Showing papers by "Akira Kadokura published in 2007"

Absence of geomagnetic conjugacy in pulsating auroras

Abstract: [1] We have examined the geomagnetic conjugacy of pulsating auroras using TV camera data obtained simultaneously at Syowa in Antarctica and at Tjornes in Iceland. In order to exclude the magnetic field mapping problem, we investigated a period during which conjugate points were unambiguously identified from large-scale discrete conjugate auroras. The conjugacy of pulsating auroras revealed in this study may be summarized as follows. Some pulsating auroras appear in both hemispheres, while others appear only in one hemisphere. Even in the former case, the shape of the auroral form is generally different between the two hemispheres, and there is little or no interhemispheric correlation in the intensity variations. We could not find a pulsating aurora that appeared synchronously at the two endpoints of a flux tube. From these observational results and the increasing amount of evidence in recent studies, we conclude that the conjugacy of pulsating auroras is generally poor.

Observed Tail Current Systems Associated with Bursty Bulk Flows and Auroral Streamers During a Period of Multiple Substorms

Abstract: We present a multi-instrument study of a sub- storm bursty bulk flow (BBF) and auroral streamer During a substorm on 25 August 2003, which was one of a series of substorms that occurred between 00:00 and 05:00 UT, the Cluster spacecraft encountered a BBF event travelling Earth- wards and duskwards with a velocity of 500 km s 1 some nine minutes after the onset of the substorm Coincident with this event the IMAGE spacecraft detected an auroral streamer in the substorm auroral bulge in the Southern Hemisphere near the footpoints of the Cluster spacecraft Using FluxGate Magnetometer (FGM) data from the four Cluster spacecraft, we determine the field-aligned currents in the BBF, using the curlometer technique, to have been 5 mA km 2 When pro- jected into the ionosphere, these currents give ionospheric field-aligned currents of 18 A km 2 , which is comparable with previously observed ionospheric field-aligned currents associated with BBFs and auroral streamers The observa- tions of the BBF are consistent with the plasma "bubble" model of Chen and Wolf (1993) Furthermore, we show that the observations of the BBF are consistent with the creation of the BBF by the reconnection of open field lines Earthward of a substorm associated near-Earth neutral line

Energy spectrum and arrival directions of high-energy electrons over 100 GeV observed with PPB-BETS

Abstract: We have observed cosmic-ray electrons from 10 GeV to 1 TeV with PPB-BETS by a long duration balloon flight using Polar Patrol Balloon (PPB) in Antarctica. The observation was carried out for 13 days at an altitude of 35 km in January 2004. The detector is an imaging calorimeter composed of scintillating-fiber belts and plastic scintillators inserted between lead plates. The geometrical factor of detector is about 600 cm 2 sr and the total thickness of lead absorber is 9 radiation lengths. We have collected 5.7×10 3 events over 100 GeV including nearly 100 candidates of primary electrons. During the flight, sun sensors and geomagnetic aspect meters operated to determine the attitude of the instrument. The arrival directions of high-energy electrons over 100 GeV, together with the energy spectrum, are suggested to be a powerful probe to identify nearby cosmic- ray electron sources. In this paper, we present the energy spectrum and arrival directions of cosmic-ray electrons from 100 GeV to 1 TeV observed with PPB-BETS.