Interannual Modulation of the Boreal Summer Intraseasonal Oscillation
Tomohiko Tomita (1), Tetsuzo Yasunari (2)
(1) FRSGC/IGCR
(2) Institute of Geoscience, Univ. of Tsukuba, and FRSGC/IGCR
Intraseasonal oscillation (ISO) is an important factor to determine the
features of Asian summer monsoon such as the active/break phases in the
entire monsoon period. The present work diagnostically examines the
interannual modulation of boreal summer ISO, using long-term satellite
and atmospheric assimilation data.
The boreal summer ISO is classified into two by the dominant
spatiotemporal patterns; one is the 30-60-day oscillation characterized
by the large-scale northward propagation with the tilt of in-phase axis
from northwest to southeast in the Indian Ocean through the western
Pacific, and the other is the shorter 20-40-day oscillation confined to
the western Pacific to the South China Sea with more local
northwestward propagation. The two ISOs exhibit the interannual
modulation in activity.
In the summer when the former large-scale ISO is dominant, the
southwesterly monsoon winds are weak in the Bay of Bengal and in the
Arabian Sea,the Pacific High is weaker than normal, and the East Asia
experiences the colder-than-normal summer. When the latter local ISO is
strong, the anomalous surface wind and air temperature fields are
somewhat similar to those in the El Nino event, viz., the negative
temperature anomalies around the Indonesian maritime continent and the
weaker-than-normal trades in the tropical northwestern Pacific. Further
details in development of the two ISOs will be reported at the
conference.
Submittal Information
Name :
Date :
Tomohiko Tomita
31-May-01-20:26:47
Organization :
Theme :
Frontier Research System for Global Change/Institute for Global Change Research
