Characteristics of Intraseasonal Oscillations During the 2016/2017 Boreal Winter at Mid-Latitudes and Their Relationship With Tropical Convective Activity

Abstract

Studies of Intraseasonal oscillations (ISOs) in the middle and upper atmosphere at mid- and high latitudes are limited compared to the extensive studies in the tropics. This study reports 20–25-day and 32–44-day oscillations in the zonal wind during the 2016/2017 boreal winter using meteor radar and mesosphere-stratosphere-troposphere (MST) radar observations over Beijing and Wuhan, supplemented by Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) reanalysis data. Both ISOs are observed in the troposphere, stratosphere, and mesosphere, with stronger signals over Beijing than Wuhan; these oscillations have greater amplitudes in the middle and upper atmosphere at mid- and high latitudes, originating in the tropical lower atmosphere and propagating upward over the subtropical regions and poleward in the stratosphere and lower mesosphere. The 20–25-day oscillation possesses a zonal structure of westward wavenumber 1, while the 32–44-day oscillation comprises eastward and westward wavenumber 1 components. Both ISOs modulate the diurnal tide (DT), semidiurnal tide (SDT), and quasi-16-day wave (Q16DW), with the 32–44-day oscillation exhibiting a more pronounced effect. These waves are believed to be involved in the ISO activities during the observational interval. Crucially, strong correlations are found between these ISOs at mid-latitudes and tropical convective activities, evident in Outgoing Longwave Radiation and Sea Surface Temperature (SST) anomalies. Our study highlights the significant role of ISOs in coupling the ocean and atmosphere, the lower and middle/upper atmosphere, and the atmosphere at low and mid-latitudes.