Environmental Engineering Reference
In-Depth Information
strategies will be needed for the design of ensemble climate model
projections in order to understand and quantify decadal predictability and
how it may be affected by forced climate change (Murphy et al. 2010).
According to Murphy et al. (2010), several of the main indexes of DCV
(
decadal climate variability
) which deserve to be considered in the present
analysis are:
The North Atlantic Oscillation and the Atlantic Multidecadal
Oscillation
Sir Gilbert Walker of the India Meteorological Department fi rst discovered
a north-south atmospheric pressure “seesaw” which he termed as the
North Atlantic Oscillation (NAO) in the late 1920s (Walker and Bliss 1932).
This north-south pattern oscillates at a variety of timescales, among them
decadal and longer periods (Hurrell 1995, Hurrell and van Loon 1997). In
the last 10-15 years, the Arctic and Antarctic Oscillations (AO and AAO,
respectively) have been associated with climate variability over the two
respective high latitude regions (Thompson and Wallace 2000). The NAO
is believed to be the North Atlantic component of the AO (Marshall et al.
2001).
The Atlantic Multidecadal Oscillation (AMO) (Delworth and Mann
2000, Knight et al. 2005) is a broad hemispheric pattern of multidecadal
variability in surface temperature, centred on the North Atlantic basin
(Fig. 3a).
The Tropical Atlantic SST Gradient Oscillation
The tropical Atlantic Sea Surface Temperature (SST) gradient (TAG) across
the equator is known to vary at the 12 to 13 year period (Chang et al. 1997,
Sutton et al. 2000). Variability of many atmosphere and ocean variables are
associated with the TAG variability, such as winds in the lower troposphere;
heat transferred between the Atlantic Ocean and the overlying atmosphere;
cloudiness; rainfall in North-east Brazil and West Africa; Atlantic hurricanes;
and water vapour infl ux and rainfall in the southern, central, and mid-western
United States (e.g., Mehta 1998, Hurrell et al. 2006, Murphy et al. 2010).
The North Pacifi c Oscillation, the Pacifi c Decadal Oscillation and the
Interdecadal Pacifi c Oscillation
Sir Gilbert Walker also discovered a phenomenon which he termed as
the North Pacifi c Oscillation (NPO) in the 1920s (Walker 1925). The NPO
is a seesaw in atmospheric pressure between sub-polar and sub-tropical
latitudes in the North Pacifi c region (Murphy et al. 2010). Subsequently,
when longterm SST data in the Pacifi c Ocean became available in the
1990s, a number of researchers found that the dominant pattern of SST
variability in the extra-tropical North Pacifi c varied at timescales of one or
