statistical behavior of the longitudinal variations of daytime electron density in the topside ionosphere at middle latitudes electron density in the topside ionosphere has significant variations with latitude longitude altitude local time season and solar cycle this paper focuses on the global and seasonal features of longitudinal structures of daytime topside electron density ne at middle latitudes and their possible causes we used in situ ne measured by demeter and f2 layer peak height hmf2 and peak density nmf2 from cosmic the longitudinal variations of the daytime topside ne show a wave number 2 type structure in the northern hemisphere whereas those in the southern hemisphere are dominated by a wave number 1 structure and are much larger than those in the northern hemisphere the patterns around december solstice ds in the northern hemisphere winter are different from other seasons whereas the patterns in the southern hemisphere are similar in each season around march equinox me june solstice js and september equinox se in the northern hemisphere and around me se and ds in the southern hemisphere the longitudinal variations of topside ne have similar patterns to hmf2 around js in the southern hemisphere winter the topside ne has similar patterns to nmf2 and hmf2 does not change much with longitude thus the topside variations may be explained intuitively in terms of hmf2 and nmf2 this approach works reasonably well in most of the situations except in the northern winter in the topside not too far from the f2 peak in this sense understanding variations in hmf2 and nmf2 becomes an important and relevant subject for this topside ionospheric study

ionospheric annual anomaly new insights to the physical mechanisms the ionospheric annual anomaly or nonseasonal anomaly of the ionosphere is characterized by globally increased ionization in december solstice than in june solstice though this phenomenon was reported several decades ago the causal mechanisms have not been fully understood till today in this paper the f2 layer peak electron density nmf2 data from formosa satellite 3 constellation observing system for meteorology ionosphere and climate radio occultation observations during the low solar activity year 2009 were systematically analyzed to investigate the physical mechanisms responsible for annual anomaly and its local time latitudinal and longitudinal variability it is found that the annual anomaly is primarily dominant at southern hemisphere at all local times with significant enhancements at equatorial ionization anomaly crest latitudes during noon to afternoon hours and at high latitudes during nighttimes the annual anomaly in northern hemisphere occurs with relatively smaller magnitudes and confined only to morning to early afternoon hours 08 14 lt this study brings out the important roles of effective neutral winds due to the geomagnetic field configuration and the offset between geomagnetic equator and subsolar point for the enhanced plasma density in the southern hemisphere during december that majorly contributes to the ionospheric annual anomaly these results provide new insights to the responsible mechanisms behind the ionospheric annual anomaly and its local time latitudinal and longitudinal variation

a total electron content space weather study of the nighttime weddell sea anomaly of 1996 1997 southern summer with topex poseidon radar altimetry this paper reports on a total electron content space weather study of the nighttime weddell sea anomaly overlooked by previously published topex poseidon climate studies and of the nighttime ionosphere during the 1996 1997 southern summer to ascertain the morphology of spatial tec distribution over the oceans in terms of hourly geomagnetic longitudinal and summer winter variations the topex tec magnetic and published neutral wind velocity data are utilized to understand the underlying physical processes the tec results are combined with inclination and declination data plus global magnetic field line maps to investigate spatial and temporal tec variations geographic magnetic latitudes and local times are computed as results show the nighttime weddell sea anomaly is a large 1 600 2 22 million km2 estimated for a steady ionosphere space weather feature extending between 200 e and 300 e geographic it is an ionization enhancement peaking at 50 s 60 s 250 e 270 e and continuing beyond 66 s it develops where the spacing between the magnetic field lines is wide medium easterly declination is large medium 20 50 and inclination is optimum 55 s its development and hourly variations are closely correlated with wind speed variations there is a noticeable 43 reduction in its average area during the high magnetic activity period investigated southern summer nighttime tecs follow closely the variations of declination and field line configuration and therefore introduce a longitudinal division of four indian western eastern pacific atlantic northern winter nighttime tecs measured over a limited area are rather uniform longitudinally because of the small declination variation topex maps depict the expected strong asymmetry in tec distribution about the magnetic dip equator

east west differences in f region electron density at midlatitude evidence from the far east region the global configuration of the geomagnetic field shows that the maximum east west difference in geomagnetic declination of northern middle latitude lies in the us region similar to 32 degrees which produces the significant ionospheric east west coast difference in terms of total electron content first revealed by zhang et al 2011 for verification it is valuable to investigate this feature over the far east area which also shows significant geomagnetic declination east west gradient but smaller similar to 15 degrees than that of the us the current study provides evidence of the longitudinal change supporting the thermospheric zonal wind mechanism by examining the climatology of peak electron density nmf2 electron density ne of different altitudes in the far east regions with a longitude separation of up to 40 60 degrees based on ground ionosonde and space based measurements although the east west difference r ew over the far east area displays a clear diurnal variation similar to the us feature that is negative r ew west ne east ne in the noon and positive at evening night the observational results reveal more differences including 1 the noontime negative r ew is most pronounced in april june while in the us during february march thus for the late spring and summer period negative r ew over the far east region is more significant than that of the us 2 the positive r ew at night is much less evident than in the us especially without winter enhancement 3 the magnitude of negative r ew tends to enhance toward solar maximum while in the us showing anticorrelation with the solar activity the altitude distribution of pronounced negative difference 300 400 km moves upward as the solar flux increases and hence produces the different solar activity dependence at different altitude the result in the paper is not simply a comparison corresponding to the us results but raises some new features that are worth further studying and improve our current understanding of ionospheric longitude difference at midlatitude citation zhao b m wang y wang z ren x yue j zhu w wan b ning j liu and b xiong 2013 east west differences in f region electron density at midlatitude evidence from the far east region j geophys res space physics 118 542 553 doi 10 1029 2012ja018235

the midlatitude summer night anomaly as observed by champ and grace interpreted as tidal features this paper presents a description of the midlatitude summer night anomaly msna in terms of solar tidal signatures based on in situ observations from champ challenging minisatellite payload and grace gravity recovery and climate experiment during the solar minimum years 2008 and 2009 our analysis is focusing on 40 to 60 magnetic latitude ranges in both hemispheres where the reversed diurnal variations of the electron density are strongest the results revealed that in the southern hemisphere the longitudinally symmetric tide d0 is particularly strong during december solstice the well known weddell sea anomaly is caused by a simultaneous constructive interference of three components d0 dw2 and spw1 during june solstice the eastward propagating tide de1 is the strongest in the northern hemisphere which causes a wave 2 longitudinal pattern the two crests of the wave 2 pattern at nighttime correspond well with the msna feature in the northern hemisphere the msna feature over the usa continent is particularly strong which can be explained by the combined contributions of the components de1 d0 and dw2 the diurnally varying difference in electron density between the usa east and west coast can also be explained by the phase propagation of the de1 a similar effect has also been observed in the asian region the peak electron densities of the tidal component d0 appear around 0700 lt and 2000 lt in the southern and northern hemispheres respectively the time shift suggests that the two hemispheres move in antiphase up and down the planetary wave spw1 exhibits an electron density crest near longitude sectors where the dip equator reaches far into the summer hemisphere

longitudinal variations of positive dayside ionospheric storms related to recurrent geomagnetic storms 1 we have performed an analysis of case events and statistics of positive ionospheric storms in the dayside region of the equatorial ionization anomaly during recurrent geomagnetic storms rgss which dominate in geomagnetic and ionospheric conditions on the declining phase of solar activity in 2004 to 2008 it is shown that total electron content tec has a tendency to minimize before the beginning of rgss and to peak 3 to 4 days after i e on the rgs recovery phase produced by high intensity long duration continuous auroral activity the maximum of tec coincides with the maximum of solar wind velocity within high speed solar wind streams an analysis of electron content vertical profiles derived from two independent methods using ionosondes and constellation observing system for meteorology ionosphere and climate formosa satellite mission 3 radio occultation showed that in the maximum of an ionospheric storm on 28 march 2008 the f2 layer thickens nmf2 increases by 50 and hmf2 elevates by a few tens of kilometers the response of positive ionospheric storms to solar heliospheric and geomagnetic drivers reveals a prominent longitudinal asymmetry in the longitudinal range from 90 to 90 the solar illumination plays a major role and in the range from 90 to 120 the influence of heliospheric and geomagnetic drivers becomes significant the highest correlations of the tec enhancements with the heliospheric and geomagnetic drivers were found during december february r increased from 0 3 to 0 5 we speculate that the dynamics controlling this might result from an effect of solar zenith angle storm time effects of thermospheric o n2 enhancement and penetrating electric fields of interplanetary and magnetospheric origin

investigating the relationships among the south atlantic magnetic anomaly southern nighttime midlatitude trough and nighttime weddell sea anomaly during southern summer 1 this study utilized the multi instrument data of the defense meteorological satellite program to investigate the evening nighttime topside ionosphere during the 1996 1997 southern summer a series of regional surface maps were constructed and permitted the tracking of the topside ionosphere s plasma density features plasma composition thermal structures and vertical and horizontal plasma flows these maps tracked a complete nighttime weddell sea anomaly wsa and strong horizontal plasma flows that registered the high conductivity regions of the south atlantic magnetic anomaly sama these regions developed over the southeastern pacific just equatorward of the wsa and over the south atlantic a heavy ion stagnation trough developed poleward of the sama affected regions thus the trough appeared on the wsa s equatorward side during periods of increasing magnetic activity the plasmapause was the wsa s poleward boundary a statistical study modeled the trough s magnetic activity dependence and revealed a strong east west hemispherical difference that was due to the sama effects when the ae6 was 0 nt the trough appeared at 57 49 2 82 s geomagnetic over the southwestern hemisphere owing to the sama s special electrodynamic effects the trough developed at lower latitudes 42 39 3 04 s over the southeastern hemisphere meanwhile the plasmapause occurred at 62 5 4 s and the wsa s peak appeared at 56 2 4 s hence there was a 20 lat separation between the trough and the plasmapause over the southeastern hemisphere between 210 e and 330 e geographic the wsa filled this gap with increasing magnetic activity the trough in the sama affected regions moved poleward at a rate of 0 0157 0 004 s nt elsewhere it had a 0 0196 0 002 s nt equatorward movement

simulated midlatitude summer nighttime anomaly in realistic geomagnetic fields 1 in the present work using the three dimensional theoretical ionospheric model of the earth in institute of geology and geophysics chinese academy of sciences time3d iggcas we simulate the temporal spatial distribution of the midlatitude summer nighttime anomaly msna and the influences of thermospheric meridional and zonal winds on the formation of msna msna mainly appears in three distinct regions the east asian region the northern atlantic europe region and the south pacific region msna in the south pacific region is obviously stronger than that in the other two regions in these three regions msna not only occurs in local summer but also often occurs in equinox through lifting up or lowering the f region ionization thermospheric winds mainly drive the formation of msna in the east asian region and the northern atlantic europe region msna are mainly driven by the thermospheric meridional wind and the influence of the thermospheric zonal wind can be neglected however although msna in the south pacific region or weddell sea anomaly are mainly driven by the thermospheric meridional wind the thermospheric zonal wind also plays an important role in the formation of msna

geological results of deep exploration in the vienna basin die exploration auf kohlenwasserstoffe im tiefsten geologischen stockwerk unter dem wiener becken in 6 5 bis 8 5 km tiefe in den jahren zwischen 1975 und 1985 stutzte sich auf einige wesentliche voraussetzungen die annahme eines sedimentmantels uber dem kristallinen untergrund bohmische masse unter dem neogen und unter den alpin karpatischen decken die existenz ausgepragter hochzonen im wiener becken mit zielen die bohrtechnisch erreichbar sind die ansammlung von ol und gasfeldern in seichteren positionen im bereich der bohrprojekte

theoretical study of the ionospheric weddell sea anomaly using sami2 1 the ionospheric weddell sea anomaly wsa was first reported more than five decades ago based on ionosonde data near the antarctica peninsula the wsa is an ionospheric structure characterized by a larger nighttime electron density than daytime density recent satellite observations indicate that the wsa can extend from south america and antarctica to the central pacific the major physical mechanisms that have been suggested for the wsa formation are an equatorward neutral wind an electric field the photoionization and the downward diffusion from the plasmasphere on the basis of the theoretical modeling performed in this study using the sami2 model an equatorward neutral wind is identified as the major cause of the wsa while the downward flux from the plasmasphere provides an additional plasma source to enhance or maintain the density of the anomalous structure

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 climatology of middle and upper atmosphere radar observations of thermospheric winds shigaraki middle and upper atmosphere mu radar observations of horizontal thermospheric winds in the magnetic meridian plane over the period september 1986 to september 1996 are reported as climatological averages in the form of time of day variations for several combinations of seasonal and solar activity conditions and are compared with winds predicted by the horizontal wind model hwm and with winds measured at saint santin and millstone hill the dominant feature of the mu wind behavior is its mean diurnal variation of northward flow by day and southward flow by night with the nighttime wind smoothly approaching and receding from a midnight maximum while the daytime wind tends to show two peaks a strong one in the early daylight hours and a weak one in the afternoon evening hwm shows the same unimodal nighttime and bimodal daytime behavior but the hwm pattern is shifted about 2 hours later in time the amplitude of the diurnal harmonic decreases from 78 m s at solar minimum to 45 m s at solar maximum while hwm shows a corresponding increase from 53 to 62 m s the diurnal amplitude is remarkably stable with season but is superposed on a steady wind of 41 m s southward in summer 15 m s northward in winter and midway between these limits at the equinoxes hwm shows a symmetric pattern of 30 m s southward in summer and 30 m s northward in winter ion drag appears to be the main regulator of wind speed and the seasonal wind patterns have a profound effect on the seasonal behavior of the ionosphere

variation of the topside ionosphere during the last solar minimum period studied with multisatellite measurements of electron density and temperature using the ionospheric measurements of champ demeter and dmsp f15 the seasonal and spatial variations of the topside ionosphere during the last solar minimum period were investigated and compared with ionospheric models in all the satellite measurements equatorial ionization anomaly eia shows clearly longitudinal asymmetry with wave number 3 or 4 patterns anomalous increases of ne in the nighttime surpassing daytime ne known as the weddell sea anomaly wsa or mid latitude summer nighttime anomaly msna were also observed in the global ne distribution with differences in detailed geometry of the geomagnetic field according to the altitude in the nighttime ionosphere the reduced te in the equatorial region at the dmsp altitude identified as the equatorial plasma temperature anomaly epta was ascribed to the leftover of the prereversal enhancement of the upward plasma drift though the eia wsa msna and epta are all associated with the upward plasma movement the difference in the thermal evolution is ascribable to the geometry of drift in which the plasma moves across the geomagnetic field line for the eia and the epta while along the field line for the wsa and the msna

field aligned neutral wind bias correction scheme for global ionospheric modeling at midlatitudes by assimilating formosat 3 cosmic hmf2 data under geomagnetically quiet conditions this study demonstrates the usage of a data assimilation procedure which ingests the formosat 3 cosmic f3 c hmf2 observations to correct the model wind biases to enhance the capability of the new global ionosphere plasmasphere electrodynamics ipe model under geomagnetically quiet conditions the ipe model is built upon the field line interhemispheric plasma model with a realistic geomagnetic field model and empirical model drivers the hmf2 observed by the f3 c radio occultation technique is utilized to adjust global thermospheric field aligned neutral winds i e a component of the thermospheric neutral wind parallel to the magnetic field at midlatitudes according to a linear relationship between time differentials of the field aligned wind and hmf2 the adjusted winds are further applied to drive the ipe model the comparison of the modeled electron density with the observations of f3 c and ground based gps receivers at the 2012 march equinox suggests that the modeled electron density can be significantly improved in the midlatitude regions of the southern hemisphere if the wind correction scheme is applied moreover the f3 c observation the ipe model and the wind bias correction scheme are applied to study the 2012 southern hemisphere midlatitude summer nighttime anomaly southern msna weddell sea anomaly wsa event at december solstice for examining the role of the neutral winds in controlling the longitudinal variation of the southern msna wsa behavior with the help of the wind bias correction scheme the ipe model better tracks the f3 c observed eastward movement of the southern msna wsa feature the apparent eastward movement of the southern msna wsa features in the local time coordinate is primarily caused by the longitudinal variation in the declination angle of the geomagnetic field that controls the field aligned projection of both geographic meridional and zonal components of the neutral wind both the ipe simulations and the f3 c observations show the significant longitudinal variation in the speed of the eastward movement of the southern msna wsa

a study of the weddell sea anomaly observed by formosat 3 cosmic 1 more than two years of cosmic electron density profiles at low solar activities are collected to study the evolution of the weddell sea anomaly wsa which appears as an evening enhancement in electron density during local summer observations show that the change in nmf2 the f2 peak electron density is associated with the change in hmf2 the f2 peak height while the latter is correlated closely with the components of the geomagnetic field we find that 1 in the afternoon hmf2 is more liable to rise drastically in regions with a larger jsin 2i j value which would occur early at certain declinations eastward in the southern hemisphere and westward in the northern hemisphere 2 subsequently a larger increment of hmf2 is coincidentally followed by a stronger enhancement of nmf2 and the enhancement ends just around the local sunset and 3 in midlatitudes the evolution pattern of hmf2 in the evening of equinoxes and winter is similar to that in summer albeit without a lasting nmf2 enhancement as that in summer these features suggest that the nmf2 enhancement and the hmf2 increase could arise from the thermospheric wind effect and solar photoionization plays a crucial role in the enhancement as well the general midlatitude f2 layer enhancement in local summer evening is consistent with the wsa on the above features indicating that the wsa is a manifestation with a particular geometry of the magnetic field of the evening enhancement induced by the winds

taming the torrents the hydrological impacts of ancient terracing practices in jordan extensive terracing was an important component of the water and agricultural management regime of nabatean petra the exact function s of these terraces qualitatively and quantitatively is herein investigated field studies and computer modeling for two sites within the drainage basin of petra show that these terraces were highly effective at reducing surface runoff different design features seem to have been adapted in order to achieve different objectives at varying sites for example the beidha site in the lower reaches of the catchment area falls within the higher relief ordovician disi sandstone formation area here the terrace system was designed to slow water flow and trap sediments the terracing greatly reduced surface water flow through the entrapment of sandy loam sediments behind it on the other hand the baqa a site falls in the upper reaches of the drainage basin within the upper cretaceous amman silicified limestone formation the effect of the terrace system here on runoff is significant but less than that seen at beidha this system was more suited for soil conservation and agriculture as the soil here in its natural state already had a high infiltration rate neglect and abandonment of these terraces at both sites have led to increased runoff as evidenced by the development of gullies and by periodic flooding downstream in the core of the ancient city based on the six modeled cases terraces can minimize the surface flow by an average of 28 with values as high as 90 when 2010 precipitation data were used conducting an intensive survey within the catchment area surrounding the ancient city of petra mapping the ancient terraces and reviving their function may produce significant results in flood mitigation and control there

structure and origins of the weddell sea anomaly from tidal and planetary wave signatures in formosat 3 cosmic observations and gaia gcm simulations the weddell sea anomaly wsa is a recurrent feature of the austral summer midlatitude ionosphere where electron densities are observed to maximize during the local nighttime in this study tidal decomposition is applied to formosat 3 formosa satellite constellation observing system for meteorology ionosphere and climate cosmic total electron content tec and electron density observations between 2007 and 2012 to quantify the components dominating local time and spatial variation in the wsa region our results present some of the first three dimensional spaceborne analyses of the wsa from a tidal perspective over multiple years we find that the features of the wsa can be reconstructed as the result of superposition between the dominant diurnal standing d0 eastward wave number 1 de1 westward wave number 2 dw2 and stationary planetary wave 1 spw1 components in tecs producing the characteristic midnight wsa peak the d0 de1 dw2 and spw1 components are found to be an interannually recurring feature of the southern midlatitude to high latitude ionosphere during the summer manifesting as enhancements in electron density around 300 km altitude of the summer middle to high magnetic latitudes the phases of the aforementioned nonmigrating diurnal signatures in electron density in this region are near evanescent suggesting in situ generation rather than upward propagation from below however the spw1 signature shows some signs of an eastward tilt with altitude suggesting possible downward propagation the relation of these components to possible generation via in situ photoionization or plasma transport along magnetic field lines is also discussed using results from the ground to topside model of atmosphere and ionosphere for aeronomy gaia general circulation model gcm connecting the tidal interpretation of the wsa to previously examined generation mechanisms

daytime ionospheric longitudinal gradients seen in the observations from a regional beidou geo receiver network many studies have devoted to the longitudinal variations of the ionosphere globally however the ionospheric longitudinal variations in a small region are rarely reported in this paper we for the first time use tec data from a beidou geostationary orbit geo receiver network to observe and investigate ionospheric longitudinal variations within the zonal scale of 1000 km over central china 112 122 e 27 31 n 20 24 n magnetic latitudes during june 2015 december 2016 the beidou geo tec provides a good dataset to study longitudinal variations compared with non geo tec without contaminating the spatial variations and elevation changes due to satellite motion pronounced daytime longitudinal gradients within the distance of 1000 km are present in beidou geo tec it was found that the tec is generally larger in the west than in the east in some cases the tec gradient magnitude is larger than 45 tecu for most events the obvious daytime longitudinal gradients are accompanied by the tec enhancement the occurrence rate of daytime longitudinal gradients under different geomagnetic activities is similar whereas strong daytime longitudinal gradients mainly occur under the moderate and strong disturbance geomagnetic activities these observations suggest that the electric field disturbances could have significant effects on producing the observed ionospheric longitudinal gradients

first observations of the midlatitude evening anomaly using super dual auroral radar network superdarn radars 1 under geomagnetically quiet conditions the daytime midlatitude ionosphere is mainly influenced by solar radiation typically electron densities in the ionosphere peak around solar noon previous observations from the millstone hill incoherent scatter radar isr have evidenced the presence of evening electron densities higher than daytime densities during the summer the recent development of midlatitude super dual auroral radar network superdarn radars over north america and japan has revealed an evening enhancement in ground backscatter during the summer superdarn observations are compared to data from the millstone hill isr confirming a direct relation between the observed evening enhancements in electron densities and ground backscatter statistics over a year of data from the blackstone radar show that the enhancement occurs during sunset for a few hours from april to september the evening enhancement observed by both superdarn and the millstone hill isr is shown to be related to recent satellite observations reporting an enhancement in electron densities over a wide range of longitudes in the northern hemisphere midlatitude sector during summer time finally global results from the international reference ionosphere iri and the horizontal wind model hwm07 are presented in relation with previously published experimental results and proposed mechanisms of the evening enhancement namely thermospheric horizontal winds and geomagnetic field configuration it is shown that the iri captures the features of the evening enhancement as observed by superdarn radars and satellites

first tomographic observations of the midlatitude summer nighttime anomaly over japan 1 recently a chain of digital beacon receivers has been established over japan mainly for the tomographic imaging of the ionosphere these receivers are installed at shionomisaki 33 45 n 135 8 e shigaraki 34 85 n 136 1 e and fukui 36 06 n 136 e which continuously track the low earth orbiting satellites leos and the simultaneous line of sight total electron content tec data are used for tomographic reconstruction in the images obtained during july 2008 it is seen that the nighttime electron densities exceed the daytime values on almost all days over latitudes 33 34 n on several days these northern latitudes show enhanced electron densities compared to the low latitude region during nighttime these are the prominent features of the midlatitude summer nighttime anomaly msna that is recently observed in the northern hemisphere and is considered similar to the nighttime weddell sea anomaly wsa this is the first study of the msna using tomographic technique and found its significant day to day variability the ionosonde data from wakkanai 45 4 n 141 7 e ground based gps tec observations using the geonet champ in situ electron density measurements and formosat3 cosmic f3 c occultation measurements are also used to confirm the presence of msna over this region and to examine its variability it is seen that in general during the local summer period electron density over the northern latitudes is highest at 2000 2100 lt and the latitudinal enhancement in electron density also begins to appear around the same time which continues to exist even at later hours

topside ionospheric electron temperature and density along the weddell sea latitude it has been well known that the ionospheric electron density ne is greater in the summer nighttime than daytime around the weddell sea region which is named weddell sea anomaly wsa this paper for the first time reports unusual increases decreases of the daytime nighttime electron temperature te at about 830 km altitude over the wsa latitudes probed by tatiana 2 during december 2009 to january 2010 concurrent measurements at 660 830 km altitude observed by tatiana 2 detection of electro magnetic emissions transmitted from earthquake regions demeter and formosa satellite 3 constellation observing system for meteorology ionosphere and climate f3 c reveal the anticorrelation between te and ne along the wsa latitudes in the daytime and nighttime based on f3 c ne along the wsa latitudes observed at various local times the associated te values are computed the tatiana 2 and demeter observations as well as the computed results show that te yield the maximum values over the wsa region during daytime and over the indian and atlantic ocean area during nighttime the maxima or minima in f3 c ne and the computed te reveal eastward phase shifts

three dimensional ionospheric electron density structure of the weddell sea anomaly 1 this paper provides the first three dimensional description of the ionospheric density structure of the weddell sea anomaly wsa the wsa is characterized by a nighttime ionospheric density greater than that in daytime in the weddell sea region around the antarctic peninsula during the southern hemisphere summer it was first observed by ground based ionosondes located in the antarctica back in the 1950s and was further investigated by two dimensional maps over the oceans using tec measurements collected by the topex poseidon recently although these tec maps have provided two dimensional views for tracking the time evolution and spatial coverage of the wsa the vertical distribution of this peculiar feature is still unavailable with the vertical ionospheric density profiles observed by the formosat 3 cosmic three dimensional density structure of the wsa is presented here for the first time meanwhile a similar wsa signature is observed in the northern and eastern hemisphere during june solstice by both the gps tec and the formosat 3 cosmic electron density observations from the observed altitudinal structure of the wsa during 1800 2400 lt and the similar feature occurred in the opposite hemisphere suggest that the southward offset of the magnetic equator with respect to the geographic equator plays a major role for the wsa formation

phase reversal of the diurnal cycle in the midlatitude ionosphere 1 the typical diurnal cycle of the midlatitude f region electron density consists of a midday maximum and a midnight minimum however a phase reversal of this diurnal cycle has been found to occur in three distinct regions on the globe they are the east asian ea region centered around 53 n 150 e the northern atlantic na region centered around 45 n 50 w and the south pacific sp region centered around 60 s 110 w the intensively reported weddell sea anomaly falls inside the sp region the phase reversal occurs during march august in ea and na regions and between august and march in sp region being most prominent in local summer furthermore this diurnal anomaly is more pronounced at solar minimum than at solar maximum and more pronounced in sp region than in na and ea regions in terms of larger diurnal magnitude and more months it lasts in a year it is emphasized that the diurnal anomaly consists of not only a nighttime enhancement but also a concurrent noontime depletion hence midlatitude summer nighttime enhancements reported in previous studies are just part of this reversed diurnal cycle the cause for the phase reversal involves several interplaying physical processes among these the neutral wind combined with the geomagnetic field configuration plays a pivotal role it generates a one wave longitudinal pattern at southern middle latitudes and a two wave pattern at northern middle latitudes whose wave peaks correspond to the center of the sp ea and na regions respectively the seasonal variation of neutral winds and downward motion of the ionization induced by thermal contraction of the ionosphere at sunset may largely control the occurring local time of the nighttime density enhancement and how long it persists in different months the phase reversal occurs as a result of close ion neutral coupling it is further noted that winter anomaly in the ea na and sp regions is very weak or missing