The impact of dropsonde data on the performance of the NCEP global forecast system during the 2020 Atmospheric Rivers observing campaign. Part II: Dynamic variables and humidity

Two experiments were executed for the period from 24 January to 18 March 2020 using the National Centers for Environmental Prediction (NCEP) Global Forecast System version 15 (GFSv15) with a four-dimensional hybrid ensemble-variational (4DEnVar) data assimilation system.

The control run (CTRL) used all of the routinely assimilated data and included data from 628 ARR dropsondes, whereas the denial run (DENY) excluded the dropsonde data. Results from 17 intensive observing periods (IOPs) indicate a mixed impact for mean sea level pressure and geopotential height over the Pacific-North American (PNA) region in CTRL compared to DENY. The overall local impact over the U.S. West Coast and Gulf of Alaska for the 17 IOPs is neutral (20.45%) for integrated vapor transport (IVT), but positive for wind and moisture profiles (0.5%-1.0%), with a spectrum of statistically significant positive and negative impacts for various IOPs.