SM059-08
Statistical Study of Foreshock Bubbles and Comparisons of MMS Observations with the Global Hybrid Simulations

Wednesday, 16 December 2020: 16:21
Virtual
SUN Lee1, David G Sibeck2, Nick Omidi3, Marcos D. Silveira4, Andrew Vu5, Drew L. Turner6, Sarah K. Vines7, Barbara L Giles8, Stephen A Fuselier9, Ian J. Cohen10, Roy B Torbert11, Christopher T Russell12 and James Burch9, (1)Catholic University of America, Washington, DC, United States, (2)NASA/GSFC, Greenbelt, MD, United States, (3)Solana Scientific Inc, Solana Beach, CA, United States, (4)INPE, Sao Jose Dos Campos, Brazil, (5)University of Alaska Fairbanks, Physics Department & Geophysical Institute, Fairbanks, AK, United States, (6)Johns Hopkins University Applied Physics Laboratory, Laurel, MD, United States, (7)University of Texas at San Antonio, San Antonio, TX, United States, (8)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (9)Southwest Research Institute, San Antonio, TX, United States, (10)The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, United States, (11)Univ New Hampshire, Durham, NH, United States, (12)University of California, Los Angeles, CA, United States
Abstract:
Foreshock bubbles (FBs) occur when interplanetary magnetic field (IMF) discontinuities encounter the Earth’s foreshock. These transient (1-5 min) features exhibit depressed densities and magnetic field strengths, enhanced temperatures, and deflected plasma flows trailed by a region of enhanced densities and magnetic field strengths. We used Magnetospheric Multiscale (MMS) spacecraft observations to identify 23 FBs from September 2015 to January 2020. Most (17 of 23) occurred upstream from the dusk bow shock. We investigate FB occurrence patterns versus prevailing solar wind conditions. The Parker Spiral angles ranged from -75 to 60 degrees. The Alfvén Mach number was generally about 10 for 11 FBs. The cone angles downstream (before the events) from 6 FBs ranged from 30 to 40 degrees. The cone angles upstream (after the events) are larger than downstream for 14 FBs. We compare proton spectra observed by the Hot Plasma Composition Analyzer (HPCA) and Energetic Ion Spectrometer (EIS) before, during, and after FBs. Ion intensities at energies for 5.2 to 37.4 keV are generally greater during than before or after the events, suggesting that FBs can accelerate particles to these energies. However, there were higher ion intensities from 53 to 172 keV outside 8 of 23 events, suggesting that the foreshock bubbles may not be the source of these energetic ions. Results from global hybrid simulations for 2nd order Fermi acceleration are consistent with observed ion acceleration.
<< Previous Abstract | Next Abstract >>