Showing papers by "Akira Kadokura published in 2002"

Detailed analysis of a substorm event on 6 and 7 June 1989 1. Growth phase evolution of nightside auroral activities and ionospheric convection toward expansion phase onset

Abstract: [1] We have analyzed in detail the evolution of nightside auroral activities and ionospheric convection during the growth phase of an isolated substorm. The following three characteristic auroral activities were identified by meridian scanning photometers (MSP) at ground stations: (1) proton main oval, (2) fast equatorward moving (FEM) arc, and (3) near plasma sheet boundary layer (NPSBL) aurora. The proton main oval corresponds to the main part of the proton auroral region and was located at the equatorward-most region of the electron auroral emissions and gradually moved equatorward during the growth phase. The FEM arc was a discrete auroral arc having a clear longitudinally elongated form. It appeared about 20 min before the onset on the high-latitude side of the auroral region and moved equatorward toward the proton main oval. Its equatorward motion gradually slowed as it approached the proton main oval. As the FEM arc moved equatorward, the location of the peak velocity in the nightside return flow of the two-cell convection also moved equatorward. The auroral breakup occurred in a localized area around the demarcation region between the two return flows, close to the latitude of the FEM arc. This was observed by the UV imager aboard the Akebono satellite. The NPSBL aurora appeared a few minutes before the onset around the poleward-most region of the aurora and continued even after the onset. Our detailed analysis of these phenomena can give us important clues as to how the growth phase proceeds toward the expansion phase onset.

Detailed analysis of a substorm event on 6 and 7 June 1989. 2. Stepwise auroral bulge evolution during expansion phase

Abstract: [1] We have analyzed in detail the auroral bulge evolution during the expansion phase of an isolated substorm, which was observed by the UV imager aboard the Akebono satellite. It was found that there were three distinct stages in the evolution. Stage 1 was characterized by rapid poleward and azimuthal ( predominantly westward) expansions in a short time (about 2 min). Stage 2 was characterized by a very slow poleward and slower and continuous azimuthal expansions. There was a certain period for transition between stage 1 and stage 2, and it was characterized by a very slow poleward and rapid eastward expansions. Stage 3 started about 11 min after the onset and was characterized by a sudden reactivation of the rapid poleward and azimuthal expansions. The reactivation started around the initial onset meridian and then spread both eastward and westward. At the azimuthal front, the expansion first occurred at the lowest latitudes, spread poleward to around the highest latitudes of stage 1, and then spread further poleward after a brief interval. Hence, the local expansion also had three distinct stages similar to the global one. The ground-based observations showed that the highest latitude of the local first stage was very close to the latitude of auroral activity that appeared near the ionospheric plasma sheet boundary layer (PSBL) region a few minutes before the onset. The further poleward expansion during the local third stage started with a significant intensification of the poleward-most auroral activity. During the local third stage, the bright electron auroral region was bifurcated into a poleward expanding part and an equatorward moving part. The proton auroral emission coexisted in the bulge during the local first and second stages and almost disappeared soon after the bifurcation during the local third stage. Based on these observations, we discuss the evolution in the magnetosphere during the expansion phase.

Polar Patrol Balloon experiment in Antarctica during 2002-2003

Abstract: The first scientific campaign of the Polar Patrol Balloon (PPB) experiment ( !st-PPB) was performed at Syowa Station in Antarctica during 19901991 and 1992-1993. Based on the fruitful results of the !st-PPB experiment, the next campaign (2nd-PPB) will be carried out in the austral summer of 2002-2003. This paper summarizes the 2nd-PPB experiment. Four balloons in total will be launched to make astrophysics observations ( 1 balloon) and upper atmosphere physics observations (3 balloons). The first payload will carry a very sophisti­ cated instrument that will observe primary cosmic-ray electrons in the energy range of 10 GeV-1 TeV. The payloads of the latter 3 flights are identical to each other. They will be launched in as rapid a succession as weather conditions permit to form a cluster of balloons during their flights. Such a \"Balloon Cluster\" is suitable for observing the temporal evolution and spatial distribution of various phenomena in the various magnetospheric and ionospheric regions and their boundaries that the balloons will traverse during their circumpolar trajectory. The expected flight duration of each balloon is 20 days. Observation data will be obtained mainly by a satellite communication system with a much higher temporal resolution than that used in the I st-PPB experiment.