Spatial structure of rain pool observed on the Kuroshio and Baiu fronts in the East China Sea

Abstract Spatial three-dimensional structure of low-salinity water on the Baiu and Kuroshio fronts is shown using intensive observation results by three ships in the East China Sea. The surface low-salinity pool along the Kuroshio front was formed by rainfall of the Baiu front during the observations. The horizontal distribution of the low-salinity pool with about 130 km long, 40 km wide, and 9–12 m thick along the Kuroshio front is consistent with the precipitation map of the weather radar. The relationship between the surface low-salinity water and precipitation was also quantitatively explained by the conservation of volume. Barrier layer below the surface rain pool had a thickness from several meters to a maximum of 46 m. Subsurface (~ 20-m depth) low-salinity patches were observed below the barrier layer. Based on the order of vertical flow, it is considered that the low-salinity patches moved from the sea surface to the subsurface layer in about 1 day, and their origin is presumed to be rainfall several days earlier. Below the low-salinity patches, we detected temperature inversion layer with warm and saline water, which is thought to have an effect similar to the barrier layer.