The Rocketsonde Buoy System (RBS) is a new atmospheric observation system being developed for deployment in the in-situ data-poor region west of N. America. It is one of the in-situ sounding systems being developed under the umbrella of THe Observing-system Research and Predictability Experiment (THORpex). A network of buoys would be moored in the deep Pacific Ocean, each of which would hold about 200 weather rockets in sealed launch tubes. Every day within a synoptic observation window, one rocket would be launched from each buoy into the mid-troposphere. An automatic launch-control system would monitor buoy tilt, heave, and surface winds, and would initiate launch at the optimum time.

Each rocket consists of a Vaisala rocketsonde payload in a custom-designed composite and aluminum body of length about 2m and diameter 54 mm. A dual-pulse single-stage solid-fuel motor accelerates the rocket Mach 1.5 twice during 2 s burns, and the rocket then coasts for 30 s to apogee. After separating at apogee, the sonde descends by parachute while transmitting temperature, humidity, and pressure observations to the buoy. The buoy relays the atmospheric sounding, surface weather, and ocean-surface data by satellite to shore, where it is added to the Global Telecommunications System.

To determine the potential impact of this system on numerical-weather-prediction (NWP), Observing System Simulation Experiments (OSSEs) were performed to find the optimum RBS design and deployment. Each OSSE starts with an Eta analysis, inserting virtual in-situ atmospheric soundings at selected locations over the NE Pacific Ocean, and then assimilating this data into the initial conditions for a 60-hour NWP. The NCAR/Penn State MM5 model is used for these OSSEs, and the resulting NWP forecasts are verified downstream against subsequent Eta analyses over data-rich North America. Eta data from Winter 2001-2002 and Summer 2002 are used for this study.

Results show that western North America paid a penalty of between 20% and 35% in forecast accuracy during the 2001-2002 winter storm season, caused by the upstream data-poor region over the NE Pacific. This penalty is reduced significantly with the following optimum system: 6 buoys arrayed in a cross centered near 50N 142W, each with one sounding per day at 12 UTC during only the Fall-Winter-Spring storm season, with sounding height to 6 km (although 4 km may be adequate). If this optimum system is not economically feasible, then a minimal system of 3 buoys roughly 200 to 300 km west of the British Columbia and Washington coasts would still offer some NWP improvement over N. America, and would help protect existing coastal radiosonde soundings from being rejected during the quality-control phase of operational data assimilation. If government economics preclude adding any new stations, then some net improvement is still possible by keeping the existing number of N. American radiosonde stations, but spreading them to cover both N. America and the N.E. Pacific Ocean.