Open Access

Dynamics of Neutral Wind in the polar region observed with two Fabry-Perot Interferometers

  • M. Ishii1Email author,
  • S. Oyama2,
  • S. Nozawa2,
  • R. Fujii2,
  • E. Sagawa1,
  • S. Watari1 and
  • H. Shinagawa2
Earth, Planets and Space201451:BF03353242

https://doi.org/10.1186/BF03353242

Received: 10 August 1998

Accepted: 7 July 1999

Published: 26 June 2014

Abstract

Optical observations were made at Ramfjord, Norway from January 10 to February 14,1997. Two types of Fabry-Perot interferometers (FPIs), Doppler-imaging and scanning, were installed at the EISCAT radar site and were used to acquire data simultaneously with radio instruments. Both FPIs can observe emissions of two different wavelengths simultaneously. We can estimate the horizontal and vertical wind in different emission layers simultaneously with high time-resolution (1 min). The observations on February 8 and 9, 1997, show some notable characteristics: (1) large-scale perturbations (≈ ±150 m/s) are observed in the upper thermospheric wind. They seem to begin 30 min after the onset of a magnetic substorm and to stop when the next substorm begins. (2) Clear wave-like structures are found in the horizontal wind variations. Some of them can be seen over the entire sky, and one of them is found in a restricted regions. (3) A clear wave-like structure is also found in the vertical wind in the upper thermosphere. A similar structure can be seen in the lower thermosphere, but these structures are not always in phase. This phases difference starts at the same time that horizontal winds between the two layer has their phase difference. (4) The relation between the vertical wind and the divergence of horizontal wind seems to change with time. The correlation coefficient between them changes one-hours before and on-time of a substorm on-set. This sign of the coefficient is negative in most of the time, with considering about time-lag. It means the vertical morion is caused by divergent flow of horizontal wind.