Republished from Dr. Roy Spencer's Weblog
I personally criticized Dr. Spencer for including an virtually full merchandise to my to-do listing. ~ Ctm
June 11, 2019 by Roy W. Spencer, Ph.D.
Over the subsequent few weeks, observers at mid-latitudes may observe one of the best nighttime cloud observing their lives.
Noctilucent clouds on the excessive altitude (good night time) seen from Corvallis, Oregon on June 10, 2019 (Tucker Shannon, Google Pixel telephone).
Observers from the northern half of the US report one thing that they had by no means seen earlier than: noctilucent clouds of an electrical blue. They’ve a vaporous look and frequently change form. They are often seen when the solar is about 6 to 16 levels. below the horizon, about 1 to 2 hours after sundown or earlier than dawn. Throughout this hour of the night time, the solar all the time shines on these clouds, however not on the traditional clouds associated to the climate situations.
Yearly, on the finish of spring, folks from very northern latitudes usually noticed them in clear or partly cloudy climate. However the minimal photo voltaic situations, with little or no sunspots, trigger the higher excessive environment to chill to about 80 km excessive, the place the bottom atmospheric temperatures are recorded, round -150 levels. F (-100 ° C). This altitude is bigger than 99.999% of the air within the environment.
Clear clouds noticed from the Worldwide Area Station on June 13, 2012 (NASA).
Atmospheric methane, which is transformed to water vapor at these altitudes, provides to the spectacular electrical blue display screen, in addition to atmospheric carbon dioxide, leading to elevated cooling of the higher environment. Consequently, the situations essential for the formation of the NLC lengthen additional south than ever earlier than.
The undulating and wavy look of clouds is because of upwardly propagating gravity (air density) waves that trigger rising and falling temperatures, which kind within the coldest elements of those waves. Ice develops on meteorite mud particles, making a (close to) spatial model of cirrus clouds. Accelerated pictures has been used to point out how clouds change form when gravity propagates within the extraordinarily chilly excessive mesosphere:
2017 NOCTILUCENT CLASUS CHASING SAASON TEASER – 4K (UHD) from Evening Lights Movies on Vimeo.
When you miss seeing them over the subsequent few weeks, don’t worry: the minimal photo voltaic situations are anticipated to persist till the subsequent CNL season, making the summer season of 2020 an excellent alternative to observe the present as nicely.
You may see latest images of the Northern Hemisphere CNL up to date every day right here.