ECMWF Newsletter #163

Drifting buoys deployed in the northeast Pacific

David Lavers
Bruce Ingleby (both ECMWF)
Luca Centurioni
Anna Wilson
Marty Ralph (all Scripps Institution of Oceanography, US)
Aneesh Subramanian (University of Colorado Boulder, US)

 

In January and February 2020, 64 drifting buoys were deployed in the northeast Pacific Ocean. For ECMWF, a key feature of these buoys is their pressure sensors, which provide valuable sea-level pressure observations in this data-sparse region. These pressure measurements are crucial for numerical weather prediction because (1) pressure at mean sea level is an important variable linked to the main mode of extratropical synoptic variability; (2) in many ocean areas there are very few other in-situ observations; and (3) satellite data still only provide a small amount of information about pressure at mean sea level. The buoys can operate for up to two years and are a cost-effective component of the global observing system. Unfortunately, up to 50% of drifting buoys globally still do not have pressure sensors.

This latest mission to increase the number of buoys in the northeast Pacific was part of the Atmospheric River Reconnaissance (AR Recon) field campaign and was funded by NOAA’s Global Drifter Program, the California Department of Water Resources, and the U.S. Army Corps of Engineers. Two types of buoys were deployed: 16 Directional Wave Spectra Barometer drifters (DWSB; https://gdp.ucsd.edu/ldl/dwsbd/) and 48 Surface Velocity Program Barometer drifters (SVPB; https://gdp.ucsd.edu/ldl/svpb/). This year marks the first time that the DWSB drifters were deployed. Like the SVPB drifters, the DWSB drifters measure sea-surface temperature and barometric pressure; however, DWSB drifters also compute the directional wave spectrum via a high-performance GPS engine. The Center for Western Weather and Water Extremes (CW3E) and the Lagrangian Drifter Laboratory, both at Scripps Institution of Oceanography, led the deployment planning, with input provided by ECMWF, the University of Colorado Boulder, and the United States Air Force. This latest deployment follows 32 SVPB buoys which were launched during AR Recon in January 2019 (ECMWF Newsletter No. 159), of which 24 were still reporting in February 2020. The total number of AR Recon- launched buoys reporting in February 2020 was thus 88.

This year, two platforms were used to release the buoys: a ship of opportunity releasing buoys every 100 km from Los Angeles to Honolulu and from Honolulu to San Francisco; and US Air Force flights to the northeast of Hawaii. These extra buoys benefit the ECMWF Integrated Forecasting System across the northern Pacific Ocean and may improve forecast skill over Europe in the medium range. The AR Recon campaign also involves releasing dropsondes and radiosondes into storm systems with the aim of improving forecasts of storms and extreme precipitation in the western United States. An evaluation of the impact of the 2019 buoy deployment is under way.

Drifting buoys in the northeast Pacific. The figure shows the location of all drifting buoys in the northeast Pacific Ocean in February 2020. These buoys provide valuable observations of sea-surface temperature, and in this ocean area 53% of them also have pressure sensors.