Performance of NOGAPS on the Predictions of tropical cyclones using different convective parameterization schemes

The Arakawa-Schubert (A-S) scheme (Arakawa and Schubert 1974) and the Emanuel scheme (Emanuel 1991) for cumulus paramterization are tested in the Navy Operational Global Atmospheric Prediction System (NOGAPS) with T79 spectral representation and 24 vertical levels. Predictions of the six tropical cyclones in August of 1998 are evaluated. The overall performance of NOGAPS using the Emanuel scheme is better than that using the A-S scheme. The average position error at 120 h is 358 NM using the Emanuel scheme verse 416 NM using the A-S scheme. The precipitation patterns generated by NOGAPS using the Emanuel scheme over the U. S. continent compare more favorable with the NCEP rain analysis than the A-S scheme and the Emanuel scheme generates more realistic precipitation associated with tropical cyclones. The Emanuel scheme alleviates the problem of vertical de-coupling occured in some weak storms using the A-S scheme, but it does not improve the poor performance of NOGAPS on the irreular motion of Typhoon Rex in the western Pacific. The drawback of the A-S scheme may be attributed to the lack of downdraft in the current version of the scheme used in NOGAPS. More analyses will be reported.