| Co-Investigator(Kenkyū-buntansha) |
OYAMA Shin-ichiro Comunications Reserch Laboratory, Research Fellow, 専攻研究員
FUJIWARA Hitoshi Tohoku University, Graduate School of Science, Research Associate, 大学院・理学研究科, 助手 (50298741)
FUJII Ryoichi Nagoya University, Solar-Terrestiral Environment Laboratory, Professor, 太陽地球環境研究所, 教授 (00132712)
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| Research Abstract |
We have studied the atmospheric dynamics in the polar mesosphere/lower thermosphere. The atmospheric dynamics in the lower thermosphere and upper mesosphere is strongly controlled by atmospheric waves such as gravity, tidal, and planetary waves which mainly propagate upward from below. To understand the lower thermospheric wind dynamics more fully, therefore, in addition to examining the lower thermospheric wind variations, it is of vital importance to examine how these waves propagate and dissipate and what kind of role these waves play in the lower thermosphere. Seasonal and solar cycle variations of the lower thermospheric wind system were widely examined based on the European Incoherent Scatter (EISCAT) radar as well as NCAR Thermosphere-Ionosphere-Mesosphere-Electrodynamics general circulation model. It is found that, for example, a strong eastward mean wind (about 40 m/s) in summer maximizing at 101 km, and suggested that this feature in the altitude wind profile is produced by g
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ravity wave drag.
We made comparison studies of three methods of the EISCAT UHF radar for furnishing E region neutral wind data. An EISCAT Special Program was conducted for 24 hours starting at 10 UT on July 14, 1997. Derived wind velocities by the three methods are compared, and fairly good agreement is found in terms of a relatively longer temporal variation (a few hours). The comparison of the derived velocities shows that the tristatic method is superior to the monostatic method in terms of an instantaneous measurement, while the monostatic method has an advantage on a tidal study. Regarding the meridional wind component, the filed-aligned method has significant advantages compared to the other methods concerning temporal data coverage, error, and height coverage.
We also examined how we can use two radars such as the EISCAT UHF radar and ME radar for study of the coupling process of the mesosphere and lower thermosphere. Comparisons of winds are made in case studies as well as on a statistical basis. Based on the comparisons, we raise strong concerns regarding the use of summer wind data above 91 km obtained by ME radar located at high latitude under high solar activity conditions. The wind values during the winter and equinox observed by the 2 radars are complementary. Less
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