Small‐scale longitudinal variations in the daytime equatorial thermospheric wave dynamics as inferred from oxygen dayglow emissions

Abstract

The equatorial upper atmospheric dynamic processes show both latitudinal and longitudinal variabilities. While the variability in latitudes can exist over small distances (approximately hundreds of kilometers), the longitudinal behavior has been shown to be existing mainly over large spatial separations (approximately thousands of kilometers). In the present work we have used variations in thermospheric optical dayglow emissions at OI 557.7, 630.0, and 777.4 nm, as tracers of neutral dynamics. These emissions are obtained simultaneously from a high‐resolution slit spectrograph, Multi wavelength Imaging Spectrograph using Echelle grating, from a low‐latitude location, Hyderabad (17.5°N, 78.4°E; 8.9°N magnetic latitude) in India, to investigate the longitudinal differences in the upper atmospheric processes over short separations. Spectral analyses of gravity waves carried out on the dayglow emission intensity variations for different independent viewing directions on some days show dissimilar periodicities suggesting the existence of longitudinal differences. Gravity wave scale sizes and the propagation characteristics on these days are different from those in which longitudinal differences are not seen. Further, the zenith diurnal emission intensity patterns are different on the days with and without the observed longitudinal variability. This work shows for the first time that longitudinal differences in upper atmospheric processes can exist at even as small as 3° longitude separations. Such longitudinal differences seen in the neutral dayglow emission intensities are attributed to the zonal variation in the daytime equatorial electrodynamics.

Daytime Periodic Wave‐like Structures in the Ionosphere Observed at Low Latitudes over the Asian‐Australian Sector Using Total Electron Content from Beidou Geostationary Satellites

“…For example, Jonah et al (, ) reported that in some cases daytime MSTIDs observed in the summer at low geomagnetic latitudes over Brazil could be induced by the GWs from the low atmosphere. The wave characteristics of upper atmosphere at low latitudes over India were also revealed in some cases (Karan & Pallamraju, ; Pallamraju et al, ). However, with the exception of these case studies of daytime MSTIDs, few investigations have been conducted on daytime periodic wave‐like ionospheric structures at low latitudes, especially regarding the statistical analysis.…”

On Deriving Gravity Wave Characteristics in the Daytime Upper Atmosphere Using Radio Technique

“…Ground-based airglow emission measurements yield column integrated values; however, as they emanate from a finite thickness, they retain the information of fluctuations of smaller timescales as the reactants responsible for the airglow emissions do get affected by the passage of any wave-like fluctuations in the medium (e.g., Karan & Pallamraju, 2017, 2018Laskar et al, 2015;Pallamraju et al, 2010Pallamraju et al, , 2014Pallamraju et al, , 2016. Conventionally, established method for deriving GW periodicities, scale sizes, and propagation speeds has been through the analysis of temporal variation in optical airglow emission intensities.…”

“…Conventionally, established method for deriving GW periodicities, scale sizes, and propagation speeds has been through the analysis of temporal variation in optical airglow emission intensities. Ground-based airglow emission measurements yield column integrated values; however, as they emanate from a finite thickness, they retain the information of fluctuations of smaller timescales as the reactants responsible for the airglow emissions do get affected by the passage of any wave-like fluctuations in the medium (e.g., Karan & Pallamraju, 2017, 2018Laskar et al, 2015;Pallamraju et al, 2010Pallamraju et al, , 2014Pallamraju et al, , 2016.…”

“…In addition to airglow intensities, some of the optical measurements can yield information on the variation of temperatures, and winds, which also have been used to obtain information on GW characteristics. While GW periodicities can be obtained from a single point measurement (e.g., Chakrabarty et al, 2008;Pallam Raju et al, 1996), large field-of-view optical measurements are required for deriving information on scale sizes and propagation directions of the GWs (e.g., Karan & Pallamraju, 2017, 2018Lakshmi Narayanan et al, 2010;Pallamraju et al, 2013Pallamraju et al, , 2014Pallamraju et al, , 2016Shiokawa et al, 2009).…”

Constraints on Scale Lengths of Equatorial Electrojet and Counter Electrojet Phenomena From the Indian Sector

“…The scatter in CEJ amplitude distribution is larger than the scatter of EEJ amplitude at 5° spatial separations (Figure and ), implying that CEJ is caused by shorter‐scale phenomena (~100, 1,000 km), where as the EEJ is driven by stronger effects, with large spatial scale length (Lühr et al, ). Experimental evidence of the short‐scale length perturbations were also obtained by direct measurements of wind and temperature in mesosphere (Abdu et al, ; Karan & Pallamraju, ; Tsuda, ; Vineeth et al, ).…”