A Numerical Experiment on the Interaction between Sea Breeze and Valley Wind to Generate the so-called "Extended Sea Breeze"

Abstract

A two-dimensional numerical experiment with sea, plain, slope and plateau and a three-dimensional numerical experiment with sea, plain, slope, valley and plateau were executed to investigate the interaction between the sea breeze and the thermally and topographically induced flow. Generation of the so-called "extended sea breeze (ESB)" was also investigated. In the two-dimensional experiment with sea, plain, slope and plateau, a weak wind towards inland appeared between the sea breeze front and inland slope over the plain whose length was 113.3km. The topography was changed to a valley in the three-dimensional model. The mouth and end of the valley were located 20km and 106.7km from the coastline, respectively. The addition of this valley caused the surface wind in the area between the sea breeze front and the end of the valley to become stronger, and showed the long-range penetration of the ESB. The depth of the wind system in the valley was equal to or greater than the depth of the mixing layer in the valley. The additional experiments in which the width of the valley was changed showed that the wind in the valley was strongest in the narrowest valley. The mechanism was basically consistent with the discussion by Defant (1951). In the case that the distance between the coastline and inland topography was short, the sea breeze was enhanced in the morning; however, the same topography worked to stop the advance of the sea breeze in the late afternoon. The non-linear effect was important to the development of the combined sea breeze and valley wind and the generation of a unified circulation (i. e. the ESB).