Distribution of wet bulb potential temperature in latitude and altitude

Abstract

If potential temperature is denoted by θ and wet bulb potential temperature by θ', then log θ is proportional to the entropy of dry air and log θ' to the entropy of the mixture of air and water vapour. Because air is compressible, entropy is a guide to its motion, and Sir Napier Shaw was the first to prepare a diagram of the variation of log θ or θ with latitude and height, and to use it as a text on which to expound the stratification of the atmosphere. When, however, cloud in convection penetrates the air strata, log θ' takes the place of log θ as an operative factor. A world picture of θ' is required to complement that of θ.