The first thing to understand when studying weather is how air moves in the atmosphere. Watch this video on air masses and fronts and answer the questions that follow to learn how and where they originate.
Air masses are large bodies of air that have similar properties of temperature and humidity. For an air mass to form uniform characteristics, it needs to originate over a homogeneous surface for an extended period of time. This is known as the source region. Air masses are defined by their source regions and identified by letters, which describe their properties.
The first letter describes the moisture of the air mass. c stands for continental, air that is dry and originates over land and m stands for maritime, air that is moist and originates over water.
The second letter describes the thermal characteristics of the air mass. T for tropical, P for polar, A for Arctic or Arctic and E for equatorial. Combinations of these letters communicate information about the air mass. For example, in most of North America, we usually experience continental Tropical air masses, but in winter, some portions of North America will see continental Arctic, air masses that originate over ice and snow which cause bitterly cold temperatures.
When air moves from its source region it exchanges heat and moisture with the surface and can rise or fall through the atmosphere. As these air masses move around the Earth, they come in contact with one another at boundaries called Fronts. Fronts are transition zones between two air masses that have different densities due to temperature and moisture content. Because fronts are boundaries, they are characterized by sharp changes in temperature, moisture, pressure and wind direction. Clouds and precipitation are common in frontal areas. We???ll explore more about this phenomenon later.