealised sst forcing in the latter experiments ssts are kept as observed over one ocean basin e g pacific and as climatology over the other two basins e g atlantic indian or as climatology over one basin and as observed over the other two basins in order to help understand which of these three basins may have contributed most to the observed rainfall anomalies in summer 2009 2010 it is found that pacific ocean forcing contributed to the summer rainfall anomalies over most regions of southern africa with the atlantic acting to oppose the effects of the pacific however over mozambique and to some extent zimbabwe the indian ocean was more important with the atlantic again acting in opposition the increased rainfall over most of southern africa appears mainly due to a stronger angola low circulation system and to anomalously strong moisture flux from the tropical western indian ocean and to lesser extent the tropical south east atlantic ocean

evidence from magnetic fabric for the flow pattern of magma in the mackenzie giant radiating dyke swarm continental flood basalts and their associated swarms of mafic dykes are thought to result from melting in mantle plumes1 3 but the processes by which the resulting magma makes its way from mantle to crust remain obscure here we use magnetic anisotropy measurements to reconstruct the pattern of magma flow in the proterozoic mackenzie dyke swarm our results indicate that magma was injected vertically within 500 km of the focal point of the dyke swarm and then travelled horizontally at all further distances out to at least 2 100 km the sharp transition from vertical to horizontal flow at between 500 and 600 km may correspond to the outer boundary of melt generation in the mantle plume believed to be responsible for the mackenzie igneous events

extensive hesperian aged south polar ice sheet on mars evidence for massive melting and retreat and lateral flow and ponding of meltwater local and regional mars orbiter laser altimeter mola topographic data support the presence of an extensive hesperian aged volatile rich south polar deposit the dorsa argentea formation hd and related units underlying the present amazonian aged polar cap api residual ice and apl layered terrain and covering a surface area that could be as large as 2 94 106 km2 about 2 of the surface of mars over twice the area of the present amazonian aged south polar deposits the deposit characteristics indicate that it contained significant quantities of water ice in amounts comparable to present day polar deposits several lines of evidence for melting indicate that the ice sheet deposits underwent melt back and liquid water drainage into surrounding lows including a large valley near the crater schmidt and the argyre basin narrow sinuous ridges lie in a broad linear depression extending from a high near the present polar cap continuously downslope to near the distal portion of hd the new topographic data support the interpretation of these ridges as eskers representing meltwater distribution networks at the base of the receding deposit extensive development of large pits and depressions cavi have previously been interpreted as eolian etching or basal melting of ice rich deposits analysis of mola topography supports the interpretation that they represent basal melting of ice rich deposits and shows that they have links to the esker systems volumetric considerations and topographic lineations suggest that some of the basal melting occurred beneath regions presently occupied by apl and that some of the liquid water formed ponds and lakes in the distal parts of hd the presence of pedestal craters is further evidence of the removal of extensive volatile rich deposits and contributes to the quantitative measure of the former deposit thickness where did the melt products go inspection of the margins of the dorsa argentea formation reveals several large channels that begin there and drain downslope for distances between 900 and 1600 km onto the floor of the argyre basin some 3 5 4 0 km below their origin these channels do not exhibit tributaries their broad lateral distribution supports other evidence that deposit melting was areally very widespread and volumetrically significant and that a large part of the meltwater entered the surface distribution system and was deposited on the floor of the argyre basin over 1000 km away estimates of the present deposit thicknesses together with amounts of the deposit removed by meltback suggest that the original volume could have been as much as 5 9 106 km3 equivalent to a global layer of water 20 m deep if the deposit consisted of 50 volatiles a portion of these volatiles migrated across the surface to pond in adjacent valleys and basins and into the groundwater system a significant portion of the volatiles remain in the deposit representing a net removal from the atmosphere and from the active hydrologic system in early to middle mars history and forming an accessible record of aqueous conditions and possible biological environments dating from that time

nature of local magma storage zones and geometry of conduit systems below basaltic eruption sites pu u o o kilauea east rift hawaii example the fluid dynamics of the well documented eruptive episodes at pu u o o kilauea wolfe et at 1987 are used to investigate quantitativeely the size and shape of the shallow conduit system beneath the vent cooling calculations are employed to study the long term survival of conduits and the consequences of multiple dike injection events we find that the subvent conduit must have a planar geometry at depths greater than a few tens to at most a few hundreds of meters with a width of less than a few meters a length of the order of 100 m and a height of the order of 1 kin this structure is clearly the residue of the preeruption dikes although such a feature can be widened somewhat by repeated dike emplacement events there is no evidence to suggest that a larger and much more equant magma reservoir should develop at shallow depth the extensive degassing often occurring after single eruptions or between repeated eruptions previously thought to imply the presence of a large equidimensional shallow magma chamber can be readily explained by the volume of magma in a dikelike subvent planar magma storage zone on the basis of these observations which we infer to apply commonly to basaltic eruption sites we suggest that the terms chamber or reservoir be used with caution because they most often connote a relatively large equant magma body distinct from the feeder dike lying just below the vent we find that the subvent region has the same basic geometric characteristics as the parental dike and we propose that it be referred to as a planar magma storage zone

major episodes of geologic history of isidis planitia on mars abstract we have mapped the area of isidis planitia 1 27 n 75 103 e in order to assess the geologic history of this region using modern data sets such as mola topography and the high resolution images provided by the hrsc ctx and hirise cameras results of our mapping show that the geologic history of isidis planitia consists of three principal episodes 1 impact dominated episode noachian until 3 8 ga during this time the oldest materials in the study area were formed mostly by impact reworking and mass wasting other processes e g volcanism and fluvial glacial activity likely operated at this time but played a subordinate role 2 an episode related to volcanic and fluvial glacial activities late noachian early amazonian 3 8 2 8 ga volcanism appears as the most important process at the beginning of this episode 3 8 3 5 ga and was responsible for the formation of a large circum isidis volcanic province by the early hesperian epoch volcanic materials covered large portions of the isidis rim almost completely buried the previous crater record on the floor of the isidis basin and probably were the major contributors to the filling of the basin fluvial glacial processes prevailed closer to the end of the episode early hesperian early amazonian 3 5 2 8 ga and were responsible for widespread resurfacing in the isidis planitia region mostly at 3 1 3 4 ga glaciers and or ice sheets probably resulted in a massive glaciation of the rim and the floor of the isidis basin the total volume of material eroded from the isidis rim by glacial and fluvial activity is estimated to be about 35 000 50 000 km 3 which is equivalent to a composite layer about 40 60 m thick on entire floor of the basin more important however is that the eroded materials were likely saturated with ice water and could form wet deposits on the floor 3 wind dominated episode since early amazonian 2 8 ga wind activity dominated the later geologic history of isidis planitia but resulted only in minor modification of the surface

subtropical indian ocean sst dipole events and southern african rainfall an atmospheric general circulation model agcm is used to examine how the regional atmospheric circulation and rainfall over southern africa respond to a recently observed dipole in subtropical sea surface temperature sst over the south indian ocean observations suggest that when sst is warm to the south of madagascar and cool off western australia increased summer rains occur over large areas of southeastern africa the model results suggest that this sst pattern leads to increased rainfall via enhanced convergence of moister than average air over the region increased evaporation occurs over the warm pole in the south west indian ocean and this moist air is advected towards mozambique and eastern south africa as a result of the low pressure anomaly generated over this pole which strengthens the onshore flow

on the generation and propagation of the southern african coastal low the time height variability of the lower marine atmosphere during the eastwards propagation of coastal lows around the coast of southern africa is presented these coastal lows are shallow mesoscale disturbances that are trapped vertically by a strong subsidence inversion and horizontally through coriolis effects against the steep escarpment that fringes the subcontinent prior to the event warm offshore flow descending off this escarpment at about the inversion level provides an input of buoyancy which together with the cyclonic vorticity acquired during the descent acts to generate a coastal low rather than a high analysis of the data shows that coastal lows are characterized by a marked lowering of the inversion level a switch in the direction of the winds below the inversion and a drop in the near surface temperature which are all consistent with the hypothesis that the coastal low is an internal kelvin wave propagating in the marine layer good agreement between the observed propagation speed of the coastal low and the theoretical phase speed of such a wave reinforces this hypothesis a model of the vertical buoyancy advection into the marine atmosphere that results from the warm offshore flow is presented it is illustrated that an internal kelvin wave in the form of a coastal low results from this buoyancy advection comparisons are made between coastal low dynamics and those characteristics of other mesoscale coastally trapped disturbances which propagate in the marine layers of california and south eastern australia

high resolution satellite measurements of the atmospheric boundary layer response to sst variations along the agulhas return current abstract the marine atmospheric boundary layer mabl response to sea surface temperature sst perturbations with wavelengths shorter than 30 longitude by 10 latitude along the agulhas return current arc is described from the first year of sst and cloud liquid water clw measurements from the advanced microwave scanning radiometer amsr on the earth observing system eos aqua satellite and surface wind stress measurements from the quikscat scatterometer amsr measurements of sst at a resolution of 58 km considerably improves upon a previous analysis that used the reynolds sst analyses which underestimate the short scale sst gradient magnitude over the arc region by more than a factor of 5 the amsr sst data thus provide the first quantitatively accurate depiction of the sst induced mabl response along the arc warm cold sst perturbations produce positive negative wind stress magnitude perturbations leading to short scale perturbations in the wind stress curl and divergence fields that are li

a model study of the angola benguela frontal zone sensitivity to atmospheric forcing 1 a regional ocean model is applied to the tropical south east atlantic ocean in order to investigate the sensitivity of the intensity and position of the angola benguela frontal zone the results suggest that the position of the angola benguela frontal zone is mainly determined by opposing northward and southward flow within 2 degrees off the coast the windstress curl plays a major role in altering the position of the angola benguela frontal zone as it controls the southeastward flow of the south equatorial counter current the opposing northward flow is mainly the result of geostrophic adjustment to coastal upwelling driven by the meridional windstress the strength of the frontal zone is found to be related to the strength of the southerly windstress that controls the coastal upwelling

interactions between synoptic intraseasonal and interannual convective variability over southern africa after removing the annual cycle a principal component analysis is applied to the daily outgoing longwave radiation anomaly field used here as a proxy for atmospheric convection the analysis is carried out over the southern african region 7 5 e 70 e 10 s 40 s for austral summer november through february for the period 1979 1980 to 2006 2007 the first five principal components pc are retained the first two pcs describe spatial patterns oriented north west to south east from tropical southern africa sa to the mid latitudes they are interpreted to be different possible locations for synoptic scale tropical temperate troughs ttt one dominant rainfall producing synoptic system in the region the phase relationship between these two pcs describes a tendency for these ttt to propagate eastwards from sa to the mozambique channel and southern madagascar the next three pcs describe convective fluctuations respectively located over the north west the south and the centre of sa their time series are significantly associated with madden julian oscillation mjo activity in the tropics however we find that ttt systems are statistically independent of the mjo i e they are equally liable to occur during any phase of the mjo three pcs out of five also show a significant association with el nino southern oscillation confirming that el nino years mostly coincide with suppressed convection at the intraseasonal time scales a result consistent with its impact on seasonal averages diagnosed in previous studies

tropical extratropical interactions over southern africa three cases of heavy summer season rainfall abstract the synoptic evolution of three tropical extratropical te interactions each responsible for extreme rainfall events over southern africa is discussed in detail along with the consideration of previously studied events common features of these heavy rainfall producing tropical temperate troughs ttts over southern africa are discussed it is found that 2 days prior to an event northeasterly moisture transports across botswana set up by the angola low are diverted farther south into the semiarid region of subtropical southern africa the ttts reach full maturity as a te cloud band rooted in the central subcontinent which is triggered by upper level divergence along the leading edge of an upper tropospheric westerly wave trough convection and rainfall within the cloud band is supported by poleward moisture transports with subtropical air rising as it leaves the continent and joins the midlatitude westerly flow it is shown that these systems fit within a theoretical framework describing

preservation of late amazonian mars ice and water related deposits in a unique crater environment in noachis terra age relationships between lobate debris tongues and gullies abstract the amazonian period of mars has been described as static cold and dry recent analysis of high resolution imagery of equatorial and mid latitude regions has revealed an array of young landforms produced in association with ice and liquid water because near surface ice in these regions is currently unstable these ice and water related landforms suggest one or more episodes of martian climate change during the amazonian here we report on the origin and evolution of valley systems within a degraded crater in noachis terra asimov crater the valleys have produced a unique environment in which to study the geomorphic signals of amazonian climate change new high resolution images reveal hesperian aged layered basalt with distinctive columnar jointing capping interior crater fill and providing debris via mass wasting for the surrounding annular valleys the occurrence of steep slopes 20 relatively narrow sheltered valleys and a source of debris have provided favorable conditions for the preservation of shallow ice deposits detailed mapping reveals morphological evidence for viscous ice flow in the form of several lobate debris tongues ldt superimposed on ldt are a series of fresh appearing gullies with typical alcove channel and fan morphologies the shift from ice rich viscous flow formation to gully erosion is best explained as a shift in martian climate from one compatible with excess snowfall and flow of ice rich deposits to one consistent with minor snow and gully formation available dating suggests that the climate transition occurred 8 ma prior to the formation of other small scale ice rich flow features identified elsewhere on mars that have been interpreted to have formed during the most recent phases of high obliquity taken together these older deposits suggest that multiple climatic shifts have occurred over the last tens of millions of years of martian history

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen

surface deformation and shallow dike intrusion processes at inyo craters long valley california the inyo craters are the two largest of four phreatic craters that lie within a 2 5 km long 500 to 700 m wide n s trend of faults and fissures at the south end of the inyo volcanic chain in eastern california the alignment of these features with dike fed silicic volcanic centers of the same age a few kilometers to the north suggests that they were produced during intrusion of a dike at about 650 550 yr b p e w extension south of south inyo crater is ten to several tens of meters suggesting that the dike is at least that thick to understand how the faults and fissures developed we mapped and studied the fault and fissure pattern used a theoretical boundary element model to determine the surface strain profile above a shallow dike in a purely elastic medium and conducted physical model experiments of fault and fissure growth results of the field studies and experiments indicate that deformation develops according to the following sequence 1 extension fractures and perhaps other inelastic deformation develop immediately above the dike top and on the limbs of a shallow syncline which forms above the dike 2 fissures form along two parallel trends at the surface on opposite sides of the dike plane leaving a relatively unfractured region in between 3 dip slip movement on subsurface fractures and linkage of these fractures with surface fissures produces inward facing normal fault scarps that bound a nested graben above the dike experimental graben widths are up to several times narrower than predicted from the locations of theoretical strain maxima above a dilating crack in a linearly elastic medium this fact is apparently due to the growth of a zone of inelastic deformation above the experimental dike top in the subsurface if the ratio between the depth to the dike top and the distance between the outermost surface fissures at inyo craters is within the range of ratios measured experimentally then the depth to the dike top is between 250 m and several times that a slant hole drilled in the summer of 1987 by the department of energy office of basic energy sciences intersected three breccia bodies of possibly intrusive origin directly below the center of south inyo crater between 550 m and 610 m below the crater rim no intact juvenile igneous rock was intersected suggesting that the hole passed above the magma filled dike top perhaps passing through the zone of inelastic deformation which is inferred to exist from our model results

the formation of small cones in isidis planitia mars through mobilization of pyroclastic surge deposits abstract we investigate the distinctive distribution and pattern of subkilometer sized cones in isidis planitia and their relationship to the material that fills the basin we observe that 1 the cones show uniform size spacing and morphology across the entire basin 2 they have large central depressions relative to cone basal diameters that are generally filled in and commonly show layering 3 cone chains form highly organized spatial patterns cones are also found in isolation and in dense fields 4 many adjacent chains are parallel and evenly spaced creating a pattern that mimics lava flows that have experienced compressional folding 5 no flows are associated with the cones even where summit crater rims are breached 6 the cones are at least temporally related to basin fill 7 the basin fill material is largely fine grained but with locally indurated layers at shallow depth blocks ejected by small craters from these locally indurated layers are commonly dark in color and 8 relationships between cones along a chain show no systematic temporal formation sequence along the chain we conclude that the basin was likely inundated by one or more hot partially welded pyroclastic flows devolatilization of these flows remobilized volcaniclastic material to form the cones without associated lava flows the volume of gas required to account for the observed number of cones is low and does not require the presence of ground water or ice