SM012-04
Magnetotail Dipolarizations and Ion Flux Variationsduring the Main Phase of Magnetic Storms
Magnetotail Dipolarizations and Ion Flux Variationsduring the Main Phase of Magnetic Storms
Tuesday, 8 December 2020: 17:51
Virtual
Abstract:
Near-Earth tail dipolarizations are usually associated with fast plasma flows and an increase in energetic particle fluxes. Yet the role of these dipolarizations in energetic ion flux transport towards the inner magnetosphere and in ring current (including partial ring current) development during the main phase of a geomagnetic storm is not fully understood.
We investigated simultaneous Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes A, D, and E with apogee at -13 RE and Los Alamos National Laboratory (LANL) geosynchronous spacecraft observations in the midnight MLT sector (21.5 - 1.5 hr. MLT) during the main phases of storms with integrated Dst exceeding 600 nT*hr from the 2010 to 2016 THEMIS tail seasons. We selected 10 storms during which at least one of the THEMIS probes was in the midnight sector during a storm's main phase and identified 39 dipolarization events with a Bz increase exceeding 10 nT within 500 s during these storms' main phases. In 21 of the 39 events an increase in the magnetic field elevation angle estimated from LANL Magnetospheric Plasma Analyser (MPA) data was detected at geosynchronous orbit (GEO). In only 10 of those 21 events, however, did ion fluxes at energies from 50 to 500\,keV increase in three or more consecutive energy bins at LANL. Comparisons of Ion spectra at THEMIS and LANL during dipolarizations revealed that energetic ions from the tail reached GEO. Our results indicate that a global dipolarization is necessary but not sufficient conditions for energetic ion flux enhancements at GEO. As suggested in previous studies, an increase in the azimuthal electric field (i.e., enhanced earthward magnetic flux transport) is most likely required
for an ~100 keV ion flux increase at GEO.
We investigated simultaneous Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes A, D, and E with apogee at -13 RE and Los Alamos National Laboratory (LANL) geosynchronous spacecraft observations in the midnight MLT sector (21.5 - 1.5 hr. MLT) during the main phases of storms with integrated Dst exceeding 600 nT*hr from the 2010 to 2016 THEMIS tail seasons. We selected 10 storms during which at least one of the THEMIS probes was in the midnight sector during a storm's main phase and identified 39 dipolarization events with a Bz increase exceeding 10 nT within 500 s during these storms' main phases. In 21 of the 39 events an increase in the magnetic field elevation angle estimated from LANL Magnetospheric Plasma Analyser (MPA) data was detected at geosynchronous orbit (GEO). In only 10 of those 21 events, however, did ion fluxes at energies from 50 to 500\,keV increase in three or more consecutive energy bins at LANL. Comparisons of Ion spectra at THEMIS and LANL during dipolarizations revealed that energetic ions from the tail reached GEO. Our results indicate that a global dipolarization is necessary but not sufficient conditions for energetic ion flux enhancements at GEO. As suggested in previous studies, an increase in the azimuthal electric field (i.e., enhanced earthward magnetic flux transport) is most likely required
for an ~100 keV ion flux increase at GEO.