throughgoing crustal faults along the northern margin of the south china sea and their role in crustal extension a study of the rifled northern margin of the south china sea based on new single ship and two ship multichannel seismic data has revealed the presence of highly reflective steeply dipping normal faults which cut through the entire crust these faults with dips of 25 40 are associated with localized crustal thinning of 5 15 km and represent horizontal extension of the order of tens of kilometers a range of 5 20 km of horizontal extension has been measured along individual faults although the relative amount of horizontal extension taken up by these faults is modest compared to the total extension across the margin only about 15 or less the amount of localized crustal thinning which takes place along these fault surfaces is quite significant at one fault location the crustal thickness is reduced by 40 although the faults described have been recognized at three separate locations along the margin their trends appear to differ at each in two examples the faults are oblique to the inferred general north south extension direction of the margin this characteristic taken with the fact that some of the crustal faults also appear to serve as abrupt boundaries between broad regions of differing crustal thickness and reflectivity of the lower crust suggests that at least some of these faults were present prior to rifting such faults are postulated to have been former thrust faults perhaps associated with a triassic suture zone and or cretaceous subduction margin which have been reactivated as normal faults during subsequent rifting alternatively some of the throughgoing faults may represent crustal detachment surfaces that first formed as the result of a simple shear response to crustal extension

the formation of longitudinal fronts in a coastal plain estuary longitudinal estuarine fronts aligned parallel to the axis of the estuary are characteristic of the york river their time scale for genesis and decay is of the order of hours they are usually located at the inner edge of the shoals or over the main channel field measurements have shown marked intratidal differences in density and current speeds across this estuary these can be correlated with changes in depth and the strength of the advective processes differential advection between the channel and shoal regions when acting upon a constant longitudinal density gradient is shown to be of sufficient magnitude to generate strong lateral density gradients and thus fronts at particular times within the tidal cycle

on the nature of transverse variability in a coastal plain estuary even though estuarine processes are inherently three dimensional most of the previous studies have focused primarily on the axial longitudinal and vertical variabilities recent surveys in the lower delaware bay indicate the presence of significant transverse variability in the salinity distribution and residual circulation pattern conceptual models are developed to examine the mechanisms which might explain the observed transverse structure results indicate that both the gravitational effect and wind forcing are capable of generating substantial transverse structure in drowned river valley estuaries with triangular cross sections

the effects of channels and shoals on exchange between the chesapeake bay and the adjacent ocean the role of bathymetric changes in determining the transport of water and salt in the lower chesapeake bay lcb was investigated using high resolution acoustic doppler current profiler adcp and conductivity temperature depth profiles a cross channel transect was repeated eight times during neap tides on october 6 7 1993 which illustrated the lateral structure of the longitudinal and transverse flow fields and the intratidal variations in the flow structure across the lcb amplitude and phase of the m2 tidal component as well as the mean flow velocity were calculated using least squares fitting at every point of a uniform grid obtained from the adcp data the results differ from the classical two layer pattern of estuarine circulation modified by coriolis effects but are consistent with recent hydrographic observations semidiurnal flow was highest over the navigational channels and lateral gradients were strongest in regions of sharp bathymetric changes the phase lag of the semidiurnal flow also showed lateral and vertical gradients that represented advances at the bottom with respect to the surface and over the shoals in relation to the channels the section of the water column measured indicated a mean outflow of 0 7 104 m3 s and a mean inflow of 1 3 104 m3 s the apparent gain of water by the estuary during the period of observation can be explained by meteorologically forced net barotropic inflow the depth averaged mean longitudinal flow consisted of inflow in the navigational channels and outflow over the shoals the mean transverse flow showed near surface convergence over the channels we propose a possible explanation for the observed flow and density structure as follows the barotropic and baroclinic forcing interact with the bathymetry to extend the inflow from the bottom to the surface thereby inducing a transverse circulation that yields near surface convergence over the channels

ionospheric response to the interplanetary magnetic field southward turning fast onset and slow reconfiguration 1 this paper presents a case study of ionospheric response to an interplanetary magnetic field imf southward turning it is based on a comprehensive set of observations including a global network of ground magnetometers global auroral images and a superdarn hf radar there is a clear evidence for a two stage ionospheric response to the imf southward turning namely fast initial onset and slow final reconfiguration the fast onset is manifested by nearly simultaneous within 2 min rise of ground magnetic perturbations at all local times corroborated by a sudden change in the direction of line of sight velocity near local midnight and by the simultaneous equatorward shift of the auroral oval the slow reconfiguration is characterized by the different rising rate of magnetic perturbations with latitudes faster at high latitude than at lower latitudes furthermore a cross correlation analysis of the magnetometer data shows that the maximum magnetic perturbation is reached first near local noon and then spread toward the nightside corresponding to a dayside to nightside propagation speed of 5 km s along the auroral oval global ionospheric convection patterns are derived based on ground magnetometer data along with auroral conductances inferred from the polar uv images using the assimilative mapping of ionospheric electrodynamics amie procedure the amie patterns especially the residual convection patterns clearly show a globally coherent development of two cell convection configuration following the imf southward turning while the foci of the convection patterns remain nearly steady the convection flow does intensify with time and the cross polar cap potential drop increases the overall changes as shown in the amie convection patterns therefore are fully consistent with the two stage ionospheric response to the imf southward turning

initial ionospheric observations made by the new resolute incoherent scatter radar and comparison to solar wind imf 1 the first resolute incoherent scatter radar observations of the polar ionospheric f region show the fine control of the ionospheric plasma density and flow electric field by the solar wind interplanetary magnetic field imf a summary of 8 days of observations is presented and 10 imf bz southward turning events during this period are analyzed in terms of the time delay of plasma density enhancements and ionospheric convection intensification with respect to the timing of bz southward turning we find that ne enhancements are strongly tied to strong 5 nt imf bz southward turnings arrive 25 75 mins depending on mlt after the imf pulse arrives at the bowshock nose last as long as bz stays southward contain as small as 25 km horizontal substructures are altitudinally smooth a characteristic of a solar produced plasma the most predictable response of ionospheric convection is anti sunward flow intensification on average 25 mins after bz southward change

on the entry and transit of high density plasma across the polar cap 1 observations are presented from superdarn and the eiscat svalbard radar of two intense polar cap patch events on 6 february 2001 the interplanetary magnetic field imf was dominated by a large positive by component and for both events the electron density exceeded 1012 m 3 in the f region with superdarn we tracked the events all the way across the polar cap from the dayside svalbard sector to the nightside alaska sector the flow speed was highly dynamic and pulsed and both patches underwent substantial rotation in the polar cap on the nightside the leading edge had become the trailing edge it suggests that the first patch to enter the polar cap on the dayside may not always be the first patch to reach the nightside plasma might be stagnant in the polar cap or even overtaken the study also provides evidence that momentum transfer in the dayside polar cap can last significantly longer than 10 min after reconnection especially for extremely long field lines where imf by is dominating i e on old open field lines knowledge of the solar wind driver and the coupling processes is therefore extremely important for predicting the motion of a polar cap patch event across the polar cap gradients in the plasma flow associated with the rotation of the extreme density may in itself lead to a stronger growth of ionospheric irregularities these irregularities may continue to grow all the way across the polar cap the result is more efficient creation of ionospheric irregularities

space time variability of polar cap patches direct evidence for internal plasma structuring 1 coordinated observations of ionospheric variability near the geomagnetic pole using the resolute bay incoherent scatter radar risr n super dual auroral radar network superdarn high frequency hf radars and all sky imagers have clarified the relative contribution of structuring mechanisms operating on polar plasma patches from the multipoint risr n observations a three dimensional image can be constructed of the plasma parameters the colocated coherent echoes from the superdarn radars provide information on field aligned irregularities and from all sky imagers located in resolute bay canada and qaanaaq greenland information is obtained on the emission brightness at different wavelengths a good correlation is found between the location of the coherent incoherent and optical signals of patches from the superdarn radar data it is evident that plasma irregularities seem to be present throughout the region of enhanced electron density the patches are observed to be formed in the cusp region due to bursty flux transfer events and are then transported across the polar cap during the time period of about 10 minutes when a patch drifted through the risr n field of view the patch seemed to undergo significant deformation in all three spatial dimensions with density fluctuations of about 10 and spatial variations leading to stretching and tilting of the patch the findings show that plasma structuring can likely occur within polar cap patches which support previous suggestions that a patch is highly variable as it drifts across the polar cap with a faster spread of irregularities throughout the patch as a result

modeling influence of stratification on lateral circulation in a stratified estuary abstract the dynamics of lateral circulation in the passaic river estuary is examined in this modeling study the pattern of lateral circulation varies significantly over a tidal cycle as a result of the temporal variation of stratification induced by tidal straining during highly stratified ebb tides the lateral circulation exhibits a vertical two cell structure strong stratification suppresses vertical mixing in the deep channel whereas the shoal above the halocline remains relatively well mixed as a result in the upper layer the lateral asymmetry of vertical mixing produces denser water on the shoal and fresher water over the thalweg this density gradient drives a circulation with surface currents directed toward the shoal and the currents at the base of the pycnocline are directed toward the thalweg in the lower layer the lateral circulation tends to reduce the tilting of isopycnals and gradually diminishes at the end of the ebb tide a lateral baroclinic pressure gradient is a dominant dri

statistical characteristics of polar cap mesospheric gravity waves observed by an all sky airglow imager at resolute bay canada 1 an airglow imager at resolute bay canada 74 7 n 265 1 e has been used for the observation of gravity waves in the polar cap mesosphere since january 2005 on the basis of the long term imaging observations obtained over 137 nights during the winter seasons of 2005 and 2006 we extracted 143 events of small scale 100 km gravity waves using airglow keograms which represent a time series of the horizontal cross sections of the airglow images the horizontal wavelengths and phase speeds of the large scale waves were typically 100 400 km and 60 100 ms 1 respectively the propagation directions of these large scale waves also showed a westward preference the wave parameters appeared to have no relation with the geomagnetic activities represented by the kp index on the other hand the propagation directions of the observed waves were consistent with the prevailing eastward winds in the mesosphere and the updraft associated with a low pressure area that generally appears to the east of resolute bay at tropospheric altitudes these results suggest that the main source of the gravity waves in the polar cap mesosphere is tropospheric dynamics rather than auroral activities

on the symmetry of ionospheric polar cap patch exits around magnetic midnight in this paper we examine how polar cap patches which have been frozen into the antisolar flow over the polar cap are transported into the nighttime auroral oval first we present a detailed case study from 12 january 2002 with continuous observations of polar cap patches exiting into the nighttime auroral oval in the scandinavian sector satellite images of the auroral oval and all sky camera observations of 630 0 nm airglow patches are superimposed onto super dual auroral radar network convection maps these composite plots reveal that polar cap patches exit on both the dusk and on the dawn convection cells then we present statistics based on 8 years of data from the meridian scanning photometer at ny aalesund svalbard to investigate the possible interplanetary magnetic field imf by influence on the distribution of patch exits around magnetic midnight the magnetic local time distribution of patch exits is almost symmetric around magnetic midnight independent of imf by polarity synthesizing these observations with previous results we propose a three step mechanism for why patch material exits symmetrically around midnight first intake of patch material occurs on both convection cells for both imf by polarities second plasma intake by transient magnetopause reconnection stretches the newly cut polar cap patches into dawn dusk elongated forms during their transport into the polar cap and finally at exit dawn dusk elongated patches are split and diverted toward both the dawn and dusk flanks when grabbed by transient tail reconnection

gps total electron content variations associated with a polar cap arc 1 we report an example of total electron content tec variations using global positioning system gps measurements associated with a polar cap arc detected by an all sky imager and ionosonde at a polar cap station during the transit of the arc gps signals along the arc length showed an increase of 2 tec units whereas gps signals perpendicular to the arc showed only an increase of 0 3 tec units this indicates that the gps tec variations associated with a polar cap arc are dependent on the geometry of the gps raypaths with respect to the arc ionosonde measurements confirm that this arc was an e region feature at 110 km with peak electron density of 5 4 1011 el m3 estimated speed of the arc using a gps triangulation method was about 300 m s

relationship between polar cap patches and field aligned irregularities as observed with an all sky airglow imager at resolute bay and the polardarn radar at rankin inlet 1 simultaneous two dimensional observations of airglow enhancement and radar backscatter from field aligned irregularities fais associated with polar cap patches were conducted the spatial structure of 630 nm airglow from polar cap patches was imaged using an all sky airglow imager at resolute bay canada while backscatter echoes from decameter scale fais were observed using the newly constructed hf polar dual auroral radar network polardarn radar at rankin inlet canada both the airglow enhancement and the radar backscatter appeared within a structured region with the spatial extent of about 500 1000 km the decameter scale fais were found to extend over the entire region of airglow enhancement associated with polar cap patches indicating that the polar patch plasma became almost fully structured soon after initiation within approximately 20 25 min these findings imply that some rapid structuring process of the entire patch area is involved in addition to the primary gradient drift instabilities

direct three dimensional imaging of polar ionospheric structures with the resolute bay incoherent scatter radar 1 ionospheric plasma density structures in the dayside f region of the polar cap are commonly occurring events but adequate measurements of their formation and evolution have been sparse with the advent of the advanced modular incoherent scatter radar risr n resolute bay incoherent scatter radar it is now possible for the first time to study the temporal evolution of the plasma properties in the polar cap region in three dimensions with a spatial resolution of tens of kilometers from which the plasma rest frame can be experimentally established we demonstrate the strength of the diagnostic with observations from an event of enhanced plasma density observed over resolute bay in december 2009 a colocated all sky imager showed faint 630 0 and 557 7 nm emission corresponding to the plasma enhancements and the structures could be traced back to a formation region in the open closed field line boundary this new plasma imaging technique will provide important information on the mechanisms controlling the structuring in the high latitude ionosphere

substorm onset and expansion phase intensification precursors seen in polar cap patches and arcs 1 localized transient polar cap flows impinging on the poleward boundary of the nightside auroral oval have been suggested to precede poleward boundary intensifications pbis which are often followed by auroral streamers some of which propagate equatorward and appear to lead to substorm auroral onset while echo coverage often limits radar flow measurements imaging of polar cap patches and arcs has the potential to monitor localized polar cap flows by tracing emission structures previously associated with enhanced flows over long distances we use such imaging to examine if polar cap patches and arcs moving over large distances can be seen as possible precursors to presubstorm onset pbis we find evidence that such features which are longitudinally narrow propagate from the dayside polar region toward the nightside polar cap boundary prior to pre onset pbis this sequence indicates that transient activity in the dayside polar region may initiate polar cap patches and arcs that propagate across the polar cap and are followed by pre onset pbis furthermore we find evidence that expansion phase active aurora expanded poleward soon after additional polar cap patches and arcs reached close to the nightside polar cap boundary the expansion phase auroral activity significantly weakened when polar cap patches arcs disappeared our findings suggest that plasma transport originating from the dayside and reaching the nightside open closed boundary may trigger in plasma sheet flow bursts and play a crucial role in pre and post onset auroral activity polar cap imaging offers the possibility for monitoring such localized transient plasma transport over large distances

severe and localized gnss scintillation at the poleward edge of the nightside auroral oval during intense substorm aurora in this paper we study how gps glonass and galileo navigation signals are compromised by strong irregularities causing severe phase scintillation 1 in the nightside high latitude ionosphere during a substorm on 3 november 2013 substorm onset and a later intensification coincided with polar cap patches entering the auroral oval to become auroral blobs using global navigation satellite systems gnss receivers and optical data we show severe scintillation driven by intense auroral emissions in the line of sight between the receiver and the satellites during substorm expansion the area of scintillation followed the intense poleward edge of the auroral oval the intense auroral emissions were colocated with polar cap patches blobs the patches did not contain strong irregularities neither before entering the auroral oval nor after the aurora had faded signals from all three gnss constellations were similarly affected by the irregularities furthermore two receivers spaced around 120km apart reported highly different scintillation impacts with strong scintillation on half of the satellites in one receiver and no scintillation in the other this shows that areas of severe irregularities in the nightside ionosphere can be highly localized amplitude scintillations were low throughout the entire interval

the lateral density distribution in a partially mixed estuary abstract the density distribution across the york river is characterized by distinct inhomogeneities especially in the upper 2 m of the water column the pattern of variability is repetitive and closely correlated with the semi diurnal tidal cycle and water depth in the shallow areas the water column remains vertically well mixed at all times the density differences are greatest at times of minimum currents at slack before flood the least dense water is located in a lens over the main channel towards the end of the flood cycle and at slack before ebb this is reversed with the least dense water situated over the shoals these density differences result in horizontal pressure gradients which at times may be of sufficient strength to generate localized lateral circulations such circulation patterns would form zones of convergence or divergence across the estuary depending on the particular density distribution

interhemispheric study of polar cap patch occurrence based on swarm in situ data the swarm satellites offer an unprecedented opportunity for improving our knowledge about polar cap patches which are regarded as the main space weather issue in the polar caps we present a new robust algorithm that automatically detects polar cap patches using in situ plasma density data from swarm for both hemispheres we compute the spatial and seasonal distributions of the patches identified separately by swarm a and swarm b between december 2013 and august 2016 we show a clear seasonal dependency of patch occurrence in the northern hemisphere nh patches are essentially a winter phenomenon as their occurrence rate is enhanced during local winter and very low during local summer although not as pronounced as in the nh the same pattern is seen for the southern hemisphere sh furthermore the rate of polar cap patch detection is generally higher in the sh than in the nh especially on the dayside at about 77 magnetic latitude additionally we show that in the nh the number of patches is higher in the postnoon and prenoon sectors for interplanetary magnetic field imf by 0 respectively and that this trend is mirrored in the sh consistent with the ionospheric flow convection overall our results confirm previous studies in the nh shed more light regarding the sh and provide further insight into polar cap patch climatology along with this algorithm we provide a large data set of patches automatically detected with in situ measurements which opens new horizons in studies of polar cap phenomena

gps scintillation and irregularities at the front of an ionization tongue in the nightside polar ionosphere in this paper we study a tongue of ionization toi on 31 october 2011 which stretched across the polar cap from the canadian dayside sector to svalbard in the nightside ionosphere the toi front arrived over svalbard around 1930 ut we have investigated gps scintillation and irregularities in relation to this toi front this is the first study presenting such detailed multi instrument data of scintillation and irregularities in relation to a toi front combining data from an all sky imager the european incoherent scatter svalbard radar the super dual auroral radar network hankasalmi radar and three gps scintillation and total electron content tec monitors in longyearbyen and ny alesund we observe bursts of phase scintillation and no amplitude scintillation in relation to the leading gradient of the toi spectrograms of 50hz phase measurements show highly localized and variable structuring of the toi leading gradient with no structuring or scintillation within the toi or ahead of the toi

reorganization of polar cap patches through shears in the background plasma convection 1 on the night of december 20 2006 630 nm airglow images obtained by an all sky camera at resolute bay canada 74 73 n 265 07 e altitude adjusted corrected geomagnetic aacgm latitude 82 9 showed the passage of successive polar cap patches shortly after convection came to a temporary halt one of the patches was reorganized into two substructures in approximately 8 min the two dimensional background ionospheric convection pattern measured using the newly deployed polardarn radar at rankin inlet 62 82 n 93 11 w aacgm latitude 72 96 showed that a velocity shear of approximately 120 m s 1 340 km suddenly appeared in the vicinity of the patch at the time of reorganization a qualitative analysis of the relationship between the magnitude of the velocity shear and the distance between the divided patches indicates that the shear in the background plasma convection velocity significantly contributed to the reorganization of the patch this shear structure appeared soon after a southward turning of the interplanetary magnetic field imf and was probably associated with the reconfiguration of the convection pattern from a pre existing northward oriented imf pattern to a southward oriented one the present observations indicate that the reconfiguration deformation of patches because of a shear in the background convection field especially reorganization of patches into smaller substructures may play an important role in the rapid structuring of patches

dependencies of high latitude plasma convection consideration of interplanetary magnetic field seasonal and universal time factors in statistical patterns 1 the database of the nine radars of the super dual auroral radar network superdarn in the northern hemisphere has been analyzed for information on factors that influence the convection of plasma in the high latitude ionosphere the velocity measurements were collected over the period 1998 2002 the data were first used to derive a new statistical model of convection that improves upon the earlier one radar model of ruohoniemi and greenwald 1996 in its specification of the dependence of the convection pattern on the magnitude and direction of the imf in the gsm y z plane we then derived average patterns for secondary sortings by season year and radar such dependencies as emerged were most clearly seen by contrasting the results for by and by the seasonal effect in the convection pattern is found to have similarities to that of the sign of by in particular the combination of by summer by winter reinforces the tendency of the by sign factor to sculpt the dusk and dawn cells into more round crescent crescent round shapes and to shift the crescent cell across the midnight mlt meridian however these combinations are associated with lower estimates of the total cross polar cap potential drop pc while the nonreinforcing combinations produce elevated pc especially by summer there is an overall tendency for pc to increase from winter to summer although the pure seasonal effect on the potential drop is weaker than that of the by sign season factor we did not find pronounced differences among the patterns derived for the 5 individual years which spanned the most recent interval of solar cycle maximum sorting by radar we found few differences among the patterns for by but for by variations emerged that are consistent with a possible dependence on universal time ut the impacts of season and ut on convection in the high latitude ionosphere thus depends on the imf especially the sign of by we speculate that variability in the ionospheric conductivity has a greater effect on magnetosphere ionosphere coupling under by conditions

initial development of hf radar polar patch caused by azimuthal flow burst in the cusp 1 in this study we report evidence proving the existence of a close relationship between the initial development of a poleward propagating feature of the hf radar backscatter that is hf radar polar patch and a fast azimuthal flow in the cusp we focus on two events in which the hf radar polar patch was formed and was identified by the super dual auroral radar network radars at saskatoon canada and prince george canada on 27 march 2001 we examine their spatial and temporal development the two events occurred at the interface between the interplanetary magnetic field imf by controlled azimuthal flow and the antisunward flow typical of a negative imf bz they developed in a longitudinally asymmetric manner the increase in by bz when bz was negative triggered the fast azimuthal flow we interpret the temporal and spatial development of the hf radar polar patch in terms of the plasma density gradient created by the azimuthal flow and in terms of the subsequent development of the gradient in the direction of both the azimuthal flow and the antisunward flow

dynamic temporal evolution of polar cap tongue of ionization during magnetic storm 1 during a magnetic storm on 14 16 december 2006 a polar cap tongue of ionization toi was detected by an all sky imager asi at resolute bay canada 74 73 n 265 07 e we investigate the temporal evolution and spatial structure of the toi in detail by combining the optical data with other observations e g solar wind gps total electron content superdarn and dmsp and noaa poes satellites the toi was observed as a bright and elongated 630 nm airglow plume for 4 h during the main phase of the storm this interval corresponded to a period of prolonged stable large amplitude southward imf during a coronal mass ejection cme one to one and a half hours before the appearance of toi the polar cap boundary expanded rapidly far equatorward and a positive ionospheric storm occurred this implies that both the expansion of the high latitude plasma convection and build up of the source plasma in the midlatitudes are necessary conditions for the formation of a toi because both of them were triggered by a major southward turning of the imf the prolonged large amplitude southward imf orientation in the trailing part of the cme was primarily responsible for the generation of toi after its appearance the toi exhibited dynamic motion in the dawn to dusk direction simultaneous superdarn data suggest that a longitudinal progression of subauroral polarization stream controlled this dynamic motion the optical toi was found to be a continuous stream elongated in the noon midnight direction although it contained some mesoscale patterns absence of large scale temporal changes in the cusp plasma flow during the stable imf period allowed the toi to remain continuous without being broken into polar cap patches the mesoscale structures within the toi were probably produced by small scale velocity fluctuations in the cusp plasma flow the toi as visualized with the all sky airglow imager was found to be much more dynamic and much more complicated than we ever thought the current study indicates that such a behavior of the toi was presumably caused by a combination of temporal variations in the global scale plasma circulation system expansion and contraction of the polar cap area and plasma density changes in the dayside low to midlatitudes

decay of polar cap patch 1 we report an event in which a polar cap patch was detected with an all sky imager asi at resolute bay canada 74 73 n 265 07 e aacgm latitude 82 9 on the nightside the patch stopped its antisunward motion associated with a northward turning of interplanetary magnetic field and stayed within the field of view of the asi for more than 1 h when the patch stagnated its luminosity decreased gradually which allows us to investigate how the patch plasma decayed in a quantitative manner the decay of the patch can be quantitatively explained by the loss through recombinations of o with ambient n2 and o2 molecules if we assume the altitude of the optical patch to be around 295 km the derived altitude of the patch around 295 km is much higher than the nominal value at 235 km obtained from the msis e90 and iri 2007 models indicating that climatological models such as iri are not suitable for describing the actual density profile of patches this is probably because the loss process was much faster in the lower altitude part of the patch thus the peak altitude of the patch increased as it traveled across the polar cap because of rapid recombination at the bottomside of the f region this suggests that we should employ higher emission altitude when we investigate optical patches transported deep into the nightside polar cap such information is important when we compare the optical data with other instruments such as coherent radars and gps scintillation measurements by mapping the all sky image on the geographic coordinate system with an assumption of the patch emission altitude

frictional estuarine flow in juan de fuca strait with implications for secondary circulation estuarine flow in juan de fuca strait is highly seasonal in nature and an appreciable along channel surface pressure gradient is coincident with the peak fraser river discharge an upper layer momentum balance requires the vertical eddy viscosity av to be of the order of 0 02 m2 s 1 slightly larger than implied by conventional empirical formulae and used in current models mixing in an estuarine channel and a large vertical eddy viscosity should lead to significant cross channel flows this secondary circulation which may resemble internal ekman layers and intrusions of water mixed at the sloping sides of the strait is much less understood than the basic along channel estuarine exchange unfortunately historical current meter data in juan de fuca strait are of insufficient spatial resolution to show the predicted patterns

a study of the dusk convection cell s response to an imf southward turning one example of the response of ionospheric convection and the polar cap boundary to a sudden change in the interplanetary magnetic field imf orientation has been studied by using ground magnetometers the super dual auroral radar network superdarn and defense meteorological satellite program dmsp particle detectors when the imf suddenly changed from northward 6 nt to strongly southward a19 nt at 1716 ut on 5 september 1995 the b z component was fairly constant for 2 hours before and 25 min after the sudden imf change the convection flow changed almost simultaneously over a global extent this initial change of the convection pattern can be characterized by a sudden formation of a large flow vortex in the afternoon sector this agrees with the earlier findings by ruohoniemi and greenwald 1998 and ridley et al 1998 on the other hand the response of the polar cap boundary or its proxy is more complicated the saskatoon radar located in the late morning sector observed an equatorward shift of the cusp scatter region simultaneously with the initial response of the convection flows the dmsp particle data also showed a simultaneous equatorward expansion of the auroral oval in the 2100 magnetic local time mlt sector the radar and particle data indicate the immediate equatorward expansion of the precipitation regions in the noon and premidnight sectors about 10 20 min after the initial change there were changes observed in the dusk region namely an equatorward expansion of the current reversal boundary observed by the greenland magnetometer chain in the dusk sector between 1740 and 1750 ut and an equatorward expansion of the convection reversal boundary detected by the stokkseyri halley and syowa radars the delayed responses were observed 18 8 min before a substorm onset was recorded at midlatitude stations at 1756 ut these observations indicate that there were two kinds of ionospheric responses to the southward turning of the imf the first response is the formation of the convection vortex and the equatorward shift of the polar cap boundary at noon and at 2100 mlt and the second response is the equatorward expansion of the convection reversal boundary in the dusk sector we make the case that the first response is associated with the propagation of magnetosonic waves and that the second response is consistent with the cowley and lockwood 1992 picture of the redistribution of the newly created open flux in the polar cap region

exchange fluxes between the ria de vigo and the shelf a bidirectional flow forced by remote wind 1 in the ria de vigo western coast of the iberian peninsula the seasonal pattern associated with shelf winds at these latitudes produces upwelling downwelling episodes that affect the residual circulation the aim of this paper is to go deeply into the interaction between remote winds and the dynamics of the ria aided by an inverse model in the galician r ias the box models inverse models have been developed from a two dimensional 2 d point of view since the classical baroclinic residual circulation in positive estuaries has a vertical distribution freshwater outflow through the surface layer and inflow through the bottom layer however recent work in the ria de vigo has shown the existence of a 3 d residual circulation in the seaward region of the ria during upwelling downwelling conditions a coastal jet enters leaves the ria through the northern mouth and leaves enters through the southern mouth the inverse model developed in this paper is a 3 d kinematic box model based on tracer and volume balances with the constraint of nonnegative vertical exchange coefficients the fluxes obtained confirm during some periods the 3 d residual circulation overlying the classical 2 d scheme it is shown how the 3 d pattern affects the inner ria causing transversal differences in the flow field in addition the model results have been helpful in the discussion of a possible barotropic bidirectional flow associated with remote winds the results have set the basis for the existence of a bidirectional flow originated by a barotropic interaction with the shelf upwelling

motion of polar cap patches a statistical study with all sky airglow imager at resolute bay canada 1 a highly sensitive all sky airglow imager part of the optical mesosphere thermosphere imagers omtis has been operating for 3 years at resolute bay canada geographic latitude 74 7 n geomagnetic latitude 82 9 n since january 2005 one of its major applications is the observation of polar cap patches polar cap patches are generated in the vicinity of the cusp during southward interplanetary magnetic field imf conditions and they exhibit dynamic movement possibly in association with the changes in the imf orientation in order to determine how their motions are controlled by the upstream imf conditions we applied a motion tracking algorithm that was based on two dimensional cross correlation analysis to consecutive images obtained from january 2005 to december 2007 by the all sky airglow imager at resolute bay we identified and extracted 561 individual patches and then carried out a statistical study of their motion it is demonstrated that the speed of patches is primarily controlled by the imf bz furthermore the dawn dusk component of the patch drift velocities is well correlated with the imf by which is in good agreement with the published by dependence of the nightside polar cap convection this enables us to monitor the plasma convection within the polar cap by using polar cap patches as tracers

tidal riverine and wind influences on the circulation of a macrotidal estuary abstractthe effect of tides river wind and earth s rotation on the three dimensional circulation in the dee a macrotidal estuary are investigated using a fine resolution model the interactions of the large tidal amplitude currents river and wind generated circulation require baroclinic and unsteady studies to properly understand the estuarine dynamics assessment of the model skill has been carried out by model observation comparisons for salinity which is the main control for density surface elevation current and turbulence stationary nondimensional numbers were only partially able to characterize the dynamics in this real complex macrotidal estuary at low water tidal straining and constrained river flow cause stratification large spatial variability occurs in the current and residual patterns with flood dominated maximum values occurring within the tidal channels the tides control residual circulation by modulating stratification through tidal straining and bathymetric constraint on

estimating drift velocity of polar cap patches with all sky airglow imager at resolute bay canada 1 highly sensitive all sky airglow imager has been operative at resolute bay canada 74 73 n 265 07 e aacgm latitude 82 9 since january 2005 we present as a first result from the imager an event of polar cap patches drifting anti sunward during the southward imf conditions magnitude and direction of patch drift velocities are computed with a temporal resolution of 2 min by using the newly developed patch tracking algorithm based on 2d cross correlation analysis it is well visualized that the patches change their moving speed and direction drastically in a short time scale a few minutes speed of the patch is primally controlled by the imf bz dawn dusk component of the patch drift velocities is well correlated with the imf by in agreement with published by dependence of the nightside polar cap convection however response of the patch drift direction to the imf by is found to be much slower 20 min than that of the drift speed to the imf bz almost instantaneous

the response of high latitude convection to a sudden southward imf turning we describe the response of the high latitude convection to a sudden southward turning of the imf in this event bz recorded at the wind satellite switched from 6 nt to 6 nt in 2 minutes and effects in the ionosphere were observed by the superdarn hf radars in the vicinity of noon mlt the convection switched suddenly 2 min from sunward to antisunward with the velocity change reaching magnitudes as great as 1500 m s in about 6 minutes surprisingly the responses at the other mlts distributed from noon to midnight began at virtually the same time meridional flows near 22 mlt were observed to reverse direction in about 4 minutes with the velocity change reaching magnitudes as great as 750 m s in about 8 minutes this example shows that the convection can respond to a sudden imf change practically simultaneously 2 min over the entire high latitude zone and reconfigure from a pattern characteristic of bz to one characteristic of bz in a very short 2 4 min time

effect of the earth s rotation on the circulation in regions of freshwater influence recent surveys in various regions of freshwater influence have shown considerably different flow patterns in each region an analytical model including viscous effects and the earth s rotation is proposed to examine the along channel flow pattern and to explain the differences model results show that the flow pattern is strongly dependent on the ekman number e with a large ekman number e 1 the system is governed by gravitational circulation and thus horizontal density gradients in along channel direction are important the whole water column is in the ekman layer and consequent jet inflow penetrates the surface over a deep depression if the bottom topography varies in a cross channel direction with an intermediate ekman number e 0 1 this jet inflow concentrates in the lower layer in which the viscosity still plays an important role the flow in the upper layer is on the other hand determined by the geostrophic balance the contribution by the geostrophic flow becomes larger so that the cross channel density gradients are important when die ekman number is small e 0 01 since the ekman layer is clung to the bottom the jet inflow exists only in the thin bottom layer the hydrographic and acoustic doppler current profiler surveys were conducted in ise bay japan both the density structure and the flow pattern were different from those observed in many drowned river valleys a strong jet inflow existed in the lower layer over the depression while the flow in the upper layer suggested anticyclonic circulation the estimated ekman number is 0 07 in the bay and thus the observed pattern is consistent with the model result when e 0 1