SM046-02
The Changing Source of the Plasma Sheet During Geomagnetic Storms

Tuesday, 15 December 2020: 11:36
Virtual
Lynn M Kistler, University of New Hampshire Main Campus, Space Science Center, Durham, NH, United States, Christopher Mouikis, Univ New Hampshire, Durham, NH, United States, Kazushi Asamura, ISAS/JAXA, Sagamihara, Japan, Satoshi Kasahara, The University of Tokyo, Tokyo, Japan, Yoshizumi Miyoshi, ISEE, Nagoya University, Nagoya, Japan, Kunihiro Keika, University of Tokyo, Department of Earth and Planetary Science, Bunkyo-ku, Japan, Petrinec M Steven, Lockheed Martin Advanced Technology Center, Palo Alto, CA, United States, Tomoaki Hori, Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Japan, Shoichiro Yokota, Osaka University, Osaka, Japan and Iku Shinohara, JAXA Japan Aerospace Exploration Agency, ISAS, Sagamihara, Japan
Recorded Presentation
Abstract:
In this study, we investigate how the solar wind and ionospheric source contributions change during storms in the near-earth plasma sheet, using Arase, and further down the tail, using MMS. The ionospheric and solar wind contributions to the magnetosphere can be distinguished by their composition. While both sources contain significant H+, the heavy ion species from the ionospheric source are generally singly ionized, while the solar wind consists of highly ionized ions. Both the solar wind and the ionosphere contribute to the plasma sheet. It has been shown that with both enhanced geomagnetic activity and enhanced solar EUV, the ionospheric contribution, and particularly the ionospheric heavy ions contribution increases. However the details of this transition from a solar wind dominated to more ionospheric dominated plasma sheet are not well understood. An initial study using AMPTE/CHEM data, a data set that includes the full charge state distributions of the major species, shows that the transition can occur quite sharply during storms, with the ionospheric contribution becoming dominant during the storm main phase. However, during the AMPTE time-period, there were no continuous measurements of the upstream solar wind, and so both the simultaneous solar wind composition and the driving solar wind and IMF parameters were not known. The HPCA instrument on MMS and both the LEPi and MEPi instruments on Arase are able to measure He++. With these data sets, the He++/H+ ratio can be compared to the simultaneous He++/H+ ratios in the solar wind to more definitively identify the solar wind contribution to the plasma sheet. This allows the ionospheric contribution to the H+ population to be determined, so that the full ionospheric population is known. Initial results confirm the picture from the AMPTE study that during the storm main phase the plasma sheet comes predominantly from the ionosphere, while prior to the storm and during the recovery phase the plasma sheet source is predominantly the solar wind. In addition, they show that these transitions are related to changes in the IMF direction.
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