About the annual distribution of magnetically disturbed cloudless days and nights over Abastumani (41.75N, 42.82E)

TL;DR

This study analyzes the annual distribution of magnetically disturbed cloudless days and nights over Abastumani from 1957 to 1993, revealing semi-annual and seasonal variations linked to space weather effects on regional climate.

Contribution

It provides the first detailed analysis of the relationship between geomagnetic activity and cloudless day/night distribution over a specific region.

Findings

Semi-annual variation of Ap index on cloudless days with maxima in March and September.

Seasonal-like variation of Ap index on cloudless nights.

Coupling between magnetically disturbed days/nights and regional climate patterns.

Abstract

The annual distribution of the planetary geomagnetic Ap index monthly mean values on visually cloudless days and nights at the Abastumani Astrophysical Observatory (41.75N, 42.82E) in 1957-1993 is analyzed. Cloudless days were selected from day-time observations of the total ozone content and cloudless nights from night-time measurements of the mesosphere-thermosphere nightglow intensity. Both series of observations were carried out almost uninterrupted during the referred time period. The distribution of long-term monthly mean Ap values on cloudless days shows a semi-annual variation with maxima on the equinoctial months (March and September), while on cloudless nights it displays a seasonal-like character. The semi-annual and seasonal-like variations of Ap modulate the annual distribution of long-term monthly numbers of cloudless days with maximum in August and that of cloudless nights with maximum in September. The lowest monthly mean Ap value for cloudless days and its highest value for cloudless nights fall on June. Different annual distributions of long-term monthly numbers of cloudless days and nights, when sudden storm commencements are present, have been found. This coupling between the visually cloudless days/nights and the magnetically disturbed days may be considered as a manifestation of the influence of space weather/cosmic factors on the regional and global climate.