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Over Which Type of Earth Surface Does a CT Air Mass Usually Form?

Critically important to shaping the weather, air masses are large bodies of air with relatively consistent levels of heat and moisture, covering thousands of square miles. It takes between ten days and two weeks for an air mass to take shape, so a relatively flat region of the Earth with stable weather conditions is required for one to develop. A continental tropical (cT) air mass will typically form over arid, inland regions close to the equator.

Types of Air Masses
- Air masses are categorized by their "source region," the surface of the Earth over which they form. They can be polar or tropical depending on their latitude, or distance from the equator, and maritime or continental, depending on whether they form over land or sea. The four main types of air mass that affect the USA, as described by the National Weather Service, are continental tropical, maritime tropical (mT), continental polar (cP) and maritime polar (mP).
Characteristics
- Maritime air masses are very moist, as they can draw on evaporated sea water, while continental air masses are much drier, as they form over land. Their heat will depend on the latitude of their source region, with polar air masses, which take shape near the poles at 60 degrees north or south, being very cold, while tropical air masses, which develop at 25 degrees north or south of the equator, are much hotter. As air masses come into contact with one another and interact they produce "fronts," creating complex weather patterns.
Source Regions
- As cT air masses form over land regions near to the equator, they are both dry and hot. Major source regions are the Saharan, Arabian and Australian deserts, in addition to the deserts of Northern Mexico during the summer, according to Michael E. Ritter of the University of Wisconsin. They will usually bring clear skies, allowing for hot days and cool nights, and a stationary cT air mass can produce severe droughts.
The Dryline
- More complex weather is produced when a cT mass interacts with a warm, moist mT mass to create a "dryline." In the U.S., this dynamic begins as the sun heats the ground in the Southwest, causing a hot, dry wind to blow down the east side of the southern Rocky Mountains. The dryline will move east during the day as heated moist air mixes with the dry air of the cT mass, then drop back west at night as the moist air slopes back underneath to create a "cap" of dry air. If the cap breaks and allows moist air to rise suddenly, severe thunderstorms can result.

Nature