<span style="font-size:11.0pt;mso-bidi-font-size: 10.0pt;font-family:"Times New Roman","serif";mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-GB;mso-fareast-language:EN-US;mso-bidi-language:AR-SA" lang="EN-GB">Study of O⁺(²P-²D) 732.0 nm dayglow emission under geomagnetic storm conditions</span>

Abstract

<span style="font-size:11.0pt;mso-bidi-font-size: 10.0pt;font-family:" times="" new="" roman","serif";mso-fareast-font-family:"times="" roman";="" letter-spacing:-.1pt;mso-ansi-language:en-gb;mso-fareast-language:en-us;="" mso-bidi-language:ar-sa"="" lang="EN-GB">The effect of geomagnetic storms on <span style="mso-bidi-font-weight:bold">O⁺(²P<span style="mso-bidi-font-weight:bold">-²D<span style="mso-bidi-font-weight:bold">)<b> </b>732.0 nm dayglow emission is studied using recently updated photochemical model of Thirupathaiah <i>et al. </i>[An updated model of O⁺(²P) 7320 Å dayglow emission, <i style="mso-bidi-font-style:normal">Indian J Radio Space Phys</i>, 44 (2015), 7]. Three geomagnetic storms, which occurred on 23-27 August 2005, 13-17 April 2006 and 1-5 February 2008 are chosen in the present study. A negative correlation is found between the volume emission rate (VER) and the Dst index for all the three geomagnetic storms. The present study shows that the relative variation of VER with respect to the initial value of VER (before the onset of a geomagnetic storm) during the main phase increases above 260 km. It is also found that the altitude of the peak emission rate does not show any appreciable variation with the activity of geomagnetic storm. A positive correlation is found between the zenith intensity and the atomic oxygen number density. The atomic oxygen number density obtained from NRLMSISE-00 model is compared with the measurements of Earle <i>et al. </i>[Low latitude thermospheric responses to magnetic storms, <i style="mso-bidi-font-style:normal">J Geophys Res</i> <i style="mso-bidi-font-style:normal">(USA)</i>, 118 (2013), 3866] during a geomagnetic storm. This comparison shows that the atomic oxygen number density as provided by NRLMSISE-00 model is significantly lower than the measured value. Consequently, the atomic oxygen number density is treated as a variable parameter in the photochemical model and its effect on the VER of 732.0 nm dayglow emission is further studied. The zenith intensity is found to increase about 70% even in the case of weakest storm when the atomic oxygen number density is doubled. <span style="mso-bidi-font-weight:bold">The latitudinal effect on the VER and zenith intensity of 732.0 nm is also studied. It is found that the VER decreases as the latitude increases. The decrease in VER from low to mid latitudes is due to the decrease in atomic oxygen number density with latitude. The zenith intensity at the maximum geomagnetic activity is about 12% higher than the zenith intensity before the start of the geomagnetic storm in equatorial region. However, no appreciable change in the zenith intensity is found at higher latitudes.</span></span></span></span></span>