On October 3rd, four Saildrones were launched from Keehi Marine Center in Honolulu, HI to begin a six-month research mission in the tropical Pacific Ocean. This mission is part of a series of Saildrone missions to the tropical Pacific, focusing on how this new technology could best be used within the Tropical Pacific Observing System (TPOS) to improve longterm weather forecasts.
The Saildrones demonstrated their adaptability right at the start of this mission. After the launch, they were scheduled to do some initial testing just offshore of Hawaii. There turned out to be too much commercial and recreational boater traffic in the planned work area. Instead, the pilot redirected the drones to a new area, and the PI’s adapted their testing plans. The major goals of the tests were still successfully accomplished, just in a different location.
Pre-mission tests conducted right after launch included performing a series of checks for the Acoustic Doppler Current Profiler (ADCP). The ADCP measures the currents in the surface ocean, to a depth of about 80m (260ft.). Measuring currents from a platform that is moving through the water is complex, and these initial tests help to ensure the measurements are being made correctly.
The Saildrones visited a PMEL carbon buoy on the east side of Oahu, sailing boxes around the buoy for hours. Measurements made by the Saildrone instruments during this visit were compared to the instruments on the buoy. Particularly, the systems that measure carbon dioxide levels in the air and water were validated, agreeing within 2µatm of the moored system. This is one more way to check that all Saildrone systems are functioning properly before heading out on the science mission.
The Saildrones are underway to the TAO mooring at 9°N, 140°W, and are expected to arrive there by early November. They will spend about a day sailing a box around the buoy. This will allow additional validation against the moored sensors, and also provide information about spatial and temporal gradients around the mooring.
NOAA has issued an “El Niño Watch,” and we hope to capture this warming event on the equator. The latest forecast indicates a 70% – 75% chance that an El Niño is favored to form in the next couple of months, and will continue through the Northern Hemisphere winter 2018 – 2019.
There has been a level of uncertainty in the El Niño forecast so far this year, highlighting one of the primary goals of this mission. This Saildrone project is part of a larger effort (TPOS 2020) to improve the observing system in way that will increase prediction skill for longterm weather forecasts, including for El Niño.