Initialization of Moisture in Primitive Equation Models

Abstract

An explicitly integrated primitive equation grid-point model is used as a tool to study the impact of some variables on the hemispheric average precipitation rate in the model. The experiments show that the model needs 15 h to create vertical velocities and build up a moisture field which gives a constant rate of precipitation, starting from an initial state adjusted by the balance equation. Two kinds of moisture initializations are discussed, and it is shown that if the moisture field is perfectly initialized, i.e., if the moisture can be specified in the most consistent manner, it still takes several hours for the rate of precipitation to become constant, again starting from an initial state adjusted by the balance equation. The reason for this is the lack of initial vertical velocities. The results suggest that vertical velocities initially are of equal or higher importance than details in the moisture.