On the surface of the Earth, the heat of the sun obtained by the atmosphere is distributed unevenly. Respectively, the air in different parts of the troposphere will also be different. Due to the uneven distribution of temperatures and moisture content in the atmosphere, the movements of huge volumes of air arise.
The concept of air masses
The air masses are impressive volumes of the air of the troposphere (nearEarth atmospheric layer) formed over a certain territory or what otherwise they are called the underlying surface, and having similar, almost homogeneous in horizontal planes, temperature values and moisture indicators.
These volumes in the horizontal direction are measured by several hundred (sometimes thousands) of kilometers, and in the vertical direction they reach 20-25 km (but on average their height is about 5 km).
Temperature and radiation balance should be established above the underlying surface. In addition, it is necessary to create such conditions for air circulation, under which it would be possible for a long stay of a large volume of air in a particular place. Then the homogeneity of the air mass system is achieved.
Any air mass is separated from another by clear boundaries. Meteorological quantities within the limits of the mass practically do not change. Their sharp increase or decrease occurs at the border of two air masses, in the transition zone (the zone of the atmospheric front).
Formation of air masses
The air mass, having formed in a certain area, acquires its permanent properties. This area is called the focus of formation. It must have specific properties:
Typically, the foci of formation are anticyclones (eddy currents with increased pressure in the center), which are less mobile compared to cyclones (they are characterized by low pressure). Here the air descends and begins to spread in a horizontal direction.
Thermal depressions occur over heated areas of land areas with low atmospheric pressure. Such conditions also contribute to the emergence of a focus.
At the border of various neighboring air masses there are transitional areas or zones fronts. They are tilted relative to the earth’s surface due to the fact that the air masses are moving. The atmospheric front always precedes the mass of air following it.
Depending on the places of occurrence associated with climatic zones, there are such fronts as arctic, polar, tropical. The first is cold, the rest are considered warm.
Fronts have a direct effect on the pressure in the atmosphere and determine the weather in a particular place. This is expressed in the appearance and disappearance of clouds, winds, precipitation.
Movement and circulation. Change of air masses
The air mass does not remain in the area where it formed. Under the influence of the volatility of circulation conditions, it begins to move and transform.
The flow of air masses is global in nature, because their formation and movement covers the oceans, continents, vast areas of the planet. Thus, the totality of air masses makes up the atmospheric circulation of the planet.
The processes of circulation in the atmosphere are mainly influenced by solar energy. Moreover, this energy acts differently on all parts of the planet due to the heterogeneity of the underlying surface. Hence the temperature difference. High-density cold air creates increased pressure and always tends to a warmer area with rarefied air.
While moving from one area to another, the air mass changes its properties. It depends on what territory it passes over, what air masses it borders on, and how much time has passed since its formation. Moreover, the speed of air movement inside the mass is not constant and varies with height. This results in turbulent mixing.
A change in the properties of an air mass is called its transformation or change. It lasts from three to seven days and is considered completed when a constant average daily temperature is established in all layers of the mass day after day. Thus, a new air mass is formed.
Types and types of air masses
Air masses depend on the place of formation, on temperature, on the type of underlying surface.
According to thermodynamic criteria, air masses are divided into three types.
- A warm air mass is one whose temperature is higher than the ambient temperature. Cooling, she seeks to balance. An air mass is cold if its temperature rises in a particular area.
- Neutral (local) air mass is in thermodynamic equilibrium with the environment surrounding it. The masses carrying cold and warm air turn into local masses, gradually transforming in a certain region.
- Air masses are marine and continental. It depends on the nature of the territory of their formation.
The center of formation of sea masses occurs above the surface of the ocean, so their air is saturated with moisture. The emergence of continental air masses occurs over the land of the continents, and therefore their air is dry and dusty.
The emergence of air masses occurs in different latitudes of the planet. Based on this, they are divided geographically into four types:
- equatorial. The source of formation of such masses is located in the region of the equator and nearby latitudes. Characterized by temperatures from 20 ° C and high humidity. When moving from the ocean to land, precipitation occurs in the form of rain.
- tropical. Formed in the latitudes of the tropics. They are characterized by elevated temperatures. Continental air dry and dusty. And the sea is wet.
- Moderate. Occurs between 45 and 65 degrees north latitude. Formed over the continent in winter, they are dry and cold, while in summer their temperature and humidity are much higher. The air of sea masses is humidified and low-temperature constantly.
- Arctic and Antarctic. Appear in latitudinal zones close to the poles. Have low temperature and moisture content. Continental land, marine wetter.
Impact on climate
Climate is a cyclically repeating weather pattern that has formed in a particular area over many years.
Air masses have a huge impact on the climate. It was by their type that the main belts were distinguished: polar (at the north and south poles), temperate, tropical and equatorial. Between them lie transitional belts: subpolar, subtropical, and also subequatorial. All of them differ in the change of air masses in strict accordance with seasonality. In winter, climatic conditions determine the air masses of such a belt, which is closer to the equator, and in summer to the pole. For example, moderate air masses come to the subtropical zone in winter, and tropical air masses in summer.
In the polar zones, which include the territories of the Arctic and Antarctic, cold and dry air masses are formed. Low temperatures prevail here, there is practically no precipitation, and the snow cover remains year-round.
Air masses of temperate latitudes determine the climate of temperate zones. They are dominated by positive temperatures in summer and negative temperatures and solid precipitation in winter.
Tropical air masses form in the tropics. The air here is mostly warm with low humidity. Equatorial air mass occurs in the equatorial belt and sets a very high air temperature. There is a lot of rainfall throughout the year.
In the areas of transitional zones, weather conditions determine those air masses that dominate these territories in a given season of the year.
Properties and characteristics of air masses
The properties of air masses depend on the thermal radiation of the Sun, as well as on the underlying surface. These include such quantities as temperature, relative humidity, transparency (visibility), air pressure.
At the place of formation of the air mass, its properties are preserved until the moment of its movement. Being over a different territory with different properties and characteristics, the initial signs of mass change. It can warm up (cool down), or moisten (dry out).
To characterize air masses, you need to remember that they are formed in different zones of our planet: over the seas and oceans and over the continents.
The Arctic sea air, which comes to the Atlantic and Europe, is transparent and brings with it a cold snap, winds. It is characterized by the presence of cumulus clouds, precipitation in the form of thunderstorms. Its continental subspecies, covering Asia and North America, in summer, in addition to the above, carries low clouds and light winds. Sets clear weather with good visibility in winter.
Sea air in temperate latitudes in summer manifests itself similar to Arctic sea air, and in winter, moderate masses contribute to the formation of stratus clouds, drizzling rain and fog. Continental in winter manifests itself with clear weather, poor visibility and low temperatures. In summer, thunderstorms, cumulus clouds, fog and haze are often.
Tropical sea masses dominate the Atlantic and Pacific oceans, bringing warming and creating stratus clouds, fogs. And the masses formed over land (Europe, Asia, ocean coasts) in summer and winter over water surfaces set clear weather with low transparency, and in winter fogs and stratus clouds are not uncommon over land.
As for the equatorial air masses “migrating” along the equator, at any time of the year they carry heavy and abundant precipitation in the form of heavy rains.
Air masses of Eurasia
The climatic features of our country are influenced by several types of masses: arctic, temperate, tropical, as well as their marine and continental subspecies. The territory of the country is a hotbed of formation of temperate continental masses. They carry air with low humidity, cold in winter and warm in summer. Sea air of temperate latitudes moves from the west from the northern part of the Atlantic, and from the east from the Pacific waters. It has low humidity. It brings coolness in the summer months and warmth in the winter months. Moving eastward, the ISW undergoes a transformation and partially becomes continental.
Air masses of the planet’s tropical belts affect the climate of southern Eurasia. Dry dusty tropical masses carry out their formation over the lands of Kazakhstan and Central Asia. They are characterized by elevated temperatures. Humidified and warm marine air of the tropics invades the Caucasus region and the territory of Eurasia to the Ural Mountains from the Mediterranean Sea. And to the Far East from the central Pacific regions.
The focus of the formation of dry Arctic masses is the waters of the Arctic Ocean. They form the climate of the Russian north, in particular Siberia. They carry low temperature air with good visibility.
The air masses of the Earth’s atmosphere are of impressive size and impact. They, along with other phenomena and processes, affect the climate of individual regions and the planet as a whole. If not for their movement, the temperatures in some belts would be much less comfortable, and perhaps not at all suitable for the existence of living organisms.