THE INTERTROPICAL CONVERGENCE Zone (ITCZ) is a narrow band where the trade winds of the two hemispheres collide. At or near the ITCZ, sea-surface temperature (SST) is at a maximum. As the winds travel over the tropical water, they pick up moisture; where they collide, they are driven upward. The air is also forced upward by convection resulting from heating by the ocean. As the air rises, it cools, the moisture condenses, and heavy rain results. The heat released drives the regional and global atmospheric circulation. It also makes the ITCZ an origin site for cyclones. Another effect of the upward movement of air is relatively calm surface winds. This causes the ITCZ to be an area of downwelling, and, thus, low nutrients and productivity. ...