Relationship of the nightglow 630.0nm emission intensity to the solar extreme ultraviolet.

Abstract: It is well known that the 630.0nm nightglow emission intensity at mid latitudes increased more than twofold in periods of maximum sunspot activity. It is assumed that this phenomenon is caused by variations in solar ultraviolet radiation intensity in solar activity cycles (Fishkova, 1983). In this paper, we present the results of photometric measurements of the nightglow emission intensity at 63°N and 130°E (Yakutsk) in 1990–2007. Moreover, we show the dependence of the 630.0nm emission intensity in magnetically quiet days on solar activity in the 22nd and 23rd cycles. It was established that there is a close relationship between the 630.0nm line nightglow intensity and the solar extreme ultraviolet (EUV) intensity based on SOHO/SEM data, obtained in 1997–2007 with a correlation coefficient of 0.8–0.9. The changes of ionization level of nighttime F2 layer at the Yakutsk station and neutral composition of the upper atmosphere (thermosphere) during the photometric observations have been analyzed. It is shown that the long-term variations of the red line emission intensity are caused by the change of nighttime F2 layer electron density. The nighttime ionization level is related to the electron density of the daytime F2 region which depends on the EUV flux intensity during a solar activity cycle. [Copyright &y& Elsevier]