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the climate system: variability of the sun's output, variability of volcanic
injections of aerosols to the atmosphere, variability of emissions of anthropogenic aerosols, land use changes, etc.
2. Stochastic forcing of the ocean (and land) by the white noise synoptic scale variability of the atmosphere, i.e. by weather (the so-called
Hasselmann mechanism).
3. ENSO variability, namely the decadal-to-centennial variability induced by nonlinear processes modulating essentially seasonal-to-interannual
processes and, by extension, variability of normal patterns affected by
ENSO (i.e. the PNA pattern) and perhaps normal oscillatory patterns
not known to be affected by ENSO (e.g. the North Atlantic Oscillation).
4. Internal ocean variability, where the variability arises from internal
processes in the ocean without reinforcement from a changing atmosphere.
This includes variability from decadal to millennial time scales.
5. Coupled atmosphere-ocean modes: variability that would not exist
either in the atmosphere or in the ocean but arises solely from their joint
interaction.
6. Abrupt transitions of climatic regimes, for example the return from
the Younger Dryas cooling eleven thousand years ago which seemed to have
happened on exceedingly rapid (decadal) time scales.
These are the same mechanisms cited by CLIVAR (1995) and it is one of
the purposes of these lectures to look more critically at each of the mechanisms to decide which are the most plausible and what are the implications
of each mechanism for the predictability of climate. A review of some of
these decadal mechanisms, in a spirit similar to that taken in this article,
is given in Rind and Overpeck (1993).
2 Forcing Function Variability
2.1 Solar Output
The sun radiates as a black body with surface temperature of about 5770 K.
The variability of the sun's output cannot accurately be measured by earthbased measurements since clouds, aerosols, ozone, and other radiatively
active components of the atmosphere in the visible and ultraviolet spectrum
interfere with the incoming solar beam on its way to the earth's surface.
Satellite measurements of solar output, however, have been going on for
the last 15 or so years. It is observed (Lean, 1991) that total solar output
the climate system: variability of the sun's output, variability of volcanic
injections of aerosols to the atmosphere, variability of emissions of anthropogenic aerosols, land use changes, etc.
2. Stochastic forcing of the ocean (and land) by the white noise synoptic scale variability of the atmosphere, i.e. by weather (the so-called
Hasselmann mechanism).
3. ENSO variability, namely the decadal-to-centennial variability induced by nonlinear processes modulating essentially seasonal-to-interannual
processes and, by extension, variability of normal patterns affected by
ENSO (i.e. the PNA pattern) and perhaps normal oscillatory patterns
not known to be affected by ENSO (e.g. the North Atlantic Oscillation).
4. Internal ocean variability, where the variability arises from internal
processes in the ocean without reinforcement from a changing atmosphere.
This includes variability from decadal to millennial time scales.
5. Coupled atmosphere-ocean modes: variability that would not exist
either in the atmosphere or in the ocean but arises solely from their joint
interaction.
6. Abrupt transitions of climatic regimes, for example the return from
the Younger Dryas cooling eleven thousand years ago which seemed to have
happened on exceedingly rapid (decadal) time scales.
These are the same mechanisms cited by CLIVAR (1995) and it is one of
the purposes of these lectures to look more critically at each of the mechanisms to decide which are the most plausible and what are the implications
of each mechanism for the predictability of climate. A review of some of
these decadal mechanisms, in a spirit similar to that taken in this article,
is given in Rind and Overpeck (1993).
2 Forcing Function Variability
2.1 Solar Output
The sun radiates as a black body with surface temperature of about 5770 K.
The variability of the sun's output cannot accurately be measured by earthbased measurements since clouds, aerosols, ozone, and other radiatively
active components of the atmosphere in the visible and ultraviolet spectrum
interfere with the incoming solar beam on its way to the earth's surface.
Satellite measurements of solar output, however, have been going on for
the last 15 or so years. It is observed (Lean, 1991) that total solar output