A Lagrangian View of Seasonal Stratosphere‐Troposphere Exchange

Abstract

Stratosphere-troposphere exchange (STE) is the key process regulating the flow of ozone-depleting trace gases, water vapor and other constituents into and out of the stratosphere. The overall circulation responsible for this exchange was first deduced by Brewer (1949), and it consists of upwelling in the tropics and downwelling at extratropical latitudes. This circulation is now referred to as the Brewer-Dobson circulation (BDC). Holton et al. (1995) provides a modern dynamical perspective on STE. Basically, planetary wave-breaking in the extratropical lower stratosphere drives a fluid-dynamical pump that draws air upward in the tropics and drives air downward at the pole (Haynes et al., 1991). The upward moving tropical air is forced out of radiative equilibrium, and thus the air is radiatively heated producing a net diabatic heating in the tropical upper troposphere and lower stratosphere (UTLS). Stratospheric planetary-wave breaking is most intense during winter in the Northern Hemisphere. As a result, the BDC is stronger during boreal winter and the tropical tropopause temperatures are colder than during austral winter (Yulaeva et al., 1994). Holton et al. (1995 noted that the global mass exchange rate is thus determined by the fluid-pump and not by overshooting convection or extra-tropical tropopause folding as had been previously argued.With the broad details of BDC mechanics in hand, more recent efforts have focused on the dynamics of the very lowest part of the stratosphere and the upper tropical troposphere. The BDC appears to consist of two branches: a deep branch that is forced by planetary-scale wave breaking in the mid-stratosphere (Gettelman et al., 2011;

The Observed Impact of the Lower Stratospheric Thermodynamic Environment on Overshooting Top Characteristics During the RELAMPAGO‐CACTI Field Campaign

“…While this may induce a high bias in OTD, choosing the lower altitude tropopause is an attempt to combat the known high bias in MERRA‐2 tropopause altitudes, especially prevalent in the Southern Hemisphere midlatitudes (Fujiwara et al., 2022; Xian & Homeyer, 2019). This also helps combat double tropopause profiles (Schoeberl et al., 2022).…”

“…Defining the tropopause accurately is important for characterizations of OTs. For this study, the tropopause pressure is the highest pressure (lowest altitude) between the thermal and potential vorticity tropopauses from MERRA-2, similar to the method used in Schoeberl et al (2022). While this may induce a high bias in OTD, choosing the lower altitude tropopause is an attempt to combat the known high bias in MERRA-2 tropopause altitudes, especially prevalent in the Southern Hemisphere midlatitudes (Fujiwara et al, 2022;Xian & Homeyer, 2019).…”

The Observed Impact of the Upper Tropospheric/Lower Stratospheric Thermodynamic Environment on Overshooting Top Characteristics during the RELAMPAGO-CACTI Field Campaign

“…Defining the tropopause accurately is important for characterizations of OTs. For this study, the tropopause pressure is the highest pressure (lowest altitude) between the thermal and potential vorticity tropopauses from MERRA-2, similar to the method used in Schoeberl et al (2022). While this may induce a high bias in OTD, choosing the lower altitude tropopause is an attempt to combat the known high bias in MERRA-2 tropopause altitudes, especially prevalent in the Southern Hemisphere midlatitudes (Fujiwara et al, 2022;Xian & Homeyer, 2019).…”

“…While this may induce a high bias in OTD, choosing the lower altitude tropopause is an attempt to combat the known high bias in MERRA-2 tropopause altitudes, especially prevalent in the Southern Hemisphere midlatitudes (Fujiwara et al, 2022;Xian & Homeyer, 2019). This also helps combat double tropopause profiles (Schoeberl et al, 2022).…”

The Different Characteristics of the Mass Transport between the Stratosphere and the Troposphere in Two Types of Cyclonic Rossby Wave-Breaking Events

“…RWB events are associated with severe distortion of the PV contours, as high PV contours stretch from the polar vortex system to low latitudes and low PV contours escape Remote Sens. 2023, 15, 3286 2 of 13 from the tropical tropopause layer to high latitudes, resulting in stratosphere-troposphere exchange (STE) [2,6,[9][10][11][12][13][14][15]. This process involves the crossing of air masses across the tropopause, leading to the coupling of the troposphere and stratosphere, which have different dynamic, thermal, and chemical characteristics.…”