Sky Anomaly

  • Sometime around the stroke of midnight on February 17, weather radars on the island city of Key West in Florida were swarmed not by a gust of wintry showers, but by a storm of migrating birds.

    At one point blanketing the entire island, this flock’s radius stretched at least 145 kilometres (90 miles) wide, according to local meteorologists.

    A GIF produced by the local National Weather Service (NWS) station shows the massive cloud of migrating birds in green and yellow, along with a smattering of rain in darker blue.

    “Key West radar has had a busy night, but not because of weather,” NWS Key West tweeted.

    “The most impressive display of migratory birds so far this year occurred overnight.”

    This massive migration, which can include hundreds of thousands – if not millions – of birds, takes place starting around February each year, but it usually occurs under the cover of night while we’re busy sleeping.

    Over the next few months, researchers from Cornell University figure more than 118 species of bird will start returning to North America after wintering in Central and South America or the Caribbean, including sandpipers, sparrows, orioles, flycatchers, warblers, martins and thrushes.

    Still, even in such huge numbers, these birds are stealthier than you’d think. Traversing huge distances using only the stars and Earth’s magnetic field as guides, conditions have to be just right for us or our radars to notice anything peculiar.

    Incidentally, it was a remarkably still night when Key West was smothered by a migrating flock from Cuba.

    “There was kind of a stable layer of air above us that was deflecting the radar beam closer to the surface,” meteorologist Kate Lenninger told the Tampa Bay Times.

    “So, we were able to pick up more low level objects.”

    In this case, that meant birds upon birds upon birds, probably sparrows, wrens, warblers and kites.

    But the island was never the destination for these birds, just a tiny part of a much larger journey. For instance, the pectoral sandpiper (Calidris melanotos), which is known to fly over this region, makes a round trip each year totalling some 30,000 kilometres (19,000 miles), so it doesn’t have much time to stop and enjoy Florida’s beaches.

    After several hours, this massive flock of birds had moved beyond Key West, and according to meteorologists in Miami, they landed safely on the mainland just before sunrise.

  • A spectacular outbreak of polar stratospheric clouds (PSCs) is underway around the Arctic Circle. "This is a once in a lifetime event," says Chad Blakley, who runs the Lights over Lapland aurora tour service in Abisko, Sweden. "No question, this is the best that any of us have ever seen." Tour guide Paige Ellis took this video showing the clouds' aurora-like colors on Dec. 29th:

    "They were so intense that lots of the tourists on the ground thought they were looking at daytime auroras. I had to explain that they were actually clouds in the stratosphere," says Blakley.

    Polar stratospheric clouds are newsworthy because normally the stratosphere has no clouds at all. Home to the ozone layer, the stratosphere is arid and almost always transparent. Only when the temperature drops to a staggeringly cold -85C can sparse water molecules assemble themselves into icy stratospheric clouds. PSCs are far more rare than auroras.

    "Local villagers in both Abisko and Kiruna who are more than 70 years old confirmed they have never seen anything of the size, scale, or intensity," reports Blakley. "At one point I would say that close to 25% of the sky was filled with the clouds. PSCs in previous winters have been closer to 1% or 2%."

    The outbreak has continued on Dec. 30th. "Today I got to see some of the brightest PSCs I've ever seen during all of my years watching the sky," reports Göran Strand, who sends this picture from Jämtland, Sweden:

    "They were so bright, they even lit up the surrounding landscape," he marveled.

    PSCs are intensely colorful because they are made of a special type of ice. High-altitude sunlight shining through microscopic crystals only ~10µm across produce a bright iridescent glow unlike the lesser iridescence of ordinary tropospheric clouds.

    Stay tuned for updates as the outbreak continues.

    Polar stratospheric clouds above Abisko National park, Sweden from Lights Over Lapland on Vimeo.

  • December 31, 2019: As the year came to an end, an amazing spectacle took place in the sky over Sweden. Check it out!

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