Wu, Xiangbai2016-03-242016-03-242015http://udspace.udel.edu/handle/19716/17570The emission of greenhouse gases (GHGs) from human economy and social activity, such as burning of fossil fuel, cement industry, deforestation and so on, contribute to continuously increasing of GHGs, CO2 for example. The increased GHGs concentration leads to the energy imbalance at the top of atmosphere and heat cumulating within the earth climate system. Understanding the ocean’s role in Earth’s energy budget is fundamental to evaluate climate variability and change, including the rate of global warming and the recent 18-years’ so-called Global Surface Warming Hiatus (GSWH). Progress has been made continuously on this topic: studies show that the GSWH is related to external forcing changes, internal variability induced by trade wind and wind-driven circulation adjustment with the resulting heat redistribution within the climate system, and the warming up in subsurface and deeper ocean. There are a wide range of opinions among climate scientists and no unanimous conclusion has been drawn about the mechanism of the global warming hiatus. In this dissertation, the spatio-temporal variations of the Ocean Heat Content (OHC) were investigated to reveal the physical mechanisms of the global warming hiatus and the regional climate response in East Asia. Firstly, methods were developed to estimate temperature anomaly for subsurface and deeper layer from sea surface parameters provided by remote sensing, to generate new data sets for decadal climate variability research. A Self-Organizing Map Neural Network (SOM) was developed from Argo gridded data sets in order to estimate subsurface temperature anomaly (STA) from remote sensing data. The SOM maps were trained using anomalies of sea surface temperature (SST), height (SSH) and salinity(SSS) data from Argo gridded monthly anomaly data sets, labeled with Argo STA data for 2005∼2010 and then used to estimate the STAs at different depths in the North Atlantic from the sea surface data. The estimated STA maps and time series were compared with Argo STAs including independent data sets for validation. In the Gulf Stream Path areas, the STA estimations from the SOM algorithm show good agreement with in situ measurements taken from the surface down to 700m depth, with a correlation coefficient lager than 0.8. Sensitivity of the SOM, when including salinity shows that with SSS anomaly data in the SOM training process, reveal the importance of SSS information, which can improve the estimation of STA in the subtropical ocean by up to 30%. In subpolar basins, the monthly climatology SST and SSH can also help to improve the estimation by as much as 40%. STA time series for 1993∼2004 in the mid-latitude North Atlantic were estimated from remote sensing SST and altimetry time series using the SOM algorithm. Limitations for the SOM algorithm and possible error sources in the estimation are briefly discussed. Secondly, OHC spatio-temporal variations were analyzed using the empirical orthogonal function analysis. A meridional dipole has dominated the variation of the ocean heat content in the upper layer, and the warming in the upper layer of the Indian Ocean has been in “hiatus” since early 1980s. Further, a very new and sophisticated causal analysis method revealed that the warming in the southern subtropical Indian Ocean contributed to the pre-conditioning and warming in the southern and tropical Atlantic since 1980s and to the heat sequestration at the deeper layer in the Southern Ocean during the global surface warming hiatus period. In addition, zonal ocean heat content anomaly were found to shift westwards in a way that resembles Rossby wave, with a period of about 30 years, and phase speed of 1.8-2.5 cm/s. It takes about 60 years for the anomaly signal to travel from east Pacific to the Western Atlantic via the Indian Ocean. The redistribution of OHC in upper layer follows the surface branch of the Global Ocean Conveyor belt to travel westward from Pacific to the Atlantic via Indian Ocean. With an embedded atmospheric bridge linking the Atlantic SST with the Pacific trade winds, the global ocean and atmosphere forms a closed loop. This finding explains not only the occurrence of global warming hiatus, but also sheds light on the multi-decadal climate variability. Thirdly, the decadal variation of vertical OHC distribution and its impact on air-sea interaction in Western North Pacific were studied to reveal regional climate respond to global warming hiatus. The decadal variation of rapid intensification of Tropical Cyclones (TCs) in Western Northern Pacific were studied using TC best track datasets. The intensity and frequencies of intense TC peaked in 1960s, and have not increased in a global warming climate. Compared to previous tropical cyclone (TC) studies that focus on the frequency of rapid intensification (RI), a new index (RITC) is proposed to measure the RI-level for category 4-5 TCs (Saffir–Simpson scale) in the western North Pacific. RITC is the maximum increase in the sustained-wind-speed per 24-hour during the lifetime of a TC. The results show that the PDO modulation of the interannual ENSO-RI relationship is better represented with the new RITC than with the RI number. The interannual relationship between ENSO and RITC is strong and statistical significant in warm PDO while not significant in cold PDO, mainly attributed to the variation of zonal wind speed. On decadal time scales, the PDO’s modulations of ENSO’s effects on RITC are mainly attributed to the variations of upper ocean heat content and vertical wind shear. Our results have significant implications for the prediction of RI and long-term projections of major TC activity. In summary, OHC was used as tracer to study the decadal heat redistribution, horizontal and vertical, in Indian Ocean, Atlantic and Southern Ocean. Indian Ocean was found to be the accelerator for the global surface warming hiatus through supplying heat to the southern Atlantic Ocean. The redistribution of OHC in upper layer explains not only the global warming hiatus, but also the multi-decadal climate variability. The decadal variation in rapid intensification of intense TCs provides a better understanding of the decadal variation of the TC in Western North Pacific and a new perspective for the regional climate responding to the decadal variability of OHC under the changing climate.Ocean temperature -- East Asia.Climatic changes -- East Asia.Thesis945550107