clustered impacts experiments and implications impact by clusters of projectiles rather than a single projectile can result from several processes atmospheric breakup tidal breakup and ejecta from a large primary impact experiments have been performed in order to establish the characteristics of such events over a wide range of impact velocities 15 m s to 6 km s at very low impact velocities 15 200 m s clustered impacts were produced by launching a grouped projectiles of aluminum shot steel shot iron filings and sand at moderate to high velocities 0 8 6 km s pyrex spheres were shattered above the target during passage through aluminum foil or paper thereby forming a well defined cluster of fragments of overall radius rc the ratio of the overall radius rc of the cluster to the radius rs of a solid impactor of the same mass provides a measure of the cluster dispersion sand and compacted pumice targets were used in order to compare qualitatively the additional effect of slight differences in target strength the experiments reveal marked contrasts between impacts by clusters of projectiles and impacts by a single solid body tight clusters rc rs 20 displace a factor of 10 less mass this reduction in cratering efficiency is largely expressed as a shallow crater with an aspect ratio diameter depth as large as 30 for open clusters the size and velocity of the cluster as well as the density and strength contrast between the impactor and target can dramatically affect crater morphology open clusters impacting compacted pumice produce a flat hummocky floor with an incipient multiring pattern whereas a tight cluster impacting the same target produces a central floor mound oblique impacts by symmetrical clusters form a characteristic array of v shaped ridges pointing uprange the apex angle of the ridges depends on the cluster dispersion and impact angle inventories of postimpact projectile material reveal that the projectile is largely retained on the surface and spread downrange from the impact direction the amount of projectile material retained on the surfaces increases with decreasing impact angle from the horizontal and with increasing strength of the target relative to the projectile clustered impact craters and lunar secondary craters bear striking similarities over a broad range of morphologic features on this basis and on the basis of reasonable models of ejecta curtain structure we suggest that these experiments provide new clues for understanding ejecta emplacement around large lunar impact craters when the ejecta curtain around large impacts is viewed as a thick wall of debris and clustered impactors are viewed as a unit section of such a curtain then experimental results indicate that the continuous ejecta facies even for lunar craters larger than 100 km could contain as much as 90 primary material such a conclusion contrasts with many existing models that derive mixing ratios implicitly based on single noninteracting impact events beyond the continuous ejecta facies impacting clusters of ejecta provide a physical basis for understanding the wide variety of secondary morphologies and the large range in spectral signatures of primary material in crater rays

the importance of secondary cratering to age constraints on planetary surfaces small craters less than one kilometer diameter can be primary craters produced by impact of interplanetary debris or they can be secondary craters produced by fallback of high velocity ejecta blocks from much larger but infrequent primary impacts the prevalent assumption over recent decades has been that primaries are most abundant so most small craters are independent random events and can be used for dating however recent results from europa and mars support the early theory that distant secondaries globally dominate the number of small lunar craters this would invalidate part of production functions that have been widely used for age dating crater excavation results in higher mean ejection velocities for smaller fragments resulting in a steeper size frequency distribution for secondary craters than is produced by the same size frequency distribution of interplanetary debris this review also discusses how small craters can sometimes be used to derive meaningful age constraints

numerical simulations of tropical cyclone ocean interaction with a high resolution coupled model the tropical cyclone ocean interaction was investigated using a high resolution tropical cyclone ocean coupled model the model design consisted of the noaa geophysical fluid dynamics laboratory tropical cyclone prediction model which was coupled with a multilayer primitive equation ocean model coupling between the hurricane and the ocean models was carried out by passing into the ocean model the wind stress heat and moisture fluxes computed in the hurricane model the new sea surface temperature sst calculated by the ocean model was then used in the tropical cyclone model a set of idealized numerical experiments were performed in which a tropical cyclone vortex was embedded in both easterly and westerly basic flows of 2 5 5 and 7 5 m s 1 with a fourth experiment run with no basic flow specified initially the profile of the tangential wind for hurricane gloria at 1200 utc 22 september 1985 was used as the initial condition of the tropical cyclone for each of the experiments the model ocean was initially horizontally homogenous and quiescent to clarify the impact of the ocean response to the hurricane s behavior analogous experiments were also carried out with the sst kept constant control cases the experiments indicated that the cooling of the sea surface induced by the tropical cyclone resulted in a significant impact on the ultimate storm intensity due to the reduction of total heat flux directed into the tropical cyclone above the regions of decreased sst the sea surface cooling produced by the tropical cyclones was found to be larger when the storms moved slower in the experiments run without an initial basic flow the maximum sst anomaly was about 5 6 c with a resulting difference in the minimum sea level pressure and maximum surface winds of 16 4 hpa and 7 m s 1 respectively in contrast in the experiments run with the 7 5 m s 1 basic flow the maximum sst anomalies ranged from about 2 6 to 3 0 c with a difference in the minimum sea level pressure and maximum surface winds of about 7 3 hpa and 2 7 m s 1 the tropical cyclone ocean coupling significantly influenced the storm track only for the case with no basic flow and the 2 5 m s 1 easterly flow in these cases the storm with the ocean interaction turned more to the north and east no basic flow or the north 2 5 m s 1 easterly flow of the experiments with constant sst in the first case the storm by 72 hours was located over 70 km to the east southeast of the control case a possible explanation for this track deviation is related to a systematic weakening of the mean tangential flow at all radii of the storm due to the interaction with the ocean and resulting alteration of the beta drift

possible long term decline in impact rates 1 martian geological data abstract quantin et al quantin c allemand p mangold n delacourt c 2004a icarus 172 555 572 tabulated crater count data for 56 landslides along the walls of valles marineris under the assumption of a constant cratering rate after about 3 gyr ago as used in the 1999 2005 iterations of the crater chronology isochron system of hartmann and in the hartmann and neukum system these data indicate a regularly increasing rate of landslides which would be difficult to explain we suggest that these data may support a decline in inner solar system cratering rates by about a factor of 3 since 3 gyr ago not unlike predictions based on asteroid belt collision models such a decline is also supported by our review of data on lunar impact melts and glass spherules in a companion paper hartmann w k quantin c mangold n 2007 icarus 186 11 23 such models produce not only a more uniform rate of landslides over the last 3 gyr but also a more uniform rate of resurfacing processes which also had an apparent increase under the assumption of a constant cratering rate

on the relative motion of binary tropical cyclones abstract the interaction between spatially proximate binary tropical cyclones is such that relative rotation in the counterclockwise sense and decreasing separation distance between the two storm centers can be expected this is referred to as the fujiwhara effect this study analyzes this effect for 43 binary tropical cyclone systems which occurred over the western north pacific 1949 78 it is shown that most demonstrated mutual interaction according to fujiwhara expectations however there were notable apparent exceptions further analysis of these exceptional cases shows that environmental currents in which the storms were embedded had a significant effect on relative motion and masked the fujiwhara effect additionally it was found that storms exhibiting behavior most in accordance with fujiwhara expectations were located in or near the intertropical convergence zone the main conclusion of the study in confirmation of earlier studies is that forces relative to environmental steering must be de

a strain based porosity model for use in hydrocode simulations of impacts and implications for transient crater growth in porous targets numerical modelling of impact cratering has reached a high degree of sophistication however the treatment of porous materials still poses a large problem in hydrocode calculations we present a novel approach for dealing with porous compaction in numerical modelling of impact crater formation in contrast to previous attempts e g p alpha model snowplow model our model accounts for the collapse of pore space by assuming that the compaction function depends upon volumetric strain rather than pressure our new e alpha model requires only four input parameters and each has a physical meaning the model is simple and intuitive and shows good agreement with a wide variety of experimental data ranging from static compaction tests to highly dynamic impact experiments our major objective in developing the model is to investigate the effect of porosity and internal friction on transient crater formation we present preliminary numerical model results that suggest that both porosity and internal friction play an important role in limiting crater growth over a large range in gravity scaled source size

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

well preserved low thermal inertia ejecta deposits surrounding young secondary impact craters on mars following the most recent updates to the mars odyssey thermal emission imaging system themis daytime and nighttime infrared global mosaics a colorized global map was produced that combines the thermophysical information from the nighttime infrared global mosaic with the morphologic context of the daytime infrared global mosaic during the validation of this map large numbers of low thermal inertia ejecta deposits surrounding small young impact craters were observed a near global survey 60 n 60 s identified 4 024 of these low thermal inertia ejecta deposits which were then categorized based on their apparent state of degradation mapping their locations revealed that they occur almost exclusively in regions with intermediate to high thermal inertias with distinct clusters in northern terra sirenum solis planum and southwestern daedalia planum high resolution imaging science experiment hirise images show that the thermophysically distinct facies of the deposits are well correlated with the estimated average ejecta grain sizes which decrease with radial distance from the crater comparisons with recent primary impact craters and secondary impact craters surrounding zunil crater show that the low thermal inertia ejecta deposits very closely resemble the secondary craters but not the primary craters we conclude that the low thermal inertia ejecta deposits are secondary impact crater ejecta deposits many of which originated from the rayed crater primary impact events and are both well preserved and easily identifiable due to the absence of dust cover and aeolian modification that would otherwise reduce the thermal contrast between the ejecta facies and the surrounding terrain

investigations of fennoscandian glacial isostatic adjustment using modern sea level records we present a new method for determining the rates from a network of regional tide gauge data the method involves using a model for the sea level observations annual averages of relative sea level that explicitly includes a term for the interannual sealevel variations which are assumed to be constant for all sites in the network the resulting simultaneous analysis of all the sea level observations yields sea level rates which are biased by the unknown temporal slope of the interannual variations by differencing sea level rate estimates with respect to one site site referenced sea level rates are calculated which are free from this bias the differencing procedure also removes any signal due to a common sea level rate such as might be associated with eustatic sea level rise the resulting site referenced sea level rates therefore in principle reflect only the relative vertical crustal motions of the tide gauge sites with respect to the geoid these site referenced sea level rates represent a potentially more accurate data set than have previously been used for sea level studies we have used these rates to investigate glacial isostatic adjustment gia in fennoscandia specifically we have used the site referenced sea level rates within the baltic sea to estimate adjustments to the ice history and earth model which are used to calculate vertical rates of adjustment due to gia a method never before used for fennoscandia the parameters selected were lithospheric thickness the viscosities of assumed isoviscous upper and lower mantles and a fennoscandian ice thickness scaling parameter we present the results of this estimation procedure for a specific test ice model we also find evidence that the sea level record for the site nearest the center of uplift furuogrund may be contaminated by systematic errors of unknown origin data from this site have previously been used to determine a rate for the maximum uplift that we find is perhaps 1 mm yr 1 or 10 too large

itrf2000 a new release of the international terrestrial reference frame for earth science applications 1 for the first time in the history of the international terrestrial reference frame the itrf2000 combines unconstrained space geodesy solutions that are free from any tectonic plate motion model minimum constraints are applied to these solutions solely in order to define the underlying terrestrial reference frame trf the itrf2000 origin is defined by the earth center of mass sensed by satellite laser ranging slr and its scale by slr and very long baseline interferometry its orientation is aligned to the itrf97 at epoch 1997 0 and its orientation time evolution follows conventionally that of the no net rotation nnr nuvel 1a model the itrf2000 orientation and its rate are implemented using a consistent geodetic method anchored over a selection of itrf sites of high geodetic quality ensuring a datum definition at the 1 mm level this new frame is the most extensive and accurate one ever developed containing about 800 stations located at about 500 sites with better distribution over the globe compared to past itrf versions but still with more site concentration in western europe and north america about 50 of station positions are determined to better than 1 cm and about 100 sites have their velocity estimated to at or better than 1 mm yr level the itrf2000 velocity field was used to estimate relative rotation poles for six major tectonic plates that are independent of the trf orientation rate a comparison to relative rotation poles of the nuvel 1a plate motion model shows vector differences ranging between 0 03 and 0 08 m y equivalent to approximately 1 7 mm yr over the earth s surface itrf2000 angular velocities for four plates relative to the pacific plate appear to be faster than those predicted by the nuvel 1a model the two most populated plates in terms of space geodetic sites north america and eurasia exhibit a relative euler rotation pole of about 0 056 0 005 m y faster than the pole predicted by nuvel 1a and located about 10 n 7 e more to the northwest compared to that model

evidence of marine isotope stage 5 5 highstand in liguria italy and its tectonic significance abstract the quaternary shoreline displacements in liguria are still poorly known this paper completely revises and reinterprets the literature on this topic taking into account only those markers that allow precise estimates of altitude and age of sea level highstands among the sites showing geomorphological evidence of mis 5 5 present in liguria three were considered reliable in eastern liguria a beach deposit with a terrace inner margin at 28 m a s l villa monteverde was dated by osl in western liguria in a site close to the french border balzi rossi a notch present inside two caves indicating a sea level altitude of 12 m is associated with a deposit containing a faunal assemblage with strombus bubonius this gastropod appeared in the italian seas only during the last interglacial highstand and provides a unique marker of the mis 5 5 horizon eastward near imperia another site madonna dell arma shows similar evidence but in this case the notch is not preserved because the cave is carved in a very soft oligocene conglomerate late quaternary tectonic movements along the different tracts of the ligurian coast seem to have occurred apparently with different although rather low uplift rates the connection between the alpine and apennine chains sestri voltaggio line divides the ligurian arch into two parts the alpine sector can be considered stable whereas the apennine relief displays in its central part an uplift rate of 0 16 mm yr

on the interaction of tropical cyclone scale vortices i observations a detailed analysis is made of the observed behaviour in interaction tropical cyclone scale vortices in the western north pacific region it is found that all multiple vortex interactions can be broken down into a common model of binary interaction the classical fujiwhara model of converging cyclonic rotation about a centroid followed by merger is rarely followed capture tends to occur rapidly within several hours and is followed by a period of relatively stable cyclonic orbit cyclone merger occurs by one vortex experiencing a loss of convective organization followed by horizontal shearing and incorporation into the outer circulation of the other vortex however a substantial proportion of interacting cyclones escape from the interaction and the changeover from a stable orbiting configuration occurs rapidly a model of binary interaction is presented cases where swarms of mesoscale vortices are formed in convectively active regions without tropical cyclones are also documented these vortices have a much narrower range of influence a few hundred kilometres then that observed for tropical cyclones when groups of vortices come within this range they are observed to conform to the same interaction model as observed for tropical cyclones

orbital change experiments with a mars general circulation model abstract we use a mars general circulation model to examine the effect of orbital changes on the planet s general circulation and climate system experiments are performed for obliquities ranging from 0 to 60 for two different longitudes of perihelion each experiment simulates a full mars year assuming a fixed atmospheric dust distribution and fixed amount of co 2 in the atmosphere cap system we find that global mean surface temperatures and pressures decline with increasing obliquity due to the increasing extent of the winter polar caps the seasonal co 2 cycle and intensity of the solstice circulation amplify considerably with increasing obliquity such that global dust storms are likely at both solstices the most significant feature of the high obliquity solstice circulations is the development of an intense low level jet associated with the return branch of the hadley circulation model surface stresses are used to map regions of preferred dust lifting which are defined in terms of an annual deflation potential for the present obliquity the model predicted regions of high deflation potential are in good agreement with cantor et al s 2001 j geophys res 106 23653 23688 observations which gives us some confidence in the model s ability to predict where lifting might occur when mars orbit parameters are different than they are today in general we find that the dust lifting potential increases sharply with obliquity and is greatest at times of high obliquity when perihelion coincides with northern summer solstice over an obliquity cycle the model global annual deflation potential ranges from several tenths of a millimeter at 0 obliquity to almost 15 mm at 60 obliquity much higher values are possible when the atmosphere is very dusty we find a strong correlation between the deflation potential and surface thermal inertia regions of high deflation potential correspond to regions of high thermal inertia high rock abundance and regions of low deflation potential correspond to regions of low thermal inertia high dust sand abundance furthermore while the regions of preferred lifting high deflation potential expand somewhat with increasing obliquity and dust loading the central parts of tharsis arabia and elysium show no tendency for significant lifting at any obliquity or longitude of perihelion these regions may therefore be very old and represent net long term sinks for atmospheric dust it is the topography of the planet through its influence on surface pressure and wind systems which ultimately determines where dust accumulates finally as was found by fenton and richardson 2001 j geophys res 106 32885 32909 we find no tendency for the development of east southeasterly winds at the pathfinder site for any of our orbital change experiments this suggests that the ancient wind regime discussed by greeley et al 2000 j geophys res 105 1829 1840 was produced by other factors such as polar wander

sorted stone circles in elysium planitia mars implications for recent martian climate we have found sorted stone circles and polygons near the equator of mars using new 25 cm pixel nasa hirise high resolution imaging science experiment images the sorted circles occur in geologically recent catastrophic flood deposits in the equatorial elysium planitia region and are diagnostic of periglacial processes sorted polygons do not form from volcanic activity as has been suggested for non sorted polygons in this region these landforms indicate that i a long lived geologically recent active cryoturbation layer of ground ice was present in the regolith ii there was some degree of freeze thaw and thus iii there were sustained period s likely within the last 10 ma in which the martian climate was 40 to 60 k warmer than current models predict

objective determination of hurricane tracks from aircraft observations abstract an algorithm for location of hurricane centers by least squares using aircraft data has been developed as the aircraft traverses the eye lines of position normal to the wind are constructed each 100 m along its track an additional line of position is constructed normal to the track at the closest point of approach to the center the center coordinates are then chosen such that the sum of the squares of the normal distances from the center to the lines of position is minimized a cubic spline storm track is first constructed using centers based on winds in a coordinate system fixed to the earth a track based upon winds in moving storm centered coordinates may be obtained by transformation of the winds into such a coordinate system and iterative redetermination of the centers for intense hurricanes the centers can be located with an accuracy of 3 km and the mean motion over a period of four to six hours determined to within 4 of direction and 0 5 m s 1 of speed the details of the track osc

changes in blast zone albedo patterns around new martian impact craters abstract blast zones bzs around new martian craters comprise various albedo features caused by the initial impact including diffuse halos extended linear and arcuate rays secondary craters ejecta patterns and dust avalanches we examined these features for changes in repeat images separated by up to four mars years here we present the first comprehensive survey of the qualitative and quantitative changes observed in impact blast zones over time such changes are most likely due to airfall of high albedo dust restoring darkened areas to their original albedo the albedo of adjacent non impacted surfaces although some sites show drastic changes over short timescales nearly half of the sites show no obvious changes over several mars years albedo changes are more likely to occur at higher latitude sites lower elevation sites and at sites with smaller central craters no correlation was seen between amount of change and dust cover index relative halo size or historical regional albedo changes quantitative albedo measurements of the diffuse dark halos relative to their surroundings yielded estimates of fading lifetimes for these features the average lifetime among sites with measurable fading is 15 mars years the median is 8 mars years for a linear brightening however at approximately half of sites with three or more repeat images a nonlinear function with rapid initial fading followed by a slow increase in albedo provides a better fit to the fading behavior this would predict even longer lifetimes the predicted lifetimes of bzs are comparable to those of slope streaks and considered representative of fading by global atmospheric dust deposition they last significantly longer than dust devil or rover tracks albedo features that are erased by different processes these relatively long lifetimes indicate that the measurement of the current impact rate by daubar et al daubar i j et al 2013 icarus 225 506 516 http dx doi org 10 1016 j icarus 2013 04 009 does not suffer significantly from overall under sampling due to blast zones fading before new impact sites can be initially discovered however the prevalence of changes seen around smaller craters may explain in part their shallower size frequency distribution

zumba crater daedalia planum mars geologic investigation of a young rayed impact crater and its secondary field abstract zumba is a 2 9 km diameter rayed crater on mars located on extensive lava plains in daedalia planum to the southwest of arsia mons it is a well preserved young crater with large ejecta rays that extend for hundreds of kilometers from the impact site the rays are thermally distinct from the background lava flows in themis daytime and nighttime thermal infrared data a unique characteristic among martian rayed craters concentrated within the rays are solitary or dense clusters of secondary craters with associated diffuse dark toned deposits along with fewer secondary craters lacking dark toned deposits using ctx images we have mapped secondary craters with dark toned deposits collectively termed secondary fields to investigate their distribution as a function of distance from the impact site the mapped secondary field was then used to investigate various aspects of the crater forming event such as the surface angle and direction of the projectile the effect of secondary craters on surface age estimates and the number of secondary craters produced by the impact event from our mapping a total of 13 064 secondary fields were documented out to a 200 km radial distance beyond a 15 km wide non secondary zone around zumba crater results show that the highest areal coverage of secondary fields occurs within 100 km of zumba and within its rays decreasing radially with distance to a background scattering of small secondary fields that are 2 in size 91 9 of the total population the strong east west asymmetry of crater rays and low areal coverage of fields to the south of zumba correlate well with studies of zumba impact melt deposits indicating a moderately oblique impact projectile coming from the south using primary craters in a 101 km 2 sample region and all craters primaries and secondaries from 43 select secondary fields in two map sectors in the study area we obtain ages of 580 100 ma and 650 70 ma respectively for the lava flows into which zumba impacted these ages are consistent with and intermediate to 0 1 1 ga volcanic flow units within and near daedalia planum for craters within the secondary fields a log differential plot of the data shows a pronounced downward deflection of the binned points for craters 100 m we estimate that 352 000 secondary craters were produced by the zumba impact event

sea level change along the french mediterranean coast for the past 30 000 years abstract observational evidence for sea level change along the french mediterranean coast has been examined and compared with glacio hydro isostatic models to predict the spatial and temporal patterns of change for about the past 30 000 14c years these predictions are pertinent to discussions of changing ocean volumes during this interval the tectonic stability or otherwise of the coastal areas mantle rheology and the timing of possible human occupation of the now submerged coastal plain and caves such as cosquer cave near marseille the principal results from the analysis are i sea levels along this section of the coast have risen continually since the time of the last glacial maximum lgm and at no time during the holocene has the mean sea level been higher than that of today ii the coast has been tectonically stable between marseille and nice as well as further to the west in roussillon western corsica may have experienced a slow tectonic uplift of between 0 15 0 3 mm year for the past 3000 years but northernmost corsica appears to have been stable during this same interval iii during the lgm sea levels along the coast and immediate off shore areas stood at between 105 115 m below present level the range reflecting the importance of the isostatic contributions during oxygen isotope stage 3 sea levels do not appear to have risen locally above about 60 m iv the rebound parameters describing the mantle rheology and ice sheets required to match the limited observational evidence are consistent with the results of similar analyses carried out for other parts of europe because of its distance from the former northern ice sheets the isostatic factors are particularly sensitive to the value of the lower mantle viscosity v the model predictions for sea level change at the cosquer cave site and for its immediate environments indicate that the cave was last readily accessible before about 10 700 500 14c years about 12 500 500 cal years bp and that the cave entrance was completely flooded by 9000 200 radiocarbon years bp between about 9800 and 10 300 calibrated years bp the cave was above sea level throughout the oxygen isotope stage 3

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

elysium planitia lava flows crater count chronology and geological implications mars global surveyor mgs and viking images allow analysis of chronological and geological relations among lava flows in southern elysium planitia based on crater populations mgs and viking images clearly show morphological features of lava flows with some extremely sparsely cratered young flow units atop somewhat older surfaces there is no evidence of substantial dust mantling on the young flows and hence we infer that the crater populations date not sediment accumulation but the lava flows themselves the youngest flows have some of the lowest crater densities that we have seen on mars some 1 of lunar mare values at crater diameters below about 180 to 500 m we infer that thin scattered volcanic flows some tens of meters thick have been emplaced atop stratigraphic units within the last 100 myr and possibly within the last 10 myr volcanism is thus a continuing process in the recent geologic history of mars and this must constrain geophysical models of the planet

recent flood lavas in the elysium region of mars abstract a vast area of smooth plains in southeastern elysium here referred to as the cerberus formation is interpreted to be of volcanic origin surface morphology lobate edges of the unit the identification of vents low shields and the embayment relation of the unit with adjacent older units all suggest a volcanic origin the plains were formed by the eruption of low viscosity lavas that filled a topographic depression in southeast elysium and then flowed into western amazonis planitia flow into western amazonis was facilitated by a series of channels carved by an earlier fluvial episode which were exploited by lavas as they moved down slope crater frequencies and stratigraphic relations indicate that the unit is very young upper amazonian the presence of such young flood lavas indicates 1 late in martian history large scale eruptions of low viscosity lava was still possible b sufficient heat remained in the mantle to mobilize large quantities of magma and c flood volcanism either continued or resumed in elysium after activity of the large central volcanoes had ceased each of these points are important considerations in understanding the martian thermal and volcanic history

vertical deformation of the japanese islands 1996 1999 1 the interseismic vertical deformation field of the japanese islands is derived from the global positioning system gps data between 1996 and 1999 although vertical components of the gps velocities have rarely been used as important information because of their higher noise level information on the vertical deformation field will enable us to separate rigid plate motions from deformation due to interplate coupling because horizontal displacements contain both effects whereas vertical displacements contain only the interplate coupling effect the results show that 1 the precision of the vertical velocity is generally better than 2 mm yr 2 the existence of clear uplift peaks of about 8 mm yr in the shikoku and tokai regions is consistent with strong coupling with a gradual brittleplastic transition zone at the nankai and the suruga trough respectively 3 clear uplift peaks do not seem to exist in the tohoku region because the japan trench plate boundary is too far oceanward from the gps sites 4 significant uplift is obtained in the western part of hokkaido which may be associated with the long term postseismic deformation due to the 1983 japan sea and the 1993 hokkaido nansei oki m 7 6 earthquakes and 5 uplift in northeastern japan along the japan sea coast is apparently associated with distributed compression due to incipient subduction

sinuosity of martian rampart ejecta deposits the sinuosities of 2213 martian rampart ejecta craters are quantified through measurement of the ejecta flow front perimeter and ejecta area this quantity called lobateness was computed for each complete lobe of the 1582 single lobe sl 251 double lobe dl and 380 multiple lobe ml craters included in this study a lobateness value of 1 indicates a circular ejecta blanket whereas more sinuous ejecta perimeters have lobateness values 1 although resolution does have an effect on the absolute values of lobateness the general relationships between lobateness and morphology exist regardless of resolution evaluation of the lobateness values reveals that the outer lobes of dl and ml craters have higher median lobateness values i e are more sinuous than the inner lobes the outermost lobe of ml craters displays higher lobateness values than the outer lobe of dl craters or the single lobe of sl craters previous reports of lobateness diameter lobateness latitude and lobateness terrain relationships for rampart craters are not supported by this study many of the differences between the results of this study and the previous lobateness analyses can be attributed to the inclusion of resolution effects and the distinction between different ejecta morphologies in this study the results of this study taken together with a previous analysis of the distribution and diameter dependence of different ejecta morphologies are most consistent with the theory that martian lobate ejecta morphologies form from impact into subsurface volatiles

an improved shadow measurement technique for constraining the morphometry of simple impact craters the lengths of the shadows cast within simple bowl shaped impact craters have been used to constrain their depths on a variety of planetary bodies this technique however only yields the true crater depth if the shadow transects the crater center where the floor is deepest in the past attempts have been made to circumvent this limitation by choosing only craters where the shadow tip lies very near the crater center but this approach may introduce serious artifacts that adversely affect the slope of the regressed depth vs diameter data and its variance here we introduce an improved method for deriving depth information from shadow measurements that considers three basic shape variations of simple craters paraboloidal conical and flat floored we show that the shape of the cast shadow can be used to constrain crater shape and we derive improved equations for finding the depths of these simple craters

mars at very low obliquity atmospheric collapse and the fate of volatiles 1 the obliquity of the martian spin axis is known to undergo quasiperiodic oscillations superposed over chaotic long term variations it is probable that within past history there were geologically long periods when the obliquity oscillated around low 10 15 mean values during such low obliquity epochs the climate system is controlled by deposition of permanent solid co2 deposits in the polar regions with a simple season resolved energy balance model we show that as the atmosphere collapses surface topography plays a major role in co2 condensation and sublimation processes defining distribution and dynamics of co2 deposits thick co2 deposits are formed at steep pole facing topographic slopes at moderately high latitudes not at the poles the total mass of the deposits is not a function of obliquity but strongly depends on the pre history of the climate system we outline criteria to identify such low obliquity epochs in mars history

origin of the international terrestrial reference frame 1 with recent improvements in space geodesy the earth s center of mass cm and center of figure cf are no longer indistinguishable the current origin of the international terrestrial reference frame itrf is defined as the cm which shows measured seasonal variations of several millimeters to 1 cm with respect to true cm as scientists study earth s dynamic deformations on seasonal and shorter timescales and begin to compare observed geocenter motion with predictions from geophysical models the reference frame origin presents significant error due to missing the geocenter motion this paper discusses the nature of the origin of the itrf and explores the sensitivity of gps measurements to geocenter motion we find that since the values of nonlinear geocenter motion are not included in the positions of the itrf sites the behavior of the current itrf origin reflects cm on secular timescale but reflects cf on seasonal and short timescales the nature of the itrf origin depends on both the adopted kinematic model and unmodeled network motion the realized itrf origin should be defined by a new nomenclature to reflect its nature accurately by the new nomenclature the origin will maintain its current long term stability while improving its stability on seasonal timescales to the submillimeter level with the degree 1 deformation approach gps measurements are able to provide potentially valuable information on geocenter variations on seasonal and short timescales

ejecta patterns diagnostic of planetary rotations abstract the ballistics of ejecta on a spinning planet satellite or asteroid are affected by centrifugal and coriolis forces the distribution of crater debris over a spherical body depends only on its density its rotation rate and the latitude of primary impact even on objects with spin periods of several days ray patterns are twisted and bent over wide areas near the antipodes of the source crater the peculiar morphologies include spirals loops cusps and rays resembling hyperbolae these distortions become progressively more pronounced with increasing rotation rate at periods of only a few hours the deposition of near field ejecta is also changed the patterns described herein are diagnostic of a planet s rotation rate and pole position at the time of a given impact these results could be applied for example to date the despinning of mercury relative to its latest bombardment

geology of the northeastern flank of apollinaris mons mars constraints on the erosional history from morphology topography and crater populations abstract we have utilized themis mola ctx and hirise data sets to investigate the morphologic and topographic characteristics of the northeast flank of apollinaris mons a region with evidence for significant erosion of volcanic deposits using arcgis software we mapped the geology of the northeast flank and obtained age estimates using crater size frequency distributions from crater counts of the eight mapped units three apollinaris mons upper mid and lower flank units represent volcanic flank materials in various states of preservation the late noachian early hesperian upper flank unit is massive and contains joint like vertical structures along the scarp faces of two large plateaus whose upper surfaces likely represent the original surface or near surface deposits of apollinaris mons downslope facing plateau scarps have up to 500 m of relief positioned below this unit are the mid flank and lower flank units each representing eroded surfaces within apollinaris mons flank materials that have stabilization ages between the late hesperian to early amazonian mantling material in the region contains cavities and boxwork like textures that resemble patterns in terrestrial eroded pyroclastic flow deposits dome shaped mounds west of the mapping region have morphologic similarities to terrestrial fumarolic mounds or possibly inverted impact craters both the texture and features suggest widespread pyroclastic deposits adjacent to apollinaris mons using mola gridded topography we estimate that 308 km3 of materials have been eroded along the flanks of the volcano statistical and histogram data from the thickness values of eroded materials shows that up to 300 m of material has been removed from the majority of flank surfaces assuming steady state erosion of flank surfaces we estimate an area normalized loss rate of 0 859 nm yr for northeast apollinaris mons this erosion rate is within the long term range for mars 0 01 10 nm yr as estimated from mer landing site geology by golombek et al 2006

a new global mode of earth deformation seasonal cycle detected we have detected a global mode of earth deformation that is predicted by theory precise positioning of global positioning system sites distributed worldwide reveals that during february to march the northern hemisphere compresses and the southern hemisphere expands such that sites near the north pole move downward by 3 0 millimeters and sites near the equator are pulled northward by 1 5 millimeters the opposite pattern of deformation occurs during august to september we identify this pattern as the degree one spherical harmonic response of an elastic earth to increased winter loading of soil moisture snow cover and atmosphere data inversion shows the load moment s trajectory as a great circle traversing the continents peaking at 6 9 1022 kilogram meters near the north pole in winter indicating interhemispheric mass exchange of 1 0 1016 0 2 1016 kilograms

development and nondevelopment of binary mesoscale vortices into tropical cyclones in idealized numerical experiments abstractthe evolution of two symmetric midlevel mesoscale vortices situated above a warm ocean is examined with a basic cloud resolving model idealized numerical experiments provide insight into how the evolution may vary with the initial vortex separation distance d and other parameters that influence the time scale for an isolated vortex to begin rapid intensification the latter parameters include the ambient middle tropospheric relative humidity rh and the initial midlevel wind speed of each vortex at relatively low rh there exists an interval of d where binary midlevel vortex interaction prevents tropical cyclone formation while tropical cyclones generally develop at high rh similar values of d can delay the process if the vortices are initially weak prevention or inhibition of tropical cyclone formation occurs in association with the outward expulsion of lower tropospheric potential vorticity anomalies as the two vortices merge in the middle troposphere it is proposed that the primary mecha

dark halos produced by current impact cratering on mars abstract hundreds of new impact craters have been observed to form on mars since spacecraft began imaging that planet new impact craters produced visible ejecta deposits and many of them also have visible rays similar to lunar and mercurian craters however some of the new martian impact craters have a circular feature of relatively low reflectance that we call a halo this feature is distinct from the usual visible ejecta deposits or ray patterns in this paper we present an observational study of this halo feature and we discuss the results of this study with respect to the nature of the halos what they are and how they may have formed to address these questions we measured diameters of both halos and their central craters we found a strong correlation between halo diameter and crater diameter which indicates that the nature of the halos is fundamentally governed by the amount of impact energy available at their formation specifically halo size is controlled by impact energy according to the non linear relationship dh e2 3 where dh is the diameter of the halo and e is the impact energy we also found that certain factors may influence the formation of the halos a thicker dust layer and lower elevations are both correlated with larger halos from these correlations we conclude that the local surface characteristics as well as local atmospheric pressure influence the formation of the halos our description and analysis of the martian halo features provide a framework upon which specific halo formation mechanisms can be developed and tested in the future

spatial relationships between patterned ground and ground ice detected by the neutron spectrometer on mars 1 patterned grounds like polygonal features are the signature of climatic effects in periglacial regions on earth identifying similar features on mars is important for an understanding of the past martian climate in this study we mapped fresh patterned landforms from the systematic analysis of mars orbiter camera high resolution images we show that most of them are distributed at latitudes poleward of 55 making a climatic control likely this distribution correlates to the distribution of ground ice detected by the neutron spectrometer aboard mars odyssey this correlation is likely the consequence of the neutron spectrometer detecting ice no deeper than about 1 m patterned ground formation requires ice in this range of depth because these features are triggered by the propagation of a thermal wave that is driven by seasonal or diurnal changes in insolation which affect the temperature in the uppermost ground layers sublimation seems to play a role in the shaping of many of the small patterns observed at latitudes between 55 and 70 no widespread polygonal features are correlated to the equatorial regions where hydrogen is detected by the neutron spectrometer

confirmation and utilization of the production function size frequency distributions of martian impact craters 1 on any planetary surface impacts of interplanetary bodies create an initial or production function size frequency distribution sfd of impact craters recent questions have been raised about whether this size distribution can be reliably detected especially at small sizes in a test area we confirm an excellent fit to the distribution we have used previously at diameters 11 m d 1 km at d 1 km images with the high resolution stereo camera hrsc allow us to confirm earlier proposals on how the burial of old small craters by lava flows can distort the sfd curve in some areas as a product of this analysis we present a new tool for quantitative analysis of geologic processes on mars namely use of crater statistics to interpret subsurface structure

volcano ground ice interactions in elysium planitia mars abstract the occurence within elysium planitia of meltwater deposits possible pseudocraters collapse features within troughs and outflow channels indicates that a layer of subsurface volatiles existed at the time of volcanic activity within this area the pseudocraters are interpreted to be indicators of near surface volatiles while meltwater deposits and the degree of preservation of trough walls and floors are thought to signify greater volatile depths a latitudinal variation in the distribution of these features indicates either that the depth to the volatile layer increased from less than about 50 m at 35 n to greater than 600 m at 24 n or that an ice wedge that existed at 35 n thinned to nonexistence at 24 n braided distributary channel systems within the chaotic terrain north of elysium planitia show that ephemeral lakes were repeatedly created and drained at this locality the existence of volatiles contemporaneous with volcanic activity permits a search to be made for explosively generated landforms predicted to exist by previous theoretical models morphological evidence for strombolian vulcanian and plinian eruptions is lacking within western elysium planitia there are no identifiable cinder cones pyroclastic flow deposits or mantled areas indicative of large airfall deposits at an image resolution of 50 150 m pixel however the pseudocraters indicate that small scale phreatomagmatic activity may have taken place

athabasca valles mars a lava draped channel system athabasca valles is a young outflow channel system on mars that may have been carved by catastrophic water floods however images acquired by the high resolution imaging science experiment camera onboard the mars reconnaissance orbiter spacecraft reveal that athabasca valles is now entirely draped by a thin layer of solidified lava the remnant of a once swollen river of molten rock the lava erupted from a fissure inundated the channels and drained downstream in geologically recent times purported ice features in athabasca valles and its distal basin cerberus palus are actually composed of this lava similar volcanic processes may have operated in other ostensibly fluvial channels which could explain in part why the landers sent to investigate sites of ancient flooding on mars have predominantly found lava at the surface instead

effect of planetary rotation on distal tektite deposition on mars 1 the rapid rotation of mars creates a significant pseudoforce known as the coriolis force that greatly modifies the flight paths and subsequent deposition of distal ejecta ejecta with launch velocities of 3 km s and greater an accurate depiction of the effects of the coriolis force requires the integration of the coriolis terms directly into a series of spherical ballistic equations applied within a rotating reference frame the resulting landing positions of radially ejected particles tend to form distinct wrapping patterns that are focused to specific areas in the hemisphere opposite from the source crater around the pole for high latitude craters 45 in latitude and above and in an equatorial band for low latitude craters below 45 latitude consequently particular locations on the surface receive deposits in stages direct delivery of ejecta followed by deposits of higher velocity ejecta this staged deposition leads to regions of enhanced ejecta accumulations where meters of material collect millimeters would be predicted in nonrotational radial decay models thus high latitude craters could supply a considerable amount of distal products tektites and melts to polar locations perhaps contributing to the dark circumpolar materials

cerberus fossae elysium mars a source for lava and water cerberus fossae a long fracture system in the southeastern part of elysium has acted as a conduit for the release of both lava and water onto the surface the southeastern portion of the fracture system localized volcanic vents having varying morphology in addition low shields occur elsewhere on the cerberus plains three locations where the release of water has occurred have been identified along the northwest athabasca and grjota vallis and southeast rahway vallis portions of the fossae water was released both catastrophically and noncatastrophically from these locations a fluvial system that extends more than 2500 km has formed beginning at the lower flank of the elysium rise across the cerberus plains and out through marte vallis into amazonis planitia the timing of the events is late amazonian

imaging of lunar surface maturity the physical evolution of the lunar surface with exposure to the space environment is termed maturation and maturity is the degree to which a particular lunar soil possesses quantitative characteristics consistent with that exposure several quantitative measures or indices of maturity have been proposed and employed including the abundance of solar wind gas abundance of various types of agglutinates various measures of grain size and is feo among the changes attendant with space exposure are striking changes in the optical characteristics of soils mature lunar soils are dark red and exhibit reduced spectral contrast relative to immature soils this paper presents an optical maturity index that quantifies the spectral effects of maturation we show that this optical maturity index correlates with other maturity indices about as well as the accepted maturity indices correlate among themselves and is only weakly coupled to composition the modest correlations among maturity indices suggest important controls on individual maturity indices other than age uncorrelated variations in the rates of accumulation of individual indicators or variations in depths over which indicators are emplaced in addition to mixing these effects conspire to reduce the equivalence of maturity and duration of surface exposure optical maturity illustrates some of these effects showing that ejecta of large and small craters mature at different rates and that the interiors and ejecta of large craters exhibit systematically different optical maturities the same or analogous effects are likely to influence other maturity indices

present day geodynamics in the bend of the western and central alps as constrained by earthquake analysis summary the contrasted tectonics of the western central alps is examined using a synthesis of 389 reliable focal mechanisms the present day strain regime is mapped and interpolated for the entire alpine belt based on a newly developed method of regionalization the most striking feature is a continuous area of extension which closely follows the large scale topographic crest line of the alpine arc thrusting is observed locally limited to areas near the border of the alpine chain a majority of earthquakes within the alps and its forelands are in strike slip mode stress inversion methods have been applied to homogenous subsets of focal plane mechanisms in order to map regional variations in stress orientation the stress state is confirmed to be orogen perpendicular both for 3 in the inner extensional zones and 1 in the outer transcurrent transpressional zones extensional areas are well correlated with the part of the belt which presents the thickest crust as shown by the comparison with the bouguer anomaly and the average topography of the belt in the northwestern swiss alps extension is also correlated with currently uplifting zones these observations and our strain stress analyses support a geodynamic model for the western alps in which the current activity is mostly a result of gravitational body forces earthquakes do not provide any direct evidence for ongoing convergence in the alpine system but a relationship with ongoing activity of complex block rotations of the apulian microplate cannot be ruled out

influence of glacial isostatic adjustment on tide gauge measurements of secular sea level change modem tide gage records of secular sea level change are strongly contaminated by the ongoing influence of glacial isostatic adjustment in this paper we employ an accurate high resolution model of the glacial isostatic adjustment process to filter this signal from time series consisting of annual mean heights observed on over 500 tide gages from which records of duration longer than 10 years are available these records are all contained in the archive of the permanent service for mean sea level at bidston in the united kingdom prior to removal of the isostatic adjustment contamination from these records the secular sea level change signal is seen to exhibit both rising and falling levels depending upon geographic location with regions of falling level corresponding to those that were ice covered during the last glaciation event of the present ice age after filtering the geographic heterogeneity in rates is considerably reduced so much so that a globally coherent component consisting of a rise of sea level at a rate of 2 4 0 9 mm yr 1 is revealed this could conceivably be driven by the greenhouse effect although no particular mechanism has been unambiguously identified by our analyses we investigate the impact of a number of different variants of the analysis procedure upon the inferred global signal

rootless cones on mars indicating the presence of shallow equatorial ground ice in recent times high resolution mars orbiter camera moc images have revealed the existence of clusters of small cones in the cerberus plains marte valles and amazonis planitia mars these cones are similar in both morphology and planar dimensions to the larger of icelandic rootless cones which form due to explosive interactions between surficial lavas and near surface groundwater impact crater size frequency relationships indicate that surfaces upon which the cones sit are no older than 10 ma if martian cones form in the same manner as terrestrial rootless cones then equatorial ground ice or ground water must have been present near the surface in geologically recent times

present day impact cratering rate and contemporary gully activity on mars the mars global surveyor mars orbiter camera has acquired data that establish the present day impact cratering rate and document new deposits formed by downslope movement of material in mid latitude gullies on mars twenty impacts created craters 2 to 150 meters in diameter within an area of 21 5 106 square kilometers between may 1999 and march 2006 the values predicted by models that scale the lunar cratering rate to mars are close to the observed rate implying that surfaces devoid of craters are truly young and that as yet unrecognized processes of denudation must be operating the new gully deposits formed since august 1999 are light toned and exhibit attributes expected from emplacement aided by a fluid with the properties of liquid water relatively long extended digitate distal and marginal branches diversion around obstacles and low relief the observations suggest that liquid water flowed on the surface of mars during the past decade

geomorphic analysis of small rayed craters on mars examining primary versus secondary impacts 1 twenty confirmed impacts over a 7 year time period on mars were qualitatively and statistically compared to 287 secondary craters believed to originate from zunil an 500 ka 10 km diameter primary crater our goal was to establish criteria to distinguish secondaries from primaries in the general crater population on the basis of their horizontal planforms recent primary impacts have extensive air blast zones distal ray systems 100 crater radii r and ephemeral ejecta recent primaries formed clusters of craters from atmospheric fragmentation of the meteoroid body secondary craters have ejecta blankets with shorter rays that are consistent with emplacement by low impact velocities near 1 km s the mean extent of the continuous ejecta blankets was less distal for secondaries 5 38 1 57r versus primaries 18 07 7 01r though primary ejecta were less fractal fractal dimension index fdi 1 30 and more circular on average circularity ratio cr 0 55 0 25 versus 0 27 0 13 for secondaries crater rims were remarkably circular primaries cr 0 97 0 02 secondaries at 0 94 0 05 though secondaries have the lowest values cr 0 9 secondary crater rims were elongated toward or orthogonal to their primary of origin uprange source directions for most secondaries determined by ejecta planform and crater rim ellipticity point toward zunil although contamination from other primaries is considered in some areas ejecta blanket discrepancies between recent primaries and zunil secondaries are attributable to differences in impact velocity and retention age after removal of the ejecta blanket crater rims are generally not diagnostic for determining crater origin fragmentation of primaries may play some role in steepening the size frequency distribution of crater diameters in the 5 m d 30 m range

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

are the alps collapsing abstract orogenic collapse is a process that transfers gravitational potential energy from regions of high potential energy to regions of lower potential energy this transfer is classically considered to be accomplished by extension in the orogenic core and by synchronous shortening in foreland regions of the orogen not all extensional features in collisional mountain belts need however reflect orogenic collapse normal faulting thrust faulting and strike slip faulting are all active in different parts of the alps today and reflect complex local responses to ongoing europe adria convergence the western alps is the only area today where extension and shortening radial to orogen trend occur synchronously and where orogenic collapse may be an important process elsewhere in the alps normal faults are oriented at a high angle to orogen trend and were primarily active in oligocene and miocene time most present day activity in the central and eastern alps is on strike slip faults that are accommodati

coastal deformation between the versilia and the garigliano plains italy since the last interglacial stage the opening of the north central tyrrhenian sea is the result of the cretaceous paleogene alpine collision which triggered a series of regional uplift subsidence and transcurrent tectonic mechanisms along the coastal tyrrhenian sectors of peninsular italy these tectonic pro cesses in conjunction with the effects of glacio and hydro isostasy during the quaternary produced substantial crustal responses that in some cases reached metres in extent in the study of coastal neotectonics geomorphological markers of the last interglacial maximum corresponding to marine isotope stage 5 5 are generally used to quantify the magnitude of the vertical crustal displacements that have occurred since 125 kyr through altimetrical palaeoenvironmental and chronological reinterpretation of the most significant works published since 1913 combined with an additional set of data reported here a detailed reconstruction of the shoreline displacements evident along 500 km of coast between northern tuscany and southern latium is presented the reconstruction was carried out by quantifying the vertical movement since the last interglacial period and by identifying the tectonic behaviour of different coastal sectors this has been done by carefully choosing the eustatic marker among those available at each study site in order to minimize the margin of error associated with the measurements copyright 2003 john wiley sons ltd

impact experiments i ejecta velocity distributions and related results from regolith targets velocity distributions are determined for ejecta from 14 experimental impacts into regolithlike powders in near vacuum conditions at velocities from 5 to 2321 m sec of the two powders the finer produces slower ejecta ejecta include conical sheets with ray producing jets and in the fastest impacts at vimp 700 m sec high speed vertical plumes of uncertain nature velocities in the conical sheets and jets increase with impact velocity sect 6 ejecta velocities also increase as impact energy and crater size increase a suggested method of estimating ejecta velocity distributions in large scale impacts involves homologous scaling according to r rcrater where r is radial distances from the crater sect 7 the data are consistent with holsapple schmidt scaling relationships sect 8 the fraction of initial total impact energy partitioned into ejecta kinetic energy increases from around 0 1 for the slow impacts to around 10 for the fast impacts with the main increase probably at the onset of the hypervelocity impact regime sect 9 crater shapes are discussed including an example of a possible frozen transient cavity sect 10 ejecta blanket thickness distributions as a function of r vary with target material and impact speed but the results measured for hypervelocity impacts agree with published experimental and theoretical values sect 11 the low ejecta velocities for powder targets relative to rock targets together with the paucity of powder ejecta in low speed impacts 1 projectile mass for vimp 10 m sec enhance early planetary accretion effeciency beyond that in some earlier theoretical models 100 efficient accretion is found for certain primordial conditions sect 12

on the interaction of tropical cyclone scale vortices ii discrete vortex patches the interaction of vortex patches in relation to the observed scales and features reported in part i of this paper is investigated it is found that the initial approach of compound vortices such as tropical cyclones arises from distortion of their weaker outer vorticity fields care needs to be taken in applying simple concepts such as the propagation of each vortex on the gradient of its neighbour for similar vortices the initial interaction consists of mutual orbit and approach with only minor fluctuations in shape once the vortices approach to within a critical separation distance rapid merger occurs a simplified expression for this critical distance is derived and it indicates that binary tropical cyclones must approach to within 150 300 km before merger of the cores can occur when vortices have substantial differences in size or intensity the smaller weaker system shears into the outer circulation of the other and no core merger occurs it is suggested that this is typical of the interaction between tropical cyclones and both the monsoon trough and embedded mesoscale convective complexes the motion of interacting vortices consists largely of a mutual orbit which scales according to their relative sizes and intensities an important finding however is that higher frequency meanders may develop this indicates that a tropical cyclone interacting with a monsoonal shear zone may develop internal asymmetries and a trochoidal oscillations as a direct result of such interaction further weak mesoscale vortices within the cyclone circulation may continue to cause a track meander long after they have been sheared beyond the resolving capacity of atmospheric observations

constraints on vertical crustal motion for long baselines in the central mediterranean region using continuous gps abstract gps determination of vertical crustal velocity relative to a globally defined reference frame is limited by the accuracy of the reference frame origin and scale however the precision of relative vertical rates at regional distance scales remains largely unexplored we investigated the precision of regional scale vertical velocity estimates using data from seven continuously operating gps stations located in the central mediterranean the stations form a network of aperture 500 km and each has been in operation for at least 5 yr we used published constraints on recent crustal uplift inferred from late quaternary shoreline data to aid in the definition of a local vertical reference frame for gps rates to facilitate an assessment of gps vertical precision we explored different methods of defining the local reference frame the simplest method involves the estimation of a single scalar translation parameter adjusting the reference frame by this simple method yields agreement between cgps and holocene shoreline data sets at the level of 0 2 to 0 4 mm yr relative rates determined using cgps are also consistent with tide gauge records and sea level determined by satellite altimetry at the level of about 0 2 mm yr these results suggest that regional scale relative velocity precision well below the mm yr level is now possible using continuous gps

terra mare comparison of small young craters on the moon abstract several characteristics of very small impact craters of lunar surface have recently been improved by high resolution datasets lunar impact craters with diameter below 100 m and especially below 10 m were surveyed and compared at mare and terra surfaces in this work altogether at 0 6 km2 area with 4866 craters there the surface density values of all craters km2 at the mare regions were 1 5 2 0 times larger than at the terra regions and this difference came mainly from there is an ongoing debate on the reliability and usage of small craters for age estimation xiao and strom 2012 this work provides some further information to evaluate this aspect no correlation was found between the areal density values of craters and ages determined from size frequency distributions confirming using examples of smaller craters than analysed in most earlier works that large sized craters dominate the age estimation despite the larger number of

surface uplift uplift of rocks and exhumation of rocks uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges rates of uplift of the surfaces of mountain ranges have not however been quantified sufficiently well that they provide useful constraints on those processes many reports off surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift and provide no information whatsoever on the rates of surface uplift

effect of annual signals on geodetic velocity 1 our analysis of global positioning system gps site coordinates in a global reference frame shows annual variation with typical amplitudes of 2 mm for horizontal and 4 mm for vertical with some sites at twice these amplitudes power spectrum analysis confirms that gps time series also contain significant power at annual harmonic frequencies with spectral indices 1 2 which indicates the presence of repeating signals van dam et al 2001 showed that a major annual component is induced by hydrological and atmospheric loading unless accounted for we show that annual signals can significantly bias estimation of site velocities intended for high accuracy purposes such as plate tectonics and reference frames for such applications annual and semiannual sinusoidal signals should be estimated simultaneously with site velocity and initial position we have developed a model to calculate the level of bias in published velocities that do not account for annual signals simultaneous estimation might not be necessary beyond 4 5 years as the velocity bias rapidly becomes negligible minimum velocity bias is theoretically predicted at integer plus half years as confirmed by tests with real data below 2 5 years the velocity bias can become unacceptably large and simultaneous estimation does not necessarily improve velocity estimates which rapidly become unstable due to correlated parameters we recommend that 2 5 years be adopted as a standard minimum data span for velocity solutions intended for tectonic interpretation or reference frame production and that we be skeptical of geophysical interpretations of velocities derived using shorter data spans

the distribution and behavior of martian ground ice during past and present epochs mars undergoes significant oscillations in its orbit which will have a pronounced effect on its climate and in particular on the behavior of subsurface water ice we explore and map the behavior of ice in the martian near surface regolith over the past 1 m y using a diffusion and condensation model presented in an earlier paper with two primary modifications to include orbitally induced variations in insolation and atmospheric water abundance we find that the past behavior of ground ice differs significantly from that at the present epoch primarily the result of high amplitude oscillations in obliquity presently 25 in midlatitude and equatorial regions ground ice will condense from atmospheric water during times of higher obliquity filling the top few meters of the regolith with significant amounts of ice at an obliquity of 32 ground ice becomes stable globally during times of lower obliquity ground ice will sublime and diffuse back into the atmosphere dessicating the regolith to a depth of about 1 to 2 m equatorward of 60 to 70 latitude in the high latitude regions these oscillations are considerably subdued below this depth of cyclic saturation and dessication a long term stability of ice exists in some geographic regions we present a map of the distribution of ice expected at the present epoch cyclic exchange of water between the global regolith and polar regions will have significant implications for surface geology and the polar layered deposits

dependence of secondary crater characteristics on downrange distance high resolution morphometry and simulations on average secondary impact craters are expected to deepen and become more symmetric as impact velocity vi increases with downrange distance l we have used high resolution topography 1 2 m pixel to characterize the morphometry of secondary craters as a function of l for several well preserved primary craters on mars the secondaries in this study n 2 643 span a range of diameters 25 m d 400 m and estimated impact velocities 0 4 km s vi 2 km s the range of diameter normalized rim to floor depth d d broadens and reaches a ceiling of d d 0 22 at l 280 km vi 1 1 2 km s whereas average rim height shows little dependence on vi for the largest craters h d 0 02 d 60 m populations of secondaries that express the following morphometric asymmetries are confined to regions of differing radial extent planform elongations l 110 160 km taller downrange rims l 280 km and cavities that are deeper uprange l 450 500 km populations of secondaries with lopsided ejecta were found to extend to at least l 700 km impact hydrocode simulations with isale 2d for strong intact projectile and target materials predict a ceiling for d d vs l whose trend is consistent with our measurements this study illuminates the morphometric transition from subsonic to hypervelocity cratering and describes the initial state of secondary crater populations this has applications to understanding the chronology of planetary surfaces and the long term evolution of small crater populations

neogene and quaternary rollback evolution of the tyrrhenian sea the apennines and the sicilian maghrebides reconstruction of the evolution of the tyrrhenian sea shows that the major stage of rifting associated with the opening of this basin began at similar to10 ma it involved two episodes of back arc extension which were induced by the rollback of a west dipping subducting slab the first period of extension 10 6 ma was prominent in the northern tyrrhenian sea and in the western part of the southern tyrrhenian sea the second period of extension mainly affected the southern tyrrhenian sea began in the latest messinian 6 5 ma and has been accompanied by subduction rollback at rates of 60 100 km myr 1 slab reconstruction combined with paleomagnetic and paleogeographic constraints indicates that in the central apennines the latest messinian 6 5 ma arrival of a carbonate platform at the subduction zone impeded subduction and initiated a slab tear and major strike slip faults these processes resulted in the formation of a narrow subducting slab beneath the ionian sea that has undergone faster subduction rollback and induced extreme rates of back arc extension

martian cratering vi crater count isochrons and evidence for recent volcanism from mars global surveyor this paper develops a methodology to establish absolute martian ages by deriving isochrons on a plot of martian impact crater density vs crater diameter calibrated by lunar crater age data the isochrons illustrated here are based on a mars moon cratering ratio of 1 6 at constant size but there is a factor of 2 to 4 uncertainty in this ratio and the consequent model ages martian crater diameter distributions are determined in several areas down to diameter d 16 45 m the shapes of the curves in young areas are found to be close to that of the predicted isochrons and close to the standard production function found by neukum the youngest areas studied here display the lunar like production function down to d 30 m where saturation equilibrium sets in model crater retention ages of several volcanic units are found to be a few hundred million years or less with estimated uncertainties ranging from a factor of 2 lower to a factor of 4 higher the results are consistent with martian meteorite ages volcanism on mars has probably persisted into the last 10 to 15 of the planet s history and is likely ongoing because surfaces as young as a few hundred million years have reached crater saturation equilibrium at d 60 to 100 m mars is likely to have widespread impact produced regoliths at least a few meters deep and this may contribute to the widespread mobile dust and boulder fields of mars

the morphology of small fresh craters on mars and the moon the depth diameter ratio for new meter to decameter scale martian craters formed in the last 20 years averages 0 23 only slightly deeper than that expected for simple primary craters on rocky surfaces large variations in depth diameter d d between impact sites indicate that differences between the sites such as target material properties impact velocity angle and physical state of the bolide s are important in determining the depth of small craters in the strength regime on the moon the d d of random fresh small craters with similar diameters averages only 0 10 indicating that either the majority of them are unrecognized secondaries or some proportion are degraded primaries older craters such as these may be shallower due to erosional infilling which is probably not linear over time but more effective over recently disturbed and steeper surfaces processes that are not yet acting on the new martian craters brand new meter to decameter scale craters such as the martian ones studied here are statistically easily distinguishable as primaries but the origins of older craters of the same size such as the lunar ones in this study are ambiguous

interaction of binary tropical cyclones in a coupled tropical cyclone ocean model the motion and evolution of binary tropical cyclones was investigated using a coupled tropical cyclone ocean movable nested grid model the model consists of eight layer atmospheric and seven layer ocean primitive equation models several regimes of binary storm interaction have been identified depending on the initial separation distance d and differences in storm strengths at d less than a few hundred kilometers interacting storms experienced complete merger cm or partial merger pm at larger d between about 600 km and 1000 km three regimes of storm interaction have been found pm straining out so characterized by complete disintegration of the weaker storm and mutual straining out mso characterized by weakening and dissipation of both storms so occurred when the interacting storms had substantially different intensities and strengths mso was observed when the interacting storms were comparable in size and intensity in the latter case the storms were unable to approach each other at distances smaller than a certain minimum distance of about 450 500 km without being mutually stretched out moreover initial attraction of the storms in this regime was replaced by repulsion as frequently observed in the western pacific at d exceeding about 1000 km elastic interaction ei was found when the storms interact without any significant changes in their intensity and structure in additional experiments with a conditional instability of the second kind cisk type parameterization of convective heating the storm interaction was very different the storms were nearly axisymmetric and very compact and they continued approaching each other until they merged thus more realistic simulations of binary storm interaction can be achieved by using a physically more reasonable convective parameterization

the global topography of mars and implications for surface evolution elevations measured by the mars orbiter laser altimeter have yielded a high accuracy global map of the topography of mars dominant features include the low northern hemisphere the tharsis province and the hellas impact basin the northern hemisphere depression is primarily a long wavelength effect that has been shaped by an internal mechanism the topography of tharsis consists of two broad rises material excavated from hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary the present topography has three major drainage centers with the northern lowlands being the largest the two polar cap volumes yield an upper limit of the present surface water inventory of 3 2 to 4 7 million cubic kilometers

hurricane generated depth averaged currents and sea surface elevation abstract a theory of the depth averaged currents and sea surface elevation generated by a moving hurricane in a stratified ocean with flat bottom is presented using a scale analysis of the depth integrated momentum and continuity equations it is found that the depth averaged currents are nearly nondivergent and determined entirely by the wind stress curl earth s rotation and ocean stratification have negligible effects the sea surface elevation is decomposed into four physically different parts caused by geostrophic adjustment to the depth averaged currents wind stress divergence inverted barometer offset and baroclinic effects when a hurricane moves with a uniform speed it generates quasi stationary alongtrack elongated depth averaged currents the sea surface elevation remaining after the hurricane passage is a combination of a trough geostrophically adjusted with the depth averaged currents and a sea surface elevation associated with baroclinic effects the barotropic response is analysed fo

mapping rays and secondary craters from the martian crater zunil 1 zunil a 10 1 km rayed crater in elysium planitia mars produced more than 7 107 secondary craters 15 m in diameter we mapped zunil s rays from thermal ir themis nighttime images up to 1700 km from the primary crater and mapped bright and dark ejecta craters candidate secondaries up to 3600 km range ray segments were mapped up to 450 km east of zunil and up to 1700 km to the west both rays and bright ejecta craters are best detected over terrains with moderate thermal inertia which are abundant west of but not east of zunil nevertheless our interpretation is that zunil was created by a moderately oblique impact from the east zunil secondaries are abundant over all terrain types except the medusae fossae formation mff given the likely age of zunil 100 ma parts of the mff must be eroding at 0 08 m ma the size frequency distribution of the secondaries in zunil s rays and probable distant secondaries 750 1700 km to the west of zunil have a cumulative power law exponent near 5 whereas secondaries between the major rays have an exponent near 3 4 we modeled the size velocity relationship for zunil s ejected fragments it is consistent with the predictions of melosh 1984 for spallation of a strong surface layer and demonstrates that the inverse size velocity correlation continues up to at least 2 km s

the origin of lunar crater rays abstract lunar rays are filamentous high albedo deposits occurring radial or subradial to impact craters the nature and origin of lunar rays have long been the subjects of major controversies we have determined the origin of selected lunar ray segments utilizing earth based spectral and radar data as well as feo tio 2 and optical maturity maps produced from clementine uvvis images these include rays associated with tycho olbers a lichtenberg and the messier crater complex it was found that lunar rays are bright because of compositional contrast with the surrounding terrain the presence of immature material or some combination of the two mature compositional rays such as those exhibited by lichtenberg crater are due entirely to the contrast in albedo between ray material containing highlands rich primary ejecta and the adjacent dark mare surfaces immaturity rays are bright due to the presence of fresh high albedo material this fresh debris was produced by one or more of the following 1 the emplacement of immature primary ejecta 2 the deposition of immature local material from secondary craters 3 the action of debris surges downrange of secondary clusters and 4 the presence of immature interior walls of secondary impact craters both composition and state of maturity play a role in producing a third combination class of lunar rays the working distinction between the eratosthenian and copernican systems is that copernican craters still have visible rays whereas eratosthenian aged craters do not compositional rays can persist far longer than 1 1 ga the currently accepted age of the copernican eratosthenian boundary hence the mere presence of rays is not a reliable indication of crater age the optical maturity parameter should be used to define the copernican eratosthenian boundary the time required for an immature surface to reach the optical maturity index saturation point could be defined as the copernican period

dating small fresh lunar craters with mini rf radar observations of ejecta blankets 1 the ages of large impact craters on the moon can be estimated by measuring the size frequency distribution of smaller craters superimposed on their ejecta but applying this method to individual craters under 3 km in diameter remains difficult due to their limited areal extent the ejecta blankets of fresh lunar impact craters are expressed as halos of optical and radar bright material that gradually fade with time although compositional differences make inferring crater ages from optical albedo problematic radar is less sensitive to composition and thus may provide a more reliable means of estimating age in this work we use radar data from the miniature radio frequency mini rf instrument on the lunar reconnaissance orbiter lro to characterize the radar backscatter of large numbers of ejecta blankets by analyzing the size frequency distribution of these craters we show that the lifetime of the radar bright discontinuous ejecta blanket varies with crater diameter in a predictable way for craters with diameters between 0 45 and 5 km absolute ages of individual craters can then be estimated by combining this empirically derived model with estimates of the relative degradation state of each individual crater the lifetimes of radar bright discontinuous ejecta blankets are significantly shorter in the highlands than the maria although this is likely due to local topography creating difficulties in applying the method to the highlands the cosmic ray exposure age of south ray crater a fresh crater visited by apollo 16 provides confirmation of these results this method therefore provides a new way to accurately date small fresh craters using the mini rf data set

the presence and stability of ground ice in the southern hemisphere of mars abstract we calculate new estimates of ground ice stability and the depth distribution of the ice table the depth boundary between ice free soil above and ice cemented soil below and compare these theoretical estimates of the distribution of ground ice with the observed distribution of leakage neutrons measured by the neutron spectrometer instrument of the mars odyssey spacecraft s gamma ray spectrometer instrument suite our calculated ground ice distribution contains improvements over previous work in that we include the effects of the high thermal conductivity of ice cemented soil at and below the ice table we include the surface elevation dependence of the near surface atmospheric humidity and we utilize new high resolution maps of thermal inertia albedo and elevation from mars global surveyor observations results indicate that ground ice should be about 5 times shallower than in previous predictions while results are dependent on the atmospheric humidity depths are generally between a few millimeters and a few meters with typical values of a few centimeters results are also geographically similar to previous predictions with differences due to the higher resolution of thermal inertia and the inclusion of elevation effects on humidity comparison with the measured epithermal neutron count rates in the southern hemisphere indicate that the geographic distribution of the count rate is best correlated with ground ice in equilibrium with 10 to 20 pr m precipitable micrometers column abundance of atmospheric water assuming a uniform distribution with co2 however given the uncertainties 5 to 30 pr m also may be viable this water abundance represents a longer term average over 100 to 1000 yr there is a high degree of correlation between the depth of the ice table and the epithermal count rate that agrees remarkably well with predicted count rates as a function of ice table depth these results indicate that ground ice in the upper meter of the martian soil is in diffusive equilibrium with the atmosphere since ground ice in this depth zone is expected to undergo saturation desiccation cycles with orbital variations this ice should be younger than about 500 kyr and was emplaced under similar cold and dry climate conditions of today remaining differences between the predicted depths of the ice table and those inferred from the neutron data are likely to be due to subpixel heterogeneity in the martian surface including the presence of rocks slopes and patches of soil with varying thermophysical properties

slope streak formation and dust deposition rates on mars 1 the mars orbiter camera moc has imaged sometimes repeatedly mass movements known as slope streaks which are abundant in the dust covered regions on mars they are among the few known examples of contemporary surface changes a survey of 173 collocated image pairs indicates that these features are currently forming at a high rate of 7 per existing streak per martian year either there is a complete turnover within a few decades or the streak population is currently increasing rapidly large spatial as well as possible temporal variations in the formation rate are obtained from these data streaks do not appear to fade over time periods comparable to their inverse formation rate of 28 years as seen by analysis of viking orbiter images containing streaks that are still visible in moc images gradual or stochastic variations in dust deposition may be needed to explain observations of changes in the formation rate and its current imbalance with the fading rate

present day post glacial sea level change far from the late pleistocene ice sheets implications for recent analyses of tide gauge records we examine the sensitivity of predictions of the present day rate of sea level change due to glacial isostatic adjustment gia in two regions located within the far field of the late pleistocene ice sheets europe north africa and the western pacific caribbean to variations in the mantle viscosity profile the regions considered here encompass the location of 11 of 21 sites used in a recent determination based on gia corrected tide gauge records of the global rate of secular sea level change our analysis suggests that the mean gia correction at the 11 far field sites may vary by as much as 0 5 mm yr depending on the adopted earth model and we derive a bound on the residual secular sea level rise of 1 1 to 1 6 mm yr this bound is consistent with our analysis of the tide gauge record from the u s east coast and it suggests that previous estimates of the residual sea level rise represent an upper bound