Large density depletions in the nighttime upper ionosphere during the magnetic storm of July 15, 2000

Abstract

We measured electron density and temperature of the nighttime upper ionosphere for the several key intervals during the progress of the magnetic storm on 15 July 2000 with the Langmuir probe on Korea Multipurpose Satellite‐1 (KOMPSAT‐1). During the main phase of the storm KOMPSAT‐1 detected near 0°E a very deep and extensive trough of electron density centered around the geomagnetic equator. The electron density dropped sharply from ∼4 × 105cm−3 to less than 2 × 104cm−3, with the trough region extended over 1400 km along the satellite track. Later in the recovery phase, KOMPSAT‐1 observed severe distortion still persisted near 230°E, with enhanced density in the southern hemisphere. Together with DMSP observations, we estimate the size of the observed trough to be at least 5500 km in the longitudinal direction. DMSP data indicates that the trough was caused by the enhanced eastward electric field which lifted the equatorial F‐region ionosphere upward.

Some characteristics of large-scale travelling ionospheric disturbances and a relationship between the F<sub>2</sub> layer height rises of these disturbances and equatorial pre-sunrise events

“…In summarizing SIBB results Kil et al (2006) state [1] "They occur in the equatorial region at night, are elongated in the north-south direction, have steep walls, and always coexist with plasma bubbles." Satellite recordings by Lee et al (2002) have detected displacements of over 1400 km along a satellite path and a disturbance which extends at least 4500 km in the longitudinal direction. LS-TIDs have the same characteristics as SIBBs (see Table 3).…”

On a possible relationship between density depletions in the SAA region and storm-enhanced densities in the conjugate hemisphere

“…Low-earth orbiting satellites have detected largescale ion density dropouts with a spatial width greater than 800 km in the low-latitude ionosphere during several magnetic superstorms (Greenspan et al, 1991;Basu et al, 2001;Lin et al, 2001, Lee et al, 2002Su et al, 2002;Lin and Yeh, 2005). Lin et al (2001) demonstrated that these large-scale density dropouts corotated with the South Atlantic anomaly (SAA) and were adjacent to regions of density enhancement, forming a magnetic anomaly density structure (MADS).…”

Statistical characteristics of the total ion density in the topside ionosphere during the period 1996-2004 using empirical orthogonal function (EOF) analysis

“…Sometimes the equatorial topside ionosphere can undergo a drastic depletion at 21:30 LT when a very intense magnetic storm occurs (e.g. Greenspan et al, 1991;Basu et al, 2001;Lee et al, 2002;Foster et al, 2002). Such situations are rarer during small and moderate magnetic storms.…”