The increase in the observational network and data assimilation, linked with advancements in the computational area in recent years, has led to important new findings in the meteorology and climatology of South America. Hence, here is presented a literature review that begins describing the various annual cycles of precipitation and air temperature observed across South America, highlighting two contrasting areas: the Atacama Desert, the driest place on Earth, and western Colombia, one of the wettest regions in the world. Next, we present the low- and upper-level atmospheric circulation patterns that control the continent’s diverse climates, with an emphasis on the development of the South American Monsoon System. The review also covers the major atmospheric systems affecting the continent at different temporal and spatial scales, such as the Intertropical Convergence Zone, the South Atlantic Convergence Zone, low-level jets, fronts, synoptic-scale cyclones, and mesoscale convective systems. In addition, the climate variability and main teleconnection patterns that affect South America, as well as the climate models’ present-day performance and their future climate projections for the end of the century, are addressed. We conclude by identifying some of the current gaps and discussing future research challenges within the context of South American weather and climate.

Chapter 1 provides an overview of the main features of the general circulation and climate dynamics of the Southern Hemisphere troposphere, including the role of weather systems. The aim of the chapter is to explain, in broad terms, the physical mechanisms shaping Southern Hemisphere tropospheric climate. Many treatments of the atmospheric general circulation place a strong emphasis on the governing equations, as expressed in terms of budgets and fluxes, which invariably leads to an emphasis on the zonal mean. Chapter 1 takes a complementary and more phenomenological perspective starting from regional climatic features. This aligns with the current interest in understanding regional aspects of climate change and provides a foundation for other chapters in the monograph. The chapter begins by describing these regional climatic features through spatial maps of key dynamical fields. It then explains those features in terms of phenomena anchored in dynamical theory, such as monsoon circulations and storm tracks, including their zonal asymmetries. The discussion covers tropical, subtropical, and extratropical tropospheric phenomena and the connections between them. The chapter concludes with a brief discussion of how the regional phenomena discussed here are expected to respond to climate change.

The meteorology of the Southern Hemisphere (SH) tropics is dominated by planetary-scale waves, interannual variations in sea surface temperature, and local forcing from topographic, coastal, and land-surface influences. The weather and climate of the SH tropics are inextricably linked with that of the NH tropics via the Intertropical Convergence Zone, cross-equatorial flows, and dynamically connected disturbances such as equatorial Kelvin waves. Despite this coupling to the NH, the SH tropics have distinct and fascinating characteristics, including the interaction of planetary-scale disturbances with the SH monsoons; the multi-scale interactions over the Maritime Continent; the influence of tropical waves on extreme rainfall in Africa; the ubiquitous footprint of the MJO on the SH tropics in all three continents; the enhanced wet season convective activity over the Maritime Continent, the Amazon forest and parts of Africa; the northwest-to-southeast orientation of the South Pacific and South Atlantic convergence zones; and the unique distribution of tropical cyclones which span an almost continuous zone from East Africa to the South Pacific. In this chapter, we describe the unique influences on the meteorology of the land areas of the SH tropics. The influence of large-scale circulation patterns and modes of tropical variability on the meteorology of the SH tropics is then discussed. We explore the mesoscale, coastal, diurnal, and topographic aspects of SH tropical meteorology, followed by a review of the characteristics and distribution of tropical cyclones in the Southern Hemisphere. Finally, we examine the observed trends and projections in the SH tropics before concluding with a discussion of the main gaps and future prospects for weather and climate research in the region.

Some key innovations in recent decades have led to improvements in understanding of Southern Hemisphere meteorology. These include more satellite data streams and better integration of these streams into modern data assimilation systems. These, in turn, have led to better representation of the Southern Hemisphere atmosphere in reanalysis datasets and a narrowing of the weather forecast skill gap between the Northern and Southern Hemispheres. The availability of better and longer reanalysis datasets has facilitated more study of the distributions and variability of extratropical storm systems, jetstreams, and the stormtracks in the Southern Hemisphere. These studies depict the Indian Ocean sector as the main genesis region for many extratropical cyclones, with a concentrated jetstream and highly transient synoptic systems dominating variability in the synoptic timeband. The Pacific Ocean sector is strongly influenced by the splitting of the polar and subtropical jets and features more, and longer-lived, blocking events, dominating variability in the slow synoptic band (5–10 days). The dynamical understanding of these systems has also advanced with the application of Rossby wave theory and backtracking studies that reveal the role of Rossby wave breaking in many extreme events. Even local extremes can be shown to depend on large-scale wavetrains that regulate the onset and persistence of the event. Studies of Southern Hemisphere meteorology have also highlighted major uncertainties in understanding. Climatologies of Southern Hemisphere synoptic systems, including fronts, cut-off lows, and blocking, are sensitive to the choices used to define these systems. This is particularly acute in the case of blocking, where there is no complete theory that accounts for the lifecycle, distribution, and variability of blocking events, and relatively fewer studies on Southern Hemisphere blocking characteristics. Similarly, there are a range of views (reflecting underlying choices) of what the Southern Hemisphere stormtracks look like and competing theories of how those stormtracks are influenced by tropical teleconnections.

Climate models remain an essential tool for studying the complexity of the climate system and for predicting the future evolution of the system. This chapter provides insight into the science of climate modelling in the Southern Hemisphere. It reviews the recent developments and improvements in climate modelling, including downscaling methods, parameterisation schemes, and model resolutions. It also discusses the usage of climate models, with a focus on their value in climate process studies, climate predictability, weather predictions, and seasonal forecasts, as well as climate change projections, management, detection, and attribution. This chapter reveals the challenges faced by the climate modelling community in the Southern Hemisphere and suggests directions for future research that could further unleash the potential of climate modelling in this hemisphere.

The meteorology of the stratosphere in the Southern Hemisphere (SH) plays a critical role in the variability of the ozone hole and also has a major influence on surface climate and weather. The predominant feature of the stratosphere is a band of strong mid- to high-latitude westerlies that surround a very cold pole and exist from autumn to spring. This ‘polar vortex’ is stronger and less variable in the SH than in the Northern Hemisphere, and the low temperatures and isolation within the vortex are key conditions necessary for rapid chemical destruction of Antarctic ozone. The largest interannual variability in the SH occurs in spring and is associated primarily with variability in the strength and timing of the seasonal breakdown of the polar vortex. Interannual variability and trends in the timing of the vortex breakdown are coupled to variability and trends in the summertime Southern Annular Mode and its associated influence on tropospheric and surface climate. A rapid warming of the polar stratosphere and weakening of the westerlies occurred in September 2002 and 2019, resulting in small ozone holes for those years. These are the only two observed occurrences of such events in the SH. In addition, observations show significant trends in vortex characteristics (colder, stronger winds, later breakup) during the 1980s and 1990s, but not since 2000. These pre-2000 trends and post-2000 pause are consistent with Antarctic ozone hole trends (growth, followed by initial signs of recovery) since the 1980s. Interactions between ozone chemistry and the stratospheric circulation, which occurs across timescales, can enhance the coupling of the stratosphere to the troposphere, with implications for both interannual and long-term changes in SH weather and climate.