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Open-cell cloud formation over the Bahamas
This page contains archived content and is no longer being updated. At the time of publication, it represented the best available science. However, more recent observations and studies may have rendered some content obsolete.
What atmospheric scientists refer to as open cell cloud formation is a regular
occurrence on the back side of a low-pressure system or cyclone in the
mid-latitudes. In the Northern Hemisphere, a low-pressure system will draw in
surrounding air and spin it counterclockwise. That means that on the back side
of the low-pressure center, cold air will be drawn in from the north, and on the
front side, warm air will be drawn up from latitudes closer to the equator.
This movement of an air mass is called advection, and when cold air advection
occurs over warmer waters, open cell cloud formations often result. This
MODIS image shows open cell cloud formation over the Atlantic Ocean off the
southeast coast of the United States on February 19, 2002. This particular
formation is the result of a low-pressure system sitting out in the North
Atlantic Ocean a few hundred miles east of Massachusetts. (The low can be seen
as the comma-shaped figure in the GOES-8
Infrared image from February 19, 2002.)
Cold air is being drawn down from the north on the western side of the low
and the open cell cumulus clouds begin to form as the cold air passes over the
warmer Caribbean waters. For another look at the scene, check out the MODIS Direct Broadcast Image from the University of