The equatorial westerlies

In the summer hemisphere, and over continental areas especially, there is a narrow zone of generally westerly winds intervening between the two trade wind belts (Figures 7.12 and 7.14). This westerly system is well marked over Africa and South Asia in the northern hemisphere summer, when thermal heating over the

Thermal Equator
Figure 7.12 Generalized global wind zones at 1000 mb in January (A) and July (B). The boundary of westerly and easterly zonal winds is the zero line. Across much of the central Pacific the trade winds are nearly zonal. Based on data for 1970 to 1999.

Source: NCEP/NCAR Reanalysis Data from the NOAA-CIRES Climate Diagnostics Center.

Equatorial Trade Wind System

Figure 7.13 Map of the trade wind belts and the doldrums. The limits of the trades - enclosing the area within which 50 per cent of all winds are from the predominant quadrant - are shown by the solid (January) and the dashed (July) lines. The stippled area is affected by trade wind currents in both months. Schematic streamlines are indicated by the arrows - dashed (July) and solid (January, or both months).

Figure 7.13 Map of the trade wind belts and the doldrums. The limits of the trades - enclosing the area within which 50 per cent of all winds are from the predominant quadrant - are shown by the solid (January) and the dashed (July) lines. The stippled area is affected by trade wind currents in both months. Schematic streamlines are indicated by the arrows - dashed (July) and solid (January, or both months).

Source: Based on Crowe (1949 and 1950).

Flohn Concept Monsoon

Figure 7.14 Distribution of the equatorial westerlies in any layer below 3 km (about 10,000 ft) for January and July. Source: After Flohn in Indian Meteorological Department (I960).

H July

Figure 7.14 Distribution of the equatorial westerlies in any layer below 3 km (about 10,000 ft) for January and July. Source: After Flohn in Indian Meteorological Department (I960).

continents assists the northward displacement of the equatorial trough (see Figure 11.1). Over Africa, the westerlies reach 2 to 3 km and over the Indian Ocean 5 to 6 km. In Asia, these winds are known as the 'Summer Monsoon', but this is now recognized to be a complex phenomenon, the cause of which is partly global and partly regional in origin (see Chapter 11C). The equatorial westerlies are not simply trades of the opposite hemisphere that recurve (due to the changed direction of the Coriolis deflection) on crossing the equator. There is on average a westerly component in the Indian Ocean at 2 to 3°S in June and July and at 2 to 3°N in December and January. Over the Pacific and Atlantic Oceans, the ITCZ does not shift sufficiently far from the equator to permit the development of this westerly wind belt.

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Responses

  • timothy
    How does wind belts affect climate?
    7 years ago
  • michael
    How was trade affected by the westerly wind belt in the 1800s?
    5 years ago
  • cynthia howard
    What are displaced westerlies?
    3 years ago
  • allison
    What is eqatorial westerlies?
    2 years ago
  • luis
    Where do equatorial westerlies begin?
    2 years ago

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