Radio and optical signatures of interplanetary electric fields over the dip equatorial upper atmosphere

Radio and Optical techniques from both ground and space based platforms have been used to study the effect of prompt penetration electric field over the equatorial upper atmosphere. It has been observed, for the `first time´, that the effects of penetration electric fields are not restricted to ionosphere/thermosphere only, but also seen at the mesopause altitudes owing to the ubiquitous coupling therein. An unusual decrease in the thermospheric OI 630.0 nm dayglow and an intense heating (~30 K) at OH emission altitudes over a magnetic dip equatorial station, Trivandrum, India was observed on April 09, 2006 concomitant with penetration of a noon time westward interplanetary electric field. The SABER observations onboard TIMED satellite also revealed a conspicuous heating at mesopause during this period. The ionosonde and magnetometer observations vindicated presence of strong penetration electric fields. It is found that strong heating at the mesopause resulted in the intrusion of additional neutrals like N₂ into the emission altitudes which quenched the O(¹D) atoms therein. The reduced Cowling conductivity at the E region inferred using magnetometer observations further corroborates this mechanism.