2016). The seasonal variation of Saharan dust outflows has been reasonably well
studied in affected regions (Barnaba and Gobbi 2004; Israelevich et al. 2012;
Prospero et al. 2014). Inter-annual dust outflow variations are relatively wellknown in winter period (Nakamae and Shiotani 2013), mostly associated with the
NAO (Chiapello et al. 2005; Ginoux et al. 2004). However, only in recent years
research on inter-annual variations of Saharan dust outflows during summer period
has been carried out (i.e., Ben-Ami et al. 2009; Rodríguez et al. 2015). In this season,
Saharan dust mobilization shows its peak (Engelstaedter and Washington 2007). On
subseasonal and synoptic timescales, the Sahara Heat Low migrate around its
location, shown in Figs. 3.20 and 3.21, and pulsates in strength as it interacts with
midlatitude weather systems (Thorncroft and Flocas 1997; Chauvin et al. 2010;
Roehring et al. 2011; Cuevas et al. 2017).
Air pollution emissions by industries and large urban areas around the Mediterranean and in central Europe can further affect regional air quality, surface energy,
and water budgets (Lelieveld et al. 2002). Biomass burning and forest fires constitute
another important source of carbonaceous aerosols in summer (Sciare et al. 2008).
The decrease of anthropogenic aerosols over Europe resulting from air pollution
policies (Turnock et al. 2016) has been pointed out as an important contributor to the
enhanced western European summer (Junie-August) warming since the mid-1990s
(e.g., Dong et al. 2017).
3.1.4 Temperature
Mean seasonal 2m temperatures in the area are shown in Fig. 3.3. The temperature
seasonal cycle in the area is affected by the thermoregulatory effect of the sea, and
also by orography. In winter, accurate temperature gradients exist between the
mountainous high lands and the warmer Alboran Sea. On the contrary, in summer,
although there are temperature gradients from the sea toward the warmer lands, it is
outstanding the gradient across the Atlas Mountains, which form a barrier to the hot
and dry summer Sahara air mass. The SST annual cycle in the Alboran point 36
N
3
W is shown in Fig. 3.16.
In winter (also in spring and fall), extremely cold temperatures are associated with
the Atlantic Ridge weather regime (Trigo et al. 2006; Cassou 2009). In summer
extreme warm temperatures are associated with blocking conditions, subsidence and
stability, and an east–west dipole over the Euro-Atlantic sector (Xoplaki et al. 2003),
which corresponds to the Atlantic Low weather regime (Cassou et al. 2005).
Báez et al. (2013) found that variation in both mean annual SST and mean winter
SST in Alboran were significantly related to the mean autumn NAO of the previous
year, while mean summer SST was related to mean autumn AO of the previous year.
In the north coast of Alboran, extreme maximum temperature occur usually in
summer during a downslope wind event. This downslope wind occurs with advection of a warm air mass of tropical origin from the Atlantic Ocean toward the Iberian
Peninsula, followed by overheating when the air reaches the coast of Alboran as a
terral wind. In the south coast, downslope (southerly) winds are rare and its duration
46
J. M. Sánchez-Laulhé et al.
studied in affected regions (Barnaba and Gobbi 2004; Israelevich et al. 2012;
Prospero et al. 2014). Inter-annual dust outflow variations are relatively wellknown in winter period (Nakamae and Shiotani 2013), mostly associated with the
NAO (Chiapello et al. 2005; Ginoux et al. 2004). However, only in recent years
research on inter-annual variations of Saharan dust outflows during summer period
has been carried out (i.e., Ben-Ami et al. 2009; Rodríguez et al. 2015). In this season,
Saharan dust mobilization shows its peak (Engelstaedter and Washington 2007). On
subseasonal and synoptic timescales, the Sahara Heat Low migrate around its
location, shown in Figs. 3.20 and 3.21, and pulsates in strength as it interacts with
midlatitude weather systems (Thorncroft and Flocas 1997; Chauvin et al. 2010;
Roehring et al. 2011; Cuevas et al. 2017).
Air pollution emissions by industries and large urban areas around the Mediterranean and in central Europe can further affect regional air quality, surface energy,
and water budgets (Lelieveld et al. 2002). Biomass burning and forest fires constitute
another important source of carbonaceous aerosols in summer (Sciare et al. 2008).
The decrease of anthropogenic aerosols over Europe resulting from air pollution
policies (Turnock et al. 2016) has been pointed out as an important contributor to the
enhanced western European summer (Junie-August) warming since the mid-1990s
(e.g., Dong et al. 2017).
3.1.4 Temperature
Mean seasonal 2m temperatures in the area are shown in Fig. 3.3. The temperature
seasonal cycle in the area is affected by the thermoregulatory effect of the sea, and
also by orography. In winter, accurate temperature gradients exist between the
mountainous high lands and the warmer Alboran Sea. On the contrary, in summer,
although there are temperature gradients from the sea toward the warmer lands, it is
outstanding the gradient across the Atlas Mountains, which form a barrier to the hot
and dry summer Sahara air mass. The SST annual cycle in the Alboran point 36
N
3
W is shown in Fig. 3.16.
In winter (also in spring and fall), extremely cold temperatures are associated with
the Atlantic Ridge weather regime (Trigo et al. 2006; Cassou 2009). In summer
extreme warm temperatures are associated with blocking conditions, subsidence and
stability, and an east–west dipole over the Euro-Atlantic sector (Xoplaki et al. 2003),
which corresponds to the Atlantic Low weather regime (Cassou et al. 2005).
Báez et al. (2013) found that variation in both mean annual SST and mean winter
SST in Alboran were significantly related to the mean autumn NAO of the previous
year, while mean summer SST was related to mean autumn AO of the previous year.
In the north coast of Alboran, extreme maximum temperature occur usually in
summer during a downslope wind event. This downslope wind occurs with advection of a warm air mass of tropical origin from the Atlantic Ocean toward the Iberian
Peninsula, followed by overheating when the air reaches the coast of Alboran as a
terral wind. In the south coast, downslope (southerly) winds are rare and its duration
46
J. M. Sánchez-Laulhé et al.