Response of daytime low-latitude thermospheric wave dynamics to the geomagnetic storms as inferred from large field-of-view optical dayglow measurements

The low-latitude upper atmosphere (UA) is affected by the solar forcing from above, equatorial electrodynamics and the wave activities propagating from lower atmosphere below. The Travelling Atmospheric Disturbances (TADs) and Travelling Ionospheric Disturbances (TIDs) propagating from high to low latitudes during the geomagnetic disturbances and bring changes to the quiet time UA behavior. The effects/changes that the geomagnetic disturbance create/bring to the low-latitude thermospheric dynamics depend on the season and time (day/night) of its occurrence, speed and direction of the ambient winds and waves. In the present work, response of the low latitude thermosphere to the TADs and TIDs during three geomagnetic disturbances which occurred during different months have been investigated. For this, variations of the optical neutral oxygen dayglow emission intensities at 557.7, 630.0, and 777.4 nm wavelengths during each geomagnetic disturbance events are compared with the Dst index, EEJ strengths and the thermospheric O/N₂ values. The three dayglow emission intensities are obtained simultaneously by using a large field-of-view ( 100^o) high spectral resolution slit spectrograph, MISE (Multi wavelength Imaging Spectrograph using Echelle grating), from a low-latitude location, Hyderabad (17.5^o N, 78.4^o E; 8.9^o N MLAT) in India. During winter and summer solstices, the dayglow emission intensities show similar variations with thermospheric O/N₂, which is attributed to the effect of the geomagnetic disturbances over equatorial- and low-latitude thermosphere. Whereas, during equinoxes the dayglow show similar variations with the EEJ strength indicating a dominance of the equatorial electric fields over the storm influenced neutral wave dynamics. Moreover, contrasting distributions of the Gravity wave zonal scale sizes are observed on geomagnetically quiet and disturbed days in the three events. This shows that changes are brought-in in the zonal GW scale sizes during geomagnetic disturbances irrespective of the season of the storm occurrence. These are the first results of the kind on the response of daytime thermospheric wave dynamics to the geomagnetic storms.