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their influence on daytime regional and urban patterns have been presented by
Alcoforado
et al
. [ALC 06b]. When the N and NW winds weaken by late morning
or mid-afternoon, they are replaced by the Tagus and the Ocean breezes, which play
a very important role in cooling the riverside city districts, as occurs in other seaside
cities, such as Nice and Marseille [CAR 98; GAR 99]. During the heat wave of
2003, the temperature at Belém (B on Figure 5.4b) was 29.5ºC, 11ºC lower than at
Restauradores in the inner city (R on Figure 5.4b) [ALC 06b]. It is known that
breeze direction veers during the day [SIM 94]. In Lisbon it blows from the E and
SE in the morning and veers to the S and SW in the afternoon [ALC 87; VAS 04a;
ALC 06b].
For planning purposes, it is important to understand the timing and how the
Tagus and Ocean breezes penetrate the city [ALC 09]. Owing to the difficulty in
systematically measuring spatial wind-speed variations in urban areas, modeling was
carried our by Prior
et al.
[PRI 01], Neto [NET 05] and Vasconcelos
et al.
[VAS 04a
and b]. Prior
et al.
[PRI 01] used the
Topographic Vorticity Mesoscale Model
to
study the boundary layer mesoscale flows on summer days in central and southern
Portugal. He concluded that sea-breezes penetrate 80 km inland with wind speeds
from 15-20 km/h and thickness between 400 and 600 m. Neto and Vasconcelos have
used the high-resolution
Meso-NH atmospheric model
, based on an anelastic system
of equations developed by Lipps and Hemler [LIP 82].
The details of the model dynamics may be found in Lafore
et al
. (1998), quoted
by Neto [NET 05], who has adapted this methodology at the University of Évora
(Portugal).The model simulates non-hydrostatic atmospheric movements and is able
to simulate all scales ranging from turbulent large eddies to the synoptic scale.
Through nesting procedures, it is possible to simulate local ventilation patterns in a
100×100 m grid [NET 05]. Maps of estimated wind direction in Lisbon at 6 am, at
noon and at 5 pm during one warm summer day (August 10, 2000) have been
presented by Vasvoncelos
et al.
[VAS 04b].
At dawn and during late afternoon N and NW winds are generalized within the
whole area (not shown); however, breezes from the estuary reach a great part of the
city at noon (Figure 5.11). The Tagus breeze is blowing from the E and SE over the
eastern, southern, and central part of Lisbon, whereas in the western part of Lisbon's
region, moderate wind from the NW is already blowing. Air temperatures estimated
in the areas reached by the sea breeze are lower (under 30ºC) than those in the
western part of Lisbon (up to 33ºC). Temperature measurements in summer have
allowed us to validate this estimation. In fact, at noon fresh air reaches city districts
a few kilometers away from the Tagus, as for example the University of Lisbon,
southwards from the Airport, Figure 5.4b [ALC 06b; VAS 04a]. Despite having
obtained interesting results, the authors are aware of the fact that geographical
information at a convenient scale for the downscaling procedures is still missing
[NET 05].
