Studies of atmospheric waves by ground-based observations of OH(3–1) emission and rotational temperature using PRL airglow InfraRed spectrograph (PAIRS)

Abstract

We present a grating based spectrograph, Physical Research laboratory (PRL) Airglow InfraRed Spectrograph (PAIRS) which provides rotationally resolved OH(3–1) band nightglow emissions in the 1.5–1.6 μm spectral region at a resolution of 0.001 μm @ 1.532 μm that enables estimation of corresponding OH rotational temperatures from Thaltej Campus, Ahmedabad (23.0° N, 72.6° E) in India. The data cadence of PAIRS is 100 s providing an opportunity to study small timescale oscillations present at the OH emission altitude. In a first case study we present a detailed characterization of terdiurnal, large- and small-timescale gravity wave (GW) induced oscillations applying Krassovsky's method to nocturnal variations of the OH(3–1) brightness and its rotational temperatures measured with PAIRS. The amplitudes, phases, Krassovsky parameters, and vertical wavelengths of the terdiurnal tide and GWs are calculated using a least square fitting and wavelet analysis techniques. We also demonstrate capabilities of PAIRS in estimating the characteristics of GWs with periodicities smaller than 30 min, which showed upward wave propagation. The PAIRS derived rotational temperatures for 28 nights of observations for the month of December 2020 show good correspondence with the temperatures obtained from SABER for the passes close to the observational station. PAIRS has been automated for carrying out observations in an unattended mode and data analysis schemes have been developed for the derivation of mesospheric temperatures. Thus, PAIRS provides an opportunity for the detailed investigation of tides and GWs, in general, and short timescale nocturnal MLT dynamics, in particular.