Preliminary analyses on the seasonal cycles of the large-scale atmospheric mean fields and the cyclone
activity in Europe were performed based mainly on the NCEP/NCAR re-analysis data, at the viewpoint
comparing with those in East Asia.
As for the climatological monthly mean fields (1981~2010), the meridional temperature gradient in East
Asia presents striking seasonal change with the maximum in winter and the minimum in summer. It is
interesting that such transition from winter to summer and that from summer to winter occur rather rapidly
accompanied by the great temperature increase around April to June and the decrease around October to
November, respectively, in a wide region of 40~70N. On the other hand, the temperature gradient in
Europe 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 and
East Asia, the cyclone activity does not seem to be so weak even around Europe. Thus, the seasonal cycles
of the characteristics of the cyclones and their environmental fields around Europe were examined. At the
first step, we analyzed the daily cyclone activity in Europe for January and July of 2000. Many low pressure
centers at the surface level appeared in both January and July. Referring also to the daily maps of sea level
pressure and geopotential height at 500 hPa level, we found that not only the cyclones corresponding to the
baroclinic instability waves, but also to the cold vortices which amplitudes increased with height appeared
frequently. Moreover, it is interesting that the large-scale cold vortex, which embeds the shortwave trough
with 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 of
the Japan Islands.