Subtropics

The subtropics and tropics

Areas of the world with subtropical climates

The subtropics are geographic and climate zones located roughly between the tropic circle of latitude at 23.5 latitude (the Tropic of Cancer and Tropic of Capricorn) and temperate latitudes (normally temperate latitudes refer to locations higher than 40 latitude).

Subtropical climates are often characterized by warm to hot summers and cool to mild winters with infrequent frost. Most subtropical climates fall into two basic types: 1- Humid Subtropical, where rainfall is often concentrated in the warmest months (for example Brisbane, Australia or Jacksonville, Florida) and 2- Dry summer (or Mediterranean) where seasonal rainfall is concentrated in the cooler months (for example Naples, Italy or Los Angeles, California).

Subtropical climates can occur at high elevations within the tropics, such as in the southern end of the Mexican Plateau and in Vietnam and Taiwan. Six climate classifications use the term to help define the various temperature and precipitation regimes for the planet Earth.

A great portion of the world's deserts are located within the subtropics, due to the development of the subtropical ridge. Within savanna regimes in the subtropics, a wet season is seen annually during the summer, which is when most of the yearly rainfall falls. Within Mediterranean climate regimes, the wet season occurs during the winter. Areas bordering warm oceans are prone to locally heavy rainfall from tropical cyclones, which can contribute a significant percentage of the annual rainfall. Plants such as palms, citrus, mango, lychee, and avocado are grown within the subtropics. Tree ferns and sequoia also grow within subtropical climate regimes.

Definition

The tropics have been historically defined as lying between the Tropic of Cancer and Tropic of Capricorn, located at 23.45° north and south latitude respectively.^[1] The poleward fringe of the subtropics is located at approximately 40° north and south latitude respectively.^[2] Northern fringes of the type can go further north due to moderating effects of ocean streams, like in parts of Western Europe due to heat transported by the Gulf Stream.

Temperatures

Tadrart Acacus desert, part of the Sahara, in western Libya.

Several methods have been used to define the subtropical climate. In the Trewartha climate classification, a subtropical region should have at least eight months with a mean temperature greater than 10 °C (50.0 °F) and at least one month with a mean temperature under 18 °C (64.4 °F).^[3] German climatologists Carl Troll and Karlheinz Paffen defined Warm temperate zones as plain and hilly lands having an average temperature of the coldest month between 2 °C (35.6 °F) and 13 °C (55.4 °F) in the Northern Hemisphere and between 6 °C (42.8 °F) and 13 °C (55.4 °F) in the Southern Hemisphere, excluding oceanic and continental climates. According to the Troll-Paffen climate classification, there generally exists one large subtropical zone named the warm-temperate subtropical zone,^[4] which is subdivided into seven smaller areas.^[5]

According to the E. Neef climate classification, the subtropical zone is divided into two parts: Rainy winters of the west sides and Eastern subtropical climate.^[6] According to the Wilhelm Lauer & Peter Frankenberg climate classification, the subtropical zone is divided into three parts: high-continental, continental, and maritime.^[7] According to the Siegmund/Frankenberg climate classification, subtropical is one of six climate zones in the world.^[8]

In the Köppen climate classification^[9] subtropical climates are classified together with colder temperate climates in the "Warm temperate climates" (letter designation C). The overbroad class C in the Köppen classification lead to newer classification schemes that divide or redefine this class into smaller classes, like the Trewartha climate classification scheme.

Rainfall

Hadley cells located on the Earth's atmospheric circulation.

Heating of the earth near the equator leads to large amounts of upward motion and convection along the monsoon trough or Intertropical convergence zone. The upper-level divergence over the near-equatorial trough leads to air rising and moving away from the equator aloft. As the air moves towards the Mid-Latitudes, it cools and sinks, which leads to subsidence near the 30th parallel of both hemispheres. This circulation is known as the Hadley cell and leads to the formation of the subtropical ridge.^[10] Many of the world's deserts are caused by these climatological high-pressure areas,^[11] located within the subtropics. This regime is known as an arid subtropical climate, which is generally located in areas adjacent to powerful cold ocean currents. Examples of this climate, the coastal areas of southern Africa (Namibia, South Africa), south of the Canary Islands and the coasts of Peru and Chile.^[12]

The humid or monsoon subtropical climate is often located on the western side of the subtropical High. Here, unstable tropical airmasses in summer bring convective overturning and frequent tropical downpours in the hot season. In the winter (dry season) the monsoon retreats, and the drier Trade Winds bring more stable airmass and often dry weather. Areas that have this type of subtropical climate include Australia, Southeast Asia, parts of South America, and the deep south of the United States. .^[13][14][15] Monsoon regions with a wet season include western Mexico.^[16] the Desert Southwest of the United States,^[17] Within the Mediterranean climate regime, the west coast of the United States and the Mediterranean coastline of Italy, Greece,^[18] and Turkey experience a wet season in the winter months.^[19] Similarly, the wet season in the Negev desert of Israel extends from October through May.^[20] At the boundary between the Mediterranean and monsoon climates in North America lies the Sonoran desert, which receives the two rainy seasons associated with each climate regime.^[21]

In areas bounded by warm ocean, tropical cyclones can contribute significantly to local rainfall within the subtropics.^[22] Japan receives over half of its rainfall from typhoons.^[23]

Flora

Curitiba, Brazil: Live oak with araucarias.

These climates do not routinely see hard frosts or snow, which allows plants such as palms and citrus to flourish.^[24][25] As one moves toward the tropical side the slight winter cool season disappears, while at the poleward threshold of the subtropics the winters become cooler. Some crops which have been traditionally farmed in tropical climates, such as mango, litchi, and avocado, are cultivated in the subtropics. Pest control of the crops is less difficult than within the tropics, due to the cooler winters.^[26]

Tree ferns (pteridophytes) are grown within subtropical areas, primarily within the subtropics and within topography within the tropics. Dracaena and yucca can grow within the subtropics. Trees within the Taxaceae family grow within subtropical climate regimes. Apple, pear pomegranate grows well ^[27]

Varieties

Highland variety

Cumbres del Ajusco National Park in Mexico.

View of Antananarivo, Madagascar.

Saint Louis University in Baguio City, Philippines.

The subtropical highland variety (Köppen climate classification: Cfb, Cwb) of the oceanic climate exists in elevated portions of the world that are either within the tropics or subtropics, though it is typically found in mountainous locations in some tropical countries. Despite the latitude, due to the higher altitudes of these regions, it tends to share characteristics with oceanic climates.

In locations outside the tropics, other than the drying trend in the winter, subtropical highland climates tend to be essentially identical to an oceanic climate, complete with mild summers, noticeably cooler winters and in some instances, some snowfall. In the tropics, a subtropical highland climate tends to feature spring-like weather year-round. Temperatures here remain relatively constant throughout the year and snowfall is seldom seen. Areas with this climate feature monthly averages below 22 °C (72 °F) but above −3 °C (27 °F) (or 0 °C (32 °F) using American standards). At least one month's average temperature is below 18 °C (64 °F). Without the elevation, many of these regions would likely feature either tropical or humid subtropical climates. These regions usually carry a Cwb or Cfb designation.

This type of climate exists in parts of east, south and south-eastern Africa, some mountainous areas across southern Europe, sections of mountainous Latin America, some mountainous areas across Southeast Asia, higher elevations of the southern Appalachians, the Mexican Plateau down past the 19th parallel to Morelos,^[28][29] and parts of the Himalayas. It also occurs in a few areas of Australia, although average high temperatures during summers there tend to be higher and the climate drier than is typical of subtropical highland climates, with maximums sometimes exceeding 40 °C (104 °F).^[30]

Mediterranean climate

Parc Güell, Barcelona, Spain.

The Mediterranean climate regime resembles the climate of the lands in the Mediterranean Basin, parts of coastal southwestern North America, parts of Western and South Australia, in southwestern South Africa and in parts of central Chile. The climate is characterized by hot dry summers and moderate or high rainfall in winter,^[31] in areas under the constant influence of the subtropical ridge. Since mediterranean climates are primarily decided by rainfall patterns, climates that are not subtropical temperature-wise can also be mediterranean. For example San Francisco sees average highs in the warmest month below 22 °C (72 °F) with cool nights. Inland from the immediate coastlines, mediterranean climates can take on extreme temperatures. This is seen in inland California as well as Andalusia in Spain. Mediterranean climates can go as far from the equator as 49° latitude north around Vancouver, in places where a rain shadow is prevalent. Drying trends can be found even farther north, but summer precipitation usually remains significant above these latitudes. In Europe, the northernmost mediterranean climates go to around the French Riviera, located at 43° latitude. On the immediate Atlantic coastline, the mediterranean boundary goes between Porto and Vigo at around 41° latitude.

Humid variation

Wetland Park in Hong Kong.

The humid subtropical climate is a subtropical climate type characterized by hot, humid summers with frequent tropical downpours of short duration and warm to cool dry winters. Normally, rainfall is concentrated in the warmest months of the year. At times, the average annual precipitation may be evenly distributed throughout the year (Trewartha climate classification: Cfa) or marked by a dry season or drying trend during winter (Trewartha climate classification: Cwa).

^[33] Humid subtropical climates lie on the east side of continents, roughly between latitudes 25° and 35° degrees away from the equator.^[34] However, the humid subtropical climates can reach as far north as 45° degrees latitudes or even slightly north of that in Europe, due to the warming influence of the Atlantic and the Mediterranean Sea in areas that do not see the summer drought such as in Milan and the surrounding region inside Northern Italy. In Asia, the poleward cool to cold winter-area of this climate type is prevalent in most of Japan, although seldom much farther north than 40° latitude.

Semi-desert/desert climate

Mount Benacantil, Alicante, Spain.

Arid subtropical climates are characterized by an annual average temperature of 18.2 °C (64.8 °F), the absence of regular rainfall and high humidity. Mild climate variants are generally located in areas adjacent to powerful cold ocean currents. Examples of this climate, the coastal areas of southern Africa (Namibia, South Africa), south of the Canary Islands and the coasts of Peru and Chile. ^[12]

See also

Wikimedia Commons has media related to Subtropics.

• Geographical zone
• Subtropical cyclone

References