Air Masses
It is convenient to think of the lower atmosphere as one uniform and consistent mass of air. In reality this is not the case. Large pockets of air commonly form, they are distinct from the surrounding atmosphere. We call these moving pockets of air, air masses.
All air masses have three things in common. Without these three characteristics we would not consider a body of air an air mass. These three things are as follows.
Firstly, an air mass must be large in size. Often they are more than 1,000 miles (1,600 km) across. In addition to being large horizontally across the landscape, they can also extend several miles upward in altitude, extending high into the atmosphere.
Secondly, The temperature, humidity, and air pressure will be relatively the same at any point within the air mass.
Thirdly, an air mass must be physically bound together, traveling across the atmosphere as a single unit. It must be sufficiently strong so as to not break apart as it is pushed along its course.
Fronts
When two air masses meet, the air within them does not easily mix. That is to say that the air in one air mass will not easily mix with the air from another air mass. Instead the air stays within its own air mass. Because of this, phenomena a border forms between two clashing air masses, as they rub together. This border where two air masses meet is called a front.
The term ‘front’ was first used by Norwegian scientists who compared two air masses colliding to two armies as they clash on the battle front. Just like one army taking over another in a battle, one air mass ultimately takes over, pushing the other one away.
Watch a video:
Warm Fronts
Fronts that bring warm air are referred to as warm fronts. As this warm air approaches it is lifted upward above the cooler air. As the air in the warm air mass rises, it expands, causing it to cool down. As it cools, water vapor can condense creating precipitation.
This precipitation is generally light, and forms gradually. Clouds first form in the sky as the warm air is lifted upward, proceeded by thicker clouds, and ultimately some form of precipitation.
Cold Fronts
A front bringing in a cold air mass is referred to as a cold front. Because cold fronts move along the ground where they encounter friction, they move slower at ground level than they do further up in the atmosphere. For this reason, cold fronts tend to be more sloped than warm fronts.
Typically cold fronts move faster than their warmer counterparts. The combination of higher speed, and slope push warm air masses upward very quickly. This quick upward air movement causes the warm air being displaced to cool quickly, becoming turbulent. This turbulence often can be the cause of extremely violent weather.
Because cold fronts move quickly, the weather associated with them typically also moves quickly, and passes over a particular location in a short period of time. The turbulent weather generally stays right in line with the front.
There is a link to a video about the weather, try it!
And finally, play the game, follow instructions and put the weather symbols on the right location:
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