A one-dimensional mixed-layer ocean model for use in three-dimensional climate simulations

A study has been made of the dynamic interactions between the surface layer of the oceans and the atmosphere as it relates to global climate variations. The atmospheric conditions are simulated numerically with the NCAR Atmospheric General Circulation Model (AGCM), CCM3. A one-dimensional mixed layer ocean model (MLOM) for the upper ocean has been developed and coupled to the AGCM. The mixed-layer model simulates vertical ocean dynamics and demonstrates the effect of mixed-layer depth and convective instability on the sea surface temperature and on the formation of sea-ice. The purpose of the coupling was to make direct calculations of mixed-layer depth convection in a climate simulation using CCM3. The current mixed-layer model that is used in CCM3, known as the slab ocean model, contains seasonally and spatially specified depths. It also uses a prescribed horizontal heat flux (QFLUX) that determines the vertical heat transport and models the large scale heat transport by ocean currents. The MLOM allows the coupled simulation to capture the physics of sea-ice and mixed-layer interaction, and the effects of the seasonal variation of mixed-layer depth and entrainment on the sea surface temperature. This model has also been run in stand-alone simulations with data derived from the AGCM, CCM1. These simulations show that the MLOM is able to simulate SSTs and depths that closely approximate the observed climate.; The addition of the variable-depth mixed-layer model to CCM3 provides several potentially interesting features to the climate simulation. The mixed-layer model deals explicitly with vertical heat transport--one of the phenomena parameterized by QFLUX in current slab ocean models, calculates mixed-layer depth which is currently seasonally and spatially specified in CCM3, and introduces a negative feedback for sea-ice growth from the interaction between the mixed layer and sea ice. An explicit calculation of mixed-layer depth and vertical heat flux will make CCM3 better able to make physically accurate predictions of sea surface temperature and sea ice for past and future climate scenarios since these quantities will no longer be tuned to meet present-day conditions. Currently, CCM3 coupled to the slab ocean model only includes the ice-albedo feedback mechanism which is a positive feedback for sea-ice growth. Including the negative feedback from mixed-layer and sea-ice interaction provides a means for studying the competing effects of both negative and positive feedbacks on sea-ice growth.