Ctop Year2: Coupled Typhoon-Ocean Prediction System: Understanding & Forecasting the Coupled Response of Ocean and Typhoon in a Changing Climate

One of the most challenging problems in ocean, atmosphere and climate research is to understand and forecast the coupled response of ocean and tropical cyclones (TCs or typhoons). TC drives ocean currents and mixing [Price 1981; Price et al. 1994], waves [Holthuijsen et al. 2002; Moon et al. 2004; Oey et al. 2008], and sub-mesoscale cells [Huang and Oey 2015; Lin & Oey 2016], resulting in a myriad of complex upper-ocean processes which cool the SST and support phytoplankton bloom [see reference in Huang and Oey 2015]. In turn, the ocean influences air-sea fluxes, hence the moist air that spirals into the eye of the storm in the surface boundary layer [Riehl 1963; Emanuel 1986], modifying the potential vorticity (PV) structure of the TC's hot tower and its intensity [Sun and Oey 2015]. The altered surface fluxes feed back into the ocean, continuing the coupled loop. Despite the importance of air-sea coupling to upper-ocean response and TCs, our understanding of the complex physical processes remains limited [Bao et al. 2000; Chen et al. 2007; Lee and Chen 2012]. Moreover, while the skill in forecasting TC tracks has steadily improved, as TCs are primarily steered by large-scale wind [Marks and Shay 1998; Chen et al. 2006], the intensity forecast has not [Rogers et al. 2006; Houze et al. 2007; Rappaport et al. 2009; Gall et al. 2013; Rios-Berrios et al. 2014], since intensity depends on inner-core dynamics [Marks and Shay 1998; Houze et al. 2007], environment [Zeng et al. 2007; Hill and Lackmann 2009] and sea surface temperature (SST) [Emanuel 1999; Schade and Emanuel 1999; Lin et al. 2008; Emanuel et al. 2004]. A few operational forecast models are coupled [e.g. HWRF, coupling WRF with POM], and in Taiwan uncoupled typhoon forecast model is used at CWB. Under a previous support from MOST, we have successfully completed the development and testing of Advanced Taiwan Ocean Prediction (ATOP) model. ATOP now routinely forecasts sea level (waves, tides & storm surge), currents, temperature and salinity for the entire North Pacific Ocean. Since 2013 ATOP research activities have resulted in 35 SCI publications covering a broad range of topics from physics to biology, and from coastal circulation and winds in the seas around Taiwan, to Kuroshio, basin and climate-scale processes. This proposal seeks a 1-year support to continue developing and testing a Coupled Typhoon-Ocean Prediction (CTOP) model based on ATOP and WRF. The overarching goal is to validate a prototype CTOP, understand how to produce accurate intensity forecasts, and conduct research focusing on upper-ocean and typhoon processes (rather than on e.g., data assimilation and initializations). We plan to study (i) ocean's mixed-layer, sub-mesoscale physics and biogeochemical process under the TC and its wake, and how they feedback into the storm; and (ii) coupled TC-intensification process as a PV-enhancing, air-sea interactive process [Sun and Oey,2015]. Besides providing insights into ocean-typhoon coupling processes, the proposed work clearly will advance Taiwan's typhoon and ocean forecasting capability to a new level, with anticipated benefits to society and commerce.