a modeling study of the formation maintenance and relaxation of upwelling circulation on the northeastern south china sea shelf abstract we investigated persistent summer upwelling circulation in response to upwelling and downwelling favorable winds in the northeastern south china sea nscs we used a validated three dimensional ocean circulation model that was forced by realistic atmospheric fluxes and downscaled coupling of real time lateral fluxes we found that upwelling in the nscs was formed and maintained by the presence of an intensified westward along isobath pressure gradient force pgfm and bottom frictional effect that led to cross isobath currents over the unique nscs widened shelf the upwelling favorable pgfm and the frictional effect arose from the interaction between the eastward shelf current and the shelf topography these intrinsic upwelling dynamics in the nscs were largely sustained during episodic downwelling winds in the upwelling season because the retreat of the eastward shelf current from pre existing upwelling was significantly slowed by the unique widened shelf topography furthermore the upwelling dynamics could also be maintained and even developed during downwelling favorable winds when the eastward shelf current was sustained by the pumping of downstream outflow

time dependent wind driven flow over a shallow midshelf submarine bank 1 during summer 2001 high resolution hydrographic velocity and bio optical surveys were conducted over heceta bank off central oregon north of the bank upwelling over simple bottom topography exhibited a classic response with a midshelf baroclinic coastal jet and upwelled isopycnals the coastal upwelling jet follows the bank topography as it widens offshore before reaching the southern end of the bank where the shelf break turns almost 90 back toward the coast the ensuing adjustment involves the offshelf transport of coastal water and the material it contains the jet meanders anticyclonically in the lee of the bank before resuming its equatorward path seaward of the shelf break a pool of high chlorophyll 15 mg m 3 near surface water is found in the low velocity lee region created by the bank a low temperature high salinity bottom water pool supplied primarily from the south lies over the inshore region of the bank this bottom pool is up to 40 m thick and contains elevated levels of suspended material by creating an east west perturbation in the coastal upwelling front the flow topography interaction introduces an alongshore pressure gradient when southward upwelling favorable winds relax this alongshore pressure gradient can drive flow back to the north this leads to northward flow on the inshore side of the bank ultimately setting up the potential for recirculation around the entire bank complex on a timescale of about 10 days strong northward winds during summer lead to downwelling within 15 km of the coast accompanied by significant 0 2 m s 1 wind driven northward currents

enhancement of wind driven upwelling and downwelling by alongshore bathymetric variability steady wind driven flow along a shelf of changing width is described with a frictional barotropic model valid in the limit of small rossby and burger number in these limits an alongshore wind drives enhanced onshelf transport in a coastal ocean if the shelf widens downwind and the change in shelf width only affects the flow in the direction of kelvin wave propagation downwave from the change in shelf width there is enhanced onshore transport of cold nutrient laden bottom water if the winds favor upwelling and the shelf narrows in the direction of kelvin wave propagation this enhanced transport extends a considerable distance away from the change in shelf width but becomes concentrated near the shelf break far from the change in width isobath curvature on the scale of the shelf width significantly modifies local cross shelf transport the cross shelf transport of nutrient rich water during upwelling is expected to be enhanced from point eugenia to la jolla san luis obispo to monterey and point reyes to cape mendocino on the west coast of north america

dynamics of intensified downwelling circulation over a widened shelf in the northeastern south china sea abstractthis study reveals the dynamics behind the intensified downslope cross isobath transport over a widened shelf narrowing downwave in the northeastern south china sea nscs during a downwelling event utilizing a three dimensional numerical model over an idealized nscs shelf this study identified the forcing process and derived an analytical understanding of the invoked dynamics for the intensified downslope cross isobath transport this study found that the transport was formed by an amplified geostrophic transport because of an increased positive along isobath pressure gradient force pgf py and by an enhanced bottom ekman transport due to converging flow over the widened shelf based on the depth integrated vorticity dynamics py was linked with net frictional stress curl in the water column and the curl was primarily associated with the shear vorticity field induced by downwelling jet the increased positive vorticity seaside of the jet provided positive py for the downslope geostrop

progress on upwelling studies in the china seas east asian marginal seas surrounding china exhibit rich ocean upwelling mostly in response to the southwesterly summer monsoon upwelling in the china seas namely the south china sea the taiwan strait the east china sea the yellow sea and the bohai sea has become increasingly important because the potential changes in the upwelling may have dramatic ecosystem socioeconomic and climate impacts this paper reviews the progress of upwelling studies in the china seas since the year 2000 by presenting the principal characteristics and new understanding of 12 major upwelling regions in the china seas upwelling exhibits long term variability at intraseasonal to multi decadal scales as well as short term variability frequently caused by tropical cyclones it is also associated with the el nino southern oscillation local environmental variation and biogeochemical factors the coastal upwelling around hainan island and the upwelling or cold dome northeast of taiwan island are specifically highlighted because they have attracted great interest for decades this paper summarizes upwelling mechanisms in terms of wind topography tide stratification and background flow with applications mostly to the china seas finally we propose some topics for future upwelling research i e potential intensification of coastal upwelling under global climate change downwelling intrusion of upwelling into coastal embayments and the influence of upwelling on fishery and biogeochemical processes

an upwelling case study on florida s west coast using a combination of satellite sea surface temperature imagery in situ currents temperature and sea level data and a numerical circulation model we describe an upwelling event observed along florida s west coast although ubiquitous features of continental shelves descriptions of coastal upwellings or downwellings are generally complicated by the continuum of processes in which they occur for the case study presented the winds were light and the baroclinic background currents were steady for several days prior to the event these conditions allow the evolution of a specific winddriven upwelling event to be viewed as an initial value problem the data and the numerical model analysis show that the route of adjustment by the sea level and currents is a classical ekman geostrophic one sea level drops due to an offshore ekman transport causing a geostrophic alongshore jet and the associated onshore flow within the bottom ekman layer accounts for the appearance of cold water at the surface this surface manifestation occurs as an elongated feature centered about the 25 m isobath that spans roughly half of the florida peninsula from just north of tampa bay to key west the coldest water is observed offshore from tampa bay and we explain this region of locally maximum upwelling on the basis of the coastline and isobath geometries

a geometric analysis of surface deformation implications for the tectonic evolution of ganymede abstract a visual nonalignment of the furrows and the circularity of impact craters are used to study surface deformation on ganymede the furrow system is examined to test the hypothesis that lateral motion has taken place between areas of dark terrain results show that while lateral motion cannot be ruled out it may not be required to explain the geometry of the system initial nonconcentricity of the furrows or an early period of penetrative deformation shortly after furrow formation could also account for the present configuration centers of curvature of the furrows in galileo and marius regiones are numerically determined and it is shown that if lateral movement did occur it is not possible to determine the amount of displacement the axial ratios of impact craters in the uruk sulcus region which separates galileo and marius regiones are determined and show that large scale shear deformation has not occured in that area since bright terrain was emplaced deformation of impact craters within galileo regio suggests that ganymede s lithosphere has behaved rigidly throughout most of the satellite s evolution the shapes and orientations of impact craters in dark terrain around wedges of bright terrain are used to place an upper limit on the amount of extension associated with bright terrain formation

constraints on the expansion of ganymede and the thickness of the lithosphere grooves and furrows have been interpreted as grabens resulting from extension of ganymede s lithosphere geologically reasonable estimates of the dip 90 60 and displacement less than 1 km to a few hundred meters of faults bounding grooves on ganymede allow calculation of the extension and surface area increase 0 04 2 required for the formation of all grooved terrain the implied radius increase is thus limited between 0 02 and 1 1 planetary expansion is the maximum possible since formation of the grooved terrain began similar estimates for faults bounding furrows the oldest preserved tectonic features on ganymede indicate a maximum surface area increase of 0 5 for the best developed furrow system which is located in galileo regio if equivalent furrow systems existed on all of the cratered terrain then a maximum of 0 5 increase in surface area of ganymede is possible after the formation of the lithosphere and prior to the formation of grooved terrain faults bounding simple graben originate at a subsurface mechanical discontinuity and propagate upwards resulting in grabens with similar widths and similar spacings between members of a set the depth to this mechanical discontinuity for furrows and grooves on ganymede must give at least a minimum lithosphere thickness because it is impossible for faults to originate and propagate upwards from a point below the lithosphere therefore the minimum lithosphere thickness on ganymede is 5 km and 9 km in marius and galileo regiones respectively at the time of furrow formation and 4 km at the time of groove formation

global geological mapping of ganymede abstract we have compiled a global geological map of ganymede that represents the most recent understanding of the satellite based on galileo mission results this contribution builds on important previous accomplishments in the study of ganymede utilizing voyager data and incorporates the many new discoveries that were brought about by examination of galileo data we discuss the material properties of geological units defined utilizing a global mosaic of the surface with a nominal resolution of 1 km pixel assembled by the usgs with the best available voyager and galileo regional coverage and high resolution imagery 100 200 m pixel of characteristic features and terrain types obtained by the galileo spacecraft we also use crater density measurements obtained from our mapping efforts to examine age relationships amongst the various defined units these efforts have resulted in a more complete understanding of the major geological processes operating on ganymede especially the roles of cryovolcanic and tectonic processes in the formation of might materials they have also clarified the characteristics of the geological units that comprise the satellite s surface the stratigraphic relationships of those geological units and structures and the geological history inferred from those relationships for instance the characteristics and stratigraphic relationships of dark lineated material and reticulate material suggest they represent an intermediate stage between dark cratered material and light material units

viscous relaxation of ganymede s impact craters constraints on heat flux abstract measurement of crater depths in ganymede s dark terrain have revealed substantial numbers of unusually shallow craters indicative of viscous relaxation see companion paper singer k n schenk p m bland m t mckinnon w b 2017 relaxed impact craters on ganymede regional variations and high heat flow icarus submitted these viscously relaxed craters provide insight into the thermal history of the dark terrain the rate of relaxation depends on the size of the crater and the thermal structure of the lithosphere here we use finite element simulations of crater relaxation to constrain the heat flux within the dark terrain when relaxation occurred we show that the degree of viscous relaxation observed cannot be achieved through radiogenic heating alone even if all of the relaxed craters are ancient and experienced the high radiogenic fluxes present early in the satellite s history for craters with diameter 10 km heat fluxes of 40 50 mw m 2 can reproduce the observed crater depths but only if the fluxes are sustained for 1 gyr these craters can also be explained by shorter lived heat pulses with magnitudes of 100 mw m 2 and timescales of 10 100 myr at small crater diameters 4 km the observed shallow depths are difficult to achieve even when heat fluxes as high as 150 mw m 2 are sustained for 1 gyr the extreme thermal conditions required to viscously relax small craters may indicate that mechanisms other than viscous relaxation such as topographic degradation are also in play at small crater diameters the timing of the relaxation event s is poorly constrained due to the sparsity of adequate topographic information though it likely occurred in ganymede s middle history neither recently nor shortly after satellite formation the consistency between the timing and magnitude of the heat fluxes derived here and those inferred from other tectonic features suggests that a single event caused both ganymede s tectonic deformation and its crater relaxation future observations should permit more robust determination of the relative timing of the heating event that caused viscous relaxation

ganymede and callisto complex crater formation and planetary crusts new depth diameter d d rim and peak height and width measurements of fresh craters on ganymede and callisto are utilized to explore not only crater mechanics on icy satellites but intersatellite crater scaling and crustal properties and composition significant systematic differences in crater morphology on icy and rocky planets are confirmed simple to complex transition diameters on icy satellites including ganymede and callisto are much lower than those on rocky planets also complex crater depths and rim heights on ganymede and callisto are inherently 60 70 shallower than lunar complex craters despite similar surface gravity hence viscous relaxation is not as important as is generally assumed central peaks on most icy satellites are 1 2 km higher and considerably wider with respect to diameter than for similar sized lunar craters terracing and rim slumping is also rare in these craters central peaks in craters on ganymede and callisto larger than 15 km however are relatively small in both width and height however correlating with the occurrence of rim slumping thus central peak dimensions are an indirect indicator of the degree of rim slumping transition diameters for the occurrence of central peaks and rim slumps and for d d curve inflections for icy satellites scale approximately with the inverse of surface gravity except possibly at very low g the transition diameters for central peaks and for rim slumping differ however by 5 15 km on ganymede and callisto but by 50 or more km on the smaller icy satellites these large differences suggest that d d curves on icy satellites are comprised of three segments of decreasing slope one for smaller simple craters a second for central peak craters and a third for larger true complex craters with both central peaks and rim slumping the shallow slopes of d d curves on ganymede and callisto resemble that of the moon consistent with the occurrence of both central peaks and rim failure the high slopes of d d curves on the middle sized icy satellites indicate that they are middle segments consistent with the dominance of central peaks in those craters complex crater depths on icy satellites in general scale with the inverse of surface gravity the depths of all the observed large basin scale craters on these small satellites when scaled to ganymede gravity are very similar to those of complex craters on ganymede and callisto these large craters including odysseus 425 km diameter on tethys are probably true complex craters that have not undergone significant viscous relaxation ithaca chasma on tethys probably formed during the prompt collapse of the transient odysseus crater crater morphology is clearly controlled by both gravity and by large variations in material properties i e composition and should be useful in constraining bulk crustal composition i e ice rock ratios the similarity of various morphological transition diameters and complex crater depths on ganymede and callisto two geophysically very similar but geologically divergent large icy satellites indicates that the crusts of both bodies are dominated by water ice with only a minor rocky component

the oceanography of the northern south china sea shelf sea nosocs and its adjacent waters overview and highlights abstract tropical shelf seas constitute a sub set of shelf seas that has not been studied extensively the no rthern so uth c hina sea s helf sea nosocs study is a continuation of the longstanding interest in taiwan on the oceanography of the east asian shelf seas and is an attempt to provide systematic and synoptic observations on a tropical shelf sea the two basic hypotheses in the study are 1 as in the ocean interior the behaviors of the shelf seas vary with latitude and 2 the behaviors of the nosocs are representative of those of the shelf seas in the tropical zone the nosocs has been sampled bi annually in alternating seasons since 2009 the results obtained primarily in 2009 to 2012 are presented here as in the tropical ocean interior a distinguishing characteristic of the nosocs is its shallow mixed layer with depths of about 40 m in the summer and 70 m in the winter as similar mixed layer depths are found in the adjoining northern south china sea scs and they are shallower than the shelf break depth of 120 m the upper nutricline water in the northern scs extends freely into the nosocs and forms a layer of water with significant concentrations of the nutrients immediately below its mixed layer any process that can induce vertical mixing on the shelf may make the nutrients in this subsurface water available for supporting biological activities in the mixed layer in the nosocs such processes include winter convective overturn over the entire nosocs as a result of surface cooling and the strong northeast monsoonal wind winter formation of bottom water in parts of the inner and middle shelf the action of internal waves at the outer shelf and the continental slope and upwelling maintained by wind and or topography the upwelling takes place in the summer off the coasts of dongshan shantou and the northeast coasts of the hainan island but year round at the taiwan bank upwelling over the shelf break is not required for bringing the nutrients in the sub surface waters in the open scs to the nosocs and it was not observed in addition to vertical mixing terrestrial inputs especially through the outflow of the pearl river which reaches its peak in the summer also contribute to the spatial and temporal variations in the composition of the nosocs the combined effects of all these processes lead to a unique seasonal pattern in the variations of the surface concentrations of chlorophyll a in the nosocs with two distinct yearly maxima in the winter and summer

large scale response to atmospheric forcing of shelf currents and coastal sea level off the west coast of north america may july 1981 and 1982 the response of alongshore currents v over the continental shelf and of coastal sea level along the pacific coast of north america to atmospheric forcing on large alongshore scales 100 2000 km during may july 1981 coastal ocean dynamics experiment code 1 and may july 1982 code 2 has been studied using sea level and wind measurements from coastal stations and buoys between 33 n and 48 n and using current measurements from five locations between 35 n and 48 n characteristics of the large scale response of v and to fluctuations in the alongshore component of the wind stress varied with latitude and with year in relation to variations in in 1981 large scale fluctuations were coherent within but not between separate domains north and south of 42 n in 1982 large scale coherent fluctuations were found only in a northern domain that extended much farther south to near 37 n accordingly in 1981 alongshore current v fluctuations from 39 n code were coherent with v from 35 n while in 1982 v fluctuations from 39 n were coherent with those north to 48 n in 1981 the northern domain fluctuations were forced by between 42 n and 45 n with southern domain forcing at 35 36 n in 1982 northern domain fluctuations were forced by over a region of much larger along shore extent 37 48 n high values of space lagged coherences between v and y y is the alongshore coordinate indicate that v at 39 n was strongly wind driven maximum squared coherences of v versus y are found with to the south by 100 300 km for low frequencies 0 23 cpd in 1981 0 14 cpd in 1982 and with from near local stations at higher indicating the importance of remote forcing at low frequencies and local forcing at high frequencies the response of v to y at 35 n and 43 n was more complicated but evidence for strong wind forcing is found in several frequency bands for v at 43 n during 1981 and 1982 and at 35 n during 1981 at 48 n v was forced in 1982 for 0 18 cpd by from locations 300 1400 km to the south

true polar wander on europa from global scale small circle depressions the tectonic patterns and stress history of europa are exceedingly complex and many large scale features remain unexplained true polar wander involving reorientation of europa s floating outer ice shell about the tidal axis with jupiter has been proposed as a possible explanation for some of the features this mechanism is possible if the icy shell is latitudinally variable in thickness and decoupled from the rocky interior it would impose high stress levels on the shell leading to predictable fracture patterns no satisfactory match to global scale features has hitherto been found for polar wander stress patterns here we describe broad arcuate troughs and depressions on europa that do not fit other proposed stress mechanisms in their current position using imaging from three spacecraft we have mapped two global scale organized concentric antipodal sets of arcuate troughs up to hundreds of kilometres long and 300 m to approximately 1 5 km deep an excellent match to these features is found with stresses caused by an episode of approximately 80 degrees true polar wander these depressions also appear to be geographically related to other large scale bright and dark lineaments suggesting that many of europa s tectonic patterns may also be related to true polar wander

tectonic and volcanic evolution of dark terrain and its implications for the internal structure and evolution of ganymede furrows in ancient dark terrain on ganymede form three systems that are each hemispheric or greater in scale the oldest of the systems designated system iii is dominated by approximately concentric troughs centered on about 60 n 50 w system i in the anti jovian hemisphere contains concentric and subradial furrows arrayed around a large degraded palimpsest centered at 15 s 165 w furrows in each system formed on and locally are buried by dark volcanic materials that embay and infill preexisting topographic features they crosscut extremely few well preserved older craters and they occur on surfaces having significantly different relative crater ages system ii also in the anti jovian hemisphere contains widely spaced radially arrayed furrows commonly 500 2000 km in length which are organized around a large area of dark smooth resurfacing material intense dark terrain fracturing and some of the globally oldest light material the total thickness of dark terrain resurfacing estimated using the stratigraphy of different dark material deposits and the rim heights of the largest crater size class whose density was depleted by each deposit is probably in the range of 3 8 km multiple models of the origin of each furrow system were tested using observed geologic features and patterns systems i and iii were found to be most consistent with reactivation of impact generated multiringed structures by endogenic global extension during a period of widespread dark material volcanism that obliterated a dense ancient crater population system ii was found to be most consistent with fracturing of a single circular isostatic uplift covering an entire hemisphere on the basis of geologic observations and interpretations and theoretical models of convection in spheres it is hypothesized that the uplift developed by long term warming of the upwelling current of a single axisymmetric convection cell in an initially cooler undifferentiated interior such wanning would also have created global expansion and supplied the tensional stress inferred to have formed systems i and iii this hypothesis is supported by the concentration around the center of system ii of intense fracturing and relatively young dark volcanic deposits suggestive of high lithospheric heat flow lithospheric thinning and stress concentration an observed long term decrease in the width of extensional tectonic features interpreted to be of endogenic origin is also consistent with lithospheric thinning due to warming of a cool interior

cometary nuclei and tidal disruption the geologic record of crater chains on callisto and ganymede prominent crater chains on ganymede and callisto are most likely the impact scars of comets tidally disrupted by jupiter and are not secondary crater chains we have examined the morphology of these chains in detail in order to place constraints on the properties of the comets that formed them and the disruption process in these chains intercrater spacing varies by no more than a factor of 2 and the craters within a given chain show almost no deviation from linearity although the chains themselves are on gently curved small circles all of these crater chains occur on or very near the jupiter facing hemisphere for a given chain the estimated masses of the fragments that formed each crater vary by no more than an order of magnitude the mean fragment masses for all the chains vary by over four orders of magnitude w b mckinnon and p m schenk 1995 geophys res lett 13 1829 1832 however the mass of the parent comet for each crater chain is not correlated with the number of fragments produced during disruption but is correlated with the mean mass of the fragments produced in a given disruption event also the larger fragments are located near the center of each chain all of these characteristics are consistent with those predicted by disruption simulations based on the rubble pile cometary nucleus model in which nuclei are composed on numerous small fragments weakly bound by self gravity and with those observed in comet d shoemaker levy 9 similar crater chains have not been found on the other icy satellites but the impact record of disrupted comets on callisto and ganymede indicates that disruption events occur within the jupiter system roughly once every 200 to 400 years

observation of tropical cyclone induced shallow water currents in taiwan strait the data from three stations equipped with acoustic doppler current profilers adcps deployed in the shallow water of the taiwan strait tws were used to study the shallow coastal ocean response to five quasi continuous tropical cyclone tc events in the late summer 2006 we revealed that in the forced stage when the large and strong tc bilis transited the geostrophic currents were formed which dominated the whole event while the strong but relatively small one saomai or the weak one bopha primarily leaded to the generation of ekman currents in the relaxation stage the barotropic subinertial waves and or the baroclinic near inertial oscillations nios were triggered typically during the transit of the saomai subinertial waves were induced which demonstrated a period of 2 8 4 1 days and a mean alongshore phase velocity of 14 9 3 2 m s in the form of free barotropic continental shelf waves however the nios are only notable in the area in which the water column is stably stratified and also where the wind stress is dominated by the clockwise component and accompanied by high frequency near inertial variations we also demonstrated that due to the damping effects the nonlinear wave wave interaction e g between nio and semidiurnal tide in our case together with the well known bottom friction led to the rapid decay of the observed tc induced near inertial currents giving a typical e folding time scale of 1 3 inertial periods moreover such nonlinear wave wave interaction was even found to play a major role during the spring tide in tws

early thermal profiles and lithospheric strength of ganymede from extensional tectonic features abstract estimates of the brittle lithosphere thickness derived from the width and spacing of extensional tectonic features coupled with lithospheric strength envelopes brittle and ductile yield stress versus depth appropriate for ice allow the quantitative determination of early thermal profiles and lithospheric strength and stability on ganymede furrows and grooves indicate brittle lithospheric thicknesses of 5 10 and 2 5 km respectively assuming that their spacing is controlled by an extensional instability or that their width is controlled by the intersection depth of their bounding faults plots of the brittle and ductile yield stress versus depth for the icy lithosphere of ganymede show a linear increase in brittle strength with depth to a maximum at the brittle ductile transition followed by an exponential decrease in ductile yield stress with depth because the depth to the brittle ductile transition depends primarily on the thermal gradient the thickness of the brittle lithosphere can be used to calculate early thermal profiles of 1 5 6 and 4 5 20 km during the formation of the furrows and grooves respectively lithospheric strength the integral of the yield stress versus depth curve varied from 30 125 gpa m when the furrows formed to 5 30 gpa m when the grooves formed which correspond to maximum yield stresses of 6 11 and 2 5 6 mpa respectively these results indicate that the thermal gradient and lithospheric strength varied laterally by as much as a factor of 5 and that ganymede cooled in a highly inhomogeneous manner with significant lateral thermal anomalies finally this analysis provides a straightforward explanation for the stability of large remnants of cratered terrain such as galileo regio that had a low thermal gradient and strong lithosphere in contrast to small remnants of cratered terrain that were fractured and broken up by grooved terrain as a result of higher thermal gradients and weaker lithospheres

viscous relaxation as a prerequisite for tectonic resurfacing on ganymede insights from numerical models of lithospheric extension abstract ganymede s bright terrain formed during a near global resurfacing event or events that produced both heavily tectonized and relatively smooth terrains the mechanism s by which resurfacing occurred on ganymede e g cryovolcanic or tectonic and the relationship between the older dark and the younger bright terrain are fundamental to understanding the geological evolution of the satellite using a two dimensional numerical model of lithospheric extension that has previously been used to successfully simulate surface deformation consistent with grooved terrain morphologies we investigate whether large amplitude preexisting topography can be resurfaced erased by extension i e tectonic resurfacing using synthetically produced initial topography we show that when the total relief of the initial topography is larger than 25 50 m periodic groove like structures fail to form instead extension is localized in a few individual isolated troughs these results pose a challenge to the tectonic resurfacing hypothesis we further investigate the effects of preexisting topography by performing suites of simulations initialized with topography derived from digital terrain models of ganymede s surface these include dark terrain fresh relatively deep impact craters smooth bright terrain and a viscously relaxed impact crater the simulations using dark terrain and fresh impact craters are consistent with our simulations using synthetic topography periodic groove like deformation fails to form in contrast when simulations were initialized with bright smooth terrain topography groove like deformation results from a wide variety of heat flow and surface temperature conditions similarly when a viscously relaxed impact crater was used groove like structures were able to form during extension these results suggest that tectonic resurfacing may require that the amplitude of the initial topography be reduced before extension begins we emphasize that viscous relaxation may be the key to enabling tectonic resurfacing as the heat fluxes associated with groove terrain formation are also capable of reducing crater topography through viscous relaxation for long wavelength topography large craters viscous relaxation is unavoidable we propose that the resurfacing of ganymede occurred through a combination of viscous relaxation tectonic resurfacing cryovolcanism and at least in a few cases band formation variations in heat flow and strain magnitudes across ganymede likely produced the complex variety of terrain types currently observed

the schmidt hammer weathering and rock surface roughness measures of the differential relief of adjacent feldspar and pyroxene grains provide the first clear negative correlation of schmidt hammer rebound r values and degree of weathering however weathering and roughness are intimately related so the latter cannot be seen simply as a source of error limiting the utility of the schmidt hammer only where surfaces had similar textures prior to weathering can r values be compared directly even where surface texture is well controlled differences in r values should be viewed critically rather than assigned indiscriminately to differences in degree of weathering

a global system of furrows on ganymede indicative of their creation in a single impact event abstract furrows are a concentric system of tectonic troughs and are the oldest recognizable surface feature on ganymede we analyzed the distribution of furrows utilizing voyager and galileo images and found that furrows over ganymede s surface are part of a global concentric circular structure if this multi ring structure is impact origin this is the largest impact structure identified so far in the solar system deviations of the shapes of the furrows from the concentricity are small everywhere which implies that the relative location of the blocks of the dark terrains over the entire surface of ganymede has not changed appreciably even during formation of the bright terrains the estimate of the impactor size is difficult but an 150 km radius impactor is consistent with the observed properties of furrows the furrow forming impact should have significant effects on the satellite s geological and internal evolution which are expected to be confirmed by future explorations of jupiter s icy moons such as the juice jupiter icy moon explorer or europa clipper mission

modeling upwelling circulation off the oregon coast 1 time dependent three dimensional upwelling circulation on the continental shelf off the oregon coast is studied using a primitive equation numerical model a limited area domain with a high resolution curvilinear grid is utilized the response of the coastal ocean to forcing by observed wind stress and heat flux during the summer 2001 time period of the coastal ocean advances in shelf transport coast field experiment is investigated model results are compared to coast current and hydrographic measurements the shelf velocity and density fields are generally characterized by the presence of a southward alongshore coastal jet with an upwelling density front on the shoreward side of the jet the large variability in shelf topography associated with heceta bank exerts a major influence on the shelf velocity and density fields over the bank the alongshore coastal jet is displaced offshore and colder upwelled water extends farther from the coast northward mean flow and upward motion are found inshore of the jet three dimensional flow structures in response to variable shelf bottom topography are presented and an analysis of time and space dependent alongshore momentum balances is applied to clarify the associated dynamics in general northward pressure gradients set up over the bank during southward upwelling winds accelerate currents on the inshore side of the jet northward when the winds relax analysis of term balances in the depth averaged equation for potential temperature shows that during upwelling across shore advection makes the major contribution to cooling over most of the region except inshore over heceta bank where alongshore advection also plays a significant role

a simple mechanical model of valhalla basin callisto the valhalla basin on callisto is a multiringed structu e that extends over much of the satellite s surface although its appearance differs in detail from lunar multiringed basins its origin may also be attributed to lithospheric fragmentation accompanying collapse of the transient crater formed by an impact event this paper explores the mechanics of the collapse process by treating the lithosphere as a thin elastic von mises plastic sheet plane geometry or shell spherical geometry flow of the underlying asthenosphere inward toward the crater cavity induces plastic failure of the lithosphere and produces a characteristic pattern of faults in the disrupted lithosphere the pattern and extent of faulting is a function of a single dimensionless parameter that involves the strength and thickness of the lithosphere the crater depth and diameter and the surface gravity of the planet the tectonic structures of valhalla correspond well with the failure pattern expected for a large crater produced in a thin circa 30 km weak strength 100 bar lithospheric shell

intensified upwelling over a widened shelf in the northeastern south china sea 1 observational and three dimensional modeling studies reveal that the intensified upwelling in the northeastern south china sea nscs is formed as a result of intensified upslope advection of dense deep waters that cross the middle shelf toward the inner shelf over a distinctly eastward widened shelf the strongest advection occurs over the converging isobaths near the head of the widened shelf as these dense deep waters advance shoreward they are advected downstream by the quickly developed upwelling current over the inner shelf and eventually outcropped at the lee of a coastal cape dynamically the shoreward cross isobath transport over the widened shelf is geostrophically enhanced by a quasi barotropic negative westward along isobath pressure gradient force as a result of the net rate of the momentum influx and by an intensified bottom frictional transport owing to the flow confluence near the head of the widened shelf a negative pressure gradient also exists at the lee of the coastal cape over the inner shelf and locally amplifies shoreward motion induced by the respective widened shelf and the coastal promontory the along isobath variations of cross isobath transport in the water column over the middle and inner shelves interactively characterize intensified upwelling in the nscs

geology and mapping of dark terrain on ganymede and implications for grooved terrain formation geological mapping of regional and high resolution galileo images reveals a variety of units and structures within ganymede s dark terrain we have made a detailed study of areas within galileo marius and nicholson regiones in order to investigate the style of tectonic deformation experienced by dark terrain adjacent to swaths of grooved terrain dark terrain appears to become fractured as a precursor to grooved terrain formation in places dark fractured swaths are recognized which have similar characteristics to brighter grooved terrain swaths tectonic deformation may be but is not always focused through preexisting weaknesses caused by impact craters and furrows a prominent groove lane anshar sulcus is inferred to have formed by the process of hanging wall rollover accompanied by a small amount of right lateral horizontal shear offset resulting from ne sw extension

possible breakup of dark terrain on ganymede by large scale shear faulting a system of arcuate furrows in galileo regio and marius regio two large blocks of ancient dark terrain has previously been proposed to be the remnant of an originally more concentric furrow set that was disrupted by shear estimates of the two regions poles of furrow concentricity indicate a considerable westward offset of the galileo regio pole these measurements suggest the possibility of about 500 km of left lateral offset of the two areas four additional independent structural indicators support this hypothesis there is evidence that shear deformation was concentrated along a major structural lineament which closely follows a small circle about 45 of arc of radius which encloses galileo regio and that a smaller amount of distributed shear occurred across an adjacent 500 to 1500 km wide band there is also morphologic evidence for zones of minor right lateral shear between central and southern marius regio and between barnard and nicholson regio and for a zone of minor left lateral shear in nun sulci stratigraphic relations indicate that any major shear offsets occurred before and during the earliest stages of grooved terrain formation before most grooves had formed and before virtually all light material had been emplaced however regionally dominant groove orientations are generally consistent with orientations expected for transtensional features either shear strain or the shear s driving mechanism may have had a long term effect on patterns of deformation of ganymede s lithosphere

the tectonics of ganymede the surface of ganymede the largest icy jovian satellite is composed of two distinct terrain types showing abundant evidence of global scale tectonics there is geological evidence consistent with the formation of younger bright terrain by the emplacement of relatively clean ice into rift zones developed in the more silicate rich dark terrain

ring geometry on ganymede and callisto abstract arguments have been made based on geometry for both an impact and an internal origin for the ancient partially preserved major furrow system of ganymede zuber and parmentier concluded that furrows are not concentric but could be impact related if multiringed structures on icy satellites are initially noncircular we examine the geometry of the valhalla ring structure on callisto in order to assess the circularity of an unmodified ring system despite prominent local meandering the only gross deviations from concentricity in the valhalla system are found in the outer northeast quadrant of the system here a number of ring segments intersect small circles about the center at angles up to 30 the ganymede furrow system was remapped to make use of improvements in coordinate control the least squares center of curvature determined using natural weighting for all furrows in marius and galileo regio is 20 7 1 1 s 179 2 1 1 w 2 uncertainty furrows in marius and galileo regio are reasonably concentric are much more circular than previously estimated and probably once covered at least an entire hemisphere of ganymede in addition at least three other multiring systems of varying size are identified on ganymede indicative of a projectile population thus we find furrow geometry and occurrence are consistent with an impact origin deviations of some furrows from concentricity about the center of curvature on the scale of those found at valhalla do exist as in the case of valhalla these variations are principally confined to outer regions of the structure and are interpreted as inherent properties of multiringed structures on icy satellites the cause s of this may be in the ring formation mechanism itself but are more likely due to variations in preexisting lithospheric mechanical properties the perceived present nonalignment of the assumed originally concentric furrows has been used to argue for large scale lateral motion of dark terrain blocks in ganymede s crust presumably in association with bright terrain formation the overall alignment of furrows as well as the inherent scatter in centers of curvature for subregions of galileo and marius regio do not support this hypothesis

relaxation from upwelling in the coastal ocean dynamics experiment a relaxation of the upwelling system on the northern california shelf occurs when upwelling favorable winds decay or reverse observations from the coastal ocean dynamics experiment are used to investigate this process with emphasis on the near surface temperature evolution models of relaxation warming are tested for the surface layer 0 30 m over midshelf with the result that the surface heat flux and poleward alongshelf advection can account for the observed temperature behavior onshore advection of the upwelled isopycnal field is a relatively unimportant contribution the warming patterns that are observed and which provide the gradients for the advective process have wedgelike shapes warmest inshore and in the south of the experimental area these patterns appear to be related to a topographic influence of point reyes possibly through the generation of gradients in the wind field remote advection of warm water from as far south as san francisco occasionally occurs as well the nature of the relaxation mechanism has general implications a new warm saline nutrient rich water mass may be formed in the surface layer since the warming processes are not the reverse of the cooling an important asymmetry is present it causes time variable upwelling to generate conditions very different from steady upwelling a new upwelling front is created during each event with upwelled water seaward of it and reversed alongshelf flow contributes to the warming and exchange mechanisms the system cannot be described or understood without the irreversible processes during upwelling and relaxation or without a mixed layer

galileo s first images of jupiter and the galilean satellites the first images of jupiter io europa and ganymede from the galileo spacecraft reveal new information about jupiter s great red spot grs and the surfaces of the galilean satellites features similar to clusters of thunderstorms were found in the grs nearby wave structures suggest that the grs may be a shallow atmospheric feature changes in surface color and plume distribution indicate differences in resurfacing processes near hot spots on io patchy emissions were seen while io was in eclipse by jupiter the outer margins of prominent linear markings triple bands on europa are diffuse suggesting that material has been vented from fractures numerous small circular craters indicate localized areas of relatively old surface pervasive brittle deformation of an ice layer appears to have formed grooves on ganymede dark terrain unexpectedly shows distinctive albedo variations to the limit of resolution

a modeling study of shelf circulation off northern california in the region of the coastal ocean dynamics experiment response to relaxation of upwelling winds 1 a two part modeling study of the wind forced flow on the continental shelf off northern california in the region 37 40 n of the coastal ocean dynamics experiment code is pursued this paper involves a process oriented study with idealized wind stress forcing gan and allen 2002 involves forcing with observed winds and heat flux for april may 1982 and comparison of model results with code observations a characteristic but previously unexplained response observed during code following the weakening or relaxation of southward upwelling favorable winds is the time dependent development of northward currents over the inner shelf next to the coast the presence of northward winds is not necessary for this occurrence the objective in this paper is to investigate the dynamics of the shelf flow response to upwelling wind relaxation events under idealized conditions in the basic case experiment a spatially uniform upwelling favorable southward wind stress of 0 1 pa is applied to the ocean initially at rest the stress is held constant for 10 days and then decreased linearly to zero over 3 days in response to the southward wind stress southward alongshore currents develop on the shelf accompanied by upwelling of cold dense water near the coast considerable spatial variability in the shelf flow clearly related to the alongshore variations in coastline and bottom topography is found the alongshore currents tend to separate from the coast south of capes and the coldest surface water is found at those locations as the winds decrease northward currents similar to those observed develop on the inner shelf next to the coast at many alongshore locations examination of the alongshore momentum balances shows that the northward currents are forced by a northward pressure gradient force associated with negative alongshore pressure gradients these pressure gradients are set up by the interaction of the wind forced flow with the alongshore variations in shelf topography in general negative alongshore pressure gradients intensified off pt reyes and pt arena by the gradient wind balance are found south of capes the negative pressure gradients geostrophically balance onshore flow at depth and upwelling is strengthened in these locations north of capes positive pressure gradients that are primarily in balance with nonlinear advective effects are found after the winds cease the forced across shelf circulation weakens and the resulting unbalanced negative pressure gradients south of the capes accelerate the alongshore currents northward processes with similar dynamics are found embedded in the more complex coastal ocean response to observed time varying winds by gan and allen 2002

dynamics of wind driven upwelling and relaxation between monterey bay and point arena local regional and gyre scale controls 1 in north and central california equatorward winds drive equatorward flows and the upwelling of cold dense water over the shelf during the midspring and summer upwelling season when the winds temporarily weaken the upwelling flows between point reyes and point arena relax becoming strongly poleward over the shelf analytical and numerical models are used to describe the effect of alongshore variability of winds bathymetry and basin scale pressure gradients on the strength of upwelling and its relaxation alongshore winds weaken to the south of point reyes and the shelf becomes narrower from point reyes to monterey bay both of these lead to reduced upwelling at and to the north of point reyes causing an alongshore gradient of temperature and density on the shelf these alongshore gradients lead to an along isobath pressure gradient over the shelf that drive the relaxation flows a simple analytical model is used to explain the dynamics magnitude and structure of the relaxation flows the modeling also suggests that the depth of origin of the upwelled waters and thus their temperature is controlled by the along isobath pressure gradient that exists over the continental slope this along slope pressure gradient is also responsible for the california undercurrent in this region this pressure gradient is not generated in a model of the californian coast extending from 32 n to 42 n and integrated for several months suggesting it is caused by dynamics whose spatial or temporal scales are larger than the californian coast and or longer than several months

the role of wind stress curl in jet separation at a cape abstract a high resolution numerical model is used to study the importance of spatial variability in the wind forcing to the separation of a coastal upwelling jet at a cape an idealized topography and wind field based on observations from the cape blanco oregon region are used several simulations are investigated with both the intensity and the spatial structure of the wind forcing varied to isolate the importance of the observed intensification in the wind stress and wind stress curl magnitudes to the separation process a simulation using a straight coast confirms that the presence of the cape is crucial for separation wind stress intensification by itself with zero curl does not aid separation the wind stress curl intensification south of the cape on the other hand is important for controlling details of the process because the positive wind stress curl drives upwelling isotherms in the offshore region tilt upward creating a pressure gradient that sustains an intensification of the southw

modeling south china sea circulation response to seasonal forcing regimes 1 a three dimensional ocean model has been utilized to study circulation and its seasonal variation in the south china sea scs in response to the forcing of the asian monsoon and the kuroshio intrusion the scs ocean model has a resolution of approximately 10 km horizontal spacing and 30 vertical levels with a realistic bottom topography the model is forced with time dependent wind stress and heat flux from national center for environmental prediction reanalysis data as well as with lateral fluxes from a pacific ocean model of 40 km horizontal resolution this study reports on the analysis of the mean seasonal circulation and dynamic processes in response to monsoonal wind stress the kuroshio intrusion and other intrinsic forcing processes it is found that the seasonal circulation in the scs is mainly driven by the monsoonal wind stress and greatly influenced by the inflow from the kuroshio intrusion strong currents along the continental margin of the scs form mean basin wide cyclonic and anticyclonic circulations in the winter and summer respectively multiscale eddies are embedded in the general circulation across the basin while mainstream of the kuroshio passes through the luzon strait without intruding into the scs partial intrusion occurs in the upper 200 m near the shelf margin southwest of taiwan at times when winter dynamic conditions prevail in the north scs the intrusion of the kuroshio into the scs also occurs at depths in all seasons mainly along the continental slope the coastal current separation to the east off southern vietnam and the associated eddy formations characterize the circulation in the south scs the simulated results compare well with the corresponding observed fields dynamical processes involved in the forced flow fields are investigated by examination of the momentum balances the analyses reveal that the circulation in the scs is generally dominated by the geostrophic currents north of the luzon strait positive nonlinearity in the zonal direction is locally intensified which leads to the formation of centripetal acceleration for the mainstream of the kuroshio to turn eastward the kuroshio intrusion at depths is governed by the ageostrophic flows and highly associated with the net westward pressure gradient force coastal jet separation to the east off vietnam is mainly associated with the local wind stress field and with the shelf topography in the summer and winter respectively sensitivity study reveals that the weakening of the kuroshio markedly enhances kuroshio s intrusion and forms an anticyclonic eddy west of the luzon strait

brine volcanism and the interior structures of asteroids and icy satellites abstract cryovolcanism is among the foremost processes responsible for modifying the surfaces of icy satellites volcanic brine petrogenesis in ammonia deficient satellites should mainly involve eutectic melting in relevant salt water systems carbonaceous chondrites provide useful insights into the compositions of salts and aqueously altered rock in icy satellites and asteroids c1 chondrites contain about one fifth by mass of salts in various states of hydration many aspects of the petrogenesis and physical volcanology of icy satellite brines should be well described in the system h2o mgso4 na2so4 minor components include sulfates of k ni mn and ca chondrites also contain abundant carbonates but these are probably not very important in brine magmatism due to their low solubilities under expected conditions chlorides are also unimportant under most circumstances because of the low cosmic abundance ratio of cl s soluble salts may have profound effects on the geology and structure of icy satellites and asteroids in some models late episodes of water volcanism are facilitated by high buoyant forces due to the relatively high densities of sulfate rich mantle and crustal layers in other models early hypersaline brine volcanism quickly yields to plutonic magmatism due to low crustal densities europa probably has a layered crust composed of anhydrous mg na sulfates near the base and a frozen or partially molten eutectic mixture of ice and hydrated mg and na sulfates near the surface ganymede may have a crust about 300 km thick composed of a 10 1 ratio of ice mirabilite and a mantle 500 km thick composed of 50 ice phases plus 50 hydrated mg and na sulfates

dynamics of cross shelf water exchanges off pearl river estuary in summer abstract dynamics regulating the cross isobath momentum and water exchanges over the shelf in the vicinity of the pearl river estuary pre in july 2015 and 2017 are examined using comprehensive observations and multiple level nested high resolution numerical simulations although driven by the upwelling and downwelling favorable winds in july 2015 and 2017 respectively the shelf currents and the cross isobath exchanges illustrate great similarity during these two periods this study finds that the southwesterly induced flow downstream in the taiwan strait maintained the northeastward upwelling currents in the vicinity of the pre that caused the extensive upslope invasion of the deep shelf waters the cross shelf exchanges of the shelf and coastal waters mainly occur over the irregular topography off the entrance of the huangmaohai estuary to the west of the dangan island and over a shallow trough to the east of hong kong it is also rationalized that the intensified exchange flow is established by an along shelf pressure gradient force that notably exceeds the contributions from the bottom and surface ekman transport as well as the nonlinearity of the shelf current in the water column the baroclinicity of the shelf and coastal waters plays minimal roles in altering this along shore pressure gradient force especially when upwelling favorable winds prevail the exchange flows in the water column thereby show great similarity with those in the bottom layer where the bottom along shore pressure gradient force is jointly imposed by the nonlinear advection of relative vorticity and frictional stress curl in both the surface and bottom layers the spatial variation of these terms is regulated by the intensity of the shelf current and along shelf variation of bottom topography

topographically induced upwelling off eastern australia abstract a high resolution numerical study of an idealized western boundary current flow over variable topography is presented with application to the east australian current eac the results indicate that alongshelf topographic variations off australia s east coast cause the eac to accelerate over the narrowing continental shelf near cape byron this acceleration is sufficient to hinder the geostrophic adjustment in the bottom boundary layer bbl which would usually cause the eac driven bbl to shut down consequently a region of persistent high bottom stress was established off cape byron which was responsible for driving an upwelling bbl it is shown that the enhanced vertical mixing associated with a low richardson number flow beneath the eac reduced the local stratification consequently the burger number is decreased resulting in a long shutdown timescale of the bbl which enables a nearshore thermal to be established and maintained such fronts are commonly observed in the region as a p

crater densities and crater ages of different terrain types on ganymede abstract crater densities and size frequency distributions on ganymede were measured for separate areas of dark furrowed and dark smooth terrains reticulate terrain complex grooved terrain and groups of groved polygons and groove lanes having a variety of relative ages these measurements were used first together with results of previous studies to test alternate models of heliocentric and planetocentric crater forming bombardments of ganymede and callisto the spatial distribution of crater production functions on ganymede is consistent with a single impactor population having dominated cratering of that satellite s observed surface in addition relative crater ages of different ganymedean material deposits are better reconciled with the deposits stratigraphic relations if a heliocentric impactor population is assumed these results are consistent with results of previous studies interpreted here to indicate that the spatial distributions of most classes of craters on ganymede and younger craters on callisto are more consistent with heliocentric than with planetocentric bombardment the measurements were then used to infer the sequence and style of surface modification of ganymede bounds on absolute ages depend on the assumption of heliocentric bombardment dark terrain was emplaced during a prolonged period of volcanic resurfacing of older heavily cratered terrain probably at least 10 8 yrs in duration and at least 3 8 4 0 gyr ago furrows generally formed on blanket like deposits of dark material typically hundreds of meters or more in thickness soon after their emplacement furrow formation continued globally throughout the period of dark material deposition next dark terrain was deformed locally by reticulate terrain formation light terrain emplacement subsequently began at least regionally within complex grooved terrain it continued for an extended period perhaps several times 10 8 yrs in grooved lanes grooved polygons andsmooth terrain where a light material layer averaging several hundred meters or more in thickness was emplaced

the geology of callisto the geology of callisto is not boring although cratered terrain dominates callisto a key end member of the jovian satellite system a number of more interesting features are apparent cratered terrain is broken into irregular mappable bright and dark subunits that vary in albedo by a factor of 2 and several relatively smooth units are depleted of small craters some of these areas may have been volcanically resurfaced lineaments including parallel and radial sets may be evidence for early global tectonism frost deposition occurs in cold traps and impact scars have formed from tidally disrupted comets geologic evidence suggests that callisto does have a chemically differentiated crust central pit and central dome craters and palimpsests are common the preferred interpretation is that a relatively ice rich material at depths of 5 km or more has been mobilized during impact and exposed as domes or palimpsests the close similarity in crater morphologies and dimensions indicates that the outermost 10 km or so of callisto may be as differentiated as on ganymede the geology of cratered terrain on callisto is simpler than that of cratered terrain on ganymede however orbital evolution and tidal heating may provide the answer to the riddle of why callisto and ganymede are so different malhotra 1991 we should expect a few surprises and begin to answer some fundamental questions when callisto is observed by galileo in late 1996