Southern United States
Muted winter shades of green and brown dominate the hibernating foliage of the southern United States, while bright white clouds flow in wave forms across the northern end of the Gulf of Mexico in this true-color Aqua MODIS image from February 14, 2005. The Mississippi River Valley meanders south in a wide light green ribbon from the top of the image until it comes to the Delta, which is brown as it approaches the waters of the Gulf. A few red dots in the image mark where MODIS detected heat anomalies that are most likely fires.
The bright white low clouds stretching to the east form what appear to be gravity waves in some places: diagonally southwest from the Louisiana coast, and diagonally southeast at image bottom. These shapes form in the clouds when the atmospheric layer carrying them is disturbed by strong vertical air movements (usually caused by storms or mountainous geography). As the air moves up into the crest of a wave, moisture in the air condenses and forms cloud particles, and when the air movement sinks into a trough, the moisture heats up and the cloud particles dissipate. The repeating pattern looks like waves you'd see at the surface of water.