Quasi-two-day wave characteristics in the mesopause region from airglow data measured at El Leoncito (31.8°S, 69.3°W)

Abstract

A statistical study of strong quasi-two-day waves (QTDWs) is carried out from the intensities and rotational temperatures of OH(6–2) and O2b(0–1) emissions measured from the “El Leoncito” Astronomical Complex (31.8°S, 69.3°W) between 2006 and 2020. These emissions correspond to layers centered at 87 km and 95 km altitude, respectively. The period, amplitude and phase of each QTDW are obtained after applying rigorous data and spectral conditions. QTDW is the strongest planetary wave in January and is strong during the other summer months. In the rest of the year, the presence of strong QTDWs is more exceptional. Most QTDWs have periods between 45 and 52 h. In January, the periods are mostly concentrated in the range of 45–48 h, with medians of approximately 46 h, for both emissions. The peak of QTDW amplitudes is also reached in January, with total averages greater than 10 K for temperatures and 36% (45%) for OH (O2) relative intensities. Unlike what happens with the semidiurnal tide, there is no increase of the temperature amplitude with altitude: for January there is rather a slight decrease between the OH and the O2 layer. QTDWs affect airglow intensities more than temperatures, which is reflected in the large Krassovsky's η ratios (with mean vector modulus of 6.14 (±0.15) for OH and 8.08 (±0.11) for O2). In a high percentage of cases, the vertical wavelength is long (λz > 100 km), especially for the O2 layer. However, waves with λz from 20 km were also detected, and with both directions of vertical propagation. The January averages in the documented years (2008–2012, 2014–2015, 2019–2020), indicate the minimum amplitudes (in intensity and temperature) in 2009 and the maximum amplitudes in 2012. For each of the four observed parameters (intensities and temperatures of OH and O2) there is a different day-by-day evolution of the QTDW amplitudes.