Shortly speaking cyclones and anticyclones are large regions of relatively low and high pressure, respectively. They occur all over in large range of sizes varying from huge systems to smaller, highly mobile ones.
Both cyclones and anticyclones are characterized by specific circulation patterns. In the Northern Hemisphere a cyclonic circulation of air masses flows counter-clock wise while flow around an anticyclone is clock-wise. Circulation directions are reversed in the Southern Hemisphere.
The cyclones occurring outside the equatorial belt are known as extra tropical cyclones. They are described as large eddies that flow from west to east over the middle attitudes of both Hemispheres. They contribute the mechanism of transfer of excess heat received from the Sun in the equatorial zone toward cooler areas along higher latitudes.
Extra tropical cyclones affect the largest part of the Earth's surface and are most powerful. They mainly cause daily weather changes in the middle and high latitudes. For this reason they support modern forecasting with basic evaluation data.
Formation and development of cyclones is favored by strong horizontal gradients of temperature. A cyclone forms as a disturbance along a zone of big temperature contrast called a front, which in fact is the boundary between two contrasting air masses. A great amount of potential energy is accumulated over this area of strong temperature gradient, which can be readily converted into the kinetic energy of the extra tropical cyclones. As the cyclone is intensifying, the cold air streams rapidly southward forming a cold front while the warm, less dense air moving northwards flows up over the cold air east of the cyclone to produce a warm front. Both air masses blow with different speed what allows the cold front to overtake the warm front to produce a more complicated frontal structure called an occluded front, which may be followed by further storm intensification.
Generally cyclone's life cycle is several days, during which the cyclone may travel from several hundred to a few thousand kilometers.
Anticyclones. They are usually meteorologically quiet regions, larger than cyclones. Air masses of anticyclones move slowly downwards spreading horizontally many hundreds of kilometers.
Usually an anticyclone forms in the region of cold air behind a cyclone as it moves away and before the next cyclone advances. Such an anticyclone is known as a cold anticyclone. The descending air tends to increase in temperature due to its compression. Thus the anticyclone transforms into a warm one. The air layer adjacent to the ground cannot descend and therefore is not much affected by this process.
Anticyclones are areas in which the sunny and warm weather and clear skies are typical in the summer while in the other seasons it may be often cloudy and foggy. The temperatures generated by winter cyclones are colder than normal, especially if the skies are clear.the periods during anticyclones are characterized by little or no rain.