Vertical wave characteristics in the MLT region and its seasonal variations using OH(3-1) brightness and rotational temperature from Ahmedabad (23�N, 72.6�E)

Abstract

This study investigates the fundamental principles and significance of vertically propagating waves in the mesosphere and lower thermosphere (MLT) region. Key characteristics of these waves are derived using simultaneous observations of OH(3-1) airglow brightness and corresponding rotational temperature data obtained from PAIRS (PRL Airglow InfraRed Spectrograph) over Ahmedabad (23�N, 72.6�E) for the year 2023. Temperature data from SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) underscores the reliability of derived temperature from ground-based instrument PAIRS. The Krassovsky's ratio method is employed to derive the vertical wavelength (?<inf>z</inf>) of waves using simultaneously obtained brightness and temperature data. To support this method, altitude differences of approximately 3.5 km in emission brightness and temperature over the study region are calculated using SABER-derived OH volume emission rate profiles. Seasonal variations in the derived ?<inf>z</inf> are analyzed using daily calculated ?<inf>z</inf> values for the year 2023. Horizontal wind data with zonal and meridional components are presented for 2023 to observe the annual and semi-annual (AO and SAO) behavior of the resultant horizontal wind. Annual variations of nightly mean ?<inf>z</inf> and horizontal winds (U<inf>h</inf>) and their residuals showed anti-correlation between the observed AO and SAO in both parameters. A sine fitting model is proposed, accounting for the observed AO and SAO, to provide a first-order estimate of the ?<inf>z</inf> as a function of the day of the year. Such systematic investigation of the vertical wave characteristics in the MLT region reveals insights into the dynamics of wave propagation in the MLT region. � 2025 Elsevier B.V., All rights reserved.