The Alboran area is located downstream of the midlatitude western Europe ridge
and the subtropical eastern North Atlantic–North Africa trough. The climatological
strong European ridge is the region where global highest mean values of atmospheric
blocking are found. The subtropical trough extending from eastern North Atlantic to
North Africa marks the cutoff low track resulting from Rossby wave breakings
associated to blockings.
The relationship between asymmetric components of low and high levels varies
from tropics to extratropics (Chen 2005). In extratropics, where temperature advections are important, Rossby dynamics is predominant. Asymmetries in low levels are
advanced one-quarter of wavelength with respect to the corresponding ones in high
levels, being descents (ascents) and ridges/anticyclones (low-pressure systems) in
lower levels downstream ridges (troughs) in upper levels. In Tropics, effects of
temperature advections are one order of magnitude lower than effects of diabatic
heating from vertical convection, prevailing Sverdrup dynamics. Asymmetries in
low levels are in quadrature with respect to high levels: above a low-level trough
(ridge) exists a high-level ridge (trough). In agreement with Sverdrup vorticity
balance of the steady flow (Rodwell and Hoskins 2001)
Fig. 3.19 Seasonal averaged 250 hPa winds, for the ERA-40 period 1958–2001. In winter (a)
location of: SJ subtropical jet, PJ polar jet, R ridge, and T trough are marked
52
J. M. Sánchez-Laulhé et al.
and the subtropical eastern North Atlantic–North Africa trough. The climatological
strong European ridge is the region where global highest mean values of atmospheric
blocking are found. The subtropical trough extending from eastern North Atlantic to
North Africa marks the cutoff low track resulting from Rossby wave breakings
associated to blockings.
The relationship between asymmetric components of low and high levels varies
from tropics to extratropics (Chen 2005). In extratropics, where temperature advections are important, Rossby dynamics is predominant. Asymmetries in low levels are
advanced one-quarter of wavelength with respect to the corresponding ones in high
levels, being descents (ascents) and ridges/anticyclones (low-pressure systems) in
lower levels downstream ridges (troughs) in upper levels. In Tropics, effects of
temperature advections are one order of magnitude lower than effects of diabatic
heating from vertical convection, prevailing Sverdrup dynamics. Asymmetries in
low levels are in quadrature with respect to high levels: above a low-level trough
(ridge) exists a high-level ridge (trough). In agreement with Sverdrup vorticity
balance of the steady flow (Rodwell and Hoskins 2001)
Fig. 3.19 Seasonal averaged 250 hPa winds, for the ERA-40 period 1958–2001. In winter (a)
location of: SJ subtropical jet, PJ polar jet, R ridge, and T trough are marked
52
J. M. Sánchez-Laulhé et al.