東アジアとの比較の視点でみたヨーロッパにおける低気圧活動と広域場の季節サイクル（序報） [in Japanese] A preliminary study on the seasonal cycles of the cyclone activity and the large-scale fields in Europe at the viewpoint comparing with those in East Asia [in Japanese]
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Preliminary analyses on the seasonal cycles of the large-scale atmospheric mean fields and the cycloneactivity in Europe were performed based mainly on the NCEP/NCAR re-analysis data, at the viewpointcomparing with those in East Asia. As for the climatological monthly mean fields (1981~2010), the meridional temperature gradient in EastAsia presents striking seasonal change with the maximum in winter and the minimum in summer. It isinteresting that such transition from winter to summer and that from summer to winter occur rather rapidlyaccompanied by the great temperature increase around April to June and the decrease around October toNovember, respectively, in a wide region of 40~70N. On the other hand, the temperature gradient inEurope is significantly smaller with slight seasonal change than that in East Asian winter. By the way, in spite of the above difference of the horizontal temperature gradient between Europe andEast Asia, the cyclone activity does not seem to be so weak even around Europe. Thus, the seasonal cyclesof the characteristics of the cyclones and their environmental fields around Europe were examined. At thefirst step, we analyzed the daily cyclone activity in Europe for January and July of 2000. Many low pressurecenters at the surface level appeared in both January and July. Referring also to the daily maps of sea levelpressure and geopotential height at 500 hPa level, we found that not only the cyclones corresponding to thebaroclinic instability waves, but also to the cold vortices which amplitudes increased with height appearedfrequently. Moreover, it is interesting that the large-scale cold vortex, which embeds the shortwave troughwith the low center at the surface level, appeared in the northern Europe in July as in East Asian winter,when such multi-scale systems sometimes bring the persisting heavy snowfall events in the Japan Sea side ofthe Japan Islands.
- Okayama University Earth Science Report
Okayama University Earth Science Report 21(1), 23-32, 2014-12-27