Comparative studies in the local circulations induced by land-use and by topography

A two-dimensional numerical model with a simplified land-use paramaterization is used to investigate the effects of land use topography on local circulation systems. A criterion is presented indicating the relative importance of land use on local circulations. Land-use contrast in the numerical model is parameterized by moisture availability and roughness length. Numerical experiments were carried out under various atmospheric stabilities with various dimensions for the mountains. Numerical results show the following: (1) Anabatic winds prevail in high mountains, while the land-land breeze is stronger when the horizontal contrast of the heat flux from each land surface is large. (2) In the early morning, anabatic winds tend to prevail over land-land breezes, but the land-land breeze tends to prevail in the later afternoon. (3) While atmospheric stability has a large influence on the mesoscale circulation, the horizontal scale of the mountain is not as important for the intensity of the mesoscale circulation. (4) In strong stable conditions or weak insolation, the anabatic wind tends to be more active than the land-land breeze; namely, the heat flux from inhomogeneous land use becomes a less important factor for the generation of a mesoscale disturbance than the orographic forcing in the case of strong atmospheric stability. (5) The predominant mesoscale circulation is predicted by a criterion based upon the horizontal adjustment theory of the mixed layer. The criterion proposed in this study is based on the mountain height, the ratio of the heat flux from the different land use patterns, the atmospheric static stability, and the time-integrated heat flux. The criterion gives results that generally agree with the numerical results.