Relationship between the summer NAO and maximum temperatures for the Iberian Peninsula

The Summer North Atlantic Oscillation (SNAO) index is strongly linked to temperatures in the north and west of Europe although it also has a weaker relationship of an opposite sign with the temperature of the eastern Mediterranean area. The objective of this work is to determine if it is possible to find a relationship between the SNAO and daily maximum temperatures (Tx) in the Iberian Peninsula (IP) for the months of July and August. The correlation between the SNAO and the daily maximum temperatures in the IP is very weak, except for a part of the southeast of the IP and a region in the northwest of the IP where we found statistically significant correlations with opposite signs for both regions. We found that the Tx distribution of the NW region (TxNW) shows positive correlations with the SNAO as is the case with Northern Europe, while in the case of the SE region (TxSE) this distribution shows negative correlations similar to those seen in Italy and the Balkans. We found a strong relationship between the difference TxNW-TxSE and SNAO: when the SNAO is high, the absolute value of TxNW-TxSE is significantly lower (gentler Tx gradient) than average, and the opposite occurs when the SNAO is low (steeper Tx gradient). We also found that the strong increase in the SNAO from the late-1960s until the mid-1980s is reflected in the asymmetric Tx trends of the NW and SE of the IP: while the SNAO was rising, the absolute value of the difference TxNW-TxSE dropped significantly.