Scientists Studying Wintry Ice in Summer Clouds
Research Center) Winter is here, snow is falling in many areas of
the country, and some of us are already wishing for the return of
hot summer days. But, would you believe that even on the hottest
summer day the temperature inside some clouds remains icy and winter-like,
producing temperature readings as cold as negative 70 degrees Celsius
(negative 94 degrees Fahrenheit)? Would you also believe that the
ice crystals that form at the top of big summertime clouds may help
scientists predict next winter’s snowstorm?
here is a profile of ice crystals, showing the diversity
of their shapes. The larger crystals toward the bottom of
the image occur at warmer temperatures (approximately -37
degrees Celsius, or -34.6 Fahrenheit), while the smaller
images at the top occur at colder temperatures (approximately
-49 Celsius, or -52.6 Fahrenheit). At nearly 150 micrometers
wide, some of the largest ice crystals in this image are
about as thick as three strands of human hair.
by Andrew Heymsfield / NASA Photo
scientists from NASA’s Langley Research Center in Hampton, Va.
and Goddard Space Flight Center in Greenbelt, Md. published a
paper in the Journal of Geophysical Research on the importance
of classifying ice crystals within the big summertime clouds,
or convective cloud systems, as observed during a Florida-based
research campaign. In their paper, the scientists showed that
their instruments can identify the ice crystals and now they can
begin to classify the crystals. By learning to classify the ice
crystals in clouds, these scientists hope to contribute to improving
weather and climate models, the complex computer programs used
to show future atmospheric conditions.
climate computer models are complex because they must account
for hundreds of variables, including many that seem completely
unpredictable. Vincent Noel, a research scientist with Analytical
Services and Materials at NASA Langley and the author of the journal
article, explains, "Usually climate prediction means predicting
the evolution of temperature, pressure, relative humidity, and
plenty of other variables, over small (a few days) and large (a
few centuries) timeframes. However, to predict all this stuff
with enough accuracy, we need to take into account clouds — and
for the time being, clouds are the most important source of uncertainty
in climate prediction."
that clouds represent so much scientific uncertainty, some NASA
scientists and other researchers decided to study tropical convective
clouds in Florida, a type of large cloud system very common in
that area. Their research project, called CRYSTAL-FACE (Cirrus
Regional Study of Tropical Anvils and Cirrus Layers-Florida Area
Cirrus Experiment), took place in the summer of 2002 throughout
the state of Florida and the Gulf of Mexico, with the immediate
goal of studying all aspects of the unique convection cloud formations
from aircraft, land and satellite-based instruments.
If you have
spent a day at Disney World in Orlando, or if you have relaxed
on the beaches of South Florida, you have likely seen convective
or heat-generated clouds. These clouds form when the Sun’s rays
warm the ground, causing hot air to rise, and condense into clouds.
They are unique because they are massive in size, at times ranging
from 100 to 200 km wide (62 to 124 miles); they form and dissipate
very quickly, in as little as two hours; and they can be extremely
thick, reaching 15 km (9.3 miles) in height, which is 6 km (3.7
miles) taller than Mt. Everest.
At the top
of the convective clouds are cirrus clouds made of ice crystals.
These crystals effect weather and climate in two ways: first,
depending on the ice crystal’s shape, it affects the amount of
Sun’s energy reflected or trapped near Earth’s surface; and second,
in their relationship with ozone destruction in the upper atmosphere
of all this solar radiation, the Earth gets hot," said Noel.
"When any body is hot, it radiates infrared light."
Infrared is light at one end of the spectrum, and people use infrared
goggles to see things in the dark (which is how you can see people
in the dark using infrared goggles). "Clouds trap this infrared
radiation, absorb it, and re-emit it later; this is called the
greenhouse effect." Clouds, specifically cirrus clouds, are
the reason that a lot of infrared radiation stays near Earth instead
of going into space.