スペクトル法による海陸風数値モデルの構築

Abstract

A numerical model of the land and sea breeze which is based on the spectral method is proposed. This spectral model provides the diurnally cyclic solution without daily trends corresponding to the diurnally cyclic thermal boundary condition. The model takes the dependence of the eddy exchange coefficient on the atmospheric stability into account. In order to obtain the convergent solution properly by an iterative process, some elaboration is devised in the numerical aspects. Although the present model assumes a flat terrain and uniform field in the direction parallel to the coastline, the model simulates well the observed features of the land and sea breeze if observational sites satisfy the topographic conditions assumed in the model. It is evident from numerical experiments with the present model that the strength of land and sea breezes increases linearly with the temperature contrast between land and sea. Experiments with larger temperature contrast do not always provide the convergent solution for narrower land and/or sea configurations. Inclusion of the stationary components for the spectral model generates the feature of the land and sea breeze superposed on the stationary horizontal convection. However, the experiment with the present spectral model, when including the stationary components, results in divergence of the iterative process for a much smaller amplitude of temporal variation of the prescribed ground surface temperature than does the experiment excluding the stationary components.