Stratosphere–Troposphere Exchange and Its Relation to Potential Vorticity Streamers and Cutoffs near the Extratropical Tropopause

Two distinct dynamical processes near the dynamical tropopause (2-PVU surface) and their relation are discussed in this study: stratosphere–troposphere exchange (STE) and the formation of distinct potential vorticity (PV) structures in the form of stratospheric and tropospheric streamers and cutoffs on isentropic surfaces. Two previously compiled climatologies based upon the 15-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-15) dataset (from 1979 to 1993) are used to establish and quantify the link between STE and these PV structures. An event-based analysis reveals a strong relation between the two processes. For instance, on isentropes below 320 K, 30%–50% of the stratospheric streamers are associated with downward STE. In the reverse perspective, between 60% and 80% of all STE events between 290 and 350 K are found in the vicinity of at least one PV structure. On different isentropes, the averaged downward (STT) and upward (TST) mass fluxes associated with PV structures...