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.

Maghemite (γ-Fe2O3) has an inverse spinel crystal structure like magnetite, with Fe only in the 3+ valence state like hematite. It has a combined name of ‘mag’ from magnetite and ‘hem’ from hematite. Maghemite is the end member that results from complete oxidation of magnetite. ‘Maghemitization’ refers to partial low-temperature oxidation of precursor magnetite or titanomagnetite, which involves conversion from one spinel phase to another. Maghemite is an industrially important functional material, so its magnetism has been studied extensively and is generally well constrained. It has strong magnetism and low magnetocrystalline anisotropy, with low coercivity. Partial oxidation of magnetite produces particles with magnetite cores and maghemite shells with higher coercivities than magnetite or maghemite because of lattice strain at the core–shell interface. Low-temperature cycling of a room temperature saturation remanence produces characteristically humped remanence curves for maghemite. The Curie temperature of ~645°C can be obscured because maghemite is unstable at elevated temperatures and generally inverts to hematite before reaching the Curie temperature.

This chapter reviews the recent literature on the meteorology and climate of the African region in the Southern Hemisphere focusing on key features of circulation and its seasonal shifts, including the rain-bearing weather systems. It is only in the very recent literature that several very important regional circulation features have been documented in detail. These advances have been aided by more accurate reanalyses, high-resolution satellite observations, and models, augmenting vast areas of sparse surface and upper-air observations in the African region. The chapter highlights prominent synoptic and mesoscale circulation features such as the Mozambique Channel Trough, the Botswana High, the Angola Low, the Congo Air Boundary, low-level jets, atmospheric rivers, and ridging South Atlantic anticyclones. It details the dynamics and variability of rainfall-bearing synoptic-scale systems such as cut-off low-pressure systems, tropical–extratropical cloud bands, and the role of Rossby wave propagation and breaking associated with these systems. The chapter also deals with key ocean circulation features such as the Angola-Benguela Frontal Zone, the Seychelles-Chagos Thermocline Ridge, the Agulhas Current retroflection and leakage into the South Atlantic, eddies and meanders on this current and in the Mozambique Channel, as well as sea-surface temperature variability in the neighbouring oceans such as the Benguela Niño and dipoles in the Indian Ocean. In addition, the chapter covers climate variability in the region on a variety of timescales from the intraseasonal to interannual and trends at longer timescales. The latter part focuses on advances in applications of numerical weather models and ensemble prediction systems, seasonal climate forecasting, and climate change projections. In conclusion, the chapter provides an analysis of current limitations and offers recommendations for future research.

Hematite contains Fe only in the ferric state. It is the most stable iron oxide and is responsible for red pigmentations in oxidizing environments. Hematite is rhombohedral with canted antiferromagnetic structure and an additional defect magnetic moment. Above the spin–flop Morin transition temperature (262 K), the magnetization lies within the basal plane; at and below this transition, a purely antiferromagnetic structure becomes oriented perpendicular to the basal plane. The transition temperature varies with particle size, cation substitution, lattice strain, pressure, and applied field. Hematite is a weakly magnetic, high-coercivity magnetic phase with both uniaxial and triaxial magnetization switching observed at high fields. The magnetic constants and magnetic properties of hematite are known. Superparamagnetic behaviour is observed below ~28 nm; stable single domain behaviour occurs above this size to at least the tens of micron range. The multi-domain threshold size is poorly constrained, but it is large enough that most natural hematite will be in the stable single domain state and carry stable magnetizations. Hematite has a Néel temperature of ~680°C.

This chapter provides a comprehensive overview of stratosphere–troposphere interactions, with emphasis on the Southern Hemisphere. We introduce key concepts such as wave activity (Eliassen–Palm fluxes), the Charney–Drazin criterion for wave propagation, downward control, and radiative coupling. The chapter then explores the stratosphere’s influence on tropospheric timescales and the surface impacts of dynamical perturbations originating in the stratosphere. It delves into subseasonal to seasonal prediction, highlighting the enhanced forecasting skill derived from stratospheric dynamics. The discussion also addresses the impact of stationary waves and model biases on stratosphere–troposphere coupling. Furthermore, the chapter examines the stratosphere’s role in shaping tropospheric circulation over longer timescales, including the effects of climate change and the potential influence of the ozone hole. Finally, it investigates the interactions between the Quasi-Biennial Oscillation and the Madden–Julian Oscillation, providing a holistic view of the complex interplay between these atmospheric layers.

Pyrrhotite is an iron sulphide mineral (Fe1?xS, where x = 0–0.125) with variable compositions, crystal structures, Fe/S contents, and magnetic properties. Pyrrhotite polytypes occur in reducing igneous, metamorphic, sedimentary, and extraterrestrial rocks. At ambient temperatures, monoclinic (4C) pyrrhotite (Fe7S8) is ferrimagnetic; the hexagonal 3C polytype with Fe7S8 composition is also ferrimagnetic, while more S-rich compositions (Fe9S10, Fe11S12) are antiferromagnetic. Monoclinic pyrrhotite has a Curie temperature of 325°C, it passes through the low-temperature Besnus magnetic transition at 34 K, it has low to medium coercivities, and can have uniaxial and/or triaxial anisotropy. The low-field magnetic susceptibility is a complex parameter for 4C pyrrhotite because of its dependence on particle size, applied field strength, and applied field frequency. The 3C pyrrhotite polytype lacks a low-temperature magnetic transition and has higher coercivities than 4C pyrrhotite. Despite being one of the earliest studied magnetic minerals, important magnetic parameters for 4C pyrrhotite remain unknown and much more work is needed to document the magnetic properties of other polytypes.

Magnetite is the most extensively studied magnetic mineral. It is a cubic inverse spinel that occurs commonly in most rock types and is also produced by organisms. Its fundamental magnetic parameters are well known, which has enabled development of a micromagnetic framework for magnetic domain state variations with respect to particle size and shape, which complements an extensive experimental magnetic property framework. When cooling through the Verwey transition at 120 K, its structure changes from cubic to monoclinic. It also has an isotropic point where the first and second anisotropy constants change from negative above to positive below 130 K. Shape anisotropy dominates cubic magnetocrystalline anisotropy for elongated particles, which produces wider size ranges for the stable single domain state with elongation. The magnetite formation mode controls its magnetic properties because of its sensitivity to internal strain. Its magnetic susceptibility does not vary with particle size, while other laboratory-imparted remanences vary with particle size. These properties are useful for magnetic granulometry. Magnetite is a low coercivity mineral with Curie temperature of 580°C.

The question ‘what use is mineral magnetism?’ is addressed in this chapter. Magnetic rock-forming minerals can record magnetic information on timescales that exceed the age of the Earth, which enables paleomagnetism to underpin the global plate tectonic paradigm and provide the geomagnetic polarity timescale that is used to calibrate geological time. Paleomagnetic analysis also enables understanding of terrestrial and extraterrestrial magnetic fields and planetary processes that generate these fields and their variations through time. Environmental magnetism exploits the sensitivity of magnetic minerals to environmental processes at Earth’s surface, which facilitates understanding of the climatic, tectonic, or other driving forces of environmental change. The magnetic properties of nanoparticles are also exploited by organisms, as studied in biomagnetism, and are manipulated by humans in industrial, technological, and medical applications, which makes mineral magnetism useful in an exceptional range of fields. This book serves workers in these fields by providing an introduction to mineral magnetism and in-depth treatments of the magnetic properties of terrestrial magnetic minerals.

Goethite (α-FeOOH) occurs widely in soils and surface sediments as a result of surface weathering in the presence of water and oxygen. It becomes unstable compared to hematite with dehydration occurring at elevated temperatures and/or decreased humidity in practically all geological environments. Goethite has a defect antiferromagnetism with weak net magnetic moment; it also has the highest coercivity among known rock-forming minerals (although mixtures of superparamagnetic and stable single domain nanoparticles can have low coercivities). It has a low Néel temperature of 120°C, which can be lowered further in natural samples by cation substitution. Goethite lacks a low-temperature magnetic transition, although it undergoes a distinctive approximately linear remanence enhancement during cooling from room temperature to low temperatures. A combination of the distinctive low temperature magnetic properties and low unblocking temperatures of goethite can be used to identify it in complexly mixed natural samples.