AERMOD Tech Guide

Gaussian Plume Air Dispersion Model

3.1.1 Sensible Heat Flux(H) in the CBL

The fluxes of heat and momentum drive the growth and structure of the PBL. To properly characterize the PBL one first needs a good estimate of the surface sensible heat flux (H) which depends on the net radiation (Rn ). When the net radiation is positive for a given hour AERMET n defines the PBL as convective (net radiation is either measured or estimated as a function of cloud cover, solar angle, albedo, and surface temperature). In the CBL, a simple energy balance approach (as in Oke, 1978) is used to derive the following expression for H:

Equation (1)

The underlying assumption in eq.(1) is that the soil heat flux is 10% of the net radiation. If measured values for Rn are not available, Rn can be estimated from the insolation and the thermal n n radiation balance at the ground following the method of Holtslag and Van ulden (1983) where the insolation for clear skies, Ro , is calculated from Collier and Lockwood (1975).

Equation (2)
Equation (3)

Solar radiation, R, corrected for cloud cover is taken from (Kasten and Czeplak, 1980):

Equation (4)
Equation (5)