Climate analysis of evaporation ducts in the South China Sea

Abstract

Evaporation ducts have important implications for U.S. Naval activities involving electromagnetic propagation. The presence of an evaporation duct can affect naval operations involving communications, surveillance, electronic warfare, and detection of low-flying missiles, surface ships, or submarine periscopes. We conducted a climate scale analysis of evaporation duct heights (EDH) in the northern South China Sea (SCS), including how EDH varies throughout the year, how environmental variables affect EDH differently in each season, and how regional and global-scale climate variations are related to EDH. We identified climate variations that may enable skillful long-range forecasts of EDH at lead times of up to three months using anomalies in sea surface temperature, geopotential height, and outgoing longwave radiation (OLR) as potential predictors. SCS EDH showed significant correlations with several climate variation indices, including the Multivariable El Nino Southern Oscillation Index, Nino 4, and the Summer Asian Monsoon OLR Indices. Improved understanding and skillful predictions of seasonal and climate scale variations in EDH will aid in operational planning in locations for which real-time observations are sparse, and for interseasonal to seasonal lead times for which existing predictions are presently very limited. Knowledge of EDH in the SCS may become critically important given the increasing significance of the eastern and southeastern Asian area, and particularly for operations involving protection of high-value units and anti-submarine warfare.