Geography of South America

The geography of South America contains many diverse regions and climates. Geographically,

South America became attached to North America only recently (geologically speaking) with the formation of the Isthmus of Panama some 3 million years ago, which resulted in the Great American Interchange. The Andes, likewise a comparatively young and seismically restless mountain range, runs down the western edge of the continent; the land to the east of the northern Andes is largely tropical rainforest, the vast Amazon River basin. The continent also contains drier regions such as eastern Patagonia and the extremely arid Atacama Desert.

The South American continent also includes various islands, most of which belong to countries on the continent. The Caribbean territories are grouped with North America. The South American nations that border the Caribbean Sea — Colombia and Venezuela —are also known as the Caribbean South America.

Topography and geology

The geographical structure of South America is deceptively simple for a continent-sized landmass. The continent's topography is often likened to a huge bowl owing to its flat interior almost ringed by tall mountains. With the exception of narrow coastal plains on the Pacific and Atlantic oceans, there are three main topographic features: the

The Andes are a Cenozoic mountain range formed (and still forming)

South of about Santa Catarina, the highlands fade out to low plains in Uruguay.

East of the Andes in Argentina, there are a number of rugged, generally arid to semi-arid isolated mountain chains called

The largest country in South America by far, in both area and population, is Brazil. Regions in South America include the Andean States, the Guianas and the Southern Cone.

Name of territory, with flag	Area (km2)	Population (July 2021 est.[3])	Population density] (per km2)	Capital
Argentina[4]	2,766,890	45,864,941	16.6	Buenos Aires
Bolivia[5]	1,098,580	11,758,869	10.7	La Paz, Sucre[6]
Brazil[7]	8,511,965	213,445,417	25.1	Brasília
Chile[8][9]	756,950	18,307,925	24.2	Santiago
Colombia[10]	1,138,910	50,355,650	44.2	Bogotá
Ecuador[11]	283,560	17,093,159	60.3	Quito
Falkland Islands (UK)[12][13]	12,173	3,198	0.26	Stanley
French Guiana (France)	83,534[14]	283,539[15]	3.4	Cayenne
Guyana[16]	214,970	787,971	3.7	Georgetown
Paraguay[17]	406,750	7,272,639	17.9	Asunción
Peru[18]	1,285,220	32,201,224	25.1	Lima
South Georgia and South Sandwich Islands (UK)[19][20]	3,903	0	0	Grytviken
Suriname[21]	163,270	614,749	3.8	Paramaribo
Uruguay[22]	176,220	3,398,239	19.3	Montevideo
Venezuela[23]	912,050	29,069,153	31.9	Caracas

Climate

As part of the

In the Atlantic region, the ITCZ is clearly developed, and the spatial extent of the ITCZ reaches a minimum close to the equator during the

• The Pacific and Atlantic subtropical high: These are semi-permanent high pressure systems caused by descending sectors of the equatorial Hadley cells. The air masses are relatively warm and dry, and move in an
  anticyclonic
  circulation pattern over the sub-tropical oceans. The Pacific High is generally stable, whereas the Atlantic High moves throughout the year. During the summer, it covers most of the midlatitude and subtropical Atlantic Ocean. During winter, it is smaller and moves to the east.
• The Gran Chaco thermal low: A semi-permanent thermal-
  orographic depression located over the slope extending from Chaco to the Los Andes mountain range in the Argentine Northwest. It can be considered, together with the Bolivian High, as the regional response of the tropospheric circulation to the strong convective heating over the Amazon–central Brazil. The Andes effect reinforces the strength of the Chaco Low as an orographic barrier.^[31] It is present throughout the year, but is more intense during the summer, with a strong thermal component caused by the combination of high insolation and dry surface conditions. The resulting pressure gradient between the south Atlantic subtropical high and the Chaco low forces the easterly winds over the Amazon basin to turn southward, being channelled between the eastern slope of the Andes and the Brazilian Plateau.^[32][33]
• The
  meridional
  temperature gradient, intensifying the South Atlantic High and consequently the trade-winds.
• Polar outbreaks: Polar outbreaks occur when cold dense polar air masses pass beneath warmer tropical air masses, significantly cooling subtropical South America. They occur as a result of
  ageostrophic flow, causing incursions of high-latitude cold air. They generate an important drop in temperature and increase in pressure, resulting in regional precipitation for southern South America. These surges occur mainly during the winter but their impact on the precipitation is even greater during summer.^[35]
• Low Level Jet (LLJ): LLJs originate in a low pressure area over the northern Andes and provide moisture for subtropical latitudes. During summer, they operate as localised wind maximum within the lower 1–2 km of the atmosphere, channelled by the Andes, terminating in southeastern South America. They are controlled by Amazonian wind patterns, which are influenced and controlled by patterns of insolation. They transport large amounts of moisture from the Amazon basin to the monsoonal anticyclone over Bolivia. A suppressed SACZ and increased convection in the sub-tropical plains is associated with a strengthening of the LLJ. These phases are linked to short-term extreme precipitation events in the plains of central Argentina. When the LLJ is weak, there is enhanced SACZ and suppressed convection to the south and extreme heat waves over the sub-tropical regions.[30] It also generates turbulence through shear and participates actively as trigging mechanism for the formation of severe storm and Mesoscale Convective Systems over Paraguay, Northern Argentina and South of Brazil.^[36]
• Westerlies: South America experiences westerly winds in the middle latitudes, caused by the Coriolis force and associated geostrophic circulation patterns. They are more intense than their Northern Hemisphere counterparts due to the lack of continental landmass in the Southern Hemisphere. They reach their maximum speed in the troposphere, where they form jet streams. In particular, over the southern tip of South America and the adjacent south Pacific, the westerlies are strongest during austral summer, peaking between 45° and 55°S. During the austral winter, the jet stream moves into subtropical latitudes (its axis is at about 30°S) and the low-level westerlies expand equatorward but weaken, particularly at ~50°S.^[33] The pressure gradients between the polar low-pressure belt and the Pacific high-pressure cell, combined with these westerlies, results in permanent anticyclogenesis. Northward penetration of atmospheric perturbations from the westerlies is possible when the southeast Pacific anticyclone is weakened or moves equatorward, allowing penetration of westerly storm tracks to latitudes as far north as 31◦S. In the Andes, winter rains reach further north. During summer, the Pacific anticyclone shifts southward, impeding the northward migration of the westerlies.^[24]
• The Bolivian High: large anticyclonic circulation centred near 15°S, 65°W. It has been explained as the response of diabatic local heating in the Amazon region.^[30] The SACZ has a strong influence on the position and intensity of the Bolivian High^[31]
• The
  Rossby
  wave trains that propagate into South America.

The development of the SAMS during spring is characterised by a rapid southward shift of the convective region from northwestern South America to the highland region of the central Andes and to the southern Amazon basin. The South Atlantic High moves eastward, reflecting the pressure reduction over the continent and the intensity and direction of the zonal flow over the nearby tropics and sub-tropics. This change in flow direction is evident in changes to terrestrial windfields over extreme southwestern Amazonia, with winds changing from northerlies to northwesterlies, and over eastern Brazil, where the winds turn from easterlies to northeasterlies.^[37] The southward moisture flux east of the Andes also increases, bringing humidity to central and southeast Brazil.

As the SAMS progresses a continental-scale

adiabatic

warming due to the monsoonal descent.

The decay phase of the monsoon begins between March and May, as convection shifts gradually northward toward the equator. During April and May, the low-level southward flow of moisture from the western Amazonia weakens, as more frequent incursions of drier and cooler air from the mid-latitudes begin to occur over the interior of subtropical South America.

See also

• Brazil–Malvinas Confluence
• Guiana Highlands
• List of rivers of the Americas by coastline
• Tepui

Notes

1. ^ South America physical map
2. ^ Mazzoni, Elizabeth; Rabassa, Jorge (2010). "Inventario y clasificación de manifestaciones basálticas de Patagonia mediante imágenes satelitales y SIG, Provincia de Santa Cruz" [Inventory and classification of basaltic occurrences of Patagonia based on satellite images and G.I.S, province of Santa Cruz] (PDF). Revista de la Asociación Geológica Argentina (in Spanish). 66 (4): 608–618.
3. ^ Except for the figures on the Falkland Islands (which are from October 2016) and French Guiana (January 2018).
4. ^ CIA - The World Factbook - Argentina
5. ^ CIA - The World Factbook - Bolivia
6. ^ La Paz is the administrative capital of Bolivia; Sucre is the judicial seat.
   
7. ^ CIA - The World Factbook - Brazil
8. ^ CIA - The World Factbook - Chile
9. Santiago is the administrative capital of Chile; Valparaíso
   is the site of legislative meetings.
   
10. ^ CIA - The World Factbook - Colombia
11. ^ CIA - The World Factbook - Ecuador
12. ^ CIA - The World Factbook - Falkland Islands
13. ^ Claimed by Argentina.
    
14. ^ BBC NEWS | Americas | Country profiles | Regions and territories: French Guiana
15. ^ "UNSD — Demographic and Social Statistics". unstats.un.org. Retrieved 2021-06-07.
16. ^ CIA - The World Factbook - Guyana
17. ^ CIA - The World Factbook - Paraguay
18. ^ CIA - The World Factbook - Peru
19. ^ CIA - The World Factbook - South Georgia and the South Sandwich Islands
20. ^ Also claimed by Argentina, the South Georgia and the South Sandwich Islands in the South Atlantic Ocean are commonly associated with Antarctica (due to proximity) and have no permanent population, only hosting a periodic contingent of about 100 researchers and visitors.
    
21. ^ CIA - The World Factbook - Suriname
22. ^ CIA - The World Factbook - Uruguay
23. ^ CIA - The World Factbook - Venezuela
24. ^ ^{a b c} Sylvestre, F. (2009). Moisture Pattern During the Last Glacial Maximum in South America. Past Climate Variability in South America and Surrounding Regions: From the Last Glacial Maximum to the Holocene. F. Vimeux, F. Sylvestre and M. Khodri. 14.
25. ^ ^{a b} Grodsky, S. A. and J. A. Carton (2003). "The intertropical convergence zone in the South Atlantic and the equatorial cold tongue". Journal of Climate 16(4): 723–733.
26. ^ Oliver, J. E. (2005). Encyclopedia of World Climatology, Springer.
27. ^ Hastenrath, S. L. (1968). "On mean meridional circulations in the tropics". Journal of the Atmospheric Sciences 25: 979–983.
28. ^ Charney, J. G. (1971). "Dynamical theory of formation of cloud bands in tropical oceans". Bulletin of the American Meteorological Society 52(8): 778.
29. ^ Xie, S. P. and Y. Tanimoto (1998). "A pan-Atlantic decadal climate oscillation". Geophysical Research Letters 25(12): 2185–2188.
30. ^ ^{a b c} Marengo, J. A., B. Liebmann, et al. (2010). "Recent developments on the South American monsoon system". International Journal of Climatology: n/a–n/a.
31. ^ ^{a b c} Vera, C., J. Baez, et al. (2006). "The South American low-level jet experiment". Bulletin of the American Meteorological Society 87(1): 63.
32. ^ Paegle, J. N. and K. C. Mo (2002). "Linkages between summer rainfall variability over south America and sea surface temperature anomalies". Journal of Climate 15(12): 1389–1407.
33. ^ ^{a b} Garreaud, R. D., M. Vuille, et al. (2009). "Present-day South American climate". Palaeogeography, Palaeoclimatology, Palaeoecology 281(3-4): 180–195.
34. ^ Robertson, A. W. and C. R. Mechoso (2000). "Interannual and interdecadal variability of the South Atlantic convergence zone". Monthly Weather Review 128(8): 2947–2957.
35. ^ Marengo, J. and J. C. Rogers (2001). Polar Air Outbreaks in the Americas: Assessments and Impacts During Modern and Past Climates. Interhemispheric Climate Linkages. V. Markgraf, Academic Publishers: 31–51.
36. ^ Silva, G. A. M., T. Ambrizzi, et al. (2009). "Observational evidences on the modulation of the South American Low Level Jet east of the Andes according to the ENSO variability". Annales Geophysicae 27(2): 645–657.
37. ^ Raia, A. and I. F. A. Cavalcanti (2008). "The Life Cycle of the South American Monsoon System". Journal of Climate 21(23): 6227–6246.
38. ^ Rodwell, M. J. and B. J. Hoskins (2001). "Subtropical anticyclones and summer monsoons", Journal of Climate 14(15): 3192–3211.

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