Although this is largely valid over the equatorial oceans, the ITCZ and the region of maximum rainfall can be decoupled over the continents. Rainfall seasonality is traditionally attributed to the north–south migration of the ITCZ, which follows the sun. The ITCZ is commonly defined as an equatorial zone where the trade winds converge. This schematic shows that the ITCZ and the region of maximum rainfall can be decoupled over the continents. Seasonal variability of the Intertropical Convergence Zone (ITCZ), Congo air boundary (CAB), tropical rainbelt, and surface winds over Africa (adapted from Dezfuli 2017 with modification). When this occurs, a narrow ridge of high pressure forms between the two convergence zones. Sometimes, a double ITCZ forms, with one located north and another south of the Equator, one of which is usually stronger than the other. Over the oceans, where the convergence zone is better defined, the seasonal cycle is more subtle, as the convection is constrained by the distribution of ocean temperatures. As the heat capacity of the oceans is greater than air over land, migration is more prominent over land. The location of the ITCZ gradually varies with the seasons, roughly corresponding with the location of the thermal equator. The dry descending branch is the horse latitudes. The ITCZ is effectively a tracer of the ascending branch of the Hadley cell and is wet. The ITCZ is formed by vertical motion largely appearing as convective activity of thunderstorms driven by solar heating, which effectively draw air in these are the trade winds. For instance, when the ITCZ is situated north of the Equator, the southeast trade wind changes to a southwest wind as it crosses the Equator. When the ITCZ is positioned north or south of the Equator, these directions change according to the Coriolis effect imparted by Earth's rotation. In the Northern Hemisphere, the trade winds move in a southwestward direction from the northeast, while in the Southern Hemisphere, they move northwestward from the southeast. The ITCZ appears as a band of clouds, usually thunderstorms, that encircle the globe near the Equator. The ITCZ was originally identified from the 1920s to the 1940s as the Intertropical Front ( ITF), but after the recognition in the 1940s and the 1950s of the significance of wind field convergence in tropical weather production, the term Intertropical Convergence Zone ( ITCZ) was then applied. Where the ITCZ is drawn into and merges with a monsoonal circulation, it is sometimes referred to as a monsoon trough, a usage that is more common in Australia and parts of Asia. When it lies near the geographic Equator, it is called the near-equatorial trough. It encircles Earth near the thermal equator though its specific position varies seasonally. The Intertropical Convergence Zone ( ITCZ / ɪ tʃ/ ITCH), known by sailors as the doldrums or the calms because of its monotonous windless weather, is the area where the northeast and the southeast trade winds converge. The ITCZ is visible as a band of clouds encircling Earth near the Equator.
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