What can be learned about Polar Mesospheric Clouds from suborbital missions?

Details What can be learned about Polar Mesospheric Clouds from suborbital missions? What can be learned about Polar Mesospheric Clouds from suborbital missions?

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsa23c..04t&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SA23C-04

Physics

Optics

[0305] Atmospheric Composition And Structure / Aerosols And Particles, [0319] Atmospheric Composition And Structure / Cloud Optics, [0341] Atmospheric Composition And Structure / Middle Atmosphere: Constituent Transport And Chemistry, [3311] Atmospheric Processes / Clouds And Aerosols

Scientific paper

Noctilucent clouds ('night luminous' or NLC) are the highest and coldest clouds in the atmosphere. When viewed from the ground they are referred to as NLC. Viewed from space they are called Polar Mesospheric Clouds, or PMC. Occupying a narrow (81-86 km) height zone below the high-latitude mesopause (a temperature minimum versus height, located near 88 km), NLC offer a splendid sight during summer twilights. They are made visible by scattered sunlight against the dark twilight sky, when the sun lies below the horizon at angles between 6o and 16o. The state of the science has been advanced significantly since the launches of the Odin and Aeronomy of Ice in the Mesosphere (AIM) satellite missions. The spatial scales of the clouds are evident in the Cloud Imaging and Particle Size (CIPS) experiment down to its limiting resolution of 5 km. However, from ground-based photography of NLC, and from theoretical modeling of small-scale 3D instability and turbulence dynamics in the upper mesosphere, we know that there is much structure on the sub-km scale which is yet to be explored. Turbulent breakdown is expected to occur in this sub-km range. Fortunately, on the short-time scales of turbulence, ice particles should act as passive tracers, which are advected by the wind field. Sub-orbital missions provide an ideal observing platform for extending the PMC 'spatial spectrum' ranging currently from hundreds to tens of km (which we now know from CIPS) down to tens of meters, a 'leap' of three orders of magnitude. A high resolution camera with a CMOS chip, is easily capable of sub-km resolution, with S/N ratios exceeding 100 for a bright PMC. A wide (150 nm) bandpass centered on the blue portion of the PMC spectrum isolates the most intense portion of the scattered brightness. Movies of the clouds as the sub-orbital vehicle approaches, and penetrates the cloud, would be valuable, both for the scientific goal of studying the 'transition to turbulence', but also for educational visualization. The 'up-close and personal' nature of the sub-orbital trajectory makes it an ideal way to study the microphysics of PMC, down to scales never before reached.

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