storm time electric fields in the equatorial ionosphere observed near the dusk meridian 1 we compare the dynamics of plasma drifts vp and ionospheric electric fields ei measured near the dusk meridian at the magnetic equator by the defense meteorological satellite program dmsp f13 satellite with those of the dawn to dusk component of the interplanetary electric field ief ey during four large magnetic storms presented data indicate that during the main phase of the magnetic storms when the interplanetary magnetic field imf had a southward component vp had upward and westward components that ranged up to 120 and 210 m s 1 the corresponding eastward and upward components of ei were approximately 5 and 10 of ey the persistence of eastward ei for many hours indicates that electric field shielding of the inner magnetosphere is ineffective during prolonged periods of southward imf during periods of northward imf ey 0 ionospheric responses depended on prior history no ionospheric response is apparent after strong northward imf turnings preceded by geomagnetic quiet if they occurred after a long southward interval ei often had westward and downward components the polarity of the zonal component of ei remained well correlated with that of ey for up to 21 h during periods of slowly varying imf phenomena associated with southward imf periods are consistent with models that allow for prolonged penetration electric field from high latitudes superposed on those of the sq current system however it is not understood why the remarkable correspondence between the polarities of the zonal component of ei and the ief ey occurs during northward imf in some ey 0 periods the vertical component of ei remained upward dmsp detections of upward ei westward vp during periods of ey 0 are not predicted by existing models

global sea level rise published values for the long term global mean sea level rise determined from tide gauge records exhibit considerable scatter from about 1 mm to 3 mm yr this disparity is not attributable to instrument error long term trends computed at adjacent sites often agree to within a few tenths of a millimeter per year instead the differing estimates of global sea level rise appear to be in large part due to authors using data from gauges located at convergent tectonic plate boundaries where changes of land elevation give fictitious sea level trends in addition virtually all gauges undergo subsidence or uplift due to postglacial rebound pgr from the last deglaciation at a rate comparable to or greater than the secular rise of sea level modeling pgr by the ice 3g model of tushingham and peltier 1991 and avoiding tide gauge records in areas of converging tectonic plates produces a highly consistent set of long sea level records the value for mean sea level rise obtained from a global set of 21 such stations in nine oceanic regions with an average record length of 76 years during the period 1880 1980 is 1 8 mm yr 0 1 this result provides confidence that carefully selected long tide gauge records measure the same underlying trend of sea level and that many old tide gauge records are of very high quality

advection of the equatorial anomaly over arecibo by small storm related disturbance dynamo electric fields during highly disturbed geomagnetic periods both the arecibo radar and the ramey ionosonde have recorded impressive nighttime ionospheric enhancements in which the peak electron density exceeded 1 1012 m 3 and the f2 peak height went above 400 km in the past it has been suggested that these events could be caused by either a downward plasmaspheric flux that increases the density in the f region or by an eastward electric field that pushes the equatorial anomaly poleward to the caribbean sector on february 17 18 1999 the arecibo radar made observations during an event in which the electron density again rose to daytime values near midnight for this event the peaks in density were observed predominantly southeast of arecibo while the ions sustained a northward eastward motion due to an eastward southward storm dynamo electric field tec maps from gps for this night confirmed that the density enhancements were due to a poleward expansion of the equatorial anomaly

f region behavior in the sed plume during a geomagnetic superstorm a case study 1 we report observations from the gps total electron content tec ionosonde and millstone hill incoherent scatter radar showing some interesting features of the height profile of the ionospheric electron density that occurred during a passage of a storm enhanced density sed plume during the geomagnetic superstorm on 20 november 2003 first the tec increases to about 6 58 times the quiet day value while the f peak plasma density nmf2 only enhances by a factor of 1 37 second the f2 layer peak height hmf2 is dramatically lifted from the quiet time altitude of 250 km to an unusual altitude of 577 km furthermore the topside chapman scale height ht is larger by a factor of 6 25 compared to the quiet time value as a result the electron density content with an chapman function above 700 km contributes about 59 to the total content during the sed event our analysis shows that during a passage of the sed plume the enhancement of tec is mainly attributed to the great increase of ht with a very high hmf2

f2 region response to geomagnetic disturbances across indian latitudes o 1s dayglow emission the morphology of ionospheric storms has been investigated across equatorial and low latitudes of indian region the deviation in f 2 region characteristic parameters f o f 2 and hf along with modeled green line dayglow emission intensities is examined at equatorial station thiruvananthapuram 8 5 degrees n 76 8 degrees e 0 63 degrees s geomagnetic latitude and low latitude station delhi 28 6 degrees n 77 2 degrees e 19 2 degrees n geomagnetic latitude during five geomagnetic storm events both positive and negative phases have been noticed in this study the positive storm phase over equatorial station is found to be more frequent while the drop in ionization in most of the cases was observed at low latitude station it is concluded that the reaction as seen at different ionospheric stations may be quite different during the same storm depending on both the geographic and geomagnetic coordinates of the station storm intensity and the storm onset time modulation in the f 2 layer critical frequency at low and equatorial stations during geomagnetic disturbance of 20 23 november 2003 was caused by the storm induced changes in o n 2 it is also found that international reference ionosphere 2012 model predicts the f 2 layer characteristic f o f 2 and hf parameters at both the low and equatorial stations during disturbed days quite reasonably a simulative approach in glow model developed by solomon is further used to estimate the changes in the volume emission rate of green line dayglow emission under quiet and strong geomagnetic conditions it is found that the o s 1 dayglow thermospheric emission peak responds to varying geomagnetic conditions

a case study of the ionospheric storm dusk effect the initial ionospheric storm positive phase often appears as a large enhancement in f region electron density at middle latitudes in the evening hours following a storm sudden commencement the cause of this dusk effect is still not well understood though several mechanisms have been proposed this phenomenon is studied using incoherent scatter radar data collected at millstone hill and total electron content data from a north south chain of stations during the may 26 27 1990 storm nine position millstone hill radar data allows estimation of gradients in electron density and in velocity components above the station from these the motion term in the continuity equation is calculated and used along with wind electric field data and modeling to assess the relative importance of the proposed mechanisms during this storm it is shown that a combination of mechanisms appear to have been involved including a traveling atmospheric disturbance advection of high density plasma from lower latitudes and neutral composition changes

long duration penetration of the interplanetary electric field to the low latitude ionosphere during the main phase of magnetic storms 1 it is well known that the interplanetary electric field can penetrate to the low latitude ionosphere it is generally believed that the penetration of electric fields can last only for 30 min because of the shielding effect in the ring current in this paper we present the observations of the dayside ionospheric electric field enhancements at middle and low latitudes in association with reorientations of the interplanetary magnetic field imf in six cases the eastward electric field in the dayside equatorial ionosphere measured by the jicamarca incoherent scatter radar was enhanced for 2 3 hours after the imf turned southward and remained continuously southward in one case the eastward electric field in the dayside midlatitude ionosphere measured by the millstone hill incoherent scatter radar was continuously enhanced for 10 hours during southward imf since millstone hill is close to the equatorward boundary of the auroral zone during magnetic storms the penetration electric field there may be different from that at the equatorial ionosphere the most striking feature of the measurements is that the enhancements of the ionospheric electric field can last for many hours without significant decay the electric field enhancements in the middle and low latitude ionosphere are closely related to magnetic activity and occur during the main phase of magnetic storms the observations show that the interplanetary electric field can continuously penetrate to the low latitude ionosphere without shielding for many hours as long as the strengthening of the magnetic activity is going on under storm conditions

multi instrument observations of sed during 24 25 october 2011 storm implications for sed formation processes 1 we present multiple instrument observations of a storm enhanced density sed during the 24 25 october 2011 intense geomagnetic storm formation and the subsequent evolution of the sed and the midlatitude trough are revealed by global gps vertical total electron content maps in addition we present high time resolution poker flat incoherent scatter radar pfisr observations of ionospheric profiles within the sed we divided the sed observed by pfisr into two parts both parts are characterized by elevated ionospheric peak height hmf2 and total electron content compared to quiet time values however the two parts of the sed have different characteristics in the electron temperature te the f region peak density nmf2 and convection flows the first part of the sed is associated with enhanced te in the lower f region and reduced te in the upper f region and is collocated with northward convection flows the nmf2 was lower than quiet time values the second part of the sed is associated with significantly increased nmf2 elevated te at all altitudes and is located near the equatorward boundary of large northwestward flows based on these observations we suggest that the mechanisms responsible for the formation of the two parts of the sed may be different the first part is due to equatorward expansion of the convection pattern and the projection of northward convection flows in the vertical direction which lifts the ionospheric plasma to higher altitudes and thus reduces the loss rate of plasma recombination the second part is more complicated besides equatorward expansion of the convection pattern and large upward flows evidences of other mechanisms including horizontal advection due to fast flows energetic particle precipitation and enhanced thermospheric wind in the topside ionosphere are also present estimates show that contribution from precipitating energetic protons is at most 10 of the total f region density the thermospheric wind also plays a minor role in this case

the long duration positive storm effects in the equatorial ionosphere over jicamarca the long duration positive storm lps in the equatorial regions is relatively poorly understood in this report we conducted a statistical analysis of the lps effects in the equatorial ionosphere over jicamarca 12 0 s 283 2 e in 1998 2010 there are 250 geomagnetic storms minimum dst 50 nt in 1998 2010 but the ionosonde observations at jicamarca are available only for 204 storms a total of 46 lpss are identified in terms of the criterion that the storm time relative deviation of peak density of f2 layer nmf2 exceeds 25 for more than 6 h a salient feature is that the occurrence of lpss tends to decay approximately exponentially on the following days after the main phase of geomagnetic storms the ratios of the number of equatorial lpss to that of geomagnetic storms have no obvious dependence on season and solar activity during the daytime lpss the disturbed zonal electric field is mostly westward as indicated from the geomagnetic field changes in the equatorial american region for the nighttime lpss the significant uplifting of f2 layer caused by an eastward electric field is the most important feature therefore the disturbed electric field should play an essential role in forming the equatorial lpss

observations from millstone hill during the geomagnetic disturbances of march and april 1990 the incoherent scatter radars at millstone hill operated continuously during the periods march 16 23 and april 6 12 1990 providing observations of large scale ionospheric structure and dynamics over a large portion of eastern north america major geomagnetic storms occurred during each of these periods with deep nighttime ionospheric troughs and large magnetospheric convection electric fields observed equatorward of millstone the millstone observations provide a comprehensive data set detailing storm induced ionospheric effects over a 35 span of latitude during both of these intervals at the latitude of millstone the ionospheric peak height hmf2 rose above 600 km in the trough on march 22 and 23 and reached 500 km at night on april 11 and 12 increased recombination apparently due to the strong electric fields the temperature dependent recombination rate coefficient and neutral composition changes greatly depleted the f2 region over a wide latitude range during the day on april 10 1990 this resulted in an ionosphere dominated by molecular ions with ionospheric peak heights below 200 km on this day a number of frictional heating events during the disturbed periods are seen from comparison of ion temperature and velocity measurements the most intense event took place near 1200 ut 0715 lmt on april 10 1990 when kp reached 8 at 0110 ut on march 21 line of sight ion velocities in excess of 500 m s 1 were observed at the extreme southern limit of the millstone steerable radar s field of view 40 apex magnetic latitude at an altitude of 700 km these could be due to penetration of magnetospheric electric fields or electric fields associated with ring current shielding in the storm time outer plasmasphere about an hour later ion outflow was observed just equatorward of millstone this is most likely due to heating from a latitudinally confined region of intense westward convection neutral meridional winds above millstone were obtained by three different techniques employing radar and fabry perot measurements the latitude variation of the winds was also estimated from radar measurements of hmf2 and electric fields using the servo model method strong equatorward nighttime neutral wind surges were found during both the march and april disturbances which reached the equatorward limit of the observations at f peak heights

earthquakes and relative sealevel changes 1 using a spherical model of postseismic deformation for the first time we have computed the global contribution of large earthquakes to the relative sealevel variations in the twentieth century we have found that great earthquakes have the overall tendency to produce a sealevel rise and that they affect the measurements taken at those tide gauge sites that are commonly employed to obtain global estimates of sealevel rise though on a global scale most of the signal is associated with thrust events on a regional scale the effects of great transcurrent earthquakes cannot be neglected depending on the viscosity of the asthenosphere the contribution of earthquakes to the long term sealevel changes amounts to at least 0 1 mm yr thus the climate driven long term sealevel changes deduced by tide gauge observations may be slightly but not negligibly overestimated

ionospheric and magnetic signatures of a space weather event on 25 29 august 2018 cme and hssws we present a study concerning a space weather event on 25 29 august 2018 accounting for its ionospheric and magnetic signatures at low latitudes and midlatitudes the effects of a storm in several longitudinal sectors asia africa america and the pacific have been analyzed using various parameters such as total electron content tec geomagnetic field and column o n2 ratio positive ionospheric storms are found in all the longitudinal sectors having its maximum effects in the asian sector whereas the negative ionospheric storms have been observed in the summer hemisphere northern hemisphere a large decrease in o n2 ratio in the northern hemisphere is a possible cause of the observed negative storm effects ionospheric f2 region maximum electron density nmf2 and tec have shown a positive correlation during this storm the study suggests that storm time generated wind does not have a uniform planetary extension and mainly affects dayside america and pacific and duskside africa sectors during the space weather event we observe an asymmetric variation of the magnetic field as a function of the longitude on the other hand the magnetic variations at midlatitudes are found to be symmetric in both hemispheres a signature of the disturbance dynamo anti sq circulation has been observed mainly at low latitudes we emphasize that the partial ring current prc estimated by the asym h magnetic index must also be taken into account along with the sym h index for a better approximation of ionospheric currents the study further suggests existence of several electric current cells in the ionosphere which is consistent with the blanc richmond model

theoretical study of new plasma structures in the low latitude ionosphere during a major magnetic storm 1 theoretical model simulations for an intense magnetic storm show the creation of a low latitude electron density arch aligned along the geomagnetic field created by strong uplift of the f2 layer that is driven by the penetration electric field when the arch forms during the day a new f2 layer is created at the original altitude by photoionization and a density hole can be created between this new f2 layer and the arch when the arch forms during the night the f2 layer is not recreated and no hole forms in a vertical profile of electron density the daytime elevated ionospheric layer can appear distinctly from the recreated f2 layer in which case the elevated layer is called the f3 layer a latitude cut through the night side arch shows the characteristics of an equatorial electron density trough bounded to the north and south by enhanced densities associated with plasma that has diffused down along the geomagnetic field from the elevated layer it is pointed out that the signature of the night side arch has been seen in low earth orbit spacecraft data but has not been previously associated with an arch structure

mechanism of graben formation the wedge subsidence hypothesis abstract isostatic subsidence of a downward narrowing wedge of the brittle upper crust bounded by normal faults is shown to provide a viable mechanism of graben formation energy balance calculations indicate that the mechanism depends on the occurrence of substantial deviatoric tension but it requires a much smaller extension than the lithospheric stretching hypothesis for the mechanism to be effective a relatively high geothermal gradient is required to allow ductile flow of the lower crust and the friction on the faults must be much less than that appropriate to dry rock the amount of subsidence also depends on the narrowness of the graben the strength of the tensile stress field in the upper crust and sediment loading preliminary finite element analysis has been carried out in an attempt to model the subsidence process it is suggested that the tension causing the majority of the present day rift systems is produced by the topographical loading and isostatic body forces related to the associated uparching present plate boundary forces may be of some importance in the vicinity of convergent plate boundaries and in forming pull apart basins along transform faults where they bend on the other hand plate boundary forces may have been of much greater significance at certain periods in the past when large continental regions such as pangaea in the early mesozoic may have been subjected to general tension resulting from the trench suction force acting at the subduction zones on opposite sides

ionospheric electron concentration imaging using gps over the usa during the storm of july 2000 a new technique for ionospheric imaging is demonstrated during a severe geomagnetic storm of 15th july 2000 the three dimensional time dependent imaging algorithm is applied to multi directional ground based gps data and yields spatial maps of electron concentration this technique is demonstrated by showing a series of images of the mid latitude ionosphere over the usa during the storm of july 2000 a strong uplift in the height of the f layer is observed after 20 ut on 15th july followed by a severe latitudinal electron concentration gradient independent verification of the images is provided by the ionosondes and incoherent scatter radar data the gps images reveal the large scale dynamics of the ionosphere during the disturbed conditions and show the potential of geophysical imaging for storm time ionospheric studies

on the generation decay of the storm enhanced density plumes role of the convection flow and field aligned ion flow storm enhanced density sed plumes are prominent ionospheric electron density increases at the dayside middle and high latitudes the generation and decay mechanisms of the plumes are still not clear we present observations of sed plumes during six storms between 2010 and 2013 and comprehensively analyze the associated ionospheric parameters within the plumes including vertical ion flow field aligned ion flow and flux plasma temperature and field aligned currents obtained from multiple instruments including gps total electron content tec poker flat incoherent scatter radar pfisr super dual auroral radar network and active magnetosphere and planetary electrodynamics response experiment the tec increase within the sed plumes at the pfisr site can be 1 4 5 5 times their quiet time value the plumes are usually associated with northwestward e b flows ranging from a couple of hundred m s 1 to 1 km s 1 upward vertical flows due to the projection of these e b drifts are mainly responsible for lifting the plasma in sunlit regions to higher altitude and thus leading to plume density enhancement the upward vertical flows near the poleward part of the plumes are more persistent while those near the equatorward part are more patchy in addition the plumes can be collocated with either upward or downward field aligned currents facs but are usually observed equatorward of the peak of the region 1 upward fac suggesting that the northwestward flows collocated with plumes can be either subauroral or auroral flows furthermore during the decay phase of the plume large downward ion flows as large as 200 m s 1 and downward fluxes as large as 1014 m 2 s 1 are often observed within the plumes in our study of six storms enhanced ambipolar diffusion due to an elevated pressure gradient is able to explain two of the four large downward flow flux cases but this mechanism is not sufficient for the other two cases where the flows are of larger magnitude for the latter two cases enhanced poleward thermospheric wind is suggested to be another mechanism for pushing the plasma downward along the field line these downward flows should be an important mechanism for the decay of the sed plumes

a strong positive phase of ionospheric storms observed by the millstone hill incoherent scatter radar and global gps network 1 during geomagnetic storms the ionospheric f region electron density may be greatly increased or decreased which are termed positive storms or negative storms it is generally accepted that negative storm phases are caused by neutral composition changes in contrast different mechanisms have been proposed to explain the generation of positive storm phases in this paper we present observations of a strong positive storm at middle latitudes the millstone hill incoherent scatter radar detected significant increases of the midlatitude ionospheric f region electron density during a magnetic storm on 3 april 2004 the positive phase of the ionospheric storm started to occur in the morning sector 0912 lt at millstone hill and lasted for more than 10 hours compared with the quiet time ionosphere the daytime f peak altitude over millstone hill during the storm was 80 km higher the f region electron density was increased by a factor of 2 4 and the f region electron temperature was decreased by 1000 k or 40 the radar also measured an enhanced eastward electric field and a slightly more equatorward neutral wind global gps measurements show that total electron content tec was increased at middle latitudes and decreased at lower latitudes and the large tec enhancements occurred primarily in the atlantic sector we suggest that electric fields may play an important role in the generation of the observed positive storm phase the eastward electric field will cause increases in the midlatitude ionospheric electron density by moving the plasma particles upward and decreases in the equatorial ionospheric electron density by strengthening the fountain effect the daytime poleward wind was reduced or even reversed during the storm which may also contribute to the occurrence of the positive storm

relative importance of horizontal and vertical transports to the formation of ionospheric storm enhanced density and polar tongue of ionization there are still uncertainties regarding the formation mechanisms for storm enhanced density sed in the high and subauroral latitude ionosphere in this work we deploy the thermosphere ionosphere electrodynamic general circulation model tiegcm and gps total electron content tec observations to identify the principle mechanisms for sed and the tongue of ionization toi through term by term analysis of the ion continuity equation and also identify the advantages and deficiencies of the tiegcm in capturing high latitude and subauroral latitude ionospheric fine structures for the two geomagnetic storm events occurring on 17 march 2013 and 2015 our results show that in the topside ionosphere upward e b ion drifts are most important in sed formation and are offset by antisunward neutral winds and downward ambipolar diffusion effects in the bottomside f region ionosphere neutral winds play a major role in generating seds sed signature in tec is mainly caused by upward e b ion drifts that lift the ionosphere to higher altitudes where chemical recombination is slower horizontal e b ion drifts play an essential role in transporting plasma from the dayside convection throat region to the polar cap to form tois inconsistencies between model results and gps tec data were found 1 gps relative tec difference between storm time and quiet time has holes in the dayside ion convection entrance region which do not appear in the model results 2 the model tends to overestimate electron density enhancements in the polar region possible causes for these inconsistencies are discussed in this article

a thin viscous sheet model for continental deformation summary for the purposes of describing its large scale and long term deformation the continental lithosphere is regarded as a continuum obeying a newtonian or a power law rheology the flow of a thin sheet of power law material overlying an inviscid substrate is studied under the assumption that vertical gradients of the horizontal velocity are negligible a numerical model is used to investigate the deformation of such a sheet under conditions approximating those of continent continent collision the material flows in response to forces applied to its boundaries for example the indenting of one continent by another and to forces in its interior arising from gradients in crustal thickness the horizontal divergence of the flow produces changes in the crustal thickness and hence a time dependent form to the flow itself for a given set of boundary conditions the flow depends on the stress exponent in the power law rheology n and on the argand number which is a measure of the ratio between the stress arising from crustal thickness contrasts and the stress required to deform the material at the ambient strain rates when the effective viscosity of the medium is very high ar o crustal thickness variations do not influence the flow if the material is newtonian n l the deformation associated with an influx of material approximating an indenter is of much greater lateral dimension than the width of the indenter whereas when material has a power law rheology n 3 5 are used the deformation is confined to a region of lateral extent comparable to that of the indenter as ar increases the forces arising from crustal thickness contrasts exert more influence on the flow and the maximum crustal thickness that can be sustained by a given influx of material is related by a simple expression to the effective viscosity of the medium at the ambient strain rates in the limit of a very weak medium ar 10 the lithosphere is unable to sustain appreciable crustal elevation contrasts the results of these numerical experiments show that systems in which the effective viscosities are such that the maximum deviatoric stresses are between 1 kbar

observations of the ionospheric response to the 15 december 2006 geomagnetic storm long duration positive storm effect 1 the long duration positive ionospheric storm effect that occurred on 15 december 2006 is investigated using a combination of ground based global positioning system gps total electron content tec topex and jason 1 tec and topside ionosphere plasmasphere tec gps radio occultation and tiny ionospheric photometer tip observations from the constellation observing system for meteorology ionosphere and climate cosmic satellites this multi instrument approach provides a unique view of the ionospheric positive storm effect by revealing the storm time response in different altitude regions the ground based gps tec topex jason 1 tec and topside ionosphere plasmasphere tec all reveal significant enhancements at low latitudes to midlatitudes over the pacific ocean region during the initial portions of the storm main phase from 0000 0400 universal time ut on 15 december at low latitudes the topside ionosphere plasmasphere tec increase represents greater than 50 of the tec enhancement that is observed by ground based gps receivers moreover electron density profiles obtained using the technique of gps radio occultation demonstrate that the f layer peak height increased by greater than 100 km during this time period the effects of soft particle precipitation are also apparent in the cosmic observations of topside ionosphere plasmasphere tec the positive storm effects over the pacific ocean region remain present in the equatorial ionization anomaly crest regions beyond 1200 ut on 15 december this long lasting positive storm effect is most apparent in ground based gps tec and cosmic tip observations while only a small increase in the topside ionosphere plasmasphere tec after 0400 ut is observed this indicates that the long lasting positive storm effect occurs predominantly at f region altitudes and furthermore that refilling of the topside ionosphere and plasmasphere is not the primary mechanism for producing the long lasting positive storm phase during this event the observations suggest that the enhanced eastward electric field and equatorward neutral wind are likely to play a significant role in the generation of long lasting positive storm effects

westward electric field penetration to the dayside equatorial ionosphere during the main phase of the geomagnetic storm on 22 july 2009 1 the moderate geomagnetic storm minimum sym h 89 nt that occurred during the period from 21 to 25 july 2009 is anomalous because the storm main phase developed during northward interplanetary magnetic field imf a reduction for 4 h in the daytime e region westward drift eastward electric field over the magnetic equatorial location of trivandrum 8 5 n 77 e dip latitude 0 5 n in india is observed during the storm main phase this reduction in the drift is also indicated by the disappearance of the equatorial sporadic e region esq echoes on the ionograms it is suggested that an additional westward prompt penetration electric field characterized by the northward imf bz is superposed on the ionosphere during the storm main phase which contributed to the observed reduction in the drift these are the first observations which indicate the effects of the dusk to dawn penetration electric fields on the east west drifts during northward imf

statistical analysis of dayside equatorial ionospheric electric fields and electrojet currents produced by magnetospheric substorms during sawtooth events 1 substorms cause significant disturbances in the ionosphere however it has not been well understood how the electric field and electrojet in the dayside equatorial ionosphere respond to substorm onset previous studies found that the equatorial electric field after substorm onset could be eastward or westward because the onset of isolated substorms is often related to a northward turning of the interplanetary magnetic field imf the measured total electric field is determined by contributions from both imf northward turning and substorm onset and is not necessarily the signature of the onset in order to exclude the effect of imf northward turning we analyze the variations of ionospheric electric field and electrojet during storm time substorms when the imf remains stable thus the ionospheric variations can be identified to be caused solely by substorms the electric field data are measured by the jicamarca radar and the electrojet is derived from magnetometers at jicamarca and piura it is found that substorm onset induces an eastward electric field and electrojet in the dayside equatorial ionosphere when the imf remains continuously southward across the onset the equatorial electrojet starts to increase at the onset reaches a maximum value 30 min after the onset and then decreases to the pre onset value 60 min after the onset westward electric field and counter electrojet occur only if the substorm onset is associated with a northward turning of the imf it is concluded that the effect of substorm onset on the dayside equatorial ionosphere without involvement of imf reorientations is an enhanced eastward electric field

positive and negative ionospheric disturbances at middle latitudes during geomagnetic storms the morphology of middle latitude ionospheric disturbances in response to geomagnetic storms has been investigated to determine the phenomenological differences between positive and negative ionospheric storm effects using fof2 observations from azimuthal chain of stations to better organize the disturbance signatures two ionospheric indices were introduced to describe the maximum positive dfu index and negative dfl index deviation observed during an ionospheric storm a systematic appearance of nighttime positive effects was determined with a 24 hour recurrence the thermospheric ionospheric view associated with positive and negative storm effects proposed by prolss 1993 was extended to encompass our observations this test clearly demonstrates that such a model can capture most of the basic aspects of ionospheric storms nevertheless the prominent feature of large nighttime enhancements in the ionization density have yet to be explained

correction to a thin viscous sheet model for continental deformation summary the governing equation derived by england mckenzie for the deformation of a thin viscous shell contains an error we give the correct derivation here and correct those figures where the change makes a visible difference the correct results differ quantitatively from those of england mckenzie but their conclusions are not affected

estimates of terrestrial heat flow from deep petroleum tests along the rio grande rift in central and southern new mexico twenty six new estimates of heat flow are calculated for the albuquerque belen basin and the basins of the southern rio grande rift in new mexico from these and previous data the following heat flow patterns may be suggested the regional or background heat flow in the albuquerque belen basin is 77 mw m 2 there is also a ne sw trend of higher heat flow 92 110 mw m 2 across the region in the southern rio grande rift between socorro and las cruces the regional heat flow appears to be 95 mw m 2 in this region there are also higher heat flows 117 135 mw m 2 at widely scattered sites south of las cruces near the international border between mexico and the united states preliminary and perhaps suspect data suggest the possibility of a transition to the intermediate heat flows previously estimated at sites throughout much of northeastern chihuahua mexico regional heat flow values in the albuquerque belen basin and in the basins of the southern rio grande rift are consistent with but do not constrain simple models of crustal thinning higher heat flows in these two areas are thought to be caused by hydrothermal fluids largely groundwaters but possibly magma in some areas transporting heat upward along crustal fracture zones

buoyancy tectonic models of uplift and subsidence along high angle faults in extensional and compressional tectonic regimes abstract this study models the potential uplift and subsidence of brittle upper crustal trapezoidal blocks which move along pre existing high angle faults in extensional tectonic regimes similar models for uplift in compressional tectonic regimes are also presented a force balance is assumed to exist between the weight of the trapezoidal block the buoyancy force derived from the lower ductile crust the supporting forces from the neighboring blocks and the frictional resistance to motion across the fault generally the weight of the brittle crustal block is effectively opposed by the buoyancy force making vertical movement quite dependent on tectonic forces redirected along the high angle bounding faults the analysis relates the state of stress in the brittle upper crust and other critical parameters such as structure width thickness of the brittle upper crust frictional resistance along faults mobility of the brittle ductile transition which is related to slow and fast geologic movement different lower crustal densities and deposition and erosion to possible uplift or subsidence greater vertical displacement is generally compatible with narrower crustal blocks more deviatoric tectonic stress lower fault friction a thicker brittle crust and similar upper and lower crustal densities without deposition or erosion approximately equal amounts of vertical movement appear possible for trapezoidal blocks with similar conditions however deposition can typically induce far more subsidence than erosion can induce uplift although large amounts of uplift appear possible in both extensional and compressional regimes the effects of erosion and the higher stresses possible with tectonic compression should produce larger amounts of uplift in compressional vs extensional regimes slow or fast geologic movement can be defined as whether the brittle ductile transition remains at a constant depth or is displaced if the brittle ductile transition remains at a constant depth slow movement uplift is enhanced in both extensional and compressional regimes low resistance to motion along faults is necessary for vertical movement and is consistent with several other recent studies the models suggest that much of the observed relief on the earth s surface up to several tens of kilometers width can be caused by the dynamics in the earth s crust however related to deeper earth processes i e much topography can be analyzed in terms of stresses in the brittle crust and the buoyancy effect of the lower crust however the stresses in the brittle crust may be generated by deeper and more global processes

rotational buoyancy tectonics and models of simple half graben formation a buoyancy model for half graben development based on the stability of floating bodies assumes parallel high angle normal faults which penetrate the brittle crust and define half graben parallelograms buoyancy forces balance the weight of the half grabens and torques generated by buoyancy forces are balanced by opposing torques arising from crustal stresses model results indicate that widths of developing half grabens depend on the state of stress in the brittle crust thickness of the brittle crust and spacing of boundary faults for a given thickness of elastic crust in a constant state of stress narrower half grabens will experience greater rotation increasing deviatoric tension and or thickening of the brittle crust will enable rotation of wider half grabens the effective coefficient of friction across the fault must be 0 1 0 2 for half graben rotation to occur and probably 0 1 for wider half grabens to form or any half grabens to rotate through large angles these conclusions contribute to an explanation of half graben formation in the socorro new mexico area where decreasing heat flows and associated thickening of the brittle crust allowed for development of wider half grabens as rifting progressed

a dayside ionospheric positive storm phase driven by neutral winds 1 this paper presents observations and numerical simulations of ionospheric and thermospheric disturbances associated with a moderate geomagnetic storm on 10 september 2005 during the event the incoherent radars located in millstone hill and arecibo observed a dayside positive storm phase as manifested by the enhanced electron density in the f region the universal time ut altitude profile of electron density measured by both radars displayed a structure that closely resembles the greek letter a similar structure is also reproduced by the thermosphere ionosphere electrodynamics general circulation model tiegcm this peculiar electron density distribution is found to be associated with vertical ion drift which initially was upward and then became downward using realistic time dependent ionospheric convection and auroral precipitation as inputs the tiegcm reveals that the primary cause of the positive storm response was the enhanced meridional neutral wind rather than the penetration magnetospheric electric field this study reiterates the importance of neutral wind effects on ionospheric disturbance

midlatitude tec enhancements during the october 2003 superstorm 1 we use observations from the array of north american gps receivers to examine the formation and severity of midlatitude enhancements and steep gradients in total electron content tec during the october 30 31 2003 superstorm a large 10x enhancement in dayside tec was observed over the us mainland during these events as dst decreased sharply and strong saps electric fields eroded the outer reaches of the post noon plasmasphere boundary layer pbl forming poleward streaming plumes of storm enhanced density tec increased to 250 tecu equatorward of the pbl tec gradients across the pbl over the central us exceeded 60 tecu per deg latitude while intense these features are qualitatively similar to those seen in lesser storms

analyzing the hemispheric asymmetry in the thermospheric density response to geomagnetic storms 1 the thermospheric densities derived by champ star accelerometer within the time period from 01 may 2001 to 31 december 2007 are utilized to investigate the hemispheric asymmetry in response to strong storm driving conditions the geomagnetic storms of 03 07 april 2004 are first studied since the storms occurred close to the vernal equinox allowing the seasonal asymmetry to be eliminated to the greatest extent the averaged density enhancements in the southern polar region were much larger than that in the northern polar region the comparisons of density versus dst and apindex indicate a strong linear dependence with the slopes of the fitted lines in the southern hemisphere being 50 greater than that in the northern hemisphere this effect can possibly be attributed to the non symmetric geomagnetic field 102 storm events are used to conduct a statistical analysis for each storm a linear fit is made between the averaged mass density and thedst and ap indices independently in each hemisphere the seasonal variation of the intercepts and the slopes of the fitted lines are further explored the baseline is strongly dependent on season with the hemisphere receiving the larger amount of sunlight having larger density the slopes showed considerable hemispheric differences around the vernal equinox yet no statistical differences around other seasons it is speculated that competing mechanisms cancel each other during the solstices while during the equinoxes the lower magnetic field in the southern hemisphere may allow stronger ion flows thereby causing more joule heating it is uncertain why the vernal equinox would be favored in this explanation though

millstone hill incoherent scatter f region observations during the disturbances of june 1991 the extreme geomagnetic disturbances of early june 1991 were accompanied by dramatic effects in the earth s thermosphere and ionosphere which are the subject of coordinated analysis by the coupling energetics and dynamics of atmospheric regions cedar storm study project f region observations taken at millstone hill over the interval june 5 11 using a nine position experiment allow estimation of spatial gradients in ionospheric parameters above the station from these gradients the motion term in the f region continuity equation is obtained and combined with calculations of rates of production and loss of the major ions in a semiempirical model of the f region ionosphere above millstone hill electron densities calculated from this semiempirical model using msis 86 are generally much smaller than the measurements this discrepancy could be explained by the presence of vibrationally excited n sub 2 combined with a decrease in the atomic oxygen to molecular composition ratio of approx 2 or more on the most disturbed days neutral winds calculated by using the incoherent scatter line of sight ion drifts show a strong equatorward surge during the day on june 5 and strong equatorward surges during all the disturbed nights synoptic observations taken from millstone hill by using elevation and azimuth scans duringmore the nights of june 12 13 and 14 illustrate the large scale structure of electron density and its relation to neutral winds and electric fields observed over much of eastern north america 58 refs 12 figs 1 tab less

simulation study of a positive ionospheric storm phase observed at millstone hill simulation results from the nrl ionospheric model sami2 indicate that the changes in the f region over millstone hill during the geomagnetic storm beginning on 3 april 2004 are primarily due to the influence of a long lasting eastward electric field as was previously suggested by c huang et al 2005 a simulation of the storm day agrees well with the observational data and shows that compared with the ionosphere of the previous quiet day the peak electron density in the f region n m f 2 increased by a factor of 2 the altitude of the peak density h m f 2 rose by 80 km and the f region electron temperature decreased by 1000 k further simulations in which either the neutral atmosphere and winds or the electric field were replaced by their quiet day counterparts clearly suggest that the electric field played the dominant although not exclusive role in producing these effects

modeling the ionospheric response to traveling atmospheric disturbances anomalous increases of the ionization density at middle latitudes positive ionospheric storms are often a prominent feature of upper atmospheric storms one of their possible causes are traveling atmospheric disturbances tads which propagate from polar to equatorial latitudes carrying along equatorward directed meridional winds at middle latitudes these winds cause an increase in the height of the f2 layer which in turn will lead to an enhancement of the ionization density using a simple description of a tad and an ionospheric model we are able to reproduce the basic properties of such perturbations we also attempt to simulate an actually observed storm period rough agreement is obtained when the wind speed is derived from the height of the f2 layer peak a more detailed simulation of the initial phase of the storm requires a more refined tad model with time dependent height gradients in the wind field

continuous penetration of the interplanetary electric field to the equatorial ionosphere over eight hours during intense geomagnetic storms 1 the interplanetary electric field penetrates to the low latitude ionosphere and has significant influence on the ionospheric electrodynamics during intense geomagnetic storms it is critical to understand how much of the interplanetary electric field can penetrate to the ionosphere and how long penetration electric fields can exist in this study we present the defense meteorological satellite program dmsp satellite measurements of the equatorial ionospheric ion vertical velocity in the dusk sector during two intense geomagnetic storms we find that the equatorial ionospheric electric field at dusk is approximately proportional to the interplanetary electric field for 8 10 hours during the storm main phase the penetration efficiency is relatively constant over the entire interval and is 5 at dusk in one storm case the long lasting storm time penetration electric field causes significant redistribution of the ionospheric plasma this study reveals that penetration electric fields can last for 8 10 hours without effective shielding when the magnetic storm activity is strengthening during continuous southward interplanetary magnetic field the result implies that the interplanetary electric field is linearly coupled with the dusk equatorial ionosphere during the entire main phase of intense magnetic storms which is very important for understanding the storm time ionospheric electric field and electrodynamics

influences of stress and temperature regimes on graben subsidence a note abstract a model is presented for isostatic subsidence of a crustal graben block within a regional stress field that varies linearly with depth in this model an idealized trapezoidal block of brittle upper crustal material subsides along frictionless bounding normal faults into the ductile lower crust an analytical expression is derived relating subsidence to regional stress and the dimensions of the block we find that deviatoric tension is required in order for graben subsidence to occur and that greater deviatoric tension promotes greater subsidence deeper normal faulting and narrower graben widths promote deeper graben subsidence the depth of faulting is presumably limited by the depth of the brittle ductile transition in the crust which is mainly a function of temperature extensional areas in which grabens can form tend to have elevated heat flows implying a shallow brittle ductile transition shallow normal faulting and therefore limited graben subsidence post extension or post rift cooling would reduce the heat flow and therefore allow deeper normal faulting and the potential for greater graben subsidence in addition to regional subsidence however the stress regime in cooling continental crust tends to be compressive e g passive margins which would suppress further differential graben subsidence in effect graben subsidence depends on the geometry of the block and is naturally limited by the elevated geothermal conditions associated with extension and or by the compressive stresses associated with cooling or cooled continental crust

electrodynamic disturbances in the brazilian equatorial and low latitude ionosphere on st patrick s day storm of 17 march 2015 the st patrick s day storm of 17th march 2015 has a long lasting main phase with the dst reaching a minimum of 223 nt during the main phase two strong prompt penetration electric field ppef phases took place first with the southward turning of imf bz around 1200 ut and the second with the onset of a substorm around 1725 ut leading to strong equatorial zonal electric field enhancements the consequent spatio temporal disturbances in the ionospheric total electron content tec and the resultant modifications in the equatorial ionization anomaly eia over the brazilian longitudinal sector are investigated in detail the simultaneous measurements from a large network of gps receivers ionosonde and magnetometers over the brazilian longitudinal sector are used for this study in the presence of enhanced zonal electric field the equatorial f2 layer peak hmf2 experienced a rapid uplift without any significant change in the base height h f while the f2 layer is redistributed into f2 and f3 layers the enhanced zonal electric filed due to ppef led to the strong super fountain effect under which the anomaly crest departed poleward to 40o s latitude in the presence of westward and equatorward wind surge over brazil with the co existing disturbance dynamo fields strong hemispheric asymmetry is seen in the storm time response of eia during both the ppef phases

midlatitude ionospheric disturbances during magnetic storms and substorms 1 we present periodic 2 hour magnetospheric and ionospheric oscillations observed with multiple space based and ground based instruments during the severe magnetic storm of 25 september 1998 periodic particle injections were observed at geosynchronous orbit ground magnetometers registered very large as high as 3000 nt magnetic deviations in the nightside auroral zone the millstone hill incoherent scatter radar at magnetic latitude 55 measured periodic enhancements of ionospheric eastward ion velocity from midnight to 1000 mlt the periodic variations in the magnetometers and millstone hill radar were well correlated with the magnetospheric particle injections the observations are consistent with the occurrence of periodic magnetospheric substorms during a magnetic storm during each substorm cycle the ionospheric auroral zone expanded to the latitude of the millstone hill radar so the radar was periodically within the auroral zone and detected the auroral plasma return flows after substorm activity stopped the millstone hill radar measured near noon in phase periodic oscillations of the ionospheric f region electron density and temperature which may be due to particle precipitation from the ring current and or plasmasphere into the midlatitude ionosphere we suggest that magnetospheric substorms during magnetic storms have a cycle time of 2 hours the magnetosphere can sustain similar oscillations for several cycles even though the substorm activity has stopped all the observed periodic variations in the geosynchronous particle injections in the auroral magnetic deviations and in the ionospheric ion velocity are related to the periodic magnetospheric substorms and oscillations

was magnetic storm the only driver of the long duration enhancements of daytime total electron content in the asian australian sector between 7 and 12 september 2017

impact of global seismicity on sea level change assessment 1 we analyze the effect of seismic activity on sea level variations by computing the time dependent vertical crustal movement and geoid change due to coseismic deformations and postseismic relaxation effects seismic activity can affect both the absolute sea level changing the earth s gravity field and hence the geoid height and the relative sea level rsl i e the radial distance between seafloor and geoid level by using comprehensive seismic catalogs we assess the net effect of seismicity on tidal relative sea level measurements as well as on the global oceanic surfaces and we obtain an estimate of absolute sea level variations of seismic origin we modified the approach adopted in our previous analysis considering the issue of water volume conservation by applying the sealevel equation and we improved our computational methods enabling us to evaluate the effect of an extremely large number of earthquakes on large grids covering the whole oceanic surface these new potentialities allow us to perform more detailed investigations and to discover a quantitative explanation for the overall tendency of earthquakes to produce a positive global relative sea level variation our results confirm the finding of a previous analysis that on a global scale most of the signal is associated with a few giant thrust events and that rsl estimates obtained using tide gauge data can be sensibly affected by the seismically driven sea level signal the recent measures of sea level obtained by satellite altimetry show a wide regional variation of sea level trends over the oceanic surface with the largest deviations from the mean trend occurring in tectonically active regions while our estimates of average absolute sea level variations turn out to be orders of magnitude smaller than the satellite measured variations we can still argue that the mass redistribution associated with aseismic tectonic processes may contribute to the observed regional variability of sea level variations a detailed study of these tectonic contributions is important to acquire a complete understanding of the global sea level variations and will be the subject of future investigations

general featurecollisional plateaus in the fifteen years since the importance of collisional plateaus with thickened continental crust began to be recognized as one of the inevitable consequences of the processes of plate tectonics rapid progress in their understanding has come from studies of the world s only active terminal collision zones in the himalayan tibetan and turkish iranian plateaus ancient collisional plateaus are being recognized throughout the geological record back to 3 8 ga from the occurrence of extensive areas typically 500 000 km2 of 8 kbar metamorphism in granulite facies or from the occurrence of extensive areas of higher level minimum melt composition granite rocks whose isotopic signatures indicate reactivation of existing continental crust rather than addition of new crust from the mantle at the time of collision recognition of strike slip faulting in the ancient collisional plateau areas indicates that tectonic escape may have been as important in the past as it is today earth may not be the only planet on which collisional plateaus are important the highlands of venus approximately 7 of the surface with elevations over 1 5 km above mean planetary radius can only exist as a result of crustal thickening and not as a product of lithospheric thinning most of these highlands can be explained by models involving volcanic construction however the highest peaks including maxwell montes the highest mapped area of venus rising over 10 km above mean planetary radius require much greater crustal thickening to support them than can reasonably be explained by a volcanic mechanism geological features of maxwell montes inferred from radar images suggest some analogy between maxwell montes and the tibetan plateau it is somewhat paradoxical that extensional tectonics are commonly associated with continental collision and that collision related rifts may be the only sites where the uppermost layers of a collision thickened crust are preserved from erosion extensional stress fields are generated during continental collision primarily in areas associated with strike slip faulting and tectonic escape additional extensional stresses are gravitationally generated associated with the topography and thickened crust in a collision zone tectonically thickened crust is particularly susceptible to rifting as its lithosphere is weak as a result of heating associated with magmatism this lithosphere is also compositionally weak because of the relatively thick crust dominated by a weak quartz rheology and thin mantle lithosphere dominated by a strong olivine rheology in comparison with a lithosphere with a more normal crustal thickness thus the common association of rifts and collision zones may be a consequence of both stresses generated during collision and modification of the lithosphere by collision

topside ionospheric irregularities as seen from multisatellite observations we use in situ data from champ and dmsp satellites along with data of gps receiver onboard champ satellite and ground based gps receivers to study the occurrence and global distribution of ionospheric irregularities during the main phase of the geomagnetic storm of 29 31 august 2004 minimum dst excursion of a128 nt using the champ gps measurements we created maps of gps phase fluctuation activity and found two specific zones of the most intense irregularities 1 the region of the auroral oval at high latitudes of both hemispheres and 2 the low latitudes equatorial region between africa and south america at high latitudes the topside ionospheric irregularities appeared to be more intensive in the southern hemisphere which is most likely due to seasonal variations in the interhemispheric field aligned currents system an analysis of multi instrumental observations reveals reinforcement of the equatorial ionization anomaly after sunset in atlantic sector on 30 august and formation of the significant plasma depletions and irregularities over a large longitudinal range equatorial irregularities were also found in the morning sector at the recovery phase of the storm in addition to low earth orbit leo gps measurements we analyze the leo in situ measurements and we show that these two techniques cannot be interchangeable in all cases because of the altitudinal extent of plasma irregularities overall we demonstrate that the leo gps technique can serve a useful tool for detection of the topside ionospheric irregularities during space weather events and may essentially contribute to other methods based on various instruments

storm time plasma transport at middle and high latitudes associated with the large scale enhancement of the ionospheric convection electric field during disturbed geomagnetic conditions solar produced f region plasma is transported to and through the noontime cleft from a source region at middle and low latitudes in the afternoon sector as a result of the offset between the geomagnetic and geographic poles the afternoon sector region of strong sunward convection is shifted to increasingly lower geographic latitude throughout the interval between 12 ut and 24 ut a snowplow effect occurs in which the convection cell continually encounters fresh corotating ionospheric plasma along its equatorward edge producing a latitudinally narrow region of storm enhanced plasma density sed and increased total electron content which is advected toward higher latitudes in the noon sector the millstone hill incoherent scatter radar regularly observes sed as a spatially continuous large scale feature spanning local times between noon and midnight and at latitudes between the polar cap and its mid or low latitude source region for local times away from noon the latitude of most probable sed occurrence moves equatorward by 6 for an increase of 2 in the kp index during strong disturbances the topside sed is observed to be convecting sunward at 750 m s 1 with a flux of 1014 m 2 s 1 this feature accounts for the pronounced enhancement of ionospheric density near dusk at middle latitudes observed during the early stages of magnetic storms called the dusk effect and constitutes a source for the enhanced f region plasma observed in the polar cap during disturbed conditions

analysis of the global ionospheric disturbances of the march 2015 great storm the global ionospheric storm in march 2015 was investigated using data from over 3000 gps stations worldwide in this study total electron content tec rate of tec rot and rot s standard deviation roti as well as the second order difference operator tect were considered as main characteristic methods to distinguish ionosphereic disturbances the results show that 1 based on the multiple methods above we all observed that for the first time there were three equatorward traveling ionospheric disturbances tids in the main phase of this storm in north america the disturbance zone expanded to 40 n the disturbance periods and ae peak stages were roughly synchronous we suggest that these three tids were induced by the propagation of agws to low latitudes under the action of ae 2 the most intense positive storm occurred over south america and the south atlantic over 300 enhancement 00 00 05 00 ut march 18 whereas a negative storm was observed in the corresponding region of the nh such inverse hemispheric asymmetry in intensity and structure can be explained by the variations of the thermospheric composition the imf by component and the geomagnetic intensity 3 on march 18 a negative storm dominated globally except at certain low latitudes and tended to propagate equatorward and decay with time which could be largely attributed to the storm circulation theory and the evolution of the negative storm was further characterized by the fof2 variations of ionosondes

prompt midlatitude electric field effects during severe geomagnetic storms meridian plane elevation scans with the millstone hill incoherent scatter radar provide evidence of a strong perturbation of the coupled mid latitude magnetosphere ionosphere system during the early phases of the november 4 1993 magnetic storm a narrow ionospheric trough formed at l 3 5 in the pre midnight sector immediately poleward of the millstone hill site the most pronounced radar signature of the developing activity was a brief 20 min uplifting of the f region plasma equatorward of the trough such that the peak altitude increased with distance away from the trough a similar signature had been observed during storm onset on march 20 1990 and in that event a pronounced topside ionospheric depletion developed in the region far equatorward of the mid latitude trough and was observed by the radar and the dmsp f9 satellite during the november 4 1993 event the dmsp f10 satellite observed narrow magnetically conjugate regions of plasma density depletion and strong horizontal and upward plasma velocity 1500 m s at l 1 5 at the time of the uplifting of the mid latitude f region observed by the radar these observations were confined to longitudes near the south atlantic magnetic anomaly and in the nov 1993 case the perturbation was coincident with the peak of the precipitating particle fluxes associated with innerbelt losses at the anomaly both the uplifting of the ionospheric f layer and the triggering of topside density perturbations can be explained in terms of an eastward electric field imposed on the mid and low latitude ionosphere during the initial stages of the geomagnetic storm the low latitude ionospheric perturbations in these events were similar to supersonic equatorial bubbles triggered by the destabilizing effects of the upward e b drift associated with the eastward electric field

on the vertical drift of ionospheric f layer during disturbance time results from ionosondes the morphology of low latitude ionosphere is greatly affected by the zonal electric field especially at disturbance time in this study historical data from two low latitude ionosondes located at haikou and chongqing china are used to study the disturbance vertical drift properties of ionospheric f layer during the initial and main phases of 50 intense storms the disturbance drift from an empirical model is used as an indicator to denote the e x b disturbance magnitude it is found that the drifts both at the base and at the peak height are increased in magnitude when the disturbance becomes stronger for the same disturbance ionospheric vertical drifts at the base height are comparable with those at the peak height over haikou but they are larger than the latter over chongqing both drifts being smaller than those at the magnetic equator the drifts are larger in daytime than in nighttime but no rule is found on their seasonal dependence this indicates that low latitude storm time ionospheric vertical drift of the ionospheric layer exhibits both consistent and individual properties at different locations

ionospheric signatures of plasmaspheric tails 1 we make direct comparisons between gps maps of total electron content tec over the north american continent millstone hill radar observations of storm enhanced density and low and high altitude satellite measurements of the perturbation of the outer plasmasphere during the march 31 2001 geomagnetic storm we find that storm enhanced density sed and plumes of greatly elevated tec are associated with the erosion of the outer plasmasphere by strong sub auroral polarization electric fields the sed tec plumes identified at low altitude map closely onto the magnetospheric determination of the boundaries of the plasmapause and plasmaspheric tail determined by euv imaging from the image spacecraft characteristics of the sed tec plumes tails for the march 31 2001 event are tec 100 tecu f region sunward velocity 1000 m s sunward flux 5 1024 ions s 1 total transport to dayside magnetopause merging region 3 hr event 5 1028 ions

crustal doming and the mechanism of continental rifting abstract bott m h p 1980 crustal doming and the mechanism of continental rifting in j h illies editor mechanism of graben formation tectonophysics 73 1 8 a mechanical explanation of the relationship between crustal uparching and graben formation is suggested based on the geologically supported assumption that doming precedes rifting rifting and graben formation can occur under conditions of crustal tension by the vening meinesz wedge subsidence mechanism modified to apply to the uppermost 20 km or thereabouts of the continental crust if sediment filled troughs of around 5 km depth are to be formed by this mechanism then a persistent tension of about 200 mpa 2 kbar is required such a stress system may result from the combined effect of the topographic load of the uplifted region and the upthrust caused by the underlying low density upper mantle region below if the upper 10 to 20 km of the crust is elastic but the underlying region can deform slowly by visco elastic creep then stress differences of the order of 200 mpa can occur in the upper elastic crust by this process it is suggested that such a stress system rather than one arising from bending of the uparched crust or from plate boundary stresses may be the primary cause of the rifting

global postseismic gravity changes of a viscoelastic earth a spherically symmetric earth model with a viscoelastic mantle and an inviscid core is used to study the gravitational perturbation due to a lithospheric shear dislocation in the coseismic and postseismic regime our approach is based on a quasi static solution of the equilibrium equations taking advantage of the normal mode technique for a layered incompressible earth with linear viscoelastic rheology we perform a systematic study of space and time evolution of gravity changes associated with a wide selection of seismic sources investigating the effects of several different mantle viscosity profiles our results show that the gravitational signal is sensitive not only to the viscosity of the asthenosphere but also to that of the mantle including the portion below the 670 km discontinuity as a case study we compute the coseismic and postseismic gravity perturbation due to the 1964 alaska earthquake the last section is devoted to the analysis of the postseismic relaxation rates of the gravitational perturbation following that earthquake for several different viscosity profiles of the mantle our results show that experimental attempts to obtain reliable detection of static and quasi static gravitational perturbation associated with seismic events would be of great importance in understanding the dynamic and viscosity profile of both upper and lower mantle

formation of polar ionospheric tongue of ionization during minor geomagnetic disturbed conditions previous investigations of ionospheric storm enhanced density sed and tongue of ionization toi focused mostly on the behavior of toi during intense geomagnetic storms little attention has been paid to the spatial and temporal variations of toi during weak to moderate geomagnetic disturbed conditions in this paper we investigate the source and development of toi during a moderate geomagnetic storm on 14 october 2012 multi instrumental observations including gps total electron content tec defense meteorological satellite program dmsp in situ measured total ion concentration and ion drift velocity superdarn measured polar ion convection patterns and electron density profiles from the poker flat incoherent scatter radar pfisr have been utilized in the current analysis gps tec maps show salient toi structures persisting for about 5 h over high latitudes of north america on 14 october 2012 in the later recovery phase of the storm when the magnitudes of imf by and bz were less than 5 nt the pfisr electron density profiles indicate that the extra ionization for tec enhancements mainly occurred in the topside ionosphere with no obvious changes in the bottomside ionosphere and vertical plasma drifts additionally there were no signatures of penetration electric fields in the equatorial electrojet data and upward ion drifts at high latitudes at the same time strong subauroral polarization streams with ion drift speeds exceeding 2 5 km s carried sunward fluxes and migrated toward lower latitudes for about 5 based on the dmsp cross track drift measurements based on those measurements we postulate that the combined effects of initial build up of ionization at midlatitudes through daytime production of ionization and equatorward or less poleward than normal daytime neutral wind reducing downward diffusion along the inclined filed lines and an expanded polar ion convection pattern and its associated horizontal plasma transport are important in the formation of the toi