3
terdecadal climate variability are not particularly strong. Much of the
observed variability can be described as separable functions of space
and time (§3).
One-dimensional time series will be considered in the next section and
multi-dimensional time series in the following one.
2 Climate time series
The evolution of the climate system can assume a wide variety of forms,
but for the purpose of this chapter, it will be convenient to group them into
the following categories: periodic and quasi-periodic phenomena, aperiodic
and random variability, low-frequency trends, and distinctive temporal signatures such as discrete jumps.
2.1 Periodic phenomena
For the range of time scales emphasized in this volume, by far the most
important periodic climate signal is the response to the annual march in
the intensity and latitudinal distribution of incoming solar radiation. Even
the more subtle features associated with the annual march are comparable
to or larger in amplitude than the strongest interdecadal to century scale
climatic signals and, because of their regularity, they are much easier to
isolate and diagnose in observations and model output. The most dramatic
and easily explained features of the annual march are the large summerwinter swings in temperature throughout extratropical latitudes and the
related summer monsoon rainfall maxima over the subtropical continents.
Let us pass over these and consider a few of the more subtle, less easily
explained features of the annual march, which lend insight into the inner
workings of the climate system.
The annual march of zonally averaged temperature at the mesopause
level, near 80 km is exactly the opposite of what one would expect on the
basis of radiative considerations: the summer hemisphere is cold and the
winter hemisphere is warm. This anomalous behaviour is a consequence of
a seasonally reversing pole-to-pole mean meridional circulation cell, characterized by ascent and adiabatic expansion over the summer pole and
subsidence and adiabatic compression over the winter pole which drives
the temperatures away from local radiative equilibrium. Throughout most
terdecadal climate variability are not particularly strong. Much of the
observed variability can be described as separable functions of space
and time (§3).
One-dimensional time series will be considered in the next section and
multi-dimensional time series in the following one.
2 Climate time series
The evolution of the climate system can assume a wide variety of forms,
but for the purpose of this chapter, it will be convenient to group them into
the following categories: periodic and quasi-periodic phenomena, aperiodic
and random variability, low-frequency trends, and distinctive temporal signatures such as discrete jumps.
2.1 Periodic phenomena
For the range of time scales emphasized in this volume, by far the most
important periodic climate signal is the response to the annual march in
the intensity and latitudinal distribution of incoming solar radiation. Even
the more subtle features associated with the annual march are comparable
to or larger in amplitude than the strongest interdecadal to century scale
climatic signals and, because of their regularity, they are much easier to
isolate and diagnose in observations and model output. The most dramatic
and easily explained features of the annual march are the large summerwinter swings in temperature throughout extratropical latitudes and the
related summer monsoon rainfall maxima over the subtropical continents.
Let us pass over these and consider a few of the more subtle, less easily
explained features of the annual march, which lend insight into the inner
workings of the climate system.
The annual march of zonally averaged temperature at the mesopause
level, near 80 km is exactly the opposite of what one would expect on the
basis of radiative considerations: the summer hemisphere is cold and the
winter hemisphere is warm. This anomalous behaviour is a consequence of
a seasonally reversing pole-to-pole mean meridional circulation cell, characterized by ascent and adiabatic expansion over the summer pole and
subsidence and adiabatic compression over the winter pole which drives
the temperatures away from local radiative equilibrium. Throughout most