noctilucent clouds
DESCRIPTION
Observations, Frequency & Linkage to Climate Change. Noctilucent Clouds. Noctilucent Clouds taken from 36,000 feet above the South of Nunivak Island, Alaska on June 20, 2006. Image credit: John Boardman. http://www.nasa.gov/mission_pages/aim/multimedia/nocticulant_clouds.html. - PowerPoint PPT PresentationTRANSCRIPT
NOCTILUCENT CLOUDSObservations, Frequency & Linkage to Climate Change
Jenell Walsh-ThomasCSI 655 Atmospheric PhysicsMonday, May 16, 2011
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Noctilucent Clouds taken from 36,000 feet above the South of Nunivak Island, Alaska on June 20, 2006.Image credit: John Boardman. http://www.nasa.gov/mission_pages/aim/multimedia/nocticulant_clouds.html
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Presentation Outline Introduction What are noctilucent clouds? Observations
Location, formation & propertiesObservation techniquesOccurrence & observation frequency
Linkage to Climate Change Conclusion
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Introduction Purpose: develop an understanding of
noctilucent clouds (NLC) First reported June 8, 1885
Timeframe when industrial revolution began…coincidence?
Increased frequency of occurrence/observationIndicator of global change in the middle
atmosphere?Linkage to climatic changes?
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What are noctilucent clouds? Clouds that form at
very high altitudes: 82 km
Primarily composed of microscopic ice crystals
Seen at twilight & glow a white to bluish color
NLC vs. (high) Cirrus clouds
Peak observations around summer solstice
NLCs/PMCs; “night shining clouds”
Atmospheric historical importance
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Formation & Properties Formation conditions
Atmospheric environment: extremely low T at mesopause, very low P, high amount of water vapor, presence of condensation nuclei
Time of day: twilight Size & shape of particles
Average radius 150 nm Actual shape speculated to be non-
spherical, possibly needle or cubic Cloud shape & form: veil, bands,
waves & whirls Bluish-white in color with
occasional red edge
Summary of average properties of NLCs (Kokhanovsky 2005).
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Observation Techniques Ground-based (NLCs)
Direct & photographic Space-based (PMCs)
2 important first observationsConclusions from space:
○ Asymmetrical in N & S hemispheres○ S hemisphere contain smaller particles
AIM
Geometry of observing NLCs (Avaste 1993).
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Occurrence & Observation Frequency Typical occurrence:
around the summer solstice at twilight
First observed in 1885
Provide insight into conditions of mesosphere
Asymmetrical observation numbers between N & S hemisphere
Determining frequency
Increase in frequency & brightness
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Linkage to Climate Change Two major greenhouse gases: CO2 & CH4
CO2: causes cooling CH4: dissociation occurs, adds H2O vapor Also influencing increase in brightness Indicators of change in upper atmosphere
indicator of future change in lower layers & at mid-latitudes?
July 2009 mid-latitude outbreak event
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Conclusion NLC/PMC rare & exquisite site for
observers Much more to be learned about their
properties, formation & possible foreshadowing for future changes
Limited time & geographic range Both ground & space-based improving
AIM satellite mission Standard need for observations
QUESTIONS? COMMENTS?
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Noctilucent cloud (NLC), polar mesospheric cloud (PMC) or "night-shining" cloud (Russell et al 2009). (Photographed by Tom Eklund, July 28, 2001, Valkeakoski, Finland.)