Gravity Waves and Sunglint, Lake Superior
From the vantage point of the International Space Station, astronauts
frequently observe atmospheric and surface phenomena in ways that are impossible
to view from the ground. Two such phenomena—gravity waves and sunglint—are
illustrated in this photograph of northeastern Lake Superior.
At the top of the image, the Canadian Shield of southern Ontario is covered
by an extensive forest canopy typical of early summer. Offshore and to the west
and southwest of Pukaskwa National Park, several distinct sets of parallel cloud
bands are visible. Gravity waves are produced when moisture-laden air encounters
imbalances in air density, such as might be expected when cool air flows over
warmer air. This can cause the flowing air to oscillate up and down as it moves,
causing clouds to condense as the air rises and cools and to evaporate away as
the air sinks and warms. This produces parallel bands of clouds oriented
perpendicular to the wind direction. The orientation of the cloud bands in this
image, parallel to the coastlines, suggests that air flowing off of the land
surfaces to the north is interacting with moist, stable air over the lake
surface, creating gravity waves.
The second phenomenon—sunglint—affects the water surface around and to the
northeast of Isle Royale. Sunglint is caused by light reflection off a water
surface; some of the reflected light travels directly back towards the observer,
resulting in a bright mirror-like appearance over large expanses of water. Water
currents and changes in surface tension—typically caused by presence of oils or
surfactants—alter the reflective properties of the water and can be highlighted
by sunglint. For example, surface water currents are visible to the east of Isle
Royale that are oriented similarly to the gravity waves, suggesting that they
too are the product of winds moving off of the land surface.
Astronaut photograph ISS036-E-11843
was acquired on June 24, 2013, with a Nikon D3S digital camera using a 50
millimeter lens, and is provided by the ISS Crew Earth Observations experiment
and Image Science & Analysis Laboratory, Johnson Space Center. The image was
taken by the Expedition 36 crew. It has been cropped and enhanced to improve
contrast, and lens artifacts have been removed. The International Space Station
Program supports the laboratory as part of the ISS National Lab to help
astronauts take pictures of Earth that will be of the greatest value to
scientists and the public, and to make those images freely available on the
Internet. Additional images taken by astronauts and cosmonauts can be viewed at
the NASA/JSC Gateway to Astronaut Photography
of Earth.
Image Credit: NASA
Caption: William L. Stefanov (Jacobs/JETS) and Michael H. Trenchard (Barrios/JETS), NASA Johnson Space Center
Caption: William L. Stefanov (Jacobs/JETS) and Michael H. Trenchard (Barrios/JETS), NASA Johnson Space Center
NASA
Guillermo Gonzalo Sánchez Acutegui
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