An Intercomparison between Reanalysis and Dropsonde Observations of the Total Water Vapor Transport in Individual Atmospheric Rivers

A recent study presented nearly two decades of airborne atmospheric river (AR) observations and concluded that on average an individual AR transports roughly 5×10⁸ kg/s of water vapor. The study here compares those cases to ARs independently identified in atmospheric reanalyses with the dual-purpose of validating reanalysis ARs against observations, and evaluating dropsonde representativeness relative to reanalysis.

The dropsondes transected 21 northeastern Pacific ARs during 6 years over 1998–2016. The reanalysis, ERA-Interim, consists of 5636 ARs detected during 1979–2016 over the domain and days of the year encompassing the observations. The first comparison is based on the 21 dropsonde-observed ARs and those matched in the reanalysis, which indicates a mean reanalysis error of −2% in AR width, and +3% in total integrated water vapor transport (TIVT) and supports the effectiveness of the AR detection algorithm applied to the reanalysis. The second comparison is between the 21 dropsonde ARs and all 5636 reanalysis ARs, which indicates a 5% mean difference in both AR width and TIVT and suggests the limited number of dropsonde observations is a highly representative sampling of ARs in the northeastern Pacific. Sensitivities of the AR width/TIVT comparison to the selection of season and geographic specifications for the reanalysis ARs are also examined.

The results provide a case where dedicated observational efforts in specific regions corroborate with global reanalysis in better characterizing the geometry and strength of ARs regionally and over the globe. The results also illustrate that the reanalysis depiction of ARs can help inform the selection of locations for future observational and modeling efforts.