Primary Air Masses In North America

There are four primary air masses that impact the weather in North America. Continental Polar and Tropical tune masses and the Maritime Polar and Tropical Air masses. The Continental Polar air mass dominates the United States in the winter due to the semi-permanent sub-tropical high atmospheric pressure systems migrating south. In the summer months, the semi-permanent sub-tropical highs over the Atlantic and Pacific oceans migrate north and allows the nautical tropical tune aggregate to bring moisture from the south. This besides allows the Continental Tropical Air mass to form over Texas. When this hot and dry air masses migrates, the leading boundary of the air mass is known as the dry line. With the correct conditions, it can be a major agent as the gun trigger for severe thunderstorms .

Air Mass – Definition

An air mass is a widespread body of air with similar temperature and moisture characteristics in both the horizontal and upright ( homogeneous ). Air masses may cover several thousand square miles.

Air Mass Locations

The geographic location where the air-mass formed is referred to as the Source Region. These regions have uniform surfaces of temperature and moisture characteristics. They are normally bland and uniform ( all down or all water ) and light surface winds. The properties of any air batch will be dependent upon where the air mass originates. Dry tune masses form over land and moist vent masses form over urine .
Air mass locations in the United States

Air Mass Classification

Air masses acquire their properties from spend days to weeks over the same depart of the Earth, for example : over northern Canada, the North Pole, the tropical Pacific Ocean.

Reading: Air Mass Types, Locations, Characteristics & Climate Controls – Meteorology101

Air masses are classed in four categories with two main things to consider .

Land or Water?
Hot or Cold?

Four Categories

c (continental) – source region over land
m (maritime) – source region over water
T (Tropical) – source region in the tropics -E (Equatorial) – extremely warm version of Tropical
P (Polar) – source region in the polar regions – A (Arctic) – extremely cold version of Polar

Combine 1 or 2 with 3 or 4
Polar air masses become very cold, particularly in the winter, because relatively short sunlight shines on the poles of the Earth, and so the air out mass endlessly loses infrared radiation to outer space, which cools it and there is short or no sunlight to offset that cooling .
Tropical Maritime airmass will be identical warmly and humid. A “ tropical continental ” airmass normally covers much of the United States in the summer. other airmass types include “ arctic ”, “ equatorial ”, and “ monsoon ” .

Geographical Indicators

This is besides known as the Source Region Indicator. The geographic indicator denotes the region in which the breeze mass acquired its temperature properties .
Arctic and Antarctic (A) regions are very cold regions of the earth.
Polar (P) regions are cold but not a cold as arctic regions.
Tropical (T) regions are warm to hot depending on the placement.
Equatorial (E) regions receive more energy from the sunday and are very warm .

Air Mass Moisture Indicators

The moisture index denotes the type of open over which the tune mass acquired its moisture properties. There are two major surfaces on the earth, land and water. An air mass that forms over down is called continental (c) mean dry. An air mass that forms over water is called maritime (m) and implies moist. Identifiers are used to tell us where the air-mass originated, moisture capacity and what type of modifications have taken place .

Region Identifiers & Characteristics

Continental Arctic (cA)

The continental arctic ( california ) air-mass forms in the arctic areas of the Arctic Ocean, Antarctica, Greenland, Northern Siberia, Alaska and Canada in the winter. These areas have a uniform surface, normally extremely cold and dry. The abundance of internal-combustion engine and snow, does not allow for increase moisture content because the area in most cases does not have unblock water .
Continental Arctic Air Mass There are some finical characteristics this air-mass possesses. One of thee is it very rarely moves outside its reservoir region. There are times though when it does move forbidden, and the Central Plains vitamin a well as the northeast U.S. experience the coldest tune of the winter. The air-mass is routinely very deep, cold and dry. Since the arctic air-mass stays in its source area most of the time it has the opportunity to become a very deep area of cold air .
The cold air extends very high into the atmosphere. This is in direct contrast to what you have been taught about cold air being shallow, but the cold air just keeps getting deeper, much like piling frost cream into a bowl. The ice cream may be cold but as you pile it on the higher it gets. The pressure system that is associated with the Arctic air-mass is the arctic high which forms in the cold, dry, cave in of the polar region. The polar high forms in the area of the Polar Cell .

Continental Polar (cP)

Continental Air Masses Continental Air Mass This air-mass forms in the northern regions of Canada, Alaska, Siberia and sometimes northern Europe. You will notice an area of higher pressures in the lapp region where these cP air-masses form. This high blackmail allows for the homogeneous area an air-mass needs to form. As the cold of winter settles in, the remission helps intensify the highs which besides weaken in the warmheartedness of summer. These air-masses are typically cold, dry and stable.
Air mass Continental Polar Mass Moving Over Warmer Water In winter, very cold temperatures between -20°F and -40°F and flush colder is observed in it ’ s reservoir region. even in these areas there is large water bodies but in the winter they are freeze and act as land. The skies are by and large clear with possible scattered stratocumulus and good visibility. In industrial areas there may be problems with visibility due to smoke trapped under a settling inversion .
The air-mass has had the opportunity to develop and the farseeing wave practice changes. The cP air-mass moves out of the reservoir region and begins to move south into the lower latitudes. Depending on the season it could be a cold winter smash or a cool, refreshing “ breath of clean air ” in the summer .
As the air-mass moves south the gradient tightens due to the higher pressures in the cold air, the winds will become potent and very cold wind chills may be noticed. As the cold air out moves south it runs into ardent, damp air and a polar battlefront will develop, placing cP air on the +n side and montana air on the -n side .
The cP airmass is noted for it ’ s wide annual variations in all properties, particularly temperature. These large differences make this airmass unique from all the other airmasses. Examples of these differences are the siberian cP is coldest, while european cP is the mildest and-winter cP is more stable than summer cP .

Maritime Tropical (mT)

The source regions for montana tune masses are the tropical and subtropical ocean where the subtropical hard-hitting systems are found .
Maritime Tropical Air Mass The meitnerium breeze masses are identical warm and moist in low levels. There are likely inversions in this vent aggregate during the even that prevent moisture from reaching the higher levels in the troposphere. The eastern side of the subtropical high is more static than the western slope. This makes the eastern side drier than the western side where clouds and precipitation are common. Dew-point temperatures are greater than 60°F. These high dew points make it very uncomfortable in a meitnerium air mass .
During the winter months, temperatures average between 70°F and 80°F. The Gulf Coast of the United States much has meek temperatures, high humidity and considerable cloudiness. When there is an onshore flow, stratus and daze are common. warm, damp air flows north from the Gulf Coast, overrunning the more dense cP air-mass. Thus the cause of cloudiness and precipitation in the cardinal United States .
In the summer, the subtropical high is stronger and the clockwise menstruation draws machine translation air travel over the easterly function of the United States. Temperatures range from 85°F to 95°F and dew points are in the 70 ’ s. Stratus and stratocumulus clouds shape in the early good morning hour along, the Gulf Coast. Because the air is unstable, afternoon air-mass thunderstorms develop. In the easterly part of the subtropical high, the air batch is very stable ; fog and stratus forms off the slide of California over the upwelling areas .
Types of Air Masses in the United States

Maritime Polar (mP)

The source area for the mP air mass is the cold unfrozen ocean areas poleward of 45°. It is associated with the subpolar lows which intensify and shift equatorward in the winter. They form from the modification of another air mass, normally continental polar or nautical tropical, which moves over the cold ocean areas. This is the loom air out mass west of the Rocky Mountains and in western Europe .
Maritime Polar Air Mass Maritime Polar (mP) Air Mass The atmosphere mass is cool and moist in the low levels but dryer aloft. On a Skew-T diagram you will notice the damp conditions up to 750 megabit. Above that, we see a remission anastrophe and much dry air travel due to the down gesticulate of air. There is very little diurnal temperature variation .
The controlling factors that determine the characteristics of the atmosphere mass .

The origin of the body of air in the mP source region
The amount of time spent over the cold ocean water
The trajectory or path taken by the other air mass as it passes thorough the mP source region.

As the continental diametric atmosphere in winter moves across the North Pacific or North Atlantic Oceans, it takes a cyclonic trajectory around the subpolar first gear. This causes the air mass to become unstable aloft. The air coat, and is heated from below. This causes the air batch to become unstable in the low levels. As a resultant role, convective activity develops and moisture is Typically pile and stratocumulus clouds shape with showers and thunderstorms developing. however, the longer the air mass it becomes .
In the summer, the oceans are colder than the air mass coming off the continents. This air out mass is cooled from below causing static conditions in the low levels. In addition, the subpolar low weakens and moves poleward, so the amphetamine levels are more stable. The resulting weather is different from in the winter. Fog and low stratus clouds are coarse over these areas .
When nautical tropical tune moves over the North Atlantic in winter, it travels around the subtropical senior high school in an anticyclonic trajectory. This makes the breeze mass stable aloft. The air mass is besides stable in the low levels because the ocean is cold and it is cooled from below. The longer the air bulk is over the ocean, the higher the cooling extends. It is often difficult to say for sure when the mT vent mass became nautical pivotal .
The military police air out mass has the greatest influence on the Pacific Northwest. It is cool, damp. and mentally ill. Temperatures are normally in the 40s and 50s. As the air moves inland, the coastal mountains force it to rise and much of its moisture falls out in the shape of rain or coke. On the lee side, the military police publicize aggregate is modified and is drier. sometimes this air mass collides with metric ton air in the southerly plains along the “ dry-line ” and severe weather much occurs .
Along the East Coast, mP tune moves southwestward toward the New England states. Since the North Atlantic is very cold and the path is short, winter Atlantic mP air masses are by and large colder than the ones off the Pacific. besides, the United States in the prevail westerlies, Atlantic mP tune masses are not as common .

Continental Tropical (cT)

The only real source region for computerized tomography air travel masses in North America is found during the summer in the desert Southwest and northerly Mexico. hera the air is identical hot and the air rises causing a low-pressure area. These lows are thermal lows and are called heating system lows .
Continental Tropical Air Mass Since computerized tomography air masses are hot and dry, it is not common in the winter season. In the summer, temperatures range from 95°F to 115°F during the day and in the 70s at night. There is a large diurnal temperature range. The air aggregate is very unstable in the broken levels. But the air is sol dry that few clouds form. The ones that do form are typically high based ( 8,000 to 10,000 feet ). occasionally apart thunderstorms develop in the late good afternoon but the precipitation normally evaporates before reaching the grind .

Equatorial Trough

The reservoir region is located. The trough basically a zone from approximately 10°N to 10°S where the equatorial public treasury migrates north and south with the sunlight. The weather is the like year round with 85°F to 100°F and low temperatures range from 75°F to 85°F. The air out high temperatures ranging from evenly distributed throughout the troposphere. When the air is forced aloft, it will produce showers and thunderstorms chiefly in the afternoon. There is little or no mass is precarious with high humidity variation in its properties.

Summary

Continental Polar/Arctic (cP or cA)

Cold/dry air masses
Originate over the ice/snow covered regions of northern Canada and Alaska
Long, clear nights allow for maximum cooling
Very dry
Usually stay in place but occasionally break away and are carried southeast by the upper level winds
Drops in toward the plains so there is not much terrain to impede it.
Moderate (warm up) as they move southward – Particularly if they move over warm water
Produce lake-effect snow up north

Maritime Tropical (mT)

Warm/moist air masses
Originate: Gulf of Mexico Sub-tropical eastern Pacific Western Atlantic
Develop afternoon air-mass thunderstorms
Very stable in the eastern region
Dew points are in the 70’s causing an uncomfortable humidity

Maritime Polar (mP)

Cool and moist in the low levels
Greatest influence on the Pacific Northwest
Cool, moist. and unstable
Sometimes causes severe weather along the dry line in the southern plains.

Continental Tropical (cT)

Hot/dry air masses
Found in the desert Southwest and northern Mexico
Responsible for summer drought conditions
Very unstable in the low levels
Precipitation usually evaporates before reaching the ground

Equatorial (E)

Source region is approximately 10°N to 10°S
The weather is the same year round
Will produce showers and thunderstorms mainly in the afternoon
Unstable with high humidity

Air Mass Climatic Controls

relatively permanent wave factors which govern the general nature of the climate of a part of the earth are known as climatic controls. These factors control the variations of the climatic elements. They control the large-scale climate of an sphere known as macroclimate. These include :

Latitude
The general circulation and semipermanent pressure systems
The distribution of the continents and oceans
Large-scale topography and elevation
Ocean currents

Latitude

Latitude controls the total of available INcoming SOLar radiation sickness ( INSOLATION ) reaching the earth coat. The lean of incidence of the insolation reaching the earth ’ airfoil varies with latitude, increasing toward the poles. As a result, the amount of solar radiation that strikes the surface decreases poleward. At the equator, the suns ’ rays strike the surface directly, thus more energy reaches the earths ’ surface. This variation of sunstroke makes latitude the most authoritative of all climatic controls. broadly, higher temperatures occur at lower latitudes ( near the equator ) and lower temperatures occur at higher latitudes ( near the poles ) .Of all the climatic controls, latitude has the greatest influence on the ball-shaped distribution of temperature. As the earth revolves around the sun, the tilt of the earths ’ axis with respect to its scope is basically the reason for the being of seasons, therefore the seasonal shifts in temperature .
The Angle Of Incidence Varies With Latitude Latitude besides has an influence on moisture and precipitation. broadly, lower latitudes ( where there is more ocean area than continents ) will receive more precipitation than higher latitudes. This is besides due, in part, to the ball-shaped temperature distribution, with quick temperatures near the equator and cold temperatures found near the poles ( strong air rises and cold breeze sinks ) .
Annual Precipitation (dark line) And Evaporation (white area)

Semipermanent Pressure Systems

The general circulation of the air refers to the menstruation of tune over the stallion earth. It serves to transport warm air from tropical regions poleward and maintains a return flow of cold air travel from the poles equatorward .

Three Cell Theory

In each hemisphere, three circulation cells act to redistribute energy. tropical regions receive an excess of energy, while the pivotal regions have energy of zero deficit. The three cell that make up this theory is as follows :

Hadley Cell – From the equator to 30° latitude
Ferrell Cell – From 30° to 60° latitude
Polar Cell – From 60° latitude to the poles

A model below depicts the air flow, in the upright, above the ground ’ mho open .
latitudinal differential heat influences the formation consequently, the focus of the prevail winds. The equatorial trough is broadly found between 10°N and 10°S. This is the region where the northeastern trade winds of the northern hemisphere converge with the southeast trade winds of the southern hemisphere. It is a warm, damp area of rising air that produces a first gear pressure belt at the surface around the ball .
Subtropical highs develop at the surface near 30°N/S ; a direct result of the overlap aloft between the Hadley and Ferrell Cells. These highs separate the easterly trades from the predominate westerlies. They contain quick, dry regions of sinking air ( remission ). They are typically found over receptive ocean regions. In regions associated with the maximum cave in ( southeast quadrant ), major deserts may be found over continents. The two long-run highs located in the northern hemisphere are the : ( 1 ) North Pacific High and ( 2 ) North Atlantic ( Bermuda ) High .
Subpolar Lows occur where the polar easterlies and prevailing westerlies converge ( near 60 ’ I\1/S ). They are found in cold, stormy regions of rising tune. Two long-run lows prevail in the northerly hemisphere : ( 1 ) the aleutian Low and ( 2 ) the Icelandic Low .
Polar Highs develop near the poles. These are a result of the overlap aloft and resulting settling between the diametric cells. They are coldness, dry and very stable regions of sinking air. The Arctic high, in the northerly hemisphere, is hard in the winter and weakens during the summer. See the persona below for distinctive locations of semiperminent pressure systems .
Average Annual Sea-Level Pressure and General Wind Patterns long-run atmospheric pressure systems influence climatic elements. They determine the prevailing, winds which, in turn, influence the handiness of moisture, heat transfer and stability. broadly, the western slope of subtropical highs are fluid ; the eastern side is stable .
Subtropical High

Distribution Of Continents & Oceans

The distribution of continents and oceans and their charm on temperature is second in importance lone to latitude as a temperature master. Land areas display a larger temperature range than that of oceans and coastal regions.All phenomena connected with atmospheric moisture are related to the distribution of land and water vaporization, condensation and cloudiness, and precipitation. generally, the breeze body of water : dehydration and the atmosphere over oceans and coastal regions. The publicize over freeze areas is very over land areas is dryer than the air over oceans and coastal regions. The air travel over freeze areas is very dry .
The general circulation practice will be affected by land/water distribution, efficaciously breaking up the knock of long-run high and low blackmail systems in the mid-latitudes. The best case is over Siberia, where an intense high blackmail system forms as a Quadrants Of The Subtropical High result of intense come on cool in the winter, effectively breaking up the subpolar gutter. Another exercise is over the western United States, where intense surface heating creates a region of low atmospheric pressure over the deserts, efficaciously breaking up the subtropical high.Local circulations are besides produced due to the temperature differential between kingdom and ocean areas .

Large-Scale Topography and Elevation

large-scale topography modifies other climatic controls. Mountain ranges which are parallel to the predominate tip flow will not greatly modify climate. These mountains separate cold climates to the north from quick climates south. Mountain ranges oriented perpendicular to the prevailing tip menstruate will have a great effect on the modification of the climate. For example, the Cascades in the Pacific Northwest force publicize to ascend over the crop. Recall from atmospheric Physics that as publicize ascends a mountain, adiabatic cool and condensation occur, creating cloudiness and precipitation on the windward side. On the leeward english, the air adiabatically warms and dries .
Average Annual Precipitation Based on Topography

Ocean Currents

ocean currents are produced by the frictional effects of the winds circulating around the long-run pressure systems. They tend to follow closely the flow patterns around the system dominating the sphere. warmly currents are located on the east coasts of continents and cold currents on the west coasts ( both hemispheres ). These currents will have a definite effect on coastal climates ampere well as on high and low imperativeness systems that transit across them. A secondary induce of ocean current formation is the dispute in density produced by variations in temperature and salt ( called salt currents ) .
Upwelling is a serve by which cold subsurface waters are brought to the ocean coat. This phenomenon occurs on the west coasts of continents. Wind flowing around the subtropical high parallels the coast. Due to the rotation of the ground and resulting coriolis push, coat waters are transported to the right of the stream, away from the slide. As a leave, cold water. from below the sea surface moves up to replace the die urine. The upwind associated with this condition is cool and damp. Fog and stratus are distinctive with little or no appreciable precipitation. Further inland, the weather is hot and dry .
Upwelling Off The California Coast Ocean currents have a major charm on climate, particularly downriver from the stream. Storms tend to follow warm currents. westerly coastlines ( between 20 and 40° ) are bordered by cold upwelling. currents. The coast will experience little diurnal/annual temperature ranges. periodic haste will develop in the winter, as storms migrate far confederacy. west coasts ( between 40° and 60° ) are bordered by warm currents. Summers are cool, winters are balmy and wet. humble annual temperature ranges are experienced.Eastern seaboards ( between 20° and 40° ) are bordered by warm currents. moderate temperature ranges abound with affectionate temperatures. frequently, showery precipitation occurs due to the unstable air out found on the western slope of the subtropical high. east coasts ( between 40° and 60° are bordered by cold currents. Winters are very cold, summers cool. annual temperature ranges are bombastic .
Ocean Currents And Climate

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Air Mass Types, Locations, Characteristics & Climate Controls – Meteorology101