Discussion About the Method of CAPE Calculation with Virtual Temperature Correction
Convective available potential energy (CAPE) is an important parameter in severe weather analysis and forecasting. The virtual temperature correction should be used in accurate CAPE calculation. MICAPS and GRADS both choose previous values of level of free convection (LFC) as the integral starting points in CAPE calculation when using virtual temperature corrections. LFC is defined as the altitude in the atmosphere where the temperature difference between air parcel and the environment turns from negative to positive. Using the same altitude of LFC in CAPE calculation with virtual temperature correction, is obviously contrary to the definition of LFC. Theoretical analysis in this paper indicates that LFC changes in CAPE calculation with virtual temperature correction, since two temperature profiles of air parcel and the environment change after correction, and their crossing point (LFC) also changes. The altitude of LFC is usually decreased using virtual temperature correction. Case study shows that although the CAPE increment is not so obvious when using the revised LFC in CAPE calculation with virtual temperature correction, it will be more reasonable in graphical representation and more precise for its physical meaning when considering the variation of LFC.