Many of us are aware of what a tropical cyclone (hurricane) is, but what about an extratropical one? Extratropical cyclones (aka mid-latitude cyclones) are those that we witness all year round here in the continental U.S. They are simply low pressure systems. Low pressure systems, unlike high pressure systems, rotate counterclockwise. This helps to create convergence since the air is converging towards the center and will want to rise. Thus, clouds and precipitation usually form, if other conditions are also right. These extratropical systems are frequently the cause of our precipitation, especially the stronger and heavier storms. This is because of the greater instability that is present, meaning the atmosphere has a lot of energy to work with. Typically, the stronger the system, the stronger the storm . For instance, many tornadic storms are the result of strong extratropical systems.
An extratropical cyclonegets its energy from the horizontal temperature contrasts that exist in the atmosphere. The temperature contrasts help to provide the forcing and instability needed for storm development in the form of frontal systems. These include cold fronts, warm fronts, and occluded fronts.On the other hand, tropical cyclonesare barotropic in nature, meaning there is constant pressure and density. This type of atmosphere results in no fronts and little temperature differences across the storm at the surface. Tropical cyclone winds are derived from the release of energy in the form of latent heat. Latent heat is energy which is transferred from one substance to another, such as evaporation and condensation processes. In the case of a tropical cyclone, it is due to cloud/rain formation from the warm moist air of the tropics. Furthermore, Tropical cyclones have their strongest winds near the surface of the Earth. In contrast, extratropical cyclones have their strongest winds near the tropopause, which is about 8 miles above the surface. These differences are due to the tropical cyclone being "warm-core" in the troposphere, whereas extra-tropical cyclones are "warm-core" in the stratosphere and "cold-core" in the troposphere. A “warm-core” system refers to a system which is warmer than its surroundings. A schematic view which shows the difference between “warm-core” cyclones (tropical) and “cold-core” cyclones (extratropical) are shown below.
As far as the similarities between the two, tropical cyclones and extratropical cyclones are both symmetrical. They also have surface areas of low pressure with winds that rotate counter clockwise. Furthermore, both produce very heavy precipitation and often times results in flooding. Both tropical cyclones and mid-latitude cyclones can last for several days, and sometimes as long as a week or more.
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@2019 Meteorologist Corey Clay