20 June 2017 from 16:00 to 17:00

Colloquium Annalisa Cherchi, CMCC, Bologna, Italy

Remote influence and teleconnection of the Euro-Mediterranean summer climate

The Mediterranean sector is characterized by dry summers with descending motion and typical northerly winds at the surface and mostly westerlies in the mid-troposphere. In the summer mean the subsidence over the eastern Mediterranean has been related to the tropical monsoon southeastward (i.e. the South Asian) through the monsoon-desert mechanism by linear models theory and then verified both in atmospheric re-analyses and in CMIP5 historical simulations.

Following from this it is expected that year-to-year variations in monsoon intensity (i.e. severe strong or weak monsoon years exceeding 15% of summer mean climatology) may affect abnormal summer seasonal climate variations over the Euro-Mediterranean region. In the second half of the 20th century the correlation between Asian monsoon rainfall index and precipitation averaged over the eastern Mediterranean sector is about -0.3, while that with vertical velocity in the mid-troposphere is about 0.5. This weak relationship is also reproduced in few CMIP5 models experiments. The relative low correlation values, in the observations and in the models, suggest the involvement of other factors, as documented for the summer North Atlantic Oscillation (SNAO) or for blocking events and related feedbacks, in determining the intensity of Mediterranean summer climate variations.

In 2014 Italy and the surrounding Mediterranean countries experienced an unusual wet summer: analysis of data and available coupled model experiments suggested that the anomalously high precipitation was associated with positive sea surface temperature and convective anomalies in the tropical Pacific through atmospheric teleconnection. An anomalous cyclonic circulation settled in Southern Europe, weakening the seasonal high and causing heavy precipitation.

 

Start date and time
20 June 2017 16:00
End date and time
20 June 2017 17:00