Cumulonimbus Cloud over Africa
Perhaps the most impressive of cloud formations, cumulonimbus (from the Latin for “pile” and “rain cloud”) clouds form due to vigorous convection (rising and overturning) of warm, moist, and unstable air. Surface air is warmed by the Sun-heated ground surface and rises; if sufficient atmospheric moisture is present, water droplets will condense as the air mass encounters cooler air at higher altitudes. The air mass itself also expands and cools as it rises due to decreasing atmospheric pressure, a process known as adiabatic cooling. This type of convection is common in tropical latitudes year-round and during the summer season at higher latitudes.
Astronaut Ed Lu snapped this oblique photo of Hurricane Isabel from the International Space Station on September 15, 2003 at 10:54 UTC. At the time, Isabel was heading for the east coast of the US . It had dropped to a Category 3 hurricane on the Saffir-Simpson Hurricane Scale. After originating in the eastern Atlantic west of the Cape Verde Islands, Isabel became the second major hurricane of the 2003 Atlantic season when it was declared a Category 3 storm by the National Hurricane Center on September 8. Over the next four days, Isabel strengthened into an extremely powerful Category 5 hurricane with winds estimated at 160 mph before dropping in strength as it approached the US.
These two images were taken 9 seconds apart as the STS-97 Space Shuttle flew over equatorial Africa east of Lake Volta on December 11, 2000. The top of the large thunderstorm, roughly 20 km across, is illuminated by a full moon and frequent bursts of lightning. Because the Space Shuttle travels at about 7 km/sec, the astronaut perspectives on this storm system becomes more oblique over the 9-second interval between photographs. The images were taken with a Nikon 35 mm camera equipped with a 400 mm lens and high-speed (800 ISO) color negative film.
Time-lapse photography captures multiple cloud-to-ground lightning strokes during a night-time thunderstorm in Norman, Oklahoma in March, 1978.
Globular mammatus clouds with radar in foreground. Often associated with thunderstorms and severe weather.