Introduction

Earth’s polar regions play a pivotal role in climate, both as an important mediator in exchanges between the atmosphere and global ocean, and as a harbinger of climate change. Central to this impact is a thin layer of sea ice that is predominantly seasonal, and at maximum extent (at the end of austral winter) covers roughly 8% of the world ocean area. Sea ice affects climate in several important ways. It effectively insulates the ocean from the cold polar atmosphere, reducing both outgoing longwave radiation and convective heat exchange; it reflects a much higher proportion of incoming shortwave radiation than does open water; and by rejecting salt as it freezes, is capable of producing the cold, saline water that constitutes the end point in mixing processes that determine the density of the abyssal ocean. This chapter discusses the rationale behind a monograph on how sea ice affects atmosphereocean exchanges and how studies of turbulent exchange in the ice-ocean boundary layer have revealed much about how planetary boundary layers (where rotation is important) work in general. It briefly describes pertinent ice-station exercises, and lays out the framework for subsequent chapters.