Air mass types - Met Office
When air masses form, they are taking on the temperature and The boundary where a cold air mass meets a cool air mass under a warm air mass is called an . 2. Measure the tank's width and height, and then use those. When a moving cold air mass meets a warm air mass, that is lighter, it tends to At our latitudes, over the Atlantic, cyclonic areas form continuously, these are. air masses form north of 50° north latitude and south The boundary where the air masses meet becomes a front. Storms and changeable weather often develop along fronts. Page 2 Since cold fronts tend to move quickly, they can.
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.Air Masses - An Introduction
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. 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.
Air masses and fronts
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. 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.
High School Earth Science/Changing Weather - Wikibooks, open books for an open world
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. High in the atmosphere, winds blow ice crystals from the tops of these clouds to create cirrostratus and cirrus clouds. At the front, there will be a line of rain or snow showers or thunderstorms with blustery winds.
Behind the front is the cold air mass. This mass is drier and so precipitation stops. The weather may be cold and clear or only partly cloudy. Winds may continue to blow into the low pressure zone at the front. The weather at a cold front varies with the season. Thunderstorms or tornadoes may form in spring and summer, when the air is unstable. In the spring, the temperature gradient can be very high, causing strong winds to blow at the front.
In the summer, thunderstorms may be severe and may also include hailstorms. In the autumn, strong rains fall over a large area.
Visibility is usually moderate or poor due to the air picking up pollutants during its passage over Europe and from sand particles blown into the air from Saharan dust storms. Occasionally, the Saharan dust is washed out in showers producing coloured rain and leaving cars covered in a thin layer of orange dust.
Tropical maritime The source region for this air mass is warm waters of the Atlantic Ocean between the Azores and Bermuda. The predominant wind direction across the British Isles, in a tropical maritime air mass, is south-westerly. Tropical maritime air is warm and moist in its lowest layers and, although unstable over its source region, during its passage over cooler waters becomes stable and the air becomes saturated.
Consequently when a tropical maritime air mass reaches the British Isles it brings with it low cloud and drizzle, perhaps also fog around windward coasts and across hills.
Air mass types
To the lee of high ground though, the cloud my break up and here the weather, particularly in the summer months, can be fine and sunny. This is a mild air stream and during the winter month in particular, can raise the air temperature several degrees above the average. Polar continental This air mass has its origins over the snow fields of Eastern Europe and Russia and is only considered a winter November to April phenomena.
During the summer with the land mass considerably warmer, this air mass would be classed as a tropical continental. The weather characteristics of this air mass depend on the length of the sea track during its passage from Europe to the British Isles: With a longer sea track over the North Sea, the air becomes unstable and moisture is added giving rise to showers of rain or snow, especially near the east coast of Britain.
Polar maritime This air mass has its origins over northern Canada and Greenland and reaches the British Isles on a north-westerly air stream. Polar maritime is the most common air mass to affect the British Isles. This air mass starts very cold and dry but during its long passage over the relatively warm waters of the North Atlantic its temperature rises rapidly and it becomes unstable to a great depth. This air mass is characterised by frequent showers at any time of the year.