• Remotely-piloted sailboats monitor 'cold

    From ScienceDaily@1:317/3 to All on Thu Jul 8 21:30:34 2021
    Remotely-piloted sailboats monitor 'cold pools' in tropical environments


    Date:
    July 8, 2021
    Source:
    University of Washington
    Summary:
    Researchers used remotely-piloted sailboats to gather data on cold
    air pools, or pockets of cooler air that form when rain evaporates
    below tropical storm clouds. These hard-to-study phenomena are
    thought to have broader effects on tropical weather.



    FULL STORY ========================================================================== Conditions in the tropical ocean affect weather patterns worldwide. The
    most well-known examples are El Nin~o or La Nin~a events, but scientists believe other key elements of the tropical climate remain undiscovered.


    ==========================================================================
    In a study recently published in Geophysical Research Letters, scientists
    from the University of Washington and NOAA's Pacific Marine Environmental Laboratory use remotely-piloted sailboats to gather data on cold air
    pools, or pockets of cooler air that form below tropical storm clouds.

    "Atmospheric cold pools are cold air masses that flow outward beneath
    intense thunderstorms and alter the surrounding environment," said lead
    author Samantha Wills, a postdoctoral researcher at the Cooperative
    Institute for Climate, Ocean and Ecosystem Studies. "They are a key
    source of variability in surface temperature, wind and moisture over
    the ocean." The paper is one of the first tropical Pacific studies to
    rely on data from Saildrones, wind-propelled sailing drones with a tall,
    hard wing and solar- powered scientific instruments. Co-authors on the NOAA-funded study are Dongxiao Zhang at CICOES and Meghan Cronin at NOAA.

    Atmospheric cold pools produce dramatic changes in air temperature and
    wind speed near the surface of the tropical ocean. The pockets of cooler
    air form when rain evaporates below thunderstorm clouds. These relatively
    dense air masses, ranging between 6 to 125 miles (10 to 200 kilometers)
    across, lead to downdrafts that, upon hitting the ocean surface, produce temperature fronts and strong winds that affect their surroundings. How
    this affects the larger atmospheric circulation is unclear.

    "Results from previous studies suggest that cold pools are important for triggering and organizing storm activity over tropical ocean regions,"
    Wills said.

    To understand the possible role of cold pools in larger tropical climate cycles, scientists need detailed measurements of these events, but it
    is hard to witness an event as it happens. The new study used uncrewed
    surface vehicles, or USVs, to observe the phenomena.

    Over three multi-month missions between 2017 and 2019, 10 USVs covered
    over 85,000 miles (137,000 kilometers) and made measurements of more
    than 300 cold pool events, defined as temperature drops of at least 1.5
    degrees Celsius in 10 minutes. In one case, a fleet of four vehicles
    separated by several miles captured the minute-by-minute evolution of
    an event and revealed how the cold pool propagated across the region.

    "This technology is exciting as it allows us to collect observations
    over hard- to-reach, under-sampled ocean regions for extended periods
    of time," Wills said.

    The paper includes observations of air temperature, wind speed, humidity,
    air pressure, sea surface temperature and ocean salinity during cold
    pool events.

    The authors use the data to better describe these phenomena, including how
    much and how quickly air temperatures drops, how long it takes the wind to reach peak speeds, and how sea surface temperature changes nearby. Results
    can be used to evaluate mathematical models of tropical convection and
    explore more questions, like how the gusts created by the temperature difference affect the transfer of heat between the air and ocean.

    ========================================================================== Story Source: Materials provided by University_of_Washington. Note:
    Content may be edited for style and length.


    ========================================================================== Journal Reference:
    1. Samantha M. Wills, Meghan F. Cronin, Dongxiao Zhang. Cold Pools
    Observed
    by Uncrewed Surface Vehicles in the Central and Eastern Tropical
    Pacific.

    Geophysical Research Letters, 2021; 48 (10) DOI:
    10.1029/2021GL093373 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2021/07/210708170337.htm

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