Introduction to THEORETICAL METEOROLOGY

The theoretical branch of meteorology is based upon the fundamental postulate that the behavior of the atmosphere is capable of being analyzed and understood in terms of the basic laws and concepts of physics. The three fields of physics which are most applicable to the atmosphere are thermodynamics, radiation, and hydrodynamics. Thermodynamics is the study of the initial and final equilibrium states of a system which has been subjected to a specified energy process or transformation. By “system” we mean a specific sample of matter. It has been found through experiment that the “equilibrium state” of a system can be completely specified for our purposes by a finite number of properties such as pressure, temperature, and volume. These properties are known as variables of state, or thermodynamic variables. An example of the kind of question that can be answered by reference to the laws of thermodynamics is the following: What is the final temperature of 1 gram of air saturated with water vapor, initially at a pressure of 1000 millibars and a temperature of 0° C, if it is allowed to expand without the addition or loss of energy from or to its surroundings until its pressure is 500 millibars ? Note that a definite system is delineated, an initial state is specified, and an explicit process for the energy transformation is given (condensation of water vapor and no exchange of energy with the surroundings); with these data one must determine the final state of the system