5.10: Review

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Thermo diagrams are useful for estimating thermodynamic state (pressure, temperature, and moisture) of the air without having to solve equations. There are many different types of thermo diagrams: Emagram, Skew-T, Stüve (or Pseudoadiabatic Diagram), Tephigram, and θ-Z diagram. They all serve the same purpose, and all have isotherms, isobars, isohumes, dry and moist adiabats, and height contours (in some cases).

You can also track state changes caused by physical processes acting on the air. In this chapter you read about processes such as radiative heating and cooling, evaporation and condensation, and precipitation falling into or out of an air parcel. You also learned how to estimate cloud-base altitude from the lifting condensation level, and cloud-top altitude from nonlocal stability and buoyancy. You saw how potential temperature is a convenient way to describe the state of vertically moving air parcels.

Thermo diagrams are often used to plot upperair soundings made with rawinsonde balloons or calculated from computerized forecasts. Soundings plotted on thermo diagrams allow you to find the depth of the mixed layer and the top of the troposphere (i.e., the tropopause). They also allow you to calculate important parameters such as the BruntVäisälä frequency and the Richardson number.

Air flow can change from laminar to turbulent if the flow is unstable. Instability can be due to the vertical variation of temperature alone (as quantified by static stability), or be due to the combined effects of wind and temperature variations with height (as quantified by dynamic stability). By plotting soundings and analyzing stability you can anticipate turbulence such as causes rapid dispersion of air pollutants and transport of heat, moisture, and momentum.