| Popis: |
Based on the very high frequency (VHF) radar data during 2014.03–2019.02 from Fuke station, we presented a statistical analysis of the presunset bottom-type scattering layers (BSLs) on geomagnetic quiet days at low latitudes and preliminarily discussed the relationship between geomagnetic activities and presunset BSLs. It is found that when the seasonally mean F10.7 index is less than 120 during the descending phase of solar cycle (2015–2018), the occurrence rate (OR) of presunset BSLs in the same season also decreases year by year. Except for 2014, all the highest OR values in each year appear in the equinoctial months, but the equinoctial asymmetry is also obvious. Besides the peak values in equinoctial months (mainly March and September), there is also a crest of OR in May during 2015–2017. As for the temporal and altitudinal characteristics, the peak OR of presunset BSLs always appears during 10:45-11:00UT (18:03–18:18LT) and the height ranges from 190 km to 306 km. In addition, it seems that the geomagnetic disturbances might have certain positive impacts on the generation of low-latitude presunset BSLs. |
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