The Hadley Circulation: Present, Past, and Future

Abstract

Near the turn of the eighteenth century, two eminent British scientists—Sir Edmund Halley (of comet fame) and Sir George Hadley—put forth a conceptual framework aimed at explaining the nature of the observed wind patterns in the tropics. These early attempts at synthesizing what was known about the causes of the large-scale atmospheric circulation were amazingly prescient, providing the first scientific explanations of the phenomenon that now bears Hadley’s name (see Chapter 1, by P. Webster). This large-scale meridional overturning circulation spans half the area of the globe, and variability within this system affects the lives of billions of people. Along with the large-scale zonal tropical cells named after Sir Gilbert Walker, the Hadley circulation comprises fundamental regulators of the earth’s energy budget. Although the Hadley circulation is a well-known concept, surprisingly little attention has been paid to understanding the variability of the system on long time scales. This book is a step towards addressing the question of the nature and causes of changes in the Hadley circulation on multiple time scales.