Diagnosis and correction of systematic humidity error in a global numerical weather prediction model

Abstract

It was found that significant systematic specific humidity errors exist in the much-used FGGE IIIb analyses. However, when a correction on the analyses was imposed and the PL GSM forecasts rerun, forecast errors similar to the forecast errors generated from the uncorrected analyses were observed. The errors were diagnosed through an evaluation of the tendency terms in the model's specific humidity prognostic equation. The results showed that systematic low-level tropical drying and upper-level global moistening could be attributed to the convective terms and the horizontal and vertical advection terms, respectively. The authors conclude that the nonconvective modifications could be instituted in the model as is. -from Authors