The Dynamics of the Atmospheric Surface Layer

Abstract

The Earth’s surface is a rigid lower boundary of the atmosphere. Due to this, a boundary layer exists in the wind velocity field or in other meteorological elements. Because the air flow is generally turbulent, this is a turbulent boundary layer rather than molecular. Naturally, the influence of the underlying surface is greatest in the air layer immediately adjacent to it, and depends on the distribution of its properties in a horizontal direction. The latter indicates the existence of horizontal gradients of the averaged quantities, which only exceptionally are greater than vertical ones (see below Section 6). That is why in all other sections of this chapter we shall refer only to the case of a horizontally-homogeneous underlying surface — e.g., a vast, even steppe area (bare or evenly covered with one and the same vegetation or a similar type of agricultural tract). This presupposes a uniform distribution of soil characteristics (temperature, moisture, heat conductivity, etc.) which may exert some influence on the atmospheric processes.