3.2.3 Mediterranean Cyclones
The Mediterranean region is characterized by high frequency of cyclones. The near
subtropical location of the basin suppresses cyclonic activity in summer, whereas it
is highly populated by cyclones in winter (Petterssen 1956; HMSO 1962; Reiter
1975; Radinovic 1987; Campins et al. 2000; Nissen et al. 2010). This last fact is
synthesized by the presence of a winter stationary Mediterranean trough (Fig. 3.20).
In this season, the basin presents all the cyclogenetic factors: high baroclinicity,
warmer than its surrounding lands, and positioned at the lee of mountain ridges (e.g.,
Lionello et al. 2006). The frequency of passage and the intensity of the midlatitudes
cyclones play a dominant role in determining local weather and climate, being the
prime contributors to precipitation (Trigo et al. 2000), but also in a way important for
cloudiness, radiation, temperature, etc. (Radinovic 1987).
Most cyclones affecting the Mediterranean region develop within the basin itself
and nearby areas. Although HMSO (1962) found that 42% of the cyclones were
formed outside the Basin, Romem et al. (2007) estimated that only 13% of the
cyclones were generated outside the Mediterranean Basin, entering the region along
three different routes. The largest number of entering cyclones (46%) originated
from the Sahara Desert, at the lee of the Atlas Mountains (e.g., Egger et al. 1995).
The second area of origin was the Atlantic Ocean (31%), whose cyclones entered the
Mediterranean Basin through Gibraltar and Biscay and continued their track eastward, mostly along the Mediterranean northern coast. The third area of origin is
Western Europe (23%), mostly through the Gulf of Genoa.
Most Mediterranean cyclones are generated in the basin itself under the influence
of a PV streamers, widely recognized as upper-tropospheric precursors (“parent
cyclones”), playing a primary role in the development and intensification of these
(Emanuel 2005; Fita et al. 2006; Chaboureau and Claud 2006; Chaboureau et al.
2012; Flaounas et al. 2015; Raveh-Rubin and Flaounas 2017). Consequently, the
highly variable behavior of the storm tracks, particularly in the eastern North
Atlantic, affects the frequency of cyclones having profound impact on the
hydroclimate of the Mediterranean region.
Cyclones in the Mediterranean region are conditioned by topography in both their
origin and life cycle. They tend to be meridionally confined and hence, have a
smaller scale than north Atlantic ones and shorter lifetimes (Trigo et al. 1999). Their
horizontal size differs between mesoscale (Alpert et al. 1999) and synoptic-scale
(Campins et al. 2000; Trigo et al. 2002) and a number of identification and tracking
methods have been developed or specifically adapted for them (e.g., Campins et al.
2011).
Passage of Mediterranean cyclones along the Alboran Sea is very infrequent
because, although sometimes they originate over Alboran, they usually propagate
eastward along the northern coast of the Mediterranean until reaching the Levant
region where they weaken or even dissipate (Kahana et al. 2002; Flocas et al. 2010).
Two major branches of cyclones initiate in western Mediterranean: (1) from the
northwest Mediterranean descends along the Tyrrhenian and Adriatic Sea, (2) from
3 Alboran Sea Area Climate and Weather
61
The Mediterranean region is characterized by high frequency of cyclones. The near
subtropical location of the basin suppresses cyclonic activity in summer, whereas it
is highly populated by cyclones in winter (Petterssen 1956; HMSO 1962; Reiter
1975; Radinovic 1987; Campins et al. 2000; Nissen et al. 2010). This last fact is
synthesized by the presence of a winter stationary Mediterranean trough (Fig. 3.20).
In this season, the basin presents all the cyclogenetic factors: high baroclinicity,
warmer than its surrounding lands, and positioned at the lee of mountain ridges (e.g.,
Lionello et al. 2006). The frequency of passage and the intensity of the midlatitudes
cyclones play a dominant role in determining local weather and climate, being the
prime contributors to precipitation (Trigo et al. 2000), but also in a way important for
cloudiness, radiation, temperature, etc. (Radinovic 1987).
Most cyclones affecting the Mediterranean region develop within the basin itself
and nearby areas. Although HMSO (1962) found that 42% of the cyclones were
formed outside the Basin, Romem et al. (2007) estimated that only 13% of the
cyclones were generated outside the Mediterranean Basin, entering the region along
three different routes. The largest number of entering cyclones (46%) originated
from the Sahara Desert, at the lee of the Atlas Mountains (e.g., Egger et al. 1995).
The second area of origin was the Atlantic Ocean (31%), whose cyclones entered the
Mediterranean Basin through Gibraltar and Biscay and continued their track eastward, mostly along the Mediterranean northern coast. The third area of origin is
Western Europe (23%), mostly through the Gulf of Genoa.
Most Mediterranean cyclones are generated in the basin itself under the influence
of a PV streamers, widely recognized as upper-tropospheric precursors (“parent
cyclones”), playing a primary role in the development and intensification of these
(Emanuel 2005; Fita et al. 2006; Chaboureau and Claud 2006; Chaboureau et al.
2012; Flaounas et al. 2015; Raveh-Rubin and Flaounas 2017). Consequently, the
highly variable behavior of the storm tracks, particularly in the eastern North
Atlantic, affects the frequency of cyclones having profound impact on the
hydroclimate of the Mediterranean region.
Cyclones in the Mediterranean region are conditioned by topography in both their
origin and life cycle. They tend to be meridionally confined and hence, have a
smaller scale than north Atlantic ones and shorter lifetimes (Trigo et al. 1999). Their
horizontal size differs between mesoscale (Alpert et al. 1999) and synoptic-scale
(Campins et al. 2000; Trigo et al. 2002) and a number of identification and tracking
methods have been developed or specifically adapted for them (e.g., Campins et al.
2011).
Passage of Mediterranean cyclones along the Alboran Sea is very infrequent
because, although sometimes they originate over Alboran, they usually propagate
eastward along the northern coast of the Mediterranean until reaching the Levant
region where they weaken or even dissipate (Kahana et al. 2002; Flocas et al. 2010).
Two major branches of cyclones initiate in western Mediterranean: (1) from the
northwest Mediterranean descends along the Tyrrhenian and Adriatic Sea, (2) from
3 Alboran Sea Area Climate and Weather
61