Introduction

Radiation is the ultimate driver of atmospheric circulations, since radiation passes through the atmosphere and reaches the Earth's surface in amounts that are unequally distributed in space and time. This unequal energy distribution, due in part to the Earth's spherical shape, produces horizontal gradients in temperature, which produce atmospheric motions. Radiation not only determines the Earth's climate, but also plays a significant role in local energy budgets by providing the largest energy source terms. Radiation is unique among atmospheric processes since it can transport energy without a medium, yet it interacts with gases, liquids, and solids in very different ways.

Changes in the mean annual net radiation of a fraction of 1% can lead to significant changes in global climate when this change persists over a number of years. This highlights the importance of accurate radiation parameterizations to global climate models that are being used both to understand how increasing greenhouse gas concentrations affect future climate and to provide guidance to policy makers across the world. However, radiation also is important in the day-to-day weather events that influence our lives. Just think of a chilly fog-filled morning that breaks into a sunny and warm afternoon and the effects of radiation on the weather we experience become clear. Radiation is a key player in the atmosphere, both on very short and very long timescales. Thus, radiation needs to be parameterized accurately under a wide variety of atmospheric conditions.