274
MJ. Esteban-Parra, D. Pozo-Vazquez, F.S. Rodrigo, Y. Castro-Dfez
although it was problably less pronounced for the Western and Central
Mediterranean areas (Maheras, 1988; Maheras et aI., 1992). There is also a good
concordance between dry periods. The dry period around 1920 appears also in a
general way in the Mediterranean and Southern Central Europe (Brazdil et aI. 1985;
Maheras 1990). The 1 sl annual series centred on the Andalusia and Interior region
of Spain is similar to the Central Europe series, particularly those located in the
south (Bnizdil et aI., 1985) from 1920 until the end of the records. The decreasing
trends found for the pI and 2 nd PC series (Andalusia and Interior, Mediterranean
Coast) are common for Southern Europe. The annual series corresponding to the
Cantabric are more similar with series corresponding to Northern Europe (Bnizdil
et aI., 1985).
The presence and intensity of the Azores High is a determinant in the Iberian
precipitation regime. Effectively, the coincidence between the annual average central
pressure value of the Azores High and its mean position (Sahsamanogluo, 1990) and
the I sl annual PC series is very clear; low precipitation are related to high values of
Azores central pressure or an eastwards shift of its mean position. There is also a
concordance with the evolution of the other two annual series, specially during the
relatively dry years betweenl940 and 1960, when the Azores High shifted to the
east, and during the 1980s when the intensification of the Azores high coincided
with a new period oflow precipitation. As a proof ofthis relation, Table 5 shows the
correlation coefficients between the PC series and the seasonal and annual series of
MSLP at Ponta Delgada (Azores) for which there is data from 1894 to 1981. The use
of these data as representative of the Azores High is necessarily limited because this
action centre has not a fixed position from year to year and from season to season
(Sahsamanogluo, 1990). The relation is quite good for the 1 sl PC time series, where
the Azores High influence is particularly significant, and for the winter season,
when the position of the Azores High is to the south east of Ponta Delgada and in
an optimum position for controlling the precipitation in Western Iberia (Capel
Molina, 1981). It is worth mentioning the positive correlation between the autumn
series for Cantabric and Azores, similar to the situation for Western Northern
Europe.
There is also a good concordance between the evolution of the precipitation over
the Mediterranean Coast and the mean sea level pressure over the Mediterranean
(Makrogiannis and Sahsamanogluo, 1990), so the negative anomalies of the pressure
in the 40$"0$N from 1880 to 1900 and from 1930 to 70 coincide with the rainy
period in the beginning of the series and during the 60s and 70s, and positive
anomalies in 1900-1930 and I 970-80,correspond to the dry periods of the decades
1910 and 1920 and 1980. There is not concordance between the positive anomalies
of pressure on the400N and the precipitation during the first decade of this century,
although it occured with the negative anomalies during these years over the 30 o N.
One of the most useful parameters to analyse the circulation of the North Atlantic
is the North Atlanctic Oscillation (NAO) index. A high NAO index represents
strong westerlies, and low index, a predominant meridional circulation. We have
compared our results with two different indices of the zonality over the North
MJ. Esteban-Parra, D. Pozo-Vazquez, F.S. Rodrigo, Y. Castro-Dfez
although it was problably less pronounced for the Western and Central
Mediterranean areas (Maheras, 1988; Maheras et aI., 1992). There is also a good
concordance between dry periods. The dry period around 1920 appears also in a
general way in the Mediterranean and Southern Central Europe (Brazdil et aI. 1985;
Maheras 1990). The 1 sl annual series centred on the Andalusia and Interior region
of Spain is similar to the Central Europe series, particularly those located in the
south (Bnizdil et aI., 1985) from 1920 until the end of the records. The decreasing
trends found for the pI and 2 nd PC series (Andalusia and Interior, Mediterranean
Coast) are common for Southern Europe. The annual series corresponding to the
Cantabric are more similar with series corresponding to Northern Europe (Bnizdil
et aI., 1985).
The presence and intensity of the Azores High is a determinant in the Iberian
precipitation regime. Effectively, the coincidence between the annual average central
pressure value of the Azores High and its mean position (Sahsamanogluo, 1990) and
the I sl annual PC series is very clear; low precipitation are related to high values of
Azores central pressure or an eastwards shift of its mean position. There is also a
concordance with the evolution of the other two annual series, specially during the
relatively dry years betweenl940 and 1960, when the Azores High shifted to the
east, and during the 1980s when the intensification of the Azores high coincided
with a new period oflow precipitation. As a proof ofthis relation, Table 5 shows the
correlation coefficients between the PC series and the seasonal and annual series of
MSLP at Ponta Delgada (Azores) for which there is data from 1894 to 1981. The use
of these data as representative of the Azores High is necessarily limited because this
action centre has not a fixed position from year to year and from season to season
(Sahsamanogluo, 1990). The relation is quite good for the 1 sl PC time series, where
the Azores High influence is particularly significant, and for the winter season,
when the position of the Azores High is to the south east of Ponta Delgada and in
an optimum position for controlling the precipitation in Western Iberia (Capel
Molina, 1981). It is worth mentioning the positive correlation between the autumn
series for Cantabric and Azores, similar to the situation for Western Northern
Europe.
There is also a good concordance between the evolution of the precipitation over
the Mediterranean Coast and the mean sea level pressure over the Mediterranean
(Makrogiannis and Sahsamanogluo, 1990), so the negative anomalies of the pressure
in the 40$"0$N from 1880 to 1900 and from 1930 to 70 coincide with the rainy
period in the beginning of the series and during the 60s and 70s, and positive
anomalies in 1900-1930 and I 970-80,correspond to the dry periods of the decades
1910 and 1920 and 1980. There is not concordance between the positive anomalies
of pressure on the400N and the precipitation during the first decade of this century,
although it occured with the negative anomalies during these years over the 30 o N.
One of the most useful parameters to analyse the circulation of the North Atlantic
is the North Atlanctic Oscillation (NAO) index. A high NAO index represents
strong westerlies, and low index, a predominant meridional circulation. We have
compared our results with two different indices of the zonality over the North