Robust Enhancement of Tropical Convective Activity by the 2019 Antarctic Sudden Stratospheric Warming

Abstract

Tropical tropospheric responses to a sudden stratospheric warming (SSW) event that occurred over Antarctica in September 2019 have been investigated by conducting a series of ensemble forecast experiments. Comparative examinations between the normal forecast and the partially nudged forecast, whose stratospheric circulation is constrained to a reanalysis, reveal a significant enhancement/suppression in the convective activity (upwelling/downwelling) over the northern/southern part of the tropics. Such an acceleration of the Hadley circulation is set up by thermal structural changes in the upper troposphere and lower stratosphere. The tropical cooling caused by the enhanced Brewer‐Dobson circulation destabilizes the environment there and stimulates deep cumulus convections. In this case, the southern area of the Asian monsoon region is particularly sensitive. Although details of the triggered response depend on the adopted cumulus parameterization scheme, a boosting tendency of the convective upwelling via the SSW is robust.

Influence of High Latitude Sudden Stratospheric Warming on Tropical Weather: Observations From a 205 MHz Stratosphere Troposphere Radar and Surface Meteorological Parameters

“…The observational finding noted in the present study on the effect of northern hemispheric SSW events on the convection and rainfall events observed in winter at Cochin, a southern region of the Asian summer monsoon, agrees very well with the outcome of the ensemble forecasting experiments by Noguchi et al. (2020).…”

“…(2014) reported that the decrease in temperature in the UTLS region induces upward vertical motion in the equatorial troposphere that enhances convective activity. The enhanced Brewer‐Dobson circulation disrupts the tropical environment generates deep cumulus convection (Nagouchi et al., 2020). Bal et al.…”

“…Another study by Noguchi et al (2020) on the coupling of the Antarctic sudden stratospheric warming of September 2019 on the tropical troposphere using a series of ensemble forecasting methods shows a substantial development/decay of convective activity in the tropics. The Hadley circulation in the tropical belt is thereby modulated by the changing temperature of the upper troposphere and lower stratosphere.…”

Unusual Changes in the Antarctic Middle Atmosphere During the 2019 Warming in the Southern Hemisphere

“…Thus, the state of the Antarctic stratosphere during the 2019 winter and spring was unusual due to the large enhancement of the PWs. Noguchi et al (2020) observed the effect of 2019 unusual warming due to PW1 enhancement in the B‐D (Brewer‐Dobson) circulation through the tropical and polar stratosphere temperature change.…”

Stratospheric drivers of extreme events at the Earth’s surface

“…Variability in the Brewer-Dobson circulation driven by tropospheric waves can affect tropical upwelling, with implications for tropical convective patterns and precipitation 93 . For example, accelerations of the Brewer-Dobson circulation associated with SSWs lead to enhanced tropical upwelling 94,95 , which may reduce the static stability in the tropical tropopause layer and enhance SH tropical convection 96,97 (Fig. 2).…”