DOTSTAR (Dropwindsonde Observations for Typhoon Surveillance near the TAiwan Region) and  Targeted observation  Prof. Wu established the DOTSTAR program from scratch since 2003 with full successes. Widely recognized as a fully-developed program, DOTSATR played a pivotal role in the international THORPEX/PARC initiative under the World Meteorological Organization.  This is the first and pioneering field program in which four airplanes (two jets for surveillance, and a P-3 and a C-130 for reconnaissance) were simultaneously deployed for scientific observations of typhoons in the North western Pacific. DOTSTAR became operational at Central Weather Bureau (CWB) since 2013. DOTSTAR has provided the pivotal realtime in-situ observations for the analysis of storm wind structure at CWB.

Prof. Wu developed a new theory to identify the sensitive areas for TC targeted observations based on the adjoint model.  By appropriately defining the response functions to represent a typhoon’s steering flow at the verifying time, a unique new parameter, Adjoint-Derived Sensitivity Steering Vector (ADSSV), was designed to identify the sensitivity locations at the observing time. Additionally, data from the 751 dropwindsondes deployed in 35 typhoons during 2003-2009 were verified to improve the 48-120-hour track forecast of the USA NOAA/NCEP Global Forecasting System by about 20% (statistically significant at the 95% confidence level). 

Typhoon-ocean interaction  Prof. Wu constructed an idealized and comprehensive typhoon-ocean coupled model to study the influence of the ocean mixed-layer structure and the warm ocean eddy on typhoons, especially that of the feedback of the typhoon-induced SST cooling on typhoon intensity. Numerical experiments with different oceanic thermal structures were designed to elucidate the responses of tropical cyclones to the ocean eddy and the effects of tropical cyclones on the ocean. based on detailed in situ air-deployed ocean and atmospheric measurement pairs collected, the unprecedented “Impact of Typhoons on the Ocean in the Pacific (ITOP)” field campaign were successfully carried out in 2010.

Typhoon Dynamics

Potential vorticity diagnostics of TC motion  Prof. Wu is the pioneer to employ the concept of potential vorticity to understand the hurricane dynamics, i.e., proposing and identifying the baroclinic effect on hurricane motion, and quantitatively evaluating the typhoon steering flow and its connection to the large-scale dynamical systems based on potential vorticity inversion.  The centroid-relative diagram was uniquely designed by Prof. Wu to evaluate the binary interaction (Fujiwhara effect). 

Dynamics of TC intensity and (concentric) eyewall  A new pathway controlling the secondary eyewall formation (SEF) in TCs had been identified by Prof. Wu.   Consequently, a deeper understanding of the underlying dynamics of SEF was obtained, which is an attractive paradigm on the physical grounds because of its simplicity and consistency with the 3-D numerical simulations presented.  Application of the two spin-up mechanisms set the scene for a progressive boundary layer control pathway to SEF.  The response of the unbalanced boundary layer to an expanding swirling wind field is an important mechanism for concentrating and sustaining deep convection in a narrow supergradient-wind zone in the outer-core region of a mature TC.  His findings point to a sequence of structural changes in the outer-core region of a mature TC, which culminates in the formation of a secondary eyewall.

TC rainfall and climate change  A series of numerical (ensemble) experiments has been conducted to examine the capability of a high-resolution mesoscale model to simulate the track, intensity change, and detailed mesoscale precipitation distributions associated with typhoons under the influence of Taiwan terrain. Prof. Wu has carried out milestone works on the rainfall simulation issue in Taiwan. The TC-monsoon-terrain interaction, or the so-called remote rainfall, was highlighted based on two newly-proposed mechanisms: monsoon mode and topographic mode. Prof. Wu also analyzed the high-density rain-gauge data in Taiwan to understand the rainfall characteristics and its reliability, providing new insights on the link between extreme rainfall in Taiwan and global climate change.