Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsm41b0824f&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SM41B-0824
Physics
2407 Auroral Ionosphere (2704), 2724 Magnetopause, Cusp, And Boundary Layers, 2731 Magnetosphere: Outer, 2752 Mhd Waves And Instabilities, 2772 Plasma Waves And Instabilities
Scientific paper
Using ULF wave data measured by search coil magnetometers installed at Automatic Geophysical Observatories (AGOs) and South Pole station in the Antarctic, the occurrence conditions of Pc 1 waves at high latitudes covering the dayside cusp, LLBL and BPS region have been investigated in detail. It is found that intense Pc 1 waves with frequencies from 0.1 to 0.6 Hz are excited in the invariant latitude range of 70 to 75 degrees by the arraival of solar wind fast shocks such as SSCs and SIs. It is also found that Pc 1 waves with frequencies from 0.1 to 0.4 Hz are excited in the localized regions of traveling convection vortices (TCVs) accompanying magnetic impulse events (MIEs). The most striking feature is that these Pc 1 waves often show falling tone spectral structures, as changing the frequencies from 0.3 - 0.4 Hz to 0.1 - 0.2 Hz over the durations of MIEs/TCVs (typically about 5 min). Since these transient Pc 1 waves are suggested to be generated by the electromagnetic ion cyclotoron (EMIC) instability, we have investigated the behaviors of protons in the dayside cusp, LLBL and BPS region using images of proton aurora obtained by the all-sky imager installed at Longyearbyen (75.3 degrees in invariant latitude), Svalbard and the FUV instrument onboard the IMAGE satellite. We have also investigated the solar wind conditions and the energy spectra of precipitating protons during Pc 1 activity using WIND, Geotail, DMSP and Akebono spacecraft. These analyses suggest that SSC/SI-related Pc 1 waves are excited by the compression of the dayside LLBL/BPS region by fast shocks, while the outward motion of the magnetopause due to the formation of hot flow anomalies (HFAs) induce ion cyclotron wave instability in the LLBL region, resulting in occurrences of MIE-related falling tone Pc 1 waves.
Arnoldy Roger L.
Engebretson Mark J.
Frey Harald U.
Fukunishi Hiroshi
Kataoka Ryuho
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