Comparative Studies In The Local Circulations Induced By Land-Use And By Topography

A two-dimensional numerical model witha simplified land-use paramaterizationis used to investigate the effects of land usetopography on local circulationsystems. A criterion is presented indicating therelative importance of land use onlocal 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 fluxfrom each land surface is large. (2) In the early morning, anabatic winds tend to prevailover 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, thehorizontal scale of the mountain is not as important for the intensity of the mesoscalecirculation. (4) In strong stable conditions or weak insolation, the anabatic wind tendsto be more active than the land–land breeze; namely, the heat flux from inhomogeneousland use becomes a less important factor for the generation of a mesoscale disturbancethan the orographic forcing in the case of strong atmospheric stability. (5) The predominantmesoscale circulation is predicted by a criterion based upon the horizontal adjustmenttheory of the mixed layer. The criterion proposed in this study is based on the mountainheight, the ratio of the heat flux from the different land use patterns, the atmospheric staticstability, and the time-integrated heat flux. The criterion gives results that generally agreewith the numerical results.