April 17, 2014
NASA’s AIM Mission Unlocks The Secrets Of Noctilucent Clouds
[ Watch the Video: Unexpected Teleconnections in Noctilucent Clouds ]
April Flowers for redOrbit.com - Your Universe Online
When you think about the North and South poles, they seem to be worlds apart. They are separated by four oceans, six continents, and more than 12,000 nautical miles.
AIM has revealed "teleconnections" in the planet's atmosphere that stretch from the North Pole to the South Pole, and back again. These teleconnections link weather and climate more closely than one might infer from simple geography.
Cora Randall, AIM science team member and Chair of the Dept. of Atmospheric and Oceanic Sciences at the University of Colorado, says, "We have found that the winter air temperature in Indianapolis, Indiana, is well correlated with the frequency of noctilucent clouds over Antarctica."
As Earth's highest clouds, noctilucent clouds (NLCs) form at the edge of space 51 miles over the polar regions. Located in a layer of the atmosphere known as the mesosphere, NLCs are seeded by "meteor smoke" and consist of tiny ice crystals that glow electric blue when sunlight pierces through the cloud-tops.
Launched in 2007 to investigate the "night-shining" clouds, AIM's mission is to discover how the NLCs form, and to learn more about their inner chemistry. There are always surprises when exploring the unknown, however, and the surprise from AIM is teleconnections.
"It has been a surprise," says Hampton University professor of atmospheric and planetary science James Russell, Principal Investigator of the AIM mission. "Years ago when we were planning the AIM mission, our attention was focused on a narrow layer of the atmosphere where NLCs form. Now we are finding out this layer manifests evidence of long-distance connections in the atmosphere far from the NLCs themselves."
The Antarctic mesosphere is linked to the Arctic stratosphere by one of the teleconnections.
"Stratospheric winds over the Arctic control circulation in the mesosphere," explains Randall. "When northern stratospheric winds slow down, a ripple effect around the globe causes the southern mesosphere to become warmer and drier, leading to fewer NLCs. When northern winds pick up again, the southern mesosphere becomes colder and wetter, and the NLCs return."
NLCs are usually abundant during the winter months, however, this past January AIM detected a sudden and unexpected decline in the clouds. The researchers found it interesting that approximately two weeks prior, winds in the Arctic stratosphere were strongly perturbed, leading to a distorted polar vortex.
"We believe that this triggered a ripple effect that led to a decline in noctilucent clouds half-way around the world," says Laura Holt of the University of Colorado's Laboratory for Atmospheric and Space Physics. "This is the same polar vortex that made headlines this winter when parts of the USA experienced crippling cold and ice."
After a careful examination of meteorological data, Holt discovered that there was indeed a statistical link between winter weather in the US and the decline in noctilucent clouds over Antarctica.
"We picked Indianapolis as an example, because I have family living there," says Randall, "but the same was true of many northern cities: cold air temperatures on the ground were correlated with NLC frequencies high above Antarctica two weeks later," she says.
Two weeks is apparently the time it takes for the teleconnection signal to propagate through the three layers of atmosphere—troposphere, stratosphere and mesosphere—and from pole to pole.
The topic remains challenging, but the team is sure that this much is clear: "NLCs are a valuable resource for studying long-distance connections in the atmosphere," says Russell, "and we are just getting started."