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A study of the transfer of heat and water vapour above a surface of short grass
Author(s) -
Rider N. E.,
Robinson G. D.
Publication year - 1951
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49707733305
Subject(s) - water vapor , humidity , atmospheric sciences , convection , apparent temperature , wind speed , bowen ratio , sensible heat , heat flux , meteorology , environmental science , thermodynamics , heat transfer , physics
The profiles of temperature, humidity and wind have been determined by conventional methods in the lowest 2 m of the atmosphere above a close‐cut grass surface, with simultaneous observations of the heat absorbed in the soil and of the short‐wave and long‐wave radiative flux of heat. Twentynine sets of observations were made; the details are given in Appendix I. The ratio of the gradients of temperature and humidity is found to be independent of height, and changes with height of the vertical convective flux of heat and of water vapour are relatively small; the ratio of the coefficients of eddy diffusion of heat and water vapour is therefore independent of height. These coefficients are then assumed equal and the convective fluxes of heat and of water vapour determined (Bowen's method). The fluxes are also determined by an aerodynamic method which assumes equality of the eddy viscosity and the appropriate diffusion coefficient. The results of the two methods agree in most cases, in both stable and unstable stratifications, but there are some exceptions which cannot be explained. Absorption of radiation by the air is investigated. It is shown that this is comparable in effect with convection in the control of temperature and relative humidity. Particular attention is paid to four occasions with very light wind (including two with fog formation) when horizontal mixing appeared to be of major importance. Some examples are presented of wind profiles which do not conform to the law proposed by Deacon. A value between 0.5 and 1.5 is suggested for the critical Richardson number.