Noctilucent clouds (NLCs) frequencies over the South Pole close to zero this year

Noctilucent clouds (NLCs) over the South Pole remain missing as of December 29, 2020– an unusual occurrence as the clouds are expected to appear in the middle of the month. The southern stratosphere seems to think it's winter.

In early December, Dr. Tony Phillips of the SpaceWeather noted that NLCs over the South Pole are missing this year, and it is just one of the curious weather patterns underway at the Earth's southern region. 

"Normally, we see the first NLCs of the southern season around November 21. But this year, it's already December and we are still waiting," said Cora Randall of the University of Colorado's Laboratory for Atmospheric and Space Physics (LASP).

Lynn Harvey, a research scientist at LASP, said noctilucent clouds were expected to appear until mid-December, however, NLCs are almost completely missing as of December 29.

Images from NASA's AIM spacecraft compare December 24, 2019, with this year's Christmas Eve, and Randall noted that the comparison is astounding. "Noctilucent cloud frequencies are close to zero this year."

Southern Hemisphere NLCs comparison 2019 vs 2020. Credit: NASA/LASP, SpaceWeather.com

Dr. Phillips noted that NLCs form during summer, and although the season has officially started in Antarctica in late December, the southern stratosphere "seems to think it's winter."

"In particular, the stratospheric polar vortex, which should be breaking up around now, is stubbornly hanging on. The polar vortex chokes off gravity waves, which would normally carry water vapor into the upper atmosphere. Without water vapor, NLCs cannot form," he explained.

"The southern hemisphere stratosphere is very unusual this year," Randall added.

"The ozone hole is exceptionally large, until recently zonal winds have been blowing in the wrong direction, and overall the stratosphere is much more ‘winter-like’ than it should be in December.”

Featured image credit: NASA/LASP