Equatorial Spread F structures and associated airglow intensity variations observed over Gadanki

Abstract

Abstract. Co-ordinated campaigns have been conducted from Gadanki (13.5 • N, 79.2 • E, dip lat 6.4 • N) by operating simultaneously the Indian MST radar in ionospheric coherent backscatter mode and by monitoring thermosphere airglow line emissions (630.0 nm and 777.4 nm) using a narrow band multi-wavelength scanning photometer during JanuaryMarch for the past five years (2003)(2004)(2005)(2006)(2007) and also during April 2006, as a special campaign. Simultaneous radar and optical observations reveal optical signatures corresponding to a variety of equatorial spread F (ESF) structures. The optical signatures corresponding to ESF structures with wavelike bottomside modulations with plasma plumes, confined bottomside flat and wavelike structures, vertically extended plume structure in the absence of bottomside structure apart from the classical plasma depletions and enhancements are obtained during these campaigns. The plasma depletions and enhancements were identified using optical measurements. In addition, estimations of zonal wavelength of the bottomside structures and the inference of shears in the zonal plasma drift in the presence of confined structures, were carried out using bi-directional airglow measurements. Furthermore, it is found that the vertical columnar intensity of OI 630.0 nm airglow exceeded the slanted columnar intensity in the presence of large bottomside structure. The need for the appropriate physical mechanisms for some of the ESF structures and their characterizations with optical observations are discussed.

Simultaneous sodium airglow and lidar measurements over India: A case study

“…The photometer was calibrated against a standard source (Labsphere INC., USS‐1200 V) which is used for calibration of imaging payloads at the Space Application Centre, Ahmedabad. The output of this photometer was also verified with an earlier photometer which was used for several ionospheric studies [e.g., Sekar et al , 2004, 2008]. Na airglow intensities with temporal resolution of 2 minutes were obtained using this photometer.…”

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

“…Overall, Gadanki and Kolhapur data show sharp fluctuations and bite outs in the O( 1 D) 630 nm night airglow intensity data. In past several reports from Indian sector have shown a close association of such bite outs with the EPBs/ESF events [e.g., Mukherjee , ; Sekar et al ., ; Taori et al ., ]. Therefore, these signatures signify the occurrence of EPBs.…”

Ionogram signatures of large‐scale wave structure and their relation to equatorial spread F

“…The presence of long‐wavelength structures modulating the multiple plume structures (meter‐scale irregularities) is actually observed by VHF radars [e.g., Kelley et al , 1981; Sekar et al , 2008]. Theoretical studies have also shown that beyond a certain wavelength, such long‐wavelength mode perturbations cannot generate rising plume structures [ Kherani et al , 2002], but can evolve into irregularities confined to the bottomside (which can cause RSF).…”