89th American Meteorological Society Annual Meeting

Tuesday, 13 January 2009: 9:30 AM
Vertical Cloud Water Structures of the Boreal Summer Intraseasonal Variability Based on CloudSat Observations
Room 129A (Phoenix Convention Center)
Xianan Jiang, JIFRESSE/UCLA and JPL/Caltech, Pasadena, CA; and D. E. Waliser, J. L. Li, and C. P. Woods
The boreal summer intraseasonal variability (BSISV), which is characterized by pronounced meridional propagation from equatorial zone to the Indian Continent, exerts significant modulation of the active/break phase of the south Asian monsoon. This form of variability provides a main source for subseasonal predictive skills of the Asian summer monsoon. Unfortunately, the current general circulation models display large deficiencies in representing this variability.

The new cloud observations made available by the CloudSat mission provides an unprecedented opportunity to advance our understanding of the BSISV. In this study, the vertical structures of cloud water content and cloud type associated with the BSISV over the Indian Ocean and subcontinent are analyzed from the CloudSat observations. It is illustrated that during the northward propagation of the BSISV, while the cloud ice water content (IWC) in upper troposphere tends to be in phase with the convection, a marked vertical tilting is observed in cloud liquid water content (LWC). Increased LWC tends to appear to the north of rainfall maximum, i.e., leads the convection, particularly in the lower troposphere. This northward shift of increased LWC could be fundamental responsible for the northward propagation of the BSISV. Further analysis indicates that IWC variability is largely associated with deep convective clouds. While LWC is mainly linked to non-precipitating alto-cumulus at mid-level and stratocumulus cloud at low-level. These aforementioned results would provide valuable information for climate modeling efforts in describing subseasonal variability of tropical convection.

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