Infrared and visible wavelength absorption by water vapour

Water vapour is the most important species in our atmosphere for both absorbing incoming sunlight and for absorbing heat leaving the earth's surface (the so-called greenhouse effect). Thus a thorough and reliable understanding of how water absorbs radiation at all wavelengths is absolutely crucial to understanding, modelling and making predictions about atmospheric processes. For example reliable predictions of water absorptions are essential for models of climate change, for studies of the concentration of trace species in the atmosphere using satellites and for modelling communications through the atmosphere. Unfortunately the way water absorbs light is (uniquely?) complicated and, despite huge scientific effort, remains insufficiently well determined for many atmospheric purposes. The proposers group have developed theoretical procedure based on the rigorous application of quantum mechanics which have allowed a significant advance in the understanding and interpretation of water absorptions. These procedures are not yet accurate enough to give a complete solution of the problem using computers. However when combined with modern laboratory experiments it should be possible to create a definitive database of water absorptions. The present proposal is ensure the reliable provision of data on the absorption of light by water vapour over a wide range of wavelengths, concentrating especially on the wavelengths where solar radiation is the largest. This will be achieved by theoretical work performed at UCL and by coordinating the leading laboratories worldwide who work on water absorptions using laboratory measurements. Extensive testing of the resulting data against laboratory and atmospheric measurements will be performed to ensure that the data is reliable.