A tropical climate in the Köppen climate classification is a non-arid climate in which all twelve months have mean temperatures warmer than 18 °C (64 °F). Tropical climates are normally found from the equator to 25 north and south latitude. Tropical climates are typically frost-free, and changes in the solar angle are small since they occupy low latitudes. In tropical climates, the temperature remains relatively constant (hot) throughout the year. Sunlight is intense.
In tropical climates there are often only two seasons: a wet season and a dry season. The wet season normally occurs at the time of high-sun (which is from May through September in the Northern Hemisphere, and from November to March in the Southern Hemisphere). The dry season often occurs at the time of low sun (November to March in the Northern Hemisphere, and from May to September in the Southern Hemisphere).
Within the tropical climate zone there are three distinct varieties based on precipitation:
Tropical rainforest climate
Tropical rainforest climates (AF) normally occur close to the equator, typically within 10 or 15 degrees north and south latitude of the equator. This climate is dominated by the doldrums or Inter-tropical Convergence Zone, and area of sinking air, calm winds, and frequent rainfall. Seasonal rainfall is heavy, often more than 200 cm (80 inches) annually. In tropical rain forest climates, there is either no dry season or at most two dry months. All 12 months have average precipitation of at least 60 mm (2.4 in).
The Amazon basin of South America, the Congo Basin of equatorial Africa and oceanic margins of parts of tropical West Africa have tropical rainforest climates. The insular and peninsular area of Southeast Asia (Malaysia, Thailand, Philippines, New Guinea. Indonesia, etc.) comprises the most extensive region with tropical rainforest climate. Eastern Central America and parts of the Caribbean islands, the Atlantic margins of Brazil, eastern Madagascar island, and southern Ceylon comprise smaller areas with tropical rainforest climate.
Cities featuring a Tropical rainforest climate
Some of the places with this climate are indeed uniformly and monotonously wet throughout the year (e.g., the northwest Pacific coast of South and Central America, from Ecuador to Costa Rica; see, for instance, Andagoya, Colombia), but in many cases, the period of higher sun and longer days is distinctly wettest (as at Palembang, Indonesia) or the time of lower sun and shorter days may have more rain (as at Sitiawan, Malaysia).
(Note. The term aseasonal refers to the lack in the tropical zone of large differences in daylight hours and mean monthly (or daily) temperature throughout the year. Annual cyclic changes occur in the tropics, but not as predictable as those in the temperate zone, albeit unrelated to temperature, but to water availability whether as rain, mist, soil, or groundwater. Plant response (e. g., phenology), animal (feeding, migration, reproduction, etc.), and human activities (plant sowing, harvesting, hunting, fishing, etc.) are tuned to this 'seasonality'. Indeed, in tropical South America and Central America, the 'rainy season' (and the 'high water season') is called Invierno or inverno, though it could occur in the Northern Hemisphere summer; likewise, the 'dry season' (and 'low water season') is called Verano or verão, and can occur in the Northern Hemisphere winter).
Tropical monsoon climate
This type of climate results from the monsoon winds which change direction according to the seasons. In this type of tropical climate, there is a short but distinct dry season. Thus, this zone falls under the influence of the Intertropical Convergence Zone at the time of high sun (summer) and under the influence of the drier Trade Winds at the time of low sun (winter). This climate has a driest month (which nearly always occurs at or soon after the "winter" solstice for that side of the equator) with rainfall less than 60 mm, but at least .
Cities featuring a Tropical monsoon climate
Tropical wet and dry or savanna climate
Aw climates have a pronounced dry season, with the driest month having precipitation less than 60 mm and less than . In the Aw tropical climate the dry season is often several months and can be severe, with most plant and animal life adapting to drought conditions for several months. Aw climates often (but not always as in Africa) occur in higher tropical latitudes, between 15 and 20 north and south. Climates often feature tree-studded grasslands, rather than thick jungle. It is this widespread occurrence of tall, coarse grass (called savanna) which has led to Aw climates often being referred to as tropical savanna. However, there is some doubt whether tropical grasslands are climatically induced. Additionally, pure savannas, without trees, are the exception rather than the rule. It is one of the two varieties of the tropical savanna climates, along with As, with the main difference being that the wet-season in Aw climates usually run in the high-sun months of the year, which runs from April to September in the northern hemisphere, and from October to March in the southern hemisphere.
This type of tropical climate occurs in northern Australia, across the Sudan and eastern Africa, and parts south-central Brazil and adjacent parts of Bolivia and Paraguay and western Madagascar in the southern hemisphere. In the northern hemisphere tropical savanna climate occurs north of the Amazon in Venezuela and Colombia, as well as parts of western Central America, western Cuba, and southern part of Florida in the United States.:208–11
Cities featuring a Tropical savanna climate
Sometimes As is used in place of Aw if the dry season occurs during the high-sun half of the year, which runs from April to September in the northern hemisphere, and from October to March in the southern hemisphere. This is the case in parts of Hawaii, parts of the Caribbean, East Africa, areas of South Asia around the Laccadive Sea and the Brazilian Northeastern Coast. In most places that have tropical wet and dry climates (Aw), however, the dry season occurs during the time of low-sun half of the year, which runs in opposition to As climates.
Intertropical Convergence Zone
Because of the effect of sun angle on climate most areas within the tropics are hot year-round, with diurnal variations in temperature exceeding seasonal variations. Seasonal variations in tropical climate are dominated by changes in precipitation, which are in turn largely influenced by the tropical rain belt or Intertropical Convergence Zone (ITCZ), a portion of the Hadley cell. The ITCZ is shown, for July average, in the graphic. Areas of ascending air have heavy rainfall; areas of descending air are dry. The ITCZ somewhat follows the solar equator throughout the year, but with geographical variations, and in some areas (India) is heavily influenced by local large-scale monsoons.
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Media related to Tropical climate at Wikimedia Commons