Monsoon trough in the context of "Australian region tropical cyclone"

Rain is a form of precipitation where water droplets that have condensed from atmospheric water vapor fall by gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water for hydroelectric power plants, crop irrigation, and suitable conditions for many types of ecosystems.

The major cause of rain production is moisture moving along three-dimensional zones of temperature and moisture contrasts known as weather fronts. If enough moisture and upward motion is present, precipitation falls from convective clouds (those with strong upward vertical motion) such as cumulonimbus (thunder clouds) which can organize into narrow rainbands. In mountainous areas, heavy precipitation is possible where upslope flow is maximized within windward sides of the terrain at elevation which forces moist air to condense and fall out as rainfall along the sides of mountains. On the leeward side of mountains, desert climates can exist due to the dry air caused by downslope flow which causes heating and drying of the air mass. The movement of the monsoon trough, or Intertropical Convergence Zone, brings rainy seasons to savannah climes.

The Intertropical Convergence Zone (ITCZ /ɪtʃ/ ITCH, or ICZ), 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. It encircles Earth near the thermal equator, though its specific position varies seasonally. When it lies near the geographic equator, it is called the near-equatorial trough. 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).

The wet season (sometimes called the rainy season or monsoon season) is the time of year when most of a region's average annual rainfall occurs. Generally, the season lasts at least one month. The term green season is also sometimes used as a euphemism by tourist authorities. Areas with wet seasons are dispersed across portions of the tropics and subtropics.

Under the Köppen climate classification, for tropical climates, a wet season month is defined as a month where average precipitation is 60 millimetres (2.4 in) or more. In contrast to areas with savanna climates and monsoon regimes, Mediterranean climates have wet winters and dry summers. Dry and rainy months are characteristic of tropical seasonal forests: in contrast to tropical rainforests, which do not have dry or wet seasons, since their rainfall is equally distributed throughout the year. Some areas with pronounced rainy seasons will see a break in rainfall mid-season, when the Intertropical Convergence Zone or monsoon trough moves to higher latitudes in the middle of the warm season.

The African easterly jet is a region of the lower troposphere over West Africa where the seasonal mean wind speed is at a maximum and the wind is easterly. The temperature contrast between the Sahara Desert and the Gulf of Guinea causes the jet to form to the north of the monsoon trough. The jet's maximum wind speeds are at a height of 3 kilometres (1.9 mi). The jet moves northward from its south-most location in January, reaching its most northerly latitude in August. Its strongest winds are in September while it begins shifting back towards the equator. Within the easterly jet, tropical waves form. Convective complexes associated with these waves can form tropical cyclones. If the jet is south of its normal location during August and September, tropical cyclogenesis is suppressed. If desertification continues across Sub-Saharan Africa, the strength of the jet could increase, although tropical wave generation probably would decrease, which would decrease the number of tropical cyclones in the Atlantic basin.