June 9, 2013
NASA AIM Satellite Spots First Noctilucent Clouds Of 2013
redOrbit Staff & Wire Reports — Your Universe Online
These clouds, which NASA calls “a delight for high-latitude sky watchers,” were spotted by NASA´s AIM spacecraft on May 13th — one week earlier than previous seasons, and possibly earlier than ever before, Cora Randall of the Laboratory for Atmospheric and Space Physics at the University of Colorado said in a statement.
The early start has scientists puzzled because of the solar cycle. Experts have long known that NLCs typically peak during solar minimum and are at their lowest during solar maximum. This year, however, the clouds have arrived early, even though the fact that the solar cycle is near its minimum suggests that they should have started later.
Noctilucent clouds, which were first observed in the middle of the 19th century, are typically seen in the sunset sky. They were first spotted following the eruption of the Krakatoa volcano, following the spread of volcanic ash throughout the atmosphere. In fact, according to NASA, some experts initially believed that the NLCs were a side-effect of the eruption. However, once the volcano quieted down, the clouds remained.
“They've been with us ever since,” Randall said. “Not only that, they are spreading.”
The causes of noctilucent clouds were still a mystery when the AIM satellite launched back in 2007, NASA said. Although scientists knew they formed nearly 52 miles above the Earth´s surface, it wasn´t until AIM began its mission that they were able to connect some of the dots and learn more about the nature of NLCs.
“It turns out that meteoroids play an important role in the formation of NLCs,” James Russell, the principal investigator of AIM and a professor at Hampton University, explained. “Specks of debris from disintegrating meteors act as nucleating points where water molecules can gather and crystallize.”
As it turns out, the clouds appear during the summer months because it´s during that time that water molecules rise from the lower atmosphere and mix with the so-called meteor smoke. In addition, the upper atmosphere is at its coldest during the summer. During the 1800s, NLCs were typically only observable in high latitudes, but they have spread southward in recent years — a phenomenon some researchers have linked to climate change.
“When methane makes its way into the upper atmosphere, it is oxidized by a complex series of reactions to form water vapor. This extra water vapor is then available to grow ice crystals for NLCs,” Russell said. “Half-a-world away from where the northern NLCs are forming, strong winds in the southern stratosphere are altering global circulation patterns. This year more water vapor is being pushed into the high atmosphere where NLCs love to form, and the air there is getting colder."
“All of this has come as an interesting surprise for us,” he added. “When we launched AIM, our interest was in the clouds themselves. But now NLCs are teaching us about connections between different layers of the atmosphere that operate over great distances. Our ability to study these connections will surely lead to new understanding about how our atmosphere works.”