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Monsoons are a central component of global climate and are critical to the global transport of atmospheric energy and water vapour. More than 70% of the world's population lives in monsoonal regions and these systems have a profound effect on society and the global economy. Zhisheng et al. (2015) proposed the following definition of the global monsoon:

The global monsoon is the significant seasonal variation of three‐dimensional planetary‐scale atmospheric circulations forced by seasonal pressure system shifts driven jointly by the annual cycle of solar radiative forcing and land‐sea interactions, and the associated surface climate is characterised by a seasonal reversal of prevailing wind direction and a seasonal alternation of dry and wet conditions.

FIGURE 2.7 Global distribution of monsoon domains and their local components, including by differences of 850 hPa wind and precipitation between the June‐July‐August and December‐January‐February mean.

Source: Zhou et al. (2016), figure 1, p. 3590. Licensed under CC BY 4.0. © Copernicus Publications.

The tropical monsoon primarily lies between the seasonal migration boundaries of the ITCZ (Figure 2.7). The seasonal migration of the ITCZ, caused by cross‐equatorial pressure gradients, produces a strong tropical monsoon under the annual cycle of solar radiation. The global monsoon is distributed primarily across several major subtropical and tropical regions: tropical Asia, Indonesia‐Australia, Africa, and South America (Figure 2.7). Although West Africa, northern Australia and parts of South America depend on much of their annual rainfall from seasonal monsoons, the archetypal monsoon system is the tropical Asian‐Australian monsoon which consists of several main subsystems: the tropical Australian monsoon, the Maritime Continent monsoon, the South China Sea monsoon, the Indochina Peninsula, and western North Pacific monsoon and the Indian or South Asian monsoon.

In the Southern and Northern Hemispheres, subtropical monsoons (Figure 2.8) are caused by the seasonal shift of the subtropical high and land‐sea distribution and are closely related to several features: large‐scale topography, the Rossby radius of deformation, the jet stream, and the interaction between the jet stream and large‐scale topography. (The Rossby radius of deformation is the length scale at which rotational effects become as important as buoyancy or gravity wave effects in the evolution of the flow about some disturbance.) The Southern Hemisphere subtropical monsoon includes the Southern Australian, South African, and subtropical South Pacific monsoons. The Northern Hemisphere subtropical monsoon consists of the East Asian, North American, North African, Tibetan Plateau, subtropical North Atlantic, and North Pacific monsoons.