In this paper we report plasma blob events (plasma density enhancements) that were observed from KOMPSAT‐1 (685‐km altitude, 2250 LT) and from DMSP F15 (840‐km altitude, 2130 LT) in the low‐latitude F region. The blobs were observed mostly along the ±15° magnetic latitudes. Their global distribution showed a seasonal‐longitudinal dependence similar to the distribution of the equatorial plasma bubbles. The blobs drifted upward relative to the ambient plasma, and the electron temperatures and H+ proportions were lower within the blobs compared to those in the background. The characteristics of the plasma blobs were similar to those of the equatorial plasma bubbles. Therefore, it is suggested that the blobs originated from the lower altitudes by a mechanism that drives an upward drift of the plasma bubbles. The blob events did not occur in a correlated way with the magnetic activity or daily variation of solar activity.
We investigated the global distribution of equatorial plasma bubbles (EPBs) using in situ plasma density measurements from Korea Multipurpose Satellite‐1 (KOMPSAT‐1) and Defense Meteorological Satellite Program (DMSP) F15 during the solar maximum period from June 2000 to August 2001. The results were generally consistent with those of previous studies. EPBs were observed at all longitudes around the magnetic dip equator in the equinoctial seasons with the peak occurrence in the American‐Atlantic‐African regions. During the June solstice, EPBs occurred predominantly in the African sector, with enhancements in the magnetic north in the Indian and west Pacific regions, but were totally suppressed in the American‐Atlantic sector. During the December solstice, EPBs occurred frequently in the American‐Atlantic sector but were suppressed in the other longitude sectors, especially in the Pacific sector. The EPB occurrence probability was seen to be correlated with the observed topside plasma density and the model prereversal upward drift speed of ambient plasmas (Fejer et al., 1999), with their respective dominance dependent on the seasons. However, the peak EPB occurrence in the American‐Atlantic sector during the December solstice was displaced somewhat from the region of peak density and upward drift, probably due to a strong solar terminator influence on the flux tube–integrated E region Pedersen conductivity and due to anomaly morphology. The peak EPB occurrence in the African sector during the June solstice is consistent only with the high ambient density in that region, for there was no coincidence with the maximum vertical drift or the minimum E region Pedersen conductivity.
[1] While the ion and electron temperatures inside equatorial plasma bubbles (EPBs) are normally lower than those in an ambient plasma, bubbles with enhanced temperatures (BETs) are found occasionally in the topside ionosphere. Here we report the characteristics of BETs identified from observations of the first Republic of China Satellite (ROCSAT-1), the first Korea Multi-purpose Satellite (KOMPSAT-1), and the Defense Meteorological Satellite Program (DMSP) F15 during the solar maximum period between 2000 and 2001. The oxygen ion fraction inside the BETs, which was no lower than that of the ambient ionosphere, was similar to the case of ordinary low-temperature EPBs. These observations indicate that the BETs and low-temperature EPBs detected on the topside were produced by the upward drift of low-density plasma from lower altitudes. The feature that distinguishes BETs from normal EPBs is the occurrence of an unusually fast poleward field-aligned plasma flow relative to the ambient plasma. The BETs occurred preferentially around geomagnetic latitudes of 10°in the summer hemisphere, where the ambient ion and electron temperatures are lower than those in the conjugate winter hemisphere. The occurrence of BETs did not show any notable dependence on geomagnetic activities. The characteristics of the BETs suggest that the BETs were produced by adiabatic plasma heating associated with a fast poleward oxygen ion transport along magnetic flux tubes.
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