``Convection jump'' as a subtropical convergence zone
N. Sato (1), M. Takahashi (2)
(1) IORGC, JAMSTEC
(2) CCSR, Univ. of Tokyo/FRCGC, JAMSTEC
It is known that the convection jump observed over the warm pool to the
south of Japan is closely related to the abrupt northward movement or
disappearance of the Baiu frontal zone. Therefore, the convection jump
is very important for midsummer climate in Japan. In the present
study, characteristics of the precipitation system corresponding to
the convection jump were examined by analyzing observational data. As
a result, a convection zone extended northeastward from the warm pool
near the Philippines was identified. Hereafter, we call this rain belt
"Marcus Convergence Zone" (MCZ). The convergence zone suddenly appears
in late July. Its horizontal distribution and abrupt seasonal march do
not directly correspond to those of sea surface temperature (SST). The
distribution of convective activity, as well as characteristics of
pressure and vorticity fields and vorticity budget, well resemble
those of subtropical convergence zones (STCZs) observed over the
South Pacific and the South Atlantic or one simulated in an idealized
numerical simulation. Therefore, it can be inferred that dynamical
forcing by active convection over the warm pool near the Philippines
contributes to the formation of the MCZ. However, the gradient of
water vapor distribution is not clear, while more water vapor exists
on the low-latitude side of the other observed STCZs. Rather, the
value of precipitable water is larger on the northwestern side,
corresponding to the moist tongue just to the south of the Baiu
frontal zone. Therefore, the MCZ may be regarded as a frontal zone
characterized by inverse specific humidity gradient. At this point,
the MCZ is quite different from the other STCZs, although it has some
common dynamical features.
Submittal Information
Name :
Date :
Naoki Sato, Dr.
30-Jul-04-09:07:22
Organization :
Theme :
Institute of Observational Research of Global Change, JAMSTEC