The Need for a Dynamical Climate Reanalysis

T he Earth’s climate is dominated by diverse and changeable natural processes over a wide range of time and space scales (e.g., Folland et al. 2001). This includes changes related to transient synoptic weather systems and to phenomena on much longer time scales, such as the quasibiennial oscillation (QBO) and El Niño–Southern Oscillation (ENSO) with time scales up to several years. Especially intriguing are the climate variations related to the North Atlantic Oscillation (NAO). The difference between a mild and cold winter in northwest Europe, for example, is mainly caused by noticeable storm-track variations that are not yet fully understood. Some of the climate variations are driven by internal phenomena in the atmosphere, others are related to interactions between the atmosphere and the oceans and between the atmosphere and the land surfaces, and still others are due to solar and volcanic influences. At the same time, Earth’s climate is increasingly exposed to anthropogenic changes, such as increasing greenhouse gases. Because of the high variability over a broad range of time scales, the climate of the Earth cannot be properly described by time averages only, but instead requires continuous monitoring on a daily resolution or higher because many atmospheric features undergo rapid changes. Such high-resolution THE NEED FOR A DYNAMICAL CLIMATE REANALYSIS