Thursday, 27 January 2011
Washington State Convention Center
To investigate the roles and impacts of the convections in the intraseasonal variations (ISV) including Madden-Julian Oscillation (MJO), we have been lead field experiments in and around the warm water pool. Among the experiments, the special sounding networks to estimate heat and moisture budget were deployed over the ocean in three field experiments: MISMO, PALAU2008, and PALAU2010. MISMO was in the central Indian Ocean (Yoneyama et al. 2008, BAMS) in the boreal autumn, while other two were in the western Pacific around the onset of the Asian summer monsoon. The three or more special sounding sites in each experiment enable us to estimate heat and moisture budget by the method of Yanai et al. (1973, JAS). The periods are 26, 22 and 38 days for each experiment, respectively. All three experiments captured the convectively active phase of the ISV. In MISMO, the eastward-proceeding ISV developed around the sounding array between Equator and 4N. In PALAU2008, northward-propagating ISV passed over the sounding array between 7N and 12N (north of ITCZ). In PALAU2010, the northward-propagating ISV was initiated around the area of sounding array between 5N and 10N (on the ITCZ). Reflecting that the all experiments captured the convectively active phase of the ISV (hereafter active phase), the period-averaged Q1 profiles in all experiments were top-heavy, with the peak at around 400- to 500-hPa height. However the other characteristics were different. In PALAU2008, the top-heavy Q1 and Q2 could be well understood as the result of excessive stratiform-type precipitation. In MISMO and PALAU2010, on the other hand, Q2 profiles had double peak at around 500 hPa and 700 hPa. Below 600-hPa height, Q1 was also relatively larger than in PALAU2008. In MISMO and PALAU2010, it is suggested that the complex of the mesoscale convections in different stages / types (convective / stratiform, shallow / deep, etc.) were dominant, even in the active phase. The differences are also found in the period toward the active phase (hereafter pre-active phase). In PALAU2008, the moist layer grew up to the middle troposphere during the pre-active phase. The large negative Q2 in the middle troposphere with the bottom-heavy Q1 profile indicate that the moistening by the congestus works to develop the moist layer. In contrast, the moist layer developed up to the upper troposphere in MISMO and PALAU2010. The vertical growth of the moist layer occurred when large Q1 and Q2 appeared in the cycle of several days. In these two fields, it is suggested that the synoptic-scale disturbances works to develop the moist layer in the pre-active period. These results suggest the difference of the dominant subsystem on the evolution of the ISV. In vicinity of the equator, the synoptic-scale disturbances with the variety of mesoscale systems could play important role, while the mesoscale systems appear more uniformly in the north of ITCZ, or off-equatorial region. The further analyses with more cases are required to examine these suggestions.
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