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In this work, we have studied the characteristics of equatorial plasma bubbles (EPBs), such as their zonal drift and tilt, from the low‐latitude and dip equatorial region in the Indian longitude sector during the main phase of the 17 March 2015 storm. All‐sky airglow imaging observations from Tirunelveli (8.7°N, 77.8°E geographic, 1.7°N dip latitude) and Kolhapur (16.7°N, 74.3°E geographic, 11.5°N dip latitude) are utilized here. On 17 March 2015, EPBs were observed to drift eastward during 14:30–16:30 UT between 3°S and 15°N dip latitudes. A westward drift presumably under the influence of the disturbance dynamo electric field initially appeared at higher dip latitudes almost 10 h after the storm onset, and subsequently, the same was observed at lower dip latitudes. The EPBs attained a peak westward drift at ~17:00 UT followed by a gradual decrease in their speed till ~18:30 UT. After regaining their westward speed, the EPBs continued to drift westward till 22:00 UT. Moreover, a latitudinal gradient in the drift motion of the EPBs was also observed on this night. Another interesting observation made from the images obtained from Tirunelveli was the presence of a large westward tilt of the EPBs. The most intriguing finding of this study, however, was the asymmetry in the tilt of the EPBs at conjugate points during the premidnight hours on 17 March 2015. In this study, the possible mechanisms that can explain these observations are discussed in light of the current understanding of the equatorial electrodynamics and EPBs.

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Key Points: 1) Good inter-comparison is obtained between Arecibo observatory spectrometer and Lidar temperatures and results are similar to previous studies. 2) The temperature comparison improves considerably when time varying weighting  functions are used instead of a single weighting function.  3) Spectrometer and Lidar temperature comparison provide better estimation of the 20 OH(6,2) peak altitudes in presence of a reference for it. Abstract Rotational temperatures in the Mesosphere-Lower Thermosphere region are estimated by utilizing the OH(6,2) Meinel band nightglow emission observed with an Ebert-Fastie Spectrometer (EFS) operated at Arecibo Observatory (AO), Puerto Rico (18.35 o N, 66.75 o W) during February-April 2005. To validate the estimated rotational temperatures, a comparison with temperatures obtained from a co-located Potassium Temperature Lidar (K-Lidar) and overhead passes of the Sounding of the Atmosphere by Broadband Emission Radiometry (SABER) instrument onboard NASA’s TIMED satellite are performed. Two types of weighting functions are applied on the K-Lidar temperatures to compare them with EFS temperatures. The first type has a fixed peak altitude and a fixed full width at half maximum (FWHM) for the whole night. In the second type, the peak altitude and FWHM vary with the local time. Average temperature difference between the EFS and K-Lidar obtained with both types of weighting functions are comparable with the previously published results from different latitude-longitude sectors. Further, it is found that temperature comparison improves when the time varying weighting functions are considered. On the other hand, we have shown that comparison of temperatures obtained from these two instruments could provide a better estimate of the OH(6,2) peak altitudes if a reference temporal trend of the OH(6,2) peak altitudes is available. Also, it is noticed that there are significant differences between the seasonal mean OH(6,2) peak altitudes obtained from SABER observation and model calculation. Such a detailed study using the AO EFS data has not previously been carried out.

Equatorial plasma bubbles resulting from equatorial spread F are well known to be aligned along the Earth's geomagnetic fields. During the geomagnetic storm on 17 March 2015, all-sky airglow observations from Tirunelveli (8.7 • N, 77.8 • E, 1.7 • N dip latitude) showed an apparent interhemispheric asymmetry in the tilt of the equatorial plasma bubbles. In this work we further investigate this case and provide a possible explanation for the asymmetry. We suggest that a variation in the altitude of the airglow layer across the image can cause the observed asymmetry. If the airglow layer is at a higher altitude in the northern portion of the image, then this would explain the observed asymmetry. This variation in the airglow layer can be caused by a variation in the height of the ionosphere. We show through modeling and ionosonde observations that it is likely that there is a variation in the airglow altitude within the field of view of the images on this night.