Large-scale Features associated with the Heavy Rainfall in Central China in the Meiyu of 1998 under the Abnormal Asian Monsoon
Kuranoshin Kato (1), Hajime Inaoka (1)
(1) Faculty of Education, Okayama University
Rainfall features and the large-scale situation associated with the
heavy rainfall events in the Meiyu of 1998 (GAME-IOP year) around the
Changjiang River Basin were examined based on the observational data,
with attention to a role of the abnormal Asian Monsoon behavior. The
two heavy rainfall periods occurred (late June and late July of 1998).
In the first period (22 to 27 June) the intense Meiyu frontal
rainfall belt was sustained, due to the day-to-day persistency of the
extremely large moisture flux toward the front. It is interesting that,
although the low-level pressure system in the subtropical high area just
to the south of the Meiyu front then was just in the transition stage,
the strong southerly wind component transporting the moisture toward the
front was maintained. That is, the pressure depression area was firstly
deepened around 25N/105E on 20 to 24 June. After that, that low
pressure was weakened, but the localized subtropical high cell just
around the Southwest Islands area of Japan had developed. These
resulted in the large eastward pressure gradient corresponding to the
strong low-level southerly wind toward the Changjiang River Basin.
The above behavior of the low-level pressure field was related to
the eastward propagation of the convective area from the Indochina
Peninsula to the South China Sea with its enhancement (around 15N).
However, in spite of the La Nina situation in the summer of 1998 (just
after the terminal of the remarkable El Nino event), the convective
activity was considerably suppressed in the western Pacific area
throughout the summer of 1998. Thus the convective area was weakened
when it reached the tropical region of the western Pacific. It is
suggested that the two heavy rainfall events in the Changjiang River
Basin in 1998 would be caused by such intraseasonal cycle under the
suppressed rainfall activity in the tropical region
