study of the effect of 17 18 march 2015 geomagnetic storm on the indian longitudes using gps and c nofs the largest geomagnetic storm in solar cycle 24 occurred during march 17 18 2015 where the main phase of the storm commenced from 07 00 ut of march 17 2015 and reached the dst negative minimum at 22 00 ut the present paper reports observations of tec amplitude and phase scintillations from different gps stations of india during the storm of march 17 and highlights its effects on gps it also presents the global esf occurrence during the storm using total ion density drift measurements from c nofs satellite tec enhancements were noted from stations along 77oe meridian around 10 00 ut on march 17 compared to march 16 and 18 indicating positive storm effects arising out of equatorward neutral wind in the local morning noon sector of the main phase intense scintillation observations from calcutta were most extensive during 15 00 16 00 ut march 17 and the receiver recorded a longitude deviation of 5 2 m during this time cycle slips of the order of 8 s could be observed during periods of intense phase scintillations on the same night intense scintillation observation from palampur is an exceptional phenomenon attributed to the dramatic enhancement of the electric field due to ppef leading to a very high upward ion velocity over the magnetic equator as recorded by c nofs the total ion density measured globally by c nofs reveals two distinct longitude regions of esf occurrence during the storm i east pacific sector and ii indian longitude during the storm the time and longitude of esf occurrence could be predicted using the time of southward turning of imf bz

middle to late epipaleolithic hunter gatherer encampments at the ashalim site on a linear dune like morphology along dunefield margin water bodies abstract this study presents distinct and small task specific sites associated with the middle to late epipalaeolithic period exposed during a salvage project at the site of ashalim at the fringe of the northwestern negev desert dunefield israel six areas spanning the geometric kebaran to harifian periods were systematically collected upon a unique 4 m high and 100 m wide linear dune like morphology this morphology was a vegetated linear dune that blocked the underlying drainage system and led to the development of standing bodies of water which together with the exposed wet bottom provided fauna and flora resources during the winter and spring the relatively large number of sickle blades and lunates uncovered during the excavations suggest cereal consumption combined with hunting activities ten optically stimulated luminescence osl measurements conducted for the dune like morphology indicate that the occupations of the site post date 15 5 3 1 ka bp while bodies of water were present intermittently until at least 11 ka bp possibly even after the harifian occupation two radiocarbon dates taken from ostrich eggshell fragments that were found upon the flat surface of the dune like morphology further support this time range the current study demonstrates how aeolian fluvial interactions and not necessarily a wetter climate are important for forming conditions conducive for occupation by prehistoric groups in arid zones

low latitude ionospheric d region dependence on solar zenith angle phase and amplitude measurements of vlf radio signals on a short nearly all sea path between two hawaiian islands are used to find the height and sharpness of the lower edge of the daytime tropical d region as a function of solar zenith angle sza the path used was from u s navy transmitter npm 21 4 khz on oahu to keauhou 306 km away on the west coast of the big island of hawaii where ionospheric sensitivity was high due to the destructive interference between the ionospherically reflected wave and the ground wave particularly around the middle of the day the height and sharpness are thus found to vary from h 69 3 0 3km and 0 49 0 02 km 1 for sza 10 at midday to h 80 km and 0 30 km 1 as the sza approached 70 90 near dawn and dusk for this tropical path additional values for the variations of h and with solar zenith angle are also found from vlf phase and amplitude observations on other similar paths the short path nwc to karratha in nw australia and the long paths nwc to kyoto in japan and nau puerto rico to st john s canada significant differences in the sza variations of h and were found between low and middle latitudes resulting from the latitudinally varying interplay between lyman and galactic cosmic rays in forming the lower d region both latitude ranges showed 0 30 km 1 during sunrise sunset conditions 1

influence of stratification on residual tidal currents in the yellow sea the m 2 tide and residual current generation in the yellow sea are examined using the blumberg and mellor 1987 numerical coastal ocean circulation model with no stratification the model tide and tidal currents show good agreement with the observed tide and tidal currents coherent residual currents are predicted around the southwest of korea flowing northward as a strong jet with a maximum speed of 8cm s 1 and around yangtze bank flowing southeastward as a weak broad current with initial stratification tidal mixing occurs in the bottom boundary layer which leads to surface tidal fronts around yangtze bank and the southwest of korea and our model experiments reproduce successfully the basic water property structure in these regions the resulting stratified tidal rectification intensifies the residual currents at the front and at the top of the bottom boundary layer over the sloping bottom so that the vertical structure of the residual currents is modified the strong residual currents in the top of the bottom mixed layer around yangtze bank support the interpretation of kim et al 1991 for the southeastward movement of yellow sea bottom cold water in summer the residual currents in the surface layer reach 40 of the mean currents observed by beardsley et al 1992 using satellite tracked drifters deployed in the yellow sea in summer these results suggest that stratified tidal rectification is an important process in driving the summertime subtidal flow in the yellow sea

fracture of antarctic shelf ice 1 we have investigated the fracture of antarctic shelf ice core using two fracture mechanics test methods the chevron notched short rod specimen loaded in tension and the chevron notched round bar specimen loaded in three point bending these tests have been used to measure the fracture initiation toughness kinit at which crack growth starts on samples taken through the entire thickness of the ronne ice shelf from low density firn through consolidated meteoric ice to basal marine ice the fracture data are presented together with depth profiles of relevant physical and mechanical properties derived from the test specimens temperature density elastic modulus and grain size it is found that the trend in measured fracture toughness closely reflects changes in ice density and elastic modulus we augment the experimental study by presenting a fracture mechanics analysis of ice shelf surface and basal crevassing which directly incorporates our measurements for the examined ice shelf profiles basal crevasses are found to be inherently unstable unless an external restraining force is imposed which has important implications for overall ice shelf stability on the other hand surface crevassing is shown to be innately stable at depth our fracture mechanics model is used to predict local ice shelf back stresses in the vicinity of basal crevassing and is validated directly against field observations of crevasse penetration on the ronne ice shelf

effects of st patrick s day geomagnetic storm of march 2015 and of june 2015 on low equatorial d region ionosphere d region effects of the 17 19 march 2015 a st patrick s day super geomagnetic storm dst 223 nt using a navigational transmitter very low frequency vlf signal nwc 19 8 khz recorded at a low latitude indian station allahabad geomag lat 16 45 n have been analyzed and compared with similar strength of the 22 25 june 2015 storm dst 204 nt during the march storm nwc signal amplitude decreased on 17 march main phase of the storm and recovered on 27 march which is 1 day after the recovery of the storm whereas for the june storm vlf amplitude decreased for 2 days only during its recovery phase the decrease in the amplitude was pronounced during evening terminator for both the storms the modeling of vlf signal anomaly on 17 march and on 25 june using long wave propagation capability code shows an increase in the d region reference height h by 2 6 km and 2 5 km for march and june storms respectively the d region electron density ne determined using storm time h and sharpness factor shows a decrease in the ne during the main phase followed by a slow recovery during the recovery phase of the march storm whereas june 2015 storm showed a decrease in the ne only on 25 and 26 june morlet wavelet analysis of the amplitude for both the storms shows a presence of strong wave like signatures suggesting propagation of atmospheric gravity waves traveling ionosphere disturbances to the low latitude d region due to the joule heating at high latitudes

tidal exchange through the kuril straits abstract the tidal exchange between the okhotsk sea and the north pacific ocean is studied numerically with particular emphasis on the predominant k1 barotropic component the calculated harmonic constants of the k1 tide in and around the okhotsk sea agree well with those obtained from extensive tide gauge observations the features of the simulated tidal fields are similar to those reported in the literature since the k1 tide is subinertial in the okhotsk sea topographically trapped waves are effectively generated contributing to strong tidal currents with a maximum amplitude of over 1 5 m s 1 in the kuril straits the structures of tide induced mean flows in most passages of the straits are characterized by bidirectional currents in which the mean flow exhibits a reversal in direction across the passages this feature is clearly indicated in noaa infrared imagery the mean transport shows significant net exchange of water via several straits in the kuril islands a transport of about 5 0 sv 1 sv

a 200 ka record of climatic change and dune activity in the thar desert india abstract an 18 4 m excavated dune section in the thar desert of india with a chronology based on 12 tl ages and a basal age of 190 ka has preserved 12 cycles of dune accretion soil formation calcrete development and subsequent erosion together with the presence of stone artefacts ranging in age from lower palaeolithic to mesolithic coeval with more humid climatic interludes phases of soil development and carbonate precipitation were relatively wet and phases of dune accretion relatively dry so that there were 12 significant moist intervals separated by 11 drier intervals during the past 190 ka the calculated time interval between successive phases of dune sand accumulation ranged from 22 2 ka to 15 8 ka with a mean of 19 0 ka these values are consistent with a precessional influence on dune activity and on the associated onset of early monsoonal activity in this region carbon isotopes measured on organic matter within the sand profiles show consistent values close to 21 6 1 pointing to deposition during a transitional climatic regime characterized by a change from open c3 grassland to c4 woodland or forest

a three dimensional baroclinic model of the irish sea formation of the thermal fronts and associated circulation a high resolution three dimensional baroclinic shelf sea model is developed and applied to the determination of the various processes influencing the generation and position of thermal fronts and the associated circulation in the irish sea the model has a horizontal grid resolution of approximately 3 6 km by 3 0 km and can resolve the thermal fronts in the region in particular in the western irish sea although the grid is not sufficiently fine to resolve small scale features along these fronts produced by baroclinic instabilities using meteorological forcing from dublin airport located close to the center of the region and tidal forcing a series of numerical experiments were performed to examine the processes influencing the location and dynamics of thermal fronts and associated circulation in the irish sea the results show a reasonable qualitative agreement with observations of the thermal stratification and the associated circulation in the western irish sea the ability of the model to reproduce the main features of the frontal structures in the region having been established it is used to examine the interannual variability of the density flow field calculations using meteorological forcing from different years show that the western irish sea fronts and the associated cyclonic circulation are persistent features although exact details of the fronts and their times of formation and breakdown show a large interannual variability model results also reveal a patch of thermal stratification in the northern part of the eastern irish sea with northward thermal density driven currents in this region

middle and low latitude ionosphere response to 2015 st patrick s day geomagnetic storm this paper presents a study of the st patrick s day storm of 2015 with its ionospheric response at middle and low latitudes the effects of the storm in each longitudinal sector asian african american and pacific are characterized using global and regional electron content at the beginning of the storm one or two ionospheric positive storm effects are observed depending on the longitudinal zones after the main phase of the storm a strong decrease in ionization is observed at all longitudes lasting several days the american region exhibits the most remarkable increase in vertical total electron content vtec while in the asian sector the largest decrease in vtec is observed at low latitudes using spectral analysis we were able to separate the effects of the prompt penetration of the magnetospheric convection electric field ppef and of the disturbance dynamo electric field ddef on the basis of ground magnetic data concerning the ppef earth s magnetic field oscillations occur simultaneously in the asian african and american sectors during southward magnetization of the b z component of the interplanetary magnetic field concerning the ddef diurnal magnetic oscillations in the horizontal component h of the earth s magnetic field exhibit a behavior that is opposed to the regular one these diurnal oscillations are recognized to last several days in all longitudinal sectors the observational data obtained by all sensors used in the present paper can be interpreted on the basis of existing theoretical models

a numerical study of stratified tidal rectification over finite amplitude banks part ii georges bank abstract tidal rectification over a two dimensional finite amplitude symmetrical bank is studied using the blumberg and mellor primitive equation coastal ocean circulation model ecom si in the homogeneous case the nonlinear interaction of tidal currents with the variable bottom topography generates an along isobath residual circulation over the bank which tends to increase as either the slope or height of the bank is increased in the stratified case internal waves at tidal and higher frequencies are generated over the sloping sides of the bank tidal mixing occurs in the bottom boundary layer leading to horizontal tidal mixing fronts the resulting stratified tidal rectification associated with the tidal mixing front the generation of internal tides and the modification of internal friction due to stratification leads to a subsurface intensification of the along isobath residual current at the front and at the top of the bottom mixed layer over the slope and a cross bank double cell circulation

on the relevance of tidal forcing in modelling the mediterranean thermohaline circulation abstract the four dominant constituents of the semi diurnal and diurnal tides have been implemented in a regional eddy resolving mediterranean version of the massachusetts institute of technology general circulation model to assess the role played by tides on the simulated mediterranean thermohaline circulation to this aim we have compared two 10 year hindcast simulations differing only for the inclusion omission of tidal forcing following the recent recommendations suggested by sannino et al 2014 both simulations use the same model having a substantial increment of the horizontal resolution in the region of the strait of gibraltar the results suggest that application of explicit tidal forcing in a mediterranean model has non negligible effects on the simulated circulation in addition to the expected intensification of local mixing processes the western basin exhibits an immediate response to the different characteristics of the inflowing aw observable in the modified deep water convection processes in the gulf of lion the inclusion of tidal forcing also induces changes in the intermediate circulation of the tyrrhenian sea bringing to a better representation of local structures and a reinforcement of the global thermohaline cell liw dispersal paths in the eastern basin are also affected by tides

processes influencing the internal tide its higher harmonics and tidally induced mixing on the malin hebrides shelf abstract a three dimensional prognostic hydrodynamic model with a turbulence energy submodel is used to examine the spatial distribution of the internal tide in the shelf edge region off the west coast of scotland in the initial series of calculations presented here the model is used in a cross shelf form the model contains all the non linear terms necessary to examine the generation of the higher harmonics of the tide and the generation of very short waves on the density interface near the shelf break initial calculations assuming a homogeneous sea region show a thick turbulent bottom boundary layer generated by bottom friction which reduces the tidal current in the near bed region although above this the flow is essential inviscid with no vertical variation calculations with a specified vertical stratification reduce the thickness of the bottom turbulent layer with an associated change in current profile in the case of specified stratification no internal tides are generated however when the density field is allowed to evolve a significant internal tide is generated with an associated internal shear giving rise to enhanced mixing in regions of largest shear results from the model show that higher harmonics of the internal tide and short internal waves are generated above the shelf break where horizontal mixing processes are important the magnitude of these short internal waves increases with increasing tidal forcing and also depends upon the size of the horizontal diffusion term regions of intense surface and bed turbulence associated with the internal tide are found in the shelf break area suggesting that turbulence energy measurements in this location may be a good test of turbulence closure models however the significant spatial variability associated with these regions shows that an intense measurement campaign is required to avoid significant undersampling

duskside enhancement of equatorial zonal electric field response to convection electric fields during the st patrick s day storm on 17 march 2015 the equatorial zonal electric field responses to prompt penetration of eastward convection electric fields ppef were compared at closely spaced longitudinal intervals at dusk to premidnight sectors during the intense geomagnetic storm of 17 march 2015 at dusk sector indian longitudes a rapid uplift of equatorial f layer to 550 km and development of intense equatorial plasma bubbles epbs were observed these epbs were found to extend up to 27 13 n and 25 98 s magnetic dip latitudes indicating their altitude development to 1670 km at apex in contrast at few degrees east in the premidnight sector thailand indonesian longitudes no significant height rise and or epb activity has been observed the eastward electric field perturbations due to ppef are greatly dominated at dusk sector despite the existence of background westward ionospheric disturbance dynamo idd fields whereas they were mostly counter balanced by the idd fields in the premidnight sector in situ observations from swarm a and swarm c and communication navigation outage forecasting system satellites detected a large plasma density depletion near indian equatorial region due to large electrodynamic uplift of f layer to higher than satellite altitudes further this large uplift is found to confine to a narrow longitudinal sector centered on sunset terminator this study brings out the significantly enhanced equatorial zonal electric field in response to ppef that is uniquely confined to dusk sector the responsible mechanisms are discussed in terms of unique electrodynamic conditions prevailing at dusk sector in the presence of convection electric fields associated with the onset of a substorm under southward interplanetary magnetic field bz

land use land cover and point sources of the 15 december 2003 dust storm in southwestern north america abstract a major dust event occurred on 15 december 2003 in the chihuahuan desert region of texas and new mexico usa and chihuahua mexico and in the southern high plains region of texas and new mexico using a modis satellite image 146 individual small scale sources plumes of dust were identified these plumes merged to form the regional scale dust storm the point sources were characterized with respect to land use and land cover using a combination of field work and aerial photography fifty eight of the sources are on cropland mostly on the southern high plains forty nine are on rangeland from across the entire region thirty of the dust plumes originate within playa basins mostly in the chihuahuan desert point sources of dust only represent a small fraction of the total land surface at any given moment i e the period when the image was acquired because most of the land within the region was not subject to erosion during the event in general land use and soil characteristics of point sources matched those of adjacent areas that were not emitting dust at the time suggesting that microscale variations in erodibility or meteorological factors may dictate the actual emission points of dust during individual events

shrub mound formation and stability on semi arid slopes in the northern negev desert of israel a field and simulation study in semi arid areas vegetation is scarce and often dominated by individual shrubs on raised mounds the processes of formation of these mounds are diverse and still debated often shrub mound formation is directly related to the formation of vegetation patterns thereby assuming that shrub mound formation is driven by biological interactions we hypothesize that water related erosion and sedimentation are also important drivers of shrub mound formation in the northern negev desert of israel we test this hypothesis by combining field observations with model simulations we studied shrub mounds in the semi arid catchment of sayeret shaked in the northern negev desert 200 mm annual precipitation height and diameter of shrub canopy and shrub mounds were measured and micro morphological techniques were used to reconstruct the formation of the shrub mounds we used landscape evolution model lapsus to simulate shrub mound formation at short single precipitation event and longer 100 years timescales at different slope angles both field and model results indicate that shrub mounds in sayeret shaked are at least partly formed by redeposition of eroded material below the shrubs and by erosion and lowering of the surrounding crust additional model simulations suggest that mounds are formed most under low shrub density and large shrub canopy diameter shrub mound formation increases with slope in dryer and wetter climates than the studied 200 mm rainfall semi arid climate zone shrub mound formation is less likely

changes in grain size of sand in transport over a foredune suspended sand is sampled at several heights and positions on a beach and foredune providing detailed insight into the vertical and horizontal variation in sand content in the air during landward transport grain size analysis is used to study the changes in grain size distribution during landward transport mean grain size and sorting decrease during transport changes in textural parameters follow a gradual and regular path when the sediment is transported into the foredune sediment trapped on the seaward slope at a height of 30 50 cm above the surface closely resembles the sediment trapped landward which implies that changes in the direction of transport are related to vertical changes within the sediment transport profiles the movement of sand over the vegetated foredunes is induced by turbulent forces created by the air flowing across the vegetation and the foredune leading to a change from saltation on the beach to modified saltation and suspension on the foredune small grains are lifted higher and fall more slowly than coarse grains and therefore are transported further landward resulting in a gradual decrease in grain size of the landward deposited sediment

the initiation of particle movement by wind when air blows across the surface of dry loose sand a critical shear velocity fluid threshold ut must be achieved to initiate motion however since most natural sediments consist of a range of grain sizes fluid threshold for any sediment cannot be defined by a finite value but should be viewed as a threshold range which is a function of the size shape sorting and packing of the surface sediment in order to investigate the initiation of particle movement by wind a series of wind tunnel tests was carried out on a range of pre screened fluvial sands and commercially available glass beads with differing mean sizes and sorting characteristics a sensitive laser monitoring system was used in conjunction with a high speed counter to detect initial grain motion and to count individual grain movements test results indicate that when velocity is slowly increased over the sediment surface the smaller or more exposed grains are first entrained by the fluid drag and lift forces either in surface creep rolling or in saltation bouncing or hopping downwind as velocity continues to rise larger or less exposed grains may also be moved by fluid drag on striking the surface saltating grains impart momentum to stationary grains this impact may result in the rebound of the original grain as well as the ejection of one or more stationary grains into the air stream at shear velocities lower than that required to entrain a stationary particle by direct fluid pressure as a result there is a cascade effect with a few grains of varying size initially moving over a range of shear velocities the fluid threshold range and setting in motion a rapidly increasing number of grains results of the tests showed that the progression from fluid to dynamic threshold based on grain movement can be characterized by a power function the coefficients of which are directly related to the mean size and sorting characteristics of the sediment

the use of microbiotic crusts as biomarkers for ponding subsurface flow and soil moisture content and duration abstract previous work at the hallamish dunefield in the western negev desert defined and mapped 5 mature types of microbiotic crusts mcs crust definition and sampling were based on 4 4 m pixels yet within these pixels microhabitats with different crust types could be noted this was also the case within crust type a that extends over the south facing slope and the sandy interdune there close examination mainly at daylight wetness duration and crust biomass were monitored during 1991 1994 in 12 habitats we habitats which exhibited the highest biomass also exhibited longer wetness duration in comparison to sh habitats both groups exhibited higher biomass and wetness duration than the control when the relation between daylight wetness duration and the chlorophyll content of the crust was compared a positive linear relation with a good correlation r 2 0 74 was found the findings indicate that crust biomass may be used as a biomarker for surface wetness duration and may thus point to habitats subjected to particular hydrological processes such as water ponding and subsurface flow they may also point to soil patches having high moisture content and therefore long wetness duration higher moisture content that lasted for a longer duration was indeed recorded during preliminary measurements that were carried out at 0 40 cm soil patches subjected to subsurface flow as indicated by their mc during the end of the winter season of 1994 95 and 1996 97 the findings may attest to differential rates of pedogenesis thus highlighting the use of mcs as possible biomarkers for small soil habitats with variable pedogenesis

observations of internal tides off the coast of shandong peninsula china abstract bottom mounted platforms equipped with current profilers meters temperature salinity and turbidity sensors were deployed for about 10 days in august 2017 over an elongated deposit off the coast of shandong peninsula in order to monitor the hydrodynamics and sediment processes in the bottom boundary layer in total semidiurnal barotropic tides dominate the measured currents accounting for 90 of total variance however in the cross shore direction greater variance is associated with the semidiurnal internal tidal currents than the semidiurnal barotropic currents both the empirical orthogonal functions and normal mode analysis demonstrate that the baroclinic velocity is dominated by the mode 1 internal tides i e the current has a vertical shear with strong opposite flows near the surface and bottom while weak in the middle although the bottom slope is subcritical in most area of the deposit the ratio between the bottom slope and the slope of internal tide characteristics is greater than 0 5 suitable for local internal tide generation the internal tides generated from the deposit are especially significant considering that the shelf of the yellow sea is usually broad and flat the quantitative estimation of the water column mixing indicate that the bottom dissipation induced by the barotropic tides 6 44 10 4 m3 s 3 is greater than the internal tides 0 95 10 4 m3 s 3 and the total dissipation rate due to bottom drag is 5 49 10 4 m3 s 3 which is much greater than the interior one due to internal tides 2 69 10 4 m3 s 3 the internal tidal current alone is not energetic enough to resuspend the local fine grained sediments however in the cross shore direction the sediment flux due to internal tides is twice as much as the barotropic component resulting in a net onshore sediment flux thus highlighting the advection effect of internal tides in the coastal mass transport

low salinity plume detachment under non uniform summer wind off the changjiang estuary abstract in the past two physical mechanisms baroclinic instability bi and strong asymmetric tidal mixing satm during the spring tidal period were proposed for the offshore detachment of the low salinity plume over the inner shelf of the east china sea ecs these two mechanisms were re examined using both observations and a fully three dimensional 3 d high resolution unstructured grid free surface primitive equation finite volume community ocean model fvcom the observed currents and salinities showed that the plume was characterized by a two layer system in which the upper layer is mainly driven by the river discharge induced buoyancy flow and the lower layer is predominantly controlled by tidal mixing and rectification the satm mechanism was based on the model run without calibration against observed currents and salinity around the plume region so that it should be applied with caution to a realistic condition observed on the inner shelf of the ecs the bi mechanism was derived under a condition without consideration of tidal mixing although bi could still occur along the frontal zone when tides were included it was unable to produce a single large detached low salinity lens observed on the inner shelf of the ecs the process oriented model experiment results suggest that for a given river discharge and realistic tidal flow the spatially non uniform southwesterly surface wind during the southeast monsoon dominant summer could increase frontal spatial variability and thus produce a significant offshore detachment of low salinity water on the inner shelf of east china sea

model study of the cross frontal water exchange on georges bank a three dimensional lagrangian experiment 1 characteristics of the cross frontal water exchange over georges bank are investigated through a sequence of numerical model experiments featuring realistic three dimensional 3 d bathmetry bi monthly averaged climatological stratification tidal forcing and mean and observed wind forcing the model used in this study is the ecom si version of the blumberg and mellor 1987 primitive equation model with mellor yamada 1982 level 2 5 turbulence closure the model domain includes georges bank and the gulf of maine and is forced at the open ocean boundary by the semidurnal m2 tide fluid particles were tracked in the 3 d time dependent eulerian flow field to examine the lagrangian flow field and passive tracer experiments were conducted to investigate the relative roles of advection and turbulent diffusion on cross frontal exchange two distinct paths for the on bank water movement were detected on georges bank one is over the northwestern flank of the bank where the bottom topography changes sharply in both along and cross bank directions and the other is near the bottom around the bank where the tidal mixing front is located over the northern flank the cross bank component of the lagrangian residual current is generally opposite in direction to that of the eulerian residual current resulting in an on bank cross frontal water transport near the bottom over the southern flank the near bottom water tends to converge toward the tidal mixing and shelf break fronts so that the near bottom flow over the shelf between these two fronts is divergent the response to wind forcing varied with ambient stratification and water depth in winter strong winds can drive a significant off bank water transport tending to wash out the bank in summer winds are generally too weak to alter the general pattern of tidal driven particle motion within the mixed region on the crest of the bank and the surrounding tidal mixing front some wind driven off bank transport occurs near the surface in the stratified region on the outer southern flank but this has little influence on water movement near the bottom passive tracer experiments reveal that the net cross frontal water flux near the bottom is caused primarily by advection and horizontal diffusion tidal induced vertical diffusion tends to make the tracer mix rapidly upward thus reducing the percent of the cross frontal flux due to advection our new model results are consistent with previous model studies of georges bank and agree in general with drifter and dye patches observed in the u s globec nw atlantic georges bank program

response of the low latitude d region ionosphere to extreme space weather event of 14 16 december 2006 the response of the d region low latitude ionosphere has been examined for extreme space weather event of 14 16 december 2006 associated with a x1 5 solar flare and an intense geomagnetic storm dst 146 nt using vlf signals from northwest cape australia nwc 19 8 khz and lualualei hawaii callsign npm 21 4 khz transmitters monitored at suva geographic coordinates 18 10 s 178 40 e fiji modeling of flare associated amplitude and phase enhancements of nwc 3 6 db 223 and npm 5 db 153 using long wave propagation capability code shows reduction in the d region reflection height h by 11 1 km and 9 4 km and enhancement in ionization gradients described by increases in the exponential sharpness factor by 0 122 and 0 126 km 1 for the nwc and npm paths respectively during the storm the daytime signal strengths of the nwc and npm signals were reduced by 3 2 db on 15 and 16 december for about 46 h and recovered by 17 december modeling for the nwc path shows that storm time values of h and were reduced by 1 2 km and 0 06 km 1 respectively morlet wavelet analysis of signal amplitudes shows no clearly strong signatures of gravity wave propagation to low latitudes during the main and recovery phases the reduction in vlf signal strength is due to increased signal attenuation and absorption by the earth ionosphere waveguide due to storm induced d region ionization changes and hence changes in d region parameters the long duration of the storm effect results from the slow diffusion of changed composition ionization at d region altitudes compared with higher altitudes in the ionosphere

circulation hydrography and transport over the summit of axial seamount a deep volcano in the northeast pacific a numerical model of ocean flow hydrography and transport is used to extrapolate observations of currents and hydrography and infer patterns of material flux in the deep ocean around axial seamount a destination node of nsf s ocean observatories initiative s cabled array using an inverse method the model is made to approximate measured deep ocean flow around this site during a 35 day time period in the year 2002 the model is then used to extract month long mean patterns and examine smaller scale spatial and temporal variability around axial like prior observations model month long mean currents flow anti cyclonically around the seamount s summit in toroidal form with maximum speeds at 1500m depth of 10 11 cm s as a time mean the temperature salinity anomaly distribution takes the form of a cold briny dome above the summit passive tracer material continually released at the location of the ashes vent field exits the caldera primarily through its southern open end before filling the caldera once outside the caldera the tracer circles the summit in clockwise fashion fractionally re entering the caldera over lower walls at its north end while gradually bleeding southwestward during the modeled time period into the ambient ocean a second tracer release experiment using a source of only two day duration inside and near the casm vent field at the northern end of the caldera suggests a residence time of the fluid at that locale of 8 9 days

current separation and upwelling over the southeast shelf of vietnam in the south china sea 1 the high resolution unstructured grid finite volume community ocean model fvcom was used to examine the physical mechanisms that cause current separation and upwelling over the southeast shelf of vietnam in the south china sea scs process oriented experiments suggest that the southwesterly monsoon wind is a key physical mechanism for upwelling in that area but not a prerequisite to cause current separation with no wind forcing current separation in summer can occur as a result of the encounter of a southward along shelf coastal current from the north and northeastward buoyancy driven and stratified tidal rectified currents from the southwest the southward current can be traced upstream to the hong river in the gulf of tonkin this current is dominated by semigeostrophic dynamics and is mostly confined to the narrow shelf along the northern vietnamese coast the northeastward currents are generated by tidal rectification and are intensified by the mekong river discharge and southwesterly monsoon wind forcing the dynamics controlling this current are fully nonlinear with significant contributions from advection and vertical turbulent mixing upwelling in the current separation zone can be produced by a spatially uniform constant wind field and can be explained using simple wind induced ekman transport theory this finding differs from previous theory in which the regional dipole wind stress curl is claimed as a key mechanism for current separation and upwelling in this coastal region our scs fvcom driven by the wind stress river discharge and tides is capable of reproducing the location and tongue like offshore distribution of temperature as those seen in satellite derived sea surface temperature imagery

seasonal migration of the yellow sea bottom cold water the three dimensional motion of the yellow sea bottom cold water ysbcw and the relevant dynamical factors are studied using a regional circulation model and the two way lagrangian particle tracking method ptm the simulated results are in good agreement with hydrographic observations the trajectories of the modeled particles show that the subsurface cold heavy water mass from the northern part of the yellow sea gradually sinks into deeper layers along the western slope of the yellow sea trough with a southward movement from spring to summer the cold water mass gradually gathers speed from early march to july or august and eventually reaches its southernmost location in late september or early october furthermore sensitivity experiments demonstrate that tide induced residual currents under baroclinic conditions are the dominant factor driving deep circulation during summertime in the yellow sea the summer southerly wind and strong surface solar radiation are the secondary factors influencing the southward migration this study also proposes an improved delimitation for the ysbcw based on temperature statistics in the central basin deeper than 40 m between 35 n and 39 n in march with an increase in rate of approximately 0 7 c month which is more appropriate than the constants of the 8 c or 10 c isotherms frequently used

ionospheric d region parameters obtained using vlf measurements in the south pacific region the diurnal variations in the phase and amplitude of nwc npm and nlk very low frequency vlf transmissions received at suva fiji have been modeled using the long wave propagation capability lwpc v2 1 code to determine the ionospheric d region parameters h reference height and rate of increase of electron density with height for different daytime and nighttime conditions along the transmitter receiver great circle paths trgcps measured vlf signal amplitude and phase show explicit variation over the day and nighttime along the trgcp also revealing amplitude minima and phase steps during sunrise and sunset as the day night terminator traverses the trgcp while the daytime signal strength is reasonably smooth at nighttime the signal exhibits a great deal of variability for three signal paths the mean daytime h and were found to be 70 7 km and 0 40 km 1 respectively while nighttime mean values of these parameters were found to be 84 2 km and 0 68 km 1 respectively the temporal and day to day variability of the nighttime d region parameters shows that h and ranges in between 83 0 85 0 km and 0 58 0 80 km 1 respectively one of the possible sources of nighttime signal variability is increase in the number of modes propagating and relative complex interference between them along the trgcps whereby the weaker modes also become significant at night due to reduced attenuation in addition the variations in the nighttime d region itself may be a cause of high signal variability

a late pleistocene linear dune dam record of aeolian fluvial dynamics at the fringes of the northwestern negev dunefield abstract a late pleistocene aeolian fluvial record within a rare vegetated linear dune like structure at the fringe of the northwestern negev dunefield israel provides direct evidence of dune damming dynamics within the structure and its environs study methods included high resolution morphology and stratigraphy micromorphology and sedimentological analyses chronology was based on eight archaeological sites from the structure and the inqua dune atlas chronologic database low energy fine grained fluvial deposits underlying the structure and extending from its flanks indicate deposition by low energy hyper concentrated flows in a floodplain environment and later in water bodies that formed by dune damming of a mid sized drainage basin interbedded sand with fine grained deposits within the linear structure indicates interchanging dominances between aeolian sand incursion and seasonal floods sand deposition during dune elongation led to structure growth and dune damming of its drainage system that in turn formed water bodies and upstream fine grained deposition following seasonal floods calculations of current sediment yields indicate that fine grained deposits accretion up to the structure s brim could possibly have rapidly occurred over a total time span of decades however artifacts dating to the geometric kebaran 17 5 12 9 cal kyr bp and harifian 12 9 11 2 cal kyr bp archaeological periods on the structure s surface indicates intermittent repetitive and short term camping utilizing adjacent water bodies over a time period of 4000 5000 years fluctuating high winds and precipitation during a time window of increased fluvial availability of fine grained sediment from the hinterland generated ample fine grained deposition after 11 cal kyr bp the abundance and recurrence of dammed water bodies decreased when reduced wind power constrained dune dam maintenance after sediment accommodation space dissipated fluvial flow of the drainage basin led to dune dam destruction and partial fluvial erosion of the fine grained deposits that continues today

a model study of tidally induced suspended sediment transport in the iberian shelf edge region abstract across shelf suspended sediment transport due to tides is investigated using a three dimensional baroclinic hydrodynamic model including a sediment transport capability and parameterizing sub grid scale diffusion using a turbulence energy model the model in cross shelf form with topography characteristic of the shelf edge off the west coast of spain is used to examine sediment movement due to both barotropic and baroclinic tides and an along shelf flow calculations showed that the bed stress due to the barotropic tide and an along shelf flow exceeded the critical bed stress for part of the tidal cycle leading to sediment suspension the across shelf residual flow due to tidal rectification and the bottom ekman transport associated with the along shelf flow was on shelf in the surface layer and off shelf near the bed and produced a net off shelf sediment transport in the bottom boundary layer when a fixed stratification representing the thermocline was imposed this inhibited the upward diffusion of sediment thereby increasing its concentration in the bottom boundary layer comparison with and without stratification allowed its influence upon sediment concentration to be quantified calculations in which the stratification evolved with the flow field produced internal tides with an associated increase in current amplitude at a number of locations leading to greater spatial variability in the tidal residual and an additional residual due to the across shelf tidally induced thermal front increased diffusion and vertical velocity associated with the internal tide produced a thickening of the sediment bottom boundary layer a detailed examination of terms in the sediment transport equation enabled the importance of each in different regions to be quantified it showed that in the near bed layer the main balance was between vertical diffusion and settling however sediment concentration in the upper part of the water column was increased by the presence of the internal tide due to enhanced vertical advection and diffusion into the region changes in vertical stratification were found to influence both the horizontal and vertical distributions of sediment due to its influence upon the internal tide

the 22 july 2009 total solar eclipse modeling d region ionosphere using narrowband vlf observations we present d region ionospheric response to 22 july 2009 total solar eclipse by modeling 19 8 khz signal from nwc very low frequency vlf navigational transmitter located in the australia nwc vlf signal was received at five stations located in and around eclipse totality path in the indian east asian and pacific regions nwc signal great circle paths to five stations are unique having eclipse coverage from no eclipse to partiality to totality regions and the signal is exclusively confined in the low and equatorial regions eclipse induced modulations in nwc signal have been modeled by using long wave propagation capability code to obtain d region parameters of reflection height h and sharpness factor long wave propagation capability modeling showed an increase in h of about 2 3 km near central line of totality 3 0 km in the region near to totality fringe and 2 4 to 3 0 km in the region under partial eclipse using h and wait ionosphere electron density ne profile at the daytime altitude of 75 km showed a decrease in ne by about 58 at a station near totality central line whereas at totality fringe and in partial eclipse region decrease in the ne was between 63 and 71 with respect to normal time values the eclipse associated variations in the h and ne are less in low latitude region as compared to midlatitude the study contributes to explain observations of wave like signature in the d region during an eclipse and difference in the eclipse effect in the different latitude longitude sectors

the role of qiongzhou strait in the seasonal variation of the south china sea circulation an analysis of the water level and current data taken in qiongzhou strait in the south china sea scs over the last 37 years 1963 to 1999 was made to examine the characteristics of tidal waves and residual flow through the strait and their roles in the seasonal variation of the scs circulation the observations reveal that qiongzhou strait is an area where opposing tidal waves interact and a source of water transport to the gulf of beibu gulf of tonkin scs a year round westward mean flow with a maximum speed of 10 40 cm s 1 is found in qiongzhou strait this accounts for water transport of 0 2 0 4 sv and 0 1 0 2 sv into the gulf of beibu in winter spring and summer autumn respectively the outflow from qiongzhou strait may cause up to 44 of the gulf water to be refreshed each season suggesting that it has a significant impact on the seasonal circulation in the gulf of beibu this finding is in contrast to our current understanding that the seasonal circulation patterns in the south china sea are primarily driven by seasonal winds several numerical experiments were conducted to examine the physical mechanisms responsible for the formation of the westward mean flow in qiongzhou strait the model provides a reasonable simulation of semidiurnal and diurnal tidal waves in the strait and the predicted residual flow generally agrees with the observed mean flow an analysis of the momentum equations indicates that the strong westward flow is driven mainly by tidal rectification over variable bottom topography both observations and modeling suggest that the coastal physical processes associated with tidal rectification and buoyancy input must be taken into account when the mass balance of the scs circulation is investigated especially for the regional circulation in the gulf of beibu

characterization of three dimensional lagrangian circulation associated with tidal rectification over a submarine bank abstract two approaches to the quantitative characterization of lagrangian circulation in three dimensional 3d time periodic current fields are used to describe major features of a model derived flow field for barotropic tidal rectification on georges bank the first approach is an extension of the 2d saddlepoint method used by ridderinkhof and loder to describe the vertically averaged lagrangian circulation associated with various forcings over outer gulf of maine banks application of the method to representative sigma terrain following surfaces and comparison with particle trajectories in the 3d current field indicate that the circulation saddlepoints and associated separation lines between recirculation and throughflow regions in the vertically averaged flow over georges bank are qualitatively representative of the entire water column but that there is significant vertical structure in the lagrangian circulation in particular the horizontal extent of the tidally rectified clockwise gyre on

tidal modulation on the changjiang river plume in summer 1 tide effects on the structure of the near field changjiang river plume and on the extension of the far field plume have often been neglected in analysis and numerical simulations which is the focus of this study numerical experiments highlighted the crucial role of the tidal forcing in modulating the changjiang river plume without the tidal forcing the plume results in an unrealistic upstream extension along the jiangsu coast with the tidal forcing the vertical mixing increases resulting in a strong horizontal salinity gradient at the northern side of the changjiang river mouth along the jiangsu coast which acts as a dynamic barrier and restricts the northward migration of the plume furthermore the tidal forcing produces a bidirectional plume structure in the near field and the plume separation is located at the head of the submarine canyon a significant bulge occurs around the head of the submarine canyon and rotates anticyclonically which carries a large portion of the diluted water toward the northeast and merges into the far field plume a portion of the diluted water moves toward the southeast which is mainly caused by tidal rectification this bidirectional plume structure is more evident under certain wind conditions during the neap tide with the reduced tidal energy the near field plume extends farther offshore and the bulge becomes less evident these dynamic behaviors are maintained and are fundamentally important in the region around the river mouth even under the summer monsoon and the shelf currents although in the far field the wind forcing and shelf currents eventually dominate the plume extension

a model of tidal rectification by potential vorticity mixing part i homogeneous ocean abstract in previous studies of tidal generation of mean flow over varying topography the rectification mechanism has generally invoked bottom friction as a source of tidal flux of momentum and vorticity hence referred as friction mechanism the author proposes a different mechanism based on horizontal mixing of potential vorticity drawing analogy from tidal dispersion of passive tracers this mixing is parameterized through a diffusivity hence called diffusivity mechanism that is quadratic in the tidal amplitude in this part 1 the mean along isobath flow near a shelf break is determined for a homogeneous ocean and contrasted with that induced by friction mechanism in part 2 the effect of a front will be considered it is found that although the mean flow is pointing in the same direction as that induced by friction mechanism i e to the right when facing deep water in the northern hemisphere it varies more slowly with the tidal amplitude in the typical situation when the mean shear is

low mid latitude d region ionospheric perturbations associated with 22 july 2009 total solar eclipse wave like signatures inferred from vlf observations we present first report on the periodic wave like signatures wls in the d region ionosphere during 22 july 2009 total solar eclipse using jji japan very low frequency vlf navigational transmitter signal 22 2 khz observations at stations allahabad varanasi and nainital in indian sector busan in korea and suva in fiji the signal amplitude increased on 22 july by about 6 and 7 db at allahabad and varanasi and decreased by about 2 7 3 5 and 0 5 db at nainital busan and suva respectively as compared to 24 july 2009 normal day the increase decrease in the amplitude can be understood in terms of modal interference at the sites of modes converted at the discontinuity created by the eclipse intercepting the different transmitter receiver great circle paths the wavelet analysis shows the presence of wls of period 16 40 min at stations under total eclipse and of period 30 80 min at stations under partial eclipse 85 54 totality with delay times between 50 and 100 min at different stations the intensity of wls was maximum for paths in the partially eclipsed region and minimum in the fully eclipsed region the features of wls on eclipse day seem almost similar to wls observed in the nighttime of normal days e g 24 july 2009 the wls could be generated by sudden cutoff of the photo ionization creating nighttime like conditions in the d region ionosphere and solar eclipse induced gravity waves coming to ionosphere from below and above the present observations shed additional light on the current understanding of gravity waves induced d region ionospheric perturbations

a nonhydrostatic version of fvcom 2 mechanistic study of tidally generated nonlinear internal waves in massachusetts bay 1 the generation propagation and dissipation processes of large amplitude nonlinear internal waves in massachusetts bay during the stratified season were examined using the nonhydrostatic finite volume coastal ocean model fvcom nh the model reproduced well the characteristics of the high frequency internal waves observed in massachusetts bay in august 1998 the model experiments suggested that internal waves over stellwagen bank are generated by the interaction of tidal currents with steep bottom topography through a process of forming a large density front on the western slope of the bank by the release of an initial density perturbation near ebb flood transition nonlinear steepening of the density front into a deep density depression and disintegrating of the density depression into a wave train earth s rotation tends to transfer the cross bank tidal kinetic energy into the along bank direction and thus reduces the intensity of the density perturbation at ebb flood transition and density depression in the flood period the internal wave packet propagates as a leading edge feature of the internal tidal wave and the faster propagation speed of the high frequency internal waves in massachusetts bay is caused by earth s rotation the model experiments suggested that bottom friction can significantly influence the cross bank scale of the density perturbation and thus the density depression during wave generation and the dissipation during the wave s shoaling inclusion of vertical mixing using the mellor yamada level 2 5 turbulence closure model had only a marginal effect on wave evolution the model results support the internal wave theory proposed by lee and beardsley 1974 but are in disagreement with the lee wave mechanism proposed by maxworthy 1979

saltwater intrusion into the changjiang river a model guided mechanism study 1 the changjiang river cr is divided into a southern branch sb and a northern branche nb by chongming island as the river enters the east china sea observations reveal that during the dry season the saltwater in the inner shelf of the east china sea flows into the cr through the nb and forms an isolated mass of saltwater in the upstream area of the sb the physical mechanism causing this saltwater intrusion has been studied using the high resolution unstructured grid finite volume coastal ocean model fvcom the results suggest that the intrusion is caused by a complex nonlinear interaction process in relation to the freshwater flux upstream tidal currents mixing wind and the salt distribution in the inner shelf of the east china sea the tidal rectification resulting from the interaction of the convergence or divergence of tidal momentum flux and bottom friction over abrupt topography produces a net upstreamward volume flux from nb to sb with river discharge the net water transport in the nb is driven through a momentum balance of surface elevation gradient forcing horizontal advection and vertical diffusion in the dry season reducing the surface elevation gradient forcing makes tidal rectification a key process favorable for the saltwater intrusion a northerly wind tends to enhance the saltwater intrusion by reducing the seaward surface elevation gradient forcing rather than either the baroclinic pressure gradient forcing or the wind driven ekman transport a convergence experiment suggests that high grid resolution 100 m or less is required to correctly resolve the net water transport through the nb particularly in the narrow channel on the northern coast of chongming island

late holocene dune migration on the south texas sand sheet abstract there are a wide variety of vegetated eolian depositional landforms associated with the south texas sand sheet attesting to the past dominance of eolian processes mapping identified two sets of parabolic dunes elongating with winds from the southeast and the northwest parabolic dunes elongated by northwesterly winds are older than ca 200 years and may be associated with eolian depositional events ca 2700 and or 2000 years ago the latest dune migration event associated with southeasterly winds occurred ca 200 years ago and at one site is inset into northwesterly extended parabolic dunes this period of dune migration may be coincident with particularly severe drought identified in the tree ring record centered at ad 1790 when the palmer drought severity index was 4 a threshold of dune movement may have occurred ca in the 11th 15th and 20th centuries when there are two or more consecutive years with a palmer drought severity index of

comparison of wind and tidal contributions to seasonal circulation of the yellow sea 1 seasonal circulation of the yellow sea ys in response to wind and tidal forces is examined using a three dimensional numerical model wind forcing affects the wintertime circulation of the ys on the other hand the summer southerly monsoon is weak and therefore has little impact on the circulation on the basis of comparative experiments with and without wind conditions results indicate that the yellow sea warm current yswc along the ys trough exists regardless of wind forcing however strong winter northerly winds intensify the southward coastal flows along both coasts of the ys and therefore the northward intrusion of the yswc becomes stronger these flows in the ys are substantially weakened when wind forcing is not applied to the model in addition to wind driven circulation tide induced circulation is also dominant in the ys particularly in summer in winter the tidal effect weakens the upwind and downwind flows in response to the strong northerly winds while in summer tidal forcing induces a strong southward residual flow along the western slope and a cyclonic gyre with a bottom cold water dome at the central region of the ys the southward residual current possibly explains the southward movement of the yellow sea bottom cold water as observed in summer comparison to the effects of parameterized tidal mixing suggests that residual flow driven by explicit tidal forcing plays an important role in the summertime circulation of the ys

the flux profile of a blowing sand cloud a wind tunnel investigation abstract the flux profile of a blowing sand cloud or the variation of blown sand flux with height is the reflection of blown sand particles that move in different trajectories and also the basis for checking drifting sand here we report the wind tunnel results of systematic tests of the flux profiles of different sized sands at different free stream wind velocities the results reveal that within the 60 cm near surface layer the decay of blown sand flux with height can be expressed by an exponential function q h a exp h b where q h is the blown sand transport rate at height h a and b are parameters that vary with wind velocity and sand size the significance of coefficient a and b in the function is defined a represents the transport rate in true creep and b implies the relative decay rate with height of the blown sand transport rate the true creep fraction the ratio of the sand transported on the surface h 0 to the total transport varies widely decreasing with both sand size and wind speed the flux profiles are converted to straight lines by plotting sand transport rate q h on a log scale the slope of the straight lines that represents the relative decay rate with height of sand transport rate decreases with an increase in free stream wind velocity and sand grain size implying that relatively more of the blown sand is transported to greater heights as grain size and wind speed increase the average saltating height represented by the height where 50 of the cumulative flux percentage occurs increases with both wind speed and grain size implying that saltation becomes more intense as grain size and or wind velocity increase

acceleration and overturning of the antarctic slope current by winds eddies and tides all exchanges between the open ocean and the antarctic continental shelf must cross the antarctic slope current asc previous studies indicate that these exchanges are strongly influenced by mesoscale and tidal variability yet the mechanisms responsible for setting the asc s transport and structure have received relatively little attention in this study the roles of winds eddies and tides in accelerating the asc are investigated using a global ocean sea ice simulation with very high resolution 1 48 grid spacing it is found that the circulation along the continental slope is accelerated both by surface stresses ultimately sourced from the easterly winds and by mesoscale eddy vorticity fluxes at the continental shelf break the asc exhibits a narrow 30 50 km swift 0 2 m s 1 jet consistent with in situ observations in this jet the surface stress is substantially reduced and may even vanish or be directed eastward because the ocean surface speed matches or exceeds that of the sea ice the shelfbreak jet is shown to be accelerated by tidal momentum advection consistent with the phenomenon of tidal rectification consequently the shoreward ekman transport vanishes and thus the mean overturning circulation that steepens the antarctic slope front asf is primarily due to tidal acceleration these findings imply that the circulation and mean overturning of the asc are not only determined by near antarctic winds but also depend crucially on sea ice cover regionally dependent mesoscale eddy activity over the continental slope and the amplitude of tidal flows across the continental shelf break

on the generation and evolution of nonlinear internal waves in the south china sea the nonhydrostatic regional ocean modeling system is applied to the nonlinear internal waves or solitons that are generated at the luzon ridge in the south china sea the luzon ridge near the batan islands is represented by an idealized ridge with a height of 2 6 km on a flat bottom model runs are performed for various ridge shapes and a symmetric tidal forcings the model is in the mixed tidal lee wave regime the barotropic tide over the ridge generates first mode waves through the internal tide release mechanism westward traveling solitons emerge from these first mode waves through nonlinear steepening in the internal tide release mechanism asymmetric tides with strong eastward currents can generate strong westward solitons the eastward current creates an elevation wave with a higher energy density west of the ridge and as soon as the current slackens the wave is released westward on its backslope strong solitons develop the energy density is further enhanced by nonlinearities such as differences in phase speeds and energy fluxes related to lee waves a modal and harmonic decomposition shows the generation of vertical modes and higher temporal harmonics and indicates significant wave wave interaction e g triads in the mixed tidal lee wave regime more energy is contained in the first mode compared to the higher modes hence linear internal tide beams are less well defined and strong solitons develop

study of the equatorial and low latitude electrodynamic and ionospheric disturbances during the 22 23 june 2015 geomagnetic storm using ground based and spaceborne techniques we use a set of ground based instruments global positioning system receivers ionosondes magnetometers along with data of multiple satellite missions swarm c nofs dmsp guvi to analyze the equatorial and low latitude electrodynamic and ionospheric disturbances caused by the geomagnetic storm of 22 23 june 2015 which is the second largest storm in the current solar cycle our results show that at the beginning of the storm the equatorial electrojet eej and the equatorial zonal electric fields were largely impacted by the prompt penetration electric fields ppef the ppef were first directed eastward and caused significant ionospheric uplift and positive ionospheric storm on the dayside and downward drift on the nightside furthermore about 45 min after the storm commencement the interplanetary magnetic field imf bz component turned northward leading to the eej changing sign to westward and to overall decrease of the vertical total electron content vtec and electron density on the dayside at the end of the main phase of the storm and with the second long term imf bz southward turn we observed several oscillations of the eej which led us to conclude that at this stage of the storm the disturbance dynamo effect was already in effect competing with the ppef and reducing it our analysis showed no significant upward or downward plasma motion during this period of time however the electron density and the vtec drastically increased on the dayside over the asian region we show that this second positive storm was largely influenced by the disturbed thermospheric conditions

tidally induced diapycnal mixing in the kuril straits and its role in water transformation and transport a three dimensional nonhydrostatic model experiment 1 baroclinic processes generated by the k1 tidal flow around the kuril straits and their role in the linkage between the okhotsk sea and the north pacific are investigated using a three dimensional nonhydrostatic model large amplitude unsteady lee waves are generated around sill tops all along the kuril island chain and induce significant density inversions from the sea surface down to the 27 6 density layer along with this wave breaking a large flow of energy takes place from the swift tidal flow regions to greater depths as a result of the clockwise propagation of both the topographically trapped waves around the islands and the remaining unsteady lee waves such wave generation and energy exchange eventually cause intense diapycnal mixing over the shallow topographic features and near the bottom leading to a maximum diapycnal diffusivity of over 103 cm2 s 1 even in the deep bussol strait which is thought to be the main exit of the okhotsk sea water considerable mixing corresponding to diapycnal diffusivity values of between 10 50 cm2 s 1 occurs vigorous mixing in the shallow regions produces low potential vorticity pv water in the upper layer and high pv water below accordingly pv fronts are formed along the island chain and sustain instabilities that in turn release baroclinic eddies with low core pv values these features are indicated in recent satellite imagery and in situ observations suggesting that the tide is the controlling factor in the formation of fronts observed in the kuril straits tidally induced mean transport across the straits is estimated to reach 26 sv 1 sv 106 m3 s 1 which is much larger than in the barotropic case however most of the exchanged water tends to circulate around the islands due to the effect of bottom topography whereas eddies pinched off from the tidal fronts carry the exchanged water offshore the amount of eddy driven offshore transport away from the islands reaches 14 sv with roughly half being directed to the north pacific this significant offshore transport spreads the effect of the diapycnal mixing taking place in the straits over wider areas of the north pacific and the okhotsk sea for example the pv values generated in the eddies differ by 30 40 from the ambient water on average whereas sea surface salinity within the eddies is 0 1 psu higher than the surroundings corresponding to the density increase of 0 08 thus the eddy transport provides significant pv and salinity fluxes to both the north pacific and the okhotsk sea hence we infer that a combination of tidally driven processes taking place at the passages leads to the formation of eddies that play a central role in water transport and transformation and are an essential aspect of the physical interplay between the okhotsk sea and the north pacific

mounds associated with shrubs in aridic soils of northeastern patagonia characteristics and probable genesis abstract studies of mounds associated with shrub clumps in northeastern patagonia indicate that these forms have an average major diameter of 355 cm and an average height of 41 cm mound cover and density are 40 and 450 mounds ha respectively mound and intermound soils present a similar textural composition as well as a similar coarse fragment content 10 20 root and organic matter contents are significantly higher whereas calcium carbonate is significantly lower in the mound than in the intermound soils mounds may represent a relict land surface level lowered in the intermound area mainly by wash erosion mound development is related to discrete shrub clumps that shelter the underlying soil once established the shrub clump and the underlying mound remain as a stable and self maintained system

influence of model geometrical fitting and turbulence parameterization on phytoplankton simulation in the gulf of maine abstract numerical experiments were made to examine the influences of model geometrical fitting and turbulence parameterization on the temporal and spatial distributions of simulated phytoplankton in the gulf of maine the assessment of the role of geometrical fitting was made by running a state of the art nutrient phytoplankton zooplankton npz model with physical fields provided from unstructured grid finite volume coastal ocean model fvcom and structured grid finite difference coastal ocean model ecom si respectively the impact of turbulence parameterization was studied by running a coupled npz fvcom system with various vertical turbulence modules implemented in the general ocean turbulence model gotm comparisons were focused on three large tidal dissipation regions georges bank characterized by strong tidal rectification over steep bottom topography and tidal mixing fronts bay of fundy featuring large semidiurnal tidal oscillations due to the gulf scale resonance and nantucket shoals a tidal energy flux convergence zone for the same given tidal forcing and initial physical and biological conditions the ability of a model to accommodate the irregular coastal geometry and steep bottom topography is critical in determining the robustness of the simulated spatial and temporal structure of n and p for the same given external forcing in fvcom turbulence parameterizations have less impact on n and p in mixed regions than in stratified regions in mixed regions both q e and q ql models reproduced the observed vertical mixing intensity since biological variables remained vertically mixed in these regions their structures were little affected by turbulence closure schemes in stratified regions q e models predicted stronger mixing than q ql models which produced more nutrient fluxes over the slope and thus influenced the growth and distribution of p around the tidal mixing front a direct comparison between observed and model predicted turbulence dissipation rates suggests that q e models with a mixing cutoff at richardson number of 1 0 predict more realistic mixing intensity than q ql models in stratified regions on georges bank

numerical simulation of aeolian dusty sand transport in a marginal desert region at the early entrainment stage abstract aeolian dusty sand transport in the marginal region of a desert is described numerically from first suspension motion at the early entrainment stage to the unsteady state within a moderate range 1000 m long 500 m high a two dimensional model is built for wind blown dust flow and the calculations are carried out using fluent software the simulation results describe an integrated picture of aeolian dusty sand transport including uplift suspension diffusion deposition and its space time concentration according to the features of a sand dust storm near the surface a volume concentration expression of ejection grains is developed as a boundary condition in the simulation approach the model is verified by comparing results with both experimental data from a wind tunnel and an analytic solution uniform dust sizes and r r distributions are used in the simulation gas solid two phase flow patterns with these grains are obtained in the downwind space including the turbulence intensity gas phase stream functions and solid volume concentration distributions the influence of wind velocities and grain sizes is analyzed from the simulation results spatial distributions of dust volume concentration in the early entrainment stage are described clearly different from coarse sands there is a clear band of uniformly saturated dust concentration in the region directly above the surface

the influence of subinertial internal tides on near topographic turbulence at the mendocino ridge observations and modeling abstractshipboard measurements of velocity and density were obtained in the vicinity of a small channel in the mendocino ridge where flows were predominantly tidal measured daily inequalities in transport are much greater than those predicted by a barotropic tide model with the strongest transport associated with full depth flows and the weakest with shallow surface confined flows a regional numerical model of the area finds that the subinertial k1 diurnal tidal constituent generates topographically trapped waves that propagate anticyclonically around the ridge and are associated with enhanced near topographic k1 transports the interaction of the baroclinic trapped waves with the surface tide produces a tidal flow whose northward transports alternate between being surface confined and full depth full depth flows are associated with the generation of a large amplitude tidal lee wave on the northward face of the ridge while surface confined flows are largely nonturbulent the regional model demons

dust emission from wet and dry playas in the mojave desert usa the interactions between playa hydrology and playa surface sediments are important factors that control the type and amount of dust emitted from playas as a result of wind erosion the production of evaporite minerals during evaporative loss of near surface ground water results in both the creation and maintenance of several centimeters or more of loose sediment on and near the surfaces of wet playas observations that characterize the texture mineralogic composition and hardness of playa surfaces at franklin lake soda lake and west cronese lake playas in the mojave desert california along with imaging of dust emission using automated digital photography indicate that these kinds of surface sediment are highly susceptible to dust emission the surfaces of wet playas are dynamic surface texture and sediment availability to wind erosion change rapidly primarily in response to fluctuations in water table depth rainfall and rates of evaporation in contrast dry playas are characterized by ground water at depth consequently dry playas commonly have hard surfaces that produce little or no dust if undisturbed except for transient silt and clay deposited on surfaces by wind and water although not the dominant type of global dust salt rich dusts from wet playas may be important with respect to radiative properties of dust plumes atmospheric chemistry windborne nutrients and human health published in 2007 by john wiley sons ltd

quantifying dust emissions from desert landforms eastern mojave desert usa abstract the measurement of natural dust emissions from desert landforms is crucial in environmental hazard assessment and field checking the accuracy of global dust models more than 500 individual dust measurements from eight common desert landforms in southern california were collected using the pi swerl portable in situ wind erosion lab the largest emitters of dust are dry washes 13 787 to 0 007 mg m 2 s 1 dunes playa margins distal alluvial fans and lacustrine beaches low emitters include salt crusted playas 0 692 to 0 002 mg m 2 s 1 silt clay crusted playas and desert pavements high emissions are a function of saltating sand that bombards the surface liberating dust sized particles for entrainment low dust emissions are primarily a function of surface crusting gravel armoring and vegetation density pi swerl measurements reveal that emission rates can vary by at least three orders of magnitude reflecting local variability in soil texture and continuity of surface crusts shear stress partitioning models can be applied to dust data measured by the pi swerl to account for large surface roughness features such as vegetation the results presented here give an approximation of the contributions to atmospheric dust loading by landforms in the mojave desert and can potentially be used to improve atmospheric dust models

long duration geomagnetic storm effects on the d region of the ionosphere some case studies using vlf signal the present work investigates the effects of long duration geomagnetic storms on vlf signal during ionospheric sunrise time commonly known as d layer preparation time dlpt depth the vlf signal at 19 8 khz transmitted from northwest cape australia and received at a low latitude station tripura india is used for the present analysis the data for the analysis are selected from november 2008 to october 2011 in the active period of the geomagnetic storms the average dlpt depth is found to have a negative correlation coefficient of 0 91 with geomagnetic ap index it is also found that with each 10 unit increase of ap index the dlpt depth the day and night asymmetry level changes by 1 25 db the results are supported with modeled international reference ionosphere iri electron density data and dlpt depth at 71 km height for the three positions namely receiver position signal hop position and the transmitter position along the total great circle path it is found that the receiver position electron density is the main controlling factor for dlpt depth the correlation between iri electron density and dlpt depth increases from 0 13 at transmitter position to 0 33 at the first hop position to 0 46 at the receiver position respectively the percentage change of post storm electron density at 71 km height is found to increase by more than 100 at the receiver position the results are discussed on the basis of the electron density changes over the signal propagation path mainly caused by the geomagnetic storms

a comparative analysis of nebkhas in central tunisia and northern burkina faso this paper reports a comparative analysis of nebkha morphology in central tunisia and northern burkina faso based on a total of 473 measured nebkhas nebkhas are mounds composed of wind borne sediment that accumulated around shrubs the size of the mounds was measured by height h and a horizontal component l the latter being the mean of the length and width of the mound in the tunisian data set three trends of development of the mounds were distinguished for ziziphus lotus nebkhas initially the height increases linearly with the increase in the horizontal component until it reaches about 17 m when the horizontal component exceeds 17 m the height stabilizes before a decreasing trend of the height occurs these results provided the basis for mathematical modelling of nebkha development a non linear and a linear fit were compared and a second order polynomial function was found to best fit the data on nebkha size from tunisia the results indicate that nebkhas have three stages of development a growing a stabilizing and a degrading stage the model was applied to data on acacia sp nebkhas and balanites aegyptiaca nebkhas from burkina faso with good results the non linear fit was slightly better than the linear fit nebkhas exist at all three stages of development in tunisia whereas burkina faso has nebkhas that are mainly at the growing stage these differences are a function of time lag in land degradation between the two study areas because the wind transport of sediment and the sediment supply are highly related to the density of the vegetation cover in semiarid areas this conclusion in further supported by dating of nebkhas and of historical and recent vegetation changes in the study areas reported in the literature the results show that differences in plant ecologies however are also very important for the rate of development of nebkhas which is demonstrated by the much faster growth of balanites nebkhas as compared to acacia nebkhas even though they occur in the same type of environment

near surface horizontal convergence and dispersion near the tidal mixing front on northeastern georges bank abstract horizontal dispersion and convergence are evaluated from near surface drifter data collected during the summer and autumn of 1988 and summer of 1989 in the vicinity of the tidal mixing front on northeastern georges bank the effective horizontal diffusivity coefficient k e estimated from the relative motion of the drifters over the duration of the cluster tracking increases as the cluster length scale with a range from approximately 100 to 450 m 2 s 1 for length scales of approximately 5 to 58 km at length scales k e is near zero with many negative estimates indicative of convergence at length scales 20 km k e increases in magnitude and scatter above 30 km length scales k e is typically between 200 400 m 2 s 1 the dispersion as a function of length scale is compared to published estimates using apparent diffusivities which are adjusted for the finite size of the drifter cluster at release georges bank shows lower apparent diffusivities at length scales 20 km the latter are believed to be principally due to the large horizontal gradients in the seasonal flow field although other processes perhaps associated with the large tidal currents may also contribute at the shorter length scales the low dispersion is due to convergent processes examples of convergence at different locations and under different wind and stratification conditions are presented convergence near the tidal mixing front tends to occur under light wind conditions and was observed in both seasons and in both years during two intense southwestward windstorms drifters also converged in the bank s vertically well mixed zone apparently due to a combination of spatially varying ekman depth and topographic effects

nighttime ionospheric d region equatorial and nonequatorial 1 nighttime ionospheric d region parameters are found to be generally well modeled by the traditional h and as used by wait and by the u s navy in their earth ionosphere vlf radio waveguide programs new comparisons with nonequatorial mainly all sea vlf path observations reported over several decades are shown to be consistent with the previously determined height h 85 0 km and sharpness 0 63 km 1 these paths include npm hawaii to washington d c omega hawaii and nlk seattle to japan nwc n w australia to madagascar and nba panama to colorado in marked contrast transequatorial path observations even when nearly all sea are found to be often not well modeled for example for omega japan and jji japan to dunedin new zealand the observed amplitudes are markedly lower than those which would be expected from h 85 0 km and 0 63 km 1 or any other realistic values of h and other transequatorial observations compared with modeling include nwc to japan omega hawaii to dunedin and npm hawaii to dunedin it is suggested that the effects of irregularities in the equatorial electrojet may extend down into the nighttime d region and so account for the observed equatorial vlf perturbations through scattering or mode conversion

runoff induced sediment yield over dune slopes in the negev desert 2 texture carbonate and organic matter runoff induced sediments were collected in the hallamish dune field for four years 1990 1994 runoff and consequently water transported sediments were generated on the dunes owing to the presence of a thin microbiotic crust these sediments were analysed for their particle size distribution and carbonate content in addition the organic matter content was calculated by measuring the chlorophyll content within the runoff the results were compared to the slope parent material i e the crust and the underlying sand as well as to playa sediments which are scattered within the hallamish interdunal areas and which were previously hypothesized to originate from runoff induced sediments higher amounts of fines silt and clay and carbonate characterize the footslopes in comparison to the midslopes intermediate contents of fines 17 per cent and carbonate 8 per cent characterized the sediments in comparison to the fines 27 per cent and carbonate 15 per cent of the crust and to the fines 4 per cent and carbonate 4 per cent of the underlying sand the runoff induced fines and carbonate contents were significantly different from those of the playas suggesting that the playa flats do not originate from runoff induced sediments the sediments were enriched with organic matter organic matter which originates from the crust amounted to 0 3 0 4 per cent as compared to 0 1 per cent in the bare sand nevertheless the crust was found to be relatively resilient to water flow only 0 1 0 5 per cent of the crust was annually eroded off the slope by water with south facing crusts showing higher resilience than north facing crusts the data may thus assist in the evaluation of the crust s residence time copyright 2001 john wiley sons ltd

under canopy microclimate within sand dunes in the negev desert summary scattered shrubs are a common phenomenon in many arid landscapes once established shrubs are known to create islands of fertility i e preferential habitats for annuals and animals in an attempt to characterize the physical conditions prevailing under the shrub radiation temperatures and soil moisture 0 40 cm following rain were measured during 1993 1995 at the shaded under canopy uc and at the exposed inter shrub habitat exp of two pairs of shrubs located at the north and south facing slopes of dunes in the nizzana research site western negev desert israel in addition the soil organic matter som and the fine silt and clay content fc were also measured whereas the differences in the amounts of som and fc were small daylight temperatures at uc were substantially lower 6 15 c subsequently resulting in extended time during which the uc habitat remained wet moisture was retained for up to 10 5 42 6 longer at uc in comparison to exp mainly explained by the shading effect som was found to explain only 8 6 19 6 of the results by shading shrubs in the negev desert may thus provide relatively wetter conditions for annuals rendering them an advantage over inter shrub habitats at this harsh arid environment

phytogenic mounds of four typical shoot architecture species at different slope gradients on the loess plateau of china abstract in semi arid regions the spatial pattern of vegetation usually appears as a mosaic of plants surrounded by bare soil phytogenic mounds often develop under these plants and create microenvironments that promote plant establishment this study examined the effects of ground slope and plant shoot architecture on mound formation four species representing different shoot architectures artemisia gmelinii with dense shoot architecture artemisia giraldii with expanding shoot architecture tussock forming bothriochloa ischaemum and sophora viciifolia with a main stem shoot architecture and four classes of slope were selected a two dimensional microprofilemeter was used to measure mound shape and height and mound area was measured using the image pro plus software with a planer mound picture phytogenic mound shapes changed from symmetrical mound type to asymmetrical terrace type as slope increased with increasing slope mound height increased for all species the mound area of s viciifolia decreased and that of a giraldii increased a gmelinii and b ischaemum had a relatively constant mound area irrespective of slope among the plant shoot architecture parameters the basal diameter along the slope d ba significantly correlated with mound height while the plant basal diameter perpendicular to the slope d bp and the total cross sectional area of the stem at the base s n were related to mound area the results indicate that phytogenic mounds on gentler slopes are formed due to the difference in rain splash erosion beneath the plant canopy and surrounding bare surfaces on steeper slopes mounds are formed due to water erosion on bare soil and the prevention of erosion and sediment accumulation under plants plant shoot architecture also influences mound formation species with expanding shoot architecture such as a giraldii that spread laterally to create high density stems and occupy a large area can create relatively large mounds species with main stem shoot architecture such as s viciifolia have a mound area that shrinks rapidly with increasing slope

geospace system responses to the st patrick s day storms in 2013 and 2015 this special collection includes 31 research papers investigating geospace system responses to the geomagnetic storms during the st patrick s days of 17 march 2013 and 2015 it covers observation data assimilation and modeling aspects of the storm time phenomena and their associated physical processes the ionosphere and thermosphere as well as their coupling to the magnetosphere are clearly the main subject areas addressed this collection provides a comprehensive picture of the geospace response to these two major storms we provide some highlights of these studies in six specific areas 1 global and magnetosphere plasmasphere perspectives 2 high latitude responses 3 subauroral and mid latitude processes 4 effects of prompt penetration electric fields and disturbance dynamo electric fields 5 effects of neutral dynamics and perturbation and 6 storm effects on plasma bubbles and irregularities we also discuss areas of future challenges and the ways to move forward in advancing our understanding of the geospace storm time behavior and space weather effects

perturbations of midlatitude subionospheric vlf signals associated with lower ionospheric disturbances during major geomagnetic storms 1 we examine the effects on the midlatitude ionospheric d region of the 7 april 2000 storm and the halloween storm of late october 2003 by means of the associated perturbations of several subionospheric vlf signals propagating in both the northern and southern hemispheres we use vlf nighttime data from the holographic array for ionospheric lightning research hail located in the united states l 2 3 as well as data from palmer station antarctica l 2 4 on 7 april 2000 a 5 db depression in vlf amplitudes is observed at multiple hail stations with a depression onset that occurs later for vlf signal paths at lower latitudes on both 7 april 2000 and 31 october 2003 fluctuations in the amplitude of the vlf signals are first observed in the premidnight sector and persist through the end of the data recording period dawn the frequency content of the fluctuations is predominantly in the 0 01 to 0 02 hz range but extends up to 0 03 hz increases in the energetic electron flux in the loss cone as measured by the noaa poes satellites are observed on both 7 april 2000 and 31 october 2003 we suggest that both the signal depressions and subsequent fluctuations are associated with variations in the precipitation flux of energetic electrons onto the upper atmosphere auroral activity patterns based on data from the noaa poes satellites show that the equatorward edge of the auroral oval expanded equatorward to lower l shells l 3 during both geomagnetic storms using the auoral activity patterns and multiple vlf lf signal paths we provide evidence that the fluctuations and the signal depression coincide with the equatorward edge of the auroral oval extending over the perturbed vlf lf great circle paths quantitative modeling of subionospheric vlf wave propagation incorporating energetic electron flux measurements and the associated altitude profiles of secondary ionization yields results consistent with the variations in the vlf signal amplitude observed

the influence of wind effects upon internal tides in shelf edge regions the interaction of the internal tide with wind induced currents in the shelf edge region off the west coast of scotland is studied using a baroclinic shelf edge model the model is used in cross shelf form with a horizontal finite difference grid of the order of 0 6 km and 50 sigma levels in the vertical to study the modification of the internal tide produced by upwelling and downwelling winds horizontal mixing in the model is parameterized using either the laplacian form of the horizontal diffusion or the biharmonic form and the sensitivity of the solution to both forms is examined coefficients for the vertical diffusion of momentum and density are determined using either an algebraic expression involving the richardson number or from a two equation turbulence energy submodel calculations show that in the case of an upwelling favorable wind the density gradient in the near bed region is increased leading to a slight modification compared to the tide only solution of the internal tide at the fundamental frequency with significant increases in amplitude of the higher harmonics due to the increase in the nonlinear terms produced by the increase in the density gradient with a downwelling favorable wind the amplitude of the current and internal displacement of the internal tide at the fundamental frequency are significantly reduced due to the change in the density field in the region of internal tidal production this also leads to a reduction in the amplitude of the higher tidal harmonics by using a fine grid in the horizontal the coefficients in the horizontal diffusion terms were set at a minimum and no significant difference in solutions computed with the laplacian or biharmonic diffusion terms was found similarly there are no differences in the major features of the flow field computed with the various parameterizations of the vertical diffusion although there are some differences in the magnitude of the diffusion coefficients

perturbations to the lower ionosphere by tropical cyclone evan in the south pacific region very low frequency vlf electromagnetic signals from navigational transmitters propagate worldwide in the earth ionosphere waveguide formed by the earth and the electrically conducting lower ionosphere changes in the signal properties are signatures of variations in the conductivity of the reflecting boundary of the lower ionosphere which is located in the mesosphere and lower thermosphere and their analysis is therefore a way to study processes in these remote regions here we present a study on amplitude perturbations of local origin on the vlf transmitter signals npm nlk naa and jji observed during tropical cyclone tc evan 9 16 december 2012 when tc was in the proximity of the transmitter receiver links we observed a maximum amplitude perturbation of 5 7db on jji transmitter during 16 december event from long wave propagation capability model applied to three selected events we estimate a maximum decrease in the nighttime d region reference height h by 5 2 km 13 december npm and maximum increase in the daytime d region h by 6 1 km and 7 5 km 14 16 december jji the results suggest that the tc caused the neutral densities of the mesosphere and lower thermosphere to lift and sink bringing the lower ionosphere with it an effect that may be mediated by gravity waves generated by the tc the perturbations were observed before the storm was classified as a tc at a time when it was a tropical depression suggesting the broader conclusion that severe convective storms in general perturb the mesosphere and the stratosphere through which the perturbations propagate

estimates of the transport through the east river new york the hydrodynamic characteristics of the east river new york which connects long island sound to new york harbor have been investigated via a high resolution topographically conformal and orthogonal curvilinear grid together with high quality acoustic doppler current profiler measurements the objective is to determine the volume flux of water through this important water body the model was calibrated and validated through comparisons with measured salinities water levels current velocities and data based estimates of volume flux detailed statistical analyses demonstrated that both the tidal and meteorological bands spanning inverse frequencies between 3 hours and 5 days were well simulated by the model the climatological band inverse frequencies greater than 5 days did not exhibit uniformly good agreement because of the paucity of salinity and temperature measurements available for use as model forcing functions results from an 18 month 1988 to 1989 simulation indicate that the net long term flux of water is directed out of long island sound and toward new york harbor the total rate was found to be about 310 m3 s 1 at the eastern end of the east river near its confluence with long island sound the net flow was distinctly two layered with flows of about 260 m3 s 1 directed toward the sound in the surface layer and flows of approximately 570 m3 s 1 in the bottom layer directed toward new york harbor there appeared to be a 100 m3 s 1 monthly variation about the mean transport at the eastern end however on shorter timescales the transport reversed direction for days at a time

offshore detachment process of the low salinity water around changjiang bank in the east china sea abstract a patchlike structure of low salinity water detached from the chanjiang diluted water cdw is frequently observed in the east china sea ecs in this study the offshore detachment process of cdw into the ecs is examined using a three dimensional numerical model the model results show that low salinity water is detached from the cdw plume by the intense tide induced vertical mixing during the spring tide period when the tidal current becomes stronger during the spring tide thickness of the bottom mixed layer in the sloping bottom around changjiang bank reaches the mean water depth implying that the stratification is completely destroyed in the entire water column as a result the offshore detachment of cdw occurs in the sloping side of the bank where the tidal energy dissipation is strong enough to overcome the buoyancy effect during this period on the other hand the surface stratification is retrieved during the neap tide period because the tidal current becomes substantially weaker

relict nebkhas pimple mounds record prolonged late holocene drought in the forested region of south central united states the origin and significance of pimple mounds low elliptical to circular dune like features found across much of the south central united states have been debated for nearly two centuries we cored pimple mounds at four sites spanning the ozark plateau arkansas river valley and gulf of mexico coastal plain and found that these mounds have a regionally consistent textural asymmetry such that there is a significant excess of coarse grained sediment within their northwest flanks we interpret this asymmetry as evidence of an eolian depositional origin of these mounds and conclude they are relict nebkhas coppice dunes deposited during protracted middle to late holocene droughts these four mounds yield optically stimulated luminescence ages between 2400 and 700 yr that correlate with well documented periods of eolian activity and droughts on the southern great plains including the medieval climate anomaly we conclude vegetation loss during extended droughts led to local eolian deflation and pimple mound deposition these mounds reflect landscape response to multi decadal droughts for the south central u s the spatial extent of pimple mounds across this region further underscores the severity and duration of late holocene droughts which were significantly greater than historic droughts