Vertical Wind Speed Variations in the Polar Stratosphere of Northern Hemisphere from ERA5 Reanalysis Data and their Correlation with the Lunar Tide

Abstract

The NH Earth polar stratospheric vortex significantly varies from year to year in winter, which periodically leads to the occurrence of sudden stratospheric warmings (SSWs). Such events significantly disturb the circulation and chemical composition of the polar stratosphere. Our understanding of the wave processes that are recorded in the stratosphere and are directly involved in the occurrence of SSWs remains incomplete to date. Oscillations of the polar stratosphere of the Northern Hemisphere in the period from 1979 to 2023 are studied based on ERA5 reanalysis data. The method of current spectra is used to study the variations in the periodicity of wave processes in the polar stratosphere for different time intervals. As the main indicator of the wave properties of the stratosphere, we use the field of the vertical component of the wind velocity in the region between 60° and 90° N. It is shown that in some years, oscillations of the stratosphere coincide with or are close to the periods of the main waves of the fortnightly and monthly lunar gravitational tide. The causes and consequences of the oscillatory processes synchronization in the polar stratosphere with the lunar gravitational tide are discussed. The results can be useful for improving the understanding of the mechanisms of occurrence of SSWs, as well as for improving the forecast of such events.