Review of summer 2009 in Europe

Temperature

Fig. 1. SAT anomalies in the summer (JJA) of 2009.

The 2009 summer temperature anomaly in Europe as a whole (approximated roughly by the area 35-65°N, 10°W-40°E) was 0.84°C (or 1.98 std) above the 1971-2000 average. It was 0.17°C (0.41 std) warmer than the summer of 2008 and close to the average temperature for the past 10 years.

As shown in Fig. 1, the summer was particularly warm in southeast Europe and western Mediterranean, where seasonal temperature anomalies exceeded the 1968-1996 average by more than 2.5°C and 2°C, respectively. Colder or near-normal temperatures were observed in northern Russia and the Baltic countries.

A characteristic feature of atmospheric circulation this summer was a strong center of negative 500-hPa height anomalies in the Northeast Atlantic (Fig. 2). Geographically the center was close to the northern center of the East Atlantic (EA) pattern. Although the southern center of the EA dipole was less pronounced than the northern one, the EA index for the summer of 2009 was strongly positive. In August, the index reached 2.57, the highest value for that month since the record began in 1950. The summer EA index has been consistently positive since 1996. When the index is positive, summers tend to be anomalously warm in southern Europe, particularly in the Balkan region.

Fig. 2. 500-hPa anomalies in the summer (JJA) of 2009.

Another prominent feature of the atmospheric circulation was a strongly negative phase of the North Atlantic Oscillation (NAO). The summer (JJA) EOF-based NAO index was -1.18, the fourth lowest value on record (since 1950). Although the correlation between the NAO and European temperature is much weaker in summer than in winter, there is still some tendency for temperature to be below normal in Scandinavia and above normal in southeast Europe when the NAO index is negative (rule 392).

It is also worth mentioning the state of the Indian Ocean dipole (IOD). Although the IOD index decreased from the previous summer, it still remained positive. When the index is positive, summer temperatures over much of central Europe and the Mediterranean tend to be anomalously warm.

Precipitation

Fig. 3. Precipitation anomalies in the summer (JJA) of 2009.

The trough over the eastern North Atlantic, contributed to above average precipitation across the British Isles and southern Scandinavia (Fig. 3). Thus, it was the second wettest July on record in Wales (in a series from 1914), with only July 1939 being wetter. Over the UK, it was also wetter than July 2007 and 2008 and provisionally ranks 4th but close to the July totals in 1936, 1939 and 1988. August was the wettest month on record for southwest Scotland (see UK Review for July and August). Drier than normal conditions were observed in Spain, France, Romania, Moldova, Ukraine and southern Russia.