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August-September 2012 Slides for Met Office Seasonal Forecast Discussion 20 September 2012 Mike Blackburn National Centre for Atmospheric Science, University.

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Presentation on theme: "August-September 2012 Slides for Met Office Seasonal Forecast Discussion 20 September 2012 Mike Blackburn National Centre for Atmospheric Science, University."— Presentation transcript:

1 August-September 2012 Slides for Met Office Seasonal Forecast Discussion 20 September 2012 Mike Blackburn National Centre for Atmospheric Science, University of Reading Met Office Seasonal Forecast Discussion, 20 September 2012

2 Recent circulation Circulation change at beginning of September (N.Hem, inc. Arctic) Atlantic jet moved north – dry here, but not the forecast blocking signal? Moderate MJO activity but strong S. American descent anomaly in September (expected lack of OLR signal for descent) c.f. Autumn possible origin of N. Atlantic wavetrain Met Office Seasonal Forecast Discussion, 20 September 2012

3 Asian monsoon 2012 IITM, Monsoon Online All India rainfall Indian monsoon recovery since mid-August

4 Asian monsoon NOAA ESRL + SOEST, Hawaii Streamfn, σ=0.210 JJA Weak monsoon anticyclone in recent summers Impact of La Niña bias?

5 MJO propagation - moderate amplitude continues CAWCR & CPC Last 90 days ECMWF forecast

6 Tropical convection – recent S. American descent NOAA ESRL & CPC

7 1-15 September August 2012 Descent over S. America + Caribbean NOAA ESRL (NCEP/NCAR Reanalysis) Velocity potential anomaly, σ=0.210

8 NH circulation change, Aug-Sept NOAA CPC & ESRL Aug July Z250, 45°-60°N Sept Streamfn. σ= Aug Streamfn. σ= Sept

9 NH circulation change, Aug-Sept NOAA CPC & ESRL Aug July Z250, 45°-60°N Sept Streamfn. σ= Aug Streamfn. σ= Sept

10 Jun-Aug Northern hemisphere jet stream 250hPa NOAA ESRL Climatology: SeptOct-Nov Jun to Aug: ClimatologyOct to Nov: ClimatologySep: Climatology

11 Jun-Aug Northern hemisphere jet stream 250hPa NOAA ESRL SeptOct-Nov Southward shift Northward shift

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