a new look at the saturn system the voyager 2 images voyager 2 photography has complemented that of voyager i in revealing many additional characteristics of saturn and its satellites and rings saturn s atmosphere contains persistent oval cloud features reminiscent of features on jupiter smaller irregular features track out a pattern of zonal winds that is symmetric about saturn s equator and appears to extend to great depth winds are predominantly eastward and reach 500 meters per second at the equator titan has several haze layers with significantly varying optical properties and a northern polar collar that is dark at short wavelengths several satellites have been photographed at substantially improved resolution enceladus surface ranges from old densely cratered terrain to relatively young uncratered plains crossed by grooves and faults tethys has a crater 400 kilometers in diameter whose floor has domed to match tethys surface curvature and a deep trench that extends at least 270 around tethys circumference hyperion is cratered and irregular in shape iapetus bright trailing hemisphere includes several dark floored craters and phoebe has a very low albedo and rotates in the direction opposite to that of its orbital revolution with a period of 9 hours within saturn s rings the birth of a spoke has been observed and surprising azimuthal and time variability is found in the ringlet structure of the outer b ring these observations lead to speculations about saturn s internal structure and about the collisional and thermal history of the rings and satellites

clouds and hazes vertical structure of a saturn s giant vortex from cassini vims v data analysis abstract we studied the evolution of a giant tropospheric vortex formed in the wake of the storm that encircled saturn from december 2010 to july 2011 fletcher et al 2011a science 332 1413 1417 fletcher et al 2012 icarus 221 560 586 sanchez lavega et al 2011 nature 475 71 74 sanchez lavega et al 2012 icarus 220 561 576 sayanagi et al 2013 icarus 223 460 478 fischer et al 2011 nature 475 75 77 taking advantage of the observations acquired by the instruments on board the cassini spacecraft in particular the visual and infrared mapping spectrometer vims imaged the vortex several times in this work we analyzed two observations registered by the visual channel of vims vims v on 08 24 2011 and 01 04 2012 both after the active phase of the storm and characterized quantitatively the vertical structure of the clouds and hazes above the vortex until now vims v dataset has been scarcely exploited to perform such an analysis the ir channel of vims has always been preferred since it covers wavelengths containing spectral information on a wider range of altitudes in the atmosphere nevertheless in our analysis we investigate the information content of vims v observations and demonstrate that the covered spectral range contains valuable information that are helpful to improve our knowledge on the properties of saturn s upper atmosphere we developed a forward radiative transfer model to describe saturn s atmosphere and simulate vims v spectra in the 0 35 1 05 m wavelength range the analysis has then been performed by means of an inverse model that we built on the basis of the bayesian approach spatial distributions of effective radii column number densities and top pressures of the cloud decks have been mapped and as a by product of our analysis we also suggest a modified spectral shape for the imaginary part of the refractive index of the tropospheric haze with respect to the shape described in the study of karkoschka and tomasko 2005 icarus 179 195 221 the results suggest that the processes responsible for the formation and persistence of the vortex weakened between august 2011 and january 2012 even if the differences that we observe could be due to the fact that the vortex has moved in different positions between the two dates we found that in august 2011 the upper haze was arranged in a dome like structure with the center at 8 mbar and the boundaries at 12 mbar moreover we detected a zone in the lower haze at 135 mbar characterized by higher optical thickness with respect to the surrounding regions located at 85 mbar in january 2012 the dome in the upper layer has diluted into a more homogeneous structure and the haze appears to be overall shifted to less than 6 mbar similarly the 135 mbar high optical depth zone previously detected in the lower layer has disappeared

potential field inversion for a layer with uneven thickness the tyrrhenian sea density model abstract inversion of large scale potential field anomalies aimed at determining density or magnetization is usually made in the fourier domain the commonly adopted geometry is based on a layer of constant thickness characterized by a bottom surface at a fixed distance from the top surface we propose a new method to overcome this limiting geometry by inverting in the usual iterating scheme using top and bottom surfaces of differing but known shapes randomly generated synthetic models will be analyzed and finally performance of this method will be tested on real gravity data describing the isostatic residual anomaly of the southern tyrrhenian sea in italy the final result is a density model that shows the distribution of the oceanic crust in this region which is delimited by known structural elements and appears strongly correlated with the oceanized abyssal basins of vavilov and marsili

a geomagnetic record over the last 3 5 million years from deep tow magnetic anomaly profiles across the central indian ridge high resolution records of the geomagnetic field intensity over the last 4 myr provided by paleomagnetic analyses of marine sediments have shown the occurrence of short lived low field intensity features associated with excursions or short polarity intervals in order to evaluate the ability of marine magnetic anomalies to record the same geomagnetic events we have collected six deep tow 500 m above the seafloor and several sea surface magnetic anomaly profiles from the central indian ridge across the brunhes matuyama and gauss chrons i e from the ridge axis to anomaly 2a after removal of topography latitude and azimuth effects we converted distances into time sequences using well dated polarity reversal anomalies as tie points we calculated the average signal to test the robustness of the short wavelength anomalies the resulting stacked profile is very similar to stacked sea surface and downward continued profiles from the central indian ridge the east pacific rise and the pacific antarctic ridge our results suggest that in addition to polarity reversals to previously suggested geomagnetic events subchrons or excursions within the brunhes and matuyama chrons a new small scale magnetic anomaly likely generated by several closely spaced geomagnetic field intensity variations represent the major contributor to the detailed shape of recent marine magnetic anomalies in investigated areas we observe a dense succession of microanomalies that are correlated excursions ontong java 1 and 2 and gilsa is found after the olduvai chron the near bottom results support the existence of three geo magnetic features between the gauss matuyama boundary and olduvai they also suggest three geomagnetic events during the c2a i n subchron within the gauss chron this study emphasizes the potential of deep tow magnetic surveys in detecting fluctuations in geo magnetic field intensity and in particular short lived excursions a poorly constrained part of the geomagnetic field temporal variation spectrum

saturn s zonal winds at cloud level we present an analysis of new cloud motion measurements in saturn s atmosphere from voyager 1 and 2 images and define a nominal zonal wind velocity vs latitude profile for the cloud top level that can be used as reference for the upcoming cassini mission improvements over previous studies include i twice the number of wind vectors used ii independent measurements of cloud tracers iii extended latitudinal coverage iv strict error control and evaluation and v a new zonal averaging methodology mean zonal wind velocities are given for the latitude range 81 to 71 planetographic in steps of 0 5 with a gap between 0 and 10 due to ring shadowing this research also includes the study of the morphology and motions of cloud systems in the equator and in the southern hemisphere which have not been described previously we give an ephemeris motion equation for several long lived features that could be observable if they survive until cassini arrives on saturn the long term behavior of the zonal wind profile is studied by comparing it with a complete set of wind velocities compiled from historical and modern ground based and hst observations significant changes are noted in the equatorial jet between this set and the nominal voyager profile we discuss in detail the possible origin for such differences

dynamics of saturn s south polar vortex the camera onboard the cassini spacecraft has allowed us to observe many of saturn s cloud features we present observations of saturn s south polar vortex spv showing that it shares some properties with terrestrial hurricanes cyclonic circulation warm central region the eye surrounded by a ring of high clouds the eye wall and convective clouds outside the eye the polar location and the absence of an ocean are major differences it also shares properties with the polar vortices on venus such as polar location cyclonic circulation warm center and long lifetime but the venus vortices have cold collars and are not associated with convective clouds the spv s combination of properties is unique among vortices in the solar system

testing and application of a model for snow redistribution snow_blow in the ellsworth mountains antarctica wind driven snow redistribution can increase the spatial heterogeneity of snow accumulation on ice caps and ice sheets and may prove crucial for the initiation and survival of glaciers in areas of marginal glaciation we present a snowdrift model snow blow which extends and improves the model of purves mackaness and sugden 1999 journal of quaternary science 14 313 321 the model calculates spatial variations in relative snow accumulation that result from variations in topography using a digital elevation model dem and wind direction as inputs improvements include snow redistribution using a flux routing algorithm dem resolution independence and the addition of a slope curvature component this paper tests snow blow in antarctica a modern environment and reveals its potential for application in palaeoenvironmental settings where input meteorological data are unavailable and difficult to estimate specifically snow blow is applied to the ellsworth mountains in west antarctica where ablation is considered to be predominantly related to wind erosion processes we find that snow blow is able to replicate well the existing distribution of accumulating snow and snow erosion as recorded in and around blue ice areas lastly a variety of model parameters are tested including depositional distance and erosion vs wind speed to provide the most likely input parameters for palaeoenvironmental reconstructions

uranus southern circulation revealed by voyager 2 unique characteristics abstract revised calibration and processing of 1600 images of uranus by voyager 2 revealed dozens of discrete features south of 45 latitude where only a single feature was known from voyager images and none has been seen since tracking of these features over five weeks defined the southern rotational profile of uranus with high accuracy and no significant gap the profile has kinks unlike previous profiles and is strongly asymmetric with respect to the northern profile by sromovsky et al sromovsky l a fry p m hammel h b de pater i rages k a 2012 icarus 220 694 712 the asymmetry is larger than that of all previous data on jovian planets a spot that included the south pole off center rotated with a period of 12 24 h 2 h outside the range of all previous observations of uranus the region between 68 and 59 latitude rotated almost like a solid body with a shear that was about 30 times smaller than typical shears on uranus at lower latitudes features were sheared into tightly wound spirals as voyager watched the zone at 84 latitude was exceptionally bland reflectivity variations were only 18 ppm consistent with a signal to noise ratio estimated at 55 000 the low noise was achieved by smoothing over dozens of pixels per image and averaging 1600 images the presented data set in eight filters contains rich information about temporal evolution and spectral characteristics of features on uranus that will be the basis for further analysis

the structure and temporal stability of jupiter s zonal winds a study of the north tropical region abstract this paper investigates possible long term zonal wind variations using voyager 1979 hubble space telescope hst 1995 1997 1998 and galileo orbiter 1997 data that has all been processed and analyzed in the same manner for consistency previous attempts to measure the zonal wind profile in voyager data had yielded inconsistent results for the maximum eastward jet near 23 7 n latitude from different studies a p ingersoll et al 1979 nature 280 773 775 ibid 1981 j geophys res 86 8733 8743 t maxworthy 1984 planet space sci 32 1053 1058 s limaye 1986 icarus 65 335 352 this paper compares previous measurements and includes new independent analysis to conclude that the correct wind jet velocity at the time of voyager is close to 182 m s 1 most consistent with the reported results of maxworthy 1984 in the data sets from different epochs the overall shape of the wind profile and locations of the prograde and retrograde jets remain constant but there are amplitude changes at a few latitudes the largest velocity deviations between the voyager and the 1995 1997 hst profiles occurred in the maximum eastward jet near 23 7 n and at 6 s and 20 s planetographic latitude possible causes for an apparent zonal wind decrease were explored using galileo visible and hst near infrared data and the wind velocity change was determined to be real a very definite change in cloud structure and brightness has also occurred at 23 7 n additionally surface brightness changes seen at 6 s and 20 s also correlated with changes in wind speed hst wfpc2 data obtained in 1998 showed the recovery of the 23 7 n region to a voyager like appearance and an increase in wind velocity to the voyager value

magnetic anomalies at the puna ridge a submarine extension of kilauea volcano implications for lava deposition high resolution magnetic data collected along the axis and the south flank of the puna ridge the submarine extension of the east rift zone of kilauea volcano hawaii aid in the interpretation of magmatic processes crustal magnetization varies along the crest of the puna ridge three prominent magnetization highs are located between the depths of 1500 and 2500 m each of the magnetization highs is associated with distinct volcanic features a flow field on top of fissured terrain a lava plateau and a staircase of lava terraces the crustal magnetization highs can be explained by the presence of these volcanic features taking into account water depth and the size of the volcanic features and making simple assumptions about the rock magnetization no measurements of rock magnetization have been made on puna ridge samples we assume two values 50 and 10 a m based on values from mid ocean ridge basalts and the estimated ages of puna ridge rocks clague et al 1995 the two shallowest magnetization highs are adjacent to a landslide scarp lava flows overtop the scarp suggesting that a dike has been emplaced and eruptions have occurred since the landslide formed a possible scenario is that the collapse of the flank led to dike intrusion and eruption at this location because of a reduction in the horizontal stress within the edifice our observations suggest that flows are starting to fill in the gap caused by the landslide to rebuild this section of the north flank

saturn s cloud structure and temporal evolution from ten years of hubble space telescope images 1994 2003 abstract we present a study of the vertical structure of clouds and hazes in the upper atmosphere of saturn s southern hemisphere during 1994 2003 about one third of a saturn year based on hubble space telescope images the photometrically calibrated wfpc2 images cover the spectral region between the near uv 218 255 nm and the near ir 953 1042 nm including the 890 nm methane band using a radiative transfer code we have reproduced the observed center to limb variations in absolute reflectivity at selected latitudes which allowed us to characterize the vertical structure of the entire hemisphere during this period a model atmosphere with two haze layers has been used to study the variation of hazes with latitude and to characterize their temporal changes both hazes are located above a thick cloud putatively composed of ammonia ice an upper thin haze in the stratosphere between 1 and 10 mbar is found to be persistent and formed by small particles radii 0 2 m the lower thicker haze close to the tropopause level shows a strong latitudinal dependence in its optical thickness typically 20 40 at the equator but 5 at the pole at 814 nm this tropospheric haze is blue absorbent and extends from 50 to 100 mbar to about 400 mbar both hazes show temporal variability but at different time scales first there is a tendency for the optical thickness of the stratospheric haze to increase at all latitudes as insolation increases second the tropospheric haze shows mid term changes over time scales from months to 1 2 years in its optical thickness typically by a factor of 2 such changes always occur within a rather narrow latitude band width 5 10 affecting almost all latitudes but at different times third we detected a long term 10 year decrease in the blue single scattering albedo of the tropospheric haze particles most intense in the equatorial and polar areas long term changes follow seasonal insolation variations smoothly without any apparent delay suggesting photochemical processes that affect the particles optical properties as well as their size in contrast mid term changes are sudden and show various time scales pointing to a dynamical origin

cassini iss observation of saturn s north polar vortex and comparison to the south polar vortex we present analyses of saturn s north pole using high resolution images captured in late 2012 by the cassini spacecraft s imaging science subsystem iss camera the images reveal the presence of an intense cyclonic vortex centered at the north pole in the red and green visible continuum wavelengths the north polar region exhibits a cyclonically spiraling cloud morphology extending from the pole to 85 n planetocentric latitude with a 4700 km radius images captured in the methane bands which sense upper tropospheric haze show an approximately circular hole in the haze extending up to 1 5 latitude away from the pole the spiraling morphology and the eye like hole at the center are reminiscent of a terrestrial tropical cyclone in the system iii reference frame rotation period of 10h39m22 4s seidelmann et al 2007 archinal et al 2011 the eastward wind speed increases to about 140 m s 1 at 89 n planetocentric latitude the vorticity is 6 5 1 5 10 4 s 1 at the pole and decreases to 1 3 1 2 10 4 s 1 at 89 n in addition we present an analysis of saturn s south polar vortex using images captured in january 2007 to compare its cloud morphology to the north pole the set of images captured in 2007 includes filters that have not been analyzed before images captured in the violet filter 400 nm also reveal a bright polar cloud the south polar morphology in 2007 was more smooth and lacked the small clouds apparent around the north pole in 2012 saturn underwent equinox in august 2009 the 2007 observation captured the pre equinox south pole and the 2012 observation captured the post equinox north pole thus the observed differences between the poles are likely due to seasonal effects if these differences indeed are caused by seasonal effects continuing observations of the summer north pole by the cassini mission should show a formation of a polar cloud that appears bright in short wavelength filters

an objective classification of saturn cloud features from cassini iss images abstract a k means clustering algorithm is applied to cassini imaging science subsystem continuum and methane band images of saturn s northern hemisphere to objectively classify regional albedo features and aid in their dynamical interpretation the procedure is based on a technique applied previously to visible infrared images of earth it provides a new perspective on giant planet cloud morphology and its relationship to the dynamics and a meteorological context for the analysis of other types of simultaneous saturn observations the method identifies 6 clusters that exhibit distinct morphology vertical structure and preferred latitudes of occurrence these correspond to areas dominated by deep convective cells low contrast areas some including thinner and thicker clouds possibly associated with baroclinic instability regions with possible isolated thin cirrus clouds darker areas due to thinner low level clouds or clearer skies due to downwelling or due to absorbing particles and fields of relatively shallow cumulus clouds the spatial associations among these cloud types suggest that dynamically there are three distinct types of latitude bands on saturn deep convectively disturbed latitudes in cyclonic shear regions poleward of the eastward jets convectively suppressed regions near and surrounding the westward jets and baroclinically unstable latitudes near eastward jet cores and in the anti cyclonic regions equatorward of them these are roughly analogous to some of the features of earth s tropics subtropics and midlatitudes respectively this classification may be more useful for dynamics purposes than the traditional belt zone partitioning temporal variations of feature contrast and cluster occurrence suggest that the upper tropospheric haze in the northern hemisphere may have thickened by 2014 the results suggest that routine use of clustering may be a worthwhile complement to many different types of planetary atmospheric data analysis

large scale storms in saturn s atmosphere during 1994 large scale storms are rarely observed in saturn s atmosphere but their appearance traces the wind velocity field providing information on the vertical structure of the clouds and on the dynamics of the atmosphere two large scale atmospheric disturbances formed by clouds highly reflective in the visible part of the spectrum were observed on saturn during 1994 an equatorial disturbance with a longitudinal size of 27 000 kilometers drifted in longitude with a velocity of 273 6 meters per second a second disturbance a rapidly evolving convective storm with an initial size 7000 kilometers was observed at 56 degrees south moving with a zonal velocity of 15 5 meters per second

extremely asymmetric magmatic accretion of oceanic crust at the ends of slow spreading ridge segments we report the results of a deep towed magnetic survey of part of a mid atlantic ridge spreading segment analysis of the magnetic reversals indicates that for the past 0 7 m y magmatic accretion at the end of the segment has been effectively one sided with new crust being added only to the outside corner of the ridge offset eastern flank and not to the inside corner western flank spreading on the inside corner was accommodated by significant displacement on a single large fault the area between the fault and the axial volcanic ridge was effectively a thin static sliver at the plate boundary during this process in the short term asymmetric magmatic accretion was probably accomplished by progressively shifting the axial volcanic ridge to a new location at the inside corner western edge of the old one asymmetric spreading is unlikely to be sustainable as a steady state process the termination of a period of asymmetric spreading may be achieved either by establishing a new axial volcanic ridge to a position on the outside corner eastern plate thus isolating the old axial volcanic ridge on the inside corner plate or by simply arresting movement on the large fault and reverting to symmetric spreading at the axial volcanic ridge highly asymmetric accretion may be a common process at slow spreading segments particularly near discontinuities this asymmetry cannot be maintained for long periods and may be directly linked to intervals of spreading by tectonic extension

haze and cloud structure of saturn s north pole and hexagon wave from cassini iss imaging abstract in this paper we present a study of the vertical haze and cloud structure in the upper two bars of saturn s northern polar atmosphere using the imaging science subsystem iss instrument onboard the cassini spacecraft we focus on the characterization of latitudes from 53 to 90 n the observations were taken during june 2013 with five different filters vio bl1 mt2 cb2 and mt3 covering spectral range from the 420 nm to 890 nm in a deep methane absorption band absolute reflectivity measurements of seven selected regions at all wavelengths and several illumination and observation geometries are compared with the values produced by a radiative transfer model the changes in reflectivity at these latitudes are mostly attributed to changes in the tropospheric haze this includes the haze base height from 600 200 mbar at the lowest latitudes to 1000 300 mbar in the pole its particle number density from 20 2 particles cm3 to 2 0 5 particles cm3 at the haze base and its scale height from 18 0 1 km to 50 0 1 km we also report variability in the retrieved particle size distribution and refractive indices we find that the hexagonal wave dichotomizes the studied stratospheric and tropospheric hazes between the outer equatorward regions and the inner polar regions this suggests that the wave or the jet isolates the particle distribution at least at tropospheric levels

cloud features and zonal wind measurements of saturn s atmosphere as observed by cassini vims 1 we present an analysis of data about saturn s atmosphere from cassini s visual and infrared mapping spectrometer vims focusing on the meteorology of the features seen in the 5 m spectral window we present vims mosaics and discuss the morphology and general characteristics of the features backlit by saturn s thermal emission we have also constructed a zonal wind profile from vims feature tracking observation sequences using an automated cloud feature tracker comparison with previously constructed profiles from voyager and cassini imaging data reveals broad similarities suggesting minimal vertical shear of the zonal wind however areas of apparent wind shear are present in the vims zonal wind profile at jet stream cores in particular our analysis shows that the equatorial jet reaches speeds exceeding 450 m s 1 similar to speeds obtained during the voyager era this suggests that recent inferences of relatively slower jet speeds of 275 375 m s 1 are confined to the upper troposphere and that the deep 1 bar jet has not experienced a significant slowdown our measurements of the numerous dark spotted features seen in the vims mosaics reveals that most of these features have diameters less than 1000 km and reside in confined zonal bands between jet stream cores we propose that these spot features are vortices and that vims and imaging science subsystem are sensing the same vortices at two different pressure levels the local structure at the zonal jet streams remains complex as vims may be sensing cloud features that are deeper than the nh3 cloud deck

locating the spreading axis along 80 km of the mid atlantic ridge south of the atlantis transform the zone of active eruptive fissuring the spreading axis is investigated at an accretionary segment of the mid atlantic ridge high resolution side scan images are used to produce a detailed geologic map of the median valley floor of segment 18 located immediately south of the atlantis transform 30 n the spreading axis is defined by distinguishing between primary eruptive vents seamounts and hummocky ridges fed by underlying dikes and secondary vents seamounts and terraces fed from lava tubes or channels and is found to be about 2 km wide or less along the entire segment it is impossible to narrow the width further with the data we have in hand for comparison at faster spreading ridges such as the east pacific rise the spreading axis is generally equated to the width of the axial summit trough typically 50 100 m wide within the brunhes anomaly the high resolution structure of the central anomaly magnetic high camh obtained from several cross axis deep tow tracks is used to define regions of recent major volcanism the locations of the camh peaks generally conform to our pick of the spreading axis in some places the peaks are located several kilometers away from the spreading axis possibly indicating that large volumes of lava have been deposited there our interpretation of many volcanic structures as secondary vents at segment 18 leads to the conclusion that lava channels and tubes commonly develop to transport lava to these off axis deposition sites

geomagnetic field variability during the cretaceous normal superchron during the cretaceous normal superchron 121 83 million years ago the polarity of the earth s geomagnetic field remained stable for an unusually long time deep tow magnetic data suggest that despite the stability of the polarity the field varied greatly throughout the interval

a study of the stability of jovian zonal winds from hst images 1995 2000 abstract we present a five year study of the temporal stability of jupiter s zonal wind velocity profile at cloud level based on hubble space telescope images obtained from 1995 to 2000 we used the correlation of east west albedo scans in pairs of images separated by one jovian rotation to retrieve the zonal winds the resolution in the hst images ranged from 140 to 190 km pixel 1 independent measurements of the motions of individual cloud tracers were used to control the above profiles three wavelengths were used in this analysis 410 nm violet continuum 892 nm methane absorption band and 953 nm red continuum our study indicates that globally jupiter s zonal flow did not change during this five year interval and it does not depend on the observed wavelengths when comparing our mean profile with that obtained 16 years ago using voyager data we find a reasonable agreement we note however a small shift in the latitude of the jets poleward of latitude 30 probably due to image navigation uncertainties however true changes in the intensity of the jets at 24 n and 32 n are found results also indicate that the 7 s jet has remained stable since the voyager era in addition we extend in this paper our previous study of the 24 n with new data from year 2000 the new data confirm the jet s stability during the 1995 2000 period finally we present the average profile for this period including error estimation in a table that extends the latitudinal coverage of limaye s 1986 icarus 65 335 352 voyager profile up to latitudes 68 s and 77 n

crustal magnetization of brothers volcano new zealand measured by autonomous underwater vehicles geophysical expression of a submarine hydrothermal system near bottom magnetic anomaly data have been acquired using autonomous underwater vehicles at brothers volcano southern kermadec arc new zealand crustal magnetization for the study area was obtained by inverting the magnetic data and shows a strong correlation between areas of low magnetization and four hydrothermal fields one of which was unknown prior to our surveys the magnetization pattern is consistent with a model of discrete individual zones of fluid upflow focused along caldera ring faults that provide preferred pathways for the ascent of the hydrothermal fluids differences in the amplitude of the magnetization over the vent fields appear to correlate with age and temperature variations of the hydrothermal fields

temporal behavior of cloud morphologies and motions in saturn s atmosphere saturn s atmosphere displays a variety of temporal changes in its cloud morphology at synoptic and planetary scales hemispheric long term albedo variations which are more pronounced at ultraviolet and blue wavelengths have been well established and are apparently linked to the seasonal insolation cycle short term changes of the order of months have been observed in the spectral reflectivity of the belt zone pattern mainly at mid latitudes some appear to be related to discrete spot activity but for the majority of the changes no such signs of spot activity were detected up to a resolution 2000 km in particular the ribbon structure at 45 n could have been affected by this activity and probably is a transient phenomenon the polar belts at 65 north and south and those at 75 north hexagon and south show a long term stability in their location perhaps for more than a century the most prominent belts located in the equator and the equatorial zone are persistent features of saturn s globe their main changes took place during the development of a rare planetary scale disturbance known as great white spots only five such events have been observed at repetitive regular intervals of about one saturn year since the first report in 1876 and at different latitudes from the equator to 60 n they are probably convective in origin with the seasonal heating of the upper atmosphere acting as a trigger mechanism during its life cycle of 2 3 years the disturbance shows turbulent planetary scale patterns of clouds that might be related to a wave dynamical phenomenon other distinct nonaxisymmetric cloud systems at synoptic scale are very scarce in saturn s atmosphere we observed new isolated features at several latitudes during 1990 and 1991 these spots together with those available from historical records are used as tracers for determining the latitude dependence and time variability of saturn s zonal winds the winds tend to exhibit a long term stability in their latitudinal positions and average wind speed although some significant departures from the zonal mean voyager profile have been detected during the development of the equatorial disturbance in 1990 and 1991

variations in layer 2a thickness and the origin of the central anomaly magnetic high the seismically determined off axis thickening of the extrusive layer is apparently at odds with the magnetic anomaly high t ypic ally associated with the ridge crest the positive magnenzauon contrast at the ridge crest is most likely caused by rapid alteration of the extrusive source layer which occurs over spatial scales 2 3 km comparable to that of the proposed layer 2a thickening we present magnetic rema nence data from basalts dredged on and near the east pacific rise axis at 12on which are compatible with a rapid magnetization reduction 20 k y to decay to l e together with near bottom magnetic profiles from the ultra fast spreading east pacific rise at 19 5os these data suggest that previous estimates of the time constant of alteration inferred from slow spreading ridges 0 5 m y may be more than an order of magnitude too high seismic studies of the fast spreading east pacific rise epr indicate a rapid thickening of seismic layer 2a within a few kilometers of the ridge axis vera et al 1990 toomey et ai 1990 detrick et al 1993 these seismic data have been interpreted to reflect an approximate doubling of the extrusive layer thickness from 100 200 m to 300 500 m through addition of flows whi ch may extend 1 2 km off axis christeson et al 992 vera and diebold in press such thickening of the extrusive source layer had been argued on the basis of the widths of magnetic reversal transitions e g macdonald et al 1983 however this geometry for a uniformly magnetized source layer should produce a marked magnetic anomaly minimum over the ridge axis and is therefore difficult to reconcile with the pronounced anomaly high typically associated with the ridge crest klitgord 1976 sea surface magnetic profiles from the ultra fast spreading 77 mrn yr half rate epr near 19 5os figure 1 illustrate the short wavelength axial anomaly high within the 120 km wide central anomaly which has been termed the central anomaly magnetic high camh klitgord 1976 the camh typically has a wavelength of 8 10 km in sea surface profiles at in termediate spreading ridges 15 45 mm yr the camh occupies a larger proportion of the central anomaly and at slow spreading ridges it is not readily distinguishable in sea surface profiles from the central anomaly because the wavelengths become similar near bottom magnetic profiles figure 1 typically have higher amplitude and shorter wavelength 2 4 kin axial anomalies as expected from the closer proximity to the source klitg6rd et al 1975 miller 1977 perram et al 1990 and even allow distinction of the camh from the central anomaly at some slow spreading ridges macdonald 1977 the higher temporal resolution of faster spreading ridges therefore provides the best opportunity to evaluate the processes responsible for the camh thickness variations in the extraslye layer at fast spreading fi dges have a profound effect on the axial magnetic anomaly since the presence of an axial magma chamber and the low re rnanent intensity of intrusive rocks e g smith and banerice 1986 pariso et al 1991 minimize deeper source contributions in the near ridge environment based on seismic

magnetic structure of a slow spreading ridge segment insights from near bottom magnetic measurements on board a submersible 1 near bottom magnetic measurements on board submersible nautile were carried out on the mid atlantic ridge 21 40 n segment and deep sea geomagnetic vector anomalies along 19 dive tracks were obtained by applying the processing method for shipboard three component magnetometer data a forward modeling technique using short wavelength components of the anomalies arising from local topography and vertical motion of the submersible was designed to estimate the absolute magnetization intensity of the seafloor in the vicinity of the spreading axis a considerable number of magnetization estimations are reliably confirmed by the high correlation between observed and modeled anomalies whereas less reliable estimations are obtained off axis probably because the sediment buries the basement topography the natural remanent magnetization nrm measured on basalt samples collected during these dives is compared with the magnetization from anomalies though both results give a similar range of magnetization intensity no correlation is confirmed between them possibly because the magnetization from anomalies represents laterally averaged seafloor magnetization whereas the nrm has variations at the scale of individual pillow or lava pile equivalent magnetization inverted from the sea surface magnetic anomalies shows axial magnetization increases significantly from the segment center to the segment ends however the results of eight dives conducted near the spreading axis at different locations along the segment show much less variation in magnetization intensity along the axis we ascribe the high equivalent magnetization at segment ends to preferential serpentinization of peridotite near the segment ends and the associated formation of magnetite the results of three across axis transects composed of 15 dives running in the spreading direction can be consistently interpreted as recording geomagnetic paleointensity variations during the brunhes epoch although magnetization lows are generally correspondent to periods of low paleointensity they show deeper drop than predicted from the paleointensity variation

dynamics of saturn s polar regions we analyze data retrieved by the imaging science system onboard the cassini spacecraft to study the horizontal velocity and vorticity fields of saturn s polar regions latitudes 60 90 n in june december 2013 and 60 90 s in october 2006 and july december 2008 including the northern region where the hexagonal wave is prominent with the aid of an automated two dimensional correlation algorithm we determine two dimensional maps of zonal and meridional winds and deduce vorticity maps we extract zonal averages of zonal winds providing wind profiles that reach latitudes as high as 89 5 in the south and 89 9 in the north wind measurements cover the intense polar cyclonic vortices that reach similar peak velocities of 150 m s 1 at 88 5 the hexagonal wave lies in the core of an intense eastward jet at planetocentric latitude 75 8 n with motions that become nonzonal at the hexagonal feature in the south hemisphere the peak of the eastward jet is located at planetocentric latitude 70 4 s a large anticyclone the south polar spot sps similar to the north polar spot nps observed at the voyager times 1980 1981 has been observed in images from april 2008 to january 2009 in the south polar region at latitude 66 1 close to the eastward jet the sps does not apparently excite a wave on the jet we analyze the stability of the zonal jets finding potential instabilities at the flanks of the eastward jets around 70 and we measure the eddy wind components suggesting momentum transfer from eddy motion to the westward jets closer to the poles

the great white spot and disturbances in saturn s equatorial atmosphere during 1990 a giant storm the great white spot erupted at the end of september 1990 as a localized bright cloud system close to saturn s equator its evolution produced a complex planetary disturbance which affected the whole equatorial region a month later similar spots have appeared approximately once every saturnian year about 30 earth years implying that a seasonal change in solar heating for example may be responsible for their occurrence

shallow water simulations of saturn s giant storms at different latitudes abstract shallow water simulations are used to present a unified study of three major storms on saturn nicknamed as great white spots gws at different latitudes polar 1960 equatorial 1990 and mid latitude 2010 sanchez lavega 2004 sanchez lavega et al 2011 in our model the three gws are initiated by introducing a gaussian function pulse at the latitude of the observed phenomena with controlled horizontal size and amplitude this function represents the convective source that has been observed to trigger the storm a growing disturbance forms when the pulse reacts to ambient winds expanding zonally along the latitude band of the considered domain we then compare the modeled potential vorticity with the cloud field adjusting the model parameters to visually get the closest aspect between simulations and observations simulations of the 2010 gws planetographic latitude 40o zonal velocity of the source 30 m s 1 indicate that the coriolis forces and the wind profile structure shape the disturbance generating as observed a long region to the east of the convective source with a high speed peripheral anticyclonic circulation and a long lived anticyclonic compact vortex accompanied by strong zonal advection on the southern part of the storm forming a turbulent region simulations of the equatorial 1990 gws planetographic latitude 12o 5o zonal velocity of the source 365 400 m s 1 show a different behavior because of the intense eastward jet meridional shear at the equatorial region and low latitude dynamics a round shaped source forms as observed with the rapid growth of a kelvin helmholtz instability on the north side of the source due to advection and to the strong meridional wind shear whereas at the storm latitude the disturbance grows and propagates eastward the storm nucleus is the manifestation of a rossby wave while the eastward propagating planetary scale disturbance is a gravity rossby wave trapped around the equator the simulated 1960 gws disturbance planetographic latitude 56o zonal velocity 4 m s 1 formed a chain of periodic oval spots that mimic the few available observations of the phenomenon for the mid and high latitude storms simulations predict a strong injection of negative relative vorticity due to divergence of the upwelling storm material which may produce large anticyclones on the anticyclonic side of the zonal profile and a quick turbulent expansion on the background cyclonic regions in general simulations indicate that negative relative vorticity injected by storms determines the natural reaction to zonal winds at latitudes where coriolis forces are dominant

vertical cloud structure in saturn s 1990 equatorial storm abstract we present a model study of the evolution of the vertical cloud structure and aerosol optical characteristics of the giant storm that erupted in saturn s atmosphere in september 1990 this analysis is based on the photometric measurements of the reflected intensity of the equatorial region in the optical range 336 890 nm continuum and methane absorption bands that were previously published a sanchez lavegaet al 1994 icarus108 158 168 different stages of the storm evolution are analyzed preoutburst onset and mature october november 1990 and evolved july 1991 good fits between the observations and radiative transfer calculations are found using a three layer model a gas layer a haze layer and a semiinfinite cloud deck two term henyey greenstein and mie phase functions are used for the scattering particles according to the models the main change during the evolution of the disturbance took place in the altitude of the cloud layer cloud tops elevated by 1 2 1 5 scale heights during the onset and mature storm stage relative to the undisturbed atmosphere descending later during the evolved phase by 0 7 scale heights relative to the altitude of the mature clouds the altitude location of the haze layer did not change during the storm development but the single scattering albedo of the haze particles increased significantly during the onset and mature stages in the uv blue wavelengths if the haze particles are modeled as mie spheres their mean radius varied from 0 83 to 0 64 m with real refractive index 1 5 and extreme values of the imaginary index 0 01 370 nm and 0 0005 830 nm

hubble space telescope observations of the 1990 equatorial disturbance on saturn zonal winds and central meridian albedos abstract two sets of hubble space telescope hst data obtained in august 1990 and november 1990 are compared with voyager 1 and 2 data acquired in 1980 and 1981 a rare disturbance developed in the equatorial region of saturn in late september 1990 due to the large equatorial wind shear this disturbance generated inhomogeneous bright cloud structures in the equatorial region that extended to 25 north latitude in november 1990 meridional albedo scans and wind measurements from the voyager northern spring equinox and the hst northern summer observations are compared differences in average zonal winds in the images obtained with the green f547m and the methane f889n filters are interpreted as evidence of vertical shear in the zonal winds longitudinal variations in the equatorial zonal winds are interpreted as evidence of interaction between the storm nucleus generated during the disturbance and the local wind field

near bottom magnetic signatures of submarine hydrothermal systems at marsili and palinuro volcanoes southern tyrrhenian sea italy near bottom magnetic field data were collected using a towed magnetometer over selected parts of palinuro and marsili submarine volcanoes in the southern tyrrhenian sea italy we obtained equivalent magnetizations maps at these sites by inverting the corresponding magnetic anomalies highlighting the seafloor expression of hydrothermal alteration zones of reduced magnetization are interpreted as evidence for alteration related to hydrothermal processes they are associated with water column and seafloor observations of hydrothermal activity and altered host rocks at marsili volcano a large elliptical area of reduced magnetization is located south of the summit cone and perpendicular to the trend of marsili volcano itself this confirms the presence of a large hydrothermal system centered over the more recent eastern volcanic ridge and its associated magma chamber similarly areas of reduced magnetization over palinuro caldera are consistent with hydrothermal venting occurring along the caldera walls consistent with permeability structures related to caldera ring faults providing preferred pathways for the upflow of hydrothermal fluids

reduction of potential field data to a horizontal plane most existing techniques for potential field data enhancement and interpretation require data on a horizontal plane hence when observations are made on an irregular surface reduction to a horizontal plane is necessary to effect this reduction an equivalent source distribution that models the observed field is computed on a mirror image of the observation surface this irregular mirror image surface is then replaced by a horizontal plane and the effect of the equivalent sources is computed on the required horizontal level this calculated field approximates the field reduced to a horizontal plane the good quality of this approximation is demonstrated by two dimensional synthetic data examples in which the maximum errors occur in areas of steep topographic gradients and increased magnetic field intensity the approach is also applied to a portion of a helicopter borne aeromagnetic survey from the gaspe region in quebec canada where the results are a horizontal shifting of anomaly maxima of up to 150

quantifying tectonic strain and magmatic accretion at a slow spreading ridge segment mid atlantic ridge 29 n high resolution deep towed side scan sonar data are used to characterize faulting and variations in tectonic strain along a segment of the slow spreading mid atlantic ridge near 29 n sonar data allow us to identify individual fault scarps to measure fault widths and spacing and to calculate horizontal fault displacements heave and tectonic strain we find that over long periods of time 1 myr on average tectonic strain is 10 on average and does not vary significantly along axis there is a marked asymmetry in tectonic strain that appears to be linked to asymmetric accretion along the whole segment indicated by 50 lower tectonic strain on the east flank than on the west flank these variations in tectonic strain do not correlate directly with changes in fault spacing and heave fault spacing and heave increase from the center of the segment toward the end inside corner on the west flank and from the outside to the inside corner across the axis these parameters remain relatively constant along the segment on the east flank and across the axis at the segment center tectonic strain appears to be decoupled from magmatic accretion at timescales 1 myr as the decrease in magma supply from the segment center toward the end inferred from variations in crustal thickness along the axis is not correlated with a complementary increase in tectonic strain instead tectonic strain remains relatively constant along the axis at 7 on the east flank and at 15 on the west flank these results indicate that variations in fault development and geometry may reflect spatial differences in the rheology of the lithosphere and not changes in tectonic strain or magma supply along axis

absolute magnetization of the seafloor at a basalt hosted hydrothermal site insights from a deep sea submersible survey the analysis of high resolution vector magnetic data acquired by deep sea submersibles dsss requires the development of specific approaches adapted to their uneven tracks we present a method that takes advantage of 1 the varying altitude of the dss above the seafloor and 2 high resolution multibeam bathymetric data acquired separately at higher altitude by an autonomous underwater vehicle to estimate the absolute magnetization intensity and the magnetic polarity of the shallow subseafloor along the dss path we apply this method to data collected by dss nautile on a small active basalt hosted hydrothermal site the site is associated with a lack of magnetization in agreement with previous findings at the same kind of sites the contrast between nonmagnetic sulfide deposits stockwork zone and strongly magnetized basalt is sufficient to explain the magnetic signal observed at such a low altitude both normal and reversed polarities are observed in the lava flows surrounding the site suggesting complex history of accumulating volcanic flows

near bottom magnetic survey of the mid atlantic ridge axis 24 24 40 n implications for crustal accretion at slow spreading ridges near bottom magnetic field measurements provide increased spatial resolution over sea surface magnetic data and allow a detailed analysis of the accretionary and tectonic processes at work in a slow spreading environment through the use of magnetic inversion methods and forward modeling we investigate the fine scale magnetic structure of young oceanic crust along four near bottom profiles that cross the two bathymetric segments immediately north of the kane transform on the mid atlantic ridge our results show the presence of a narrow peaked central anomaly magnetic high camh located over the zone of most recent volcanism we hypothesize that the pattern of high magnetization at segment ends and relatively low values at their centers is largely the result of increased iron and titanium content away from segment centers magnetization lows which are not observed in the sea surface data flank the camh and are associated with the axial valley walls these lows may locate areas of intense magnetic source layer disruption blocks of relatively high magnetization found outside the valley walls suggest a cyclic faulting process whereby discrete blocks of relatively unaltered crust are transported out of the rift valley by adjacent zones of faulting these observations of fine scale magnetic structure show that while the emplacement of crust at slow spreading ridges is highly focused subsequent tectonic disruption and alteration at the rift valley walls degrades the crustal magnetization signal and may be the primary reason for atlantic magnetic anomaly variability

constraints on saturn s tropospheric general circulation from cassini iss images abstract an automated cloud tracking algorithm is applied to cassini imaging science subsystem high resolution apoapsis images of saturn from 2005 and 2007 and moderate resolution images from 2011 and 2012 to define the near global distribution of zonal winds and eddy momentum fluxes at the middle troposphere cloud level and in the upper troposphere haze improvements in the tracking algorithm combined with the greater feature contrast in the northern hemisphere during the approach to spring equinox allow for better rejection of erroneous wind vectors a more objective assessment at any latitude of the quality of the mean zonal wind and a population of winds comparable in size to that available for the much higher contrast atmosphere of jupiter zonal winds at cloud level changed little between 2005 and 2007 at all latitudes sampled upper troposphere zonal winds derived from methane band images are 10 m s 1 weaker than cloud level winds in the cores of eastward jets and 5 m s 1 stronger on either side of the jet core i e eastward jets appear to broaden with increasing altitude in westward jet regions winds are approximately the same at both altitudes lateral eddy momentum fluxes are directed into eastward jet cores including the strong equatorial jet and away from westward jet cores and weaken with increasing altitude on the flanks of the eastward jets consistent with the upward broadening of these jets the conversion rate of eddy to mean zonal kinetic energy at the visible cloud level is larger in eastward jet regions 5 2 10 5 m 2 s 3 and smaller in westward jet regions 1 6 10 5 m 2 s 3 than the global mean value 4 1 10 5 m 2 s 3 overall the results are consistent with theories that suggest that the jets and the overturning meridional circulation at cloud level on saturn are maintained at least in part by eddies due to instabilities of the large scale flow near and or below the cloud level

potential vorticity of saturn s polar regions seasonality and instabilities we analyze the potential vorticity of saturn s polar regions as it is a fundamental dynamical tracer that enables us to improve our understanding of the dynamics of these regions and their seasonal variability in particular we present zonally averaged quasi geostrophic potential vorticity maps between 68 planetographic latitude and the poles at altitudes between 500 and 1 mbar for three different epochs i june 2013 early northern summer for the north polar region ii december 2008 late northern winter for both polar regions and iii october 2006 southern summer for the south computed using temperature profiles retrieved from cassini composite infrared spectrometer data and wind profiles obtained from cassini s imaging science subsystem the results show that quasi geostrophic potential vorticity maps are very similar at all the studied epochs showing positive vorticities at the north and negative at the south indicative of the dominance of the coriolis parameter 2 sin at all latitudes except near the pole the meridional gradients of the quasi geostrophic potential vorticity show that dynamical instabilities mainly due to the barotropic term could develop at the flanks of the hexagon at 78 n the jet at 73 9 s and on the equatorward flank of both polar jets there are no differences in potential vorticity gradients between the two hemispheres that could explain why a hexagon forms in the north and not in the south no seasonal variability of the potential vorticity and its meridional gradient has been found despite significant changes in the atmospheric temperatures over time

saturn s magnetospheric planetary period oscillations neutral atmosphere circulation and thunderstorm activity implications or otherwise for physical links 1 suggestions that the planetary period oscillations ppos observed in saturn s magnetosphere may be driven or influenced by neutral atmospheric perturbations motivate an exploratory comparison of ppo rotation periods with available tropospheric and stratospheric determinations nonpolar atmospheric rotation periods occupy the range 10 2 10 7 h associated with the latitudinal jet structure are similar north and south and are independent of season while ppo periods lie in a narrower partly overlapping range 10 6 10 8 h are persistently shorter north than south and undergo a seasonal cycle in this cycle widely separated north south ppo periods during southern summer converge across equinox to values lying within the atmospheric west jet band remaining well separated from east jet periods closest convergence occurred 1 year post equinox contemporaneously with the switch in seasonal thunderstorm activity from southern to northern hemispheres since most large scale atmospheric phenomena are related to the west jets rotating with closely similar periods they also rotate with periods close to the ppos under post equinoctial conditions but not otherwise specifically post equinox northern ppos rotate with a period close to the southern thunderstorms as well as the north polar spot and hexagon features while the post equinox southern ppos rotate with a period close to the pre equinox northern string of pearls and the first colocated post equinox northern thunderstorm the great white spot event however even under these conditions no consistent correspondences in period are found at a detailed level which taken together with the lack of correspondence at other times does not suggest a direct physical link exists between these phenomena

fault structure and detailed evolution of a slow spreading ridge segment the mid atlantic ridge at 29 n we present preliminary results of a detailed near bottom study of the morphology and tectonics of the 29 n broken spur segment on the slow spreading mid atlantic ridge using principally the tobi deep towed instrument the survey covered two thirds of the segment length including all of its southern non transform boundary and extended off axis of 40 km 3 3 ma on either side we obtained nearly complete near bottom sidescan sonar coverage and deep towed three component magnetic observations along 2 km spaced e w tracks sidescan data reveal new details of fault structure and evolution faults grow by along axis linkage in the inside corner they also link in the axis normal direction by curving to meet the next outer older fault this leads to wider spaced faults compared to segment centre or outside corner outward facing faults exist but are rare the non transform offset is characterised by faults that are highly oblique not parallel to the spreading direction and show cross cutting relations with ridge parallel faults to the north suggesting along axis migration of the offset almost all volcanic activity occurs within 5 km of the axis most fault growth is complete within 15 km of the axis 1 2 ma though large scarps continue to be degraded by mass wasting beyond there crustal magnetisation is strongly three dimensional the current neovolcanic zone is slightly oblique to earlier reversal boundaries and its magnetisation rises to a maximum of 30 a m 1 near its southern tip the central magnetisation high tapers southwards and is asymmetric with a sharp western but gradual eastern boundary we infer a highly asymmetric accretion of layer 2 near the segment end older magnetic anomalies are kinked and sometimes missing we interpret these observations as evidence of a rapid 18 km southward migration of the segment boundary during the past 1 8 ma and present a series of reconstructions illustrating this tectonic history

near ir spectrophotometry of saturnian aerosols meridional and vertical distribution abstract photometrically calibrated grism spectra of saturn in the h 1 45 1 80 m and k band 1 95 2 50 m are presented the spectra were obtained with the 200 inch hale telescope at palomar mountain three days after the ring plane crossing of august 10 1995 by inversion of the spectra the vertical distribution of the scattering density is obtained as a function of latitude along the central meridian for pressures ranging from about 10 to 600 mbar at all latitudes we find a vertical structure consisting of a stratospheric haze layer and a more dense upper tropospheric haze layer with density minima both above and below the tropospheric layer at northern midlatitudes the upper tropospheric haze is located deeper into the atmosphere than at similar southern midlatitudes this hemispherical asymmetry can be explained by seasonal influences the largest scattering densities in the upper tropospheric haze layer are found at tropical latitudes between about 10 and 15

thermal structure of saturn from voyager infrared measurements implications for atmospheric dynamics abstract saturn atmospheric temperatures at the 150 mbar level retrieved from voyager iris measurements indicate the presence of small scale meridional gradients which are approximately symmetric with respect to the equator but are superposed on a large scale hemispheric thermal asymmetry under the assumption that the retrieved values at this atmospheric level represent kinetic temperatures on a constant pressure surface it is suggested that the small scale structure is produced by a meriodional circulation associated with the dissipative decay of the zonal winds with height while the hemispheric asymmetry represents a thermal response to the seasonally varying insolation the small scale gradients are correlated with zonal winds derived from voyager images at mid and high latitudes through the thermal wind relation the calculated thermal wind shears suggest a decay with height of the jet system toward a state of uniform eatward flow the existence of the approximately symmetric zonal winds and associated temperature gradients in the presence of a large scale seasonal thermal response suggests that the jet system is driven at depths substantially below the levels where seasonally modulated insolation is important p 0 5 bar

the onset and growth of the 1990 equatorial disturbance on saturn abstract the development of cloud structures at low saturnian latitudes in september 1990 can be divided into three phases the onset and expansion of the initial disturbance popularly known as the great white spot the eastward and westward expansion of the bright cloud and the eventual formation of wave like structures encircling the equator the three phases of this storm are consistent with a single convective event this event is evaluated within the historical context of previous occurrences and general seasonal mechanisms are considered

saturn s zonal wind profile in 2004 2009 from cassini iss images and its long term variability abstract five years of cassini imaging science subsystem images from 2004 to 2009 are analyzed in this work to retrieve global zonal wind profiles of saturn s northern and southern hemispheres in the methane absorbing bands at 890 and 727 nm and in their respective adjacent continuum wavelengths of 939 and 752 nm a complete view of saturn s global circulation including the equator at two pressure levels in the tropopause 60 mbar to 250 mbar with the mt filters and in the upper troposphere from 350 mbar to 500 mbar with the cb filter set is presented both zonal wind profiles available at the supplementary material section show the same structure but with significant differences in the peak of the eastward jets and the equatorial region including a region of positive vertical shear symmetrically located around the equator between the 10 c

crustal structure of the mid atlantic ridge south of the kane fracture zone from seafloor and sea surface gravity data seafloor and sea surface gravity data are inverted together to construct a model for the near axis crustal structure of a slow spreading ridge the seafloor data set offers two main advantages it allows us to recover shorter wavelengths signal and to constrain the value of a potential field at two different levels the model we propose here would not have been derived from sea surface data alone it is based on a dense sea surface gravity coverage and on 121 sea bottom gravity measurements collected in the mid atlantic ridge at kane mark area during the hydrosnake 1988 and gravinaute 1993 cruises the primary goal of the seafloor surveys was to test for the presence of a magma reservoir beneath the axial neovolcanic ridge first a forward two dimensional 2 d model of the crustal structure across the axis is fit to observed gravity anomalies using constraints from geological and structural observations bouguer anomalies computed from sea bottom measurements and downward continuation of sea surface measurements both constrain the forward modeling this forward model is the starting point of a 2 d monte carlo inversion of seafloor and sea surface data in addition to the crustal thickness variations along axis our data document the amplitude variations of the crustal thickness and or its density in the across axis direction the model resulting from our inversion exhibits several features of the crustal structure in the mark area 1 the presence of a low density ap 300 50 kg m 3 body beneath the neovolcanic ridge is suggested and could correspond to a magma chamber or more probably to a highly hydrothermally fissured zone 2 both long and short wavelength gravity signals exhibit a difference between the western and eastern sides of the axial domain the mean value and the amplitude of bouguer anomalies are higher on the western part this difference suggests that axial processes in this area are very asymmetric 3 abyssal hills are not associated with a single gravity signature for instance on the west side of the axis one of the explored hills has no bouguer anomaly and is interpreted as a neovolcanic ridge whereas the others are associated with a shifted bouguer anomaly high and are interpreted as having thinner magmatic crust 4 the last feature of the crustal fabric we document here is the asymmetric emplacement of some deep rocks outcrops in the mark area we find that pink hill a topographic high where serpentinized peridotites are outcropping is much more serpentinized on its east flank toward the axial valley than on its west flank alteration occurring mainly by fluid circulation through faulted zones the asymmetric serpentinization suggests that deep origin rocks have outcropped by means of a main fault zone and are not emplaced by diapirism

origin of magnetic highs at ultramafic hosted hydrothermal systems insights from the yokoniwa site of central indian ridge high resolution vector magnetic measurements were performed on an inactive ultramafic hosted hydrothermal vent field called yokoniwa hydrothermal field yhf using a deep sea manned submersible shinkai6500 and an autonomous underwater vehicle r2d4 the yhf has developed at a non transform offset massif of the central indian ridge dead chimneys were widely observed around the yhf along with a very weak venting of low temperature fluids so that hydrothermal activity of the yhf was almost finished the distribution of crustal magnetization from the magnetic anomaly revealed that the yhf is associated with enhanced magnetization as seen at the ultramafic hosted rainbow and ashadze 1 hydrothermal sites of the mid atlantic ridge the results of rock magnetic analysis on seafloor rock samples including basalt dolerite gabbro serpentinized peridotite and hydrothermal sulfide showed that only highly serpentinized peridotite carries high magnetic susceptibility and that the natural remanent magnetization intensity can explain the high magnetization of yokoniwa these observations reflect abundant and strongly magnetized magnetite grains within the highly serpentinized peridotite comparisons with the rainbow and ashadze 1 suggest that in ultramafic hosted hydrothermal systems strongly magnetized magnetite and pyrrhotite form during the progression of hydrothermal alteration of peridotite after the completion of serpentinization and production of hydrogen pyrrhotites convert into pyrite or nonmagnetic iron sulfides which considerably reduces their levels of magnetization our results revealed origins of the magnetic high and the development of subsurface chemical processes in ultramafic hosted hydrothermal systems furthermore the results highlight the use of near seafloor magnetic field measurements as a powerful tool for detecting and characterizing seafloor hydrothermal systems

motions in saturn s atmosphere observations before voyager encounters abstract a summary is presented of all the telescopic observations of the clouds in saturn s atmosphere made prior to the voyager encounters with the planet saturn displays a pattern of belts and zones like jupiter although they are practically constant in latitude and without significant changes over the last century some dark and white spots with diameters of about 6000 to 10 000 km have been observed allowing us to ascertain the atmospheric rotational period only a strong equatorial jet can be inferred from these measurements the most obvious features of saturn are the great white spots gws with diameters of 20 000 km or more but only five outbursts have been detected since 1876 corrected measurements have been obtained of the zonal velocities at different latitudes u with variations between 430 and 14 msec 1 with respect to the magnetic rotation of the planet m l kaiser m d desch j w warwick and j b pierce science 209 1238 1240 1980 the expansion velocities of some gws have been measured to be u 30 to 100 msec 1 and their lifetimes l from 30 to 150 days a possible subatmospheric origin for the gws is proposed in which it is due to a temporary and local anisotropy in the internal heat source a hot spot in the deeper atmosphere all the multiple features seen in both 1903 and 1933 appear to be linked to a unique system of longitudes rotating with the magnetic period

dynamics of saturn s great storm of 2010 2011 from cassini iss and rpws saturn s quasi periodic planet encircling storms are the largest convecting cumulus outbursts in the solar system the last eruption was in 1990 sanchez lavega a 1994 chaos 4 341 353 a new eruption started in december 2010 and presented the first ever opportunity to observe such episodic storms from a spacecraft in orbit around saturn fischer g et al 2011 nature 475 75 77 sanchez lavega a et al 2011 nature 475 71 74 fletcher l n et al 2011 science 332 1413 here we analyze images acquired with the cassini imaging science subsystem iss which captured the storm s birth evolution and demise in studying the end of the convective activity we also analyze the saturn electrostatic discharge sed signals detected by the radio and plasma wave science rpws instrument the storm s initial position coincided with that of a previously known feature called the string of pearls sops at 33 n planetocentric latitude intense cumulus convection at the westernmost point of the storm formed a particularly bright head that drifted at 26 9 0 8 m s 1 negative denotes westward motion on january 11 2011 the size of the head was 9200 km and up to 34 000 km in the north south and east west dimensions respectively rpws measurements show that the longitudinal extent of the lightning source expanded with the storm s growth the storm spawned the largest tropospheric vortex ever seen on saturn on january 11 2011 the anticyclone was sized 11 000 km by 12 000 km in the north south and east west directions respectively between january and september 2011 the vortex drifted at an average speed of 8 4 m s 1 we detect anticyclonic circulation in the new vortex the vortex s size gradually decreased after its formation and its central latitude shifted to the north the storm s head moved westward and encountered the new anticyclone from the east in june 2011 after the head vortex collision the rpws instrument detected that the sed activities became intermittent and declined over 40 days until the signals became undetectable in early august in late august the sed radio signals resurged for 9 days the storm left a vast dark area between 32 n and 38 n latitudes surrounded by a highly disturbed region that resembles the mid latitudes of jupiter using iss images we also made cloud tracking wind measurements that reveal differences in the cloud level zonal wind profiles before and after the storm

saturn atmospheric dynamics one year after cassini long lived features and time variations in the drift of the hexagon abstract we examine saturn s atmospheric dynamics with observations in the visible range from ground based telescopes and hubble space telescope hst we present a detailed analysis of observations acquired during 2018 obtaining drift rates of major meteorological systems from the equator to the north polar hexagon a system of polar storms that appeared in the planet in march 2018 and remained active with a complex phenomenology at least until september is analyzed elsewhere sanchez lavega et al 2019 many of the regular cloud features visible in 2018 are long lived and can be identified in saturn images in 2017 and in some cases for up to a decade using also cassini iss images without considering the polar storms the most interesting long lived cloud systems are i a bright white spot in the equatorial zone that can be tracked continuously since 2014 with minimal changes in its zonal velocity which was 444 3 3 1 m s 1 in 2014 and 452 4 1 7 m s 1 in 2018 this velocity is remarkably different from the zonal winds at the cloud level at its latitude during the cassini mission and is closer to zonal winds obtained at the time of the voyagers flybys and to zonal winds from cassini vims infrared images of the lower atmosphere ii a large long lived anticyclone vortex here av that formed after the great white spot of 2010 2011 this vortex has changed significantly in visual contrast drift rate and latitude with minor changes in size over the last years iii a system of subpolar vortices at latitudes 60 65 n present at least since 2011 these vortices and additional atmospheric features here studied follow drift rates consistent with zonal winds obtained by cassini we also present a study of the positions of the vertices of saturn s north polar hexagon from 2015 to 2018 these measurements are compared with previous analyses during the cassini mission 2007 2014 observations with hst in the 90s and data from the voyagers in 1980 1981 to explore the long term variability of the hexagon s drift rate we find variations in the drift rate of the hexagon through these epochs that can not be fit by seasonal changes in the polar area instead the different drift rates reinforce the role of the north polar spot that was present in the voyager epoch and in the early 90s to cause a faster drift rate of the hexagon at that time compared with the current slower one

cassini imaging of saturn southern hemisphere winds and vortices high resolution images of saturn s southern hemisphere acquired by the cassini imaging science subsystem between february and october 2004 are used to create maps of cloud morphology at several wavelengths to derive zonal winds and to characterize the distribution frequency size morphology color behavior and lifetime of vortices nonequatorial wind measurements display only minor differences from those collected since 1981 and reveal a strong prograde flow near the pole the region just southward of the velocity minimum at 40 7 s is especially active containing numerous vortices some generated in the proximity of convective storms the two eastward jets nearest the pole display periodicity in their longitudinal structure but no direct analogs to the northern hemisphere s polar hexagon or ribbon waves were observed characteristics of winds and vortices are compared with those of saturn s northern hemisphere and jupiter s atmosphere

magnetic structure of an oceanic core complex at the southernmost central indian ridge analysis of shipboard and deep sea three component magnetometer data 1 we investigated the magnetic structure of an oceanic core complex occ at the southernmost central indian ridge cir near 25 s on the basis of newly collected magnetic and bathymetric data and submersible dives the occ is located off axis on the western flank of the cir and is characterized by typical megamullion morphology with flow line parallel corrugations the occ is similar in size to those found along the mid atlantic ridge mar but the cir occ formed in an estimated 0 8 ma which is slightly shorter than the average time for the formation of occs along the mar the magnetization intensity over the cir occ is quite weak compared to that over adjacent seafloor of the same age mostly gabbroic rocks were recovered from outcrops during submersible dives fault rocks were also recovered from the corrugated surface suggesting that the occ surface represents the plane of a detachment fault although the magnetization intensity is rather low we were able to identify the brunhes matuyama boundary and the jaramillo and olduvai subchrons on and around the occ using vector magnetic analysis over the occ the jaramillo subchron which cannot be recognized from magnetic data acquired at the sea surface was identified using data from a magnetometer attached to a submersible the locus of this subchron is consistent with that observed over the seafloor adjacent to the occ combining the results of magnetic survey and rock sampling we would like to point out the possibility that the gabbroic rocks constituted the occ and preserved seafloor spreading history although there are several interpretations of the low magnetization

atmospheric dynamics of saturn s 2010 giant storm great white spot a rare planet encircling storm raged on saturn in 2010 2011 analyses of high resolution spacecraft imagery and numerical modelling reveal a dynamic storm head powered by sustained convection in the zonal flow of saturn s atmosphere

thermal structure and dynamics of saturn s northern springtime disturbance saturn s slow seasonal evolution was disrupted in 2010 2011 by the eruption of a bright storm in its northern spring hemisphere thermal infrared spectroscopy showed that within a month the resulting planetary scale disturbance had generated intense perturbations of atmospheric temperatures winds and composition between 20 and 50 n over an entire hemisphere 140 000 kilometers the tropospheric storm cell produced effects that penetrated hundreds of kilometers into saturn s stratosphere to the 1 millibar region stratospheric subsidence at the edges of the disturbance produced beacons of infrared emission and longitudinal temperature contrasts of 16 kelvin the disturbance substantially altered atmospheric circulation transporting material vertically over great distances modifying stratospheric zonal jets exciting wave activity and turbulence and generating a new cold anticyclonic oval in the center of the disturbance at 41 n

dyking at epr 16 n hypermagmatic ridge segment insights from near seafloor magnetics abstract high resolution near seafloor magnetic data have been acquired over the 16 n hypermagmatic segment of the east pacific rise using an autonomous underwater vehicle this survey proves to be ideal to test the relative efficiency of various inversion methods applied to data acquired at a more or less constant altitude above the seafloor unlike other methods a recently published bayesian inversion preserves the short wavelengths and allows for the resolution of a high resolution reduced to the pole magnetic anomaly this anomaly unveils the presence of several laterally adjacent dykes associated with individually separated axial summit troughs the observation of such anomalies and therefore of shallow dykes confirms the hypermagmatic character of the segment in a location where complex magma chambers have been imaged in seismic reflection studies variable intensity of the magnetic anomalies reflects the depth of the dyke swarms and ultimately the timing and style of eruptive events helping to constrain the spreading axis evolution

seasonal evolution of saturn s polar temperatures and composition abstract the seasonal evolution of saturn s polar atmospheric temperatures and hydrocarbon composition is derived from a decade of cassini composite infrared spectrometer cirs 7 16 m thermal infrared spectroscopy we construct a near continuous record of atmospheric variability poleward of 60 from northern winter southern summer 2004 l s 293 through the equinox 2009 l s 0 to northern spring southern autumn 2014 l s 56 the hot tropospheric polar cyclones that are entrained by prograde jets within 2 3 of each pole and the hexagonal shape of the north polar belt are both persistent features throughout the decade of observations the hexagon vertices rotated westward by 30 longitude between march 2007 and april 2013 confirming that they are not stationary in the voyager defined system iii longitude system as previously thought tropospheric temperature contrasts between the cool polar zones near 80 85 and warm polar belts near 75 80 have varied in both hemispheres resulting in changes to the vertical windshear on the zonal jets in the upper troposphere and lower stratosphere the extended region of south polar stratospheric emission has cooled dramatically poleward of the sharp temperature gradient near 75 s by approximately 5 k yr coinciding with a depletion in the abundances of acetylene 0 030 0 005 ppm yr and ethane 0 35 0 1 ppm yr and suggestive of stratospheric upwelling with vertical wind speeds of w 0 1 mm s the upwelling appears most intense within 5 latitude of the south pole this is mirrored by a general warming of the northern polar stratosphere 5 k yr and an enhancement in acetylene 0 030 0 003 ppm yr and ethane 0 45 0 1 ppm yr abundances that appears to be most intense poleward of 75 n suggesting subsidence at w 0 15 mm s however the sharp gradient in stratospheric emission expected to form near 75 n by northern summer solstice 2017 l s 90 has not yet been observed so we continue to await the development of a northern summer stratospheric vortex the peak stratospheric warming in the north occurs at lower pressure levels p 1 mbar than the peak stratospheric cooling in the south p 1 mbar vertical motions are derived from both the temperature field using the measured rates of temperature change and the deviations from the expectations of radiative equilibrium models and hydrocarbon distributions solving the continuity equation vertical velocities tend towards zero in the upper troposphere where seasonal temperature contrasts are smaller except within the tropospheric polar cyclones where w 0 02 mm s north polar minima in tropospheric and stratospheric temperatures were detected in 2008 2010 lagging one season or 6 8 years behind winter solstice south polar maxima appear to have occurred before the start of the cassini observations 1 2 years after summer solstice consistent with the expectations of radiative climate models the influence of dynamics implies that the coldest winter temperatures occur in the 75 80 region in the stratosphere and in the cool polar zones in the troposphere rather than at the poles themselves in addition to vertical motions we propose that the uv absorbent polar stratospheric aerosols entrained within saturn s vortices contribute significantly to the radiative budget at the poles adding to the localised enhancement in the south polar cooling and north polar warming poleward of 75

measurement and implications of saturn s gravity field and ring mass the interior structure of saturn the depth of its winds and the mass and age of its rings constrain its formation and evolution in the final phase of the cassini mission the spacecraft dived between the planet and the innermost ring at altitudes 2600 3900 km above the cloud tops during six of these crossings a radio link with earth was monitored to determine the gravitational field of the planet and the mass of its rings we find that saturn s gravity deviates from theoretical expectations and requires differential rotation of the atmosphere extending to a depth of at least 9000 km the total mass of the rings is 1 54 0 49 10 19 kg 0 41 0 13 times that of the moon mimas indicating that the rings may have formed 10 7 10 8 years ago

direct inversion of potential fields from an uneven track with application to the mid atlantic ridge current methods of potential field inversion require measurements to be reduced onto a level plane resulting in a loss of resolution this is especially true for draped surveys in areas of extreme topography we examine a method that bypasses this limiting step by making use of an approximately equivalent geometry from which data are directly inverted corrections are applied to an initial solution to account for errors generated by the transformation of geometries a numerical model and an example data set are used to explore this method s benefits and drawbacks in relation to the conventional approach of data reduction onto a level plane prior to inversion we show that this direct inversion method is particularly better than the conventional approach at resolving fine scale features such as the narrow zone of crustal emplacement at the mid atlantic ridge and adjacent areas of tectonic disruption and magnetic source alteration