Air masses affect weather in a number of different ways. In this lesson, you will learn about the different types of air masses found on Earth and how the movement of air masses creates changes in the weather.
Types of Air Masses
Weather is controlled by a variety of factors.
One of the most important is Earth’s air masses. Air masses are huge parcels of air with specific characteristics. What’s interesting about the characteristics of an air mass is that, not only do they describe the air mass, but they also tell you where you can find that air mass on Earth.Let’s look at the different types of air masses found on Earth to see how this works. Air masses can be divided into two main categories based on whether they are found over land or water. If the air mass is found over land, this is a continental air mass.
If the air mass is found over water, this is a maritime air mass. This makes sense: continental air masses occur over the continents, maritime air masses occur over the water, or marine environments. These categories are represented by a lowercase ‘c’ for continental or ‘m’ for maritime.The source region of the air mass helps us classify it even further, and for this, we have three categories. Arctic air masses occur over arctic regions, like Greenland and Antarctica.
Polar air masses occur a little bit farther from the poles, like in Siberia, Canada and the northern Atlantic and Pacific Oceans.Finally, tropical air masses occur in the tropics, so along the equator and over Mexico and the Southwest U.S. Makes sense, right? These categories are represented by the first letter of the source region, but this time we use an uppercase letter. So, ‘A’ stands for arctic, ‘P’ for polar and ‘T’ for tropical.
That’s pretty easy to remember!Each source region can also be either continental or maritime, and to represent this, we simply combine the category letters. This gives us six total types of air masses on Earth: maritime arctic (mA), maritime polar (mP), maritime tropical (mT); and continental arctic (cA), continental polar (cP) and continental tropical (cT).
Air Masses and Weather
You can understand a lot about weather from air masses just by looking at the name. Maritime air masses are going to produce moist weather because they occur over oceans, and oceans are filled with water! The air blowing over the ocean regions, either arctic, polar or tropical, picks up that moisture as it travels along. In maritime arctic and polar regions, this moist air is cool (as you probably expected), and the maritime tropical air mass produces the warm, humid conditions you would expect along the tropics, like Florida and the Caribbean.
In contrast, continental air masses produce dry weather. This is because the continents just can’t compete with the oceans when it comes to moisture! The continental arctic and polar air masses produce dry, cold weather in the winter and pleasant weather conditions in the summer.If you’ve ever been to the Northeast U.S., you know what this weather is like. If you can make it through the bitter, dry winter, you get heavily rewarded with a wonderfully cool and beautiful summer! Continental tropical air masses produce hot, dry conditions like you see in the Southwest U.
S. and Mexico.Just because air masses are found over a region of Earth doesn’t mean that they stay put. In fact, they can move both horizontally and vertically! When air masses move, we can have some drastic changes in weather.One way that air can move vertically is through convectional lifting. Convection is the cyclical process of warm air rising and cool air sinking.
This happens because, just like your black t-shirt absorbs sunlight better than your white t-shirt, some spots on Earth absorb solar radiation better than others. When air comes in contact with these unusually warm spots, it heats up and rises. As it rises, it expands and cools and then sinks back down to the ground. Thus, we have the convection cycle.If there is moisture in the air, it creates a cumulus cloud when it rises. These are the big, fluffy clouds you can identify different shapes and objects in. As the air sinks, the cloud dissipates, which is what creates all that empty sky between cumulus clouds.
Think about it – you usually see a bunch of cumulus clouds in the same area, but not one large, continuous one.The cloud is where the air is rising and releasing moisture. The space in between is where it’s sinking back down to the ground. Each cloud is a convection cycle! If a cumulus cloud grows tall enough, it can turn into a thunderstorm cloud. So, you can see that convectional lifting has the power to change the weather – just by air rising or falling in the same place.
Another way that air masses affect weather is when the air is lifted up over an obstacle, like a mountain. This type of lifting is called orographic lifting. Orographic lifting is responsible for the different weather conditions you see on opposite sides of a mountain. As the air rises up over the mountain, it cools and expands, and any moisture in the air is pushed out.You now know that this forms a cloud, and if there’s enough moisture, the cloud may produce rain. The rain occurs on the windward side of a mountain because this is the side the wind is traveling up. The leeward side of the mountain is the opposite.
The air falling back down is dry because it left all its water in the cloud on the other side!Finally, when air masses meet, they create fronts. Fronts are the contact zone between two different air masses. They may differ in pressure, temperature, density and moisture, but usually it’s a combination of all these factors.
Air masses are like people with differing opinions – one may eventually win over the other, but the disagreement itself creates storms and changes along the zone of contact as the air masses fight it out.
Air masses are large parcels of air with distinct characteristics, and they occur all over Earth. They are classified based on where they’re found.
Continental air masses are found over land (like the continents), and maritime air masses are found over water (like marine environments). We can also classify air masses based on their source region: arctic, polar or tropical.When these two classifications are put together, we get very specific descriptions of the type of air and weather that are produced. Continental air masses produce dry conditions, while maritime air masses produce wet conditions because they can draw water from the oceans they blow over. Similarly, you would probably expect arctic and polar air masses to be cold and tropical air masses to be hot. Put together, you can have dry, cool air (cA or cP); moist, cool air (mA or mP); dry, warm air (cT); or moist, warm air (mT).
Air masses are not stationary, and their movement affects weather. When air masses experience convectional lifting, or the rising of warm air and sinking of cool air, we get cumulus clouds. If they grow large enough, cumulus clouds can turn into thunderstorm clouds and produce some pretty intense storms.Orographic lifting is when an air mass is lifted over an obstacle, usually something like a mountain. The warm air is lifted, and as it rises, it cools and expands. The water in the air creates a cloud and rain over the windward side of the mountain (where the wind initially blows up) and dry conditions on the leeward side.
Fronts occur where two different air masses meet. The type of front depends on which air mass is advancing onto the other. Along the zone of contact, we get changes in weather, such as storms, rain and clouds. Fronts are very much like a disagreement between two people with opposing viewpoints. One may eventually win over the other, but the argument itself can create some serious friction between the two!
Upon completing this lesson, you will be able to:
- Define air masses and identify their classifications
- Explain how cumulus clouds are formed and how they can turn into thunderstorm clouds
- Summarize the effect of orographic lifting
- Describe what a front is