Noctilucent (or night luminous) clouds have
been reported glowing in the nighttime summer skies since the
1880s. These clouds form in summer when the mesosphere is
coldest near 82 km. The clouds are highly sensitive to the
ambient temperature and humidity and have attracted attention
as a diagnostic of the meteorological conditions. Diagnostic
studies span investigations of long-term climate as well as
investigations of short-term wave breaking and turbulence.
Studies have focused on the natural occurrence of the clouds
as well as their formation by exhaust from the Space Shuttle.
The Super Soaker experiment was designed to better understand
the effects of water vapor on the mesosphere. Water was
released from a sounding rocket payload at 85 km in January
2018. A cloud formed rapidly after the release and was
detected from the ground by lidar (laser radar). A cloud
microphysical model was used to investigate the observations.
The model investigation indicates that the cloud formation was
due to the combination of rapid radiative cooling as well as
an increase in the frost point temperature. The study further
suggests that water vapor can act as a thermostat where
radiative cooling by vapor is balanced by absorption of heat
by ice crystals. The colloquium will discuss the meteorology
of noctilucent clouds, recent research, and the insights from
the Super Soaker experiment.
About the Speaker:
Richard Collins is a professor of
atmospheric sciences and director of the graduate school at
the University of Alaska Fairbanks. He has conducted studies
on the ozone hole, the meteorology of the stratosphere and
mesosphere, fluid dynamics of waves and turbulence,
noctilucent clouds, volcanic plume tracking, forest fires, and
fisheries. Collins' research has primarily focused on the
weather and climate of the middle and upper atmosphere based
on observational studies employing lidars and radars. Collins
directs the lidar research laboratory at Poker Flat Research
Range. He has participated in several sounding rocket
investigations. Collins received his PhD in electrical
engineering in 1994 from the University of Illinois that
included a year of field work at the South Pole. Collins is a
recipient of the Optical Society of America's Allen Prize and
has been a Fulbright Fellow at the University of Rostock.