| dc.description.abstract | The weather and climate in Taiwan are regulated by East Asian monsoon systems including both summer and winter monsoons. Due to the modulation of intraseasonal oscillation, the seasonal marching of the East Asian summer monsoon posses a clear onset, active, break, revival and withdrawal life cycle. Meanwhile, the cold surge originated from Siberia with cold and dry air mass will penetrate Taiwan during the winter. Furthermore, cold surge also will induce a strong midlatitude – tropical interaction. After launching in April 2006, FORMOSAT-3 could provide relative abundant temperature and moisture atmospheric profile by using radio occulation method (RO). The most advantage with this FORMOSAT-3 RO data is not only offering a better global coverage but also providing more vertical observation in the ocean that was scarcely obtained by traditional radiosonde observation. Therefore, it makes possible for us to apply this observational RO data in the East Asian monsoon study, particularly for the summer active monsoon phase and winter cold surge phenomena.
During active summer monsoon period, FORMOSAT-3 GPS RO observation depicts a more reasonable atmospheric feature in the tropical cooler ocean area if compared to the NCEP analysis data. Through the water budget analysis, the GPS RO data also demonstrates a better water supply in the hydrological process of the summer rainstorm events. Particularly around the heavy rainfall area with strong convergence of moisture flux, the GPS RO observation shows more agreement than that of NCEP analysis data.
Two heavy rainfall events occur during early summer: June 3-9 and June 10-16, 2007. In order to further investigate the possible maintenance mechanisms of these two rainstorms, the high resolution NCEP/GFS analysis data was adopted to perform the detail analysis. It shows that the rainstorm, formed at the southern China, propagates eastward toward Taiwan. During its redeveloping stage, the latent heat release by precipitation together with the coupling of lower boundary moisture convergence and mid-tropospheric vorticity will play significant roles in generating heavy shower resulting in floods in Taiwan.
For the winter cold surge events, a cases-composite strategy was used to depict the surge daily development during its life cycle. It appears that the GPS RO observations delineate the surge structure both horizontally and vertically much better than NCEP reanalysis II data, especially the cold dry air mass and water vapor transport. In addition, the GPS RO exhibits a relative stronger divergence of moisture flux in the cold surge rainfall events. | en_US |