The air mass is a layer of air with a radius of about 1000 km and a thickness of several kilometers. The layer is homogeneous and is characterized by a certain temperature and humidity. Air masses can form both over the continents and over the oceans and seas. How sea air masses differ from continental ones, the article will answer.
The term "air masses"
This concept was first applied in the 20s of the last century by Norwegian scientists. By this term they meant huge volumes of air, which are characterized by relative equality of physical properties. They in space can be located above the surface in hundreds and thousands of kilometers, covering a strip of up to 20 o in units of latitude. Moreover, in different parts of the layers the temperature and humidity will differ, however, the difference is small compared to the scale of the mutual effects of the air mass and the surface over which it is located on each other.
Movement and interaction with the surface
Considering the question of how sea air masses differ from continental ones, one should get to know better the general properties of air masses.
Air mass (VM) is not a stationary object, it is constantly moving. The process of moving a VM above the surface of the earth is perceived as wind. Due to its enormous size, the same layer of air can be above a specific area for several days, which means that constant weather will be observed here during this period.
When a VM passes over a surface, it interacts with it. As a result of this, the physical conditions of both objects change. For example, if a VM passes over a terrain heated by the sun's rays, then it warms up itself, its humidity increases, and the formation of clouds and clouds accelerates, which ultimately leads to rains and thunderstorms. If the VM spreads over a cold surface, then its temperature decreases and the dew point decreases, which entails the formation of fogs.
Sources of air masses
The area over which the mass of air is formed with the given characteristics is called the source of the VM. For its formation, not every surface on the planet is suitable. In order for a VM to form over a specific territory, the following conditions must be met:
- The territory should have homogeneous properties. For example, the area where water spaces alternate with land, or where mountains are replaced by plains, is not suitable for the formation of VMs.
- Above the territory, air should be able to stay sufficient time to establish equilibrium.
A good place for the formation of VM is a stationary anticyclone, which is located above the relatively flat land surface. On the contrary, cyclones almost never lead to the formation of VMs, since they are characterized by moderate winds, and the air in them is constantly mixed and flows from different regions of the planet.
Classification of air masses according to the breadth of their formation
As noted above, all VMs are characterized by two main parameters: temperature and humidity. Often add a third parameter - the stability of the mass. In this regard, the following types of VM are distinguished:
- air masses of the Arctic belt;
- moderate VM;
- tropical VMs;
- equatorial.
The zones of formation of these masses are as follows: equatorial VMs are formed at latitudes +/- 20 o of the northern and southern hemispheres, tropical ones - at latitudes 20-35 o of each hemisphere, moderate - within 50-65 o , arctic form at the poles and adjacent areas of our planet.
Note that the breadth of the formation of VMs directly correlates with their temperature, so the air masses of the Arctic belt are extremely cold, their temperature can drop below -50 ° C. In turn, tropical VMs are quite warm, their temperature can exceed 40 ° C.
How are marine air masses different from continental?
Not only temperature, but also humidity determines the properties of this VM. Given that the source of air mass can be either the land surface or the surface of the water, continental and marine VMs are distinguished. How are marine air masses different from continental? Of course, the humidity level. Marine VMs are formed above the surface of the seas and oceans; therefore, they are characterized by air saturation with water vapor, as well as the formation of cumulonimbus clouds. Continental climate air masses are dry volumes of air that can be distinguished by the presence of layered and cirrus clouds.
There is another feature that distinguishes marine and continental VMs from each other - this is the temperature. So, sources of warm and dry masses practically do not exist, all VMs of the tropical and equatorial climate are humid, since there are many seas and oceans in the low and middle latitudes of our planet. Very cold and wet VMs also practically do not exist, since the Arctic are dry layers of air, and the temperature limits of the sea moderate air mass are in the range 0-15 ° C.
The issue of air mass stability
As soon as a VM has formed over a certain territory, it gradually leaves it and begins to move to places that have different physical characteristics than the source of its formation. For example, the prevailing air masses in the maritime climate area form over the oceans and then move across continents.
There are two main types of changes in VMs that can affect their stability. These changes are associated with the temperature difference of the VM itself and the surface over which it moves:
- If the VM is colder than the surface, then it heats up in its lower layers and creates ideal conditions for mixing air and the formation of precipitation. That is, the mass becomes unstable.
- If the VM has a higher temperature than the surface, then its lower layers are cooled, there are no conditions for the formation of ascending air currents, and the mass is stabilized.
In addition to the temperature difference, the stability of the VM is also affected by cyclones and large differences in elevation on the surface.