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 (similar to 972-1220 km) in the mid-latitude region +/-(25 degrees-55 degrees) 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 (similar to 19%) and June-August in the Southern Hemisphere (similar to 29%). The minimal values take place in the local summer: June-August in the Northern Hemisphere (similar to 3%) and December-February in the Southern Hemisphere (similar to 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.