赤道帯600ｋｍ高度における電子温度，密
度の季節，経度，緯度及び地方時に対する振る舞い

*小山 孝一郎[1], 渡部 重十[2]

宇宙科学研究所[1]
北海道大学[2]

Season,longitude,latitude,and local time behavior of Te and Ne of the equatorial ionosphere at the height of 600km

*Koh-ichiro Oyama[1] ,Shigeto Watanabe [2]
Institute of Space and Astronautical Science[1]
Hokkaido University[2]

Study of electron temperature(Te) and density(Ne) observed with Hinotori satellite in 1981-1982 is still being conducted from various aspects. The recent study shows clear seasonal and longitudinal dependence in the local time behavior. The result is understood as due to the effect of the neutral wind. Solar activity dependence is also found in the Te/Ne behaviors.

Japan's solar observatory "Hinotori" was in a equatorial orbit at the height of 600 km from February 1981 to December 1982. Except solar flare events,the spacecraft continued Te/Ne measurements. The data compiled with a tremendous efforts made by Professor T.Takahashi and K.-I.Oyama turned out to be the best quality data set of equatorial ionosphere in the world and many scientists are currently using through NSSDC . We have examined the longitudinal,latitudinal,and local time behaviors of both electron density and temperature obtained during geomagnetically calm days. Details of the behaviors,such as a small change of Te at two longitude zones,difference of Te between summer /winter hemispheres at different seasons,are well explained by taking the effects of both zonal and meridional winds into account.The electron density which was used here was originally measured by Professor H. Oya and T Takahashi.

References

Su.Y.Z.,K.-I.Oyama,G.J. Bailey,T.Takahashi,and S.Watanabe, Comparison of the satellite electron density and temperature measurements with plasmasphere-ionosphere model,J. G. R,100, 14591-14604,1995.
Oyama,K.-I.,S.Watanabe,and Y.Z.Su,Season,local time,and longitude variations of electron temperature at the height of 600 km in the low latitude,Adv.Space.Res.18(6),269-278,1996.
Oyama K.-I.N,Balan,S.Watnabe,T,.Takahashi,F.Isoda,and H. Oya,Morning overshoot of Te enhanced by downward plasma drift in the equatorial topside ionosphere,J.G.G,48,959-966, 1996.
Oyama K.-I.,M.A.Abdu,N.Balan,and G,J,Bailey, High electron temperature associated with the prereversal enhancement, .G.R,102,417-424,1997.
Bailey,G.J.,Y.Z.Su,and K.-I.Oyama,Yeary variations in the low latitude topside ionosphere,Ann Geophycae,18,789-795,2000.