polygonal cracks in the seasonal semi translucent co2 ice layer in martian polar areas 1 in this paper we use morphological and numerical methods to test the hypothesis that seasonally formed fracture patterns in the martian polar regions result from the brittle failure of seasonal co2 slab ice the observations by the high resolution imaging science experiment hirise of polar regions of mars show very narrow dark elongated linear patterns that are observed during some periods of time in spring disappear in summer and re appear again in the following spring they are repeatedly formed in the same areas but they do not repeat the exact pattern from year to year this leads to the conclusion that they are cracks formed in the seasonal ice layer some of models of seasonal surface processes rely on the existence of a transparent form of co2 ice so called slab ice for the creation of the observed cracks the ice is required to be a continuous media not an agglomeration of relatively separate particles like a firn the best explanation for our observations is a slab ice with relatively high transparency in the visible wavelength range this transparency allows a solid state green house effect to act underneath the ice sheet raising the pressure by sublimation from below the trapped gas creates overpressure and the ice sheet breaks at some point creating the observed cracks we show that the times when the cracks appear are in agreement with the model calculation providing one more piece of evidence that co2 slab ice covers polar areas in spring

numerical study of the orographic forcing of heavy precipitation during map iop 2b abstract this paper investigates the local circulation associated with a heavy orographic rainfall event during 19 21 september 1999 mesoscale alpine programme intensive observing period 2b map iop 2b this event was simulated with a 5 km horizontal grid spacing using the fifth generation pennsylvania state university ncar mesoscale model mm5 the mm5 simulation reproduced the basic features such as the timing and location of the deep trough and the associated precipitation evolution though the total amount of precipitation is slightly higher than that measured by rain gauges 30 in 24 h the near surface flow was dominated by an easterly jet originally from the adriatic sea and a southerly jet from the gulf of genoa a significant westward turning occurred when the southerly flow approached the south side of the alps this deflection was caused by boundary layer friction and rotation as well as mountain blocking effects flow was generally from the south above the surface precipitation was ma

origins of the reversed flow over the windward alpine foothills during map iop3 and iop8 the synoptic scale situations during the two intensive observing periods iops of the mesoscale alpine programme map characterized by persisting precipitation and down valley flow as observed by the doppler on the wheel radar dow over the two alpine valleys toce and ticino were investigated the first period iop3 24 27 september 1999 was characterized by a south westerly flow and convective precipitation whereas the second period iop8 20 21 october 1999 by a down valley flow and stratiform precipitation during iop3 the down valley northerly flow over the north western part of the po valley was confined within a thin layer of 200 300 m depth during iop8 the northerly flow extended from the alps foothills to the ligurian sea in a deep layer of 1 2 km height the meso nh numerical model with a 2 5 km horizontal mesh grid reproduced the characteristics of both cases from the valley scale to the meso scale sensitivity experiments were furthermore performed in order to highlight the relationships between wet or dry drainage flow channelled by the alpine orography mesoscale upstream flow blocked by the alps and a regional cold pool at the foothills inside the po valley during iop8 the diabatic processes were dominant at local scales in confirmation of steiner results based on the dow observations and they were significant at regional scales upstream of the alps by maintaining a cold pool over the po valley the iop3 low level flow reversal occurred as the flow began to cross over the alps instead of turning around a downslope flow is associated with the blocked regime period upstream of the alps copyright 2006 royal meteorological society

autumnal precipitation distribution on the southern flank of the alps a numerical model study of the mechanisms during the autumn there are frequent events of heavy precipitation on the southern slopes of the meso scale alpine chain moreover the accompanying climatology exhibits a distinctive spatial distribution with some meso scale regions of enhanced precipitation such as the wet spot in the vicinity of lago maggiore possible mechanisms to account for the observed spatial distribution are established using a heuristic model based approach it is shown using a mesoscale model that the response to a steady horizontally uniform and moisture laden flow impinging upon a comparatively realistic representation of the alpine chain can reproduce both the overall meso scale precipitation distribution and its meso scale sub structure the nature of the simulated flow regime over around or intermediate is sensitive to the strength of the ambient geostrophic flow and its modification in the planetary boundary layer contrariwise the simulated precipitation distribution in the lago maggiore wet spot is comparatively insensitive to the changes in direction of the incident geostrophic flow from south to south west and in strength in the range 10 30 m s 1 although there is a marked change in the structure of the near alpine flow this systematic precipitation enhancement appears to be related to the relative strength and compensating effects of an easterly barrier jet tracking along the zonally elongated part of the alps and an air stream channelled between the maritime alps and the apennines further evidence to the above interpretation of the meso scale precipitation distribution is given with simulations conducted using a smoothed and schematic representation of the alpine chain likewise the sensitivity to the presence of a lago maggiore like indentation of the topography is tested and evidence is provided of a further indentation induced precipitation enhancement at the local scale copyright 2004 royal meteorological society

analysis and simulation of local and regional conditions for the rainfall over the lago maggiore target area during map iop 2b the mesoscale alpine programme map operational and research network collected a large variety of measurements during the two days of intensive observing period iop 2b 19 and 20 september 1999 which is one of the most intense rainfall episodes during the special observing period over the lago maggiore area the synoptic situation is a typical one of a southerly flow and associated convection over alpine orography simulations with the non hydrostatic meso nh model are used to describe the rainfall conditions and are successfully validated at the different scales allowed by the map data the two types of pre frontal orographically triggered convective episodes are described 1 sporadic and shallow convection occurs over the coastal mountains and propagates over the po valley the chronology and the intensity of these convective episodes are driven by two main features the low level humidity anomalies and the middle troposphere dry anomaly present over the mediterranean sea 2 the lago maggiore orographic convection has a very long duration and is mainly controlled by both the intensity of the easterly low level wind in the north part of the po valley and the upper level clouds of the cold front the different origins of the air masses transported by this easterly barrier wind and the associated local circulations are detailed copyright 2003 royal meteorological society

duration dependence of magnetic susceptibility enhancement in the chinese loess palaeosols of the past 620 ky abstract past climate has been interpreted from the loess palaeosol record found in china there is no argument that the palaeosols are more strongly weathered than the underlying less well weathered loess and that these changes have been governed by glacial interglacial climate fluctuations however the duration of pedogenesis may have also contributed to the development of palaeosol properties previous studies have not attempted to separate these two factors which both affect the intensity of soil formation and have assumed that the degree of soil development and pedogenic magnetic susceptibility enhancement depended solely on the climate conditions we show that the magnetic susceptibility enhancement of palaeosols of the lower malan and upper lishi formations s 1 s 5 correlated to the interglacials of the past 620 ky depends partly on the duration of pedogenesis this suggests that pedogenic magnetic susceptibility enhancement of palaeosols should not be used for such direct palaeoclimate reconstructions as determining the amount of rainfall or the temperature of the soil forming intervals however used in combination with other proxies other magnetic properties fe d fe d fe t color indices the depth of decalcification particle size magnetic properties of palaeosols and loess layers can provide valuable insight into climatic conditions of soil forming episodes it follows that multiproxy evidence provides better insight into climate dynamics than the interpretation of a single proxy

sub surface co2 gas flow in mars polar regions gas transport under constant production rate conditions 1 sublimation at the ice substrate interface with pressure build up is an accepted mechanism for the production of fan deposits on the southern polar co2 ice cap on mars fluid dynamics modeling has been used to investigate gas outflow through vents in a co2 slab ice small 5 25 m in length fan deposits seen on the annual southern co2 ice cap can be produced by a steady state in which open vents continuously outgas in response to sub surface sublimation generated by diurnal energy input through translucent impermeable to gas ice slabs this would produce diurnally controlled deposits which would change orientation with time in response to winds thereby explaining observations made by hirise on mro gas flow below the ice can reach up to 25 m s close to the vent dust flow in the sub ice cavity has also been computed but velocities are much lower with the main acceleration occurring 0 5 m from the vent this indicates that erosion is likely to be restricted to the immediate vicinity of the vent unless channels form in the cavity between the ice and the surface

quantitative estimates of pedogenic ferromagnetic mineral formation in chinese loess and palaeoclimatic implications abstract the quasi continuously deposited loess sediments of the central chinese loess plateau constitute one of the most complete and long lasting records of quaternary palaeoclimate on land much of this record has been uncovered by measurement and interpretation of the magnetic properties of the loess the polarity of natural remanent magnetization has provided absolute age dates by correlation with the geomagnetic polarity time scale magnetic low field susceptibility has been used to reconstruct the cyclic changes of pleistocene palaeoclimates although the origin of the signal is still poorly understood from comparison with the 10 be concentration throughout the sequence we are able to determine the contributions to susceptibility from inherited and authigenic sources for the last 130 ky since the production of authigenic magnetite is directly related to regional precipitation annual palaeoprecipitation rates can be calculated palaeoprecipitation rates similar to present day rates are derived for oxygen isotope stage 5 including the last interglacial in contrast cold periods corresponding to oxygen isotope stages 2 and 4 experienced negligible precipitation the beginning and end of the time interval represented by oxygen isotope stage 3 however was characterized by short episodes when precipitation exceeded the holocene average

review of recent developments in mineral magnetism of the chinese loess mineral magnetism of the chinese loess has been investigated for more than 20 years although there is a consensus that the neoformation of fine grained maghemite particles in the superparamagnetic sp and single domain sd grain size regions accounts for the magnetic enhancement in the chinese paleosols quantitative retrieval of paleoclimatic signals in terms of rock magnetic proxies is still a subject of debate the ambiguities arise from the inherent complexities of magnetic proxies as well as the multiple factors that control the pedogenic processes therefore a better description of the magnetic assemblage including its mineralogy grain size distribution and stoichiometry of two distinct origins pedogenic and eolian can help us better understand mechanisms behind variations in magnetic proxies at different timescales in order to link them to the paleoclimatic processes this review focuses on recent developments in loess magnetism and carefully evaluates merits and limitations of rock magnetic proxies furthermore several currently unsolved problems are addressed

modern sangamon and yarmouth soil development in loess of unglaciated southwestern illinois abstract the thebes section in unglaciated southwestern illinois contains a well preserved 500 kyr loess paleosol sequence with four loesses and three interglacial soils various magnetic mineralogical and elemental properties were analyzed and compared over the thickness of soil sola these proxies for soil development intensity have the following trend yarmouth geosol sangamon geosol modern soil quartz plagioclase zr sr and tio 2 na 2 o ratios were most sensitive to weathering frequency dependent magnetic susceptibility and anhysteretic remanent magnetization greatest in a horizons also correspond well with soil development intensity neoformed mixed layered kaolinite expandables suggestive of a warm humid climate were detected in the sangamon and yarmouth soil sola clay illuviation in soils was among the least sensitive indicators of soil development differences in properties among interglacial soils are interpreted to primarily reflect soil development duration with climatic effects being secondary assuming logarithmic decreases in weathering rates the observed weathering in the sangamon geosol is consistent with 50 kyr of interglacial weathering oxygen isotope stage 5 compared to 10 kyr for the modern soil oxygen isotope stage 1 we propose that the yarmouth geosol in the central midwest formed over 180 kyr of interglacial weathering including oxygen isotope stages 7 9 and 11

paleorainfall reconstructions from pedogenic magnetic susceptibility variations in the chinese loess and paleosols the rock magnetic properties of the chinese loess and paleosols constitute a unique and sensitive record of east asian paleoclimate through the quaternary period systematic variations in the concentration and grain size of the magnetic minerals in these sediments have produced systematic variations in the magnetic susceptibility signal which can be easily and rapidly measured at many sites across the loess plateau variations in many other rock magnetic properties can be used to identify the key shifts in ferrimagnetic grain size but magnetic susceptibility alone is sufficiently sensitive to record stadial and interstadial climate stages as well as glaciations and interglaciations past changes in rainfall and monsoon activity for this region are reconstructed from the susceptibility variations the susceptibility record is calibrated using the modern relationship between rainfall and pedogenic susceptibility on the loess plateau our rainfall reconstructions identify enhanced summer monsoonal activity in the chinese loess plateau region in the early holocene and the last interglaciation in the presently semiarid western area of the plateau annual precipitation in interglacial times was up to 80 higher than at present in the more humid southern and eastern areas values were up to 20 higher than today s levels during the last glaciation precipitation decreased across the entire plateau typically by 25 the relationship between pedogenic susceptibility climate and weathering age was examined over the northern hemisphere temperate zone and the observed positive correlation between rainfall and susceptibility indicates that climate rather than soil age is the predominant factor that controls pedogenic susceptibility enhancement in loess soils

direct estimates of pedogenic magnetite as a tool to reconstruct past climates from buried soils 1 variations in magnetic properties of buried soils can be used to reconstruct past climatic conditions during paleosol formation most methods however are based on comparisons between the magnetically enriched upper soil horizons and the magnetically unaltered parent material in thin loess paleosol sequences such a comparison can be problematic because all horizons soil and underlying loess may be affected to varying degrees by pedogenesis we propose two direct estimates of pedogenic magnetite based on the analysis of anhysteretic remanent magnetization ratios carm isothermal remanent magnetization and coercivity distributions these estimates are independent of any information regarding the parent material and are possible if pedogenic minerals have similar magnetic properties throughout the study region this condition seems to be met throughout the midwestern united states and a few loessic soils elsewhere the remanence carrying part of pedogenic magnetite is composed of single domain particles with consistent well constrained magnetic properties these particles are extremely well dispersed in the soil matrix as indicated by the absence of noticeable magnetostatic interaction effects our analyses of over 70 modern loessic soil profiles demonstrate that the abundance of pedogenic magnetite correlates well with modern climate and that the method is suited for reconstruction of past climates from paleosols

wide distribution and glacial origin of polar gypsum on mars the north polar cap of mars is associated with different kinds of superficial sediments including the circumpolar dune field interior dune fields and sedimentary veneers scattered over the ice cap in order to resolve the mineralogical composition and the regional distribution of these sediments we processed omega and crism hyperspectral data with an original method based on spectral derivation we find that gypsum is present in all areas where undefined hydrated minerals had been previously detected including superficial sedimentary veneers covering the north polar cap interior dune fields and the whole circumpolar dune field morphological and structural analyses reveal that these gypsum crystals derive directly from the interior of the ice cap the source of superficial sedimentary veneers is the dust that was previously contained in the upper part of the ice cap the ice rich north polar layered deposits npld this gypsum bearing dust was released on south facing slopes of spiral troughs and arcuate scarps by ice ablation controlled by katabatic winds by the analysis of all associations of erosional scarps and dune fields over the north polar cap we also demonstrate that the polar dunes are composed of sand sized particles that were previously contained in the sediment rich basal unit bu corresponding to the lower part of the ice cap these particles contain gypsum and were released from the bu by regressive ablation of ice at marginal scarps that border the north polar cap and by vertical ablation of ice on olympia planum from a reconstruction of wind streamlines over and around the ice cap we infer that katabatic winds descending from the polar high and rotating around the north polar cap control the release of these gypsum bearing particles by ice ablation and the redistribution of these particles in the circumpolar dune field 2011 elsevier b v

upstream effects of mesoscale mountains abstract the alpine experiment alpex has revealed that low level air is typically diverted around the alps without reaching the mountaintop in pursuit of an understanding of the physical basis of this phenomenon and of its generality we have explored the characteristics of orographic blocking of a rotating continuously stratified quid as revealed in a simple model problem retaining full nonlinear and transient effects hydrostatic dynamics is assumed and the obstacle is taken to be an infinitely long ridge with height h x the key questions treated are the strength of the upstream deceleration of cross mountain flow and the length scale over which the decelerated region extends by means of scale analysis the controlling parameters are found to be the rossby number ro u fl and the froude number fr nhm u where u is the speed of the oncoming flow f is the coriolis parameter l the mountain half width n the brunt vaisala frequency and hm is the maximum mountain height the scale analysis also

paleoclimatic significance of the mineral magnetic record of the chinese loess and paleosols the origins of the magnetic susceptibility variations of the chinese loess and paleosols are explored by scanning and transmission electron microscopy of magnetic extracts and by magnetic modeling of magnetic hysteresis data to provide quantified estimates of the major magnetic components microscopy identifies several distinct size and shape characteristics in the magnetic carriers lithogenic magnetites intact and abraded dominate the coarse grained magnetic fraction the smallest of the coarse grains is 2 i m the remaining magnetic materal is ultrafine in size with two types of magnetite particles present type a particles strongly resemble soil magnetites produced by inorganic precipitation type b particles which occur rarely are probably bacterial in origin quantitative modeling of these magnetic assemblages shows that over 90 of the susceptibility variations is accounted for by the superparamagnetic magnetite component compared to the loess units the paleosols are richer in magnetite particularly of superparamagnetic size and have a threefold higher ratio of magnetite to hematite we identify pedogenic formation of magnetite as the major contributor to the loess magnetic record matching this record against other paleoclimatic records we find an extremely high correlation with the standard 18o record the chinese loess sequences record a very high resolution magnetic stratigraphy directly related to changing climate

interaction between dynamics and cloud microphysics in orographic precipitation enhancement a high resolution modeling study of two north alpine heavy precipitation events abstract interactions of atmospheric dynamics and cloud microphysics with the alpine orography are investigated for two north alpine heavy precipitation cases 20 22 may 1999 and 22 23 august 2005 both cases were related to a deep cyclone propagating slowly eastward along the alps advecting moist air of mediterranean origin toward the northern side of the alps a validation against high resolution rain gauge data reveals that the average model bias is below 15 in the region of interest but there is a tendency to systematically underestimate very heavy precipitation a scale decomposition of the discrepancies between model and observations reveals that errors on the meso scale contribute at least as much to the total model error as discrepancies on the meso scale on the scale of single mountain ridges and valleys the formation of precipitation maxima at valley locations is investigated with particular emphasis on a region in which a valley receives systematically more precipitation than the adj

magnetic enhancement and palaeoclimate study of a loess palaeosol couplet across the loess plateau of china summary the origin of the milankovitch palaeoclimatic signal so dramatically recorded in the chinese loess remains uncertain at least five hypotheses have been put forward to explain the well documented enhancement of magnetic susceptibility in palaeosols which formed when conditions were warmer and wetter we report here a magnetic study of a prominent loess soil couplet l4 s3 at three widely separated sites where present day mean annual rainfall and temperature range from 350mm to 700mm and from 6 c to 13 c the properties determined are laboratory remanences isothermal irm anhysteretic arm viscous vrm including viscous decay room temperature susceptibility and thermomagnetic behaviour at fields beyond 100 mt the irm spectra are all essentially identical both in shape and in absolute magnitude suggesting a uniform magnetic component widespread across the plateau subtracting the signal of this component isolates a second component the amount of which varies by an order of magnitude between sites the magnetic properties of this latter material are remarkably similar to those reported for bacterial magnetite in geological sediments and modern soils viscous decay of vrm takes place in two distinct stages one of which falls to zero in 10min we attribute magnetic enhancement which is the source of the palaeoclimatic signal to in situ pedogenetic formation of magnetite which we characterize in our interpretation as two separate forms of bacterial magnetofossils the most magnetic sample requires a mass fraction of about half of one per cent of this biogenic material

winter and spring evolution of northern seasonal deposits on mars from omega on mars express the omega visible near infrared imaging spectrometer on mars express has observed the retreat of the northern seasonal deposits during martian year 27 28 from the period of maximum extension close to the northern winter solstice to the end of the retreat at l s 95 we present the temporal and spatial distributions of both co 2 and h 2o ices and propose a scenario that describes the winter and spring evolution of the northern seasonal deposits during winter the co 2 rich condensates are initially transparent and could be in slab form a water ice annulus surrounds the sublimating co 2 ice extending over 6 of latitude at l s 320 decreasing to 2 at l s 350 and gradually increasing to 4 5 at l s 50 this annulus first consists of thin frost as observed by the viking lander 2 and is then overlaid by h 2o grains trapped in the co 2 rich ice layer and released during co 2 sublimation by l s 50 h 2o ice spectrally dominates most of the deposits in order to hide the still several tens of centimeters thick co 2 ice layer in central areas of the cap we propose the buildup of an optically thick top layer of h 2o ice from ice grains previously embedded in the co 2 ice and by cold trapping of water vapor from the sublimating water ice annulus the co 2 ice signature locally reappears between l s 50 and 70 what emerges from our observations is a very active surface atmosphere water cycle these data provide additional constraints to the general circulation models simulating the martian climate copyright 2011 by the american geophysical union

mesoscale organization and structure of orographic precipitation producing flash floods in the lago maggiore region this article investigates the mesoscale precipitation mechanisms affecting the severest flood events observed from 2005 to 2012 in the maggia river located in the lago maggiore region on the southern side of the european alps high resolution volumetric radar data are used to describe the horizontal and vertical structure of precipitation while sounding data depict the airflow conditions the events causing the nine highest peak discharge rates in the river in the last eight years are characterized by the presence of convection which is generally absent in the storms that produced lower peak flow rates during major floods convective cells repeatedly propagate over the watershed over time at large temporal scales precipitation patterns assume the form of an elongated band of precipitation the main reason for the formation of the band is the different direction of the low level and upper level flow in relation to the orientation of the alpine orography when pre frontal moist and conditionally unstable air over the po valley is advected towards the alpine chain by a southsoutheasterly low level jet convection develops over the slopes west of lago maggiore where the low level flow is perpendicular to the terrain orientation convective cells are then transported towards the northeast by the upper level southwesterly steering flow reaching maturity over the maggia watershed this mesoscale process can trigger and maintain moist convection for a long time over the same region statistical analyses show that the strength and stability of the upstream flow at low levels 1 5 km determine to what extent precipitation will be convective a comparison with the mesoscale alpine program intensive observing period map iop precipitation cases shows that map iop 2b and 3 are representative of the type of event that produces the biggest floods in the lago maggiore area

theoretical considerations on the anhysteretic remanent magnetization of interacting particles with uniaxial anisotropy 1 the anhysteretic remanent magnetization arm is widely used in rock magnetism and paleomagnetism because of its sensitivity to the domain state of magnetic particles and the close analogy to natural remanent magnetizations on the other hand the arm shares with other weak field magnetizations the property of being extremely sensitive to magnetostatic interactions therefore it is desirable to model the effects of interactions on natural assemblages of magnetic particles direct micromagnetic calculations of the arm acquisition process are not practicable therefore an analytical approach is used calculate the arm susceptibility of a system of interacting single domain sd particles the model is based on a statistical description of the interaction field the equations obtained have been used to evaluate the dependence of the arm on the packing fraction of the magnetic particles the effect of interactions on the anisotropy of arm aarm was evaluated as well the aarm of densely packed particles is complex and depends critically on the microcoercivity a physical interpretation of the aarm of highly interacting particles is therefore difficult

seasonal h2o and co2 ice cycles at the mars phoenix landing site 1 prelanding crism and hirise observations 1 the condensation evolution and sublimation of seasonal water and carbon dioxide ices were characterized at the mars phoenix landing site from martian northern midsummer to midspring ls 142 ls 60 for the year prior to the phoenix landing on 25 may 2008 ice relative abundances and grain sizes were estimated using data from the compact reconnaissance imaging spectrometer for mars and high resolution imaging science experiment aboard mars reconnaissance orbiter and a nonlinear mixing model water ice first appeared at the phoenix landing site during the afternoon in late summer ls 167 as an optically thin layer on top of soil co2 ice appeared after the fall equinox by late winter ls 344 the site was covered by relatively pure co2 ice 30 cm thick with a small amount of 100 m diameter water ice and soil as spring progressed co2 ice grain sizes gradually decreased a change interpreted to result from granulation during sublimation losses the combined effect of co2 sublimation and decreasing h2o ice grain sizes allowed h2o ice to dominate spectra during the spring and significantly brightened the surface co2 ice disappeared by early spring ls 34 and h2o ice by midspring ls 59 spring defrosting was not uniform and occurred more rapidly over the centers of polygons and geomorphic units with relatively higher thermal inertia values

characterisation of soils by mineral magnetic measurements processes of iron mineral authigenesis diagenesis and dissolution in interaction with primary inputs of iron minerals act to produce vertical differentiation of soil magnetic properties thus magnetic iron oxides in common with other iron forms may both respond to and reflect soil forming processes investigation of the degree of detectable and persistent magnetic differentiation within different soil materials can provide insights into the nature and direction of distinct sets of soil processes evidence of clear association between magnetic variation and discrete types of soil environment also has applied significance in several areas of environmental study for example the observed magnetic variation can be used to discriminate between individual soils and soil horizons for the purposes of soil surveying sediment tagging and tracing and empirical modelling of source sediment linkages this paper reports the use of mineral magnetic techniques to characterise the iron oxide assemblages within soils of varying type and provenance the effect of different pedogenic regimes have been investigated through measurement of a range of magnetic parameters including magnetic susceptibility frequency dependent susceptibility and anhysteretic and saturation remanences contrary to current pedological thought but in accord with other magnetically based studies e g mullins the presence of magnetite maghemite typically of superparamagnetic single domain grain size within soils has been found to be an extremely widespread phenomenon its contemporary neoformation within the soil environment is inferred however the input of artificially generated ferrimagnetic material is indicated for one of the magnetically enhanced soils examined here and the possibility of extraneous sources of magnetite in topsoils should be considered before pedogenic processes of magnetic enhancement are inferred from the data presented discrimination of industrially derived magnetic particles appears possible on the basis of their very low levels of frequency dependent susceptibility fd low anhysteretic remanence arm and dissociation from the finer clay sized not the formation but the active dissolution of ferrimagnetic minerals is indicated for soils affected by the processes of gleying and podsolisation eluvial horizons of podsolised profiles demonstrate almost total loss of detectable magnetic content variations in the form of the iron reprecipitated in the underlying illuvial layers may reflect differences in the pedological characteristics of these horizons within gleyed waterlogged soils processes of magnetite dissolution appear to be grain size specific preferential reduction of those grains of ultrafine superparamagnetic and fine single domain magnetic grain size is indicated where soil forms a major contributor to catchment sediment loads this has significance in the area of source sediment modelling soil derived from permanently wet or highly leached catchment areas is unlikely to contribute to peaks in the magnetic content of deposited sediments further only those erosional processes that operate at a faster rate than those of magnetic depletion will have the capacity to produce peaks in sediment ferrimagnetic concentrations such as have been observed within the historical magnetic record

how abundant is pedogenic magnetite abundance and grain size estimates for loessic soils based on rock magnetic analyses 1 the upper soil horizons of many modern and ancient soils are enriched in fine grained pedogenic ferrimagnetic minerals we use three grain size and concentration dependent proxies anhysteretic remanent magnetization isothermal remanent magnetization ratios coercivity spectra derived from alternating field demagnetization of saturation isothermal remanent magnetization and hysteresis properties to quantify the abundance and grain size of the pedogenic magnetic component our analyses of modern loessic soils from the midwestern united states show that relatively small additions 2 10 vol of the total ferrimagnetic component of fine grained coarse superparamagnetic to fine pseudosingle domain magnetite or maghemite are sufficient to explain the changes in concentration and grain size dependent properties observed in the upper soil horizons furthermore the pedogenic components of all studied sites display a narrow range of magnetic properties which argues for a common origin of these particles over a wide range of climatic conditions

lagrangian description of airflows using eulerian passive tracers a method of tracking coherent lagrangian airmasses is presented it is not based on the computation of individual trajectories but rather on three eulerian passive tracers initialized with the coordinates of each grid cell this initial coordinates method allows the later unambiguous identification of each lagrangian air parcel by referring to its initial position further the physical history of each parcel can be retrieved the advantages of this method in the framework of mesoscale numerical modelling are discussed with respect to trajectory based methods preliminary examples are given by studying idealized airflows i a two dimensional stratified flow past an isolated obstacle generating gravity wave breaking ii a deep convective squall line then the method is applied to a heavy rain situation over the alps during the mesoscale alpine programme map field phase a coherent mesoscale pool of dry air is identified over the mediterranean and tracked with the aid of the initial coordinates method its influence on the rain distribution over the ligurian alps and apennines is demonstrated copyright 2002 royal meteorological society

new views of mars eolian activity materials and surface properties three vignettes from the mars global surveyor mars orbiter camera prior to the mars global surveyor mgs mission a very general view had emerged in which martian surface materials were seen as consisting of a mixture of bright dust dark sand and rocks the configuration of these materials and the winds that transport and deposit sand and dust have been thought to be directly linked to the albedo patterns that have been observed on mars for centuries high spatial resolution images 1 4 20 m pixel obtained by the mgs mars orbiter camera moc between september 15 1997 and july 4 1999 provide new information about the physical nature of the windblown material on the martian surface and show that the pre mgs view was much too simple in addition to bright dust and dark sand moc images show evidence of bright sediment that can be transported by saltation e g sand and dark material that can be transported in suspension e g silt new views of eolian wind streaks in daedalia planum show that part of this region thought to be mantled by bright dust based upon viking and mariner observations is instead covered by a thin veneer of bright windblown sand moc images of sinus sabaeus and parts of syrtis major two regions thought to be sandy based upon viking era observations exhibit thick mantles that are inferred to consist of fine grained sediment deposited from eolian suspension low albedo wind streaks in western arabia terra are also dark mantles and their association with eroded crater floors and megaripples dunes on these floors suggest that these particular wind streaks are deposits of silt sized material that was only briefly suspended before settling to the surface moc images also show evidence that some eolian dunes are active on mars today i e in 1998 and 1999 the evidence for activity is largely based upon wind and avalanche induced streaks superposed on or eroded into seasonal frost on high latitude dune fields moc images show that some other dunes are inactive but the albedo of dunes relative to surrounding terrain is not a good indicator of dune activity because some inactive dunes are not mantled by dust inactive dunes are best identified by superposed features such as impact craters landslide deposits and yardangs

multiple precipitation mechanisms over mountains observed by airborne doppler radar during map iop5 abstract this study uses airborne doppler radar measurements from the special observing period of the mesoscale alpine programme map to document the detailed airflow and precipitation structure over the mountainous regions near the border of northeastern italy and slovenia as a cold frontal system moved eastward and encountered the eastern alps on 4 october 1999 during map iop5 in contrast to previously documented map cases the environmental conditions associated with this case are characterized by a deep layer of strong convective instability in the lower troposphere and by a cold northeasterly continental flow coming down from the mountains the so called bora wind along the southeastern alps over the study region there are two primary mountain barriers the julian alps oriented roughly west east with a peak mountain height of 2500 m and a significant variation in terrain height along its length and the other the dinaric alps a relatively lower mountain range oriented northwest southeast

orographic precipitation and air mass transformation an alpine example a case of orographic precipitation in the alps on 20 september 1999 was studied using several models along with rain gauge and radar data the objective of the study is to describe the orographic transformation of an air mass including multi scale aspects several new and some conventional diagnostic quantities are estimated including drying ratio precipitation efficiency buoyancy work condensed water residence time parcel changes in heat moisture and altitude and dominant space and time scales for the case considered the drying ratio was about 35 precipitation efficiency values are ambiguous due to repeated ascent and descent over small scale terrain the sign of buoyancy work changed during the event indicating a shift from stratiform orographic to weak convective clouds cloud water residence times are different for the two mesoscale models 400 compared to 1000 s due to different cloud physical formulations the two mesoscale models agree that the dominant spatial scale of lifting and precipitation is about 10 km smaller than the scale of the main alpine massif trajectory analysis of air crossing the alps casts doubt on the classic model of fohn few parcels exhibit classic pattern of moist ascent followed by dry descent parcels that gain latent heat descend only briefly before rising into the middle troposphere parcels that descend along the lee slope originate in the middle troposphere and gain little or even lose latent heat during the transit as parcels seek their proper buoyancy level downstream a surprising scrambling of the air mass occurs radar data confirm the model prediction that the rainfall field is tightly controlled by local terrain on scales as small as 10 km rather than the full 100 km cross alpine scale a curious pulsing of the precipitation is seen indicating either drifting moisture anomalies or weak convection copyright 2003 royal meteorological society

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

hirise observations of gas sublimation driven activity in mars southern polar regions iii models of processes involving translucent ice abstract enigmatic surface features known as spiders found at high southern martian latitudes are probably caused by sublimation driven erosion under the seasonal carbon dioxide ice cap the mars reconnaissance orbiter mro high resolution imaging science experiment hirise has imaged this terrain in unprecedented details throughout southern spring it has been postulated kieffer h h titus t n mullins k f christensen p r 2000 j geophys res 105 9653 9700 that translucent co 2 slab ice traps gas sublimating at the ice surface boundary wherever the pressure is released the escaping gas jet entrains loose surface material and carries it to the top of the ice where it is carried downslope and or downwind and deposited in a fan shape here we model two stages of this scenario first the cleaning of co 2 slab ice from dust and then the breaking of the slab ice plate under the pressure built below it by subliming ice our modeling results and analysis of hirise images support the gas jet hypothesis and show that outbursts happen very early in spring

small scale rainfall mechanisms for an idealized convective southerly flow over the alps rain producing flows over the south side of the alps are investigated with an idealized high resolution 2 5 km numerical configuration where only three basic ingredients of typical heavy precipitation situations have been retained 1 a uniform and stationary southerly flow far upstream from the alps which drives 2 a conditionally unstable atmosphere towards 3 the real topography of the alps and the surrounding secondary mountains attention is given to small scale mechanisms of rainfall over the po plain and the alpine slopes these are linked with two orographically induced low level wind jets the easterly barrier wind jet along the southern flank of the alps and a south easterly jet formed over the sea along the south western flank of the apennines and continuing over land up to the alps the specific role of the secondary relief upstream from the alps in inducing or influencing these low level flow features and also in triggering organized convection is studied by means of experiments on the sensitivity to topography the idealized configuration also allows the advantages of a convection resolving model for modelling precipitation distributions at the alpine valley scale to be considered copyright 2007 royal meteorological society

formation mechanisms for convection over the ligurian sea during map iop 8 abstract the dynamical impacts of an unusually strong stable layer that developed over the po valley and northern ligurian sea during mesoscale alpine program map intensive observation period 8 iop 8 on the formation of convection over the ligurian sea are explored based on numerically simulated equivalent potential temperature wind vectors and by a trajectory analysis of parcels both beneath and above the stable layer it is shown that the stable layer behaved as a material surface or effective mountain to the airstreams impinging on it from the south additional analyses show that the leading edge of the stable layer was collocated with maxima in upward motion and a strong positive moisture flux hence it was further argued and demonstrated through inspection of soundings upstream of the cold dome and trajectory analyses that lifting by the stable layer enhanced convective activities over the ligurian sea finally processes contributing to the maintenance of the stable layer during iop 8 were

some new aspects for the modelling of isothermal remanent magnetization acquisition curves by cumulative log gaussian functions rock samples containing ferri magnetic minerals acquire an isothermal remanent magnetization irm after exposure to a direct magnetic field measuring irm b allows to produce irm acquisition curves which were modelled by cumulative log gaussian clg functions robertson and france 1994 to discriminate the different magnetic phases an approach of how to find the best model has been added to this method from the investigation of a magnetite sample it is inferred that with the method the remanence acquisition coercive force for each magnetic component in a sample can be deduced the method allows to detect minute concentrations of magnetically hard material in a predominant magnetically soft sample and vice versa it furthermore allows to extrapolate the irm behaviour of samples that do not reach saturation irm in the experiment the study of a natural hematite renders it possible that even well defined hematite may be contaminated by ferri magnetic impurities biasing the remanence acquisition coercive force of the sample towards lower values

transport direction of wisconsinan loess in southeastern minnesota a study of wisconsinan loess in part of southeastern minnesota confirms earlier suggestions that much of the loess in this region was not derived flora the floodplain of the mississippi river two wisconsinan loess units the peoria loess and roxana silt occur in the study area peoria loess 1 8 m thick fines systematically eastward from an abrupt western border toward the mississippi there are no apparent grain size trends away from other adjacent rivers peoria loess thickness generally decreases eastward but is highly variable probably because of differential erosion potential sources for this unit are pre wisconsinan sediments on the iowan erosion surface immediately west of the border of thick loess and wisconsinan glacial sources tens or hundreds of kilometers to the west the underlying roxana silt up to 1 m thick occurs only near the mississippi and fines away from that river the roxana silt deposit could reflect aggradation of the mississippi floodplain because of glacial activity upstream and does not have clear implications for upland vegetation near the study area by contrast transport of the peoria loess from distant glacial sources or wind erosion of upland surfaces closer to the loess deposit both imply extensive very sparsely vegetated surfaces west of the study area when the peoria loess accumulated

cold jets in the martian polar caps 1 mars seasonal polar caps display dark ice local darker spots aligned elongate patches and radially dendritic forms that reverse albedo contrast the unexpected variety and sequence of these features are explained on the basis of processes involving co2 dust sand and h2o these processes are largely related to the atmosphere being near its saturation temperature and they have few terrestrial analogies in the simplest case the 1 m thick seasonal cap initially dusty cleans itself and becomes translucent after sunrise and is impermeable over extensive regions except for local vents the slab ice sublimates at the base and is levitated on high pressure gas causing humidity exchange with deeper layers subslab gas converging toward the vents erodes channels in the soil and ejects this material in high velocity jets recent spectral observations indicate great variety in the details

sublimation of mars s southern seasonal co2 ice cap and the formation of spiders 1 in this paper we define and describe morphological features that have colloquially been termed spiders and map their distribution in the south polar region of mars we show that these features go through a distinct seasonal evolution exhibiting dark plumes and associated fan shaped deposits during the local defrosting of the seasonal cap we have documented the seasonal evolution of the cryptic region and have found that spiders only occur within this terrain these observations are consistent with a geyser like model for spider formation association with the transparent cryptic portion of the seasonal cap is consistent with basal sublimation and the resulting venting of co2 gas also consistent with such venting is the observation of dark fan shaped deposits apparently emanating from spider centers spiders are additionally confined to the polar layered deposits presumably due to the poorly consolidated and easily eroded nature of their upper surface

alpine gravity waves lessons from map regarding mountain wave generation and breaking the two month special observing period of the mesoscale alpine programme map in autumn 1999 included a variety of complex mountain wave events seven wave events were carefully analyzed compared with numerical models and described in published papers these detailed investigations revealed some common dynamical elements i e the importance of low level processes involving the slow moving boundary layer low level wind shear causing either wave absorption or decoupling spilling upstream blocking and latent heat release based on these studies it is clear that any quantitative prediction of mountain wave generation must take full account of these lower troposphere processes the newest numerical models show significant skill in simulating these effects using these models the climatology of waves over the alps can be studied copyright 2007 royal meteorological society

orographic modification of convection and flow kinematics by the oregon coast range and cascades during improve 2 abstract this paper describes the kinematic and precipitation evolution accompanying the passage of a cold baroclinic trough over the central oregon coast range and cascades during 4 5 december 2001 of the second improvement of microphysical parameterization through observational verification experiment improve 2 field project in contrast to previously documented improve 2 cases the 4 5 december event featured weaker cross barrier winds 15 20 m s 1 weaker moist static stability nm 0 006 s 1 and convective cells that preferentially intensified over oregon s modest coastal mountain range these cells propagated eastward and became embedded within the larger orographic precipitation shield over the windward slopes of the cascades the weather research and forecasting model version 2 2 at 1 33 km grid spacing was able to accurately replicate the observed evolution of the precipitation across western oregon as a result of the convective cell development the precipitation enhancement over the co

dependence of near surface magnetic susceptibility on dust accumulation rate and precipitation on the chinese loess plateau magnetic susceptibility ms of surface sediment varies systematically across the loess plateau in central china decreasing exponentially from 200 10 8 m3 kg at the northern margin of the qinling shan to 30 10 8 m3 kg near the southern margin of the mu us desert ms correlates highly with loess median grain size r2 0 79 which decreases south southeastward across the plateau it also correlates with mean annual temperature mat and mean annual precipitation map r2 0 58 and 0 60 respectively and with their product mat map r2 0 83 which is considered a measure of potential pedogenic activity because regional isopleths depicting grain size and the primary meteorological parameters are nearly parallel it is difficult to determine their relative influence on ms a simple ms model based on the observed spatial variation in loess thickness permits quantitative assessment of the effect of the dust accumulation rate on the ms signal of surface sediment and isolates the likely role of climate in the production of magnetic minerals the model suggests that 84 of the loess ms variance is dictated by the diluting effect of dust and 10 11 is associated with meteorological factors primarily precipitation the observed and modeled relationships support hypotheses that attribute variations in ms in the loess paleosol succession to varying rates of dust deposition and in situ production of magnetic minerals in the accretionary soils both of which are controlled by monsoon climate

time dependence of magnetic susceptibility of soil chronosequences on the california coast abstract as the age of the soils in a chronosequence on the california coast increases the difference between the magnetic susceptibility of eluvial and illuvial horizons increases and the residual susceptibility after extraction with citrate bicarbonate dithionite cbd decreases enhanced susceptibility results from the conversion of nonferrimagnetic minerals to secondary ferrimagnetic forms most likely maghemite and the preferential accumulation of inherited and pedogenic magnetic minerals little enhancement occurs for pedons younger than 40 000 yr by 124 000 yr most of the magnetic susceptibility can be attributed to forms soluble in cbd magnetic susceptibility appears to vary systematically over time for three chronosequences from areas with mean annual precipitation ranging from 650 to 1500 mm yr 1 magnetic susceptibility enhancement may be a useful parameter for estimating soil age in certain climates

hirise observations of gas sublimation driven activity in mars southern polar regions i erosion of the surface the high resolution imaging science experiment hirise on the mars reconnaissance orbiter mro has imaged the sublimation of mars seasonal co2 polar cap with unprecedented detail for one complete martian southern spring in some areas of the surface beneath the conformal coating of seasonal ice radiallyorganized channels are connected in spidery patterns the process of formation of this terrain erosion by gas from subliming seasonal ice has no earthly analog the new capabilities high resolution color and stereo images of hirise enable detailed study of this enigmatic terrain two sites are analyzed in detail one within an area expected to have translucent seasonal co2 ice and the other site outside that region stereo anaglyphs show that some channels grow larger as they go uphill implicating gas rather than liquid as the erosive agent dark fans of material from the substrate are observed draped over the seasonal ice and this material collects in thin to thick layers in the channels possibly choking off gas flow in subsequent years resulting in inactive crisscrossing shallow channels in some areas there are very dense networks of channels with similar width and depth and fewer fans emerging later in the season are observed subtle variations in topography affect the channel morphology a new terminology is proposed for the wide variety of erosional features observed

triple doppler radar analysis of the heavy rain event observed in the lago maggiore region during map iop 2b this paper presents analyses of data collected with three ground based doppler radars during the mesoscale alpine programme map intensive observation period iop 2b from 1900 utc 19 september until 1100 utc 20 september 1999 during this period the synoptic situation was characterized by the propagation of a deep upper tropospheric trough towards the alps as often observed when heavy precipitation occurs on the southern slopes of the alpine massif a frontal cloud system with embedded convective cells passed over northern italy in association with the trough moving rapidly eastwards ahead of the advancing cold front a strong south to south easterly low level flow impinged on the mountains near lago maggiore and produced copious amounts of rain 200mm at several locations an analysis of three dimensional radar derived wind and precipitation fields shows that the most intense precipitation occurred where and when the easterly component of the low to mid level flow was the strongest with however a preferential location on the southern slopes of the alps this phenomenon can be explained by enhanced confluence between the main southerly flow and an intensifying easterly flow and or more favourable orientation of the moist inflow perpendicular to the mountain slopes in addition the propagation of convective cells from the po valley toward the alps led to enhanced precipitation over the mountainous area taking advantage of the approximately two dimensional character of the event the different terms of the water budget are calculated for a series of 25 successive vertical cross sections to analyse the transformation of atmospheric moisture into surface rainfall copyright 2003 royal meteorological society

exploration of some convective regimes over the alpine orography a numerical exploration of several airflow regimes is performed by means of the non hydrostatic model meso nh the alpine orography has been selected together with a uniform conditionally unstable profile extracted from the mesoscale alpine programme database the stationary solution is obtained at the fine scale after three successive simulations using three nested levels 40 10 and 2 5 km the variation of the non dimensional height of the alps leads to the following regimes no convection upstream propagating convection and stationary convection over the alps the last two regimes correspond to regimes i and ii of the chu and lin 2000 study the sensitivity of the convective response to the fine scale orography is found to be more important for regime ii than for regime i moisture budgets confirm the importance of the barrier wind to determine the rain distribution in the centre of the alpine orography for regime ii and away from it for regime i the drying ratio is more influenced by the comparative value of the advective time to a characteristic microphysical time scale than by the orographic forcing itself finally for this sounding the diabatic effects change the critical value of the non dimensional height for the transition between the flow over and flow around configurations copyright 2004 royal meteorological society

impact of holocene dust aggradation on a horizon characteristics and carbon storage in loess derived mollisols of the great plains usa the amount and vertical distribution of soil organic carbon soc storage is primarily a function of vegetation type and climate with influence from soil and landscape properties and human activities the influence of dust aggradation on landscapes during the holocene has largely been ignored as a factor in long term soc storage dust aggradation is important to soil horizonation and c sequestration since the dust deposit buries the landscape and increases solum thickness mollisols on loess covered upland tables in central nebraska have aggraded throughout the holocene as bignell loess accumulated above the late pleistocene brady soil in the loess tablelands the thickness of mollic colors a horizon properties and soc storage all decrease with distance from the source of bignell loess which is along a gradient of increasing precipitation for example along a 140 km transect of decreasing bignell loess thickness and increasing rainfall total thickness of a horizons decreases by 70 cm and the thickness of mollic colors decreases by 93 cm total soc storage decreases from 17 5 to 7 7 kg m2 a portion of the soc in subsurface horizons of modern soils was likely inherited from the brady soil which probably formed in a climate different than the present suggesting that soc storage is probably not in equilibrium with modern climatic conditions dust aggradation on a biologically active surface in a steppe environment has affected horizonation pigmentation and soc storage in central great plains loess derived mollisols

magnetic grain size distribution of the enhanced component in the loess palaeosol sequences in the western loess plateau of china summary rock magnetic measurements of chinese loess palaeosol samples from the beiyuan section in linxia city suggest the presence of two magnetic components a background component and an enhanced component the magnetic properties of the enhanced component suggest strong grain size control which is in contrast with variable grain size distribution in loess palaeosol from the central loess plateau chemically formed magnetic grains do not fulfil the requirements in the case of the western loess plateau because they may show shifts in the grain size distribution the difference in climate between the western and central loess plateau may lead to different origins and different preservation conditions of the pedogenic magnetite

spatial and temporal reconstructions of changes in the asian palaeomonsoon a new mineral magnetic approach abstract a new quantitative approach is proposed for estimating palaeoprecipitation across the chinese loess plateau at present there is a strong rainfall gradient across the plateau from 300 mm yr in the near desert conditions in the northwest to over 750 mm yr in the southeast just 700 km distant we find that the concentration of ferrimagnetic iron oxide minerals in nine modern soil types represented by 37 individual soil profiles is strongly correlated with this contemporary rainfall gradient the ferrimagnetic concentration rises along this gradient from 0 01 in the northwest to over 0 2 in the southeast the nine modern soil types have been used in the construction of a rainfall vs magnetic susceptibility least squares regression climofunction past variations of loess soil iron oxide content are easily established through magnetic susceptibility measurements and so can be used to reconstruct the rainfall of former interglacial and glacial periods the physical and pedological basis of the rainfall vs susceptibility relationship is discussed and potential limitations of our rainfall reconstruction method are explored our palaeoclimate reconstructions indicate dramatic changes in rainfall due to variations in the structure of the asian monsoon the rainfall variations are about four times greater than has been suggested for this region by atmospheric general circulation modelling our data indicate increased rainfall throughout central china both in interglacial periods and in the early holocene the increases in monsoonal rain were particularly pronounced at our westernmost sites adjacent to the northeastern edge of the tibetan plateau in contrast for glacial periods a reduction in rainfall is found across the whole loess area with the greatest decreases in the southeast

theory and application of the day plot mrs ms versus hcr hc 2 application to data for rocks sediments and soils 1 new theoretical curves relating the hysteresis parameters mrs ms and hcr hc for single domain sd superparamagnetic sp pseudo single domain psd and multidomain md grains and their mixtures are applied to published data for natural materials the day plot of mrs ms versus hcr hc has been used to crudely classify samples into box like sd psd and md or sometimes incorrectly md sp regions with arbitrary boundaries new type curves for md psd sd md and sd sp grains and mixtures permit more subtle and precise modeling the predicted md trend and its junction with the psd trend are observed in two data sets for magnetite spherules from carbonate rocks and for temperature varying hysteresis results spanning the verwey transition the latter data are the basis of a suggested new method for pinpointing the psd md threshold size selected data for pottery clays soils and paleosols generally follow sd md type curves and indicate intermediate size psd magnetite with narrow to broad size distributions a lake sediment section with known grain size progression tracks in the predicted sense along the sd md trend selected data for glaciomarine and pelagic sediments are also generally compatible with sd md trends examples of remagnetized carbonate rocks submarine basaltic glasses and glassy rims of pillow basalts all follow predicted sp sd or sp psd mixing curves with a large range in volume fraction of sp grains 0 75 but a narrow range of sp particle sizes 10 2 nm larger sp grains spanning the range to sd size 25 30 nm are absent for unknown reasons oceanic dolerites gabbros and serpentinized peridotites in some cases fall in a novel region of the day plot parallel to but below magnetite sd md mixing curves

observations of the northern seasonal polar cap on mars ii hirise photometric analysis of evolution of northern polar dunes in spring we present an overview of our analyses of hirise observations of spring evolution of selected dune areas of the north polar erg the north polar erg is covered annually by seasonal volatile ice layer a mixture of co2 and h2o with mineral dust contamination in spring this layer sublimes creating visually enigmatic phenomena e g dark and bright fan shaped deposits dark bright dark bandings dark down slope streaks and seasonal polygonal cracks similar phenomena in southern polar areas are believed to be related to the specific process of solid state greenhouse effect in the north it is currently unclear if the solid state greenhouse effect is able to explain all the observed phenomena especially because the increased influence of h2o on the time scales of this process has not yet been quantified hirise observations of our selected locations show that the ground exhibits a temporal behaviour similar to the one observed in the southern polar areas a brightening phase starting close to the spring equinox with a subsequent darkening towards summer solstice the resolution of hirise enabled us to study dunes and substrate individually and even distinguish between different developments on windward and slip face sides of single dunes differences in the seasonal evolution between steep slip faces and flatter substrate and windward sides of dunes have been identified and compared to crism data of co2 and h2o distributions on dunes we also observe small scale dark blotches that appear in early observations and tend to sustain a low reflectivity throughout the spring these blotches can be regarded as the analogue of dark fan deposits in southern polar areas leading us to the conclusion that both martian polar areas follow similar spring evolutions

mechanisms of intense alpine rainfall abstract numerical studies by the authors and others of the 1994 piedmont flood show that the orographically modified flow was a critical element for the production of extraordinary rainfall to uncover the precise mechanism of orographic rainfall occurring in full physics mm5 simulations of the 1994 piedmont flood the authors carried out simulations with the same real data initial and boundary conditions but with the real orography replaced by an idealized one with excellent agreement between real and idealized orography on the rainfall rate versus time in the piedmont area analysis of the idealized orography simulation provides a clear picture of the model s mechanism of orographically induced rainfall as noted in previous studies of the 1994 piedmont case a moist saturated airflow has a reduced effective static stability and tends to flow over the mountains while an unsaturated airstream is stable and tries to flow around toward the left in the northern hemisphere in the 1994 piedmont case t

effects of the alps and apennines on forecasts for po valley convection in two hymex cases two intensive observation periods iops of the hydrological cycle in the mediterranean experiment hymex are examined in this study iop6 and iop13 were characterized by troughs with associated cold fronts entering the western mediterranean and in both cases organized frontal convection in the po valley was observed these similarities notwithstanding predictability of the po valley convection was limited for iop6 for most of the forecast models available during hymex but not for iop13 using the weather research and forecast wrf model in research mode the present study confirms the relatively good forecast for frontal convection in iop13 is not very sensitive to modeling assumptions in contrast it is found that only a two way nested simulation initialized close to the event was able to produce a realistic representation of the squall line in the po valley for iop6 a comparison between a successful and an unsuccessful simulation of the po valley convection in iop6 suggests the sensitivity lies with the orographic flow modification which was at the threshold between flow over and flow around responses to the maritime alps in particular in the flow over regime downslope winds from the maritime alps and apennines suppress the convergence uplift where the front encounters the barrier wind in the po valley while in the flow around regime it is unimpeded a delicate balance between the competing mechanisms of orographically induced subsidence on the lee side of the apennines and frontal uplift in the po valley is found to be crucial for squall line survival

evolution of mars northern polar seasonal co2 deposits variations in surface brightness and bulk density small scale variations of seasonal ice are explored at different geomorphic units on the northern polar seasonal cap npsc we use seasonal rock shadow measurements combined with visible and thermal observations to calculate density over time the coupling of volume density and albedo allows us to determine the microphysical state of the seasonal co2 ice we find two distinct end members across the npsc 1 snow deposits may anneal to form an overlying slab layer that fractures these low density deposits maintain relatively constant densities over springtime 2 porous slab deposits likely anneal rapidly in early spring and fracture in late spring these high density deposits dramatically increase in density over time the end members appear to be correlated with latitude

hirise observations of gas sublimation driven activity in mars southern polar regions ii surficial deposits and their origins abstract the high resolution imaging science experiment hirise onboard mars reconnaissance orbiter mro has been used to monitor the seasonal evolution of several regions at high southern latitudes and in particular the jet like activity which may result from the process described by kieffer jgr 112 e08005 doi 10 1029 2006je002816 2007 involving translucent co 2 ice in this work we mostly concentrate on observations of the inca city 81 s 296 e and manhattan 86 s 99 e regions in the southern spring of 2007 two companion papers hansen et al this issue and portyankina et al this issue discuss the surface features in these regions and specific models of the behaviour of co 2 slab ice respectively the observations indicate rapid on set of activity in late winter initiating before hirise can obtain adequately illuminated images ls 2 titus et al 2007 agu abstract p41a 0188 these deposits originate from araneiform structures spiders boulders on ridges cracks on slopes and along linear cracks in the slab ice on flatter surfaces the type of activity observed can often be explained qualitatively by considering the local topography some dark fans are observed to shorten enormously in length on a timescale of 18 days we consider this to be strong evidence that outgassing was in progress at the time of hirise image acquisition and estimate a total particulate emission rate of 30 g s 1 from a single typical jet feature brighter deposits at inca city become increasingly hard to detect after ls 210 in the inca city region the orientations of surficial deposits are topographically controlled the deposition of dark material also appears to be influenced by local topography suggesting that the ejection from the vents is at low velocity 1 and that a ground hugging flow process a sort of cryo fumarole may be occurring the failure up to this point to obtain a clear detection of outgassing though stereo imaging is consistent with low level transport the downslope orientation of the deposits may result from the geometry of the vent or from catabatic winds at many sites more than one ejection event appears to have occurred suggesting re charging of the sources around ls 230 the brightness of the surface begins to drop rapidly on north facing slopes and the contrast between the dark deposits and the surrounding surface reduces this indicates that the co 2 ice slab is being lost completely in some areas at around this time by ls 280 at inca city the ice slab has effectively gone crism band ratios and themis brightness temperature measurements are consistent with this interpretation

observations of the northern seasonal polar cap on mars i spring sublimation activity and processes abstract spring sublimation of the seasonal co2 northern polar cap is a dynamic process in the current mars climate phenomena include dark fans of dune material propelled out onto the seasonal ice layer polygonal cracks in the seasonal ice sand flow down slipfaces and outbreaks of gas and sand around the dune margins these phenomena are concentrated on the north polar erg that encircles the northern residual polar cap the mars reconnaissance orbiter has been in orbit for three mars years allowing us to observe three northern spring seasons activity is consistent with and well described by the kieffer model of basal sublimation of the seasonal layer of ice applied originally in the southern hemisphere three typical weak spots have been identified on the dunes for escape of gas sublimed from the bottom of the seasonal ice layer the crest of the dune the interface of the dune with the interdune substrate and through polygonal cracks in the ice pressurized gas flows through these vents and carries out material entrained from the dune furrows in the dunes channel gas to outbreak points and may be the northern equivalent of southern radially organized channels araneiform terrain albeit not permanent properties of the seasonal co2 ice layer are derived from timing of seasonal events such as when final sublimation occurs modification of dune morphology shows that landscape evolution is occurring on mars today driven by seasonal activity associated with sublimation of the seasonal co2 polar cap

observations of the northern seasonal polar cap on mars iii crism hirise observations of spring sublimation we analyze a series of targeted crism and hirise observations of seven regions of interest at high latitudes in the northern polar regions of mars these data allow us to investigate the temporal evolution of the composition of the seasonal ice cap during spring with a special emphasis on peculiar phenomena occurring in the dune fields and in the vicinity of the scarps of the north polar layered deposits nplds the strength of the spectral signature of co2 ice continuously decreases during spring whereas the one of h2o ice first shows a strong increase until ls 50 this evolution is consistent with a scenario previously established from analysis of omega data in which a thin layer of pure h2o ice progressively develops at the surface of the volatile layer during early spring ls 10 widespread jet activity is observed by hirise while strong spectral signatures of co2 ice are detected by crism later around ls 20 40 activity concentrates at the dune fields where crism also detects a spectral enrichment in co2 ice consistent with kieffer s model kieffer h h 2007 j geophys res 112 e08005 doi 10 1029 2006je002816 for jet activity effects of wind are prominent across the dune fields and seem to strongly influence the sublimation of the volatile layer strong winds blowing down the scarps could also be responsible for the significant spatial and temporal variability of the surface ice composition observed close to the npld

heavy precipitation on the alpine southside an upper level precursor analyses of four separate autumnal events of very heavy precipitation on the southern slopes of the european alps indicate that each was accompanied by a strikingly similar anomaly at upper tropospheric levels it took the form of a narrow 500km deep 4km and elongated 2000 km streamer of intruded stratospheric air sic high potential vorticity air extending north south from the british isles to the western mediterranean in each case the streamer translated comparatively slowly eastward and the storm event ensued as its forward flank approached the alpine ridge empirical indicators and theoretical considerations support the thesis that the streamer is an ubiquitous dynamically significant and distinctive precursor of storms on the alpine southside

evolution of south seasonal cap during martian spring insights from high resolution observations by hirise and crism on mars reconnaissance orbiter 1 we use data from the high resolution imaging science experiment hirise camera and the compact reconnaissance imaging spectrometer for mars crism imaging spectrometer onboard the mars reconnaissance orbiter to follow the evolution of the appearance and composition of 12 regions of the south polar layered deposits from spring to summer time we distinguish three steps in the evolution of the volatile layer a decrease of both co2 band strength and albedo until ls 190 210 a significant increase in both until ls 240 260 and finally a rapid decrease until the complete defrosting of the ground in contrast the water ice band displays a more monotonic decrease analysis of hirise color images acquired simultaneously with crism data allows a plausible interpretation of this evolution in early springtime ls 200 intense jet activity results in deposition of fans of large mineral grains and a wide spatial distribution of fine grains the small scale topography controls the presence and location of the jets by allowing more solar energy to be collected on slopes grains from the dust fans warm and sink through the co2 layer resulting in a bluish color at the locations of the fans around ls 190 210 as the atmosphere warms up the surface of the ice layer sublimes and releases dust and water resulting in its brightening the last phase of the process consists in a progressive defrosting resulting in a patchwork of frozen and unfrozen areas

agents of change on mars northern dunes co2 ice and wind abstract both wind and seasonal co 2 ice sculpt the dunes of mars in today s climate the high resolution imaging science experiment hirise on the mars reconnaissance orbiter has returned extensive temporal coverage of changes on the north polar dunes for nearly four mars years the processes driving dune morphology changes such as the formation of new alcoves have been investigated considerable interannual variability has been observed most changes occur in the period of time when hirise cannot image late summer and fall when light levels are too low to see subtle changes on the dunes and the polar hood obscures the surface and winter when the cap is in polar night this is consistent with seasonal control but does not allow us to directly differentiate between eolian processes vs co 2 ice as the driving agent for alcove formation circumstantial evidence and observations of analog processes in the southern mid latitudes however implicates processes associated with frost emplacement and removal

palaeoclimatic and sedimentary history from magnetic susceptibility of loess in china the magnetostratigraphic age of the oldest loess sediments in the central chinese loess plateau investigated so far has recently been placed at ca 2 4 million years b p thus glaciations in central asia which are believed to provide the detritus for the formation of chinese loess commenced at the same time as the first ice rafted debris sank into the ocean basins of the northern hemisphere shackleton et al 1984 lithologic palaeontologic geochemical and especially rock magnetic variations throughout the loess column are indicative of palaeoclimatic fluctuations during loess deposition the variations of magnetic low field susceptibility in loess closely resemble those of the marine oxygen isotope record shackleton and opdyke 1976 and establish for the first time a continuous record of the pleistocene glacial and interglacial stages in a continental section spectral analysis of the rock magnetic time series indicates slow apparent sedimentation during interglacial periods which are characterized mainly by calcium dissolution and related compaction of the soils variable aeolic sediment influx as well as erosion and or polygenetic soil formation may also strongly influence the sedimentary history

episodic holocene loess deposition in central nebraska abstract the mirdan canal section in central nebraska usa provides evidence for multiple episodes of holocene loess deposition in the central great plains this irrigation canal cut exposes more than 4 m of holocene sediment that overlies the late wisconsinan peoria loess the oldest holocene sediment is local slopewash that fills gullies but overlying beds are interpreted as holocene loess bignell loess three buried soil profiles occur within the holocene sediment and have yielded uncalibrated 14 c ages of 3010 yr bp uppermost buried soil and 8790 yr bp third buried soil from top a fourth buried soil yielded an age of 9330 yr bp and is correlated with the brady soil the bignell loess has a darker color slightly more organic matter more clay more coarse silt and sand less smectite and less volcanic glass than the underlying peoria loess the bignell loess is most plausibly interpreted as dust from local flood plains containing a mixture of reworked peoria loess and older silts with contrasting mineralogy episodes of loess deposition occurred in the early middle and late holocene probably during periods of dry climate but possibly also as a consequence of large erosive floods that made wind erodible sediment available on nearby flood plains

multiscale and unsteady aspects of a deep fohn event during map a strong fohn event occurring during the mesoscale alpine programme intensive observing period 2b 19 20 september is simulated with the non hydrostatic model meso nh the grid nesting techniques and a suitable turbulence scheme allow a coherent downscaling from the analysed scales to the movements inside the rhine valley the flow regime around the alps changes from a flow around regime to a flow partly over regime when the wind increases ahead of the cold front simplified simulations allow us to estimate a non dimensional height for the alps which controls the flow regime the fohn characteristics and its temporal evolution are discussed using both measurements and simulation backward trajectories show that the fohn air comes from an altitude around 2 km above the po valley nonlinear phenomena such as wave breaking near 5 km above sea level just behind some secondary crests and hydraulic jumps in the foothills are found in the highest resolution simulation using a mesh of 625 m this mesh clearly improves the comparison of the numerical simulation with the observations collected in the rhine valley mass budgets detail the progressive building of the fohn jet in the rhine valley copyright 2003 royal meteorological society

dark spots and cold jets in the polar regions of mars new clues from a thermal model of surface co2 ice observations of the martian co2 ice cap in late winter and spring have revealed exotic phenomena unusual dark spots fans and blotches form as the south polar seasonal co2 ice cap retreats the formation mechanisms of these features are not clearly understood theoretical models suggest that photons could penetrate deep into the co2 ice down to the regolith leading to basal sublimation and gas and dust ejection we have developed a detailed thermal model able to simulate the temporal evolution of the regolith co2 ice layer atmosphere column it takes into account heat conduction radiative transfer within the ice and the atmosphere and latent heat exchange when there is a phase transition we found that a specific algorithm fully coupling these three components was needed to properly predict ice sublimation below the surface our model allows us to determine under what conditions basal sublimation is possible and thus when and where it can occur on mars our results show that basal sublimation is possible if we consider large pathlengths and very little dust content within the ice moreover the model can explain how dark spots can appear very early after the end of the polar night at high latitudes we also evaluate the importance of the different parameters in our simulations contrary to what was suggested by theoretical models the role of seasonal thermal waves is found to be limited solar radiation alone can initiate basal sublimation which therefore only depends on the co2 ice properties three main modes were identified one where condensation sublimation only occurs at the surface in the case of small grains and or high dust content one where basal sublimation is possible large pathlengths and very little dust content and an intermediate mode where sublimation within the ice may occur we suggest that these different modes could be keys to understanding many processes that occur at the surface of mars like the anticryptic area behavior or the recent reported activity in gullies