| Budget Amount *help |
¥1,800,000 (Direct Cost: ¥1,800,000)
Fiscal Year 1999: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 1998: ¥900,000 (Direct Cost: ¥900,000)
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| Research Abstract |
Two- and Three- dimensional nonhydrostatic thermospheric models have been developed in order to study behavior of vertical wind in the thermosphere. The calculated results were compared with the observations of thermospheric wind obtained by the Fabry-Perol interferometers. When large thermospheric vertical wind is observed in the vicinity of an auroral arc, oscillatory motion of the vertical wind occasionally occurs. This kind of variation could be explained by variations driven by local Joule heating. On the other hand, the vertical wind often exhibits very complicated behavior, suggesting that the thermospheric dynamics is controlled by combination of several processes such as (1) temporal and spatial variations of heat sources, (2) propagation of large-scale gravity waves generated in other regions, (3) effects of background wind of the thermosphere, and (4) interaction between gravity waves. In previous modeling of thermospheric and ionospheric dynamics associated with auroral arcs, the auroral arcs are assumed to be fixed in space. In reality, however, most of auroral arcs move very rapidly, indicating the heating regions also move rapidly. We studied the thermospheric and ionospheric dynamics including moving auroral arcs using the nonhydrostatic thermosphere-ionosphere model. By comparing the model results with EISCAT data, we obtained the following results, (1) when an auroral arc passes above the EISCAT radar site, field-aligned ion motion with a period of 15-40 min. and an amplitude of 10 - 30 m/s are often observed by EISCAT ; (2) our numerical model shows that field-aligned ion motion with a period of 15 min. are generated associated with moving an auroral arc ; (3) the model also predicts that a gravity wave with a period of 30 - 40 min. is generated when sudden heating occurs ; (4) the model tends to give smaller filed-aligned ion velocities than the observed ion velocities.
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