Estimation of upper-ocean thermal structure in the North West Pacific Ocean by satellite remote sensing and its application to typhoon intensity change

Abstract

Lack of the information on upper-ocean thermal structure is one of the identified major reasons causing unsatisfactory typhoon intensity forecast. Therefore it is critical to study the relationship between upper-ocean thermal structure typhoon intensity change. This study uses a two-layer reduced gravity ocean model (TLM_NWPO), TOPEX/Poseidon and JASON-1 sea surface height anomaly data, TRMM/TMI sea surface temperature data and climatological ocean data estimate upper-ocean thermal structure in the Northwest Pacific Ocean. The estimated profiles were validated by 2258 co-located and near co-incident in situ profiles from the Global Temperature and Salinity Profile Program (GTSPP) and the ARGO floats. It is found that the two-layer reduced gravity model is not always applicable in the entire NWPO; depends on location and month. The ‘safe zones’ where the TLM_NWPO can accurately use are defined. It is encouraging to find that most category-4 and 5 typhoons intensify in the ‘safe zones’, thus we can apply the estimated profiles to study its association with typhoon intensity change. All 33 intense and super typhoons (category-4 and 5) occur during the typhoon season (May-October) in the past 6 years (1999-2004) are studied. The sensitivity of four possible parameters (pre-typhoon SST, inner-core SST cooling, pre-typhoon Tropical Cyclone Heat Potential and inner-core Tropical Cyclone Heat Potential) are assessed. It is found that the inner-core SST cooling is the most sensitive parameter and typhoon stops intensification when the inner-core SST cooling exceeds 2.5℃. In contrast, the often emphasized pre-typhoon TCHP is found to be insensitive. It is found that TCHP is over-supplying parameter and the available TCHP is always at least an order higher than typhoons can extract, suggesting that TCHP should not be a limiting factor controlling typhoon intensification.

Lack of the information on upper-ocean thermal structure is one of the identified major reasons causing unsatisfactory typhoon intensity forecast. Therefore it is critical to study the relationship between upper-ocean thermal structure typhoon intensity change. This study uses a two-layer reduced gravity ocean model (TLM_NWPO), TOPEX/Poseidon and JASON-1 sea surface height anomaly data, TRMM/TMI sea surface temperature data and climatological ocean data estimate upper-ocean thermal structure in the Northwest Pacific Ocean. The estimated profiles were validated by 2258 co-located and near co-incident in situ profiles from the Global Temperature and Salinity Profile Program (GTSPP) and the ARGO floats. It is found that the two-layer reduced gravity model is not always applicable in the entire NWPO; depends on location and month. The ‘safe zones’ where the TLM_NWPO can accurately use are defined. It is encouraging to find that most category-4 and 5 typhoons intensify in the ‘safe zones’, thus we can apply the estimated profiles to study its association with typhoon intensity change. All 33 intense and super typhoons (category-4 and 5) occur during the typhoon season (May-October) in the past 6 years (1999-2004) are studied. The sensitivity of four possible parameters (pre-typhoon SST, inner-core SST cooling, pre-typhoon Tropical Cyclone Heat Potential and inner-core Tropical Cyclone Heat Potential) are assessed. It is found that the inner-core SST cooling is the most sensitive parameter and typhoon stops intensification when the inner-core SST cooling exceeds 2.5℃. In contrast, the often emphasized pre-typhoon TCHP is found to be insensitive. It is found that TCHP is over-supplying parameter and the available TCHP is always at least an order higher than typhoons can extract, suggesting that TCHP should not be a limiting factor controlling typhoon intensification.