Polar cyclones, Polar lows, Extratropical cyclones, Subtropical cyclones, Tropical cyclones, and Mesocyclones.
Cyclone, in strict meteorological terminology, an area of low atmospheric pressure surrounded by a wind system blowing, in the northern hemisphere, in a counterclockwise direction. A corresponding high-pressure area with clockwise winds is known as an anticyclone. In the southern hemisphere these wind directions are reversed. Cyclones are commonly called lows and anticyclones highs. The term cyclone has often been more loosely applied to a storm and disturbance attending such pressure systems, particularly the violent tropical hurricane and the typhoon, which center on areas of unusually low pressure. 

What Are Cyclones?

Location, location, location! This is especially important when we're talking about ocean storms because the location of the storm determines what we call it. For example, if the storm occurs in the Atlantic Ocean and Northeast Pacific, it's called a hurricane. If the exact same type of storm occurs in the Northwest Pacific, this is a typhoon. And if we find those same storms in the South Pacific and Indian Ocean, these are called tropical cyclones.

Cyclone refers to any spinning storm that rotates around a low-pressure center. The low-pressure center is also referred to as the 'eye' of the storm, which is well known for being eerily calm compared with the areas under the spinning 'arms' of the storm. You could say that the eye is watching what's going on down below, so it needs a clear path, but the arms are where all the action happens because this is where the storm is throwing out all of its rain and wind.

Types of Cyclones

The term 'cyclone' actually refers to several different types of storms. They occur in different places, and some occur over land while others occur over water. What they all have in common is that they are spinning storms rotating around that low-pressure center.

Tropical cyclones are what most people are familiar with because these are cyclones that occur over tropical ocean regions. Hurricanes and typhoons are actually types of tropical cyclones, but they have different names so that it's clear where that storm is occurring. Hurricanes are found in the Atlantic and Northeast Pacific, typhoons are found in the Northwest Pacific. If you hear 'tropical cyclone,' you should assume that it's occurring in the South Pacific or Indian Ocean, but for this lesson, we'll use it refer to all types of tropical ocean cyclones.

We can also further describe tropical cyclones based on their wind speeds. They are called category 1, 2, 3, 4 or 5, increasing with intensity and wind speed as the number increases. A category 1 cyclone is the weakest, with wind speeds of 74-95 mph. A category 5 cyclone, on the other hand, is extremely dangerous and has the potential for major damage. Category 5 cyclones have wind speeds of 155 mph and above!

Polar cyclones are cyclones that occur in polar regions like Greenland, Siberia and Antarctica. Unlike tropical cyclones, polar cyclones are usually stronger in winter months. As you can see, these storms really do prefer the colder weather! They also occur in areas that aren't very populated, so any damage they do is usually pretty minimal.

A mesocyclone is when part of a thunderstorm cloud starts to spin, which may eventually lead to a tornado. 'Meso' means 'middle', so you can think of this as the mid-point between one type of storm and the other. Tornadoes all come from thunderstorm clouds, but not all thunderstorm clouds make tornadoes. In order for a tornado to occur, part of that cloud has to spin, and though you can't really see this happening, this is the intermediate, or 'meso' step from regular cloud to dangerous spinning cloud running along the ground.

Formation of a Cyclone

Even though they form over different areas, cyclones tend to come about in the same way and revolve around that low-pressure eye. Warm air likes to rise, and as it rises, it cools. Cool air can't hold as much moisture as warm air, so that water gets squeezed out of the condensing air and a cloud begins to form. If the warm air rises very quickly, this creates anupdraft.

Likewise, if the water in the cloud builds up enough, it may fall back to the ground as rain and draw cool air down with it as a downdraft. When they work together, that warm updraft and cool downdraft create a storm cell. As this process continues, the cloud grows and we eventually get a large thunderstorm cloud.

This thunderstorm cloud is now ready to diversify into other storms like tropical cyclones and tornadoes. But this can't happen unless the air in the cloud starts spinning horizontally. If this occurs over the tropical ocean, this is called a tropical depression. This is like a baby tropical cyclone, with wind speeds less than 39 mph.

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