Reposted from Dr. Roy Spencer’s Weblog
I’ve personally stubborn out Dr. Spencer for including an merchandise to my bucket checklist which had been nearly full.~ctm
June 11th, 2019 by Roy W. Spencer, Ph. D.
Over the subsequent few weeks, mid-latitude observers may expertise the perfect noctilucent cloud viewing of their lifetimes.
Extraordinarily high-altitude noctilucent (night-shining) clouds seen from Corvallis, Oregon on June 10, 2019 (Tucker Shannon, Google Pixel cellphone).
Observers over the northern half of the US are reporting one thing they’ve by no means seen earlier than — electric-blue noctilucent (night-shining) clouds. They’re wispy in look, and constantly change form. They are often seen when the solar is about 6 to 16 deg. beneath the horizon, so about 1 to 2 hours after sundown or earlier than dawn. Throughout that point of night time the solar continues to be shining on these clouds, however not on any regular weather-related clouds.
Within the late spring yearly, folks at far northern latitudes have usually seen these on clear or partly-cloudy evenings. However solar-minimum situations, with few if any sunspots, are inflicting cooling within the excessive higher environment round 80 km (~50 miles) excessive the place the bottom atmospheric temperatures are recorded, approaching -150 deg. F (-100 deg. C). That altitude is above 99.999% of the air within the environment.
Noctilucent clouds noticed from the Worldwide House Station on June 13, 2012 (NASA).
Including to the spectacular electrical blue shows is growing atmospheric methane, which will get transformed to water vapor at these altitudes, and growing atmospheric carbon dioxide, which causes enhanced cooling of the higher environment. The result’s that the situations essential for NLC formation are extending farther south than ever earlier than.
The wispy and undulating look of the clouds is because of upward-propagating gravity (air density) waves that trigger temperatures to rise and fall, and the clouds type within the colder parts of these waves. Ice grows on meteor mud particles, making a (practically) outer house model of cirrus clouds. Time lapse images has been used to point out how the clouds change form because the gravity waves effectively up via the extraordinarily chilly higher mesosphere:
2017 NOCTILUCENT CLOUD CHASING SEASON TEASER – 4K (UHD) from Night time Lights Movies on Vimeo.
For those who miss seeing them within the subsequent a number of weeks, take coronary heart — photo voltaic minimal situations ought to persist till the subsequent NLC season arrives, making the summer season of 2020 a superb viewing alternative, too.
You may see latest NLC photographs from across the Northern Hemisphere, up to date each day, right here.