west and southwest sectors of the Iberian Peninsula, including western Alboran Sea
(Hurrell and Van Loon 1997; Trigo et al. 2002). This relation can be seen in
Fig. 3.24, where winters (DEFM) series of both precipitation at Malaga station
and NAO index are shown. During the transitional seasons, NAO influence on the
Mediterranean becomes weaker (Dunkeloh and Jacobeit 2003; Türkes and Erlat
2003).
Major sudden stratospheric warmings (SSWs; see Butler et al. 2015) can influence the extratropical tropospheric circulation below for weeks to months (e.g.,
Mitchell et al. 2013; Kidston et al. 2015). SSWs on average are followed by NAO
negative phases. SSW occurs approximately once every other year, originating a
sudden warming of the polar stratosphere and the weakening and reverse in direction
of the zonal mean westerly wind of the stratospheric polar vortex over a few days.
NAO is the major factor governing air–sea interactions over the Atlantic. It affects
the ocean through changes in heat content, gyre circulations, mixed layer depth,
salinity, high latitude deep water formation, and sea ice cover. SST fluctuations and
NAO strength are related. During boreal winter, the leading pattern of SST variability consists of a tripolar configuration, with SST anomalies of one sign in the
midlatitudes, extending from the coast of North America into the center of the
basin, surrounded by anomalies of the opposite sign in the subpolar North Atlantic
and in the band between the equator and 30
N (Cayan 1992; Visbeck et al. 2003).
Since NAO is most powerful during winter, the associated SST pattern is strongest in
late winter. This configuration suggests that SST anomalies are driven by changes in
air–sea heat exchanges and surface wind-induced Ekman currents associated with
NAO variations. Thus, indices of the NAO have become widely used to document
and understand how this mode of variability alters the structure and functioning of
marine ecosystems (Hurrell and Deser 2009).
1942
900
800
700
600
500
400
300
200
100
0
6
4
2
0
–2
–4
–6
1944
1946
1948
1950
1952
1954
1956
1958
1960
1962
1964
1966
1968
1970
1972
1974
1976
1978
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
2014
2016
Fig. 3.24 Time series plot of winter (DEFM) precipitation recorded by Malaga station (blue solid
line) and Hurrell annual NAO index (red dashed line)
66
J. M. Sánchez-Laulhé et al.
(Hurrell and Van Loon 1997; Trigo et al. 2002). This relation can be seen in
Fig. 3.24, where winters (DEFM) series of both precipitation at Malaga station
and NAO index are shown. During the transitional seasons, NAO influence on the
Mediterranean becomes weaker (Dunkeloh and Jacobeit 2003; Türkes and Erlat
2003).
Major sudden stratospheric warmings (SSWs; see Butler et al. 2015) can influence the extratropical tropospheric circulation below for weeks to months (e.g.,
Mitchell et al. 2013; Kidston et al. 2015). SSWs on average are followed by NAO
negative phases. SSW occurs approximately once every other year, originating a
sudden warming of the polar stratosphere and the weakening and reverse in direction
of the zonal mean westerly wind of the stratospheric polar vortex over a few days.
NAO is the major factor governing air–sea interactions over the Atlantic. It affects
the ocean through changes in heat content, gyre circulations, mixed layer depth,
salinity, high latitude deep water formation, and sea ice cover. SST fluctuations and
NAO strength are related. During boreal winter, the leading pattern of SST variability consists of a tripolar configuration, with SST anomalies of one sign in the
midlatitudes, extending from the coast of North America into the center of the
basin, surrounded by anomalies of the opposite sign in the subpolar North Atlantic
and in the band between the equator and 30
N (Cayan 1992; Visbeck et al. 2003).
Since NAO is most powerful during winter, the associated SST pattern is strongest in
late winter. This configuration suggests that SST anomalies are driven by changes in
air–sea heat exchanges and surface wind-induced Ekman currents associated with
NAO variations. Thus, indices of the NAO have become widely used to document
and understand how this mode of variability alters the structure and functioning of
marine ecosystems (Hurrell and Deser 2009).
1942
900
800
700
600
500
400
300
200
100
0
6
4
2
0
–2
–4
–6
1944
1946
1948
1950
1952
1954
1956
1958
1960
1962
1964
1966
1968
1970
1972
1974
1976
1978
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
2014
2016
Fig. 3.24 Time series plot of winter (DEFM) precipitation recorded by Malaga station (blue solid
line) and Hurrell annual NAO index (red dashed line)
66
J. M. Sánchez-Laulhé et al.