Cyclones and Anti-Cyclones

If you want a question answered. If you know the answer to a question. This is the forum for it.
Please start a new thread for each weather question so we can all find the info quickly and easily.
WAWG Administrator
User avatar
Posts: 12284
Joined: Tue Nov 07, 2006 6:36 pm
Location: Lower West

Cyclones and Anti-Cyclones

Postby Fu Manchu » Thu Dec 08, 2011 8:05 pm


WAWG Administrator
User avatar
Posts: 12284
Joined: Tue Nov 07, 2006 6:36 pm
Location: Lower West

Re: Cyclones and Anti-Cyclones

Postby Fu Manchu » Thu Dec 08, 2011 8:06 pm

Anticyclones are basically the opposite of cyclones (Greek prefix, anti, means opposite). Cyclones are areas of surface convergence and upper level divergence, and since anticyclones are the exact opposite, anticyclones are areas of surface divergence and upper level convergence. A cyclone is formed as a result of expanding, rising, and unstable air caused by heating. However as volume increases, the temperature decreases. According to Charles law, at a constant pressure, volume varies directly with absolute temperature. But still, why is it that when the volume increases, the expanding airs temperature decreases. According to the Kinetic theory, gas molecules are in constant random motion, and thus move hither and thither. Now in most cases, heat is energy, and when heat is added into a reaction, it often acts as a catalyst. Hence, the gas molecules move faster and take up more space as they move at higher velocities, increasing the volume. So now one liter of the air parcel would now occupy more space than it did previously. Moreover as the gas molecules move faster, they interact and bounce off each other more. As they bounce off each other, they transport some of that energy to each other, but some of that energy is also released in to the ambient air (Latent heat), causing a loss of energy. It is in a sense, semi-nuclear fusion phenomena. They then become cooler as they lose energy, and if the air contains ample water vapor, it would actually condense into clouds, cooling the surrounding area even further. This is why rain and cooler weather are often associated with low pressure systems. On the other hand, anticyclones formed as a result of contracting, sinking and stable air, caused by cooling or a relatively dry environment. Now because air molecules are more contracted in anticyclones, they have less space to move, and will actually hit each other more. This causes an increase in temperature, and because there were no external forces involved, the air warms adiabatically. For example if you use an air compressor, youll notice that the more you compress the air, the warmer it will become. This is why higher temperatures are often associated with regions of high pressure. In most cases, high pressure systems are what drive atmospheric phenomena such as heat waves. But depending on which side of the cyclone or anticyclone axis you are, the temperature may vary. For example if you are at the eastern side of an anticyclone in the northern hemisphere, the temperature will likely be cooler due to northerly winds; but the temperature would be warmer at the eastern side of a cyclone due to southerly winds.

Cyclones and anticyclones work in a perpetual-unbreakable harmony; without anticyclones there would be no cyclones. Air flows from areas of higher pressure to low pressure, just as water can flow from the higher levels of a mountain to the bottom, or just as water in a sink flows from the surrounding regions to the sink hole—it is just another way nature maintain its equilibrium. As air flows away from an anticyclone to a cyclone, the air moves at a greater velocity as a near the center of the cyclone, just as a rock would roll faster as it nears the bottom of a hill, or just as water would flow faster as it nears the center of a whirlpool. However in the atmosphere the steepness of the air is known as the pressure gradient. Thus, the greater pressure difference between a cyclone and its surroundings; the greater the wind would be, likewise, the greater the steepness of a mountain; the greater the speed a rock could roll down.
There are regions in the world where high pressure systems almost constant. They are the subtropical regions, and the Polar Regions. Sinking air from the Hadley cells usually cause anticyclogenesis in numerous parts of the subtropical areas, which is why the subtropical regions have major deserts such as the Kalahari, Sahara, etc. Sinking air from the semi-perpetual polar high usually does the same thing, and that is why the Polar Regions such as Antarctica barely receive any precipitation year round. The subtropical Atlantic is dominated by the Azores and Bermuda high. Because of their predominance, they cause major capping inversions, this region of the Atlantic receives little rainfall a year. Likewise, there are places in the world where low pressure systems are almost constant. Air converges at the intertropical convergence zone (ITCZ)* year round, causing copious precipitation. The polar front at approximately 60 degrees latitude is a baroclinic perpetual low pressure system that induces the formation of numerous mid-latitude cyclones in the temperate regions of the earth.

The equatorial trough is basically the same thing as the ITCZ, but because the earth tilts, the location of the trough moves meridionally year round.

Return to Your Weather Questions

Who is online

Users browsing this forum: No registered users and 3 guests