Study of the Spacial and Temporal Structure of Turbulence in the Nocturnal Residual Layer

Abstract

Of the planetary boundary layer (PBL) sublayers defined by Stull (1988, pp. 10–11), the nighttime residual layer (RL) may be the least understood. One reason for this is that, unlike the daytime convective boundary layer and surface based nocturnal boundary layer, the RL is in general decoupled from the surface. Consequently, turbulence in the RL does not scale with surface turbulent quantities, and derivation of accurate similarity relationships is difficult, if not impossible. Although qualitative success has been achieved in relating RL turbulence to the gradient Richardson number (Ri) (Mahrt et al., 1979; Lenschow et al., 1987; Kim and Mahrt, 1992), oftentimes these scalings quantitatively fail due to overly coarse vertical differencing in computing Ri (Padman and Jones, 1985). Study of RL turbulence is further complicated by the wide variety of atmospheric forcing mechanisms present during the night. Since nighttime turbulent intensities are small, forcing by radiation, baroclinity, topographic drainage flows, and gravity waves can become important. Variability in each of these leads to a seemingly infinite number of possible RL turbulent time/height structures (e. g., Andre et al., 1978; Garratt, 1985; Lenschow et al., 1978; Heilman and Takle, 1991; Weber and Kurzeja, 1991).