BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

ESF-MedCLIVAR WorkshopTrieste 13-15 October 2008,

Influence of Mediterranean cyclones on Alpine precipitation

Herbert FormayerImran Nadeem and Patrick Haas

Universität für Bodenkultur, ViennaInstitute of Meteorology (BOKU-Met)

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

The Mediterranean sea is one of the most important moisture sources for alpine precipitation.

Of course it is the main source for the south side of the Alps.

But even on the north side of the Alps air masses from the Mediterranean sea are responsible for large scale heavy precipitation events and flooding, as in May 1999, August 2002 and August 2005

Cut-off lows centred near the Alps are mainly responsible for this heavy precipitation events .

Introduction

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

Upper level trough

Tear-off

Cut-off

Final stage

Live cycle of cut-off lows

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

Sub-regions of cut-off lows affecting the alps

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

Winter (DJF)

NW NE

SESW

Precipitation anomaly associated with cut-off lows

close to the alps

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

Precipitation anomaly associated with cut-off lows

close to the alpsSummer (JJA)

NW NE

SW SE

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

19.05.1999 20.05.1999

21.05.1999 22.05.1999

Case study: May 1999

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

20. – 22.05.1999 precipitation sum and track of the cut-off low

Case study: May 1999

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

Observed Precipitation

Case study: May 1999

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

MM5

Case study: May 1999

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

ALADIN

Case study: May 1999

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

Reanalyses

Case study: July 1981

19810718RegCM3 (50 km)

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

Case study: July 1981

19810719RegCM3 (50 km) Reanalyses

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

Case study: July 1981

19810720

ReanalysesRegCM3 (50 km)

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

Case study: July 1981

19810721

ReanalysesRegCM3 (50 km)

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

Case study: July 1981

19810718RegCM3 (50 km)

Observations

Precipitation sums (daily)

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

Case study: July 1981

19810719RegCM3 (50 km)

Observations

Precipitation sums (daily)

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

Case study: June 1988

19880605

ReanalysesRegCM3 (50 km)

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

Case study: June 1988

19880606

ReanalysesRegCM3 (50 km)

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

Case study: June 1988

19880607

ReanalysesRegCM3 (50 km)

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

Case study: June 1988

19880605RegCM3 (50 km)

Observations

Precipitation sums (daily)

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

Case study: June 1988

19880606RegCM3 (50 km)

Observations

Precipitation sums (daily)

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

Mediterranean cyclones are important for the Alpine precipitation.

Many large scale alpine flooding events even on the north side of the Alps are associated with cut-off lows, transporting Mediterranean air-masses on the north side of the Alps.

Cut-off lows are not easy to handle by regional climate models (even so in NWP).

Conclusions

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

Are GCMs able to reproduce Alpine relevant cut-off processes in a proper way concerning frequency, intensity, location and seasonality?

Can RCMs improve the behaviour of Alpine relevant cut-off lows?

If not, how can the GCMs be improved to do it in a better way and

How can hydrological modeller use the information about this important process for the interpretation of their results?

Big questions concerning climate change and cut-off

lows:

BOKU-MetHerbert Formayer

ESF-MedCLIVAR Workshop Trieste 13-15 October 2008

Thank you for your attention

We try to find some answers in the just started EC-Project:

ACQWA

http://www.unige.ch/climate/Projects/ACQWA.html