By: Sofia Mertz Chapter 6, Lesson 1 and 2

An air mass: is a large body of air with similar properties all through it. The most important properties are temperature and amount of water vapor. These are the types of air masses. Continental Polar Air: Has very little water evaporates from the land and ice near the poles. So, an air mass from this area is cold and fairly dry. Continental Tropical Air: a large hot dessert can cause the air above it to be warm and fairly dry. Maritime Polar Air: Even though the ocean near the poles is cold, water vapor evaporates into the air. An air mass forming over the ocean near the poles is cold, but relatively moist. Maritime Tropical Air: Humid air has lots of moisture. Over tropical oceans or rain forests, an air mass becomes warm very humid because water can easily evaporate there.

Atmospheric pressure /air pressure: is the weight of air pushing down on an area. Atmospheric pressure changes with height because the amount of air above each level is different. As you go higher in the atmosphere, there is less air above you to push down on you. Air pressure decreases as you go up. Lower air pressure means fewer air particles in a given location.

Convection current: is the rising and sinking of matter in a circular pattern. Temperature differences in air cause wind, storms, and all types of weather. Wind: is movement of air that happens because of differences in air pressure caused by temperature differences.

Have you ever seen a line of clouds move from the horizon until it’s over head? What you have probably seen is the arrival of a front. Front: is a boundary between two air masses. Most air masses move from west to east over North America, so fronts have the same motion.

On the Earth’s surface, high pressure air surrounds warm, low- pressure air. The high pressure causes the warm air in the center to rise. As the air rises, the high pressure air around it flows in to takes it place. This flow of air forms a wind that spirals inward and forms a weather system called a cyclone. There is also anticyclones. They form in areas of higher pressure. Winds in a anticyclone spin the opposite direction than a cyclone. North of the equator, this means winds from an anticyclone flow in a clockwise direction and away from the center.

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