Polar Mesospheric Clouds (PMCs)-also known as-

Noctilucent Clouds (NLCs)

Mark Hervig

GATS Inc.

Driggs, Idaho

Noctilucent Cloud (NLC) CharacteristicsNLCs occur:

Near 83 km altitude, almost the edge of spacePoleward of 50 degrees latitude, in both hemispheresDuring summer

NLCs are composed of water ice crystals50 nanometers in radius (the radius of human hair is 500 times larger)

Because they are ice clouds, their formation is controlled by:

temperature

humidity

NLC over Finland, photo by Pekka Parviainen

NLCs are visible from the ground

NLC over Finland, photo by Pekka Parviainen

Shortly after sunset, the observer is in darkness, but the NLC is still in sun light

The Earth’s Atmosphere, in brief

Composition of the Atmosphere

Major Constituents:Nitrogen (N), 78%Oxygen (O2), 21%Argon (Ar), 0.9%

Minor Constituents:Water vapor (H2O), up to 10000 ppmvCarbon dioxide (CO2), 350 ppmvOzone (O3), 6 ppmvMethane (CH4), 1.7 ppmv and others…..

ppmv = “parts per million by volume”

Vertical Structure of the Atmosphere

Layers in the atmosphere are defined by temperature

Weather as we know it happens in the troposphere

NLCs

Clouds in the Atmosphere

Most clouds occur in the troposphere

Except NLCs

They occur in the mesosphere

Clouds form when water vapor in the atmosphere condenses

Clouds are a collection of water drops and/or ice crystals

Water vapor condenses when the temperature cools

Rising air expands, expanding air cools, so…. rising air = clouds (sometimes)

NLC Formation

NLC formation is similar to that of “every day” clouds:

Water vapor condenses into ice when temperatures cool

This cooling is due to rising air

NLCs are different than “every day” clouds:

NLCs form 70 km (43 miles) higher

They only occur during summer

They only occur at high latitudes (50 degrees to the pole)

Why do they occur only in summer high latitudes?

weather patterns

Why should we study NLCs?• NLCs respond to atmospheric temperature and humidity

Temperature is affected by carbon dioxide (CO2)

Humidity is affected by methane (CH4):

• CO2 and CH4 are increasing due to human activities

• Increasing CO2: warms the troposphere, “greenhouse effect” cools the mesosphere, where NLCs occur

 • Increasing CH4:

methane becomes water: CH4 + OH > CH3 + H2O

• NLCs are a visible indication of climate change “The minors canary” of climate change

How do we measure NLCs?

In Situ Measurements (instrument in contact with the subject)

RocketsBalloons and Airplanes can’t fly high enough

Remote Measurements (instrument is far from the subject)

Ground observers: visual, cameras

LIDAR (light detection and ranging)

RADAR (radio detection and ranging)

Satellites: mapping, solar occultation

LIDAR

NLC measurements from satellite

examples of satellite measurements :

Limb sounding: light absorption

Nadir imaging: light scattering

NLC patterns are changing dramatically

NLCs are occurring more often than before

NLCs are occurring farther south than before

NLC photo by Timo Leponiemi

Are these changes telling us something?

NLC Occurrence Versus Time

NLCs occur nearly twice as often as they did 35 year ago

From Gaddsen, 1997

NLC Locations: Old and New

US Towns where NLCs were recently sighted:

Twin Falls,  Idaho Logan,  Utah Boulder,  Colorado Glen Ullin,  North Dakota McGuire,  New Jersey

NLCs are occurring 700 miles farther south than ever before

What is causing the changes in NLCs?

NLC over Finland, photo by Pekka Parviainen

Increasing CO2 in the Atmosphere

The increase in CO2 is due to human activities

Temperature in the Mesosphere is decreasing

This cooling is related to the increase in CO2

Temperatures near 80 km have cooled by almost 5 degrees Kelvin (K) every 10 years, since measurements were started in the 1950’s

Increasing Methane (CH4) in the Atmosphere

This increase is due to human activities

Some evidence suggests an increase in mesospheric H2O, but this is not yet clear.

What are we doing in Driggs?

NASA’s Office of Space Science has funded a project in Driggs called:

“Polar Mesospheric Clouds in the Classroom”

Goals of this project are to

Educate the public about NLCs

Observe NLCs using digital cameras

This project is a partnership between GATS Inc. and Teton High School

On the web: gwest.gats-inc.com/pic/nlc_epo_home.html

NLC Cameras

Digital Cameras will be used to look for NLCs

Our images will posted on the internet

What we learn will help scientists who study NLCs

Camera locations:

Teton High SchoolFairbanks Alaska

Finland ??Antarctica ??You decide

We will install 3 “NLC-cams” each year

What can You do?

NLC Cameras:

Choose the right cameras for the job

Install the Driggs cam

Determine the best way to operate them

Connect them to the internet

Pick good locations for future cameras, anywhere in the world

Analyze the images, look for NLCs

Project Web Pages

Develop interactive web pages

Display and archive the “NLC-cam” images

Update project information

Education

Take what we learn and share it with other students/schools