| Summary: | 碩士 === 國立臺灣大學 === 大氣科學研究所 === 99 === In existing literature, there are many studies discussing the impact of inter-annual variability on sea surface temperature (SST). In contrast, much less work has been done explore the impact of inter-annual variability to the subsurface ocean thermal structure. In this study, we aim to explore the impact of the three phases of ENSO on the ocean subsurface thermal structure in the Pacific and western North Pacific ocean. In this study, SSHA (Sea Surface Height Anomaly) data from multiple satellite altimeters are used as input to an 2-layer reduced gravity ocean model to derive the depth of the 26°C isotherm (D26) (Shay et al. 2000; Goni and Trinanes 2003; Pun et al. 2007). The altimetry-derived D26 is then used together with the TRMM (Tropical Rainfall Measuring Mission) and AMSR-E (Adavanced Microwave Scanning Radiometer) satellite-observed SST to estimate the Tropical Cyclone heat Potential (TCHP), an important parameter related to cyclone’s intensification (Shay et al. 2000; Goni and Trinanes 2003; Lin et al. 2005; 2008; 2009a; 2009b). This work first explores the impact of inter-annual variability to the upper ocean thermal structure in the North Pacific. Its subsequent impact on the typhoon-induced cold wake is also explore.
The results in the three phases of ENSO of the subsurface ocean thermal structure from 1997 to 2010 show that there are three areas with significant signals: western north pacific(130~180°E;0~15°N), central to east equatorial pacific (180°E~140°W ;5°S~5°N) and eastern pacific (120~90°W ;0~20°N).For D26 and TCHP, there are obviously positive(negative) phase in eastern (western north) pacific in traditional El Nino periods, but the positive phase is significant in central equatorial pacific in non-traditional El Nino rather than eastern, in contrast with the positive (negative) phase in western (eastern and central) pacific in La Nina and for typhoon season (July to September), the above three areas have different characters in typhoon intensification in the view of ocean condition, in the cold(warm) phase year there is a better ocean pre-condition (deeper D26) for typhoon intensification in the western pacific (eastern pacific) basin.
The other results for typhoon-induced cold wake strength and recovery show that a better ocean pre-condition (deeper D26) has a less significant SST dropped, and for the three cold wake cases in 2010, the ocean surface recovery (SST) is about 14 days least and 30 days most; the subsurface recovery (SSHA, D20,D26, TCHP) depend on the eddies surrounded the cold wake.
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