OF THE MISSING NOCTILUCENT CLOUDS: Every year in June, far-northern sky
watchers see electric-blue tendrils creeping over the western horizon
at sunset. These are noctilucent clouds (NLCs) formed by summertime
wisps of water vapor crystallizing around bits of meteor smoke at the
edge of space. Every year in June ... except this year. NLCs have
been mysteriously absent in June 2017, and researchers have just
figured out why. A 'heat wave' in the upper atmosphere has temporarily
wiped them out.
Visit today's edition of Spaceweather.com for the full
story and the prognosis for future NLCs.