P. T. Patil

Airglow Measurements of Gravity Wave Propagation and Damping over Kolhapur (16.5°N, 74.2°E)

Simultaneous mesospheric OH and O  (1S) night airglow intensity measurements from Kolhapur (16.8°N, 74.2°E) reveal unambiguous gravity wave signatures with periods varying from 01 hr to 9 hr with upward propagation. The amplitudes growth of these waves is found to vary from 0.4 to 2.2 while propagating from the OH layer (~87 km) to the O (1S) layer (~97 km). We find that vertical wavelength of the observed waves increases with the wave period. The damping factors calculated for the observed waves show large variations and that most of these waves were damped while traveling from the OH emission layer to the O (1S) emission layer. The damping factors for the waves show a positive correlation at vertical wavelengths shorter than 40 km, while a negative correlation at higher vertical wavelengths. We note that the damping factors have stronger positive correlation with meridional wind shears compared to the zonal wind shears.

First observation of interhemispheric asymmetry in the EPBs during the St. Patrick's Day geomagnetic storm of 2015

In this work, we have studied the characteristics of 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 (8.7oN, 77.8oE geographic, 1.7oN dip latitude) and Kolhapur (16.7oN, 74.3oE geographic, 11.5oN dip latitude) are utilized here. On 17 March 2015, EPBs were observed to drift eastward during 14:30-16:30 UT between 3oS and 15oN dip latitudes. A westward drift presumably under the influence of the disturbance dynamo electric field (DDEF) initially appeared at higher dip latitudes almost 10 hours 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 pre-midnight hours on 17 March 2015. In this study, the possible mechanisms that can explain these observations are discussed in the light of the current understanding of the equatorial electrodynamics and EPBs.

Probing the possible trigger mechanisms of an equatorial plasma bubble event based on multistation optical data

We analyze an equatorial plasma bubble (EPB) event observed in optical 630 nm image data simultaneously from Gadanki (13.5°N, 79.2°E), Kolhapur (16.8°N, 74.2°E), India. The total electron content data from Gadanki together with the ionosonde data from an equatorial Indian station, Tirunelveli (8.7°N, 77.8°E) confirmed the association of observed EPB event with equatorial spread F (ESF). The optical 630 nm images from a farther low-latitude Indian station Ranchi (23.3°N, 85.3°E) show clear signatures of tilted east-west wave structures propagating toward equator. Further, the upward wave energy noted in mesospheric airglow data was found to be negligible. These data suggest that possibly the off-equatorial tilted east-west structures triggered the observed EPB/ESF event.