A Lagrangian View of Seasonal Stratosphere-Troposphere Exchange

We use our forward domain filling trajectory model coupled with a new convective parcel injection system to explore stratosphere-troposphere exchange (STE). We use Modern-Era Retrospective Analysis for Research and Applications, Version 2 reanalysis and study the December-February (DJF) and June-August (JJA) seasons averaged for the years 2006–2015. Maps of age-of-air and STE regions show coincidence with stationary forced tropical Rossby waves that straddle the equator. The anticyclonic circulation generated by these waves isolates air over the Asian monsoon, the Tropical West Pacific, and North and South America. We map the preferred locations of troposphere to stratosphere (T2S) and stratosphere to troposphere (S2T) exchange. During DJF, the highest concentration of T2S locations is spread over the tropical west Pacific and in a broad region over Central/South America and Africa. During JJA, the highest concentration T2S locations is in the vicinity of the Asian monsoon. The highest concentration T2S crossing points is nearly always positioned on the eastern side of the Rossby waves where the tropopause is higher. Along the jets that bracket the tropics, the STE locations are consistent with earlier studies of Rossby wave breaking and two-way exchange. S2T exchange above 12 km occurs at the edges of the tropics along the jet boundaries for both seasons. Plain Language Summary Air exchange between the troposphere and the stratosphere determines the water vapor concentration in the stratosphere and provides a pathway for pollutants to reach the ozone layer. In this study, we use a Lagrangian model to map regions where the exchange is more frequent. Exchange regions are associated with the presence of stationary Rossby waves in the upper tropical troposphere in boreal winter, and the Asian monsoon during boreal summer. At the border between the tropical troposphere and the extra-tropical stratosphere exchange occurs due to wave breaking along the jet.