weather systems

weather systems - Weather Systems:1 Weather Systems Air...

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Weather Systems:1 Weather Systems Air Masses Fronts Cyclones & Anticyclones Polar Front Mid Latitude Cyclones Thunderstorms & Tornadoes Hurricanes Air Masses Air masses are large volumes of air that have distinctive characteristics of temperature and moisture. They are created by the exchange of energy and moisture with the land, so they tend to represent their source area , or where they formed. We classify source areas as continental (c) or maritime (m) and as arctic (A), polar (P), tropical (T) or equatorial (E). If we look at the air masses affecting climate in most of North America, we find continental polar (cP) forming in Canada and being cold and dry, maritime polar (mP) from the North Pacific and North Atlantic (cool and moist), continental tropical (cT) from Mexico (hot and dry), and maritime tropical (mT) from the Pacific, Atlantic and Gulf of Mexico (warm and moist). These air masses originate in those regions, but they don’t stay there–they travel. As they move over the surface, they slowly take on the conditions of their new locations, but that takes time. An mP air mass from the North Pacific is cool and moist, but as it travels over Western North America, it warms and dries out as it drops a lot of precipitation. An mT air mass coming north out of the Gulf, slowly loses moisture as it travels over Texas, but it can still be pretty humid when it reaches Lubbock. A cP air mass out of Canada will warm as it travels over the Great Plains, but it can still be cold when it reaches Lubbock. Precipitation Lifting Mechanisms Recall that precipitation requires lifting the air. There are four main ways that this happens. Convergent precipitation occurs when winds from two directions come together and the air has to rise. This is most pronounced along the Intertropical Convergence Zone. We have already gone over convectional lifting, where air rises over a hot surface. This can happen when one part of the ground is hotter than its surroundings (lower albedo) and also when air blows over a warmer surface, like moist air blowing from the ocean onto Florida, then rising. We have also covered orographic lifting, where air rises over mountains. Now let’s look at the fourth type of lifting, frontal . Fronts
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Weather Systems:2 When two air masses meet, they don’t automatically mix, because they have different characteristics of temperature and humidity. The boundary separating them is called a front . Air masses are being pushed together at a front. Colder air is denser than warmer air, so the colder air stays at the surface and the warmer air rises up over it. This is another way of lifting air so that it cools and causes precipitation. A cold front is found where the colder air is pushing into the area occupied by the warmer air mass. Likewise, a warm front is where the warmer air mass is moving over land occupied by the colder air. If neither side is moving, then it is a stationary front . The last type is an occluded front
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weather systems - Weather Systems:1 Weather Systems Air...

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