ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Archive > Volume 41 Issue 10 > 2015,41(10):1260-1267. DOI:10.7519/j.issn.1000-0526.2015.10.009 Prev Next
Comparative Study on Numerical Computation of Showalter Index
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Abstract:
Three computational schemes for pseudoequivalent potential temperature (PEPT) are compared, the influences of PEPT on the computational accuracy of Showalter index (SI) are analyzed, and highaccuracy computation schemes of SI are proposed. First, the airparcel temperature and pressure at the lifted condensation level are calculated on the basis of the conservation property of potential temperature and mixing ratio during dry adiabatically lifting process. Then, Bolton formula is used to calculate the initial PEPT at 850 hPa. Next, Stackpole iteration algorithm is employed to look for the airparcel temperature at 500 hPa lifted adiabatically from 850 hPa keeping PEPT conservational, and thus SI can be finally solved. It is found that the computational error of PEPT constitutes an important part of the error of SI, therefore it is quite necessary to utilize accurate formula to compute PEPT. Comparison shows that the Bolton formula and LRC formula are more precise than the conventional Rossby formula to calculate PEPT. The PEPT at 850 hPa calculated by the classic Rossby formula is systematically lower than that using the other two formulas, and the error increases with the increasing of air temperature and humidity. Consequently, the mean absolute error of SI decreases from 0.66℃ using Rossby formula to 0.45℃ using Bolton formula. In comparison with the previous studies, the computation scheme proposed in this paper shows improved accuracy, feasibility in programming, and encouraging potential in operational practices of convective weather forecasting.
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