Substorm effects on magnetospheric VLF hiss observed by ISIS satellites

• Main Author: Tadanori Ondoh
• Format: Report
• Language: English
• Published: Space Earth Environment Laboratory 2001
• Subjects: Syowa Station; Antarc*; Antarctica; Advances in polar upper atmosphere research
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=6331; http://id.nii.ac.jp/1291/00006331/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=6331&item_no=1&attribute_id=18&file_no=1

Narrow-band VLF electric field data at 300 Hz, 1.5kHz, 5kHz, 8kHz, 16kHz, and 20kHz received from ISIS satellites at Syowa station, Antarctica are compared with AE and AL indices between February, 1982 and January, 1983 for investigating substorm effects on magnetospheric VLF hiss. The telemetry coverage for ISIS satellites from Syowa Station is from about 80° to about 50° in geomagnetic invariant latitude. In geomagnetic quiet and weak substorm recovery phase periods, a narrow-band mid-latitude hiss and a broad-band polar hiss appear, respectively, at invariant latitudes from 50° to 63° and from 66° to 78° from the afternoon to the midnight in MLT. In substorm expansion phase, the polar hiss region moves to lower latitudes and approaches the mid-latitude hiss region, and also, a LHR hiss whose intensity peak latitude increases with decreasing frequency (from 20kHz to 1.5kHz) appears in the mid-latitude hiss region near the plasmapause. Statistical study of VLF hiss shows that the mid-latitude hiss occurs most often in the quiet period and is independent of the substorm activity. While, the occurrence rate of polar hiss is 61 % in the substorm period (200nT < AE ≦ 924nT and -100nT > AL ≧ -583nT) and 29% in the quiet period (30nT < AE ≦ 200nT and -2nT > AL ≧ - lOOnT). Hence, the generation of polar hiss is clearly influenced by the substorm.