Geomagnetic control of the midlatitude foF1 and foF2 long-term variations: Recent observations in Europe

Abstract

A new very simple method, allowing an easy control, has been applied to extract long-term (11 year) δfoF2 11y and δfoF1 11y variations from June foF2 and foF1 monthly median observations at European Slough/Chilton and Juliusruh stations, including recent data until 2015. The aim of the analysis was to check the validity of the geomagnetic control of foF2 and foF1 long-term variations in the 21st century with the main accent on the period including the last deep solar minimum in 2008–2009. The geomagnetic control was shown to be valid. Moreover, the dependence on geomagnetic activity has become more pronounced and explicit after 1990. A simultaneous analysis of foF2 and foF1 long-term variations improves the reliability of the obtained conclusions and helps understand the physical mechanism of these variations. Due to common neutral composition and the similarity of photochemical processes noontime foF2 and foF1 demonstrate similar long-term variations: the correlation coefficient between δfoF2 11y and δfoF1 11y is 0.834 at Slough/Chilton and 0.884 at Juliusruh with the 99% confidence level according to Fisher’s F criterion. Midnight long-term δfoF2 11y variations also manifest a pronounced dependence on Ap11y which may be interpreted in the framework of the geomagnetic control concept.