Troposphere-Stratosphere Dynamical Coupling in Regard to the North Atlantic Eddy-Driven Jet Variability

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  • IQBAL Waheed
    Department of Meteorology (MISU) and Bolin Centre for Climate Research, Stockholm University, Sweden Finnish Meteorological Institute, Finland
  • HANNACHI Abdel
    Department of Meteorology (MISU) and Bolin Centre for Climate Research, Stockholm University, Sweden
  • HIROOKA Toshihiko
    Department of Earth & Planetary Sciences, Kyushu University, Fukuoka, Japan
  • CHAFIK Léon
    Department of Meteorology (MISU) and Bolin Centre for Climate Research, Stockholm University, Sweden
  • HARADA Yayoi
    Climate Research Department, Meteorological Research Institute, Tsukuba, Japan

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Abstract

<p> For several decades, the interaction between the troposphere and the stratosphere has attracted the attention of climate scientists, not least for the benefit it has on understanding dynamical processes and predictability. This interaction has been revived recently in regard to downward disturbance propagation effects on tropospheric circulations. In the current study, we investigate such interactions over the North Atlantic region in relation to the eddy-driven jet stream. The atmospheric low-frequency variability in the winter over the North Atlantic sector is mainly associated with variations in the latitudinal positions of the North Atlantic eddy-driven jet stream. The Japanese Reanalysis JRA-55 data has been used to analyze the jet latitude statistics. The results reveal robust trimodality of the North Atlantic jet reflecting the latitudinal (i.e., northern, central and southern) positions in agreement with other reanalysis products. 30 major Sudden Stratospheric Warming (SSW) events are analyzed in relation to the three modes or regimes of the eddy-driven jet. The frequency of occurrence of the eddy-driven jet to be in a specific latitudinal position is largely related to the wave amplitude. The stratospheric polar vortex experiences significant changes via upward wave propagation associated with the jet positions. It is found that when the jet is close to its central mode the wave propagation of zonal wave number 2 (WN2) from the troposphere to the stratosphere is significantly high. Eliassen-Palm (EP) fluxes from all waves and zonal wave number 1 (WN1) depict the deceleration of the stratospheric polar vortex for the eddy-driven jet with a latitudinal position close to the northern mode. Plumb wave activity variations originate mainly in the Atlantic sector depending on the North Atlantic eddy-driven jet states. These significant associations between preferred latitudinal positions of the North Atlantic eddy-driven jet and the stratospheric dynamics may be a source of predictability.</p>

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