Evaluation of landfalling atmospheric rivers along the U.S. West Coast in reanalysis data sets

Abstract

AbstractAn intercomparison of landfalling atmospheric rivers (ARs) between four reanalysis data sets using one satellite‐derived AR detection method as a metric to characterize landfalling atmospheric rivers (ARs) along the U.S. West Coast is performed over 15 cool seasons (October–March) during the period from water years 1998 to 2012. The four reanalysis data sets analyzed in this study are the Climate System Forecast Reanalysis (CFSR), Modern‐Era Retrospective Analysis for Research and Applications (MERRA), ERA‐Interim (ERA‐I), and the Twentieth Century Reanalysis version 2 (20CR) data set. The Atmospheric River Detection Tool is used to identify AR features in the total vertically integrated water vapor (IWV) data of the reanalysis data, and validation of the reanalysis AR data are compared with AR data derived from satellite IWV observations. The AR landfall data from reanalysis were generally found to be in good agreement with satellite observations. Reanalysis data with less (CFSR) or no assimilation (20CR) of the satellite data used in this study had greater bias with AR characteristics such as IWV, width, and landfall location. The 20CR ensemble data were found to better characterize the AR landfall characteristics than the 20CR ensemble mean although all 20CR data underestimated AR landfalls particularly in the southern section of the U.S. West Coast. Overall AR landfall detections for the 15 year cool season period were within 5% of the satellite for the CFSR, MERRA, and ERA‐I data.