A54C-07
Linking Quasi- Resonant Amplification of Planetary Waves to Weather Extremes in Northern and Southern Hemisphere.

Friday, 18 December 2015: 17:30
3004 (Moscone West)
Kai Kornhuber1,2, Dim Coumou1, Vladimir Petoukhov1, Stefan Petri1, David J Karoly3 and Stefan Rahmstorf1,2, (1)Potsdam Institute for Climate Impact Research, Potsdam, Germany, (2)University of Potsdam, Potsdam, Germany, (3)School of Earth Sciences and ARC Centre of Excellence for Climate System Science, University of Melbourne, Melbourne, Australia
Abstract:
Several recent Northern Hemisphere (NH) summer heat extremes have been linked to persistent high-amplitude planetary wave patterns (e.g. heat waves in Europe 2003, Russia 2010 and in the US 2011, Floods in Pakistan 2010 and Europe 2013) with large-scale circulation patterns characterized by persistent longitudinal planetary-scale high-amplitude waves of relative high wavenumber (6-8).

Based on atmospheric wave dynamics, Petoukhov et al. (2013) proposed a so called quasi-resonant amplification (QRA) mechanism that, in case certain conditions in the NH circulation are fulfilled, can lead to such situations.

Key requirements for the amplification of a slow moving (quasi stationary) synoptic wave of wavenumber 6 – 8 are i.) the formation of a waveguide to prevent meridional dissipation of their energy and ii.)a reasonable strong thermal and orographic forcing for the respective wavenumber.

By casting these conditions into a script, we implemented an automated detection scheme to scan reanalysis data for QRA events. By employing this more objective approach, we were able to analyze duration and occurrence of QRA, investigate its role during summer extremes and put prior results to the test.

In accordance with earlier studies we identify a rise of long lasting QRA events over the last decade, primarily attributed to an increase of wave 7 QRA episodes many of them coinciding with extreme weather in the mid-latitudes. During those periods a double jet flow regime is identified as the prevalent circulation pattern.

Detected events include the summers of the record breaking heat extremes of 2003 and 2010. We employ these examples as case studies to explain evolution and effect of the QRA mechanism in detail.

In a complementary study we adapted the detection scheme to the Southern Hemisphere (SH) to investigate if the mechanism is a general feature of mid-latitude circulation or whether specific conditions are needed which might only be fulfilled in the NH.

We present preliminary results showing that the QRA conditions were met during some record-breaking Australian heatwaves.

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