Chaos and predictability of climate

While day-to-day atmospheric fluctuations are not predictable after two weeks or so because of the chaotic nature of the atmospheric dynamics, there is evidence that certain aspects of the atmospheric circulation are predictable on time scales much longer than two weeks in the presence of a time dependent climate forcing. This paper illustrates distinctions between weather predictability and climate predictability by using a truncated atmospheric model in an explicitly chaotic parameter regime. An external forcing with time scale longer than the weather tends to modulate the statistical characteristics of the chaotic atmospheric variations to enhance the predictability of time-averaged climate states. Moreover, there exist climate variables which are more predictable than others.