For the revised edition

The happy occasion of the revised paperback printing made it possible to add a section on Langmuir circulations and the Craik-Leibovich instability to chapter 11. These are important and fundamental topics that ought to have been included already in the first edition. This new material also prompted significant changes in section 13.4 on the vorticity generated by breaking surface-gravity waves, which hopefully make this crucial topic more transparent. In addition, there are smaller changes such as high-lighting the amazing curl-curvature formula for wave ray tracing in a weak vortical mean flow in §4.4.3, as well as numerous small fixes and some additional references. A small number of exercises has also been added to various chapters, which hopefully will aid the educational aspects of this book.

I am exceptionally grateful to Michael McIntyre for his very detailed reading of the first edition and for his support in preparing this revised edition. Thanks are also due to Rick Salmon and William Young for their insightful suggestions and to David Tranah for his continued support at Cambridge University Press.

Finally, I would like to dedicate this edition to the memory of my father by the last words of Mahler's Lied der Erde: “Ewig, ewig”.

New York, March 2013.

The aim of this book

This book is on waves and on their interactions with mean flows such as shear flows or vortices.