Noctilucent CloudsNoctilucent Clouds

“Night-Shining” Clouds

Image source: science.nasa.gov

Image source: nasa.gov

Image source: nasa.gov

Noctilucent CloudsNoctilucent Clouds

• Occur in Mesosphere ~80 km altitude– Highest clouds

• Made of water frozen on dust particles (condensation nucleii)

Image source: science.nasa.gov

Where does the water come Where does the water come from?from?

• Mesosphere is very dry; water must come from somewhere else

• Summer upwelling of moist air

• Space shuttle/ rockets

• Volcanic eruptions

Image source: science.nasa.gov

Where do the particles come Where do the particles come from?from?

• Micro meteors

• Comets

• Volcanic eruptions

Image source: science.nasa.gov

Can only be seen at twilightCan only be seen at twilight

Image source: science.nasa.gov

Conditions for FormationConditions for Formation

• Only form where and when mesosphere is coldest– Polar regions

• Can be seen between 50º -70º north and south of equator

– Why not seen all the way to the poles?

– Summer months• Seasonal air movements move coldest air to

poles in summer

Image source: science.nasa.gov

NASA video clip (click box)

source: nasa.gov

The MysteryThe Mystery

• No recorded observations before 1885

• Brightness, frequency and extent has been growing ever since

Why?

Image source: science.nasa.gov

First Recorded in 1885First Recorded in 1885

• Could the clouds have existed before this?

YES!

• Krakatoa erupted in 1883, creating dramatic sunsets that many enjoyed watching. The clouds could have existed unnoticed before this.

Image source: science.nasa.gov

Increasing Brightness, Frequency Increasing Brightness, Frequency and Extent:and Extent:

Related to Global Climate Change?Related to Global Climate Change?

“greenhouse” gases increase=

colder mesosphere =

more noctilucent clouds

Image source: science.nasa.gov

Effect of Greenhouse GasesEffect of Greenhouse GasesWhy does the Mesosphere get colder?Why does the Mesosphere get colder?

If more of Earth’s emitted longwave radiation is held close to the surface, it is not available to cause warming in the

upper atmosphere

(not known for sure, more study needed)

Image source: science.nasa.gov

Increasing Brightness, Frequency and Increasing Brightness, Frequency and Extent:Extent:

Not Not Related to Global Climate Change?Related to Global Climate Change?

Maybe related to increase in rocket launches in recent times.

Each launch adds significant amount of water to mesosphere. Water needed

for cloud formation.

Image source: science.nasa.gov

The Mesosphere is Important!The Mesosphere is Important!

We won’t fully understand how and why our climate is changing until we

understand what’s happening up there

The Mesosphere can no longer be the “Ignorosphere”

Image source: science.nasa.gov