Browsing by Author "Astafyeva, Elvira"
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Item Restricted Early morning irregularities detected with spaceborne GPS measurements in the topside ionosphere: A multisatellite case study(American Geophysical Union, 2015-09-09) Zakharenkova, Irina; Astafyeva, Elvira; Cherniak, IuriiWe present observations of the equatorial plasma bubbles (EPB) in the topside ionosphere at early morning hours (05–08 LT) in the recovery phase of the 18–19 February 2014 geomagnetic storm. This rare type of irregularities was detected in the Pacific sector using GPS measurements on board several low‐Earth‐orbit (LEO) satellites. We use a multisatellite constellation consisted of the three Swarm and one TerraSAR‐X satellites, that on 19 February flew in the same region and at similar altitudes ~500 km. The EPB occurrence in the LEO GPS data was observed for several consecutive orbits from ~11 UT to 16–17 UT on 19 February 2014, which suggests the following: (1) rather long duration (hours) of favorable conditions for EPB generation, (2) formation and evolution of EPB over wide longitude range of the Pacific Ocean, and (3) possible movement of the EPB region in the westward direction (with dawn). Registration of the early morning EPB in LEO GPS data was supported by concurrent in situ (Swarm and DMSP (Defense Meteorological Satellite Program)) and ground‐based (ionosonde and GPS) measurements. LEO‐based GPS technique is found to be essential and promising data source to study the topside EPB over regions with lack of the ground‐based facilities. In addition, we use the Prompt Penetration Model and the Thermosphere‐Ionosphere Electrodynamics Global Circulation Model (TIE‐GCM) to identify the possible mechanisms responsible for the observed phenomenon. The model simulation results indicate the occurrence of the zone with the enhanced vertical plasma drift (~40–45 m/s) owing to the disturbance dynamo action in the predawn/dawn sector during 09–17 UT.Item Restricted First detection of the supersonic upward plasma flow structures in the early morning sector(American Geophysical Union, 2015-11-04) Astafyeva, Elvira; Zakharenkova, IrinaWe present the first observations of the supersonic updrafting plasma drifts in the predawn sector. Two DMSP satellites quasi‐simultaneously detected two fast‐speed events: one of ~385 km spatial extension and with the maximum upward velocity of 1683 m/s appeared at ~3 LT, and the other of ~1500 km large with maximum speed of 1770 m/s occurred at ~5 LT. Both supersonic structures were observed above the eastern Pacific region, separated by ~35° of longitude in space and by 45 min in time. The events occurred at the recovery phase of the geomagnetic storm of 19 February 2014, during rapid oscillations of the interplanetary magnetic field Bz and the interplanetary electric field Ey components, which increased the eastward electric field in the equatorial nighttime ionosphere and triggered the generation of plasma irregularities. The storm time penetration electric fields seem to be the principal driver of the observed supersonic events.Item Restricted GPS and in situ Swarm observations of the equatorial plasma density irregularities in the topside ionosphere(SpringerOpen, 2016-07-15) Zakharenkova, Irina; Astafyeva, Elvira; Cherniak, IuriiHere we study the global distribution of the plasma density irregularities in the topside ionosphere by using the concurrent GPS and Langmuir probe measurements onboard the Swarm satellites. We analyze 18 months (from August 2014 till January 2016) of data from Swarm A and B satellites that flew at 460 and 510 km altitude, respectively. To identify the occurrence of the ionospheric irregularities, we have analyzed behavior of two indices ROTI and RODI based on the change rate of total electron content and electron density, respectively. The obtained results demonstrate a high degree of similarities in the occurrence pattern of the seasonal and longitudinal distribution of the topside ionospheric irregularities derived from both types of the satellite observations. Among the seasons with good data coverage, the maximal occurrence rates for the post-sunset equatorial irregularities reached 35–50 % for the September 2014 and March 2015 equinoxes and only 10–15 % for the June 2015 solstice. For the equinox seasons the intense plasma density irregularities were more frequently observed in the Atlantic sector, for the December solstice in the South American–Atlantic sector. The highest occurrence rates for the post-midnight irregularities were observed in African longitudinal sector during the September 2014 equinox and June 2015 solstice. The observed differences in SWA and SWB results could be explained by the longitude/LT separation between satellites, as SWB crossed the same post-sunset sector increasingly later than the SWA did.Item Restricted Opposite hemispheric asymmetries during the ionospheric storm of 29-31 August 2004(American Geophysical Union, 2014-12-12) Astafyeva, Elvira; Zakharenkova, Irina; Doornbos, EelcoBy making use of multiple ground‐based and spaceborne instruments, we study ionospheric and thermospheric behavior during the moderately intense geomagnetic storm of 29–31 August 2004 (minimum Dst excursion of −128 nT). Although this storm was far from the strongest in solar cycle 23, it provoked quite interesting effects in the ionosphere, such as opposite hemispheric asymmetries in the ionospheric F layer and in the topside ionosphere and a development of the ionospheric superfountain effect in the postsunset sector. Data from ground‐based GPS receivers and ionosondes revealed large increase in total electron content (TEC) and in NmF2 in the southern hemisphere, whereas in the northern hemisphere, very weak or no effect was observed. On the contrary, the topside measurements indicated the occurrence of a positive storm in the northern hemisphere. Overall, the strongest storm time disturbances were observed in the postsunset sector (~20:30–21:30 LT), where satellite radar altimeters TOPEX and Jason 1, along with the CHAMP satellite showed ~250–400% TEC increase in the middle‐ and low‐latitude regions. The signatures of the ionospheric plasma enhancement were seen up to the height of the Defense Meteorological Satellite Program (DMSP) satellites (~840 km). As for the thermospheric storm, data of the Gravity Recovery and Climate Experiment (GRACE) satellite mission revealed no asymmetry in neutral density data in the evening sector (~17 UT); however, very strong hemispheric asymmetry was observed in the postsunset sector by CHAMP (~21 UT). Overall, neutral density increase in the postsunset sector was found to be much stronger than in the evening sector.