Images
August 28, 2010 - Wave clouds off Western Sahara
Tweet
Ripple-like wave clouds dominate a complex pattern located over the Atlantic Ocean, off the coast of Western Sahara on August 25, 2010. The Moderate Resolution Imaging Spectroradiometer (MODIS) on the Aqua satellite captured this true color image as it passed overhead.
A wave cloud is created by atmospheric standing waves. A moist atmosphere allows clouds to form at the crests of the otherwise invisible waves, but the clouds evaporate in the descending part of the waves. This is due to adiabatic heating and cooling, a process that results in no net heat transfer between the air and the surrounding environment.
Because it is a gas, the temperature of air changes with atmospheric pressure. When a mass of air rises, it encounters decreasing atmospheric pressure and the air mass expands. Also, if there is adequate moisture, clouds form, as we see at the top of the waves in this image. When the air descends down the wave, it meets increasing atmospheric pressure. The air compresses under this pressure and the temperature rises – and clouds evaporate. This process leaves the
characteristic cloud-and-clear patterns seen in a cloud wave.
In this image, a pattern of swirling vortices can be seen in several areas, including underneath the cloud waves. These are called von Karman vortices, and are formed as wind flow is interrupted by a bluff body. A bluff body is a stationary, irregular flat shaped (non- aerodynamic) obstacle. In this case, the Canary Islands, which lie to the north of image and out of view, are the bluff body, with the von Karman vortices formed on the leeward side of the islands.
The patterns formed by the vortices are clear and distinct from the pattern of the wave clouds. This can only happen if each formation occurs in different levels of the atmosphere, without much commingling of wind.
Image Facts
Satellite:
Aqua
Date Acquired: 8/25/2010
Resolutions:
1km ( B), 500m ( B), 250m ( B)
Bands Used: 1,4,3
Image Credit:
Jeff Schmaltz, MODIS Land Rapid Response Team, NASA GSFC
Ripple-like wave clouds dominate a complex pattern located over the Atlantic Ocean, off the coast of Western Sahara on August 25, 2010. The Moderate Resolution Imaging Spectroradiometer (MODIS) on the Aqua satellite captured this true color image as it passed overhead.
A wave cloud is created by atmospheric standing waves. A moist atmosphere allows clouds to form at the crests of the otherwise invisible waves, but the clouds evaporate in the descending part of the waves. This is due to adiabatic heating and cooling, a process that results in no net heat transfer between the air and the surrounding environment.
Because it is a gas, the temperature of air changes with atmospheric pressure. When a mass of air rises, it encounters decreasing atmospheric pressure and the air mass expands. Also, if there is adequate moisture, clouds form, as we see at the top of the waves in this image. When the air descends down the wave, it meets increasing atmospheric pressure. The air compresses under this pressure and the temperature rises – and clouds evaporate. This process leaves the characteristic cloud-and-clear patterns seen in a cloud wave.
In this image, a pattern of swirling vortices can be seen in several areas, including underneath the cloud waves. These are called von Karman vortices, and are formed as wind flow is interrupted by a bluff body. A bluff body is a stationary, irregular flat shaped (non- aerodynamic) obstacle. In this case, the Canary Islands, which lie to the north of image and out of view, are the bluff body, with the von Karman vortices formed on the leeward side of the islands.
The patterns formed by the vortices are clear and distinct from the pattern of the wave clouds. This can only happen if each formation occurs in different levels of the atmosphere, without much commingling of wind.
Image Facts
Satellite:
Aqua
Date Acquired: 8/25/2010
Resolutions:
1km ( B), 500m ( B), 250m ( B)
Bands Used: 1,4,3
Image Credit:
Jeff Schmaltz, MODIS Land Rapid Response Team, NASA GSFC
