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processes responsible for an enhanced vapor accumulation in front of the
convection.
Figure 6 presents the latitude-pressure cross-sections of the vertical
velocity (Omega) from ECMWF analysis and the air temperature observed
by AIRS averaged along 105
◦
E-120
◦
E. A domain average over 105
◦
E-102
◦
E
and eq.-20
◦
N is removed from the air temperature at each level in order to
emphasize its north-south gradient. It can be seen that, during monsoon
onset in 2003, 2004, and 2005, the northward movement of the advanced
convection in Fig. 2 (red lines) is associated with strongly ascending motion
between 600 and 200 hPa (Fig. 6, shading). In the pre-onset phase during
early May, a weak descending branch is found in front of the convection
maximum. During the mature onset phase (middle May), the descending
motion weakens and is confined below 700 hPa in 2003 and 2004. The weak
descending motion in front of the monsoon convection helps to preserve the
converged moisture near the surface. The air temperature profile observed
from AIRS satellite show that a relatively warm center lies in front of
the rainfall maximum while a cold one overlapping the rainfall maximum.
Therefore, the monsoon rainfall maximum is overlapped and followed by a
dry-cold ABL and preceded by a warm-wet one. This provides a favorable
condition for the northward migration of the convection from southern to
northern SCS.
4. Summary and Discussion
Using the high-resolution moisture and air temperature data observed by
the AIRS, tropical rain rate and SST by TRIMM and QuiSCAT surface
wind field for 2003-2005, we investigate the 3D moisture structure and air
temperature, and air-sea interactions involved in northward movement of
the strong convective activities during the summer monsoon onset in the
SCS. Our special attention is paid to reveal how the regional circulation
related to the monsoon onset in the SCS contributes to the
in situ
air-sea interactions and moisture distributions which, in turn, provide
a favorable condition for development and maintenance of the tropical
convective activities, and the northward propagation of the monsoon
rainfall. The results show that the SCSSM onset in 2003, 2004, and 2005
shows some common features. Most interestingly, we find that the intense
convective activities are preceded by an enhanced moisture accumulation
and warm air temperature near the surface and followed by a dry and
cold ABL. The vertical profile shows a southward-tilting structure. The
