Observed

1
Probing the Baiu Dynamics
A. Kuwano-Yoshida and B. Taguchi (JAMSTEC), and
S.P. Xie (IPRC)
Observed
CFES mini
AFES
Monthly mean rainfall in mm/day (shading) and SST
(contours) in observations, CFES and AFES runs.
The Baiu is a summer rain band of great
importance for one billion people in East Asia
but poorly simulated in models. Baiu dynamics are
investigated with the Atmospheric and Coupled
GCMs on the Earth Simulator (AFES and CFES).
Despite sharing the same atmospheric model, AFES
and CFES produce very different Baiu. During
July, Baiu remains vigorous in CFES as in
observations, but has dissipated in AFES. Our
analysis shows that the mid-tropospheric westerly
jet and its thermal advection cause this
difference in simulated Baiu. In AFES, deep
convection in the subtropical Northwest Pacific
sets in prematurely, displacing the westerly
Asian jet northward over cold ocean surface. The
mid-tropospheric thermal advection is similar in
magnitude in AFES and CFES, but sea surface
evaporation is much suppressed under the Asian
jet in AFES as a result of cold ocean temperature
and surface moist advection from the south. These
results reveal important processes for Baiu the
mid-tropospheric thermal advection by the Asian
jet induces ascending motion, which is affected
in turn by subtropical convection to the south
surface evaporation east of Japan is an important
contributor to Baiu rainfall.