High School Earth Science/Changing Weather - Wikibooks, open books for an open world
Ordinarily, when fronts meet, one air mass is lifted above the other. The map symbols for the different types of fronts are shown in (Figure ): (1) cold front, (2) warm front, (3) stationary front, (4) occluded front. Learn what happens when air masses, or fronts, collide. How Weather Works Cloud formation occurs when humid or water vapor-filled air rises to the point where cooler temperatures force There are four main kinds of fronts, classified by airflow momentum. In a warm front, a warm air mass moves into a cold air mass. A warm front occurs when a mass of warm air meets a mass of cold air. The warm air slowly rises above the cold air, forming a low pressure zone. As the rising.
There are four main kinds of fronts, classified by airflow momentum. In a warm front, a warm air mass moves into a cold air mass. In a cold front, the opposite occurs. In a stationary front, neither air mass advances. Think of it as two fronts bumping into each other by accident.
In an occluded front, a cold front overtakes a moving warm front, like an army swarming over a fleeing enemy. When two air masses of the same temperature collide and neither is willing to go back down, the only way to go is up.
As the name implies, the two winds converge and rise together in an updraft that often leads to cloud formation. Remember the city example? This phenomenon employs the exact same principle, except on a smaller scale. Unequal heating on the Earth's surface can cause a pocket of air to heat faster than the surrounding air.
The pocket ascends, taking water vapor with it, which can form clouds. An example of this might be a rocky clearing in a field or an airport runway, as both absorb more heat than the surrounding area.
List the differences between stationary, cold, warm, and occluded fronts. Air Masses[ edit ] An air mass is a batch of air that has nearly the same temperature and humidity Figure An air mass is created above an area of land or water known as its source region. Air masses come to have a distinct temperature and humidity when they remain over a region for several days or longer.
High School Earth Science/Changing Weather
The heat and moisture leave the ground and move into the air above it, until the overlying air takes on the temperature and humidity characteristics of that particular region. Air masses are created primarily in high pressure zones. They most commonly form in polar and tropical regions, which have very distinctive temperature and humidity. The temperate zones are ordinarily too unstable for air masses to form. Instead, air masses move across them, making the middle latitudes the site of very interesting weather.
Air masses can be 1, km 1, miles or more across and several kilometers thick. Temperature and humidity may change a bit horizontally across the air mass, but not too much. An air mass may have more changes with altitude. The source regions of air masses found around the world. Meteorologists use symbols to describe the characteristics of an air mass. The first symbol tells whether the air mass had its origin over a continent c or over an ocean m, for maritime.
As you might expect, air masses that form over oceans contain more water vapor than those that form over land. The second symbol tells the general latitude where the air mass gained its temperature and humidity traits. The categories are arctic Apolar Ptropical Tand equatorial E. Of course, air masses that form over polar areas are colder than those that form over tropical regions. Globally, the major air masses are continental arctic or continental antarctic cA or cAA ; continental polar cP ; maritime polar mP ; continental tropical cT ; maritime tropical mT ; and maritime equatorial mE.
Maritime arctic and continental equatorial air masses rarely form. A third symbol takes into account the properties of an air mass relative to the ground it moves over. If the air mass is colder than the ground, it is given the designation k, for cold. If it is warmer than the ground, it is given the designation w. For example, a cPk is an air mass with a continental polar source region that is colder than the region it is now moving over.
Air Mass Movement[ edit ] Air masses are pushed along by high-level winds, although they move slower than the winds. An air mass gets its characteristics from the ground or water it is above, and it also shares those characteristics with the regions that it travels over.
Therefore, the temperature and humidity of a particular location depends partly on the characteristics of the air mass that sits over it. If the air mass is very different from the ground beneath it, storms may form. For example, when a colder air mass moves over warmer ground, the bottom layer of air is heated. That air rises, forming clouds, rain, and sometimes thunderstorms. When a warmer air mass travels over colder ground, the bottom layer of air is cooled.
This forms a temperature inversion, since the cold air near the ground is trapped. Inversions may form stratus clouds, advection fogs, or they may trap a layer of pollution over a city. In general, cold air masses tend to flow toward the equator and warm air masses tend to flow toward the poles. This brings heat to cold areas and cools down areas that are warm. Fronts[ edit ] Two air masses meet at a front. Because the two air masses have different temperature and humidity, they have different densities.
Air masses with different densities do not easily mix. Ordinarily, when fronts meet, one air mass is lifted above the other. Rising air creates a low pressure zone. If the lifted air is moist enough, there will be condensation and precipitation.
When air masses meet - Eniscuola
Fronts usually also have winds in them. If the temperature difference between the two air masses is high, then the winds will be strong. Fronts are the main cause of stormy weather. The map symbols for the different types of fronts are shown in Figure The map symbols for different types of fronts. The direction that fronts move is guided by pressure gradients and the Coriolis Effect. In the Northern Hemisphere, cold fronts and occluded fronts tend to move from northwest to southeast.
Warm fronts move southwest to northeast. The direction the different types of fronts move in the Southern Hemisphere is the mirror image of how they move in the Northern Hemisphere. Fronts can be slowed or stopped by a barrier such as a mountain range. The rest of this section will be devoted to four types of fronts. Three of these fronts move and one is stationary.
With cold fronts and warm fronts, the air mass at the leading edge of the front gives the front its name. In other words, a cold front is right at the leading edge of moving cold air and a warm front marks the leading edge of moving warm air. Stationary Fronts[ edit ] Most fronts move across the landscape, but at stationary fronts the air masses do not move. A front may become stationary if an air mass is stopped by a barrier.
For example, cold air masses may be stopped by mountains, because the cold air mass is too dense to rise over them. A region under a stationary front may experience days of rain, drizzle and fog. This weather may be present over a large area. Winds usually blow parallel to the front, but in opposite directions. This results in shear stress. Shear stresses result when objects are pushed past each other in opposite directions.
After several days, the front will break apart. The temperature gradient or temperature difference across the front may decrease, so the air masses start to mix. Shear stresses may force the front to break apart. Conditions may change so that the stationary front is overtaken by a cold front or a warm front.
If the temperature gradient between the air masses increases, wind and rainy weather will result. Cold Fronts[ edit ] When a cold air mass takes the spot of a warm air mass, there is a cold front Figure Since cold air is denser than the warm air, the cold air mass slides beneath the warm air mass and pushes it up.What are weather fronts?
As the warm air rises, there are often storms. A cold front with cold air advancing to displace warm air. The warm air is pushed up over the cold air. When cold air moves underneath warm air, the ground temperature drops.
The humidity may also decrease since the colder air may also be drier. Winds at a cold front can be strong because of the temperature difference between the two air masses. When a cold front is on its way, there may be a sharp change in dew point, changes in wind direction, changes in air pressure, and certain characteristic cloud and precipitation patterns. A shelf line that commonly precedes a squall. Cold fronts often move rapidly across the landscape.
Fast-moving cold fronts create a line of intense storms over a fairly short distance. A squall line is a line of severe thunderstorms that forms along a cold front Figure If the front moves slowly, the storms may form over a larger area.
Imagine that you are standing in one spot as a cold front approaches. Along the cold front, the denser, cold air pushes up the warm air, causing the air pressure to decrease. If the humidity is high enough, some types of cumulus clouds will grow.