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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