The NLCs are playing a game of hide-and-seek this season, bemusing regular observers.
Jan. 8, 2021:
They’re back. Noctilucent clouds (NLCs), recently missing, are once again circling the South Pole. And, in an unexpected twist, they’ve just appeared over Argentina as well.
“This is a very rare event,” reports Gerd Baumgarten of Germany’s Leibniz-Institute of Atmospheric Physics, whose automated cameras caught the meteoritic clouds rippling over Rio Grande, Argentina (53.8S) on Jan. 3rd:
A second camera recorded the clouds at even higher latitude: Rio Gallegos (51.6S). At this time of year, noctilucent clouds are supposed to be confined to the Antarctic–not Argentina. In the whole history of atmospheric research, NLCs have been sighted at mid-southern latitudes only a handful of times.
“Personally, I am thrilled to see NLCs in Argentina, as I had not expected them to occur so far north,” says Natalie Kaifler of the German Aerospace Center (DLR), who operates a lidar (laser radar) alongside one of Baumgarten’s cameras.
Kaifler’s lidar “pinged” the clouds during the display and confirmed that they are genuine NLCs. Echoes pinpointed their altitude more than 80 km above Earth’s surface:
Above: The ~hour-long oscillations in these lidar echoes may be caused by gravity waves propagating upward from the Andes 82 km below.
NLCs are Earth’s highest clouds. They form when summertime wisps of water vapor rise up from the poles to the edge of space. Water crystallizing around specks of meteor dust ~83 km above Earth’s surface create beautiful electric-blue structures, typically visible from November to February in the south, and May to August in the north.
This season has been unusual, though. The normal onset of NLCs over the South Pole has been delayed for more than a month as strange weather patterns played out above Antarctica. Now, suddenly, they’re back, and showing up in unexpected places.
Baumgarten has set up two cameras in southern Argentina to catch unexpected NLCs. “If it happens again,” he says, “we’ll let you know.” Stay tuned!
via Tallbloke’s Talkshop
January 14, 2021 at 07:09AM