What is Cyclogenesis?

Cyclogenesis is the strengthening and development of a cyclone. Cyclones will form as cyclonic circulation builds in a low pressure area. Cyclogenesis can form tropical cyclones, mesocyclones and extratropical cyclones. A cyclone can not only form a thunderstorm but a blizzard as well, depending on temperature conditions.

Cyclone scale sizes:

Meteorological scales divide cyclones into four main sizes. The microscale is the smallest of cyclone sizes and has a range of under 1.2 miles or 2 kilometers. This is about the scales of tornadoes. The next size is sometimes divided into two ranges and is the mesoscale. The mesoscale includes meso-alpha, a range of 125 to 1,243 miles across and is commonly a tropical cyclone. Also in mesoscale is the smaller meso-beta range of 20 to 200 miles. A cyclone of this range is referred to as a mesocyclone.

The third largest in size range is the synoptic scale with a range of 620 to 1,550 miles, or 1,000 to 2,500 kilometers, in area. Extratropical cyclones come under this category and cover large portions of a continent. The largest scale size of cyclones is the macro scale and this is a system of global proportion.

Cyclone development:

There are two commonly used models for cyclone development. The Shapiro-Keyser Model and the Norwegian model. The Norwegian model is the older of the two theories and was developed in World War I. In the Norwegian model theory, cyclones develop as they move along a frontal boundary and reach a colder atmospheric environment. This theory provides a good description for cyclones over land mass.

The Shapiro-Keyser model was developed in 1990. This model used the study of oceanic cyclones and their structure. This model is more appropriate in cases of rapid cyclone development. While this theory shows a cyclone having both warm and cold fronts, the cold front is shown to move perpendicularly to the warm front and the two fronts do not meet.

Tropical cyclones:

Tropical cyclones require warm water surface temperatures combined with high humidity, atmospheric instability, a low pressure center and vertical wind shear. Tropical cyclones can become extratropical cyclones if they have sufficient strength as they reach land.

Mesocyclones:

Mesocyclones will range between microscale to mesoscale in size. They have a mid-level rotation in severe thunderstorms and are driven by the heat of the thunderstorm. Tornadoes are formed in the warm areas of mesocyclones and extratropical cyclones. The require a strong upper level jet stream. As updrafts rotate they can form wall clouds. These wall clouds are spinning layers that descend from the cyclone. However, wall clouds do not always rotate or require a cyclone to form.

Extratropical cyclones:

Extratropical cyclones are low pressure systems that develop outside of tropical areas. Extratropical cyclones can produce anything from simple cloudiness and showers to heavy winds and thunderstorms.

References:
http://wxpaos09.colorado.edu/blizzard/background.html

http://nat.as.ntu.edu.tw/tylab/course_adv/Chap%203.pdf

http://www.imd.gov.in/section/nhac/dynamic/faq/FAQP.htm