The response of the fluid stably stratified over the infinite slope was investigated by linear theory when finite length 2l in it was heated or cooled. If the angle of the slope was small, the nature of the flow near the slope changed depending on whether the half height of the slope h*S=lsin * (* is angle of slope) was higher than that of thermal boundary layer h*T=a(*/N)1/3l1/3 (**3.5), which was developed over the heat island whose length was 2l, or not. On the real slope h*s>h*T was often

more »

... tisfied at night and the flow was close to the results from Prandtl theory, but h*s<h*T in the daytime so that the flow behaved like a convection.