Intertropical Convergence Zone (ITCZ)
An area where the Northern and Southern Hemispheric trade winds converge, usually located between 10 degrees North and South of the equator. It is a broad area of low pressure where both the Coriolis force and the low-level pressure gradient are weak, occasionally allowing tropical disturbances to form. It fluctuates in location, following the sun’s rays, so that during the Northern Hemisphere summer, the ITCZ moves northward over the southern North Atlantic and southern Asia.
Trade Winds
Two belts of prevailing winds that blow easterly from the subtropical high pressure centers towards the equatorial trough. Primarily lower level winds, they are characterized by their great consistency of direction. In the Northern Hemisphere, the trades blow from the northeast, and in the Southern Hemisphere, the trades blow from the southeast.
Equator
The geographic circle at 0 degrees latitude on the earth’s surface. It is equal distance from the North and South Poles and divides the Northern Hemisphere from the Southern.
Low Pressure System
An area of a relative pressure minimum that has converging winds and rotates in the same direction as the earth. This is counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Also known as an cyclone, it is the opposite of an area of high pressure, or a anticyclone.
Related terms: closed low, cold low, and cut-off low
Coriolis Effect
A force per unit mass that arises solely from the earth’s rotation, acting as a deflecting force. It is dependent on the latitude and the speed of the moving object. In the Northern Hemisphere, air is deflected to the right of its path, while in the Southern Hemisphere, air is deflected to the left of its path. It is greatest at the poles, North and South, and almost nonexistent at the equator.
Pressure Gradient
The amount of pressure change that occurs over a fixed distance at a fixed altitude.
Tropical Disturbance
An area of organized convection, originating in the tropics and occasionally the subtropics, that maintains its identity for 24 hours or more. It is often the first developmental stage of any subsequent tropical depression, tropical storm, or hurricane.