A Mystery in the Mesosphere

August 15, 2018: This summer, something strange has been happening in the mesosphere. The mesosphere is a layer of Earth’s atmosphere so high that it almost touches space. In the rarefied air 83 km above Earth’s surface, summertime wisps of water vapor wrap themselves around speck of meteor smoke. The resulting swarms of ice crystals form noctilucent clouds (NLCs), which can be seen glowing in the night sky at high latitudes.

And, no, that’s not the strange thing.

Northern sky watchers have grown accustomed to seeing these clouds every summer in recent years. They form in May, intensify in June, and ultimately fade in July and August. This year, however, something different happened. Instead of fading in late July, the clouds exploded with unusual luminosity. Kairo Kiitsak observed this outburst on July 26th from Simuna, Estonia:

Kairo-Kiitsak-DSC_0943_1532595355

“It was a mind-blowing display,” says Kiitsak. “The clouds were visible for much of the night, with intense ripples for 3 hours.”

Other observers saw similar displays in July and then, in August, the clouds persisted. During the first half of August 2018, reports of NLCs to Spaceweather.com have tripled compared to the same period in 2017. The clouds refuse to go away.

Researchers at the University of Colorado may have figured out why. “There has been an unexpected surge of water vapor in the mesosphere,” says Lynn Harvey of  Colorado’s Laboratory for Atmospheric and Space Physics (LASP).  This plot, which Harvey prepared using data from NASA’s satellite-based Microwave Limb Sounder (MLS) instrument, shows that the days of late July and August 2018 have been the wettest in the mesosphere for the past 11 years:

mls2

The red curve traces water vapor levels in the mesosphere for 2018.

“July went out like a lion!” says Harvey.

In addition to being extra wet, the mesosphere has also been a bit colder than usual, according to MLS data. The combination of wet and cold has created favorable conditions for icy noctilucent clouds.

Harvey and her colleagues are still working to understand how the extra water got up there. One possibility involves planetary wave activity in the southern hemisphere which can, ironically, boost the upwelling of water vapor tens of thousands of miles away in the north. The phenomenon could also be linked to solar minimum, now underway. It is notable that the coldest and wettest years in the mesosphere prior to 2018 were 2008-2009–the previous minimum of the 11-year solar cycle.

Stay tuned for updates and, meanwhile, be alert for NLCs.

Realtime Noctilucent Cloud Photo Gallery

 

Fun Ways to Observe a Partial Solar Eclipse

August 9, 2018: A partial solar eclipse happens when the Moon passes in front of the sun, off center, turning the solar disk into a fiery crescent. There are usually one or two partial solar eclipses somewhere on Earth every year. They look like this:

Dennis-Put1

Dennis Put photographed this partial solar eclipse over Maasvlakte, The Netherlands, on Jan. 4, 2011.

The first thing to remember about a partial eclipse is don’t stare at it. Even the tiniest sliver of sun left uncovered by the Moon can hurt your eyes. Instead, look at the ground. Beneath a leafy tree, you might be surprised to find hundreds of crescent-shaped sunbeams dappling the grass. Overlapping leaves create a natural array of pinhole cameras, each one casting an image of the crescent-sun onto the ground beneath the canopy.

No trees? Try this trick: Criss-cross your fingers waffle-style and let the sun shine through the matrix of holes. You can cast crescent suns on sidewalks, driveways, friends, cats and dogs—you name it. Hand shadows are fun, too, like the crescent-eyed turkey shown above.

Because partial eclipses typically last for more than an hour, there is plenty of time for shadow play and photography using safely-filtered telescopes and cameras.