HSIEH, Y.-H.Y.-H.HSIEHCHENG-SHANG LEE2021-01-272021-01-272020https://www.scopus.com/inward/record.url?eid=2-s2.0-85092249016&partnerID=40&md5=b5fb93b83c367e32d66b150193c34133https://scholars.lib.ntu.edu.tw/handle/123456789/542352Abstract A total of 14 tropical cyclones (TCs) that formed from 2008 to 2009 over the western North Pacific are simulated to examine the effects that environmental low-frequency and high-frequency vorticity (more than 10 days and less than 10 days, respectively) have on the formations of TCs [where the maximum surface wind ~25 kt (?13 m s ?1 )]. Results show that all the simulations can reproduce the formation of a TC in an environment with a large 850-hPa low-frequency vorticity, even if the high-frequency parts are removed from the initial conditions. High-frequency vorticity mainly affects the timing and location of TC formation in such an environment. The 850-hPa vorticity is also analyzed in 3854 tropical cloud clusters that developed in 1981�V2009 and may or may not have formed TCs; this reveals that the strength of the low-frequency vorticity is a crucial factor in TC formation. A tropical cloud cluster is expected to develop into a TC in an environment favorable for TC formation in the presence of a large 850-hPa low-frequency vorticity. The lead time for forecasting the formation of a TC can probably be extended under such conditions.[SDGs]SDG13[SDGs]SDG14journal article10.1175/MWR-D-19-0299.12-s2.0-85092249016