Physics
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsm42a..03p&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #SM42A-03
Physics
2752 Mhd Waves And Instabilities, 2776 Polar Cap Phenomena
Scientific paper
Although the occurrence of narrow-band Pc3 waves in the polar cap is not expected by the ULF community, we have searched for Pc3 activity using the data from the trans-Antarctic profile of search-coil magnetometers on automated geophysical observatories (AGOs) extending from A80 and A81 in the auroral zone ( at -66° and -69° , respectively), through P3 at -72° and P4 at -80° , and deep into the polar cap (P5 at -85° and P6 across the geomagnetic pole, also at -85° ). Pc3 activity was found to be high both in the dayside closed field line region adjacent to the magnetopause and in the plasma mantle and LLBL, and even in the regions mapping into the magnetotail lobe. The Pc3 waves in the polar cap were not an extension of common mid-latitude Pc3 activity to very high latitudes. Often Pc3 pulsations at P4 and P5 were not accompanied by similar wave activity at P3 and A80. We speculate that different channels of propagation of upstream turbulence to the ground are possible: via the equatorial magnetosphere; the cusp; and the lobe/mantle. In the latter case compressional fast mode waves may directly penetrate into the magnetotail lobe and yield Pc3 activity in the polar cap. Superposition of several signals from the same source may occur, but via different channels. Transfer functions of each channel may not coincide, and different filtering/amplification mechanisms are possible. Common Pc3 pulsations show a maximum at A80 in the intensity distribution along the trans-Antarctic latitudinal array. Dayside Pc3 pulsations with a latitudinal maximum at P4 (-80° ) may be related to a penetration channel via the cusp. It appears that there is an additional source of Pc3 pulsations generation in the mantle/cap, in the region with open field lines, which provides a maximum at P5 and at P4 far from noon. In some events indeed superposition of Pc3 emissions with different characteristics (bandwidth, latitudinal structure, onset and time evolution, etc) has been observed. The occurrence of narrow-band Pc3 waves in the polar cap provides a challenge to the modellers, because so far no resonant conversion/filtering mechanism on open field lines has been identified.
Chugunova O.
Engebretson Mark J.
Fukunishi Hiroshi
Pilipenko V. A.
Rodger Alan S.
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