High-order solar migrating tides quench at SSW onsets

Abstract

Sudden stratospheric warming events (SSWs) are the most spectacular atmospheric vertical coupling processes, well-known for being associated with diverse wave activities in the upper atmosphere and ionosphere. The first four solar tidal harmonics have been reported as being engaged. Here, combining mesospheric winds detected by three midlatitude radars, we demonstrate at least the first six harmonics that occurred during SSW 2018. Wave number diagnosis demonstrates that all six harmonics are dominated by migrating components. Wavelet analyses reveal that the fourth, fifth, and sixth harmonics quench after the SSW onset. The six harmonics and the quenching appear also in a statistical analysis based on near-12-year observations from one of the radars. We attribute the quenching to reversal of the background eastward wind.Plain Language Summary Solar tides are the most predictably occurring waves in the upper atmosphere. Although the dynamical theory can be dated back to Laplace in the sixteenth century, upper atmospheric tides were rarely studied observationally until satellites and ground-based radars became common. To date, observational studies have mainly dealt with low-order solar-day harmonics. Here, we combine mesospheric wind observations from three longitudinal sectors to investigate high-order harmonics. Results illustrate that the first six harmonics appear in early 2018, all of which are dominated by Sun-synchronous components. Among these harmonics, the fourth, fifth, and sixth quench at the sudden stratospheric warming onset, which we attribute to variations in the background zonal wind.