Archives for category: Clouds

An Australian “Anti-storm”

High-pressure weather systems often bring fair weather and relatively clear skies. In early June 2012, a high off the coast of Tasmania did just that…and in spectacular fashion.

The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite acquired this view of a hole in a cloud formation at 3:00 p.m. local time (05:00 Universal Time) on June 5, 2012. The weather system over the Great Australian Bight cut out the oval-shaped hole from a blanket of marine stratocumulus clouds.

The cloud hole, with a diameter that stretched as far as 1,000 kilometers (620 miles) across, was caused by sinking air associated with an area of high pressure near the surface. Globally, the average sea-level pressure is about 1013 millibars; at the center of this high, pressures topped 1,040 millibars.


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Earth Observatory, June 2012

Ever notice how in many parts of the world, puffy, cauliflower-shaped cumulus clouds are more common in the summer? There’s a reason for this: thermal convection. In winter, the sun has less time to heat the surface and cause instability in the atmosphere. But during the summer, heat from the sun warms the land surfaces so much that pockets of hot air—scientists call them thermals—bubble upward much like steam in a pot of boiling water. As the hot air rises, the water vapor trapped within condenses into microscopic cloud droplets. If the air is humid enough, rapidly changing cumulus clouds puff up in the atmosphere, sometimes bulging to heights above 39,000 feet. Watch in the visualizations below—based on a climate model that simulated cloud formation during a Southern Hemisphere summer—how cumulus clouds pop up over the forests of Africa and South America.

NASA Visualization Explorer, January 2012