2次元雲解像大気海洋結合モデルでシミュレートされた海洋混合層の温度と塩分濃度に対する降水の影響

Abstract

Impacts of small scale ocean disturbances induced by atmospheric precipitation on ocean mixed-layer heat and salt budgets are investigated by analyzing the differences in ocean mixed-layers between 1-D and 2-D ocean simulations using a two-dimensional coupled ocean-cloud resolving atmosphere model. The cloud resolving atmosphere model of coupled system is forced by large-scale atmospheric vertical velocities derived from the TOGA COARE observations during a selected seven-day period. Coupled experiments with 1-D and 2-D ocean models show that differences in the horizontal-mean mixed-layer salinity and temperature could be as large as 0.3 PSU and 0.4°C respectively. Shallow mixed layers over the convective areas due to the fresh water flux and deep mixed layers over the convection-free areas due to heat loss result in moderate deepening of the horizontal-mean mixed layers during nighttime in the 2-D ocean simulation while the persistent rainfall maintains shallow mixed layers in the 1-D ocean simulation. Such mixed-layer depth differences are responsible for the differences in saline entrainment and cooling rates, and thus differences in salinity and temperature. Heavy rainfall occurs over convective areas embedded in broad non-convective or clear areas, whereas diurnal signals over whole model areas yield high spatial correlation of surface heat flux. Thus, fresh water flux exhibits larger spatial fluctuations than surface heat flux. As a result, mixed-layer salinities contribute more to the density differences than do mixed-layer temperatures.