Impacts of Northeastern Pacific Buoy Surface Pressure Observations

Abstract Under the Atmospheric River Reconnaissance (AR Recon) Program, ocean drifting buoys (drifters) that provide surface pressure observations were deployed in the Northeastern Pacific to improve forecasts of US West Coast high-impact weather. We examine the impacts of both AR Recon and non-AR Recon drifter observations in the US Navy’s global atmospheric data assimilation (DA) and forecast system using data denial experiments and Forecast Sensitivity Observation Impact (FSOI) analysis, which estimates the impact of each observation on the 24-h global forecast error total energy. Considering all drifters in the eastern North Pacific for the 2020 AR Recon season, FSOI indicates that most of the beneficial impacts come from observations in the lowest quartile of observed surface pressure values, particularly those taken late in the DA window. Observations in the upper quartile have near neutral impacts on average and are slightly non-beneficial when taken late in the DA window. This may occur because the DA configuration used here does not account for model biases, and innovation statistics show that the forecast model has a low-pressure bias at high pressures. Case studies and other analyses indicate large beneficial impact coming from observations in regions with large surface pressure gradients and integrated vapor transport, such as fronts and ARs. Data denial experiments indicate that the assimilation of AR Recon drifter observations results in a better-constrained analysis at nearby non-AR Recon drifter locations and counteracts the NAVGEM pressure bias. Assimilating the AR Recon drifter observations improves 72-h and 96-h Northern Hemisphere forecasts of winds in the lower and middle troposphere, and geopotential height in the lower, middle, and upper troposphere.