Flavor identification of the stratospheric sudden warmings based on the downward tropospheric influence

Abstract. The downward impact of sudden stratospheric warming events (SSWs) on the troposphere is still uncertain. Using the ERA5 reanalysis data, 52 SSWs are identified over the period from 1940–2022, and 33 downward-propagating (DW) SSWs with noticeable impacts on the troposphere are selected with the remaining 19 SSW non-downward-propagating (NDW). The DW events are further classified into three types that are followed by cold surges over the Eurasia (EA), over the North America (NA), and over both (BOTH), respectively. Although the stratospheric polar vortex is weakened and deformed for both DWs and NDWs, the former are stronger and lead to more significant negative Northern Annular Mode (NAM) and North Atlantic Oscillation (NAO) response in the troposphere. For DWs, the anomalous high develops in the polar region, which deflects to lower latitudes, consistent with the frequent appearance of the polar high and the midlatitude blockings. The shape of the anomalous polar high varies with the DWs type, and the extension and deflection of the anomalous high lead to different surface responses. The DWs are also accompanied by a southward shift of the precipitation belt especially over the oceanic and coastal regions. The NDW SSWs show relatively weaker impact on the troposphere, which is primarily related to the weaker amplitude of the stratospheric disturbance. The differences among three types of DWs include diverse NAM structures in the stratosphere, various spatiotemporal evolutions of the NAO pattern in the sea level pressure, different forcing by planetary waves, and varying number ratios between displacement and split. This study reveals the diversity of the DW events and distinguish their potential impact on both continents in the Northern Hemisphere.