A method for accurate calculation of Showalter index

Since Showalter index is widely applied in convective weather analysis and forecast, it is meaningful to calculate it accurately and rapidly all the time. Based on the rule that equivalent potential temperature is unchangeable during both dry and moist processes, condensation temperature and equivalent potential temperature were calculated using a series of equations provided by David Bolton. Showalter index was computed automatically and accurately by a program in terms of radiosonde data. 11 cases were selected to calculate Showalter index using the new method. Compared with other 5 methods, the new method has characteristics of simple calculation, less average and maximum absolute errors. The possible reasons included two aspects. Many complex derivations and approximation treatments have been avoided. On the other hand, the deduced figures such as the lifting condensation level temperature, the equivalent potential temperature were more accurate than that from other methods. Based on the radiosonde data with MICAPS format from 2010 to 2011at Hankou station in Hubei province, the forecast accuracy of two methods, namely, a table method and the new method in this paper, was compared for thunderstorm. The results show that the missed number of thunderstorm is reduced if a negative Showalter index is used as a factor to show the possible presence of thunderstorm. In addition, a limitation of the new method is also discussed.