Storm‐induced plasma stream in the low‐latitude to midlatitude ionosphere

Abstract

Geomagnetic disturbances from 7 to 12 November 2004 were quite intense, and the maximum excursion of Dst reached −374 nT. Unusual ionospheric phenomena have been observed around the world that have been associated with successive magnetic storms during this period. The ionospheric total electron content (TEC) was increased at the longitudes of Japan within a short time after sunset on 8 November, from 20 TEC units at 1830 JST to 97 TEC units at 2015 JST (JST = UT + 9 h), where 1 TEC unit = 1×1016 el/m2. The enhanced TEC was significant over Hokkaido (∼43°N), and the center of the enhanced region was well within the plasmasphere as an L value of approximately 1.5. The drift velocity of the plasma in the density‐enhanced region measured by the Defense Meteorological Satellite Program (DMSP) satellite was westward with a peak value of 250 m/s in the Earth's frame, demonstrating a positive correlation between density and drift velocity. A similar TEC event was observed after sunset on 10 November: TEC was enhanced, from 15 TEC units at 1830 JST to 45 TEC units at 2030 JST. During the second event, the ionosphere was highly structured and the rate of the TEC index (ROTI) increased. The two‐dimensional map of a ROTI‐enhanced region exhibited the west to northwest transportation of plasma in which density irregularities were entrained. A physical mechanism is proposed to explain these disturbances, i.e., storm‐induced plasma stream, which is different from a phenomenon called storm‐enhanced density at midlatitudes.