airglow observations and modeling of f region depletion zonal velocities over christmas island 1 we report image measurements of plasma depletions in the equatorial f region ionosphere over christmas island 2 1 n 157 4 w dip latitude 2 8 n in the central pacific ocean the observations were made during the equinox period september october 1995 using a utah state university ccd imaging system filtered to observe thermospheric o i 630 0 nm airglow emissions centered at 280 km altitude well defined magnetic field aligned depletions were observed on 18 nights during the campaign including strong postmidnight fossilized structures enabling detailed measurements of their morphology and dynamics the number of depletions was influenced by their initial onset times and their persistence the separations between adjacent depletions ranged from 150 to 250 km in good agreement with prior observations from other sites however measurements of their eastward zonal drift speeds indicated normal behavior peaking around 90 100 m s prior to local midnight with exceptionally high velocities 80 m s during the postmidnight period that persisted until dawn these results differ markedly from optical measurements at similar equatorial latitudes but at different longitude sectors suggesting that the zonal drift velocities can have a significant longitudinal dependence model drift velocities calculated using a simple electric field model with winds defined by the horizontal wind model hwm 07 produced an eastward drift throughout the night but their postmidnight magnitudes were much smaller than observed using a modified hwm 07 wind field a basic nighttime trend similar to the christmas island trend was successfully obtained

interferometer studies of equatorial f region irregularities and drifts a radar interferometer technique developed at jicamarca peru and first used to study electrojet irregularities has now been used successfully to study plasma turbulence in the equatorial f region our first results have shown that the most turbulent echoes appear to come from a region that extends for tens of kilometers in altitude but for only a kilometer or less in the east west direction this slab may very well be the wall of a depleted region a plasma bubble sometimes the irregularities can be tracked as they move eastward or westward velocity profiles for the evening period obtained in this way show a strong shear with westward velocities at the lowest altitudes observed and eastward velocities above a plausible explanation for this shear is that the westward drifts are driven by electric fields produced by westward e region winds and mapped up along magnetic field lines while at higher heights where the electron density is greater the drifts are controlled by the f region dynamo driven by eastward winds

migrating and nonmigrating semidiurnal tides in the upper atmosphere excited by tropospheric latent heat release migrating and nonmigrating semidiurnal tides

daytime zonal drifts in the ionospheric 150 km and e regions estimated using ear observations multi beam observations of the 150 km echoes made using the equatorial atmosphere radar ear located at kototabang indonesia provide unique opportunity to study both vertical and zonal exb plasma drifts in the equatorial ionosphere in this paper we focus on estimating daytime zonal drifts at the 150 km 140 160 km and e 100 110 km regions using multi beam observations of 150 km and e region echoes made using the ear and study the daytime zonal drifts covering all seasons not studied before from kototabang zonal drifts in the 150 km and e regions are found to be westward and mostly below 80 m s 1 and 60 m s 1 respectively while the zonal drifts in the 150 km and e regions do not go hand in hand on a case by case basis the seasonal mean drifts in the two height regions are found to be in good agreement with each other zonal drifts at the 150 km region show seasonal variations with three maxima peaking around may september and january the zonal drifts at the 150 km region are found to be smaller than the f region drifts obtained from cindi onboard c nofs by about 25 m s 1 consistent with the height variations of f region zonal drifts observed by the jicamarca radar these results constitute the first comprehensive study of zonal drifts at the 150 km and e regions from kototabang indonesia and the results are discussed in the light of current understanding on the low latitude electrodynamics and coupling

low latitude zonal and vertical ion drifts seen by de 2 horizontal and vertical ion drift data from the de 2 spacecraft have been used to determine average zonal and vertical plasma flow electric field characteristics in the plus minus 26 degree dip latitude region during a time of high solar activity the data base consists of over 800 equatorial passes horizontal ion drift data were projected along magnetic field lines to the magnetic equator using a dipole model to yield their apex height dependence the average data local time profile for an apex height bin centered at 400 km indicates westward plasma flow from 0600 to 1900 solar local time slt with a maximum westward velocity of 80 m s in the early afternoon there is a sharp change to eastward flow at approximately 1900 hours with an early evening peak of 170 m s a secondary nighttime maximum exists a 0430 slt preceeding the reversal to westward flow this profile is in good agreement with jicamarca radar measurements made under similar solar maximum conditions harmonic analysis indicates a net superrotation which is strongest at lower apex altitudes the diurnal term is dominant but higher order terms through th quatradiurnal are significant vertical ion data taken at low plus minus 5 degree dip latitudes while possessing greatermore scatter generally agree wtih jicamarca values copyright american geophysical union 1989 less

equatorial zonal plasma drifts measured by the c nofs satellite during the 2008 2011 solar minimum 1 we use the measurements by the vector electric field investigation vefi on board the communication navigation outage forecasting system c nofs satellite to study the local time and seasonal and longitudinal dependent climatology of equatorial f region zonal plasma drifts during 2008 2011 these drifts are essentially westward during the day and eastward at night over jicamarca radio observatory the satellite measurements are in good agreement with incoherent scatter radar drifts our data show strong longitudinal variations particularly in the south american sector during the solstices the equinoctial data exhibit short lived and largely enhanced westward drifts near sunrise and wave 4 structures from the early afternoon to late night equinoctial periods the nighttime eastward drifts are largest near the western american sector at all seasons the june solstice postmidnight eastward drifts decrease sharply at longitudes of about 310 and have much smaller values in the entire eastern hemisphere we also briefly discuss the relationship between the longitude dependent vertical and zonal plasma drifts

climatology of the nighttime equatorial thermospheric winds and temperatures over brazil near solar minimum 1 we report on the climatology of equatorial thermospheric winds and temperatures based on fabry perot interferometer measurements of doppler shifts and doppler broadenings of the 630 0 nm spectral emission from the cajazeiras observatory located in the northeastern part of brazil 6 89 s 38 56 w these results apply to the lower thermosphere region near 240 km and were obtained during a period of weak solar activity with the solar flux typically within the range of 72 and 82 solar flux units examination of the monthly averaged meridional thermospheric winds for 1 year of measurement from october 2009 to september 2010 found the wind direction to be equatorward during summer months throughout the early evening hours with maximum speeds reaching 65 ms 1 during winter months the early evening meridional wind direction reversed to poleward with similar speeds this result is attributed to the cross hemispheric flow from the summer to winter hemisphere superimposed upon this wintertime meridional wind flow was an equatorward surge shortly before midnight this surge shifted to earlier local times in the transition from the vernal equinox to summer and to later local times between the summer solstice and the autumnal equinox this flow feature is attributed to tidal wave forcing the temperature observations exhibited the expected behavior with the midnight temperature maximum showing a greater amplitude 120 k in the vernal equinox with somewhat weaker amplitudes 75 k seen at earlier local times during the summer also observed was a phase lag of 60 to 90 min between the appearance of the equatorward meridional wind flow and occurrence of the midnight temperature maximum peak

the multi instrumented studies of equatorial thermosphere aeronomy scintillation system climatology of zonal drifts a spaced antenna scintillation system was installed at ancon peru in may 1994 to measure scintillation of 250 mhz signals from a geostationary satellite by three antennas spaced in the magnetic east west direction these measurements were used to establish the climatology of the zonal drift of the irregularities which cause equatorial scintillations the major objective of this study is to compare this drift climatology to the climatology of zonal neutral wind which is the driver of the equatorial electrodynamics a comparison of these two climatologies in conjunction with scintillation statistics may provide some clues regarding factors which help or hinder the formation of equatorial spread f esf with these objectives in mind the first year s drift and scintillation statistics have been presented as a function of local time season and magnetic activity and compared with the statistics of ion drift published earlier from incoherent scatter radar observations the scintillation drift is in good agreement with the jicamarca radar observations except for the fact that the local time dependence of our drift observations exhibit a broader maximum the broad maximum may be attributed to lower ion drag experienced in the presence of esf due to sustained uplifting of the ionosphere during magnetically active periods the scintillation drift often exhibits east to west reversals presumably because of the disturbance dynamo effects the westward drifts during such reversals may be as large as 100 m s we have also modeled the zonal drifts as a seasonal basis by using hedin s neutral wind model and anderson s fully analytical ionospheric model the modeled zonal drifts present good quantitative agreement with the drifts obtained with the scintillation technique

absence of a regional surface thermal high in the baikal rift new insights from detailed contouring of heat flow anomalies heat flow in active tectonic zones as the baikal rift is a crucial parameter for evaluating deep anomalous structures and lithosphere evolution based on the interpretation of the existing datasets the baikal rift has been characterized in the past by either high heat flow or moderately elevated heat flow or even lacking a surface heat flow anomaly we made an attempt to better constrain the geothermal picture by a detailed offshore contouring survey of known anomalies and to estimate the importance of observed heat flow anomalies within the regional surface heat output a total of about 200 new and close spaced heat flow measurements were obtained in several selected study areas in the north baikal basin with an outrigged and a violin bow designed thermoprobe of 2 3 m length both the sediment temperature and thermal conductivity were measured the new data show at all investigated sites that the large heat flow highs are limited to local heat flow anomalies the maximum measured heat flow reaches values of 300 35000 mw m2 but the extent of the anomalies is not larger than 2 to 4 km in diameter aside of these local anomalies heat flow variations are restricted to near background values of 50 70 mw m2 except in the uplifted academician zone the extent of the local anomalies excludes a conductive source and therefore heat transport by fluids must be considered in a conceptual model where all bottom floor heat flow anomalies are the result of upflowing fluids along a conduit an extra heat output of 20 mw including advection is estimated for all known anomalies in the north baikal basin relative to a basal heat flow of 55 65 mw m2 these estimations suggest an extra heat output in the northern lake baikal of only 5 corresponding to a regional heat flow increase of 3 mw m2 the source of this heat can be fully attributed to a regional heat redistribution by topographically driven ground water flow thus the surface heat flow is not expected to bear a signal of deeper lithospheric thermal anomalies that can be separated from heat flow typical for orogenically altered crust 40 70 mw m2 the new insights on the geothermal signature in the baikal rift once more show that continental rifting is not by default characterized by high heat flow

average equatorial zonal and vertical ion drifts determined from san marco d electric field measurements san marco d electric field measurements have been averaged in terms of their equivalent ion drift to produce an average pattern of equatorial zonal and vertical ion drifts variations with season solar activity kp lunar phase and longitude have been analyzed similarities and some differences from previous jicamarca de 2 and ae e results are seen confirmation is given of the dominance of the f region dynamo in the 1900 2100 local time region the daytime zonal ion drift is larger for high f10 7 values than that for low values there is little variation between high and low values of kp superrotation is evident in this data set and is larger at equinox compared to solstice at the june solstice there are significant differences between the average ion drifts in the longitude sector where the geomagnetic equator is north of the geographic equator indian sector and the sector where the geomagnetic equator is south of the geographic equator peruvian sector the daytime upward velocity is larger in the indian sector than in the peruvian sector and it reverses later in the evening in the indian sector daytime westward zonal velocities are larger and the nighttime eastward velocities are smaller in the indian sector a presunrise enhancement is seen in the downward velocity in the indian sector but not in the peruvian sector significant variations are also seen with the phase of the moon in light of current theory the lunar variations suggest a complex interaction of e and f region dynamo sources with conductivity changing in phase and character with latitude

evidence for small scale mantle convection in the upper mantle beneath the baikal rift zone 1 inversion of teleseismic p wave travel time residuals collected along a 1280 km long profile traversing the baikal rift zone brz reveals the existence of an upwarped lithosphere asthenosphere interface which causes a travel time delay of about 1 s at the rift axis central high an area with early arrivals relative to the stable siberian platform of up to 0 5 s is observed on each side of the rift about 200 km from the rift axis flank lows while the location of the central high is approximately fixed in the vicinity of the rift axis those of the flank lows vary as much as 200 km with the azimuth of the arriving rays we use three techniques to invert the travel time residuals for velocity anomalies beneath the profile two of the techniques assume an isotropic velocity structure and one of them considers a transversely isotropic velocity model with a vertical axis of symmetry we use independent geophysical observations such as gravity active source seismic exploration and crustal thickness measurements to compare the applicability of the models other types of geophysical measurements suggest that the model involving transverse isotropy is a plausible one which suggests that the central high and flank lows are caused by the combined effects of an upwarped asthenosphere with a 2 5 lateral velocity reduction and a velocity increase due to transverse isotropy with a vertical axis of symmetry we consider the anisotropy to be the result of the vertical component of a lithosphere asthenosphere small scale mantle convection system that is associated with the rifting

groundwater response to the tide in wetlands observations from the gillman marshes south australia we present results from a series of piezometers installed in the foreshore flat and mangrove environments of the gillman marshes south australia in an interdisciplinary study of the propagation of the ocean tide into the coastal aquifers a unique feature of the analysis is that all water level records were harmonically analysed so that the behaviour of the four major tidal constituents could be independently examined the main findings were that 1 the decay of the groundwater tide in the coastal aquifers was greater than that predicted by the ferris solution a theoretical model has been developed and applied to the study site the model suggests that this behaviour is due to the occurrence of a time delay in the darcian response in the shelly and muddy sand substrate 2 when the tide is incident over a gently sloping bank the time delay in response gives rise to a spiked signal in which high water is confined to a small fraction of the tidal cycle and 3 at the coastal interface tidal propagation across a sloping bank causes a rise in the water table relative to mean sea level which is proportional to the variance of tidal elevation and inversely proportional to the decay constant of the groundwater tide the model developed in this study is also applicable to other coastal groundwater systems with tidal influence

electrodynamics of the equatorial evening ionosphere 1 importance of winds in different regions the importance of winds at different altitudes and latitudes for the electrodynamics of the low latitude evening ionosphere is examined with a model of the global coupled ionosphere thermosphere system the model reproduces the main observed features of the evening equatorial plasma vortex and the prereversal enhancement pre of the vertical drift the electrodynamics is driven primarily by the zonal wind forced by the diurnally varying zonal pressure gradient force the zonal wind lags the zonal pressure gradient force owing to inertia when ion drag is important the time lag of the wind behind the pressure gradient force is shortened and the high altitude evening wind turns eastward earlier than the wind at lower altitudes where ion drag is less important therefore a vertical shear of the zonal wind tends to develop at altitudes around the transition between small and large ion drag at the bottom of the f region this wind shear is closely associated with the vertical shear in the zonal convection velocity that is part of the evening plasma vortex unlike previous studies we find that the winds driving the pre lie mainly on field lines with apexes above the peak of the equatorial f layer field lines that extend in magnetic latitude out to nearly 30 and encompass the entire evening equatorial ionization anomaly region contrary to previous suggestions the westward convection in the bottomside of the evening plasma vortex is found to weaken rather than strengthen the pre daytime winds have relatively little influence on the low latitude evening electrodynamics

tidal dynamics of the water table in beaches tidal motions of the water table height inside a sloping beach are investigated via field measurements and theoretical considerations only the movements forced by the tide are considered so a beach with negligible wave activity was chosen for the field measurements the data show that even in the absence of precipitation the time averaged inland water table stands considerably above the mean sea level also the water table at a fixed point inside the beach is far from sinusoidal even though its variation is forced by an essentially sinusoidal tide this latter effect is due to the boundary condition along the sloping beach face which acts as a highly nonlinear filter the observed behavior of the water table is explained in terms of perturbation extensions to the classical deep aquifer solution one extension deals with the nonlinearity in the interior the other with the boundary condition at the sloping beach face

comparison of nighttime zonal neutral winds and equatorial plasma bubble drift velocities over brazil 1 we present results from the first extended period of coincident observations of thermospheric zonal neutral winds and equatorial plasma bubble epb zonal drift velocities over northeastern brazil during the october to december months of 2009 and 2010 the epb zonal drift velocities are estimated utilizing images of the o i 630 0 nm emissions recorded by a wide angle imaging system at cajazeiras thermospheric neutral wind estimates are based upon common volume observations made by a bistatic fabry perot interferometer fpi experiment using fpis located at cajazeiras and cariri in brazil observing the doppler shift of the o i 630 0 nm emission the results illustrate a similar pattern of nighttime and night to night variations in the zonal neutral winds and epb zonal drift velocities in general the geomagnetic zonal neutral winds and the epb velocities show an excellent agreement illustrating that the f region dynamo is fully developed however in the early evening hours the epb zonal speed is slower than that of the background winds on several occasions we conclude that this indicates that during the bubble evolution period in the early evening the f region dynamo is not fully activated

upper mantle and mantle transition zone thermal and water content anomalies beneath ne asia constraints from receiver function imaging of the 410 and 660 km discontinuities abstract the 410 and 660 km discontinuities d410 and d660 bordering the mantle transition zone mtz beneath ne asia including ne china eastern mongolia and southern siberia are imaged in successive circular bins with a radius of 1 degree by stacking a total of 274 413 p to s radial receiver functions recorded by 799 broadband seismic stations after moveout correction based on the 1 d iasp91 earth model the resulting apparent depths of the discontinuities exhibit significant and spatially systematic variations three approximately n s elongated narrow zones with significantly thickened mtz are observed which may be associated with the thermal effect and dehydration of subducted slabs the major volcanoes in ne china are underlain by a d660 that is apparently depressed by 19 km which can be interpreted by the presence of an anomalously high water concentration in the lower mtz released from the stagnated slabs low wavespeed anomalies above the d410 west of the datong volcanic fields are underlain by an mtz with normal thickness and are attributable by dehydration of the leading portion of the stagnant pacific slab in the mtz that is revealed in an n s oriented narrow zone east of this area the lateral shift of the upper mantle low wavespeed zone and the area with thickened mtz may suggest a westward drift of the upper mantle relative to the subducted slab an abnormally thin mtz is observed beneath the hangay dome in central mongolia suggesting the possible existence of thermal upwelling from the lower mantle through the mtz

an empirical model of the earth s horizontal wind fields hwm07 1 the new horizontal wind model hwm07 provides a statistical representation of the horizontal wind fields of the earth s atmosphere from the ground to the exosphere 0 500 km it represents over 50 years of satellite rocket and ground based wind measurements via a compact fortran 90 subroutine the computer model is a function of geographic location altitude day of the year solar local time and geomagnetic activity it includes representations of the zonal mean circulation stationary planetary waves migrating tides and the seasonal modulation thereof hwm07 is composed of two components a quiet time component for the background state described in this paper and a geomagnetic storm time component dwm07 described in a companion paper

the storm time evolution of the ionospheric disturbance plasma drifts in this paper we use the c nofs and rocsat 1 satellites observations to analyze the storm time evolution of the disturbance plasma drifts in a 24 hour local time scale during three magnetic storms driven by long lasting southward imf bz the disturbance plasma drifts during the three storms present some common features in the periods dominated by the disturbance dynamo the newly formed disturbance plasma drifts are upward and westward at night and downward and eastward during daytime further the disturbance plasma drifts are gradually evolved to present significant local time shifts the westward disturbance plasma drifts gradually migrate from nightside to dayside meanwhile the dayside downward disturbance plasma drifts become enhanced and shift to later local time the local time shifts in disturbance plasma drifts are suggested to be mainly attributed to the evolution of the disturbance winds the strong disturbance winds arisen around midnight can constantly corotate to later local time at dayside the westward and equatorward disturbance winds can drive the f region dynamo to produce the poleward and westward polarization electric fields or the westward and downward disturbance drifts the present results indicate that the disturbance winds corotated to later local time can affect the local time features of the disturbance dynamo electric field

c nofs observations of deep plasma depletions at dawn 1 the communication navigation outage forecasting system c nofs satellite was launched in 2008 during solar minimum conditions an unexpected feature in the c nofs plasma density data is the presence of deep plasma depletions observed at sunrise at all satellite altitudes ionospheric irregularities are often embedded within these dawn depletions their frequencies strongly depend on longitude and season dawn depletions are also observed in coincident satellite passes such as dmsp and champ in one example the depletion extended 50 14 in the n s and e w directions respectively these depletions are caused by upward plasma drifts observed in c nofs and ground based measurements the reason for these upward drifts is still unresolved we discuss the roles of dynamo electric fields over shielding and tidal effects as sources for the reported depletions

wavenumber 4 patterns of the total electron content over the low latitude ionosphere 1 the global ionospheric maps gims produced by jpl are used to investigate the longitudinal structure of the low latitude ionosphere as a proxy of the ionization parameter at low latitudes the latitudinally integrated total electron content itec is first extracted from low latitude gims and then fourier filtered to obtain the wavenumber 4 components we then study in detail the diurnal seasonal and solar cycle variations of the wave patterns it is found that the wavenumber 4 patterns are intense and well developed in boreal summer and early boreal autumn but quite weak in boreal winter this seasonal variation is consistent with that of the zonal wind of the non migrating tide mode de3 we also found that the wavenumber 4 patterns shift eastward with a shifting speed that is smaller in daytime than at night this is attributed to the contribution of both the eastward propagation of de3 in e region and the zonal e b ion drifts in f region our results support the suggestion that the longitudinal wavenumber 4 structure of the low latitude ionosphere should be originated from the non migrating tide mode de3

a review of the shelf slope circulation along australia s southern shelves cape leeuwin to portland abstract a review is presented of the ocean circulation along australia s southern shelves and slope uniquely the long zonal shelf is subject to an equatorward sverdrup transport that gives rise to the flinders current a small sister to the world s major western boundary currents the flinders current is strongest near the 600 m isobath where the current speeds can reach 20 cm s and the bottom boundary layer is upwelling favourable it is larger in the west but likely intermittent in both space and time due to possibly opposing winds thermohaline circulation and mesoscale eddies the flinders current may be important to deep upwelling within the ubiquitous canyons of the region during winter the leeuwin current and local winds act to drive eastward currents that average up to 20 30 cm s the currents associated with the intense coastal trapped wave field 6 12 day band are of order 25 30 cm s and can peak at 80 90 cm s wintertime winds and cooling also lead to downwelling to depths of 200 m or more and the formation of dense coastal water within the great australian bight and the south australian sea within the great australian bight the thermohaline circulation associated with this dense water is unknown but may enhance the eastward shelf edge south australian current the dense salty water formed within spencer gulf is known to cascade as a gravity current to depths of 200 m off kangaroo island this dense water outflow and meanders in the shelf circulation also fix the locations of a sequence of quasi permanent mesoscale eddies between the eyre peninsula and portland during summer the average coastal winds reverse and surface heating leads to the formation of warm water in the western great australian bight and the south australian sea no significant exchange of shelf water and gulf water appears to occur due to the presence of a dense nutrient rich sub surface pool that is upwelled off kangaroo island the winds lead to weak average coastal currents increasing evidence suggests that el nino events 4 7 year period can have a major impact on the winter and summer circulation these events propagate from the pacific ocean and around the shelf slope wave guide of west australia and into the great australian bight during winter el nino events the average shelf currents may be largely shut down during summer the thermocline may be raised by up to 150 m the nature and role of tides and surface waves is also discussed along with uncertainties in the general circulation and future research

equatorial e and f region zonal electric fields in the postsunset period the e and f region eastward electric fields in the postsunset period obtained from vhf backscatter radar and ionosonde observations respectively at the magnetic equatorial station at trivandrum are compared it is found that the f region eastward electric field is greater than the e region electric field indicating latitudinal gradients in the e region electric field

superrotation of the ionosphere and quiet time zonal ion drifts at low and middle latitudes observed by republic of china satellite 1 rocsat 1 1 local time variations of zonal drifts at different latitudes longitudes and seasons are investigated using ion drift measurements from the republic of china satellite 1 rocsat 1 we select a quiet time period defined when dst 100 nt and kp 3 the ion drifts in the magnetic zonal direction are latitude apex height dependent and differ for different longitude sectors and seasons superrotation of the ionosphere is observed in the zonal drift measurements particularly at the lower latitudes the ionospheric superrotation generally decreases with increasing latitude and is attributed mainly to the f region dynamo where the features of the neutral wind and conductance affect the characteristics of the superrotation at different latitudes longitudes and seasons we suggest that the latitudinal variation of the superrotation is mainly produced by the decrease in latitude of the neutral winds in the f region a decrease of conductance with increasing latitude is also present but evidence shows that neutral winds decrease faster with latitude than the conductance for high solar flux conditions the longitudinal and seasonal variations of the superrotation are more influenced by changes in the f region conductance that is modified by vertical e b ion drift motions and neutral wind induced ion drift motions along magnetic field lines

longitudinal variations in the equatorial vertical drift in the topside ionosphere 1 the vertical ion drift is important for understanding and modeling the electrodynamics at low latitudes measurements from the ion drift meter on the defense meteorological satellite program dmsp f15 are used to examine longitudinal variations in the vertical ion drift at the dip equator in the topside ionosphere local time was restricted to 0930 and the data were organized by month for 2001 and 2002 two features were found contributing to the longitudinal variations in the electrodynamics meridional winds contribute to the equatorial vertical ion drift at the 830 km magnetic apex due to their dynamo action at the foot points of the magnetic field lines in the f region at magnetic latitudes near 15 electric fields producing a downward perturbation drift at 0930 are produced by hemispheric differences in the dynamo current due primarily to the different orientation of the magnetic meridian relative to the terminator this produces the seasonally dependent variation as a function of longitude that is observed a wavenumber 4 longitudinal variation also appears to be present throughout the year but is more influential during equinox conditions this variation also shows a seasonal cycle shifting east during northern summer and west during northern winter further analysis would be required to isolate the characteristics of a wavenumber 4 driver from the wavenumber 4 component of the fourier series used here to fit the data

the role of zonal winds in the production of a pre reversal enhancement in the vertical ion drift in the low latitude ionosphere 1 the evolution of the pre reversal enhancement in the vertical ion drift in the equatorialfregion is described via an examination of the current systems determined from a coupled ionosphere thermosphere model we find that the pre reversal enhancement is produced by a reversal in thef region zonal wind that results in an additional upward current where the e region pedersen conductivity is declining across the dusk sector the continuity of the total current is maintained through an enhancement in the eastward zonal current and an associated upward drift of the ions

coherent and incoherent scatter radar study of the climatology and day to day variability of mean f region vertical drifts and equatorial spread f

longitudinal and seasonal variations of the equatorial ionospheric ion density and eastward drift velocity in the dusk sector 1 the longitudinal and seasonal variations of the plasma density and drift velocity in the evening equatorial ionosphere show complex characteristics in this paper we analyze the ionospheric ion density and velocity measured by the defense meteorological satellites program dmsp f13 and f17 satellites at 1800 lt our analysis focuses on whether the longitudinal structure of the equatorial ionospheric density and velocity has multiple wave number components how the longitudinal structure of the equatorial ion eastward drift varies with season and year and what causes the longitudinal variations of the ion density and velocity we find that the longitudinal structure of the ion density and velocity show a wave 4 pattern during the equinox months march april september and october a wave 3 pattern in northern summer may august and a wave 2 pattern in northern winter november february the longitudinal structure of the ion density and velocity becomes significantly different from the wave 4 pattern in the longitude regions with large magnetic declination in the summer and winter the variation of the equatorial ionospheric ion density shows an in phase correspondence with the ion eastward velocity and an anti phase correspondence with the ion upward velocity we suggest that the enhanced upward drift causes the density decrease through the fountain effect and that the enhanced eastward drift causes the density increase through horizontal transport the change of the ion eastward velocity with longitude can be as high as 180 m s 1 over a longitudinal range of 120 and is related to the solar activity the results of this study reveal a number of new characteristics of the equatorial plasma horizontal drift in the east west direction

terrestrial heat flow of continental rifts abstract the results of heat flow studies in the east african rhine and baikal rift systems show the the value of terrestrial heat flow depends on the type of continental rift rifting stage intrarift structures and the age of recent tectonothermal activity in the region they are closely associated with endogenic processes and the position of asthenospheric diapirs

self consistent modeling of equatorial dawn density depletions with sami3 1 large scale dawn density depletions in the equatorial ionosphere have been observed by instruments on the stpsat1 and champ satellites the naval research laboratory nrl ionosphere model sami3 sami3 is also a model of the ionosphere is used to study this new phenomenon using a self consistent electric field two empirical horizontal wind models hwm are used in the simulation study hwm93 and hwm07 dawn density depletions are found using hwm07 but not with hwm93 the cause of the depletions is a post midnight enhancement of the eastward electric field that generates an upward plasma drift this drift lifts low density plasma to high altitudes i e 600 km we compare our model results to remote sensing data and to in situ satellite data

shrinking equatorial plasma bubbles the formation of equatorial plasma bubbles epbs associated with spread f irregularities are fairly common phenomenon in the postsunset equatorial ionosphere these bubbles grow as a result of eastward polarization electric field resulting in upward e b drift over the dip equator as they grow they are also mapped to low latitudes along magnetic field lines the epbs are often observed as airglow depletions in the images of oi 630 nm emission on occasions the growth of the features over the dip equator is observed as poleward extensions of the depletions in all sky images obtained from low latitudes herein we present interesting observations of decrease in the latitudinal extent of the epbs corresponding to a reduction in their apex altitudes over the dip equator such observations indicate that these bubbles not only grow but also shrink on occasions these are the first observations of shrinking epbs the observations discussed in this work are based on all sky airglow imaging observations of oi 630 0 nm emission made from panhala 11 1 n dip latitude in addition ionosonde observations made from dip equatorial site tirunelveli 1 1 n dip latitude are used to understand the phenomenon better the analysis indicates that the speed of shrinking occurring in the topside is different from the bottomside vertical drifts when the epbs shrink they might decay before sunrise hours

mantle transition zone discontinuities beneath the baikal rift and adjacent areas like most other major continental rifts the baikal rift zone brz in siberia ispresumably underlain by a hot and partially molten mantle which has a reduced seismicvelocity relative to surrounding areas recent seismic tomography studies however gaveconflicting results about the depth extent and even the existence of the low velocityanomaly beneath the brz suggesting that additional constraints are needed here wepresent results from stacking of about 1700 radial p to s receiver functions from asingle long running seismic station tly located at the sw tip of lake baikal a clearuplift of the 410 km discontinuity d410 with a magnitude of about 47 km relative tothe south margin of the siberian platform is observed beneath the rift currently availableseismic results suggest that the uplift is unlikely to be caused by addition of water tomantle transition zone mtz silicates but is the result of a 550 c reduction in temperaturein the vicinity of the d410 in addition the 660 km discontinuity d660 shows adownward trend toward the rift from the south suggesting that the entire mtz might havea low temperature beneath the rift the thickening of the mtz suggests a high velocityanomaly of about 2 in the mtz and rules out the possibility that the rifting is caused bya mantle plume originated in or beneath the mantle transition zone

postsunset vortex in equatorial f region plasma drifts and implications for bottomside spread f recent high resolution incoherent scatter drift measurements conducted at jicamarca during solar minimum conditions indicate that a vortical plasma flow pattern accompanies the well known prereversal enhancement events observed in the equatorial f region the vortex is centered at 250 km altitude and about 2000 3000 km east of the evening terminator and is characterized by upward and downward flows to the west and to the east and eastward and westward flows on the top and the bottom respectively postsunset bottomside spread f events are observed to commence in the interior of the vortex in regions of westward plasma drifts the formation of the vortex implies localized charging of the postsunset bottomside f region in response to eastward neutral wind driven f region dynamo action

terrestrial heat flow in the south of east siberia abstract we summarize the results of heat flow studies in the paleozoic southern parts of the siberian platform mesozoic zabaikalye and cenozoic baikal rift activity areas it is established that regional heat flow values are greatly influenced by the latest tectonic activity rather than by the age of crust formation

heat flow variations in continental rifts abstract in the terrestrial thermal field continental rifts stand out as rather narrow regional thermal anomalies in which augmented heat flow is unevenly distributed heat flow variations are discussed on the example of the baikal east african cordilleran and rhine lybian rift systems rift related disturbance of the asthenosphere lithosphere system is accompanied by a general increase in the surficial heat flow regional thermal anomalies are mainly caused by conductive heat transfer from the asthenosphere local thermal anomalies are caused by magmatic mass transfer into the crust and by fluid convection along porous fracture systems

sources of low latitude ionospheric e b drifts and their variability 1 the complete mechanism of how upward propagating tropospheric tides connect to the upper atmosphere is not yet fully understood one proposed mechanism is via ionospheric wind dynamo however other sources can potentially alter the vertical e b drift gravity and plasma pressure gradient driven current the geomagnetic main field and longitudinal variation in the conductivities in this study we examine the contribution to the vertical drift from these sources and compare them we use march equinox results from the thermosphere ionosphere mesosphere electrodynamics general circulation model we found that the gravity and plasma pressure gradient driven current and the longitudinal variation of the conductivities excluding the variation due to the geomagnetic main field do not change the longitudinal variation of the vertical drift significantly modifying the geomagnetic main field will change the vertical drift at 5 6 lt 18 19 lt and 23 24 lt at almost all longitudes in general the influence of the geomagnetic main field on the vertical drift is larger with respect to the maximum difference at 18 19 lt and 23 24 lt equal at 5 6 lt and smaller at 14 15 lt than the influence due to nonmigrating tidal components in the neutral winds examination of the contribution from e and f region neutral winds to the vertical drift shows that their importance depends on the local time and the solar activity this implies that the vertical drift has to be analyzed at specific local times to examine the relation between the wave number in the vertical drift and in the neutral winds

altitudinal dependence of evening equatorial f region vertical plasma drifts we use jicamarca incoherent scatter radar measurements to study for the first time the altitudinal variations of late afternoon and early night equatorial f region vertical plasma drifts we also present the initial vertical drift measurements over the altitudinal range from about 200 to 2000 km these data show that the afternoon drifts decrease weakly with altitude near their evening prereversal enhancements the vertical drifts generally increase with altitude below about the f layer peak decrease with height near the f layer peak and above and are nearly height independent in the solar flux dependent topside ionosphere the transition altitudes from height decreasing to height independent evening upward drifts decrease with altitude from solar maximum to solar minimum after their reversal to downward the vertical drifts do not change much with height the altitudinal dependence of the evening vertical drifts has large day to day variability and is closely related to the time dependence of the zonal drifts as expected from the curl free electric field condition

conjugate point equatorial experiment copex campaign in brazil electrodynamics highlights on spread f development conditions and day to day variability 1 a conjugate point equatorial experiment copex campaign was conducted during the october december 2002 period in brazil with the objective to investigate the equatorial spread f plasma bubble irregularity esf development conditions in terms of the electrodynamical state of the ionosphere along the magnetic flux tubes in which they occur a network of instruments including digisondes optical imagers and gps receivers was deployed at magnetic conjugate and dip equatorial locations in a geometry that permitted field line mapping of the conjugate e layers to dip equatorial f layer bottomside we analyze in this paper the extensive digisonde data from the copex stations complemented by limited all sky imager conjugate point observations the sheffield university plasmasphere ionosphere model supim is used to assess the transequatorial winds tew as inferred from the observed difference of hmf2 at the conjugate sites new results and evidence on the esf development conditions and the related ambient electrodynamic processes from this study can be highlighted as follows 1 large scale bottomside wave structures satellite traces at the equator followed by their simultaneous appearance at conjugate sites are shown to be indicative of the esf instability initiation 2 the evening prereversal electric field enhancement pre vertical drift presents systematic control on the time delay in sf onset at off equatorial sites indicative of the vertical bubble growth under weak transequatorial wind 3 the pre presents a large latitude height gradient in the brazilian sector 4 conjugate point symmetry asymmetry of large scale plasma depletions versus smaller scale structures is revealed and 5 while transequatorial winds seem to suppress esf development in a case study the medium term trend in the esf seems to be controlled more by the variation in the pre than in the tew during the copex period competing influences of the evening vertical plasma drift in favoring the esf development and that of the tew in suppressing its growth are discussed presenting a perspective on the esf day to day and medium term variabilities

heat flow and continental breakup the gulf of elat aqaba heat flow measurements were made at five sites in the major basins of the gulf of elat aqaba northern red sea the gulf is located at the southern portion of the dead sea rift which is a transform plate boundary vertical temperature gradients were measured with a probe which allows multiple penetration of the bottom during a single deployment and thermal conductivities were determined by needle probe measurements on sediment cores a mean heat flux of about 80 mwm 2 was found and the values tend to increase from north to south this latitudinal gradient corresponds to the general trend of gradual thinning of the continental crust of the gulf toward the red sea where oceanic crust exists the heat flow data together with other geophysical data are consistent with a propagation of rifting from the red sea northward along the dead sea rift where the fractures are primarily shear the gulf forms a transition between these two tectonic regimes extensional red sea to the south and transform dead sea to the north

what time scales are important for monitoring tidally influenced submarine groundwater discharge insights from a salt marsh submarine groundwater discharge sgd varies significantly across time scales ranging from hours to years but studies that allow quantitative comparisons between different time scales are few most of these studies have focused on beach settings where the combined variations in fresh and saline sgd can be difficult to interpret we calculated variations in saline sgd based on a 1 year record of hydraulic head in a salt marsh where we could isolate variations in saline tidally driven sgd observed sgd varied by an order of magnitude over the course of the year groundwater discharge was proportional to tidal amplitude and varied by at least a factor of 2 between spring and neap tides monthly average sgd was inversely proportional to average sea level it increased by nearly a factor of 2 as sea level declined by 50 cm from late summer to late winter this variation was far larger than that predicted by analytic models owing to the flat topography and inundation of the marsh platform the effect of short term days variations in sea level associated with wind events and storms was small in comparison sgd is probably proportional to tidal amplitude in nearly all coastal settings including beaches seasonal variations in sea level may not affect the volume of sgd as significantly in coastal settings where the slope of the intertidal zone is relatively constant but such variations have the potential to strongly affect the composition of sgd

on the height variation of the equatorial f region vertical plasma drifts we have used improved incoherent scatter radar measurements at the jicamarca radio observatory to study the height variation of the f region vertical plasma drift velocity driven by the zonal electric field during moderately quiet conditions preliminary results indicate a nearly linear change of the vertical drift velocity with altitude between 200 and 700 km but with considerable day to day variations in the value of the slope on the average the velocity gradients are positive in the late night and morning periods and negative during the afternoon and evening hours simultaneous vertical and zonal drift measurements confirm that the measured height variation of the vertical drift is consistent with the existence of a curl free electric field in the low latitude ionosphere the time dependence of the jicamarca vertical drifts extrapolated to higher altitudes closely resembles the diurnal variation of the drift component due to the zonal electric field observed at f region heights over arecibo

ionospheric zonal velocities at conjugate points over brazil during the copex campaign experimental observations and theoretical validations 1 we analyze in detail the zonal velocities of large scale ionospheric plasma depletions over two conjugate stations inferred from oi 630 nm airglow all sky images obtained during the conjugate point equatorial experiment copex campaign carried out in brazil between october and november 2002 the conjugate stations were boa vista bv geogr 2 8n 60 7w dip angle 22 0 n and campo grande cg geogr 20 5s 54 7w dip angle 22 32 s over campo grande the zonal velocities were measured also by a system of spaced gps scintillation receivers the airglow zonal velocities at the conjugate sites were seen to agree very closely except for a slightly increased velocity over cg which we attribute to the presence of the geomagnetic anomaly the results show a high degree of alignment of the bubbles along the geomagnetic field lines during the bubble development phase and as the bubbles travel eastward thereby suggesting that the neutral zonal wind effect in the zonal plasma motion is an integrated effect along the flux tube the zonal velocities obtained from the gps technique were always larger than those calculated by the airglow technique which permitted observation of zonal plasma velocity shear between the altitudes of the airglow emitting layer and of the gps scintillation theoretical ambient plasma zonal velocities calculated using the formulations by haerendel et al 1992 and eccles 1998 are compared with the experimental results our results also reveal some degree of dependence of the zonal velocities on the solar flux f10 7 and magnetic kp indices during the copex period

the prereversal enhancement of the zonal electric field in the equatorial ionosphere the electric fields in the ionospheric e and f regions near the magnetic equator often show a strong eastward enhancement shortly after sunset and before the eastward normally daytime field reverses to westward several theoretical models of the low latitude fields suggest that this enhancement is caused mainly or entirely by f region winds the f region dynamo but some authors have suggested that it could be produced solely by e region tidal winds we give here additional calculations and arguments in support of the f region source the enhancement of the eastward field for an eastward f region wind turns out to be a simple direct consequence of the fact that after sunset the ionospheric conductivity decreases far more rapidly in the e region than in the f region

cause of different local time distribution in the postsunset equatorial ionospheric irregularity occurrences between june and december solstices 1 global averaged postsunset equatorial ionospheric density irregularity occurrences observed by rocsat during the moderate to high solar activity years of 1999 to 2004 indicate a different local time distribution between june and december solstices the irregularity occurrences during the december solstice show a faster increase rate to peak at 2100 2200 local time while the irregularity occurrences during the june solstice have a slower increase rate and peak one hour later in local time than that in the december solstice the cause of such different local time distributions is attributed to a large contrast in the time of zonal drift reversal and the magnitude of postsunset vertical drift observed by rocsat at longitudes of large magnetic declination in the two solstices that is a delay in the zonal drift reversal in association with a smaller postsunset vertical drift observed at longitudes of positive magnetic declination has greatly inhibited the irregularity occurrences during the june solstice in contrast to an earlier zonal drift reversal together with a large vertical drift occurring at longitudes of negative magnetic declination to accelerate the irregularity occurrences during the december solstice we think that the different geomagnetic field strengths that existed between the longitudes of positive and negative magnetic declinations have played a crucial role in determining the different local time distributions of irregularity occurrences for the two solstices

observations of dc electric fields in the low latitude ionosphere and their variations with local time longitude and plasma density during extreme solar minimum 1 dc electric fields and associated e b plasma drifts detected with the double probe experiment on the c nofs satellite during extreme solar minimum conditions near the june 2008 solstice are shown to be highly variable with weak to moderate ambient amplitudes of 1 2 mv m 25 50 m s average field or drift patterns show similarities to those reported for more active solar conditions i e eastward and outward during day and westward and inward at night however these patterns vary significantly with longitude and are not always present daytime vertical drifts near the magnetic equator are largest in the prenoon sector observations of weak to nonexistent prereversal enhancements in the vertical drifts near sunset are attributable to reduced dynamo activity during solar minimum as well as seasonal effects enhanced meridional drifts are observed near sunrise in certain longitude regions precisely where the enhanced eastward flow that persisted from earlier local times terminates the nightside ionosphere is characterized by larger amplitude structured electric fields dominated by horizontal scales of 500 1500 km even where local plasma densities appear relatively undisturbed data acquired during successive orbits indicate that plasma drifts and densities are persistently organized by longitude the high duty cycle of the c nofs observations and its unique orbit promise to expose new physics of the low latitude ionosphere

maximum thickness of the lithosphere and heat flow of continents abstract the maximum thickness of the continental lithosphere is considered to be in ancient platforms this parameter can be identified with the thickness of the conductively cooling layer a thermal model of the lithosphere was constructed by taking into account erosion of an upper crust enriched with radioactive elements the results of the simulation agree with the well known relationship between the heat flow and the age of the geological units when the thickness of the lithosphere is 200 km a 200 km value is in good agreement with the lithospheric thickness estimates obtained for the siberian platform based on seismic and magnetotelluric sounding data permian triassic trap magmatism in this region seems to be associated with melting of eclogite lenses at considerable depths in the lithosphere

on the genesis of trapp magmatism of the siberian platform abstract mathematical modelling of thermal thickening of the lithosphere with time indicates that the thickness of the lithosphere beneath the siberian platform in the late permian and triassic when intensive trapp magmatism occurred differed insignificantly from the present thickness therefore we infer that the source of trapp magma mainly tholeiitic was located at the depth of 180 200 km we conclude that this tholeiitic magma was generated by complete melting of large eclogitic lenses enclosed in the lower lithosphere of the ancient craton

geothermal profiles of the lithosphere in central asia abstract we present generalized heat flow data and estimated deep temperatures in the lithosphere along two geothermal profiles in central asia geological control along these profiles is provided by boreholes and three seismic reflection profiles the 1200 c isotherm is estimated to be at depths of 180 200 km in the southern part of the siberian platform the depth of this isotherm decreases to 120 150 km in the trans baikal area and to 60 80 km in the baikal rift zone

tomography on pp p waves and its application for investigation of the upper mantle in central siberia abstract we develop the method of tomographic inversion called rr r scheme which is based on joint use of teleseismic p or s refracted rays and corresponding pp or ss rays with bounce points located within a study region this scheme allows imaging the deep seismic structure beneath blank areas where there are neither recording stations nor earthquakes utilization of differential travel times makes it possible to avoid the difficulty of source and station corrections which cause problems in teleseismic tomography the rr r scheme has been applied to more than 10 000 ray pairs from the isc database to investigate a large region from the north arctic ocean to the northern part of china and mongolia inversion was carried out in several separate windows covering the study area down to the depth of 530 km velocity anomalies were computed in grid nodes distributed in the study 3d area according to ray density the tomography results from different windows were combined into one general map of the lithospheric structure in central siberia principal positive p wave velocity anomalies 1 3 down to 400 km are associated with the precambrian siberian craton negative velocity anomalies are related to the thin lithosphere of the west siberian plate the altai mountains and the hangai plateau 3 1 in the depth range 30 to 430 km a strong negative anomaly beneath the precambrian hangai block is apparently associated with a mantle plume positive velocity anomalies in sedimentary basins at southern siberia are believed to have the crustal origin

revised global model of thermosphere winds using satellite and ground based observations thermospheric wind data obtained from the atmosphere explorer e and dynamics explorer 2 satellites have been combined with wind data for the lower and upper thermosphere from ground based incoherent scatter radar and fabry perot optical interferometers to generate a revision hwm90 of the hwm87 empirical model and extend its applicability to 100 km comparison of the various data sets with the aid of the model shows in general remarkable agreement particularly at mid and low latitudes the ground based data allow modeling of seasonal diurnal variations which are most distinct at mid latitudes while solar activity variations are now included they are found to be small and not always very clearly delineated by the current data they are most obvious at the higher latitudes the model describes the transition from predominately diurnal variations in the upper thermosphere to semidiurnal variations in the lower thermosphere and a transition from summer to winter flow above 140 km to winter to summer flow below significant altitude gradients in the wind are found to extend to 300 km at some local times and pose complications for interpretation of fabry perot observations

climatology of f region zonal plasma drifts over jicamarca 1 we use extensive incoherent scatter radar observations made at the jicamarca radio observatory between 1970 and 2003 to study and model empirically the equatorial zonal plasma drifts near the f region peak using bernstein polynomials as base functions our quiet time model results confirm that the daytime drifts are westward and are nearly season and solar cycle independent the nighttime drifts are eastward have larger magnitudes and increase strongly with solar flux particularly near equinox and december solstice enhanced geomagnetic activity drives small eastward perturbation drifts during the day and much larger westward disturbance drifts at night the nighttime drift perturbations are largest near midnight and increase strongly with solar flux near equinox and december solstice but are essentially absent near june solstice the jicamarca zonal disturbance drifts can be largely accounted for by disturbance dynamo electric fields with a dominant time delay of about 3 15 hours following enhanced geomagnetic activity in the postmidnight sector there are also smaller westward disturbance drifts associated with time delays of about 15 24 hours and perhaps even longer our results strongly suggest that the longitudinal dependence of both the quiet and disturbed equatorial nighttime zonal drifts varies with season

radar and satellite global equatorial f region vertical drift model we present the first global empirical model for the quiet time f region equatorial vertical drifts based on combined incoherent scatter radar observations at jicamarca and ion drift meter observations on board the atmospheric explorer e satellite this analytical model based on products of cubic b splines and with nearly conservative electric fields describes the diurnal and seasonal variations of the equatorial vertical drifts for a continuous range of all longitudes and solar flux values our results indicate that during solar minimum the evening prereversal velocity enhancement exhibits only small longitudinal variations during equinox with amplitudes of about 15 20 m s is observed only in the american sector during december solstice with amplitudes of about 5 10 m s and is absent at all longitudes during june solstice the solar minimum evening reversal times are fairly independent of longitude except during december solstice during solar maximum the evening upward vertical drifts and reversal times exhibit large longitudinal variations particularly during the solstices in this case for a solar flux index of 180 the june solstice evening peak drifts maximize in the pacific region with drift amplitudes of up to 35 m s whereas the december solstice velocities maximize in the american sector with comparable magnitudes the equinoctial peak velocities vary between about 35 and 45 m s the morning reversal times and the daytime drifts exhibit only small variations with the phase of the solar cycle the daytime drifts have largest amplitudes between about 0900 and 1100 lt with typical values of 25 30 m s we also show that our model results are in good agreement with other equatorial ground based observations over india brazil and kwajalein

shear in the zonal drifts of 3 m irregularities inside spread f plumes observed over sanya incoherent scatter radars near magnetic equator regularly measured a vertical shear in zonal drifts of the evening background plasma with westward drifts below the equatorial f region peak and eastward drifts above we report here observations of a clear shear structure in the zonal drifts of 3 m irregularities inside spread f sf backscatter plumes measured with a 47 5 mhz coherent scatter radar operated at a low latitude site sanya 18 4 n 109 6 e dip latitude 12 8 n the radar interferometry analysis on the zonal drifts of the 3 m irregularities yields results consistent with that estimated from the irregularity echo doppler velocity measurements with multiple beams it is shown that the sf 3 m irregularities move westward at the lowest altitudes while at higher altitudes in the same sf plume structure the 3 m irregularities drift eastward one interesting point is that the vertical shear of zonal drifts was centered at 300 km altitude over sanya which maps to an apex altitude of 650 km at magnetic equator and is thus apparently higher than the apex altitudes 250 450 km where the zonal velocity shear has usually been observed analysis of the observations suggests that while the possibility of local generation of the shear flow of the irregularities can exist the possibility of a plasma vortex appearing at relative high altitudes causing the zonal drift shear of f region 3 m irregularities measured over sanya cannot be totally ruled out

a simulation study on the impact of altitudinal dependent vertical plasma drift on the equatorial ionosphere in the evening we carry out a simulation study on the impact of altitudinal dependent plasma drift on the equatorial ionosphere in the evening under geomagnetically quiet conditions our study used the vertical plasma drift velocity data measured by an incoherent scatter radar at jicamarca 11 95 s 76 87 w the data covered the local sunset period on 15 and 16 november 2004 the plasma drift had significant altitudinal variations in the vertical component which is perpendicular to the magnetic field we employed sami2 sami2 is another model of the ionosphere to evaluate the effect of the altitude dependent ion drift on the equatorial ionosphere three types of plasma drift velocity inputs were used in our simulations the first input is calculated from an empirical model the second is a height averaged drift obtained from the observed drift velocity and the third one corresponds to the observed altitudinal dependent drift data a strong equatorial ionization anomaly occurred in the results of all numerical experiments additional layers f3 layers in electron densities over the equatorial f region and arch latitudinal structures extending to lower middle latitudes were seen in the simulations driven by the observed altitudinal dependent drift we further show that neutral winds do not have a significant effect on the simulated f3 layers the results of our numerical experiments suggest that the simulated additional ionospheric layers and arch structures are associated with the altitudinal gradients in the vertical plasma drift velocity

groundwater salinization in arid coastal wetlands a study case from playa fracasso patagonia argentina the origin of the high salinity in the groundwater of a coastal wetland in an arid climate was studied in the playa fracasso marsh located on the northwest coast of the extra andean patagonia research was carried out by means of the design of a network of soil pits and short piezometers in the marsh and the surrounding landforms continuous fluctuations of the water table in situ physical and chemical properties major ions ca2 mg2 na k cl so42 hco3 and stable isotopes 18o and 2h in groundwater as well as soil salinity were measured the combined analysis of the hydrodynamics the ion ratios rca2 rcl and rmg2 rca2 vs rcl and the isotopic composition made it possible to recognize an area within the high marsh in which the origin of groundwater is mainly marine and another in which the contributions are of mixed origin by means of the analysis of rcl vs 18o a salinization process with no change in isotopic composition was identified its interpretation together with those of the soil salinity profiles and the records of the fluctuations in electrical conductivity associated with extraordinary tides was used to define a conceptual model of salinization which could be useful to understand other coastal wetlands under similar arid climatic conditions it consists in a cyclical mechanism of evapotranspiration precipitation dissolution and transport of salts during tides

incoherent scatter radar ionosonde and satellite measurements of equatorial f region vertical plasma drifts in the evening sector studies of equatorial f region evening vertical plasma drifts using different measurement techniques have produced conflicting results we examine the relationship of incoherent scatter radar and ionosonde drift observations over the peruvian equatorial region and ae e satellite drifts for different geophysical conditions our data show that there is large day to day variability on the ratios of radar and ionosonde drifts but on the average the measurements from these two techniques are in fair agreement during low and moderate solar flux conditions for high solar activity however the jicamarca evening drifts during equinox and december solstice are significantly larger than the ionosonde drifts these results can be explained by the different height ranges of the radar and ionosonde measurements and the increase of the upward drift velocity with height below the f region peak this altitudinal variation is related to the longitudinal gradient of the zonal plasma drifts as a result of the curl free electric field condition our results also indicate that during equinox the increase of the vertical prereversal velocity enhancement with solar activity is largely longitude independent

asymmetric upwarp of the asthenosphere beneath the baikal rift zone siberia in the summer of 1991 we installed 27 seismic stations about lake baikal siberia aimed at obtaining accurately timed digital seismic data to investigate the deep structure and geodynamics of the baikal rift zone and adjacent regions sixty six teleseismic events with high signal to noise ratio were recorded travel time and q analysis of teleseisms characterize an upwarp of the lithosphere asthenosphere boundary under baikal theoretical arrival times were calculated by using the international association of seismology and physics of the earth s interior 1991 earth model and travel time residuals were found by subtracting computed arrival times from observed ones a three dimensional downward projection inversion method is used to invert the p wave velocity structure with constraints from deep seismic sounding data our results suggest that 1 the lithosphere asthenosphere transition upwarps beneath the rift zone 2 the upwarp has an asymmetric shape 3 the velocity contrast is 4 9 in the asthenosphere 4 the density contrast is 0 6 and 5 the p wave attenuation contrast t is 0 1 s

detection and estimation of equatorial spread f scintillations using synthetic aperture radar a significant amount of the data acquired by sun synchronous space borne low frequency synthetic aperture radars sars through the postsunset equatorial sector are distorted by the ionospheric scintillations due to the presence of plasma irregularities and their zonal and vertical drift in the focused sar images the distortions due to the postsunset equatorial ionospheric scintillations appear in the form of amplitude and or phase stripe patterns of high spatial frequency aligned to the projection of the geomagnetic field onto the sar image plane in this paper a methodology to estimate the height and the drift velocity of the scintillations from the stripe patterns detected in the sar images is proposed the analysis is based on the fact that the zonal and vertical drift of the plasma irregularities are at the equatorial zone perpendicular to the geomagnetic field which is almost parallel aligned to the orbit the methodology takes advantage of the time lapse and change of imaging geometry across azimuth subapertures the obtained height estimates agree well with the reference measurements and independent estimates reported in the literature while the drift velocities appear slightly overestimated this can be attributed to a suboptimum geometry configuration but also to a decoupling of the ambient ionosphere and the plasma irregularities

quiet time equatorial f region vertical plasma drift model derived from rocsat 1 observations 1 we have used five years of measurements on board the rocsat 1 satellite to develop a detailed quiet time global empirical model for equatorial f region vertical plasma drifts this model describes the local time seasonal and longitudinal dependence of the vertical drifts for an altitude of 600 km under moderate and high solar flux conditions the model results are in excellent agreement with measurements from the jicamarca radar and also from other ground based and in situ probes we show that the longitudinal dependence of the daytime and nighttime vertical drifts is much stronger than reported earlier especially during december and june solstice the late night downward drift velocities are larger in the eastern than in the western hemisphere at all seasons the morning and afternoon december solstice drifts have significantly different longitudinal dependence and the daytime upward drifts have strong wave number four signatures during equinox and june solstice the largest evening upward drifts occur during equinox and december solstice near the american sector the longitudinal variations of the evening prereversal velocity peaks during december and june solstice are anti correlated which further indicates the importance of conductivity effects on the electrodynamics of the equatorial ionosphere

effects of solar and geomagnetic activities on the zonal drift of equatorial plasma bubbles equatorial plasma bubbles are mostly generated in the postsunset sector and then move in the zonal direction plasma bubbles can last for several hours and move over hundreds of kilometers even more than 1000 km in this study we use measurements of ion density by the communication navigation outage forecasting system satellite to determine the orbit averaged drift velocity of plasma bubbles the objective of the study is to identify the dependence of the bubble drift on the solar radio flux and geomagnetic activities in total 5463 drift velocities are derived over may 2008 to april 2014 and a statistical analysis is performed the average pattern of the bubble drift is in good agreement with the zonal drift of the equatorial f region plasma the zonal drift velocity of plasma bubbles increases with the solar radio flux however the increase shows different features at different local times geomagnetic activities cause a decrease of the eastward drift velocity of plasma bubbles equivalent to the occurrence of a westward drift through disturbance dynamo process in particular the decrease of the eastward drift velocity appears to become accelerated when the dst index is smaller than 60 nt or kp is larger than 4

equatorial ionization anomaly in the low latitude topside ionosphere local time evolution and longitudinal difference although the equatorial ionization anomaly eia has been widely studied it was seldom investigated from observations for the topside ionosphere in this paper the climatology characteristics of the latitudinal structure of topside ion density ni were investigated in detail using rocsat 1 and dmsp ni observations eia double peak structure may exist at 600 km depending on longitude local time season and solar activity while it is not a prevalent characteristic at 840 km even at solar maximum sunset local time evolution of the eia at 600 km was presented the double peak structure begins to appear at noontime being later than the appearance of the eia in f2 peak region the pronounced eia induced by the strong prereversal enhancement at solar maximum begins to appear at 19 00 lt and can last to pre midnight eia crest to trough ratio ctr is largest lowest at march equinox june solstice and reaches a maximum at 20 00 lt in all seasons eia structure shows evident longitudinal difference pronounced eia exists around about 100 e at 13 00 lt at the two equinoxes and june solstice while it exists at more extensive longitudes about 90 e to 240 e at december solstice the trans equator plasma transport induced by neutral winds can weaken the double peak structure in the topside ionosphere the longitudinal difference in the eia structure at 600 km is related to the longitudinal variations of equatorial upward plasma drift and geomagnetic declination