Remote-controlled ocean drones observe atmospheric cold pools

Atmospheric cold pools are pockets of air cooler than their surrounding environment that form when rain evaporates under thunderstorms. These relatively dense air masses, with a diameter of between 10 and 200 kilometers, lead to downdrafts which, upon reaching the ocean surface, produce temperature fronts and strong winds that affect the surrounding environment. Cold pools over tropical oceans produce large changes in air temperature and wind speed in the planetary boundary layer. But how they affect the wider atmospheric circulation is unclear. To understand the role of cold basins in tropical convection, scientists need detailed measurements of these events; however, observations in hard-to-reach oceanic locations have been lacking.

Unmanned sailboats, or USVs, could be a solution. In a new study, Wills et al. describe the use of Saildrone USVs, wind-powered sailing drones with a large, hard wing, and solar-powered scientific instruments. During three 6-month missions, 10 USVs traveled over 137,000 kilometers in the central and eastern tropical Pacific Ocean regions and measured over 300 cold pool events, defined as temperature drops. at least 1.5 ° C in 10 minutes. In one case, four USVs several miles apart captured the minute-by-minute progress of an event and revealed how the cold pool spread through the area.

The Saildrone USV measured variations in air temperature, wind speed, humidity, pressure, as well as the temperature and salinity of the sea surface. these variables revealed the main characteristics of cold pool events, including the amount and speed with which air temperatures dropped, the time it took for the wind speed to peak, and the dynamics of the air temperatures. changes in sea surface temperature. The results could be used to evaluate mathematical models of tropical convection and explore other questions, such as how gusts of wind at the edge of cold pools affect air- heat fluxes. sea. (Geophysical research letters,, 2021)

—Jack Lee, science writer

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