Welcome to Chapter 8 — Turbulence — Page 104, Lesson 90

Welcome to Chapter 8 — Turbulence. This is a big topic for us as pilots, because turbulence directly affects the ride quality, the structural loads on the aircraft, and our ability to maintain a stable flight path. Let me walk you through what this chapter covers. We start with an introduction, then move into windshear — that's a sudden change in wind speed or direction over a short distance, and it's a key cause of turbulence. We'll look at the locations where turbulence tends to occur, and then we dive into the friction layer. The friction layer is the lowest part of the atmosphere, typically up to about 600 metres or so, where the Earth's surface drags on the wind, slowing it down and creating turbulence. From there, we have thermal turbulence — that's turbulence caused by rising columns of warm air, or thermals, as the sun heats the ground. Then there's mechanical turbulence, which is caused by the wind flowing over and around obstacles like buildings, trees, or hills. Next, we cover mountain waves, abbreviated MTW. These are large-scale waves that form downwind of mountain ranges when the wind is strong and the air is stable. They can produce severe turbulence, and we'll look at their effects, how to recognise them visually, and what action to take to avoid the worst of it. Then we have rotor streaming — that's a specific type of turbulent flow that can occur beneath mountain waves, where the air rolls into horizontal vortices. After that, we look at jet streams — those narrow, high-speed ribbons of wind in the upper atmosphere — and the turbulence associated with them. We also cover cumulonimbus clouds — the thunderstorm clouds — which produce some of the most severe turbulence you'll ever encounter. Then there's turbulence around upper-level troughs and ridges — those are the wavy patterns in the upper wind flow, and they can generate clear-air turbulence. We have a section on turbulence reporting criteria — that's the standard way pilots report turbulence intensity, from light to extreme. Then low-altitude windshear, which is especially dangerous during takeoff and landing. Finally, there are questions and an appendix. So that's the roadmap for this chapter. We're going to start with the introduction and work through each of these topics in detail. Let's begin.