Browsing by Author "Paxton, Larry J."
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Item Restricted Morphology of the postsunset vortex in the equatorial ionospheric plasma drift(American Geophysical Union, 2014-12-09) Lee, Woo Kyoung; Kil, Hyosub; Kwak, Young-Sil; Paxton, Larry J.The postsunset vortex in the equatorial ionosphere exhibits clockwise plasma motions after sunset in longitude (time) and altitude coordinates when the equatorial ionosphere is viewed looking northward. We describe the typical morphology of the postsunset vortex using incoherent scatter radar observations at Jicamarca in Peru during the previous solar maximum (2000–2002). A pronounced vortical plasma motion appears around 1700 LT along with the onset of the prereversal enhancement (PRE). The center of this vortex is located near an altitude of 270 km. A smaller‐scale vortex also appears about 0.5 ~ 1 h later at higher altitudes. However, the morphology and occurrence time of this small vortex depend on the characteristics of the coherent backscatter region. We find that the earlier vortex is the major feature of the postsunset vortices because it is repeatable, associated with the PRE, and independent to the occurrence of the coherent backscatter region.Item Restricted The August 2011 URSI World Day campaign: Initial results(Elsevier, 2015-11) Immel, Thomas J.; Liu, Guiping; England, Scott L.; Goncharenko, Larisa P.; Erickson, Phillip J.; Lyashenko, Mykhaylo V.; Milla, Marco; Chau Chong Shing, Jorge Luis; Frey, Harald U.; Mende, Stephen B.; Zhou, Qihou; Stromme, Anja; Paxton, Larry J.During a 10-day URSI World Day observational campaign beginning on August 1, 2011, an isolated, major geomagnetic storm occurred. On August 5, Kp reached values of 8− and Dst dropped to −113 nT. The occurrence of this isolated storm in the middle of a 10-day URSI World Day campaign provides and unprecedented opportunity to observe the coupling of solar wind energy into the magnetosphere and to evaluate the varied effects that occur in the coupled magnetosphere–ionosphere–thermosphere system. Dramatic changes in the ionosphere are seen at every one of the active radar stations, extending from Greenland down to equatorial Peru in the American sector and at middle latitudes in Ukraine. Data from TIMED and THEMIS are shown to support initial interpretations of the observations, where we focus on processes in the middle latitude afternoon sector during main phase, and the formation of a dense equatorial ionosphere during storm recovery. The combined measurements strongly suggest that the changes in ionospheric conditions observed after the main storm phase can be attributed in large part to changes in the stormtime thermosphere. This is through the generation of disturbance dynamo winds and also global neutral composition changes that either reduce or enhance plasma densities in a manner that depends mainly upon latitude. Unlike larger storms with possibly more sustained forcing, this storm exhibits minimal effects of persistent meridional stormtime wind drag, and little penetration of solar wind electric potentials to low latitudes. It is, therefore, an outstanding example of an impulsive event that exhibits longer-term effects through modification of the background atmosphere.Item Restricted The zonal motion of equatorial plasma bubbles relative to the background ionosphere(American Geophysical Union, 2014-07-09) Kil, Hyosub; Lee, Woo Kyoung; Kwak, Young-Sil; Zhang, Yongliang; Paxton, Larry J.; Milla, MarcoThe zonal motions of plasmas inside equatorial plasma bubbles are different from those in the background ionosphere. The difference was explained in terms of the tilt of bubbles by recent studies, but observational evidence of this hypothesis has not yet been provided. We examine this hypothesis and, at the same time, look for an alternative explanation on the basis of the coincident satellite and radar observations over Jicamarca (11.95°S, 76.87°W) in Peru. In the observations at premidnight by the first Republic of China satellite (altitude: 600 km, inclination: 35°), plasmas inside bubbles drift westward relative to ambient plasmas. The same phenomenon is identified by radar observations. However, the relative westward plasma motions inside bubbles occur regardless of the tilt of bubbles, and therefore, the tilt is not the primary cause of the deviation of the plasma motions inside bubbles. The zonal plasma motions in the topside are characterized by systematic eastward drifts, whereas the zonal motions of plasmas in the bottomside backscatter layer show a mixture of eastward and westward drifts. The zonal plasma motions inside backscatter plumes resemble those in the bottomside backscatter layer. These observations indicate that plasmas inside bubbles maintain the properties of the zonal plasma motions in the bottomside where the bubbles originate. With this assumption, the deviation of the zonal motions of plasmas inside bubbles from those of ambient plasmas is understood in terms of the difference of the zonal plasma flows in the bottomside and topside.