Generation of Low-Frequency Unstable Modes in a Coupled Equatorial Troposphere and Ocean Mixed-Layer Model.

摘要

An important issue presented here is the existence of two different types of correlation between time rate of change of sea surface temperature (SST) partial derivative Tau/partial derivative tau and the ocean mixed-layer (OML) depth h(omega), depending on the ocean surface conditions. In the tropics, the net heat flux (including radiation budget) at the ocean surface is generally downward and dampens the OML turbulent kinetic energy (TKE). As the ocean surface is under weak wind forcing, the OML shallows to the Monin-Obukhov length scale due to insufficient wind-generated TKE to entrain the deep cool water into the OML. Net heat gain at the ocean surface and very little heat loss at the OML base leads to a warming OML. The thinner the OML, the warmer the OML. Therefore, partial derivative Tau/partial tau and h(omega) are negatively correlated; however, as the ocean surface is under strong wind forcing, the OML deepens due to sufficient wind-generated TKE to entrain the deep cool water into OML. The excessive heat loss at the OML base (entrainment heat flux) over net heat gain at the ocean surface leads to a cooling OML. The thicker the OML, the warmer the OML. Therefore, partial derivative Tau/partial derivative tau and h(omega) are positively correlated. The shift of positive- only correlation between partial derivative Tau/partial derivative tau and h(omega) (as conventionally thought to be), to two-way correlation leads to a new theory about the interannual tropical ocean-atmosphere interaction. To investigate the impact of this new idea on the interannual tropical ocean- atmosphere interaction, an Air- Ocean Surface Heat Exchange (AOSHE) Model, which is a coupled system consisting of the Wind-Induced Surface Heat Exchange (WISHE) Model (Yano and Emanuel) and the Ocean Mixed-Layer (OML) Model (Chu and Garwood) has been developed. The major advantage of the AOSHE model is simple but contains realistic thermodynamics in both ocean and atmosphere.