Global Stratosphere-Troposphere Exchange in Modern Reanalyses

Abstract:

Stratosphere-troposphere exchange (STE) has important and significant impacts on the chemical and radiative properties of the upper troposphere and lower stratosphere. This study presents a 15-year climatology of global large-scale STE from four modern reanalyses: ERA-Interim, JRA-55, MERRA, and NCEP-CFSR. We use a 3-D trajectory model to initialize a dense grid of particles throughout the troposphere and stratosphere each day, advect them forward in time, and identify those crossing the tropopause to compute STE. Exchanged particles are separated into four categories for analysis to identify the significance of known transport mechanisms in each reanalysis: 1) vertical stratosphere-to-troposphere transport (STT), 2) vertical troposphere-to-stratosphere transport (TST), 3) lateral STT (that occurring between tropics and extratropics and across the tropopause “break”), and 4) lateral TST. We will present and discuss similarities and differences amongst the four reanalysis systems, focusing on the seasonal and annual cycle and geographic distribution of the four transport categories.