Analysis and estimation of critical depth based on SODA datasets in the Philippine Sea

This paper focuses on the estimation and analysis of the spatio-temporal features of the critical depth in the Philippine Sea. Firstly, methods for calculating the critical depth are presented. Besides a method using its definition, another method using only the sea-surface sound speed is proposed based on linear regression. Secondly, the seasonal variation and statistical characteristics of the critical depth in the Philippine Sea, as well as their mechanisms, are obtained using the data from Simple Ocean Data Assimilation (SODA) from 1996 to 2005. It is found that the currents have great effects on the spatio-temporal distributions of the critical depth. Finally, as the cycle range and the width of the convergence zone are very important features for sound propagation in the deep ocean, a model is presented to quantify the two parameters using the critical depth. The methods used in this paper also can be applied to analyze and estimate the critical depth in other sea areas.