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
Mar 28, 2015
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
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 2000 - possible origin of N. Atlantic wavetrain
Met Office Seasonal Forecast Discussion, 20 September 2012
Asian monsoon 2012
IITM, Monsoon Online
All India rainfall
• Indian monsoon recovery since mid-August
Asian monsoon 2007-2012
NOAA ESRL + SOEST, Hawaii
Streamfn, σ=0.210 JJA 2007-2012
• Weak monsoon anticyclone in recent summers
• Impact of La Niña bias?
MJO propagation - moderate amplitude continues
CAWCR & CPC
Last 90 days ECMWF forecast
Tropical convection – recent S. American descent
NOAA ESRL & CPC
1-15 September 2012
16-31 August 2012
Descent over S. America + Caribbean
NOAA ESRL (NCEP/NCAR Reanalysis)
Velocity potential anomaly, σ=0.210
NH circulation change, Aug-Sept
NOAA CPC & ESRL
Aug
July
Z250, 45°-60°N
Sep
t
Streamfn. σ=0.210 16-31 Aug
Streamfn. σ=0.210 1-15 Sept
NH circulation change, Aug-Sept
NOAA CPC & ESRL
Aug
July
Z250, 45°-60°N
Sep
t
Streamfn. σ=0.210 16-31 Aug
Streamfn. σ=0.210 1-15 Sept
Jun-Aug
Northern hemisphere jet stream 250hPa
NOAA ESRL
Climatology: 1981-2010
Sept Oct-Nov
Jun to Aug: Climatology Oct to Nov: ClimatologySep: Climatology
Jun-Aug
Northern hemisphere jet stream 250hPa
NOAA ESRL
2007-2011
Sept Oct-Nov
2007-2012 2007-2011
Southward shift Northward shiftNorthward shift
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