Analysis of the observations of long‐wave radiation from clear skies, R, made by Dines at Benson, yields a correlation coefficient of 0·99 between R and the black‐body radiation at the corresponding screen temperature T. A new series of measurements over wider ranges of temperature and humidity confirms this, with the same value for the correlation between R and σT4, the regression equation being: R = −17·195 σT4 (milliwatt cm−, T °K). An alterlative representation of equals accuracy is R = 5·31.10−14 T−6 (Milliwatt cm−2, T°K) The latter formulation is probably better founded physically, and brings out the temperature dependence of the ‘effective emissivity’ ϵ (i.e. R/σT4), which the atmosphere must exhibit. Either expression provides an estimate of R in terms of T with a probable error less than 0·5 mw cm−2. The present analysis omits any explicit reference to the influence of vapour pressure e on R, and so differs essentially from those due to Brunt and Angström. Re‐appraisal of these latter suggests that the relationships established therein between * and e result basically from a correlation between temperature and humidity. Both the nature and the degree of the correlation between RσT4 and e for a given locality would then depend on the temperature‐humidity regime occurring there. The wide variations from place to place, both in the values of the coefficients occurring in the Brunt and Angström equations, and in the degree of correlation found between R/σT4 and the corresponding function of e, are thereby explained.
SUMMARYA description is presented of the experimental techniques used on four micrometeorological expeditions. The instrumentation was designed to provide half-hourly mean values of wind speed, temperature and humidity at a number of levels up to 16 metres, and of the vertical fluxes of heat, water vapour, net radiation and sensible heat into the ground. The observational material is to be published separately.Analysis of the observations, all for the unstable case, shows close similarity between the turbulent transfer processes for heat and water vapour over the whole range of stability represented by the measurements. Both are more strongly influenced by instability than the exchange of momentum, the difference in behaviour becoming more marked with increasing instability. It is suggested that the similarity between heat and water vapour transfer is due to a correlation between the temperature and specific humidity of the air which originates at the evaporating surface.
SUMMARYFrom a definition and a hypothesis the form of the wind profile in the turbulent boundary layer when the air is thermally stratified is derived as or, in integrated form, in the usual notation.This solution is expected to be applicable in all stabilities and to all heights below which the shearing stress and the vertical heat flux remain constant.A critical examination of the experimental procedure necessary to test the validity of this, or of any, formulation for the steady-state wind profile leads to a specification which the observational site and the weather conditions should meet.The results of a series of experiments are presented and analysed. These comprise measurements of wind speed and temperature at a number of levels up to 16 metres, supplemented by observations of net radiation, heat flux into the air and into the ground, and shearing stress. The analysis affords good verification of the form proposed for the wind profile.A variety of evidence is adduced to show that buoyancy modifies the transfer of heat more strongly than that of momentum, and that the discrimination increases with height above the surface.
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