Abstract:
An anomalous behaviour of F-region neutral temperature at night, sometimes exceeding the maximum afternoon values has been recorded at equatorial latitudes. This feature is referred to as Midnight Temperature Maximum (MTM)1. The winds generated due to pressure bulge phenomena at the equator propagate polewards (northward) and its vertical component while propagating moves the F-region plasma downwards to a region of enhanced loss and airglow production. The optical signature of MTM phenomena (brightness wave) has been recorded at Kolhapur (16.8 °N, 74.2 °E, dip lat. 10.6 ºN) in India using OI 630 nm night airglow during December 2002 to April 2003 showing peaks in intensity around 0200–0400 hrs LT. The structures were prominent for about two to three hours. The digital ionosonde data of Trivandrum (8.5 ºN, 77.0 ºE, dip ~ 0.6 °S), Sriharikota (13.7 °N, 80.2 °E; dip ~ 10.5 °N) and Visakhapatnam (17.67 ºN, 83.32 ºE; dip ~ 20 °N) stations show the descent of the F-layer at all the low latitude stations during MTM disturbance. The meridional winds estimated from h'F data of Trivandrum and Sriharikota showed generation of poleward winds and time delay of about one-and-a-half hours was observed between the observed time of the descent of the layer (h'F) at Sriharikota and the time of observations of the signature of MTM phenomena at Kolhapur.
