HF Doppler observation between Vostok and Syowa, Antactica

Abstract

To study the ionization and plasma transportation around the cusp, arrangements were made to perform multi-station HF (High Frequency) Doppler measurements in Antarctica. Continuous short waves transmitted from Vostok Station (78 deg 28 min N, 106 deg 48 min E) were received at Syowa Station (69 deg 00 min S, 39 deg 35 min E) on monthly RWDs (Regular World Days). The transmitted frequencies were 14.985 MHz from 0700 to 0900 UT (Universal Time) and 9.18 MHz from 1600 to 1800 UT. The cusp approached the midpoint of the circuit at the end of the UT morning transmission. Two kinds of Doppler structures were clearly recongnized. Narrow band Doppler lines were consistently found during both morning and evening transmissions, whereas wide band Doppler structures dominated only in the morning. The wide band structures appeared and disappeared abruptly and sometimes had two spectrum peaks corresponding to velocities of separated irregularities around the midpoint. The narrow band structures still remained while the wide band structures changed spectrum shapes. Sawtooth-like Doppler structures were found in the narrow band lines in the morning transmissions.

ボストーク基地(78度28分S、106度48分E)から送信された連続短波を毎月標準世界日(RWD)毎に昭和基地(69度00分S、39度35分E)において受信した。送信周波数は0700-0900UTまでは14.985MHz、また1600-1800UTまでは9.18MHzであった。カスプはUTの朝の送信終了時に回路の中点に到達した。2種類のドップラー構造が明瞭に識別できた。狭帯域ドップラー線は一貫して朝と夕方の送信時に見られた。これに対して、広帯域ドップラー構造は朝方だけに優勢であった。広帯域構造は突然現われたり、消滅したりし、時には中点付近の分離不規則性の速度に応じて、2つのスペクトルピークを持っていた。狭帯域構造は、広帯域構造がスペクトルの形を変化させている間も依然として変らなかった。朝方の送信においては、狭帯域線中に鋸歯状ドップラー構造が見られた。