Optical Study on the Upper Atmospheric Equatorial Anomaly

1992 Fiscal Year Final Research Report Summary

• Project/Area Number: 04041121
• Research Category: Grant-in-Aid for Overseas Scientific Survey.
• Allocation Type: Single-year Grants
• Research Institution: University of Tokyo
• Principal Investigator: OGAWA Toshihiro Faculty of Science, University of Tokyo Professor, 理学部, 教授 (70011616)
• Co-Investigator(Kenkyū-buntansha): KIYAMA Yoshitaka Faculty of Science, Niigata University Research Associate, 理学部, 助手 (50018272) ; TAGUCHI Makoto Faculty of Science, Tohoku University Research Associate, 理学部, 助手 (70236404) ; OKANO Shyoichi Faculty of Science, Tohoku University Associate professor, 理学部, 助教授 (10004483) ; FUKUNISHI Hiroshi Faculty of Science, Tohoku University Professor, 理学部, 教授 (90099937) ; KITA Kazuyuki Faculty of Science, University of Tokyo Research Associate, 理学部, 助手 (30221914) ; IWAGAMI Naomoto Faculty of Science, University of Tokyo Associate Professor, 理学部, 助教授 (30143374)
• Project Period (FY): 1992
• Keywords: Equatorial anomaly / Ionospheric F region / Airglow

Research Abstract

This research is to implement one of the projects of Solar-Terrestrial Energy Program (STEP) in Japan. Japanese STEP projects include a research area entitled "Energy and Dynamics of Coupled Ionosphere-Thermosphere System", in which the equatorial anomaly of the ionospheric F-region is one of the interesting topics. The equatorial anomaly is characterized by anomalously high electron densities in the zones of geomagnetic latitudes *15ﾟ. It is a quasi-permanent structure and is created as a consequence of the coupled plasma motion due to plasma drift and ambipolar diffusion in the ionospheric electric field and in the geomagnetic field. Electron density in the equatorial anomaly exhibits a highly variable structure in space and time. Depletion of plasma occurs along the geomagnetic field lines, forming a non-linear stripe pattern in the direction rectangular to the field lines. Yet we have not fully understood the dynamical behavior of the F-region plasma in the equatorial anomaly and t he origin of the wave disturbance.
This research uses an optical sensing technique to measure the red line of atomic oxygen that is excited through the dissociative recombination of molecular oxygen ions and electrons. With this technique we can deduce a fine structure of the F-region electron density and the thermospheric wind system. The objective of this research is to illustrate the growth process of plasma instability in the F-region and to seek its excitation mechanism.
Two observation sites were selected according to logistics conveniency and cloud condition of the sky. One is Mount Haleakala located in the north zone of the equatorial anomaly. The other is Watukosek in East Java and is located in the south zone of the equatorial anomaly, where our group is making a collaborative observation for atmospheric ozone and airglow with Indonesian Space Agency(LAPAN).
Three scientists from our group stayed at Mt.Haleakala during 7 February - 7 March 1993 to make the airglow observation. The instruments used were an airglow photometer of rapid sky-scanning, a monochromatic all-sky imager and an imaging Fabry-Perot interferometer for atomic oxygen red line. We obtained the all-sky distributions of airglow intensity for atomic oxygen red line and other emission lines along with the Doppler temperature and shift of atomic oxygen red line. These data are useful to analyze the dynamics on the horizontal structure of the F-region plasma and to analyze temperature and wind system of the thermosphere.
Visit to Watukosek was made during 25 November - 6 December 1992 to repair and overhaul the airglow photometer that was already set up there. We have asked the LAPAN scientists to continue the airglow observation using that photometer.