The Inter Tropical Convergence Zone, or ITCZ, is a belt of low pressure which circles the Earth generally around the equator where the trade winds of the Northern and Southern Hemispheres come together. It is a low pressure area that can be characterized by rising air and convective activity which generates often vigorous thunderstorms over large areas. It can also be an area of calm, notoriously known to sailors as the Doldrums because of its monotonous, windless weather. On satellite images it can be seen as a band of clouds that encircle the Equator. Its movement coincides with the apparent migration of the overhead Sun, drifting northward and southward of the Equator during the Northern Hemisphere's summer and winter months respectively. For this reason it is also called the thermal equator. Its movement affects the wet and dry seasons of the Caribbean. Trinidad and Tobago, along with the southern Caribbean experiences its wet season around summer due to the presence of the ITCZ. When it drifts southwards into the Amazon Basin around January to March, we experience our dry season. Guyana has two rainy seasons as the ITCZ passes over it twice on its way northward and southward.
Anticyclones
Anticyclones are the opposite of depressions - they are an area of high atmospheric pressure where the air is sinking.
Cold fronts
Cold fronts affect the Caribbean region (especially the northern part of the region) during the northern hemisphere winter. During this period, cold air from North America moves into the Caribbean. There is a well defined boundary where this cold, dry air meets the warm, moist air of the Caribbean. The cold air is denser and heavier and so it pushes its way beneath the warm air. The warm air, which is lighter and less dense than the cold air, is forced to rise. There are strong updraughts and tall cumulonimbus clouds are formed. There is often heavy rain and thunderstorms.
Click to view the You Tube videos below that explain the formation and characteristics of the ITCZ and Cold fronts.
Anticyclones
Anticyclones are the opposite of depressions - they are an area of high atmospheric pressure where the air is sinking.
- As the air is sinking, not rising, no clouds or rain are formed. This is because as the air sinks it warms, meaning it can hold more water.
- The absence of fronts means winds may be very light and they flow in a clockwise manner.
- Consequently, high-pressure areas are often associated with settled, dry and bright conditions.
- In the Caribbean, from June to September we are sometimes affected by the Bermuda-Azores high which is a high-pressure system formed over the mid-Atlantic during the Northern Hemisphere summer.
Cold fronts
Cold fronts affect the Caribbean region (especially the northern part of the region) during the northern hemisphere winter. During this period, cold air from North America moves into the Caribbean. There is a well defined boundary where this cold, dry air meets the warm, moist air of the Caribbean. The cold air is denser and heavier and so it pushes its way beneath the warm air. The warm air, which is lighter and less dense than the cold air, is forced to rise. There are strong updraughts and tall cumulonimbus clouds are formed. There is often heavy rain and thunderstorms.
Click to view the You Tube videos below that explain the formation and characteristics of the ITCZ and Cold fronts.