The leading modes of NH extratropical tropopause variability and their connection with stratosphere-troposphere variability

Abstract

The leading modes of Northern Hemisphere tropopause variability for November–April (1979/1980–2018/2019) and the associated stratosphere-troposphere variability were analyzed based on the NCEP and ERA interim reanalysis products. For this, cyclostationary empirical orthogonal function technique is employed. The first two modes feature the intraseasonal evolution of tropopause pressure anomalies over the Arctic, which respond directly to stratospheric temperature fluctuations in association with stratospheric polar vortex variations. These two modes reflect the link between stratospheric polar vortex strength and high-latitude tropospheric circulation. The first mode represents a single-phase fluctuation of the stratospheric polar vortex from winter to early spring. The second mode describes a two-phase fluctuation of the stratospheric vortex with opposite signs in winter and in spring. Tropopause pressure anomalies near the mid-latitude tropospheric jet regions exhibit significant zonal variation. In the first mode, in particular, these mid-latitude tropopause anomalies are linked to asymmetric jet variations in the Atlantic and the Pacific regions. In regard to the Northern Annular mode, distinct vertical evolution structures of the two modes are practically related to the varying evolutionary structure of extreme vortex events with relatively long persistence.