Multiscale evaluation of NCEP and CRUNCEP data sets at 90 large U.S. cities

Abstract

The data sets of National Centers for Environmental Prediction (NCEP I and II) and Climatic Research Unit - NCEP (CRUNCEP) were evaluated by comparing against observational data from the National Oceanic and Atmospheric Administration at monthly and annual scales, site, and regional scales. The evaluations were conducted for air temperature (maximum, mean, and minimum) and precipitation at the 90 largest cities across the United States. At annual scale, NCEP I, NCEP II, and CRUNCEP were slightly yet significantly underestimated for mean temperature (1%) and maximum temperatures (1%). The NCEP I was significantly underestimated for minimum temperature (1%) while overestimated for total precipitation (16%); the NCEP II was significantly underestimated for minimum temperature (2%) and total precipitation (2%); the CRUNCEP was significantly overestimated for minimum temperature (2%) and total precipitation (6%). At monthly scale, three data sets were underestimated for a majority of months in terms of monthly mean temperature, monthly maximum temperature, monthly minimum temperature, and monthly total precipitation except an overestimation of CRUNCEP on minimum temperature (48%) and monthly total precipitation (43%). At the seasonal scale, three data sets had smaller biases in summer season and larger biases in winter season for temperature, while larger biases in summer season and smaller biases in winter seasons for precipitation. Overall, the CRUNCEP data set had a slightly better performance than NCEP I and NCEP II data sets. This multiscale evaluation of the three most widely used regional climate data sets provides insightful information for atmospheric science studies, particularly urban heat impact investigation.