| dc.description.abstract | Combining ion density and velocity observations from the ROCSAT-1 IPEI payload with the lightning data from the TRMM LIS payload during the solar maximum years of 2000 winter and 2001 summer, we investigate the relationship between atmospheric lightning and topside ionospheric irregularity.
Statistically, during the northern winter the topside ionospheric irregularities mainly occur in South America and the Atlantic Ocean, which collocated well with one of the most probable lightning regions, but the lightning events were also frequently found in Africa and Australia. Comparing the occurrence frequency on the ocean and that on the land, the irregularity distributed more on the ocean, but the lightning occurred most on the land. However, in terms of lightning radiances, the intense lightning events were usually found in the oceans, which imply the topside ionospheric irregularity is related to the intense lightning distribution.
Furthermore, we select two spatially-temporally coincident cases of the TRMM lightning events and the ROCSAT-1 plasma bubbles for detailed analysis. Case I (2001/2/2 18:26~18:33 UT): One minute after TRMM observed a group of lightning events (continued about 2 minutes) a localized structure of ionospheric irregularity was observed by ROCSAT-1 in southeast of the lightning region. From spectral analysis, we found plasma waves with wavelengths of about 20m~1000m. If we convert the ion velocity perturbation into the equivalent electric field perturbation, the magnitude is about 2.5 mV/m, which is comparable to that of the lightning induced electro-magnetic pulse transmitted to the 200km altitude. Hodograph analysis indicates that the polarization of 50m~120m waves is right-hand elliptically polarized. Case II (2001/1/26 00:36~00:51 UT): during this orbit ROCSAT-1 observed density depletions without vertical drift perturbation before the lightning events. However, after the lightning both small scale density depletions and the velocity fluctuations were observed. The spectral characteristics of these structures display wave dispersion indicating that shorter waves go faster than that of longer waves after the lightning. From the statistical or case studies, we tend to conclude that the strong lightning induced electro-magnetic waves can affect the density and velocity structures locally in the topside ionosphere, but not the main factors to trigger the occurrence of large-scale irregularities in the F-region. | en_US |