While internal atmospheric variability exhibits temporal incoherence, the ocean
tends to respond to it with marked persistence of heat content anomalies that could
feedback to the local atmosphere. Mosedale et al. (2006) have demonstrated that the
SST tripole in the Atlantic Ocean can provide a small yet statistically significant
feedback on the NAO. The level of retroaction of anomalous extratropical SST upon
weather regimes appears to be weak in mid and low latitudes except through specific
mechanisms such as the re-emergence of SST anomalies in the North Atlantic from
one winter to the next. The impact of re-emergence upon the climate system has been
investigated by Cassou et al. (2007), concluding that the atmospheric response to
reemerging SST anomalies resembled the atmospheric circulation that created them
the previous winter but with reduced amplitude. Re-emergence only occurs after an
NAOÀ winter with a strongly negative NAO index (Buchan et al. 2014; Buchan
2017). The re-emergence effects can be observed in the years following a winter
NAO index lower than À3 (1969/1970, 1996/1997, 2009/2010) in the Malaga
station winter (DEFM) precipitation series (Fig. 3.24).
The origin of low-frequency variability and NAO potential predictability is still
under discussion. As it occurs with long-lived atmospheric anomalies in middle and
high latitudes, a large amount of the interannual NAO variance may be attributed to
internal atmospheric dynamical processes (e.g., Hurrell and van Loon 1997;
Kug et al. 2010; García-Serrano et al. 2008, 2011; Jung et al. 2011; Li and Lau
2012) as, for instance, stratosphere–troposphere coupling (Scaife et al. 2005) and
Rossby wave–breaking events (Woollings et al. 2008). Feldstein (2003) found that
positive NAO phase developed after anomalous wave train propagation across the
North Pacific to the North American east coast, while the negative NAO phase
appeared to develop in situ. Other results indicate that tropical forcing mechanisms
may also play a role, (e.g., ENSO; e.g., Greatbatch and Jung 2007). Yu and Lin
(2016) have shown that NAO correlates significantly with heating anomalies associated with precipitation in the tropical Indian Ocean and tropical American–Atlantic
region, but not with the underlying SST anomalies.
While on interannual time scale the North Atlantic SST anomalies are mainly
forced by the atmosphere, on longer time scales the NAO could be influenced by
low-frequency SST variations in the North Atlantic, implying a possible predictable
oceanic influence on the NAO (e.g., Rodwell et al. 1999; Kushnir et al. 2002;
Kushnir and Held 1996; Seager et al. 2000; Watanabe and Kimoto 2000; Czaja
and Frankignoul 1999; Wang et al. 2004; Frankignoul et al. 2011; Scaife et al. 2011).
The NAO decadal behavior, influencing climate in Europe, Asia, and northern
Africa, might be associated with the underlying low-frequency SST forcing. The
SST anomalies could arise from modulations of the oceanic gyre circulation (e.g.,
Grötzner et al. 1998) or feedback processes related to the thermohaline overturning
at high latitudes (e.g., Timmermann et al. 1998), and they are likely connected to
both tropical and extratropical lower frequency SST in the Indo-Pacific and Atlantic
regions (Wanner et al. 2001).
Both the Pacific Decadal Oscillation (PDO; e.g., Deser et al. 2016) and the AMO
seem to be closely related to the NAO on frequency variations lower than decadal
timescale (Wang et al. 2010). These suggest that the longer-term variations of the
3 Alboran Sea Area Climate and Weather
67
tends to respond to it with marked persistence of heat content anomalies that could
feedback to the local atmosphere. Mosedale et al. (2006) have demonstrated that the
SST tripole in the Atlantic Ocean can provide a small yet statistically significant
feedback on the NAO. The level of retroaction of anomalous extratropical SST upon
weather regimes appears to be weak in mid and low latitudes except through specific
mechanisms such as the re-emergence of SST anomalies in the North Atlantic from
one winter to the next. The impact of re-emergence upon the climate system has been
investigated by Cassou et al. (2007), concluding that the atmospheric response to
reemerging SST anomalies resembled the atmospheric circulation that created them
the previous winter but with reduced amplitude. Re-emergence only occurs after an
NAOÀ winter with a strongly negative NAO index (Buchan et al. 2014; Buchan
2017). The re-emergence effects can be observed in the years following a winter
NAO index lower than À3 (1969/1970, 1996/1997, 2009/2010) in the Malaga
station winter (DEFM) precipitation series (Fig. 3.24).
The origin of low-frequency variability and NAO potential predictability is still
under discussion. As it occurs with long-lived atmospheric anomalies in middle and
high latitudes, a large amount of the interannual NAO variance may be attributed to
internal atmospheric dynamical processes (e.g., Hurrell and van Loon 1997;
Kug et al. 2010; García-Serrano et al. 2008, 2011; Jung et al. 2011; Li and Lau
2012) as, for instance, stratosphere–troposphere coupling (Scaife et al. 2005) and
Rossby wave–breaking events (Woollings et al. 2008). Feldstein (2003) found that
positive NAO phase developed after anomalous wave train propagation across the
North Pacific to the North American east coast, while the negative NAO phase
appeared to develop in situ. Other results indicate that tropical forcing mechanisms
may also play a role, (e.g., ENSO; e.g., Greatbatch and Jung 2007). Yu and Lin
(2016) have shown that NAO correlates significantly with heating anomalies associated with precipitation in the tropical Indian Ocean and tropical American–Atlantic
region, but not with the underlying SST anomalies.
While on interannual time scale the North Atlantic SST anomalies are mainly
forced by the atmosphere, on longer time scales the NAO could be influenced by
low-frequency SST variations in the North Atlantic, implying a possible predictable
oceanic influence on the NAO (e.g., Rodwell et al. 1999; Kushnir et al. 2002;
Kushnir and Held 1996; Seager et al. 2000; Watanabe and Kimoto 2000; Czaja
and Frankignoul 1999; Wang et al. 2004; Frankignoul et al. 2011; Scaife et al. 2011).
The NAO decadal behavior, influencing climate in Europe, Asia, and northern
Africa, might be associated with the underlying low-frequency SST forcing. The
SST anomalies could arise from modulations of the oceanic gyre circulation (e.g.,
Grötzner et al. 1998) or feedback processes related to the thermohaline overturning
at high latitudes (e.g., Timmermann et al. 1998), and they are likely connected to
both tropical and extratropical lower frequency SST in the Indo-Pacific and Atlantic
regions (Wanner et al. 2001).
Both the Pacific Decadal Oscillation (PDO; e.g., Deser et al. 2016) and the AMO
seem to be closely related to the NAO on frequency variations lower than decadal
timescale (Wang et al. 2010). These suggest that the longer-term variations of the
3 Alboran Sea Area Climate and Weather
67