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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109, D20114, doi:10.1029/2004JD004514, 2004

The summertime annular mode in the Northern Hemisphere and its linkage to the winter mode

Masayo Ogi

Frontier Research Center for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan


Koji Yamazaki

Graduate School of Environmental Earth Science, Hokkaido University, Sapporo, Japan


Yoshihiro Tachibana

Liberal Arts Education Center, Tokai University, Hiratsuka, Japan


Abstract

The seasonal variations of the Northern Hemisphere annular mode (NAM) are investigated through empirical orthogonal function analysis of the zonally averaged geopotential height fields for each individual calendar month. Patterns of the winter and summer NAMs differ not only in the geopotential height fields but also in the mean meridional circulation and eddy structure. The summer NAM has a smaller meridional scale and is displaced poleward as compared to the winter NAM. The antinode on the lower-latitude side in the summer NAM is at the nodal latitude of the winter NAM. The summer NAM is more strongly related to surface air temperatures over Eurasia than the original Arctic Oscillation. The summer NAM is a wave-driven internal atmospheric mode that is maintained by both stationary and transient waves. The summer NAM is associated with the Arctic front, polar jet, and storm track around the Arctic Ocean. The winter-to-summer linkage described by M. Ogi et al. can be interpreted as a preferred transition from one polarity of the winter annular mode to the same polarity of the summer annular mode. The spring cryosphere, i.e., snow in Eurasia and sea ice in the Barents Sea, plays a supporting role in this transition.

Received 6 January 2004; accepted 12 August 2004; published 28 October 2004.

Keywords: Northern Hemisphere's annular mode; Arctic Oscillation; winter-to-summer link.

Index Terms: 1620 Global Change: Climate dynamics (3309); 3309 Meteorology and Atmospheric Dynamics: Climatology (1620); 3319 Meteorology and Atmospheric Dynamics: General circulation; 3349 Meteorology and Atmospheric Dynamics: Polar meteorology.

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Citation: Ogi, M., K. Yamazaki, and Y. Tachibana (2004), The summertime annular mode in the Northern Hemisphere and its linkage to the winter mode, J. Geophys. Res., 109, D20114, doi:10.1029/2004JD004514.