Conjugate imaging riometer observation at polar cusp/cap stations: A daytime absorption event for a specific change of solar wind conditions (scientific paper)

• Main Authors: Masanori Nishino, Hisao Yamagishi, Natsuo Sato, Yozo Murata, Ruiyuan Liu, Peter Stauning, Jan A. Holtet
• Format: Report
• Language: English
• Published: Solar-Terrestrial Environment Laboratory, Nagoya University/National Institute of Polar Research/National Institute of Polar Research/Department of Polar Science, the Graduate University for Advanced Studies/Polar Research Institute of China/Danish Meteorological Institute/Department of Physics, University of Oslo 2001
• Subjects: Arctic; Ny-Ålesund; Zhongshan; Danmarkshavn; Antarc*; Antarctica; Memoirs of National Institute of Polar Research; Ny Ålesund; Polar Research
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=2357; http://id.nii.ac.jp/1291/00002357/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=2357&item_no=1&attribute_id=18&file_no=1

Using the imaging riometers at Ny-Ålesund and Danmarkshavn in the Arctic region, and Zhongshan in Antarctica, a daytime absorption spike event was observed at both hemispheric stations in the post-noon (13-15 h MLT) on August 3,1997. The conjugate absorption spikes with a quasi-periodic feature were associated with the sequence of solar wind dynamic pressure pulses during northward interplanetary magnetic field (IMF). In particular, the absorption spike associatied with the steep pressure increase and the synchronous short-period southward IMF change exhibited a time difference (∿1 min) between the occurrences in the two hemispheres. From comparison between the absorption images and simultaneous aurora all-sky images at Zhongshan, it is recognized that the absorption spike shows a feature of small-scale enhancement with fast eastward motion in the large-scale absorption extending by about 1000km in longitude and about 50km in latitude. Ground geomagnetic variations at the high-latitude stations in the both hemispheres showed good response to the solar wind pressure pulse sequence. These observational results indicate that magnetic compressional waves driven by the solar wind pressure pulses could stimulate energetic electrons populating in the outer magnetosphere and thus the electrons could precipitate into the polar cleft ionosphere in both hemispheres due to intensification of upward region-l field aligned currents near the duskside magnetopause.