EGU2020-20544, updated on 12 Mar 2024
https://doi.org/10.5194/egusphere-egu2020-20544
EGU General Assembly 2020
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

The Various Aspects of the Large- scale Atmospheric Circulation Response to the Northern Hemispheric Ocean Western Boundary Currents

Nour-Eddine Omrani1,2, Fumiaki Ogawa1,2, Hisashi Nakamura3,4, Noel Keenlyside1,2,8, Sandro Lubis5, and Katja Matthes6,7
Nour-Eddine Omrani et al.
  • 1University of Bergen, Geophysical Istitute, Bergen, Norway (noureddine.omrani@uib.no)
  • 2Bjerknes Centre for Climate Research, Bergen, Norway.
  • 3Research Center for Advanced Science and Technology, University of Tokyo, Tokyo, Japan.
  • 4Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan.
  • 5Department of Geophysical Sciences, University of Chicago, Chicago, Illinois, USA.
  • 6Research Division Ocean Circulation and Climate, GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany.
  • 7Kiel University, Kiel, Germany.
  • 8Nansen Environmental and Remote Sensing Center, Bergen, Norway.

Semi-idealized Atmospheric General Circulation-Model (AGCM) experiments are used, in order to study the different aspects of the hemisphere-scale wintertime troposphere/stratosphere-coupled circulation that are maintained by the North Atlantic and Pacific Ocean Western Boundary Currents (OWBCs). Here we show that the North Atlantic and Pacific OWBCs jointly maintain and shape the wintertime hemispheric circulation and its leading mode of variability Northern Annular Mode (NAM). The OWBCs energize baroclinic waves that reinforce quasi-annular hemispheric structure in the tropospheric eddy-driven jetstreams and NAM variability. Without the OWBCs, the wintertime NAM variability is much weaker and its impact on the continental and maritime surface climate is largely insignificant. Atmospheric energy redistribution caused by the OWBCs acts to damp the near-surface atmospheric baroclinicity and compensates the associated oceanic meridional energy transport in agreement with the Bjerknes compensation. Furthermore, the OWBCs substantially weaken the wintertime stratospheric polar vortex by enhancing the upward planetary wave propagation, and thereby affecting both stratospheric and tropospheric NAM-annularity. It is shown that the impact of OWBCs on northern hemisphere circulation has significant implication for stratosphere/troposphere dynamical coupling, time-scales on the NAM, frequency of Sudden stratospheric warming and potential formation of polar stratospheric clouds.

 

Reference:

Omrani et al., 2019: Key Role of the ocean Western Boundary currents in shaping the Northern Hemisphere climate, Scientific Reports, https://doi.org/10.1038/s41598-019-39392-y

 

How to cite: Omrani, N.-E., Ogawa, F., Nakamura, H., Keenlyside, N., Lubis, S., and Matthes, K.: The Various Aspects of the Large- scale Atmospheric Circulation Response to the Northern Hemispheric Ocean Western Boundary Currents, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20544, https://doi.org/10.5194/egusphere-egu2020-20544, 2020.