particular, simulations suggest an increased risk of winter flooding in southern Italy,
Greece, and the Iberian Peninsula.
Chemke et al. (2019) found that, under Arctic sea ice loss, ocean heat transport
acts by transferring the Arctic signal to the tropics and by contracting the mean
Hadley cell.
3.2.2 Synoptic Systems
Weather and climate in the extratropical latitudes are largely controlled by the passage
of synoptic systems: baroclinic extratropical cyclones (midlatitude storms), high-level
midlatitude troughs stretching toward subtropics, and high-level cut-off lows.
Observational evidence clearly shows that the midlatitude storms typically move
eastward across the major oceans along definite paths called storm tracks. Climatological regions of storm tracks have been determined using cyclone tracking algorithms that generally detect minima in mean sea level pressure, or maxima in
low-level vorticity, and identify them as cyclones’ centers. Figure 3.21 shows the
seasonal climatological maps of the Atlantic storm track obtained from the Featurebased ERA-Interim Climatologies (FEIC) datasets (Sprenger et al. 2017), which
used an algorithm based on concepts presented in Wernli and Schwierz (2006). Its
interpretation is straightforward, since it corresponds at every location to the percentage of time instants, f c , that the point is located within a cyclone. The Atlantic
storm track begins near the east coast of North America, on the immediate northern
flank of the strong subtropical jet, coinciding the zone of maximum f c with the
Iceland Low (Fig. 3.20), and tilts slightly northeast across the Atlantic toward
northwest Europe, moving away from the weak subtropical jet stream of the Central
Atlantic Ocean. Its structure is primarily a consequence of the localization and
strength of the North Atlantic subtropical jet. The storm track eddies tend to form
in the strongly baroclinic region on the poleward side of the subtropical jet (e.g.,
Simmons and Hoskins 1978, 1980; Lee and Kim 2003). When the subtropical jet is
strong, as it occurs in the eastern coast of North America, the preferred region for
eddy activity stands on the immediate northern flank of the subtropical jet. Contrary,
when the subtropical jet is weak the preferred region for eddy displaces 20
–30
poleward from the subtropical jet, as it occurs in central and eastern North Atlantic.
However, Brayshaw et al. (2008) have shown that the structure of the Atlantic storm
track is in an important part due to the characteristics of the North American
continent.
All developing cyclones are accompanied by large poleward of both heat fluxes
and zonal momentum fluxes. The poleward momentum fluxes do that the subtropical
jet stream appears to be shifted poleward over the oceans (Fig. 3.19). Indeed, this
displacement does not exist and a new jet stream is formed. Often, it is observed over
the oceans at certains longitudes the coexistence of two jet stream systems with
different characteristics: one at high latitude, denominated the eddy or polar jet, and
another in lower latitudes, the subtropical jet.
58
J. M. Sánchez-Laulhé et al.
Greece, and the Iberian Peninsula.
Chemke et al. (2019) found that, under Arctic sea ice loss, ocean heat transport
acts by transferring the Arctic signal to the tropics and by contracting the mean
Hadley cell.
3.2.2 Synoptic Systems
Weather and climate in the extratropical latitudes are largely controlled by the passage
of synoptic systems: baroclinic extratropical cyclones (midlatitude storms), high-level
midlatitude troughs stretching toward subtropics, and high-level cut-off lows.
Observational evidence clearly shows that the midlatitude storms typically move
eastward across the major oceans along definite paths called storm tracks. Climatological regions of storm tracks have been determined using cyclone tracking algorithms that generally detect minima in mean sea level pressure, or maxima in
low-level vorticity, and identify them as cyclones’ centers. Figure 3.21 shows the
seasonal climatological maps of the Atlantic storm track obtained from the Featurebased ERA-Interim Climatologies (FEIC) datasets (Sprenger et al. 2017), which
used an algorithm based on concepts presented in Wernli and Schwierz (2006). Its
interpretation is straightforward, since it corresponds at every location to the percentage of time instants, f c , that the point is located within a cyclone. The Atlantic
storm track begins near the east coast of North America, on the immediate northern
flank of the strong subtropical jet, coinciding the zone of maximum f c with the
Iceland Low (Fig. 3.20), and tilts slightly northeast across the Atlantic toward
northwest Europe, moving away from the weak subtropical jet stream of the Central
Atlantic Ocean. Its structure is primarily a consequence of the localization and
strength of the North Atlantic subtropical jet. The storm track eddies tend to form
in the strongly baroclinic region on the poleward side of the subtropical jet (e.g.,
Simmons and Hoskins 1978, 1980; Lee and Kim 2003). When the subtropical jet is
strong, as it occurs in the eastern coast of North America, the preferred region for
eddy activity stands on the immediate northern flank of the subtropical jet. Contrary,
when the subtropical jet is weak the preferred region for eddy displaces 20
–30
poleward from the subtropical jet, as it occurs in central and eastern North Atlantic.
However, Brayshaw et al. (2008) have shown that the structure of the Atlantic storm
track is in an important part due to the characteristics of the North American
continent.
All developing cyclones are accompanied by large poleward of both heat fluxes
and zonal momentum fluxes. The poleward momentum fluxes do that the subtropical
jet stream appears to be shifted poleward over the oceans (Fig. 3.19). Indeed, this
displacement does not exist and a new jet stream is formed. Often, it is observed over
the oceans at certains longitudes the coexistence of two jet stream systems with
different characteristics: one at high latitude, denominated the eddy or polar jet, and
another in lower latitudes, the subtropical jet.
58
J. M. Sánchez-Laulhé et al.