Occurrence Patterns of Magnetospheric EMIC Waves During Geomagnetic Storms: Ground-based Observations at Auroral and Subauroral Latitudes

Details Occurrence Patterns of Magnetospheric EMIC Waves During Geomagnetic Storms: Ground-based Observations at Auroral and Subauroral Latitudes Occurrence Patterns of Magnetospheric EMIC Waves During Geomagnetic Storms: Ground-based Observations at Auroral and Subauroral Latitudes

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsm21a1658m&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SM21A-1658

Mathematics

Probability

2730 Magnetosphere: Inner, 2752 Mhd Waves And Instabilities (2149, 6050, 7836), 2774 Radiation Belts, 2778 Ring Current, 2788 Magnetic Storms And Substorms (7954)

Scientific paper

Electromagnetic ion cyclotron (EMIC) waves in Earth's magnetosphere have been suggested in many theoretical and observational studies as a significant loss mechanism for both ring current ions and, via parasitic interactions, radiation belt electrons. Several early ground-based studies noted their occurrence was reduced during the main phase of geomagnetic storms and increased during recovery phase, but few comprehensive studies of the long-term occurrence of these waves have been presented. We have applied the automated wave analysis technique developed by Bortnik et al. [JGR A04204, 2007] to a set of data recorded from 1996 through 2005 by search coil magnetometers deployed at auroral and sub-auroral latitudes in Antarctica. Superposed epoch analysis of these data sets during magnetic storms and high speed stream intervals shows that at auroral latitudes (L = 6 - 8) the highest occurrence probability was near or slightly before storm onset, near or slightly after local noon, with a relative minimum soon after. The peak at onset seems quite consistent with what has been observed in earlier studies of waves stimulated by sudden impulses and magnetospheric compressions, causing Pc 1 events in the outer dayside magnetosphere. At somewhat lower latitude (Halley, L = 4.56), the local time of the occurrence peak at onset was shifted a few hours later, toward early afternoon, and there was again a relative minimum during main phase and early recovery phase. At both auroral and sub-auroral latitudes the occurrence frequency became larger and somewhat more isotropic in local time during later recovery phase, but remained high near noon. These results contrast with the recent observations at L = 1.77 of Bortnik et al. [JGR A04201, 2008], who found a strong diurnal occurrence maximum during nighttime hours during all storm phases. Longer-term variations include a relative minimum at auroral latitudes during solar maximum conditions, again consistent with earlier observations.

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