Evidence for the lowering of the centroid of daytime thermospheric O(<sup>1</sup>D) 630.0<hsp></hsp>nm emission over the magnetic equator: First results

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Evidence for the lowering of the centroid of daytime thermospheric O(¹D) 630.0nm emission over the magnetic equator: First results

Pant, T.K. / Vineeth, C. / Sumod, S.G. / Jose, Lijo

Abstract It is shown in this paper for the first time that the intensity of the daytime thermospheric O(¹D) 630.0nm airglow as measured by the ground-based dayglow photometer over Trivandrum (8.5°N; 77°E; dip lat. 0.5°N), a geomagnetic dip equatorial station, exhibit a direct correlation with the electron density at 180km. This altitude is about ∼40km lower than the believed centroid of the O(¹D) 630.0nm dayglow emission i.e. 220km. This observation is contrary to the understanding of the behavior of O(¹D) 630.0nm dayglow over equatorial/low latitudes. Over these latitudes, the variations of the measured intensity of O(¹D) 630.0nm dayglow are known to be associated with the changes in the electron density at altitudes around 220km, the centroid of this emission. In this context, the present results indicating the lowering of the peak altitude of O(¹D) 630.0nm emission from ∼220 to ∼180km over the dip equator is new. Recent results on solar XUV flux indicate that this could be an important parameter that controls the O(¹D) 630.0nm dayglow excitation rates through modulations in the neutral and ionic composition in lower thermosphere-ionosphere region. However, the lowering of the centroid of O(¹D) 630.0nm emission, as shown in this study, has been ascribed primarily to the fountain effect associated with the equatorial ionization anomaly.