NLCs are clouds that are found in the Earth’s upper atmosphere, located around 50 to 85 kilometers (31 to 53 miles) above the Earth’s surface. They are also called polar mesospheric clouds (PMCs) because they are usually found in the mesosphere and at latitudes from about 50 to 60 degrees north and south of the equator.

The AIM probe has already produced many pictures from its position of 600 kilometers above the North Pole. Some of the most dramatic ones are shown at the NASA Space Weather website.

The clouds are visible only when the Sun’s rays illuminate them from below the horizon while the ground and lower atmospheric layers are in the Earth’s shadow. That is, they are only seen just before sunrise or after sunset (twilight hours)—when sunlight is scattered in the upper atmosphere and, thus, illuminates the lower atmosphere and the surface of the Earth.

The AIM satellite, launched on April 25, 2007, by a Pegasus XL launch rocket from Vandenberg Air Force Base in California, orbits about the Earth at a polar orbit with a height of about 600 kilometers (373 miles) above the surface of the Earth. During its 26-month mission, AIM makes measurements using the instruments called the Cloud Imaging and Particle Size (CIPS), Cosmic Dust Experiment (CDE), and Solar Occultation for Ice Experiment (SOFIE). Images are made with four cameras positioned at different angles in order to get unique views of the NLCs.

AIM will be monitoring the life cycle of NLCs as to their chemical properties. Scientists want to know more about the particles that make up the clouds—specifically, if space dust helps to create them.

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