Atmospheric Gravity Waves:
Gravity waves are the oscillations of air parcels by the lifting force of bouyancy and the restoring force of gravity. These waves propagate vertically as well as horizontally, and actively transport energy and momentum from the troposphere to the middle and upper atmosphere. Gravity waves are caused by a variety of sources, including the passage of wind across terrestrial landforms, interaction at the velocity shear of the polar jet stream and radiation incident from space. They are found to affect atmospheric tides in the middle atmosphere and terrestrial weather in the lower atmosphere.
Gravity waves are investigated using pressure sensors, in situ aircraft measurement, and imaging data. Gravity waves are often seen in the lower atmosphere (~10 km) by thin bands of cloud and sky. Higher in the atmosphere (80-100km), gravity waves can be 'seen' in moving bands of atmospheric air glow. The airglow emits spectra from chemiluminescence of atmospheric molecules. By analyzing the motion of different spectra mesospheric gravity waves can be roughly plotted.

Terrestrial Observation of Gravity Waves:

Data from Grand Junction are summarized in keogram format. Each keogram shows the fluctiuations of the airglow layer at about 87 km in geographic coordinates. Fluctuations are determined as the difference between the background corrected images and take averages over approximatlely one hour. The surface meteograms provided by Unisys Weather give helpful information about observational conditions.

The scientific satellite TIMED (Thermosphere*Ionosphere*Mesosphere*Energetics*Dynamics) is currently exploring the Earth's Mesosphere and Lower Thermosphere (60 - 180 km). This region is the least explored and understood region of our atmosphere.

Coordinated airglow observations from the ground will be performed during overflights of the TIMED satellite from Colorado. The image is an example from previous observations of atmospheric gravity waves in the OH-emission.

Observations from the Air:
Waves in Airglow measured in the Space Shuttle wake
Airglow images were taken by a camera on board the Space Shuttle looking back into the wake of the flight path. These images show the airglow layer at about 93 km altitude up to the horizon of the local observer. Traveling along its flight path the camera observes new parts of the airglow layer which can be considered stationary compared to the velocity of the shuttle ( ~7 km/s).

A sequence of raw images was added according to the distance the shuttle traveled and the resulting image was projected onto a longitude-latitude map of Earth. Modern image processing techniques like Fourier transforms show short wavelength (or high frequency) modulations within the airglow.

Similar observation can be obtained from aircraft platforms operating all-sky imagers. The last image shows gravity modulated airglow recorded by an aircraft flying over the Pacific Ocean during the 1993 Aloha campaign.