The 2011 Heat Wave brought a “heat dome” across two-thirds of the United States, causing numerous deaths. Image: NASA |
The
continuing heat wave in the United States in July 2011 has broken
temperature records in many locations, killed dozens and seen nearly
half of all Americans under heat advisories at its peak. These four
movies, created from data from NASA’s Atmospheric Infrared Sounder
(AIRS) instrument on NASA’s Aqua spacecraft for the period from July
16-24, show the movement of a dome of heat across the eastern two-thirds
of the country. They highlight two familiar temperatures: surface air
temperature and surface skin temperature, during both daytime and
nighttime conditions.
Surface
air temperature is something we experience whenever we go outside. High
surface air temperature makes even shady places feel hot. Surface skin
temperature is what we feel when we touch the ground. During daytime,
the surface skin temperature is generally much warmer than surface air
temperature because dark surfaces are so effective at absorbing
sunlight. The surface air and skin temperatures are related by something
invisible but actually quite familiar: infrared?or heat?radiation. Our
skin is very sensitive to infrared radiation, making a sun-heated wall
feel warm even from a few feet away after sunset. Air absorbs very
little sunlight, but easily absorbs infrared radiation emitted by the
warm surface. It’s the sun-warmed surface?not sunlight?that heats the
air during daytime.
The
four movies illustrate the extraordinarily high temperatures in the US
heat wave. Both types of temperature, for daytime and nighttime, are
shown as a difference (anomaly) from the average over the previous eight
years of AIRS data. Over the Northeast and northern Midwest,
temperatures are 20 degrees Fahrenheit warmer than normal. During normal
weather there, daytime surface air temperatures are around 85 degrees
Fahrenheit, while nights cool to around 70 degrees Fahrenheit.
Temperatures 20 degrees above average show daytime highs over 100
degrees Fahrenheit and nighttime lows in the mid-80s. These high
temperatures, along with high humidity (also observed by AIRS but not
shown here), make the central and eastern US one of the hottest regions
on the planet in late July 2011.
AIRS
is managed by NASA’s Jet Propulsion Laboratory, Pasadena, Calif., under
contract to NASA. JPL is a division of the California Institute of
Technology in Pasadena.
