Object-Based Analysis and Verification of WRF Model Precipitation in the Low- and Midlatitude Pacific Ocean

Abstract

An extended version of the Method for Object-based Diagnostic Evaluation (MODE) was used to perform a verification of precipitation provided by the Weather Research and Forecasting (WRF) model Tropical Channel Simulation (performed by NCAR). Model 3-hourly precipitation accumulations were compared to the Tropical Rainfall Measuring Mission (TRMM) 3B42 satellite-derived precipitation in the low- and midlatitude Pacific Ocean during 1998?2000. Overall, the spatial distribution of annual mean precipitation (i.e., the clear shape of the ITCZ with two maxima?one located in the east and one in the west) was reproduced well by the WRF model; however, there was considerably more precipitation in the WRF simulation than in the TRMM dataset. Object-based analysis identified more precipitation objects with life spans less than 30 h and fewer objects with life spans longer than 60 h in the TRMM dataset compared to the WRF simulation. Objects with the longest life span (>90 h) tended to occur in similar regions in both the modeled and satellite-derived datasets. Two of these regions were in the western part of the domain and one was in the eastern portion of the ITCZ, although these regions did not necessarily coincide with the regions of maximum precipitation accumulations. Both datasets had mostly eastward movement in the midlatitudes. The datasets, however, diverged around the central part of the ITCZ where the TRMM dataset displayed both eastward and westward movement, while westward movement was dominant in the WRF simulation. The analysis also showed that precipitation object trajectories were smoother in the model than in the TRMM dataset.