Lecture10 - Aeronomy of Ice in the Mesosphere AIM A NASA Small Explorer Mission to study Polar Mesospheric Clouds(PMCs Exploring Clouds at the Edge

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1 1 A NASA Small Explorer Mission to study Polar Mesospheric Clouds (PMCs) Aeronomy of Ice in the Mesosphere: AIM Exploring Clouds at the Edge of Space AIM was launched 25 April 2007 Planned operations until at least 2014 2 What are Polar Mesospheric Clouds? Clouds made of tiny (~50 nm) water ice crystals that appear only near the polar mesopause (~83 km) during the summer Why only during the summer? Because at this time the polar mesopause is the coldest place on Earth – Summer is colder than winter because of the circulation (polar air ascends in summer, and adiabatic expansion causes cooling) – Temperatures reach ~120 K – For clouds to form, they have to be < 150 K Why don’t they form at 32ºF = 0ºC = 273 K? Atmospheric density is much lower at 83 km than near the surface Temperatures must be much lower for condensation Called Polar Mesospheric Clouds (PMCs) by satellite observers Called Noctilucent (“Night-Shining”) Clouds (NLCs) by ground-based observers
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2 3 NLC 83 km But since they occur 83 km (50 miles) above the earth surface, we can see them after sunset or before sunrise PMCs are too dim to see during the day against all the sky Rayleigh scattering 4 PMCs are structured because of atmospheric wave activity Pekka Parviainen Pekka Parviainen Pekka Parviainen
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3 5 NLCs first observed about a century ago (1885) Hypothesis: 1883 Krakatoa island volcano inserted water into mesosphere The most violent volcanic eruption in modern time ~200 megatons of TNT. Two-thirds of island was destroyed and generated the loudest sound ever historically reported. After the eruption: Global temperature decreased by 1.2º in following year Weather was chaotic until 1888 Brilliant sunsets around the globe: persisted for three years. Krakatoa:
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This note was uploaded on 01/19/2011 for the course ATOC 5235 taught by Professor Randell during the Fall '10 term at Colorado.

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Lecture10 - Aeronomy of Ice in the Mesosphere AIM A NASA Small Explorer Mission to study Polar Mesospheric Clouds(PMCs Exploring Clouds at the Edge

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