Confession

The book ends with a discussion of different viewpoints in fluid dynamics and the complexity of flow trajectories in the atmosphere. A final analogy for the jet stream is given which highlights that it is not quite as simple as the ‘river of air’ image that is often used.

Spin

The effects of Earth’s rotation on the winds is developed more generally, outlining the key discoveries of Foucault, Coriolis and Ferrel. This shows how the characteristics of weather systems are shaped by the planetary rotation, and central concepts of fluid dynamics are introduced to describe this. The discussion of how the resulting Atlantic wind patterns shaped centuries of shipping, including the infamous slave trade, is concluded.

Changes

Many aspects of climate change predicted by scientists are already appearing, with the structure and rate of warming generally proceeding as anticipated. But changes in wind patterns and circulation features such as the jet stream are much more uncertain. While the thermodynamic consequences of climate change have strongly affected the risk of several recent extreme weather events, we are only just starting to see hints of emerging dynamical changes to the jet stream.

Future

This chapter provides a brief introduction to how climate change is expected to affect the structure of the atmosphere. A key part of the story is that different parts of the atmosphere will warm at different rates, and the associated temperature contrasts will drive and interact with changes in the wind patterns. The focus is largely on hemispheric aspects such as the expansion of the tropics and general poleward shift of the jets, but some regional features are also discussed, such as the changes in Atlantic Ocean circulation which may prove especially important for Europe.

Exit

We have reached the end of the jet stream spiral and the jet exit over Europe. This chapter describes some of the jet-related phenomena here, such as occasional extreme cyclones. The prevailing westerly winds driven by the jet stream help to support Europe’s thriving wind power industry. Blocking events are discussed, which bring disruptive easterly winds and are often linked to heatwaves in summer but also cold snaps in winter.

Niño

El Niño events are the most powerful of natural climate variations, rearranging weather patterns around the world and triggering countless extreme events. This chapter gives an overview of El Niño, its history and its physics, including its important effect on the Pacific jet stream. El Niño is the main source of information for the science of seasonal forecasting, which is also introduced here.

Storm

Some of the history of the jet stream is given here, such as its early identification from Japan using an ingenious system of balloons and the importance of strong, high-altitude winds that emerged during the Second World War. The chapter also discusses mid-latitude cyclones in more detail, covering some of the key historical developments and physical concepts as well as outlining the characteristic structure of these storms.

Contrasts

The effect of the Hadley cell on regional climate is explored, in particular the dry subtropical regions where many of the world’s deserts are to be found, and the equatorial region frequented by deluges and floods. Some effects of friction in fluid dynamics are considered, which explain the rich fishing waters off the west African coast. Our discussion of the key balances in atmospheric fluid dynamics is completed, with links to the flow of energy through the atmosphere and oceans. The chapter concludes with the example of the North African Sahel, a region where dramatic swings in climate have had severe impacts on humanity.

Trades

This chapter focuses on understanding the trade winds in the tropical Atlantic. A historical approach is taken, starting from ancient Greek and Chinese theories of wind and then discussing various later theories proposed after European exploration of the Atlantic brought the trade winds into focus. The essentially correct description was provided by George Hadley in 1735, based on the concept of momentum conservation. This chapter hence introduces crucial effects of Earth’s rotation on the atmosphere and provides an overview of tropical Atlantic wind patterns.

Drivers

This chapter introduces some of the key factors which are suspected to influence the Atlantic jet, and so are potentially predictable drivers of jet variability. This includes factors we have already met, such as El Niño and other patterns of ocean temperatures. Several other possible drivers act via the stratosphere, so a more detailed picture is provided of this layer of the upper atmosphere and how changes in its wind patterns can affect the jet stream below.