Going to Extremes
From twisters on the Great Plains to massive rainstorms in the Midwest,
NCAR scientists and colleagues study some of the wildest weather
in person. By taking sophisticated instruments close to the action,
they gather observations to help understand the physical properties,
from tiny to grand scale, that drive severe weather.
Supercells—the powerful thunderstorms that rumble across the
central United States for hours at a time, spawning severe weather
along the way—are a natural target for field study. Storm
researchers at NCAR have joined colleagues elsewhere to send aircraft
in and near thunderstorms while deploying portable radars and other
observing tools at ground level.
NCAR field work has focused on some of the most damaging phenomena
spun out by severe storms, including:
 Tornadoes
In the mid-1990s, NCAR took part in the Verification
of the Origins of Rotation in Tornadoes Experiment (VORTEX), which
trekked across the Great Plains to study how tornadoes form. Since
then, NCAR has collaborated on improvements to Doppler on Wheels,
a set of truck-mounted radars. The radars help profile hurricanes
as well as tornadoes.
Lightning
During the 1980s and 1990s, NCAR cloud physicists
carried out a unique set of expeditions that sent a sailplane in
and near developing thunderstorms to analyze electrical fields
and other phenomena. Another project, called STERAO
(Stratosphere-Troposphere Experiments: Radiation, Aerosols, and
Ozone), brought lightning
and air-chemistry experts together to examine lightning and its
production of nitrogen oxides, a chemical precursor to ozone. In
2000, the Severe
Thunderstorm Electrification and Precipitation Study (STEPS) brought
storm-chasing vehicles, radars, and an armor-protected research
aircraft to the High Plains of Colorado and Kansas, where they
examined low-precipitation supercells and the types of lightning
they produce. STEPS and other field studies have confirmed that
lightning frequency and type can shift abruptly in a thunderstorm,
often at the same time as rain or hail intensifies.
Heavy rain and flooding
Several field studies have focused
on heavy rain from thunderstorms that roam the central and eastern
U.S. The International
H2O Project (IHOP2002) studied the effect of sharp contrasts in water vapor in setting
off thunderstorms and heavy rainfall across the southern Great
Plains. A year later, the Bow
Echo and MCS Experiment (BAMEX) analyzed mesoscale convective systems, which can cover an area
as big as a midwestern state and persist for many hours. BAMEX
also investigated the swaths of high wind that descend from some
of these huge convective systems. It took an array of tools to
study how rainfall varies across a region, or one storm, and assess
the life cycle of long-lived storm episodes that march across the
United States over several days. Studies such as BAMEX rely increasingly
on aircraft, portable radars, and mobile observing systems to get
much-needed data in detail.
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