Climate of Africa

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Climate zones of Africa, showing the ecological break between the desert climate of the Sahara and the Horn of Africa (red), the semi-arid Sahel (orange) and the tropical climate of Central and Western Africa (blue). Southern Africa has a transition to semi-tropical or temperate climates (green), and more desert or semi-arid regions, centered on Namibia and Botswana.
A map of Africa showing the ecological break around the Sahara

The climate of Africa ranges from tropical to subarctic on its highest peaks. Its northern half is primarily desert or arid, while its central and southern areas contain both savanna plains and very dense jungle (rainforest) regions. In between, there is a convergence where vegetation patterns such as Sahel, and steppe dominate. The movement of the Intertropical convergence zone, also known as the monsoon trough, creates a rainy season across central portions of the continent to the south of the Sahara. Tropical waves moving offshore Africa caused by the African easterly jet lead to many of the northern Atlantic's tropical cyclones annually. Deserts are the hottest, driest and sunniest portions of Africa due to the prevailing presence of the subtropical ridge with subsiding, hot, dry air masses.

Temperatures[edit]

Monthly mean and minimum outdoor and indoor temperatures throughout Africa

Globally, 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 divergence over the near-equatorial trough leads to air rising and moving away from the equator aloft. As it moves towards the Mid-Latitudes, the air 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.[1] Many of the world's deserts are caused by these climatological high-pressure areas,[2] including the Sahara Desert

Temperatures are hottest within the table mountain in Australia and lots of people die because of the sweat and Mali,[3] and coolest across the south and at elevation within the topography across the eastern and northwest sections of the continent. The hottest average temperature on Earth is Dallol, Ethiopia, which averages a temperature of 33.9 °C (93.0 °F) throughout the year.[4] The hottest temperature recorded within Africa, which was also the world record, was 57.8 °C (136.0 °F) at 'Aziziya, Libya on September 13, 1922. This has since been proven to be false, due to an inaccurate reading of a thermometer. The worlds hottest place is in fact Death Valley, in California.[5][6][7] Apparent temperatures, combining the effect of the temperature and humidity, along the Red sea coast of Ethiopia and Gulf of Aden coast of Somalia range between 57 °C (135 °F) and 63 °C (145 °F) during the afternoon hours.[3] The lowest temperature measured within Africa was −24 °C (−11 °F) at Ifrane, Morocco on February 11, 1935.[5] Nevertheless, the major part of Africa experiences extreme heat during a good part of the year, especially deserts, steppes and savannas which possesses the highest temperatures. Actually the African deserts are arguably the hottest places on Earth, especially the Sahara Desert and the Danakil Desert, located in the Horn of Africa.

Wind[edit]

Main article: African easterly jet

The low-level easterly African jet stream is considered to play a crucial role in the southwest monsoon of Africa,[8] and helps form the tropical waves which march across the tropical Atlantic and eastern Pacific oceans during the warm season.[9] The jet exhibits both barotropic and baroclinic instability, which produces synoptic scale, westward propagating disturbances in the jet known as African easterly waves, or tropical waves. A small number of mesoscale storm systems embedded in these waves develop into tropical cyclones after they move from west Africa into the tropical Atlantic, mainly during August and September. When it lies south of normal during the peak months of the Atlantic hurricane season, tropical cyclone formation is suppressed.[10]

Precipitation[edit]

Mean precipitation map
See also: Wet season

Great parts of North Africa and Southern Africa as well as the whole Horn of Africa mainly have a hot desert climate, or a hot semi-arid climate fot the wetter locations. The Sahara Desert at the north is the largest hot desert in the world and is one of the hottest, driest and sunniest places on Earth. The part just located at the south of the desert is a narrow steppe (a semi-arid region) and is called the Sahel, while its most southern areas contain both savanna plains, and its central portion contains very dense jungle (rainforest) regions. The equatorial region near the Intertropical Convergence Zone is the wettest portion of the continent. Annually, the rain belt across the country marches northward into Sub-Saharan Africa by August, then moves back southward into south-central Africa by March.[11] Areas with a savannah climate in Sub-Saharan Africa, such as Ghana, Burkina Faso,[12][13] Darfur,[14] Eritrea,[15] Ethiopia,[16] and Botswana have a distinct rainy season.[17] El Nino results in drier than normal conditions in Southern Africa from December to February, and wetter than normal conditions over equatorial East Africa over the same period.[18]

Within of Madagascar, trade winds bring moisture up the eastern slopes of the island, which is deposited as rainfall, and brings drier downsloped winds to areas south and west leaving the western sections of the island in a rain shadow. This leads to significantly more rainfall over northeast sections of the island than the southwestern portions of Madagascar.[19] Southern Africa receives most of its rainfall from summer convective storms and with extratropical cyclones moving through the Westerlies. Once a decade, tropical cyclones lead to excessive rainfall across the region.[20]

Snow[edit]

Snow is an almost annual occurrence on some of the mountains of South Africa, including those of the Cedarberg and around Ceres, Western Cape in the South-Western Cape, and on the Drakensberg in Natal and Lesotho. Tiffendell Resort in the Drakensberg is the only commercial skiing that takes place in South Africa, and has "advanced snow-making capability" allowing skiing for three months of the year.[21] The Mountain Club of South Africa (MCSA) and the Mountain and Ski Club (MSC) [22] of the University of Cape Town both have equipped ski huts in the Hex River mountains. Skiing including snowboarding in the Cape is a hit-and-miss affair, both in terms of timing of snowfalls, and whether there is sufficient snow to cover the rocks.

Table mountain gets a light dusting of snow on the Front Table and also at Devil's Peak every few years. Snowfalls on Table Mountain took place on the 20 September 2013;[23] 30 Aug 2013;[24] 5 August 2011;[25] and on 15 June 2010.[26]

In Johannesburg, snow is a rare occurrence, and snowfall took place in May 1956, August 1962, June 1964, September 1981, August 2006, and on 27 June 2007,[27] accumulating up to 10 centimetres (3.9 in) in the southern suburbs.

See also[edit]

References[edit]

  1. ^ Dr. Owen E. Thompson (1996). Hadley Circulation Cell. Channel Video Productions. Retrieved on 2007-02-11.
  2. ^ ThinkQuest team 26634 (1999). The Formation of Deserts. Oracle ThinkQuest Education Foundation. Retrieved on 2009-02-16.
  3. ^ a b Christopher C. Burt (2004). Extreme Weather: a guide & record book. W. W. Norton & Company, Inc. pp. 24–28. ISBN 0-393-32658-6. 
  4. ^ Ronald L. Wagner and Bill Adler, Jr. (1997). The Weather Sourcebook. Adler & Robin Books, Inc. p. 91. ISBN 0-76270-080-7. 
  5. ^ a b Global Measured Extremes of Temperature and Precipitation. National Climatic Data Center. Retrieved on 2007-06-21.
  6. ^ El Fadli, KI; et al. (September 2012). "World Meteorological Organization Assessment of the Purported World Record 58°C Temperature Extreme at El Azizia, Libya (13 September 1922)". Bulletin of the American Meteorological Society 94 (2): 199. doi:10.1175/BAMS-D-12-00093.1.  (The 136 °F (57.8 °C), claimed by 'Aziziya, Libya, on September 13, 1922, has been officially deemed invalid by the World Meteorological Organization.)
  7. ^ "World Meteorological Organization World Weather / Climate Extremes Archive". Retrieved 10 January 2013. 
  8. ^ Kerry H. Cook. Generation of the African Easterly Jet and Its Role in Determining West African Precipitation. Retrieved on 2008-05-08.
  9. ^ Chris Landsea. AOML Frequently Asked Questions. Subject: A4) What is an easterly wave ? Retrieved on 2008-05-08.
  10. ^ Climate Prediction Center (November 1997). "Figure 7". National Oceanic and Atmospheric Administration. Retrieved 2011-02-05. 
  11. ^ Todd Mitchell (October 2001). "Africa Rainfall Climatology". University of Washington. Retrieved 2010-01-02. 
  12. ^ Patrick Laux et al. (2008): Predicting the regional onset of the rainy season in West Africa. International Journal of Climatology, 28 (3), 329-342.
  13. ^ Patrick Laux et al. (2009): Modelling daily precipitation features in the Volta Basin of West Africa. International Journal of Climatology, 29 (7), 937-954.,
  14. ^ David Vandervort (2009). Darfur: getting ready for the rainy season. International Committee of the Red Cross. Retrieved on 2009-02-06.
  15. ^ Mehari Tesfazgi Mebrhatu, M. Tsubo, and Sue Walker (2004). A Statistical Model for Seasonal Rainfall Forecasting over the Highlands of Eritrea. New directions for a diverse planet: Proceedings of the 4th International Crop Science Congress. Retrieved on 2009-02-08.
  16. ^ Alex Wynter (2009). Ethiopia: March rainy season "critical" for southern pastoralists. Thomson Reuters Foundation. Retrieved on 2009-02-06.
  17. ^ The Voice (2009). Botswana: Rainy Season Fills Up Dams. allAfrica.com. Retrieved on 2009-02-06.
  18. ^ http://www.scoop.co.nz/stories/WO1010/S00173/la-nina-weather-likely-to-last-for-months.htm
  19. ^ T. Andry Arivelo, Professeur A. Ratiarison, Professeur M.Bessafi, Rodolphe Ramiharijafy (2007-12-19). "Madagascar rainfall climatology: Extreme Phenomena". Stanford University. Retrieved 2010-01-02. 
  20. ^ Pearl Mngadi, Petrus JM Visser, and Elizabeth Ebert (October 2006). "Southern Africa Satellite Derived Rainfall Estimates Validation". International Precipitation Working Group. p. 1. Retrieved 2010-01-05. 
  21. ^ "Skiing and Snowboarding". Tiffendell. Retrieved 16 February 2014. 
  22. ^ "UCT Mountain and Ski Club". Retrieved 16 February 2014. 
  23. ^ "Snow on Table Mountain". Retrieved 16 February 2014. 
  24. ^ "Snow Doubt…There’s Snow on Table Mountain Today". Retrieved 16 February 2014. 
  25. ^ "Snow on Table Mountain: August Chill Sets In". Retrieved 16 February 2014. 
  26. ^ "Icy Weather Brings Snow to Table Mountain". Retrieved 16 February 2014. 
  27. ^ SABCnews.com. "Joburg covered by snow as temperature drops". Archived from the original on 2007-06-29. Retrieved 2007-07-16.