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The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth. The tropics are also referred to as the tropical zone and the torrid zone (see geographical zone). The tropics include all the areas on the Earth where the Sun reaches a subsolar point, a point directly overhead at least once during the solar year. The tropics are distinguished from the other climatic and biomatic regions of Earth, the middle latitudes and the polar regions on either side of the equatorial zone. == Seasons and climate == "Tropical" is sometimes used in a general sense for a tropical climate to mean warm to hot and moist year-round, often with the sense of lush vegetation. Many tropical areas have a dry and wet season. The wet season, rainy season or green season, is the time of year, covering one or more months, when most of the average annual rainfall in a region falls.〔Glossary of Meteorology (2009). (Rainy season. ) American Meteorological Society. Retrieved on 2008-12-27.〕 Areas with wet seasons are disseminated across portions of the tropics and subtropics.〔Michael Pidwirny (2008). (CHAPTER 9: Introduction to the Biosphere. ) PhysicalGeography.net. Retrieved on 2008-12-27.〕 Under the Köppen climate classification, for tropical climates, a wet season month is defined as a month where average precipitation is or more. Tropical rainforests technically do not have dry or wet seasons, since their rainfall is equally distributed through the year.〔Elisabeth M. Benders-Hyde (2003). (World Climates. ) Blue Planet Biomes. Retrieved on 2008-12-27.〕 Some areas with pronounced rainy seasons see a break in rainfall during mid-season when the intertropical convergence zone or monsoon trough moves poleward of their location during the middle of the warm season.〔J . S. 0guntoyinbo and F. 0. Akintola (1983). (Rainstorm characteristics affecting water availability for agriculture. ) IAHS Publication Number 140. Retrieved on 2008-12-27.〕 When the wet season occurs during the warm season, or summer, precipitation falls mainly during the late afternoon and early evening hours. The wet season is a time when air quality improves, freshwater quality improves and vegetation grows significantly, leading to crop yields late in the season. Floods cause rivers to overflow their banks, and some animals to retreat to higher ground. Soil nutrients diminish and erosion increases. The incidence of malaria increases in areas where the rainy season coincides with high temperatures. Animals have adaptation and survival strategies for the wetter regime. Unfortunately, the previous dry season leads to food shortages into the wet season, as the crops have yet to mature. Regions within the tropics may well not have a tropical climate. There are alpine tundra and snow-capped peaks, including Mauna Kea, Mount Kilimanjaro, and the Andes as far south as the northernmost parts of Chile and Argentina. Under the Köppen climate classification, much of the area within the geographical tropics is classed not as "tropical" but as "dry" (arid or semi-arid) including the Sahara Desert, the Atacama Desert and Australian Outback. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tropics」の詳細全文を読む スポンサード リンク
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