Equatorial Plasma Bubble Occurrence Probability with Respect to Month of Year

In this paper, the variations of the equatorial plasma bubble occurrence probability with respect
to month of year are investigated. For this purpose, the data obtained on board the ISS-b satellite (~972–
1220 km) in the mid−latitude region ±(25°–55°) DIPLAT of the both hemispheres for a year and a half of
the observations (August 1978–December 1979) were used. The comparative analysis of the studied characteristic
with the monthly variations of the meridional wind velocity was carried out. For this purpose, the
wind velocity data calculated from the Horizontal Wind Model (HWM14) were used. 1. It was revealed that
the maximal plasma bubble occurrence probability values take place each time during the local winter: December–
February in the Northern Hemisphere (~19%) and June–August in the Southern Hemisphere (~29%).
The minimal values take place in the local summer: June–August in the Northern Hemisphere (~3%) and
December–February in the Southern Hemisphere (~4%). As a result, there is asymmetric plasma bubble
development relative to the geomagnetic equator during the solstices. 2. It was revealed that the relative
equality of the plasma bubble occurrence probability values takes place in the histograms of the different
hemispheres during the equinoxes. As a result, there is almost symmetrical plasma bubble spreading relative
to the geomagnetic equator during these periods. 3. It was revealed that the maximal plasma bubble
occurrence probability values take place in each hemisphere during the local winter, when the meridional
winds developing there favors the downward bubble plasma and, accordingly, the bubble spreading along
the flux tube. The minimal plasma bubble occurrence probability values take place in each uplift hemisphere
during the local summer season, when the meridional wind favors the bubble plasma and slows the
bubble spreading.