藤井/良一

講演予稿:
　ＥＩＳＣＡＴとＤＥ−１及びＤＥ−２人工衛星から得られた電場、磁場及び 電離圏電気伝導度データを用いて、沿磁力線電流、電離圏電流と電場、電気 伝導度の間の関係を定量的に求めた。その結果、比較的安定なオーロラに伴 う沿磁力線電流はピーダーソン電流により結ばれていること、下向き電流に 限り電気伝導度の空間不均一性が大きく貢献する場合が有り得ること、ジュ ール熱はオーロラアークの内側より外側の方が一般的には大きくなることが 分かった。サブストームに伴う強いオーロラに伴う沿磁力線電流の電離圏内 でのクロージャーには、ピーダーソン電流だけではなく、経度方向に流れる 電流も考慮しなければならないことが判明した。

abstract:
　Based on the electric field, magnetic field, the ionospheric conductivity and auroral image data obtained from EISCAT, DE 1 and DE 2 spacecraft, we have determined quantitatively relationships between the field-aligned and ionospheric currents, the electric field and the ionospheric conductivity. The results are summarized as follows 1) For a relatively stable and longitudinally-elongating aurora arc or band case, where both large (a few 100 km) and small scale field-aligned currents can be considered to be linked only to genuine Pedersen currents. 2) For this event almost all FACs were produced by the magnetospheric current source SdivE (S = Pedersen conductivity) but downward currents were produced occasionally by the ionospheric conductivity gradient term EgradS rather than SdivE. 3) The Joule heating rate in the downward FAC regions (outside the auroral arc/band) was greater than that in the upward regions (in the auroral arc/band) due to relative enhancements of the electric field in the former regions. 4) For an intense aurora case associated with a surge, the upward field-aligned current is linked not only to the Pedersen current but to longitudinal ionospheric currents. Acknowledgment. We are indebted to the director and staff　of EISCAT for operating the facility and supplying the data.　EISCAT is an International Association supported by Finland(SA), France (CNRS), the Federal Republic of Germany (MPG),　Japan (NIPR), Norway (NFR), Sweden (NFR) and the United Kingdom (PPARC).

キーワード:
沿磁力線電流，電場，オーロラ

Keywords:
field-aligned current, electric field, aurora