Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm43a2042t&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SM43A-2042
Physics
[2403] Ionosphere / Active Experiments, [2431] Ionosphere / Ionosphere/Magnetosphere Interactions, [2730] Magnetospheric Physics / Magnetosphere: Inner, [2768] Magnetospheric Physics / Plasmasphere
Scientific paper
Pi2 pulsations with the period range of 40-150 seconds appear globally from low to high latitudes on the night side on the ground. The cavity mode resonance is one possible generation mechanism of mid- and low-latitude Pi2 pulsations in the night side. In this scenario, fast (poloidal) mode waves propagate from the magnetosphere and are trapped between the plasmasphere and ionosphere. Several spacecraft observations provide evidences that the fast mode waves in the plasmasphere and F-region ionosphere are correlated with ground Pi2 pulsations at low latitudes. Although the fast mode waves associated with cavity mode resonance are transmitted through the ionosphere in the night side, spatial characteristics of Pi2 pulsations in the mid- and low-latitude ionosphere are not yet fully examined. We investigated nighttime Pi2 pulsations in the ionosphere using the SuperDARN HF radar at Hokkaido (AACGM magnetic coordinates; 36.5 and 214.7 degrees) when the radar was operating with the themisscan mode with a sampling rate of every 8 seconds for beam 4. The Hokkaido radar observes Doppler velocities associated with poloidal waves in the ionosphere over wide geomagnetic latitudes from 38 to 80 degrees. On 11 July 2010 at 14:14 UT, beam 4 of the Hokkaido radar simultaneously detected Doppler velocities of ground/sea scatter echoes and ionospheric echoes, which had high coherence (~0.9) with the H-component Pi2 pulsation at Moshiri (MSR: magnetic latitude 37.61; magnetic longitude 213.23 degrees) in the vicinity of the Hokkaido radar in the night side. The ionospheric scatter echoes and the ground/sea echoes contain information on the E region and the F mid-latitude ionospheres, respectively. The amplitudes of the east-west electric field derived from the Doppler velocities are about 0.7 mV/m in the F and E regions. The disturbance of Doppler velocities in both regions lags the MSR Pi2 by 90 degrees. This observation supports cavity mode resonance. In this presentation, we also show statistical characteristics of coherence, amplitude ratio, and cross phase between ground Pi2 pulsations at MSR and disturbance of the Doppler velocities observed by the Hokkaido radar to discuss possible generation mechanism of Pi2 pulsations in the mid- and low-latitude ionosphere in the night side.
Nishitani Nozomu
Shiokawa Kazuhiko
Teramoto M.
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