the nature of the arctic oscillation and diversity of the extreme surface weather anomalies it generates abstractthrough a cluster analysis of daily ncep ncar reanalysis data this study demonstrates that the arctic oscillation ao defined as the leading empirical orthogonal function eof of 250 hpa geopotential height anomalies is not a unique pattern but a continuum that can be well approximated by five discrete representative ao like patterns these ao like patterns grow simultaneously from disturbances in the north pacific the north atlantic and the arctic and both the feedback from the high frequency eddies in the north pacific and north atlantic and propagation of the low frequency wave trains from the north pacific across north america into the north atlantic play important roles in the pattern formation furthermore it is shown that the structures and frequencies of occurrence of the five ao like patterns are significantly modulated by el nino southern oscillation enso warm cold enso enhances the negative positive ao phase compared with enso neutral winters finally the surface weat

planetary surface dating from crater size frequency distribution measurements partial resurfacing events and statistical age uncertainty abstract we describe the procedure to fit a cumulative production function polynomial to a partial crater size frequency distribution the technique is of particular use in deriving ages for surfaces which have undergone partial resurfacing events namely erosional or depositional events which have affected a limited diameter range of the crater population we demonstrate its use in obtaining times for both the surface formation and the resurfacing event we give a practical outline of the method for making age measurements from crater counts and how to identify resurfacing effects in the results we discuss the conversion of production function polynomials between common presentations and the statistical uncertainty of the determined ages with respect to the non linear chronology function and a minor refinement of data binning

estimating the sensitivity of the atmospheric teleconnection patterns to sst anomalies using a linear statistical method abstractthe pacific north american pna pattern and the north atlantic oscillation nao are known to contain a tropical sea surface temperature sst forced component this study examines the sensitivity of the wintertime nao and pna to patterns of tropical sst anomalies using a linear statistical dynamic method the nao index is sensitive to sst anomalies over the tropical indian ocean the central pacific ocean and the caribbean sea and the pna index is sensitive to sst anomalies over the tropical pacific and indian oceans the nao and pna patterns can be reproduced well by combining the linear operator with the consistent sst anomaly over the indian ocean and the nino 4 regions respectively suggesting that these are the most efficient ocean basins that force the teleconnection patterns during the period of 1950 2000 the nao time series reconstructed by using sst anomalies over the indian ocean nino 4 region caribbean sea or the indian ocean nino 4 region is significantly correlated with t

lineated valley fill lvf and lobate debris aprons lda in the deuteronilus mensae northern dichotomy boundary region mars constraints on the extent age and episodicity of amazonian glacial events abstract in order to assess the nature degradational processes and history of the dichotomy boundary on mars we conducted a detailed morphological analysis of a 70 000 km 2 region of its northern portion north central deuteronilus mensae south of lyot in the vicinity of sinton crater this region is characterized by the distinctive sinuous 2 km high plateau scarp boundary outlying massifs to the north and extensive fretted valleys dissecting the plateau to the south these features represent the first order modification and retreat of the dichotomy boundary and are further modified by processes that form lineated valley fill lvf in the fretted valleys and lobate debris aprons lda along the dichotomy scarp and surrounding the outlying massifs we use new high resolution image and topography data to examine the nature and origin of lvf and lda and to investigate the climatic and accompanying degradational history of the escarpment on the basis of our analysis we conclude that 1 lvf and lda deposits within the study region are comprised of the same material show integrated flow patterns and originate as debris covered valley glaciers a significant amount of ice hundreds of meters is likely to remain today beneath a thin cover of sublimation till 2 there is depositional evidence to suggest glacial highstands at least 800 m above the present level implying previous conditions in which the distribution of ice was much more widespread this is supported by similar deposits within many other areas across the dichotomy boundary 3 the timing of the most recent large scale activity of the lda lvf in this area is about 100 500 million years ago similar to ages reported elsewhere along the dichotomy boundary 4 there is evidence for a secondary but significantly limited phase of glaciation the deposits of which are limited to the vicinity of the alcoves similar later phases have also been reported elsewhere along the dichotomy boundary 5 modification of the fretted valleys of the dichotomy boundary has been substantial locally but we find no evidence that the amazonian glacial epochs caused retreat of the dichotomy boundary of the scale of tens to hundreds of kilometers our findings support the results of an analysis just to the east of the study region and of studies carried out elsewhere along the dichotomy boundary that find further evidence for the remnants of debris covered glaciers and extensive valley glacial land systems

morphologic and topographic analyses of debris aprons in the eastern hellas region mars this paper presents new detailed analyses of small scale morphologic and topographic characteristics of martian debris aprons that support viking based interpretations of debris aprons as ice rich flow features derived from local uplands fifty four debris apron complexes in the eastern hellas region of mars were examined using mars global surveyor data sets including mars orbiter camera images and mars orbiter laser altimeter topographic profiles consistent patterns in a suite of small scale surface textures and geomorphic features observed throughout the population reflect a history of viscous flow and surface degradation through wind ablation and loss of contained ice a wide variety of shapes seen in topographic profile reveal variations in distribution of contained ice and different stages of apron development and degradation the results of this study provide new evidence consistent with multiple models of apron formation including rock glacier debris covered glacier and ice rich landslide models typical eastern hellas debris aprons formed from a series of large scale events emplacing debris that was enriched initially or later by ground ice complemented by small scale mass wasting of multiple styles and postemplacement flow of apron masses

theoretical analysis of secondary cratering on mars and an image based study on the cerberus plains the issue of crater retention age estimates on planetary surfaces is discussed with an attempt to quantify the effect of overlapping primary and secondary impact crater populations in restricted crater diameter ranges the approach to this problem is illustrated with a simple model production function where the secondary crater input is artificially enhanced extrapolation of such a secondary crater model distribution to a global record results in extraordinarily high crater frequencies that do not exist on mars and implies the need of detailed studies of the size frequency distribution for remote secondary craters to date poorly known a key case the martian crater zunil and its secondary crater field illustrate that reasonable predictions for the secondary crater size frequency distribution at small 100 m crater diameters affected the standard model crater retention age for the cerberus plains less than the statistical uncertainty these observations show that age determination based on appropriate crater counting statistics is valid in a wide primary crater diameter range

modification of the dichotomy boundary on mars by amazonian mid latitude regional glaciation 1 restoration of the dichotomy boundary to its original position to assess its origin requires a thorough knowledge of processes responsible for its degradation and retreat the unique fretted terrain located along the deuteronilus protonilus mensae northern mid latitude portion of the boundary has been long held to provide clues to dichotomy degradation processes we use new spacecraft data to show that fretted valleys display a multitude of characteristics typical of integrated valley glacial systems on earth multiple theater headed alcove like accumulation areas sharp arete like ridges typical of glacial erosion converging patterns of downslope valley flow valley lineation patterns typical of folding and shear wrap around features indicative of flow around obstacles and broad piedmont like lobes as the valley fill extends out into the northern lowlands the single integrated system containing these features covers about 30 000 km2 and is one of dozens of fretted valleys along the dichotomy boundary in this region these relationships suggest that the boundary area was subjected to very large scale regional glaciation during the amazonian recognition and documentation of this important late stage process provides information critical to reconstructing the original dichotomy boundary

usability of small impact craters on small surface areas in crater count dating analysing examples from the harmakhis vallis outflow channel mars abstract the availability of very high resolution images has made it possible to extend crater size frequency distribution studies to small deca hectometer scale craters this has enabled the dating of small and young surface units as well as recent short time and small scale geologic processes that have occurred on the units usually however the higher the spatial resolution of space images is the smaller area is covered by the images thus the use of single very high resolution images in crater count age determination may be debatable if the images do not cover the studied region entirely here we compare the crater count results for the floor of the harmakhis vallis outflow channel obtained from the images of the context camera ctx and high resolution imaging science experiment hirise aboard the mars reconnaissance orbiter mro the ctx images enable crater counts for entire units on the harmakhis vallis main valley whereas the coverage of the higher resolution hirise images is limited and thus the images can only be used to date small parts of the units our case study shows that the crater count data based on small impact craters and small surface areas mainly correspond with the crater count data based on larger craters and more extensive counting areas on the same unit if differences between the results were founded they could usually be explained by the regional geology usually these differences appeared when at least one cratering model age is missing from either of the crater datasets on the other hand we found only a few cases in which the cratering model ages were completely different we conclude that the crater counts using small impact craters on small counting areas provide useful information about the geological processes which have modified the surface however it is important to remember that all the crater counts results obtained from a specific counting area always primarily represent the results from the counting area not the whole unit on the other hand together with crater count results from extensive counting areas and lower resolution images crater counts on small counting areas but by using very high resolution images is a very valuable tool for obtaining unique additional information about the local processes on the surface units

origin of martian northern hemisphere mid latitude lobate debris aprons lobate debris aprons in the martian mid to high latitudes northern and southern hemispheres have been interpreted as ice related features that indicate periglacial climate conditions as recently as late amazonian using mola topographic profiles perpendicular to apron flow fronts we surveyed 36 debris aprons in the northern hemisphere found in the regions of mareotis protonilus and deuteronilus mensae and acheron fossae the profiles of these aprons were compared with idealized simple plastic and viscous power law models for ice rock mixtures all aprons studied exhibit convex profiles similar to a simple plastic model this confirms previous interpretations that debris aprons are ice rich mixtures with rheologies similar to stagnant ice sheets thus indicating high ice concentrations 40 by volume about 60 of the surveyed debris apron population significantly deviates from the idealized simple plastic model profile this may be due to locally reduced ice content which primarily controls apron topography although post emplacement modification due to near surface ice sublimation plays a secondary role in defining the overall shape of aprons it causes conspicuous surface textures degradation by ice sublimation probably results in pitted and ridge and furrow surface textures revealed by high resolution moc images such textures may indicate decreased near surface ice stability since the formation of the aprons possibly due to mars current low obliquity after their emplacement high ice content inferred from topography suggests some debris aprons have ice cores potentially exploitable water resources for future robotic human operations that could prove invaluable for missions remote from polar regions

extensive valley glacier deposits in the northern mid latitudes of mars evidence for late amazonian obliquity driven climate change understanding spin orbital parameter driven climate change on mars prior to 20 ma ago requires geological evidence because numerical solutions for that period are chaotic and non unique we show geological evidence that lineated valley fill at low midlatitudes in the northern hemisphere of mars 37 58 n originated through regional snow and ice accumulation and underwent glacial like flow breached upland craters and theater headed valleys reveal features typical of erosion in association with terrestrial glaciers parallel converging and chevron like lineations in potentially ice rich deposits on valley floors indicate that flow occurred through constrictions and converged from different directions at different velocities together these martian deposits and erosional landforms resemble those of intermontaine glacial systems on earth particularly in their major morphology topographic shape planform and detailed surface features an inferred late amazonian age combined with predictions of climate models suggest that the obliquity of mars exceeded a mean of 458 for a sustained period during this time significant transfer of ice occurred from icerich regions e g the poles to mid latitudes causing prolonged snow and ice accumulation there and forming an extensive system of valley glaciers d 2005 elsevier b v all rights reserved

evidence for multiple ice deposits on the northeastern rim of hellas basin mars abstract four prominent fluvial systems dao niger and harmakhis valles and a system of smaller channels between niger and harmakhis valles characterize a wide topographic trough that connects hesperia planum and hellas planitia hesperia hellas trough hht the source depressions of the canyons of dao and harmakhis valles are at the lowermost level about 5 4 km and lower the system of niger vallis is at medium elevation about 3 to 4 km and the small channels occur at the highest topographic levels about 2 5 to 3 2 km all systems are among the youngest features in the region they formed due to the release of subsurface water and apparently have their sources at different topographic levels below or within the layered suite of volcanic deposits in hht two scenarios can explain the subsurface nature of their sources 1 flow of liquid ground water from extensive watershed toward the source areas and accumulation of water there and 2 deposition of ice bearing materials in and around the sources the first scenario requires the existence of extensive confining layers at different topographic levels corresponding to the levels of the floors of the canyons channels because the presence of such confining layers on mars is problematic we consider the first scenario to be less likely we believe that the deposition of ice bearing materials at different levels during the growth of the lava plateau in hht can better explain the key features of the fluvial systems the subsurface nature of the sources and the relatively young age in this scenario the higher topographic position of the ice bearing deposits corresponds to the younger age of deposition the possible accumulations of ice were buried by successive volcanic deposits including lava flows in hht and later were heated from below by magmatic intrusions that caused melting of the icy deposits release of water and formation of the fluvial structures

on the separability of the north atlantic oscillation and arctic oscillation we address the issue of whether the arctic ao and north atlantic oscillations nao are inseparable forming an annular mode in the northern hemisphere atmospheric circulation this annular mode is the leading empirical orthogonal function of hemispheric sea level pressure slp data explaining the largest amount of its variability we examine whether the nao and ao are inseparable spatial modes of the atmospheric circulation using rotated principal component analysis rpca a methodology that identifies simple and unique patterns of spatial dataset variability rpca of the spring summer and autumn slp fields from 1946 1998 reveal nao and ao like patterns occurring as separate regional teleconnections forming the first and second principal components respectively the rpca based nao dipole pattern is like that observed in many prior studies while the ao like pattern exhibits high slp variability over the kara and laptev seas during winter however and in annual analyses a distinct ao like pattern is not obtained and the two patterns may be inseparable using commonly accepted rpca methods the rpca based ao like mode is significantly linked to north central siberian seasonal air temperatures and to the prevailing direction of motion of the underlying arctic ocean in summer suggesting that the non winter ao like pattern as a stand alone teleconnection separate from the nao contributes significantly to high latitude climate and ocean variability the winter nao ao inseparability is discussed as a possible effect of a shared winter storm track between the northeastern atlantic and the arctic

the east atlantic west russia ea wr teleconnection in the north atlantic climate impact and relation to rossby wave propagation large scale winter teleconnection of the east atlantic west russia ea wr over the atlantic and surrounding regions is examined in order to quantify its impacts on temperature and precipitation and identify the physical mechanisms responsible for its existence a rotated empirical orthogonal function analysis of the upper tropospheric monthly height field captures successfully the ea wr pattern and its interannual variation with the north atlantic oscillation nao as the first mode ea wr s climate impact extends from eastern north america to eurasia the positive negative ea wr produces positive negative temperature anomalies over the eastern us western europe and russia east of caspian sea with negative positive anomalies over eastern canada eastern europe including ural mountains northeastern africa and the middle east these anomalies are largely explained by lower tropospheric temperature advections positive negative precipitation anomalies are found over the mid latitude atlantic and central russia around 60 e where lower level cyclonic anticyclonic circulation anomaly is dominant eastern canada and western europe including the mediterranean region are characterized by negative positive precipitation anomalies the ea wr is found to be closely associated with rossby wave propagation wave activity fluxes show that it is strongly tied to large scale stationary waves furthermore a stationary wave model swm forced with vorticity transients in the mid latitude atlantic 40 n or diabatic heat source over the subtropical atlantic near the caribbean sea produces well organized ea wr like wave patterns respectively sensitivity tests with the swm indicate enhancement of ea wr like blocking over west of scandinavia when the mean state is modified to have a positive nao component that enhances upper level westerlies between 40 and 60 n

vertical structure and energetics of the western pacific teleconnection pattern abstractthe western pacific wp pattern characterized by north south dipolar anomalies in pressure over the far east and western north pacific is known as one of the dominant teleconnection patterns in the wintertime northern hemisphere composite analysis reveals that monthly height anomalies exhibit baroclinic structure with their phase lines tilting southwestward with height in the lower troposphere the anomalies can thus yield not only a poleward heat flux across the climatological thermal gradient across the strong pacific jet but also a westward heat flux across the climatological thermal gradient between the north pacific and the cooler asian continent the resultant baroclinic conversion of available potential energy ape from the climatological mean flow contributes most efficiently to the ape maintenance of the monthly wp pattern acting against strong thermal damping effects by anomalous heat exchanges with the underlying ocean and anomalous precipitation in the subtropics and by the effec

using a physical reference frame to study global circulation variability abstract the 3d structures of the free oscillations of an adiabatic and hydrostatic atmosphere around a basic state at rest were used as a physical filtering for atmospheric data this filtering procedure allows for the consideration of the three primitive variables u over the whole atmosphere simultaneously accordingly the computed statistics do not simply rely on the information provided by a single variable of circulation such as the 500 hpa geopotential field using this method two classical patterns were isolated in the barotropic component of the circulation one resembling the pacific north america pna pattern the other similar to the north atlantic oscillation nao pattern in summer associating the barotropic and the second baroclinic components a coupling in variability was retrieved between the strength of the winter stratospheric polar vortex and the tropospheric circulation over the north atlantic until now these modes had only been recovered by means of statistical analysis

albedo of the south pole on mars determined by topographic forcing of atmosphere dynamics the nature of the martian south polar cap has remained enigmatic since the first spacecraft observations in particular the presence of a perennial carbon dioxide ice cap the formation of a vast area of black slab ice known as the cryptic region and the asymmetric springtime retreat of the cap have eluded explanation here we present observations and climate modelling that indicate the south pole of mars is characterized by two distinct regional climates that are the result of dynamical forcing by the largest southern impact basins argyre and hellas the style of surface frost deposition is controlled by these regional climates in the cold and stormy conditions that exist poleward of 60 degrees s and extend 180 degrees in longitude west from the mountains of mitchel approximately 30 degrees w surface frost accumulation is dominated by precipitation in the opposite hemisphere the polar atmosphere is relatively warm and clear and frost accumulation is dominated by direct vapour deposition it is the differences in these deposition styles that determine the cap albedo

degradation of mid latitude craters on mars abstract recent geomorphic remote sensing and atmospheric modeling studies have shown evidence for abundant ground ice deposits in the martian mid latitudes numerous potential water ice rich flow features have been identified in craters in these regions including arcuate ridges gullies and small flow lobes previous studies such as in newton basin have shown that arcuate ridges and gullies are mainly found in small craters 2 30 km in diameter these features are located on both pole facing and equator facing crater walls and their orientations have been found to be dependent on latitude we have conducted surveys of craters 20 km in diameter in two mid latitude regions one in the northern hemisphere in arabia terra and one in the southern hemisphere east of hellas basin in these regions prominent lobes potentially ice rich are commonly found on the walls of craters with diameters between 20 100 km additional water ice rich features such as channels valleys alcoves and debris aprons have also been found in association with crater walls in the eastern hellas study region channels were found to be located primarily on pole facing walls whereas valleys and alcoves were found primarily on equator facing walls in the arabia terra study region these preferences are less distinct in both study regions lobate flows gullies and arcuate ridges were found to have pole facing orientation preferences at latitudes below 45 and equator facing orientation preferences above 45 similar to preferences previously found for gullies and arcuate ridges in smaller craters interrelations between the features suggest they all formed from the mobilization of accumulated ice rich materials the dependencies of orientations on latitude suggest a relationship to differences in total solar insolation along the crater walls differences in slope of the crater wall differences in total solar insolation with respect to wall orientation and variations in topography along the crater rim can explain the variability in morphology of the features studied the formation and evolution of these landforms may best be explained by multiple cycles of deposition of ice rich material during periods of high obliquity and subsequent modification and transport of these materials down crater walls

formation of recent martian gullies through melting of extensive water rich snow deposits the observation of gullies on mars indicates the presence of liquid water near the surface in recent times1 2 which is difficult to reconcile with the current cold climate gullies have been proposed to form through surface runoff from subsurface aquifers1 3 or through melting of near surface ice under warmer conditions4 but these gullies are observed to occur preferentially in cold mid latitudes2 where the presence of liquid water is less likely and on isolated surfaces where groundwater seepage would not be expected making both potential explanations unsatisfactory here i show that gullies can form by the melting of water rich snow that has been transported from the poles to mid latitudes during periods of high obliquity within the past 105 to 106 years refs 5 6 melting within this snow7 can generate sufficient water to erode gullies in about 5 000 years my proposed model for gully formation is consistent with the age and location of the gullies and it explains the occurrence of liquid water in the cold mid latitudes as well as on isolated surfaces remnants of the snowpacks are still present on mid latitude pole facing slopes and the recent or current occurrence of liquid water within them provides a potential abode for life

martian cratering 9 toward resolution of the controversy about small craters abstract the malin et al malin m c edgett k posiolova l mccolley s noe dobrea e 2006 science 314 1573 1577 report of ongoing production of decameter scale primary craters matches within an order of magnitude the crater production curves of hartmann hartmann w k 2005 icarus 174 294 320 and appears to contradict models that say our curves grossly overpredict primary production nonetheless such models may still predict correct order of magnitude secondary production the new observations if correct require geologically recent martian surface modification in some areas on timescales comparable to the cycles of obliquity changes suggesting episodic martian climatic environmental change driven by the obliquity cycles

robustness of low frequency circulation patterns derived from eof and rotated eof analyses abstract the robustness of low frequency circulation patterns defined by unrotated and rotated empirical orthogonal functions e0fs are compared based on the northern hemisphere 10 day low pass filtered wintertime 500 hpa height field the pacific north american pattern and the north atlantic oscillation are the most prominent modes of low frequency variability in the data the reproducibility of the spatial patterns derived from eof and rotated eof analysis is assessed by repeating the analysis on 50 subsets of the data each comprised of the maps belonging to 22 randomly selected winters from the 44 winters in the total record the results indicate that rotated spatial patterns are less sensitive to sampling fluctuations than their unrotated counterparts

geomorphic analysis of lobate debris aprons on mars at mars orbiter camera scale evidence for ice sublimation initiated by fractures 1 lobate debris aprons known to be geomorphic landform indicators of the presence of ground ice are of special interest for future missions devoted to the research of water on mars lobate debris aprons in fretted terrains of deuteronilus and protonilus mensae 35 50 n show typical convex shapes interpreted to be the result of viscous deformation at the scale of mars orbiter camera moc high resolution images the surface of these debris aprons shows complex patterns with small pits and buttes these patterns can be explained by the mantling of dust the accumulation of interstitial ice and the subsequent removal of ice by sublimation the sublimation of the ground ice is especially initiated and accelerated by subsurface heterogeneities like fractures theoretical quantification of sublimation rates therefore minimizes sublimation which is not a homogeneous process at least over the landforms studied crater counts show that the sublimation occurred in the last tens of millions of years up to the recent past in the point of view of future searching of subsurface ice only surface layers are submitted to sublimation favoring the conservation of ground ice in deeper layers since the formation of the landform the geophysical survey of lobate debris aprons would give interesting insights into the subsurface distribution of ice and its seasonal variations especially in order to measure current sublimation of ground ice

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

thermally distinct craters near hrad vallis elysium planitia mars abstract evidence of volcano ground ice interactions on mars can provide important constraints on the timing and distribution of martian volcanic processes and climate characteristics northwest of the elysium rise is hrad vallis a 370 m deep 800 km long sinuous valley that begins in a source region at 34 n 218 w flanking both sides of the source region is a lobate deposit that extends 50 km perpendicular from the source and is an average of 40 m thick previous studies have suggested the formation of the hrad vallis source region was the result of explosive magma ice interaction and that the lobate deposit is a mudflow here we use newly available mola moc and themis data to investigate the evidence supporting this hypothesis within the lobate deposit we have identified 12 craters with thermal infrared signatures and morphologies that are distinct from any other craters or depressions in the region the thermally distinct craters are distinguished by their cool interiors surrounded by warm ejecta in the nighttime themis ir data and warm interiors surrounded by cool ejecta in the daytime themis ir data the craters are typically 1100 1800 m in diameter one crater is 2300 m across and 30 40 m deep but may be up to 70 m the craters are typically circular and have central depressions several with interior dune fill surrounded by 1 to 6 concentric fracture sets the distribution of the craters and their morphology suggests that they are likely the result of the interaction between a hot mudflow and ground ice

asian jet waveguide and a downstream extension of the north atlantic oscillation abstract anomalous atmospheric fields associated with the north atlantic oscillation nao are analyzed on interannual and intraseasonal time scales in order to examine the extent to which the nao is a regional phenomenon analyses on the interannual time scale reveal that the nao signal is relatively confined to the euro atlantic sector in december while it extends toward east asia and the north pacific in february the difference is most clearly seen in the meridional wind anomaly which shows a wave train along the asian jet collocated with an anomalous vorticity source near the jet entrance diagnoses using a linear barotropic model indicate that this wave train is interpreted as quasi stationary rossby waves trapped on the asian jet waveguide and effectively excited by the anomalous upper level convergence over the mediterranean sea it is found that when the nao accompanies the mediterranean convergence mc anomaly most frequently seen in february the nao indeed has a much wider horizontal str

topographic and morphologic characteristics of reull vallis mars implications for the history of the reull vallis fluvial system 1 the eastern rim region of hellas basin is characterized by the four prominent and quite extensively researched cf crown et al 2005 and references therein outflow channels in this work we focus on the reull vallis on the basis of observations from available data sets we present a hypothesis for the evolution of reull vallis and its complimentary fluvial system we suggest that this system consists of parts that were formed during several phases rather than being a single continuous channel our results show that the fluvial system of reull vallis consists of two main parts and likely had independent formation phases and different sources of water our results also show that the upper portion of the reull vallis was formed by outflow from beneath hesperia planum as proposed already in earlier works but the suggested segments 1 and 2 mest and crown 2001 of the vallis are not directly linked there seems to have been an on surface source for the formation of the segment 2 in the form of a topographic depression that was filled before the subsequent draining and formation of segment 2 our interpretation of the evolution and formation implies a complex history for the reull vallis system

major episodes of the hydrologic history in the region of hesperia planum mars 1 the high resolution stereo color camera hrsc data over hesperia planum and its surroundings reveal important details of geologic episodes and water related processes in this region 1 the noachian fluvial events of hesperia planum depression included accumulation of water and formation of a water ice reservoir there later the reservoir was depleted in several phases reflecting diminishing amounts of water climate changes and or volcanism were important in these volatile releases 2 the massive 0 45 1 5 106 km3 erosion from the hesperia depression before the main lava eruption possibly resulted in thick 0 5 1 5 km deposits in hellas planitia 3 measurements of the flooded craters within hesperia planum provide the estimates of the thickness of lavas there about 250 500 m the final volume of lavas within hesperia planum 0 4 0 7 106 km3 is comparable with the range of some terrestrial igneous provinces such as columbia river basalts 4 extended magmatism possibly triggered formation of the outflow channel in a few locations after the lava emplacement during this episode about 0 04 106 km3 of material about 4 5 8 9 of the volume eroded in the episode of massive erosion were removed the thickness of the composite lava layer exposed on the walls of the outflow channels a few hundreds of meters corresponds well to the thickness estimates made by the measurements of the flooded craters 5 dispersed viscous flows debris aprons flow like deposits reflect the final fluvial events viscous flows from the subsurface sources in the southwestern trough associate with dao niger and harmakhis valles these flows represent the final volatile discharge from the hesperia reservoir that mostly was depleted by the earlier events of massive erosion and formation of the outflow channels viscous surface flows are mostly associated with reull vallis and probably reflect redistribution of volatiles related to the late episodes of evolution of this outflow channel

surface characteristics and degradational history of debris aprons in the tempe terra mareotis fossae region of mars abstract we have documented the surface characteristics and degradational history of a population of 65 lobate debris aprons in the tempe terra mareotis fossae region of mars these aprons were compared to other martian debris aprons to evaluate similarities and differences among different populations which can provide insight into the dominant controls on apron development tempe mareotis debris aprons found at the bases of isolated or clustered massifs escarpments and crater interior walls were studied using viking orbiter mars global surveyor and mars odyssey datasets in a gis database six textures related to degradation of apron surfaces are identified in moc images and they are divided into two groups an upper surface group and a lower surface group degradation occurs within an inferred smooth upper surface mantle of ice and debris producing a sequence of pitted ridge and valley and knobby textures of the upper surface group where upper surface materials have been removed smooth and ridged textures of the lower surface group are exposed degradation to various depths may expose lower surface materials which may consist of the main apron mass remnants of mantling deposits or both a combination of geologic processes may have caused the degradation including ice sublimation ice melt and eolian activity apron surfaces have lower maximum thermal inertias and mean surface temperatures than adjacent plains surfaces which may be explained by the trapping of unconsolidated materials in low lying pits and valleys formed by surface degradation or from the disruption of crusts on degraded portions of apron surfaces one feature observed only on tempe mareotis debris aprons are broad ridges which mimic the shape of massif bases for tens of kilometers we propose these to be constructional features that could have formed during cycles of increased debris production apron morphometric parameters including area volume slope thickness relief and h l were compiled and the results show that tempe mareotis aprons have average surface areas volumes and frontal thicknesses that are 2 3 times smaller than eastern hellas aprons within the tempe mareotis population escarpment related aprons are larger than massif related aprons suggesting that aprons with larger source areas have potentially greater volatile accumulation translating into longer apron travel distances and lower h l values

influence of the north atlantic oscillation on the canary islands precipitation abstract the aim of this paper is to investigate the relationship between the canary island rainfall and the atlantic large scale circulation characterized by the north atlantic oscillation nao index the canary islands are located in the atlantic subtropical belt under the direct influence of the azores high and the trade winds their steep orography makes the islands very sensitive to small variations in a synoptic situation thus providing an excellent natural observatory for the north atlantic variability associated with changes in pressure patterns a significant relationship between rainfall and the nao is found for five of the seven canary islands in order to characterize the physical mechanisms involved a set of automatic objective techniques for identification and detection of disturbances is applied to the 1000 and 500 hpa geopotential from the ncep ncar reanalysis for the period from 1955 to 1998 this method allows for the identification and detection of four main synoptic systems either

northern hemisphere winter atmospheric transient eddy heat fluxes and the gulf stream and kuroshio oyashio extension variability abstractspatial and temporal covariability between the atmospheric transient eddy heat fluxes i e t and q in the northern hemisphere winter january march and the paths of the gulf stream gs kuroshio extension ke and oyashio extension oe are examined based on an atmospheric reanalyses and ocean observations for 1979 2009 for the climatological winter mean the northward heat fluxes by the synoptic 2 8 days transient eddies exhibit canonical storm tracks with their maxima collocated with the gs and ke oe the intraseasonal 8 days 3 months counterpart while having overall similar amplitude shows a spatial pattern with more localized maxima near the major orography and blocking regions lateral heat flux divergence by transient eddies as the sum of the two frequency bands exhibits very close coupling with the exact locations of the ocean fronts linear regression is used to examine the lead lag relationship between interannual changes in the northward heat fluxes by the transient

understanding anomalous synoptic eddy vorticity forcing in pacific north american teleconnection pattern events abstractutilizing a decomposition of anomalous eddy vorticity forcing evf proposed by song in 2016 and a modified geophysical fluid dynamics laboratory gfdl dynamical core atmospheric model th

tropical to mid latitude snow and ice accumulation flow and glaciation on mars images from the mars express hrsc high resolution stereo camera of debris aprons at the base of massifs in eastern hellas reveal numerous concentrically ridged lobate and pitted features and related evidence of extremely ice rich glacier like viscous flow and sublimation together with new evidence for recent ice rich rock glaciers at the base of the olympus mons scarp superposed on larger late amazonian debris covered piedmont glaciers we interpret these deposits as evidence for geologically recent and recurring glacial activity in tropical and mid latitude regions of mars during periods of increased spin axis obliquity when polar ice was mobilized and redeposited in microenvironments at lower latitudes the data indicate that abundant residual ice probably remains in these deposits and that these records of geologically recent climate changes are accessible to future automated and human surface exploration

martian cratering 10 progress in use of crater counts to interpret geological processes examples from two debris aprons abstract recent controversies about systems of crater count dating have been largely resolved and with continuing refinements crater counts will offer a fundamental geological tool to interpret not only ages but also the nature of geological processes altering the surface of mars as an example of the latter technique we present data on two debris aprons east of hellas the aprons show much shorter survival times of small craters than do the nearby contiguous plains the order of magnitude depths of layers involved in the loss process can be judged from the depths of the affected craters we infer that ice rich layers in the top tens of meters of both aprons have lost crater topography within the last few 10 8 yr probably due to flow or sublimation of ice rich materials mantling by ice rich deposits associated with climate change cycles of obliquity change has probably also affected both the aprons and the plains the crater count tool thus adds chronological and vertical dimensional information to purely morphological studies

low frequency variability in the northern hemisphere winter geographical distribution structure and time scale dependence abstract low frequency variability in wintertime 500 mb height is examined with emphasis on its structure geographical distribution and frequency dependence a 39 year record of 500 mb geopotential height fields from the nmc analyses is time filtered to partition the fluctuations into frequency bands corresponding to periods of 10 60 days 60 180 days and 180 days winter is defined as the six month period november through april variance teleconnectivity and anisotropy fields and selected loading vectors derived from orthogonal and oblique rotations of the eigenvectors of the temporal correlation matrix for each band are shown and discussed the variability in all frequency bands exhibits substantial anistropy with meridionally elongated features arranged as zonally oriented wave trains prevailing over the continents and zonally elongated features organized in the form of north south oriented dipole patterns prevailing over the oceanic sectors of the hemisphere the wave trains are most pronounc

flow patterns of lobate debris aprons and lineated valley fill north of ismeniae fossae mars evidence for extensive mid latitude glaciation in the late amazonian a variety of late amazonian landforms on mars have been attributed to the dynamics of ice related processes evidence for large scale mid latitude glacial episodes existing within the last 100 million to 1 billion years on mars has been presented from analyses of lobate debris aprons lda and lineated valley fill lvf in the northern and southern mid latitudes we test the glacial hypothesis for lda and lvf along the dichotomy boundary in the northern mid latitudes by examining the morphological characteristics of lda and lvf surrounding two large plateaus proximal massifs and the dichotomy boundary escarpment north of ismeniae fossae centered at 45 3n and 39 2e lineations and flow directions within lda and lvf were mapped using images from the context ctx camera the thermal emission imaging spectrometer themis and the high resolution stereo camera hrsc flow directions were then compared to topographic contours derived from the mars orbiter laser altimeter mola to determine the down gradient components of lda and lvf flow observations indicate that flow patterns emerge from numerous alcoves within the plateau walls are integrated over distances of up to tens of kilometers and have down gradient flow directions smaller lobes confined within alcoves and superposed on the main lda and lvf represent a later less extensive glacial phase crater size frequency distributions of lda and lvf suggest a minimum youngest age of 100 ma the presence of ring mold crater morphologies is suggestive that lda and lvf are formed of near surface ice rich bodies from these observations we interpret lda and lvf within our study region to result from formerly active debris covered glacial flow consistent with similar observations in the northern mid latitudes of mars glacial flow was likely initiated from the accumulation and compaction of snow and ice on plateaus and in alcoves within the plateau walls as volatiles were mobilized to the mid latitudes during higher obliquity excursions together with similar analyses elsewhere along the dichotomy boundary these observations suggest that multiple glacial episodes occurred in the late amazonian and that lda and lvf represent significant reservoirs of non polar ice sequestered below a surface lag for hundreds of millions of years

weather regime transitions and the interannual variability of the north atlantic oscillation part ii dynamical processes inthisstudy attentionisfocused on identifyingthedynamicalprocessesthatcontributetothenegativenorth atlantic oscillation nao 2 to positive nao nao 1 and nao 1 to nao 2 transitions that occur during 1978 90 p1 and 1991 2008 p2 by constructing atlantic ridge ar and scandinavian blocking sbl indices thecompositeanalysis demonstratesthatinastrongerar sbl winter nao 2 nao 1 eventcanmore easily transition into an nao 1 nao 2 event composites of 300 hpa geopotential height anomalies for the nao 2 tonao 1 andnao 1 tonao 2 transitioneventsduringp1andp2arecalculated itisshownforp2 p1 that the nao 1 to sbl to nao 2 nao 2 to ar to nao 1 transition results from the retrograde drift of an enhanced high latitude large scale positive negative anomaly over northern europe during the decay of the previous nao 1 nao 2 event this finding cannot be detected for nao events without transition moreover itisfoundthattheamplificationofretrogradingwavenumber1ismoreimportantforthenao 2 to nao 1 transitionduringp1 but themarkedreintensificationandretrogrademovementofbothwavenumbers1 and 2 after the nao 1 event decays is crucial for the nao 1 to nao 2 transition during p2 it is further shown that destructive constructive interference between wavenumbers 1 and 2 over the north atlantic during p1 p2 is responsible for the subsequent weak nao 1 strong nao 2 anomaly associated with the nao 2 to nao 1 nao 1 to nao 2 transition also the weakening strengthening of the vertically integrated zonal wind upstream atlantic storm track is found to play an important role in the nao regime transition

styles and timing of volatile driven activity in the eastern hellas region of mars 1 recent analyses of mars global surveyor and mars odyssey data sets provide new insights into the geologic evolution of the eastern hellas region of mars in particular the role of volatiles here we present results of our recent work and integrate these with previous studies by various investigators to provide a synthesis of the history of volatile driven activity of the region we utilize high resolution images from the mars orbiter camera and thermal emission imaging system combined with mars orbiter laser altimeter digital elevation models and profiles to examine fluvial systems that dissect the circum hellas highlands to characterize stages in the development of the dao niger harmakhis and reull valles canyon systems and to evaluate evidence for ancient lakes in hellas planitia the occurrence of valley networks dissected highland crater rims and crater interior deposits such as layered plateaus suggests widespread ancient degradation of the circum hellas highlands canyon development which represents subsequent more localized activity may have included an early fluvial phase followed by the collapse and sapping dominated stages that along with recent wall erosion and floor resurfacing produced the currently observed morphologies the prominent role of collapse and sapping along the east rim of hellas along with the presence of numerous channels extending toward the basin and sequences of finely layered deposits along the basin rim suggests a volatile rich substrate across a broad depositional shelf the east rim of the basin was an accumulation zone for atmospheric volatiles and or the edge of volatile rich deposits associated with the basin floor this evidence combined with topographic data and cratered terrain preservation around the basin is consistent with a lacustrine period or periods in early martian history the style magnitude and spatial extent of volatile driven activity in eastern hellas have varied considerably with time and these variations may represent a transition from a water to an ice dominated surface environment

topography of mars from global mapping by hrsc high resolution digital terrain models and orthoimages characteristics and performance abstract we report on the results of the mars express high resolution stereo camera hrsc experiment pertaining to one of its major aims mapping the surface of mars by high resolution digital terrain models dtm up to 50 m grid spacing and orthoimages up to 12 5 m resolution we introduce the specifications and characteristics of these data products and give an overview of the procedures that have been developed and are applied for their derivation we also address the performance characteristics of the mapping project related to different aspects of internal accuracy accuracy with respect to the global reference system and regional aspects using adaptive processing techniques for terrain reconstruction and a revised approach to the improvement of orientation data a mean precision of the resulting 3d points of about 12 m is obtained exceeding the mean ground resolution of the stereo images using mars orbiter laser altimeter mola data the hrsc models are firmly tied to the global reference system at the scale of the hrsc dtm grid spacing in the lateral dimension and to within few meters vertically hrsc high resolution dtms are typically generated using a grid size of about 2 times the mean ground resolution but usually not larger than 3 times the mean ground resolution and not smaller than 3 times the precision of the integrated 3d points derived from stereo image analysis statistically every grid cell is based on at least one measured 3d point thus horizontal dtm resolution is well established with regard to the precision and density of the derived 3d points while the concurrent aim of a detailed terrain representation at maximum possible resolution is pursued comparison with the dtm derived from mola data allows us to identify specific advancements related to this updated view of martian topography we also address the mapping performance of hrsc in comparison to mola with respect to latitude and to different surface types and morphologies finally comparison with mola highlights typical complementarities of the two different approaches for mapping planetary surfaces

geologic evolution of the east rim of the hellas basin mars abstract geomorphic analyses and crater statistics indicate the distribution of materials on the east rim 27 5 42 5 s 260 275 w of the hellas basin and constrain the timing nature and interactions of geologic processes which have modified the hellas region the discernible geologic history of the area began with the formation of the impact basin and the emplacement of highlands that became heavily cratered during the noachian period the tectonic setting of the region was established at this time and basin structures promoted and influenced subsequent volcanic tectonic and fluvial activity degradation of the highland units by fluvial mass wasting and aeolian processes began in the noachian and continued into the hesperian and amazonian periods sedimentary plains covered low lying regions of the highlands their pitted surfaces in some areas suggest subsidence and the presence of volatiles emplacement of lobate debris aprons shed from highland peaks and possibly facilitated by ice creep occurred in the amazonian period the volcanic history of the east rim of the hellas basin began with the formation of the highland paterae the low dissected shields of hadriaca and tyrrhena paterae formed in the late noachian or early hesperian epochs and are older than or coeval with the ridged plains of hesperia planum volcanic activity continued throughout the hesperian period with the emplacement of the caldera filling materials at hadriaca patera and the lava flows of the flank flow unit of tyrrhena patera outflow channels and related channeled plains of the hesperian and amazonian periods suggest an extensive and complex history of volatile driven erosion and sedimentary deposition dao and harmahkis valles are interpreted to be collapsed regions of the older plains a combination of surface and subsurface flow has removed materials with deposition on the floor of the hellas basin the geologic evolution of the region determined from the observed surface morphology and stratigraphic relationships and refined by crater statistics indicates that a combination of diverse geologic processes acted in the degradation of the hellas basin the effects of volcanism and volatile driven processes were prominent throughout the hesperian and well into the amazonian periods the proposed transition from explosive to effusive volcanism in the hellas region is supported by the relative ages indicated by crater statistics the heat released by volcanism may have resulted in the melting of ground ice and contributed to the development of the channeled plains and outflow channels the presence of wrinkle ridges on units that are inferred to be relatively young from their crater size frequency distributions suggests deformation in the late hesperian or early amazonian epoch

geology of the reull vallis region mars abstract the geology and stratigraphy of the reull vallis region 27 5 47 5 s 245 270 w of the southern highlands of mars are documented through geomorphic analyses and geologic mapping at 1 2 000 000 scale crater size frequency distributions are used to constrain relative ages of geologic units and determine the timing and duration of the various geologic events the origin and evolution of the reull vallis outflow system and the extent to which reull vallis and other fluvial features modified the surrounding highlands are also evaluated rugged highland terrains were formed by repeated impact events and were extensively degraded and embayed by a series of plains highland terrains incised with well developed valley networks record some of the earliest fluvial activity in the region reull vallis originates in hesperia planum and dissects units of various types and ages truncated and bisected wrinkle ridges in hesperia planum indicate that the formation of reull vallis postdates ridge formation the morphology of reull vallis suggests it had a long and complex history including subsurface and surface movement of fluids followed by extensive modification by mass wasting volcanic and sedimentary plains units in the region record evidence of erosion by surface flow possibly related to development of reull vallis features produced by mass wasting such as debris aprons and crater fill material and aeolian processes appear to form the youngest deposits exposed in the region

intraseasonal variations in the southern hemisphere circulation abstract intraseasonal variations in the southern hemisphere atmospheric circulation have been examined through the application of a 10 50 day bandpass filter to daily ecmwf analyses for 1980 88 variations on this time scale contribute more than 40 of the daily variance in 500 hpa geopotential over much of the middle and high latitudes of the southern hemisphere eof analysis of the unnormalized variance for all seasons shows that 49 of this variance can be explained by zonal wave trains centered on the south pacific and southern atlantic indian oceans a high latitude mode of global extent and a wavenumber 3 pattern at midlatitudes these modes are essentially equivalent barotropic but slope westward with height so that the patterns at 100 hpa typically lag those at 1000 hpa by around 1o longitude there appears to be little interaction with the low latitude circulation all of the leading modes propagate eastward but the most consistent movement is shown by the south pacific wave train represented

formation of recent martian debris flows by melting of near surface ground ice at high obliquity the observation of small gullies associated with recent surface runoff on mars has renewed the question of liquid water stability at the surface of mars the gullies could be formed by groundwater seepage from underground aquifers however observations of gullies originating from isolated peaks and dune crests question this scenario we show that these landforms may result from the melting of water ice in the top few meters of the martian subsurface at high obliquity our conclusions are based on the analogy between the martian gullies and terrestrial debris flows observed in greenland and numerical simulations that show that above freezing temperatures can occur at high obliquities in the near surface of mars and that such temperatures are only predicted at latitudes and for slope orientations corresponding to where the gullies have been observed on mars

geology and landscape evolution of the hellas region of mars hellas basin on mars has been the site of volcanism tectonism and modification by fluvial mass wasting and eolian processes over its more than 4 b y existence our detailed geologic mapping and related studies have resulted in the following new interpretations the asymmetric distribution of highland massifs and other structures that define the uplifted basin rim suggest a formation of the basin by the impact of a low angle bolide having a trajectory heading s60 e during the late noachian the basin was infilled perhaps by lava flows that were sufficiently thick 1 km to produce wrinkle ridges on the fill material and extensional faulting along the west rim of the basin at about the same time deposits buried northern malea planum which are interpreted to be pyroclastic flows from amphitrites and peneus paterae on the basis of their degraded morphology topography and the application of a previous model for pyroclastic volcanism on mars peneus forms a distinctive caldera structure that indicates eruption of massive volumes of magma whereas amphitrites is a less distinct circular feature surrounded by a broad low dissected shield that suggests generally smaller volume eruptions during the early hesperian a 1 to 2 km thick sequence of primarily fined grained eolian material was deposited on the floor of hellas basin subsequently the deposit was deeply eroded except where armored by crater ejecta and it retreated as much as 200 300 km along its western margin leaving behind pedestal craters and knobby outliers of the deposit local debris flows within the deposit attest to concentrations of groundwater perhaps in part brought in by outflow floods along the east rim of the basin these floods may have deposited 100 200 m of sediment subduing wrinkle ridges in the eastern part of the basin floor during the late hesperian and amazonian eolian mantles were emplaced on the basin rim and floor and surrounding highlands their subsequent erosion resulted in pitted and etched plains and crater fill irregular mesas and pedestal craters local evidence occurs for the possible former presence of ground ice or ice sheets 100 km across however we disagree with a hypothesis that suggests that the entire south rim and much of the floor of hellas have been glaciated orientations of dune fields and yardangs in lower parts of hellas basin follow directions of the strongest winds predicted by a recently published general circulation model gcm transient frost and dust splotches in the region are by contrast related to the gcm prediction for the season in which the images they appear in were taken

formation erosion and exposure of early amazonian dikes dike swarms and possible subglacial eruptions in the elysium rise utopia basin region mars hundreds of narrow linear ridge segments are found in the transition zone between the elysium rise and the utopia basin occurring as both single and multiple ridges the ridges are distinctive because of their very linear steep sided nature their often sharp ridge crest which sometimes is fractured their association with stubby flows their continuity over long distances and their cross cutting of different terrain the linear ridges are interpreted to be single dikes and dike swarms either emplaced as normal dikes or as dikes emplaced subglacially feeding an explosive or effusive eruption five dike swarms are identified having lengths ranging from 10 45 km and being between 1 7 km wide while single ridges are up to 20 km long and 100 500 m wide in the areas of dike swarms crustal dilatation is estimated to vary from 15 60 dikes emplaced en echelon suggest that variations in the local stress field caused rotation during dike emplacement and dikes crosscutting flow units imply that dike emplacement can account for some of the observed linear fractures in the area the ridges both modify and constrain early amazonian flows and flood plain deposits suggesting intense dike emplacement in the early amazonian the association with different stages of inverted craters as well as some features of ice related origin possible ice cauldron and tindar like features indicate that the dikes may have been exposed due to eolian erosion and loss of volatile rich units subsequent to their emplacement

enso induced tropical convection variability over the indian and western pacific oceans during the northern winter as revealed by a self organizing map 1 the dominant low frequency patterns of outgoing longwave radiation over the tropical indian and western pacific oceans in response to el nino southern oscillation enso during the northern winter are investigated using the nonlinear classification method of the self organizing map som additionally aided by an empirical orthogonal function eof analysis there are at least two different air sea coupled phenomena in the tropical indian ocean i e the indian ocean dipole iod mode in late summer and fall and the wind evaporation sea surface temperature wes feedback driven mode in the winter and spring the som results exhibit that the phase of wes becomes positive negative at the el nino la nina phase which indicates a linear linkage of wes with enso in contrast few combined patterns of the negative iod and the la nina event can be extracted although the reversed pattern is prominent suggesting a nonlinear like relationship between iod and enso since the enso induced convective forcing over the tropical indian and western pacific oceans has strong asymmetric features with respect to the enso phase the remote response of the east asian winter monsoon to enso becomes complicated at the el nino event the monsoon circulation in the southern part of east asia tends to be attenuated in late winter through the dominance of the western north pacific anticyclone in the lower troposphere but at the la nina event the monsoon circulation over korea and japan is enhanced in early winter through the downstream development of stationary rossby wave packets along the south asian waveguide

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

centers of tectonic activity in the eastern hemisphere of mars we compiled a paleotectonic map for the eastern hemisphere of mars to determine if extensional tectonic features graben are radial or compressional tectonic features wrinkle ridges are concentric to centers of tectonic activity defined by axisymmetric stress fields using a vector analysis technique all latitude and longitude points 1 bins are tested to see if they lie on great circle extensions of extensional structures the plane defined by the maximum and intermediate principal stresses or great circle perpendiculars to compressional structures the plane defined by the maximum and minimum compressional stresses centers of tectonic activity are defined as 5 areas whose concentrations of great circle extensions of tectonic features are statistically significant e g 3 or 7 4 for large populations and therefore are not the result of random noise our paleotectonic investigation has identified four statistically significant centers of tectonic activity within the eastern hemisphere elysium hadriaca tyrrhena hellas isidis syrtis and arabia terra two of these centers hadriaca tyrrhena and isidis syrtis meet the 7 4 statistical criteria and thus represent primary centers of tectonic activity with axisymmetric stress fields the remaining two meet the 3 statistical criteria and thus are defined as secondary centers of tectonic activity because the structures that define the centers extend over 80 of the planet the defined centers of tectonic activity are regional in character and related to modified impact basins or volcanic centers all are more limited in extent than the tharsis stress system that extends over the entire western hemisphere the observation that statistically significant centers of tectonic activity are quantifiably and statistically identified argues that the crust and lithosphere of the eastern hemisphere at a regional scale is not dominated by regional inhomogeneities and anisotropies

a new variable threshold persistent anomaly index northern hemisphere anomalies in the era interim reanalysis abstractpersistent weather regimes characterized by anomalous temperature or precipitation are often associated with persistent anomalies pas in the tropospheric geopotential height field to ide

martian cratering 8 isochron refinement and the chronology of mars abstract this paper reviews and refines the technique of dating martian surfaces by using impact crater isochrons defined as size distributions of impact craters on undisturbed martian surfaces of specified ages in the 1970s this system identified not only abundant ancient martian volcanic surfaces but also extensive lava plains with ages of a few 108 y old this dating was initially controversial but confirmed in the 1980s and 90s by martian meteorites the present update utilizes updated estimates of the mars moon cratering ratio the most important calibration factor improves treatment of gravity and impact velocity scaling effects combines aspects of the crater size distribution data from earlier work by both neukum and hartmann and for the first time applies a correction for loss of small meteoroids in the martian atmosphere from popova et al 2003 meteorit planet sci 38 905 925 the updated isochrons are not radically different from the previous 2002 iteration but fit observed data better and give somewhat older model ages for features dated from small craters diameter d 100 m crater counts from young lava flows in various areas give good fits to the new isochrons over as much as 3 orders of magnitude in d confirming the general isochron shape and giving crater retention ages in the range of some 106 to some 108 y interpreted as lava flow ages more complex older units are also discussed uncertainties are greatest if only small craters d 100 m are used suggestions by other workers of gross uncertainties due to local secondary craters and deposition exhumation are discussed they do not refute our conclusions of significant volcanic fluvial and other geologic activity in the last few percent of martian geologic time or the importance of cratering as a tool for studying processes such as exhumation indeed crater count data suggest certain very recent episodes of deposition exhumation and ice flow possibly associated with obliquity cycles of 10 7 y timescale evidence from ancient surfaces suggests higher rates of volcanism fluvial activity glaciation and other processes in noachian hesperian time than in amazonian time

understanding anomalous eddy vorticity forcing in north atlantic oscillation events abstractthis study proposes an anomalous eddy vorticity forcing evf decomposing procedure to investigate physical mechanisms responsible for the formation of the anomalous evf associated with north atlantic oscillation nao events utilizing the geophysical fluid dynamics laboratory gfdl dynamical core atmospheric model a series of nao initial value short term experiments are conducted applying the evf decomposing procedure to the results of these experiments the anomalous nonlinear evf associated with the nao events in the model can be decomposed into several fundamental linear eddy eddy interaction terms and an unimportant nonlinear eddy eddy interaction term compared with the nao free situation synoptic scale eddies have faster slower eastward phase speeds during the positive negative nao events through a synoptic scale eddy eddy interaction mechanism the behaviors of anomalous evf components in the positive negative nao events are well explained by synoptic scale eddies with faster

modification history of the harmakhis vallis outflow channel mars based on ctx scale photogeologic mapping and crater count dating abstract harmakhis vallis is one of the four major outflow channel systems dao niger harmakhis and reull valles that cut the eastern rim region of the hellas basin the largest well preserved impact structure on mars the structure of harmakhis vallis and the volume of its head depression as well as earlier dating studies of the region suggest that the outflow channel formed in the hesperian period by collapsing when a large amount of subsurface fluid was released thus harmakhis vallis as well as the other nearby outflow channels represents a significant stage of the fluvial activity in the regional history on the other hand the outflow channel lies in the martian mid latitude zone where there are several geomorphologic indicators of past and possibly also contemporary ground ice the floor of harmakhis also displays evidence of a later stage ice related activity as the outflow channel has been covered by lineated valley fill deposits and debris apron material the eastern rim region of the hellas impact basin has been the subject of numerous geologic mapping studies at various scales and based on different imaging data sets however harmakhis vallis itself has received less attention and the studies on the outflow channel have focused only on limited parts of the outflow channel or on separated different geologic events in this work the harmakhis vallis floor is mapped and dated from the head depression to the beginning of the terminus based on the mars reconnaissance orbiter s context camera images ctx 6 m pixel our results show that harmakhis vallis has been modified by several processes after its formation age determinations on the small uncovered parts of the outflow channel which possibly represent the original floor of harmakhis imply that harmakhis may have experienced fluvial activity only 780 850 400 600 ma ago the discovered terrace structure instead shows that the on surface activity of the outflow channel has been periodic the most significant of the modification processes on harmakhis vallis has been the formation of lineated valley fill units the lineated valley fills now cover the outflow channel almost entirely they formed not later than 400 ma ago based on stratigraphic analyses and crater counts all the floor units have also been resurfaced several usually two or three times the resurfacing ages of the dated units show that the later modification processes have occurred at least on a local scale in the harmakhis vallis region not only inside the outflow channel this in turn may indicate that the processes resulted from a larger scale change for example in the local climate or endogenic conditions

formation of glaciers on mars by atmospheric precipitation at high obliquity surface conditions on mars are currently cold and dry with water ice unstable on the surface except near the poles however geologically recent glacierlike landforms have been identified in the tropics and the midlatitudes of mars the ice has been proposed to originate from either a subsurface reservoir or the atmosphere we present high resolution climate simulations performed with a model designed to simulate the present day mars water cycle but assuming a 45 obliquity as experienced by mars a few million years ago the model predicts ice accumulation in regions where glacier landforms are observed on the western flanks of the great volcanoes and in the eastern hellas region this agreement points to an atmospheric origin for the ice and reveals how precipitation could have formed glaciers on mars

thermal contraction crack polygons on mars classification distribution and climate implications from hirise observations morphology is shown to be consistent with thermal contraction cracking of an ice rich mantling unit consistent with observations of sediment wedge thermal contraction crack polygons forming in ice cemented sediment at the phoenix landing site polygon groups are distributed symmetrically in both northern and southern hemispheres suggesting strong climate controls on polygon morphology northern hemisphere polygonally patterned surfaces are found to decrease in age from low to high latitude spanning surface ages from 1 to 0 1 ma suggesting more recent deposition of ice rich material at high latitudes than at low latitudes six of the seven classes of polygons are interpreted to be capable of forming because of the combined effects of thermal contraction cracking and differential sublimation suggesting that sublimation and sand wedge polygons dominate martian high latitudes gully polygon systems present at midlatitudes suggest that small amounts of liquid water may have been involved in thermal contraction crack polygon processes producing composite wedge polygons no evidence is found for the presence of pervasive small scale ice wedge polygons

the mars observer laser altimeter investigation the primary objective of the mars observer laser altimeter mola investigation is to determine globally the topography of mars at a level suitable for addressing problems in geology and geophysics secondary objectives are to characterize the 1064 nm wavelength surface reflectivity of mars to contribute to analyses of global surface mineralogy and seasonal albedo changes to assist in addressing problems in atmospheric circulation and to provide geodetic control and topographic context for the assessment of possible future mars landing sites the principal components of mola are a diode pumped neodymium doped yttrium aluminum garnet laser transmitter that emits 1064 nm wavelength laser pulses a 0 5 m diameter telescope a silicon avalanche photodiode detector and a time interval unit with 10 ns resolution mola will provide measurements of the topography of mars within approximately 160 m footprints and a center to center along track foot print spacing of 300 m along the mars observer subspacecraft ground track the elevation measurements will be quantized with 1 5 m vertical resolution before correction for orbit and pointing induced errors mola profiles will be assembled into a global 0 2 deg x 0 2 deg grid that will be referenced to mars center of mass with an absolute accuracy of approximately 30 m other data products will include a global grid of topographic gradients corrected individual profiles and a global 0 2 deg x 0 2 deg grid of 1064 nm surface reflectivity

the continuum and dynamics of northern hemisphere teleconnection patterns this study presents an alternative interpretation for northern hemisphere teleconnection patterns rather than comprising several different recurrent regimes this study suggests that there is a continuum of teleconnection patterns this interpretation indicates either that 1 all members of the continuum can be expressed in terms of a linear combination of a small number of real physical modes that correspond to basis functions or 2 that most low frequency patterns within the continuum are real physical patterns each having its own spatial structure and frequency of occurrence daily ncep ncar reanalysis data are used that cover the boreal winters of 1958 97 a set of nonorthogonal basis functions that span the continuum is derived the leading basis functions correspond to well known patterns such as the pacific north american teleconnection and north atlantic oscillation evidence for the continuum perspective is based on the finding that 1 most members of the continuum tend to have similar variance and autocorrelation time scales and 2 that members of the continuum show dynamical characteristics that are intermediate between those of the surrounding basis functions the latter finding is obtained by examining the streamfunction tendency equation both for the basis functions and some members of the continuum the streamfunction tendency equation analysis suggests that north pacific patterns basis functions and continuum are primarily driven by their interaction with the climatological stationary eddies and that north atlantic patterns are primarily driven by transient eddy vorticity fluxes the decay mechanism for all patterns is similar being due to the impact of low frequency period greater than 10 days transient eddies and horizontal divergence analysis with outgoing longwave radiation shows that tropical convection is found to play a much greater role in exciting north pacific patterns a plausible explanation for these differences between the north atlantic and north pacific patterns is presented

glacial deposits on the rim of a hesperian amazonian outflow channel source trough mangala valles mars 1 mangala valles located in tropical regions of mars is interpreted to have formed by dike induced cracking of the cryosphere to produce a linear graben and catastrophic release of groundwater sequestered under hydrostatic pressure outpouring of water and downcutting led to erosion and widening of the graben to produce a trough patterns of ridges and lobes along the outer rims of the trough are interpreted to have formed primarily by local accumulations of snow and ice on the graben rim derived from exposed ponded groundwater in the graben and glacial like outward flow of ice lobes resulting in development of moraines and tills along the north and south rims of the trough these observations and interpretations support the concept that the climate of mars was a hyper arid cold polar like desert similar to today in the late hesperian early amazonian period

dynamics of low frequency variability barotropic mode the dynamics of low frequency variability is investigated in terms of sensitivity to the dependence of its relative zonal position of a single storm track in a simplified global circulation model a streamfunction tendency equation is derived that explicitly distinguishes between barotropic and baroclinic components one of the two low frequency patterns located in the center of the storm track grows barotropically and its decay is accomplished by low frequency eddy vorticity fluxes and the baroclinic contribution to the divergence term the growth and decay of the second pattern located at the downstream end of the storm track is dominated by nonlinear processes this indicates that the dynamical processes leading to growth and decay of low frequency patterns depend on the zonal position of the low frequency pattern relative to a storm track

extra tropical cyclonic anticyclonic activity in north eastern pacific and air temperature extremes in western north america synoptic extra tropical cyclone and anticyclone trajectories have been constructed from mean daily sea level pressure slp data using a new automated scheme frequency intensity and trajectory characteristics of these transients have been summarized to form indices describing wintertime cyclonic and anticyclonic activity over the north eastern pacific east of 170 w during 1950 2001 during this period the strength of anticyclones gradually diminished and their frequency became more variable while cyclones intensified in a discrete shift with deeper lows and further southerly trajectories occurring since the mid 1970s these changes in synoptic transients translate into anomalously low seasonal mean slp in the aleutian low a low level circulation anomaly consistent with the positive phase of the north pacific decadal oscillation with positive sea surface temperature sst anomalies along the west coast of north america and negative in the central north pacific ocean a link between cyclonic anticyclonic activity and tropical sst anomalies also exists but this link only becomes significant after the mid 1970s a period that coincides with more southerly cyclone trajectories southward excursions of mid latitude cyclones during el nino positive npo winters accomplish the northward advection of tropical air and discourage the southward penetration of polar air masses associated with transient anticyclones naturally these changes in cyclonic anticyclonic activity directly impact surface air temperatures especially at night we document these profound impacts on observed wintertime minimum temperatures over western north america

sequence and mechanisms of deformation around the hellas and isidis impact basins on mars the distribution and age of early volcanic and tectonic features surrounding the itellas and isidis impact basins are shown to fit a four stage sequence first concentric canyons form outside the basin boundary scarp at or near the time of basin formation followed shortly thereafter by radial troughs extending beyond the boundary scarp after a hiatus concentric graben develop inside the basin within the massif ring finally soon after graben formation widespread volcanic plains are emplaced between the massif ring and the boundary scarp to one side of the basin three models of basin centered deformation are compared io hese observed deformation events elastic flexure due to loading elastic flexure due to uplift and impact fracture a central load of basin fill can account for concentric fractures by elastic flexure around the load formation of the distant concentric canyons however requires lithospheric thicknesses a factor of 5 greater than those indicated by planetary thermal history models and an increase in feature width by an order of magnitude relative to flexural graben identified elsewhere on mars and the moon although inclusion of loading by basin ejecta reduces the required lithospheric thickness to acceptable values flexure still fails to account for the large canyon widths observed impact fracture from a rapid inward flow of asthenosphere during transient cavity collapse however is consistent with the three key observational constraints for the distant canyons their age width and distance from the basin as the basin then undergoes isostatic uplift soon after impact elastic flexure induces a radial pattern of failure consistent with the observed extent and timing of the radial troughs later after a long period of basin infilling elastic failure due to loading of the central basin region can account for the ring grabens in the massif ring the localization of volcanism into a single ridged plains unit on the basin rim indicates a thermal source offset from the basin which is not included in these models and perhaps reflects an additional mechanism unique to mars

evidence for recent climate change on mars from the identification of youthful near surface ground ice ground ice in the crust and soil may be one of the largest reservoirs of water on mars1 2 3 near surface ground ice is predicted to be stable at latitudes higher than 40 ref 4 where a number of geomorphologic features indicative of viscous creep and hence ground ice have been observed5 mid latitude soils have also been implicated as a water ice reservoir6 the capacity of which is predicted to vary on a 100 000 year timescale owing to orbitally driven variations in climate7 it is uncertain however whether near surface ground ice currently exists at these latitudes and how it is changing with time here we report observational evidence for a mid latitude reservoir of near surface water ice occupying the pore space of soils the thickness of the ice occupied soil reservoir 1 10 m and its distribution in the 30 to 60 latitude bands indicate a reservoir of 1 5 6 0 104 km3 equivalent to a global layer of water 10 40 cm thick we infer that the reservoir was created during the last phase of high orbital obliquity less than 100 000 years ago and is now being diminished

ancient glaciation on mars a large number of anomalous landforms on mars can be attributed to glaciation including the action of ice and meltwater glacial landscapes are concentrated south of lat 33 and in the northern plains suggesting vast austral and boreal ice sheets crater densities on the glaciated terrains indicate that the final glacial epoch occurred late in martian history thus mars may have had a relatively warm moist climate and dense atmosphere much later than previously believed

planetary surface dating from crater size frequency distribution measurements multiple resurfacing episodes and differential isochron fitting abstract the analysis of crater size frequency distributions and absolute densities forms the basis of current approaches for estimating the absolute and relative ages of planetary surfaces users of the neukum system of crater dating have conventionally used a cumulative presentation of the data but because of the recent proliferation of interest in identifying resurfacing ages it is worth emphasising the utility of the differential presentation of crater data in identifying resurfacing events and particularly in distinguishing the signature of short lived events such as volcanic flows from long acting processes such as aeolian erosion the work describes some additional considerations for making isochron fits to differentially plotted crater populations with respect to the removal of a binning bias for incrementally differentially plotted data the hartmann approach has not typically employed the fitting of isochrons but differential fitting would be a natural choice for this system and is implemented in the craterstats software a revised calculation of the martian epoch boundary times in both chronology systems is provided

the continuum of north pacific sea level pressure patterns intraseasonal interannual and interdecadal variability this study combines k means cluster analysis with linear unidimensional scaling to illustrate the spatial and temporal variability of the wintertime north pacific sea level pressure slp field daily wintertime slp data derived from the ncep ncar reanalysis are used to produce 16 slp anomaly patterns that represent a discretized approximation of the continuum of north pacific slp patterns this study adopts the continuum perspective for teleconnection patterns which provides a much simpler framework for understanding north pacific variability than the more commonly used discrete modal approach the primary focus of this research is to show that variability in the north pacific on intraseasonal interannual and interdecadal time scales can be understood in terms of changes in the frequency distribution of the cluster patterns that compose the continuum each of which has a time scale of about 10 days this analysis reveals 5 6 pacific north american like pna like patterns for each phase as well as dipoles and wave trains a self organizing map som analysis of coupled slp and outgoing longwave radiation data shows that many of these patterns are associated with convection in the tropical indo pacific region on intraseasonal time scales the frequency distribution of these patterns in particular the pna like patterns is