Thermospheric gravity wave modes over low and equatorial latitudes during daytime

Abstract

The small‐scale intensity fluctuations obtained from 56 days of observations of OI 630.0 nm dayglow emission intensities from Mount Abu (24.6°N, 73.7°E, dip latitude 19.09°N), a station under the crest of equatorial ionization anomaly (EIA), have been subjected to harmonic analysis to unravel different modes of atmospheric gravity waves (AGW). Similar analysis is carried out for 26 days of dayglow intensity data recorded from Waltair (17.7°N, 83.3°E, dip latitude 10.09°N), a low‐latitude station, and for 8 days of available data from Thumba (8.68°N, 77.0°E, dip latitude 0.45°N), an equatorial station with the same objective. The analysis reveals the relative dominance (“preferred mode”) of 0.5–1.0 hour periodic component over Mount Abu, 2.0–2.5 hour periodic component over Waltair, and 1.0–1.5 hour component over Thumba during geomagnetically quiet periods. Qualitative arguments have been propounded to explain the differences in the preferred modes over these places, and it is suggested that the source responsible for the preferred modes may lie in the lower atmosphere. Further, the analysis also indicates the presence of additional preferred modes over low latitudes during geomagnetically disturbed periods.

Effect of an X‐Class solar flare on the OI 630 nm dayglow emissions

“…Thus, it is believed that the photoelectron flux variation due to solar flare through the PE impact mechanism is mainly responsible for the observed OI dayglow emission rate. This event is strikingly in contrast to the several optical daytime redline emission investigations wherein the small-scale variations have all been attributed to the variations in the electron densities (through the DR mechanism) [e.g., Sridharan et al, 1994;Pallamraju et al, 2001Pallamraju et al, , 2004Pallamraju et al, , 2010Chakrabarty et al, 2004;Pallamraju and Chakrabarti, 2006].…”

Short‐ and long‐timescale thermospheric variability as observed from OI 630.0 nm dayglow emissions from low latitudes

“…In a similar sense there would be differences in the dynamics due to the varying inputs in solar fluxes as well. In one of the earlier studies [ Chakrabarty et al , 2004], it was shown that the preferred modes of oscillations in the OI 630.0 nm dayglow varied from around 0.5 to 2.5 h when transitioning from magnetic equatorial to tropical regions. Those measurements belonged to epochs with varying solar activity.…”

On the Cause of the Post‐Sunset Nocturnal OI 630 nm Airglow Enhancement Over Low‐Latitude Thermosphere

“…Optical emissions from the upper atmosphere act as good tracers to investigate the behavior of the altitude region of their origin. This passive remote sensing method has been used to investigate various aspects of the thermosphere‐ionosphere system, such as the vertical coupling of atmosphere (e.g., Laskar et al., 2013, 2014), wave activity in the upper atmosphere (e.g., Chakrabarty et al., 2004; Karan & Pallamraju, 2017; Laskar et al., 2015; Pallamraju et al., 2010, 2014, 2016), mesospheric temperature and wave dynamics (e.g., Lakshmi Narayanan et al., 2010; Lakshmi Narayanan & Gurubaran, 2013; Parihar & Taori, 2015; Singh & Pallamraju, 2015, 2017; Vineeth et al., 2007), and plasma irregularities in the ionosphere (e.g., Krall et al., 2010; Martinis et al., 2009; Mendillo & Baumgardner, 1982; Shiokawa et al., 2004).…”