Useful Equations and Tables in Micrometeorology

This chapter presents useful equations and tables in micrometeorology. Many different units of measure are used to describe water vapor in air, including: relative humidity, vapor pressure, specific humidity, dew-point temperature, mixing ratio, and molar density. Although formulas are available for direct conversion between units, the authors take the approach of first converting the original measurement into vapor pressure and then converting to the desired unit. This may not always be the most efficient approach, but it provides an easy framework for conversion under most circumstances. The most common units for direct measurement of water vapor are relative humidity and air temperature, dewpoint temperature, wet bulb and dry bulb temperature (i.e., psychrometer), and molar density (i.e., infrared analyzer). Density of moist air is dependent on the temperature, pressure, and humidity. It is often computed as the sum of the dry air density and the water vapor density.