Oscillations and teleconnections - The Global Climate System: Patterns, Processes, and Teleconnections - page 26

term oscillation is sometimes used for the swing from one extreme to the other,
that is a half cycle.
Fairbridge ( 1986 ) noted that a number of types of oscillation are recognized:
damped oscillation, one with constantly decreasing amplitude; neutral, persistent
or undamped oscillation, maintaining constant amplitude; unstable oscillation,
growing in amplitude and then breaking down; stable oscillation, consistent
amplitude with little change; forced oscillation, one set up periodically by an
external force; free oscillation, a motion established externally but which then
receives no further external energy.
Atmospheric oscillations can fit any number of these categories. Of singular
importance, however, are the planetary atmospheric pressure fields that are
considered here. Most of these oscillations are involved with the strength and
location of centers of action, the major global highs and lows, and sea surface
temperatures. The character of the identified oscillations is mostly derived
statistically from long-term pressure observation series.
Oscillations have various periodicities. Some, like the Madden-Julian
(Section 2.5 ), are intraseasonal, occurring at periods of less than 1 year. A
quasi-biennial (QB) occurs at approximately 2-year intervals while some peri-
odicities, such as ENSO, have a quasi-cyclic periodicity ranging from 3 to 5
years. At the same time, and as described in Section 2.8 , the ENSO phenomena
may also be considered as quasi-biennial with a 2 to 2.5 year frequency together
with a low-frequency (LF) interannual component. Thus QB ENSO and LF
ENSO signals are identified. Decadal oscillations, such as the Pacific Decadal
Oscillation (Section 2.3 ), have been linked to the 11-year sunspot cycle, while
bidecadal may be linked to the double sunspot, or Hale, cycle. Multidecadal and
longer term oscillations have been identified, some of which may be associated
with Earth orbit parameters.
Table 2.1 outlines some of the oscillations that have been identified and which
will be described in this chapter.

2.1.2 Teleconnections
Teleconnection is a term used to describe the tendency for atmospheric circula-
tion patterns to be related, either directly or indirectly, over large and spatially
non-contiguous areas. Glantz ( 2001 ) defines them succinctly as linkages

between climate anomalies at some distance from each other.
It seems that a number of late nineteenth and early twentieth century cli-
matologists believed that changes in one location were related to changes at a
different location. While the best known of such scholars was Walker, others
pointed out, for example, that drought in South Africa seemed to occur at the
same time as that in India, suggesting a connection between the hemispheres.
However, the word ''teleconnection'' was not used in a climate context until it
appeared in a paper by ˚ ngstr¨m ( 1935 ).