Evaluation of Tropical Intraseasonal Variability and Moist Processes in NOGAPS Analyses and Short-term Forecasts

The Navy Operational Global Atmospheric Prediction System (NOGAPS) analysis and operational forecasts are evaluated against the ERA-Interim reanalysis (ERAI) and satellite data, and compared with the GFS analysis and forecasts, using both performance-oriented and physics-oriented metrics. The NOGAPS analysis captures the realistic MJO signals in the dynamic fields and the low-level pre-moistening leading to active convection, but the MJO signals in the relative humidity (RH) and diabatic heating rate (Q1) fields are weaker than those in the ERAI or the GFS analysis. The NOGAPS forecasts, similar to the GFS forecasts, have relatively weak prediction skill of the MJO when the MJO initiates over the Indian Ocean and when active convection is over the Maritime Continent. The NOGAPS short-term forecasts capture the broad-scale pattern of precipitation similar to the CMORPH data, with quantitative regional differences comparable to the GFS forecasts. Further evaluation of the precipitation and column water vapor (CWV) indicates that heavy precipitation develops too early in the NOGAPS forecasts in terms of the CWV threshold, and the NOGAPS forecasts also show a dry bias in the CWV increasing with the forecast lead-time. The vertical profiles of RH reveal a dry bias in the marine boundary layer, which partly explains the poor forecast skill of the MJO. Uncertainty of the moisture bias remains in free atmosphere. Compared to the ERAI, the NOGAPS forecasts have a more top-heavy heating profile with weaker heating below 400 hPa, suggesting the overprediction of stratiform component or the lack of shallow convection. The diabatic heating biases are associated with weaker trade winds, weaker Hadley and Walker Circulations over the Pacific in the NOGAPS forecasts.