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wet ABL in front of the monsoon rainfall maximum is co-located with
easterly wind, and the maximum of the latent heat flux transporting from
the ocean to the atmosphere concurs with the burst of the westerly behind
the convective maximum and tends to coexist with a SST cooling and
a water vapor decrease near the surface. Therefore, despite the in-phase
relation between the enhanced moisture accumulation and increased SST
in front of the monsoon rainfall maximum, the SST warming and associated
evaporation do not directly contribute to the humidity increase.
Our diagnosis also shows that the warm and wet ABL in front of the
monsoon rainfall maximum tends to be concurrent with a near-surface
convergence. Therefore, it is likely that the lower-level convergence is the
major contributor for the moisture increase. In contrast to Fu
, 13
our study emphasizes the role of the regional convergence preceding the
monsoon rainfall in determining the enhanced moisture accumulation. This
result is in agreement with the observational and theoretical study by Jiang
et al.
et al.
, 16 who pointed out that the preceding distribution of the boundary-
layer convergence is one of the mechanisms that contributes to a northward
propagation of the intraseasonal convection.
A special feature of the current study is to reveal a more conclusive and
systematical scenario on the regional feedback between the atmospheric
moisture, air temperature, and SST response to the intense monsoonal
convections with the aid of the fine-resolution satellite observations from
AIRS, TMI, and QuikSCAT instruments. More detail linkage needs to
be further identified with the help of the ocean data and an accurate
estimation of the surface heat fluxes. In these feedbacks, we observe that
the warm and wet ABL provides more unstable condition preceding the
convective maximum, and strong temperature gradients associated with
warming (cooling) in front of (behind) the convection, in turn, make a
great contribution to the northward propagation of the monsoon convective
activities.
Acknowledgments
TL was supported by ONR grants N000140710145 and N000140210532
and NRL subcontract N00173-06-1-G031. The International Pacific
Research Center is partially sponsored by the Japan Agency for Marine-
Earth Science and Technology (JAMSTEC).
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