Interhemispheric conjugacy of auroral poleward expansion observed by conjugate imaging riometers at 67゜ and 75゜- 77゜ invariant latitude
Interhemispheric conjugacy of auroral poleward expansion was studied using conjugate imaging riometers at ~67° inv. (invariant latitude) (Syowa Station, Antarctica, and Tjomes, Iceland) and at 75-77° inv. (Zhongshan Station, Antarctica; Longyearbyen, Svalbard and Danmarkshavn, Eastern Greenland). Ni...
Main Authors: | , , , , , , |
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Format: | Report |
Language: | English |
Published: |
National Institute of Polar Research/Nagano JRC Co./National Institute of Polar Research/Solar-Terrestrial Environment Laboratory, Nagoya University/Danish Meteorological Institute/Polar Research Institute of China/Science Institute, University of Iceland
2000
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Online Access: | https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=6300 http://id.nii.ac.jp/1291/00006300/ https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=6300&item_no=1&attribute_id=18&file_no=1 |
Summary: | Interhemispheric conjugacy of auroral poleward expansion was studied using conjugate imaging riometers at ~67° inv. (invariant latitude) (Syowa Station, Antarctica, and Tjomes, Iceland) and at 75-77° inv. (Zhongshan Station, Antarctica; Longyearbyen, Svalbard and Danmarkshavn, Eastern Greenland). Ninety poleward expansion events at ~67° inv. observed in 1992-1993 were analyzed. The expansion at this latitude was characterized by a continuous poleward motion of cosmic noise absorption (CNA) bands with a velocity distribution that peaked at 1-1.5 km/s at a polar ionospheric altitude of ~90 km. The velocity distribution has another apparent peak at 3-5 km/s when measurements are made along the meridian. However, ~60% of the events forming this peak are overestimated because the motion of the CNA region's front was observed while the front was tilted away from the east-west direction. The difference in expansion velocities between conjugate stations remained within ±30% for half of the events. The time lag between the passage of a CNA band over conjugate stations was typically between 30-60 s. The product of this time lag and the poleward expanding velocity provides the location of the actual conjugate point. For 87% of the total number of events, the conjugate point for Syowa was located within ±200 km of Tjornes. The poleward expansion observed at 75°-77° inv. was characterized by a stepwise progression of CNA bands to higher latitudes. In other words, new CNA bands formed 50-180 km poleward of the preceding CNA band. The appearance of a new CNA band was often associated with an equatorward motion of the preceding CNA band. Equatorward moving CNA bands are thought to be located in a closed fieldline. The persistence of this band for several minutes was explained by pitch angle scattering of the trapped electrons as a result of a very stretched fieldline configuration in which the fieldline curvature was comparable to the Larmor radius of the trapped electrons. Although the conjugate pair used at these latitudes ... |
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