The computation of vertically labile energy widely applied in the adiabatic chart starts from the assumption that one and only one element of air rises in some manner through the stationary environment, and this is called the parcel method in S. Petterssen's terminology. Actually the integrated effect of the large number of particles making up the air column should be considered (slice method).
Developing Margules' classical theory on the energy of storm, one⁽¹⁾ of the authors recently calculated one example of “feuchtlabile” energy, taking into account both the ascending and the descending currents and found that the moistlabile energy is very small even in a layer of lapse-rate 3/4_??_, where _??_ is the dry adiabatic lapserate. This is because the descending current consumes the greater part of condensational energy in the atmosphere of conditional instability.
The result is very important and further investigation is desirable. Thus the present authors intend to discuss the potential energy of vertical air column unstably stratified, adopting the slice method of energy computation.
First, consider a heavy cold mass of air 1, above a potentially warmer mass 2. Each dry mass has a uniform lapse-rate smaller than the dry adiabatic and the temperature is discontinuou only at the surface of separation of the two masses. Thus the entropy increases upwards uniformly in each mass and makes a jump at the boundary of the two masses.
The interchange of the masses should occur in the form of vertical mixing, because there exists a relation that the entropy of mass 1 at pressure p₁, is equal to that of mass 2 at p_a.
The result of numerical evaluation is as follows.
The above table shows that the available energy decreases with the stability of the layer.
The problem of moist-labile energy will be reserved for the second part.