146
J. Luterbacher and E. Xop1aki
3.3
Sea Level Pressure (SLP) Fields for Mediterranean Winter
Climate Extremes Over the Last Five Centuries
Figure 5 presents the winter SLP patterns connected with the anomalous
temperature and precipitation fields from section 3.2. The coldest winter of 1891
was connected with a strong high over eastern Europe and western Russia and a low
pressure system over the entire Mediterranean. The easterly flow between the high
and the low was responsible for the reduced temperatures over the larger
Mediterranean area. The anomaly chart (SLP 1891 minus long-term 1901-1995
mean; Figure 5 middle) shows the anomalous high pressure over Central and
Northern Europe and below normal pressure over Southern Europe. For this year
around 50 station pressure series are available leading to excellent reconstruction
quality over the whole area (Figure 5 bottom).
The warm winter (1772) was connected with low pressure from the northern
Atlantic over the entire Mediterranean region with mild air advection from West,
over the eastern Mediterranean from Southwest. The SLP anomaly fields reveal
negative values over most of Europe. The reconstruction quality over most of Europe
and North Africa is very good. However, the RE values decrease towards the
southeast.
The reconstructed winter SLP field for the dry winter 1609 shows an extended
high pressure system from the Atlantic over Europe towards western Russia covering
the whole Mediterranean region. Therefore, the dryness was connected with stable
high pressure conditions. In contrast to the quality of the precipitation field, the SLP
reconstruction for 1609 shows a more homogeneous picture with reliable estimates
over the whole Mediterranean. Even without pressure predictors, the quality over
most of the reconstructed area is trustworthy. High pressure over Scandinavia and
western Russia and low pressure from Iceland towards the eastern Mediterranean
was responsible for the wet Mediterranean conditions during winter 1684. Moist air
from West and Northwest was advected towards the Iberian Peninsula and brought
above normal rainfall, whereas southerlies lead to wetness over Italy, Greece and
Turkey. The anomaly charts clearly point to negative SLP anomalies over the
Mediterranean. The quality of this SLP reconstruction is again very good. However,
the reconstruction quality of the Southeastern part of the Mediterranean is reduced.
3.4
Connection Between the NAO Index and the Mediterranean
Temperature and Precipitation Variability AD 1500-1995
We calculated the correlation between the reconstructed winter NAO Index of Cook
et al. (2001) with the Mediterranean precipitation and temperature time series for
the period AD 1500-1979. The correlations for each century and for the full AD
1500-1979 period is given in Table 1. It clearly shows the highly significant (95%
significance level) negative correlation between the NAO and precipitation. The
connection between winter Mediterranean temperature and the NAO is weak and
J. Luterbacher and E. Xop1aki
3.3
Sea Level Pressure (SLP) Fields for Mediterranean Winter
Climate Extremes Over the Last Five Centuries
Figure 5 presents the winter SLP patterns connected with the anomalous
temperature and precipitation fields from section 3.2. The coldest winter of 1891
was connected with a strong high over eastern Europe and western Russia and a low
pressure system over the entire Mediterranean. The easterly flow between the high
and the low was responsible for the reduced temperatures over the larger
Mediterranean area. The anomaly chart (SLP 1891 minus long-term 1901-1995
mean; Figure 5 middle) shows the anomalous high pressure over Central and
Northern Europe and below normal pressure over Southern Europe. For this year
around 50 station pressure series are available leading to excellent reconstruction
quality over the whole area (Figure 5 bottom).
The warm winter (1772) was connected with low pressure from the northern
Atlantic over the entire Mediterranean region with mild air advection from West,
over the eastern Mediterranean from Southwest. The SLP anomaly fields reveal
negative values over most of Europe. The reconstruction quality over most of Europe
and North Africa is very good. However, the RE values decrease towards the
southeast.
The reconstructed winter SLP field for the dry winter 1609 shows an extended
high pressure system from the Atlantic over Europe towards western Russia covering
the whole Mediterranean region. Therefore, the dryness was connected with stable
high pressure conditions. In contrast to the quality of the precipitation field, the SLP
reconstruction for 1609 shows a more homogeneous picture with reliable estimates
over the whole Mediterranean. Even without pressure predictors, the quality over
most of the reconstructed area is trustworthy. High pressure over Scandinavia and
western Russia and low pressure from Iceland towards the eastern Mediterranean
was responsible for the wet Mediterranean conditions during winter 1684. Moist air
from West and Northwest was advected towards the Iberian Peninsula and brought
above normal rainfall, whereas southerlies lead to wetness over Italy, Greece and
Turkey. The anomaly charts clearly point to negative SLP anomalies over the
Mediterranean. The quality of this SLP reconstruction is again very good. However,
the reconstruction quality of the Southeastern part of the Mediterranean is reduced.
3.4
Connection Between the NAO Index and the Mediterranean
Temperature and Precipitation Variability AD 1500-1995
We calculated the correlation between the reconstructed winter NAO Index of Cook
et al. (2001) with the Mediterranean precipitation and temperature time series for
the period AD 1500-1979. The correlations for each century and for the full AD
1500-1979 period is given in Table 1. It clearly shows the highly significant (95%
significance level) negative correlation between the NAO and precipitation. The
connection between winter Mediterranean temperature and the NAO is weak and