Aspects of micrometeorology

Abstract

This chapter reviews some aspects of micrometeorology, the study of atmospheric physics on the scale of vegetation canopies. In Environmental Physics micrometeorology has been very effectively used to study hydrology, environmental physiology, and ecology. The turbulent boundary layer that develops over extensive soil and vegetation surfaces grows at a rate depending on surface roughness and atmospheric stability. Properties of turbulence are discussed, leading to a review of the principles of the eddy covariance method of studying rates of turbulent transfer of heat mass and momentum (fluxes) in the surface boundary layer. Instrumentation requirements for, and corrections necessary to eddy covariance measurements, are summarized. The less direct method of studying turbulent fluxes by relating analyzing mean vertical gradients (profiles) of windspeed, temperature, and mass concentration is also reviewed. Roughness parameters depending on vegetation height and structure influence profile properties. Aerodynamic resistance is derived as a quantity relating momentum flux to windspeed gradients. The influence of atmospheric stability on profiles and therefore on fluxes is reviewed, including issues encountered when measuring close to vegetation elements. Principles of the aerodynamic and Bowen ratio methods for estimating fluxes from gradients are reviewed, and the strengths and weaknesses of eddy covariance and flux-gradient methods are summarized. Finally, aspects of turbulent transfer in vegetation canopies are discussed.