the landing s of philae and inferences about comet surface mechanical properties the philae lander part of the rosetta mission to investigate comet 67p churyumov gerasimenko was delivered to the cometary surface in november 2014 here we report the precise circumstances of the multiple landings of philae including the bouncing trajectory and rebound parameters based on engineering data in conjunction with operational instrument data these data also provide information on the mechanical properties strength and layering of the comet surface the first touchdown site agilkia appears to have a granular soft surface with a compressive strength of 1 kilopascal at least 20 cm thick possibly on top of a more rigid layer the final landing site abydos has a hard surface

a mechanism for the low frequency variability of the mid latitude troposphere low frequency variability of the zonal mean zonal wind in long runs of a simplified global circulation model is dominated by bands of wind anomaly which originate in the tropics and propagate slowly poleward with speeds of 0 2 m s 1 such propagation could be the result of the interaction between the zonal wind anomaly and an equatorward flux of rossby wave activity originating in middle or high latitude a barotropic weakly nonlinear model of this process has been derived it suggests propagation of zonal wind anomalies similar to those produced in the global circulation model and leads to comparable propagation speeds

dart mission determination of momentum transfer model of ejecta plume observations abstract the nasa double asteroid redirection test dart spacecraft will impact the secondary member of the 65803 didymos binary in order to perform the first demonstration of asteroid deflection by kinetic impact determination of the momentum transfer to the target body from the kinetic impact is a primary planetary defense objective using ground based telescopic observations of the orbital period change of didymos and imaging of the dart impact ejecta plume by the liciacube cubesat along with modeling and simulation of the dart impact liciacube contributed by the italian space agency will perform a flyby of didymos a few minutes after the dart impact to resolve the ejecta plume spatial structure and to study the temporal evolution liciacube ejecta plume images will help determine the vector momentum transfer from the dart impact by determining or constraining the direction and the magnitude of the momentum carried by ejecta a model is developed for the impact ejecta plume optical depth using a point source scaling model of the dart impact the model is applied to expected liciacube plume images and shows how plume images enable characterization of the ejecta mass versus velocity distribution the ejecta plume structure as it evolves over time is determined by the amount of ejecta that has reached a given altitude at a given time the evolution of the plume optical depth profiles determined from liciacube images can distinguish between strength controlled and gravity controlled impacts by distinguishing the respective mass versus velocity distributions liciacube plume images discriminate the differences in plume structure and evolution that result from different target physical properties mainly strength and porosity thereby allowing inference of these properties to improve the determination of momentum transfer

zonal flow vacillation and bimodality of baroclinic eddy life cycles in a simple global circulation model abstract a global primitive equation model of the atmosphere is used to study the relationship between the temporal variations of the zonal mean zonal flow and baroclinic eddies nonperiodic low frequency vacillation of the mean zonal flow is found in longtime integrations of the model under a perpetual condition the zonal mean jet in the extratropics changes its position nearly barotropically a potential vorticity potential temperature pv analysis is performed for two extreme periods of the zonal flow vacillation anticyclonic breakings of upper troughs are dominant in the period of a high latitude jet while cyclonic breakings are dominant in the period of a low latitude jet a statistically significant relationship between the zonal flow vacillation and the morphology of life cycles of baroclinic eddies is obtained for the entire period analyzed an index of the life cycles which is introduced in this study shows clear bimodality in its frequency distribution function the relationship is also

cross seasonal influence of the december february southern hemisphere annular mode on march may meridional circulation and precipitation abstractnew evidence suggests that interannual variability in zonal mean meridional circulation and precipitation can be partially attributed to the southern hemisphere annular mode sam the dominant mode of climate variability in the southern hemisphere sh extratropics a cross seasonal correlation exists between the december february djf sam and march may mam zonal mean meridional circulation and precipitation this correlation is not confined to the sh it also extends to the northern hemisphere nh subtropics when the preceding djf sam is positive counterclockwise and clockwise meridional cells accompanied by less and more precipitation occur alternately between the sh middle latitudes and nh subtropics in mam in particular less precipitation occurs in the sh middle latitudes the sh tropics and the nh subtropics but more precipitation occurs in the sh subtropics and the nh tropics a framework is built to explain the cross seasonal impact of sam related sst anomalies evidence indic

an objective cyclone climatology for the southern hemisphere abstract an objective method is developed and used to derive a climatology of centers of cyclonic vorticity for the southern hemisphere based on twice daily european centre for medium range weather forecasts ecmwf 1000 hpa analyses during 1980 86 these centers were computed as local minima of geostrophic relative vorticity g extending previous studies based on pressure minima this use of g avoids a bias favoring slower and or deeper cyclones that occurs when pressure is used and includes a large number of additional mobile vorticity centers in the 45 55 s band that are missed where a local pressure minimum cannot be found an automated tracking algorithm similar to that of murray and simmonds is used to match predicted location pressure and g from previous track history with available centers large numbers of g centers were found south of 60 s and near the midlatitude continents as in previous studies these were a mixture of migratory centers and other fixed topographic features the maxi

mechanisms of zonal index variability in an aquaplanet gcm abstract data from a 2025 day geophysical fluid dynamics laboratory aquaplanet gcm integration are used to examine the temporal evolution of the zonal index defined as the principal component of the first eof of the zonally and vertically integrated absolute angular momentum this eof represents meridional displacements of the subtropical jet positive negative values of the zonal index correspond to poleward equatorward displacements of the subtropical jet and are referred to as the high low zonal index composites of various quantities are used to examine the temporal evolution of both the zonal mean zonal winds and the eddy fields associated with either index the high index is initiated by an enhancement in the equatorward wave activity propagation which causes the subtropical jet to move in a poleward direction the low index is led by a weakening in the equatorward propagation which results in an equatorward displacement of the subtropical jet more importantly for the high index the corr

the structure and predictability of the high latitude mode in the csiro9 general circulation model abstract the csiro9 general circulation model shows a zonally symmetric mode of variability which closely resembles the high latitude mode hlm in middle and high latitudes of the southern hemisphere the leading eof of the zonal mean zonal wind between 30 and 68 s whose amplitude has been taken as an index of the hlm shows opposing variations centered near 40 and 60 s accounting for 43 of the daily variance analysis has concentrated on composites for periods when the index changed quickly between significant peaks of the opposite sign or persisted with a large amplitude for an extended period the momentum flux variations are small at the northern and southern boundaries and the principal variations are centered near 49 s between the maxima in the zonal wind the changes in angular momentum content are around 30 smaller in the southern band eddy heat fluxes are less coherent but help in maintaining the zonal wind anomalies against friction a simple model of the zonal wind index with stochastic

wave driven zonal flow vacillation in the southern hemisphere the variability of the zonal mean flow in the southern hemisphere during the period 1985 94 is studied using european centre for medium range forecasts analyses the dominant mode of variability has approximately equivalent barotropic variations of opposite signs centered at 40 8 and 608s this structure is dominant in all seasons and has similar variance in all seasons the temporal variance of the amplitude of this mode is well modeled as gaussian red noise with a correlation e folding time of about 10 days zonal wind anomalies are maintained against frictional drag by variations in the zonal flow accelerations driven by transient eddies and associated mean meridional circulations the eddy structures suggest that equatorward propagation is favored when the jet is displaced poleward and zonal propagation is favored when the jet is displaced equatorward

indices of the southern hemisphere zonal wind abstract the time and spatial variation of the southern hemisphere 500 hpa zonal wind has been examined using spectral analysis bandpass filtering and empirical orthogonal function eof analysis applied to a 15 year sample of australian hemispheric analyses spectral analysis of the entire 15 year record of the 500 hpa zonal mean westerly wind shows significant peaks only on the seasonal and interannual time scales the mean segmented spectra for each season failed to show any additional significant peaks at higher frequencies or any significant differences between seasons the primary pattern of variation revealed by eof analysis shows similar behavior on synoptic to seasonal time scales with compensating departures occurring at intervals of 20 latitude the first eof has opposing peaks near 40 and 60 s and shows an equivalent barotropic pattern when correlated with individual grid point values at 500 hpa and mean sea level pressure correlations of the zonal pattern with regional anomalies reveal

multiple regimes and low frequency oscillations in the southern hemisphere s zonal mean flow abstract this paper studies multiple regimes and low frequency oscillations in the northern hemisphere zonal mean zonal flow in winter using 55 yr of daily observational data the probability density function estimated in the phase space spanned by the two leading empirical orthogonal functions exhibits two distinct statistically significant maxima the two regimes associated with these maxima describe persistent zonal flow states that are characterized by meridional displacements of the midlatitude jet poleward and equatorward of its time mean position the geopotential height anomalies of either regime have a pronounced zonally symmetric component but largest amplitude anomalies are located over the atlantic and pacific oceans high frequency synoptic transients participate in the maintenance of and transitions between these regimes significant oscillatory components with periods of 147 and 72 days are identified by spectral analysis of the zonal flow time series these oscillations are described b

eddy zonal flow interactions and the persistence of the zonal index abstract an idealized atmospheric general circulation model is used to investigate the factors controlling the time scale of intraseasonal 10 100 day variability of the extratropical atmosphere persistence on these time scales is found in patterns of variability that characterize meridional vacillations of the extratropical jet depending on the degree of asymmetry in the model forcing patterns take on similar properties to the zonal index annular modes and north atlantic oscillation it is found that the time scale of jet meandering is distinct from the obvious internal model time scales suggesting that interaction between synoptic eddies and the large scale flow establish a separate intraseasonal time scale a mechanism is presented by which eddy heat and momentum transport couple to retard motion of the jet slowing its meridional variation and thereby extending the persistence of zonal index and annular mode anomalies the feedback is strong and quite sensitive to model parameters when the mod

source conveyance and fate of suspended sediments following hurricane irene new england usa hurricane irene passed directly over the connecticut river valley in late august 2011 intense precipitation and high antecedent soil moisture resulted in record flooding mass wasting and fluvial erosion allowing for observations of how these rare but significant extreme events affect a landscape still responding to pleistocene glaciation and associated sediment emplacement clays and silts from upland glacial deposits once suspended in the stream network were routed directly to the mouth of the connecticut river resulting in record breaking sediment loads fifteen times greater than predicted from the pre existing rating curve denudation was particularly extensive in mountainous areas we calculate that sediment yield during the event from the deerfield river a steep tributary comprising 5 of the entire connecticut river watershed exceeded at minimum 10 40 years of routine sediment discharge and accounted for approximately 40 of the total event sediment discharge from the connecticut river a seriesof surface sediment corestaken in floodplainponds adjacent to the tidalsec

deep impact excavating comet tempel 1 deep impact collided with comet tempel 1 excavating a crater controlled by gravity the comet s outer layer is composed of 1 to 100 micrometer fine particles with negligible strength 1000 kelvins a large increase in organic material occurred during and after the event with smaller changes in carbon dioxide relative to water on approach the spacecraft observed frequent natural outbursts a mean radius of 3 0 0 1 kilometers smooth and rough terrain scarps and impact craters a thermal map indicates a surface in equilibrium with sunlight

meter scale thermal contraction crack polygons on the nucleus of comet 67p churyumov gerasimenko we report on the detection and characterization of more than 6300 polygons on the surface of the nucleus of comet 67p churyumov gerasimenko using images acquired by the osiris camera onboard rosetta between august 2014 and march 2015 they are found in consolidated terrains and grouped in localized networks they are present at all latitudes from north to south and longitudes head neck and body sometimes on pit walls or following lineaments about 1 5 of the observed surface is covered by polygons polygons have an homogeneous size across the nucleus with 90 of them in the size range 1 5 m and a mean size of 3 0 1 4 m they show different morphologies depending on the width and depth of their trough they are found in networks with 3 or 4 crack intersection nodes the polygons observed on 67p are consistent with thermal contraction crack polygons formed by the diurnal or seasonal temperature variations in a hard mpa and consolidated sintered layer of water ice located a few centimeters below the surface our thermal analysis shows an evolution of thermal contraction crack polygons according to the local thermal environment with more evolved polygons i e deeper and larger troughs where the temperature and the diurnal and seasonal temperature range are the highest thermal contraction crack polygons are young surface morphologies that probably formed after the injection of 67p in the inner solar system typically 100 000 years ago and could be as young as a few orbital periods following the decreasing of its perihelion distance in 1959 from 2 7 to 1 3 a u meter scale thermal contraction crack polygons should be common features on the nucleus of jupiter family comets

spatial variability of sea level pressure and 500 mb height anomalies over the southern hemisphere abstract the spatial variability of mean sea level pressure slp and 500 mb height anomalies over the southern hemisphere during summer djf and winter jja is determined using eigenvector analysis based on daily synoptic maps from 1972 to 1979 the patterns of spatial distribution of pressure and height anomalies are further verified and examined by means of station data and the eigenvectors are compared between the seasons and to those found for the northern hemisphere the first eigenvector shows that midlatitude anomalies of slp and 500 mb height are of an opposite sign to those found over and around antarctica the pattern is highly barotropic and suggests strengthening and weakening of the zonal wind in alternating latitude belts the 500 mb height differences are calculated for five midlatitude to antarctic station pairs using data from the late 1950 s onward these latitudinal height differences are also used to describe the association between the hemispheric westerlies and the southern oscil

the strength of ice saturated extraterrestrial rock analogs abstract in situ resource utilization isru activities have been identified by the national research council as one of the most important scientific endeavors of the coming decade the failure of the mupus pen experiment on rosetta s philae lander to penetrate the surface of comet 67p demands knowledge of the mechanical properties of extraterrestrial materials in such environments to such an end we conducted laboratory strength measurements at cryogenic conditions of two terrestrial rocks bishop tuff and indiana limestone as potential cometary and asteroid analogs respectively we measured failure strength of dried and fully saturated samples under constant displacement rate compressional loading at temperatures of 77 k 295 k and for most confining pressure of 5 mpa the strength of saturated samples increased dramatically with decreasing temperature below the ice point saturated limestone from 30 mpa at 295 k to 200 mpa at 150 k and below and saturated tuff from 26 mpa at 240 k to 160 mpa at 150 k some ductility or distributed fracturing was evident in both saturated rock types above 150 k the saturated tuff was stronger than pure ice at all conditions but its transition from brittle to ductile deformation with temperature closely paralleled that of ice the results of this study will be useful to future sample retrieval missions or isru maneuvers the fully saturated state of our samples and use of bishop tuff as an unconsolidated cometary analog likely means our results are upper estimates for substrates we may encounter in our solar system pending corroboration and refinement of these preliminary measurements the large increase in compressive strength we observed in the saturated materials at cryogenic temperatures suggests that future missions must prepare technology with the energetic and mechanical capability to penetrate very hard substrates

the structure of the regolith on 67p churyumov gerasimenko from rolis descent imaging the structure of the upper layer of a comet is a product of its surface activity the rosetta lander imaging system rolis on board philae acquired close range images of the agilkia site during its descent onto comet 67p churyumov gerasimenko these images reveal a photometrically uniform surface covered by regolith composed of debris and blocks ranging in size from centimeters to 5 meters at the highest resolution of 1 centimeter per pixel the surface appears granular with no apparent deposits of unresolved sand sized particles the thickness of the regolith varies across the imaged field from 0 to 1 to 2 meters the presence of aeolian like features resembling wind tails hints at regolith mobilization and erosion processes modeling suggests that abrasion driven by airfall induced particle splashing is responsible for the observed formations

the philae lander reveals low strength primitive ice inside cometary boulders on 12 november 2014 the philae lander descended towards comet 67p churyumov gerasimenko bounced twice off the surface then arrived under an overhanging cliff in the abydos region the landing process provided insights into the properties of a cometary nucleus1 3 here we report an investigation of the previously undiscovered site of the second touchdown where philae spent almost two minutes of its cross comet journey producing four distinct surface contacts on two adjoining cometary boulders it exposed primitive water ice that is water ice from the time of the comet s formation 4 5 billion years ago in their interiors while travelling through a crevice between the boulders our multi instrument observations made 19 months later found that this water ice mixed with ubiquitous dark organic rich material has a local dust ice mass ratio of formula see text matching values previously observed in freshly exposed water ice from outbursts4 and water ice in shadow5 6 at the end of the crevice philae made a 0 25 metre deep impression in the boulder ice providing in situ measurements confirming that primitive ice has a very low compressive strength less than 12 pascals softer than freshly fallen light snow and allowing a key estimation to be made of the porosity 75 7 per cent of the boulders icy interiors our results provide constraints for cometary landers seeking access to a volatile rich ice sample

the southern hemisphere westerlies in the australasian sector over the last glacial cycle a synthesis abstract the southern hemisphere westerlies in the southwest pacific are known to have waxed and waned numerous times during the last two glacial cycles though even semi continuous histories of the westerlies extend back no more than about 20 000 years we have good evidence for at least three scales of events a westerly maximum occurs at the last glacial maximum there is less conclusive evidence for another westerly maximum in the late holocene and for a minimum at ca 11 ka it is too early to ascribe even a cycle to these data but there are grounds to suggest that milankovitch precessional forcing may underlie the observed pattern there is also a quasi 2600 year cycle present in antarctic ice cores that appears to correlate to variation in westerly flow there is strong centennial scale variability in historical times the little ice age lia ca 1400 1850 was associated with a poleward shift in the circumpolar trough in the southern ocean strengthened westerly circulation over tasmania and a strengthening of southwesterly circulation and neoglaciation in southern new zealand while the preceding period 800 1400 ad was less certainly marked by reduced westerly flow from modern records we know that decadal and inter annual variability is important e g pacific decadal oscillation high latitude mode also known as the antarctic oscillation el nino southern oscillation only a minority of the proxies examined can identify changes on these temporal scales but data from tree rings ice cores and laminated lake sediments do indicate systematic changes in these phenomena through time rossby wave patterns are shown to play a critical role in long duration events as well as at the synoptic scale we conclude that westerly circulation is as strong now as at any time in the last glacial cycle in addition changes in latitudinal boundaries in the westerlies may be nearly as large in inter annual zonal shifts ca 2 maximum as in glaciation interglaciation movements ca 3 4 there is however reasonable evidence of strengthening weakening across much of the westerly belt at westerly maxima minima such as the lia early holocene

the morphological diversity of comet 67p churyumov gerasimenko images of comet 67p churyumov gerasimenko acquired by the osiris optical spectroscopic and infrared remote imaging system imaging system onboard the european space agency s rosetta spacecraft at scales of better than 0 8 meter per pixel show a wide variety of different structures and textures the data show the importance of airfall surface dust transport mass wasting and insolation weathering for cometary surface evolution and they offer some support for subsurface fluidization models and mass loss through the ejection of large chunks of material

response of baroclinic life cycles to barotropic shear abstract cyclonic barotropic shear of incrementally increasing magnitude is imposed on an idealized midlatitude jet and the life cycles of baroclinically unstable wavenumber 6 perturbations growing on these jets are studied when the barotropic shear parameter passes a critical value the life cycle makes an abrupt transition from anticyclonic to cyclonic behavior the abrupt transition in behavior is most evident in the barotropic decay of eddy kinetic energy in the structure of the eddies as seen in potential vorticity maps and in the nature of the zonal flow accelerations produced during the life cycle it is suggested that the abrupt transition can be interpreted as arising from a positive feedback between eddy propagation and eddy induced zonal flow accelerations dependences on the zonal scale of the eddy are also investigated wavenumber 8 exhibits cyclonic behavior while wavenumber 4 exhibits anticyclonic behavior for all values of cyclonic shear considered this dependence on zonal scale is c

tropospheric rossby wave breaking and the sam an objective analysis of tropospheric anticyclonic and cyclonic breaking rossby waves is performed for the southern hemisphere in austral summer december february of 1979 2009 the climatology of both anticyclonicandcyclonic rossbywavebreaking rwb frequencyispresented thefrequencyofanticyclonic rwb is highest in an extended region of theeastern hemisphere on the anticyclonic side of the jet whilethat of cyclonic rwb is highest on the cyclonic side of the jet a composite analysis of anticyclonic and cyclonic rwb shows howtheycontributetoapositiveandnegativesouthernannualmode sam index respectively thetimeseries of austral summer anticyclonic rwb occurrence has a trend that closely matches the trend in the sam index regions of rwb that are significantly correlated with the sam index are objectively determined even thoughseveralsuchregionsareidentified onlytworegions anticyclonicandcyclonic covering17 ofthearea of the hemisphere are required in a linear regression model of the sam index the anticyclonic rwb region is zonally extended at 458s and explains 78 of the variability of the summer mean sam index the cyclonic region is located at high latitudes somewhat decoupled from the jet in the longitudinal sector of the indian ocean on synoptic time scales transitions of the sam index respond to rwb without time lag ensocyclespresentaninterestingzonalasymmetrytothedistributionofsouthernhemisphericrwbinthe

properties of the 67p churyumov gerasimenko interior revealed by consert radar the philae lander provides a unique opportunity to investigate the internal structure of a comet nucleus providing information about its formation and evolution in the early solar system we present comet nucleus sounding experiment by radiowave transmission consert measurements of the interior of comet 67p churyumov gerasimenko from the propagation time and form of the signals the upper part of the head of 67p is fairly homogeneous on a spatial scale of tens of meters consert also reduced the size of the uncertainty of philae s final landing site down to approximately 21 by 34 square meters the average permittivity is about 1 27 suggesting that this region has a volumetric dust ice ratio of 0 4 to 2 6 and a porosity of 75 to 85 the dust component may be comparable to that of carbonaceous chondrites

zonal flow vacillation and eddy forcing in a simple gcm of the atmosphere abstract zonal flow vacillation with very long time scales is observed in a 3070 day simple gcm simulation with zonally symmetric forcing the long lasting zonal wind anomalies suggest that zonal flow vacillation is self maintained wave mean flow interactions are investigated by composite analysis and transform eulerian momentum budget analysis nonlinear life cycle simulations are conducted to demonstrate that each extreme phase of the zonal flow vacillation is a quasi stable state and is self maintained by the embedded synoptic eddies the firm eof mode of zonal mean wind shows an out of phase relation between anomalies at 60 s and at 40 s with a barotropic structure this structure is similar to the dominant vacillation pattern observed in the southern hemisphere the composite jet stream in the high low index phase of zonal flow vacillation shifts poleward equatorward from the time mean location and becomes broader narrower and weaker stronger composite eddies in the high index phase tilt nw

the influence of persistent anomalies on southern hemisphere storm tracks abstract empirical orthogonal function eof analysis has been applied to nine years of daily 500 hpa data for the southern hemisphere from which synoptic scale variations had been removed by application of a 10 day low pass fitter this resulted in 11 principal modes accounting for 66 of the variance which were then regionalized through application of a varimax rotation these rotated patterns included a high latitude mode covering the antarctic eight others defining regional perturbation in the principal storm tracks at high latitudes and two residual patterns not used for this investigation persistent anomalies were defined as spells where the time coefficient of the rotated eof was greater than 1 standard deviation or less than 1 standard deviation for a period of 10 days or more and 220 of these spells were obtained for the nine eofs used in the analysis storm tracks were identified in two ways 1 from high pass filtering of the daily 5oo hpa geopotential height anomalies to include periods

a pv view of zonal flow vacillation abstract it is suggested here that the zonal flow vacillation of the southern hemisphere is caused by a mutual interaction between the barotropic shear of the zonal flow and the evolution of baroclinic eddies during the later stages of their lifecycle an index of the zonal wind anomaly difference between 40 and 60 s is defined for a 13 yr record of european centre for medium range weather forecasts ecmwf analyses periods are selected during which the zonal flow is at the extremes of its characteristic vacillation which are distinguished by a broad westerly jet with minor maxima near 30 and 60 s and a narrower jet peaked near 40 s the narrower 40 s jet has stronger cyclonic shear across the baroclinic zone these changes are accompanied by shifts in poleward eddy momentum flux on the 500 hpa surface and potential vorticity fluxes on the theta surfaces that lie in the midtroposphere which are both consistent with the maintenance of the zonal wind anomalies against friction series of synoptic maps