Equatorial stratospheric and mesospheric temerature & sunspot cycle

Abstract

Stratospheric and mesospheric temperature variation during a Sunspot maximum (1970) and  a minimum (1976) has been analysed at five equatorial sites, viz.. Ascension Island (8° S, 14° W), Antigua (17° N,62° W), Fort Sherman (9° N, 80" W), Kwajalein (9° N, 168° E) and Thumba, Trivandrum (8° N 77° E). The investigation is based on monthly mean temperature of the four seasons in each Period. The stratospheric and mesospheric layers showed a heating effect during the period of sunspot maximum.  The heating is more pronounced in the stratospheric layers between 30 & 35 km altitude. A warmer stratopause is observed over all the equatorial stations except over Thumba, where the soundings were usually taken during the post-sunset period. Seasonal variation of the thermal structure due to the solar cycle IS the least In the stratosphere. The warming produced In the stratopause is high In summer over Antigua, but over Fort Sherman and Ascension Island, the warming is slightly higher in winter. In the winter season large variations of temperature (of the order of 25° C) are observed in the upper mesosphere over Thumba, while there is least variation in spring. A high degree of mesospheric warming is clearly seen when the sun is more active. An attempt has been made to study the correlation between the temperature variation of the stratopause and the solar cycle.