Water vapor is also a greenhouse gas that plays a critical role in the global climate system.
This role is not restricted to absorbing and radiating energy from the sun, but includes the effect it has on the formation of clouds and aerosols and the chemistry of the lower atmosphere. Despite its importance to atmospheric processes over a wide range of spatial and temporal scales, water vapor is one of the least understood and poorly described components of the Earth's atmosphere. While an important goal in modern weather prediction is the improvement of short-term cloud and precipitation forecasts, our ability to do so is severely limited by the lack of timely and accurate water vapor data. Each of these systems has advantages and limitations. Surface-based radiometers Capable of high temporal resolution Costly, require frequent calibration, and do not function well in all weather conditions, especially rain.