The Arctic Tropopause Fold

Abstract

Analyses of research aircraft observation, satellite total columnar ozone retrievals and synoptic upper-air soundings are used to describe the structure of Arctic jetstreams and their associated frontal zones and tropopause folds. These analyses document the presence of major tropopause folding events within the Arctic that occur at the flanks of large-scale (?2000 km) polar vortices. One example shows a polar vortex and its associated tropopause fold and Arctic front that migrated from the high Canadian Arctic southward into midlatitudes over central North America. The frigid cold-air outbreak associated with this migration was an important component in the record setting daily minimum temperatures that were recorded from the Great Lakes to southern Florida. Total columnar ozone measurements from the Total Ozone Mapping Spectrometer (TOMS) are shown to identify the location of polar vortices and the mesoscale (?200 km) ozone gradients at the flanks of these vortices which coincide with regions of Arctic tropopause folding and associated stratospheric-tropospheric exchange (ST) processes. A major modification to earlier models of the meridional structure of the tropopause and primary wind systems is proposed. The model introduces the Arctic jetstream and its associated tropopause fold as a primary wind system and vehicle for ST-exchange. The model also uses the ST-discontinuity in potential vorticity to define the pole-to-equator structure of the tropopause.