Variable Influence of Stratospheric Vortex Splits on the Equatorial Troposphere
Abstract
Sudden Stratospheric Warmings (SSW) is a vivid phenomenon in the polar region of the northern hemisphere winter. They are categorized by a rapid increase of the polar temperature at about 10hPa and northward of 60N. This breakdown of polar vortex occurs due to vertically growing planetary waves coming from troposphere to stratosphere. The stratosphere troposphere coupling can significantly influence tropospheric climate after SSWs for more than two months. Zonal mean flow changes during the evolution of sudden stratospheric warming are investigated by composite analyses of 76 warming events identified in the present day simulation (PD) from 299 winters. Their dynamical signatures are compared with the 17 SSW events using Era-Interim data from 34 years (1979-2013). The main difference is that monthly distributions of the model SSW events are relatively less than reanalysis. The SSW events are classified as displacement or split events based on the geopotential field values at 10 hPa. The streographic projection of geopotential field values identifies 10 and 3split events in model and observation respectively. The model quite accurately simulates some dynamical features associated with the major SSWs. Residual mean circulation induced by EP-flux divergence, sum of advection and residual forcing are stronger in split events than displacement type SSWs has been confirmed by both simulation and observation. Composite analysis of warming events from Era-Interim (1979-2013) record a cooling of the tropical lower stratosphere with corresponding changes in the mean meridional stratospheric circulation. A cooling of the upper troposphere induces enhanced convective activity near the equatorial region of the Southern Hemisphere and suppressed convective activity in the off-equatorial Northern Hemisphere. After selecting vortex split events, the sea-saw pattern of convective activity in the troposphere is prominent and robust.
- Publication:
-
43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E..90B