1. Seasonal Climate Discussion - Summer 2009 - Mike Blackburn, Andy Turner, Brian Hoskins with input from Nick Klingaman, Jane Strachan, Pier Luigi Vidale Met Office Seasonal Forecast Adam Scaife Reading, Grantham, IIS Bangalore discussion, 25 November 2009

2. Summary Global overview Tropics, with focus on Asia Indian Monsoon very weak Strong East Asian monsoon circulation? Consistent with warm west/central Pacific SSTs Tropical cyclone activity – (contrast active W + E Pacific with quiet Atlantic) Extra-tropics & global teleconnections Monsoon / Mediterranean link Northern Hemisphere extra-tropics – (circulation, impact on UK) Met Office seasonal forecast Hemispheric wave patterns: observational + modelling studies

3. Wind 150hPa (total)Geopotential Height 200hPa (anom) Surface wind (total) JJA 2009 OLR (anomaly) Global Summary

4. Wind 150hPa (anomaly)Geopotential Height 200hPa (anom) Surface wind (anomaly) JJA 2009 OLR (anomaly) Global Summary

5. Developing El Niño – SST anomalies Source: NOAA Climate Diagnostics Bulletin June July August

6. El Niño impacts (northern summer) NOAA: Climate Prediction Center & ESRL OLR anomaly (JJA 2009) Developing El Niño – impacts?

7. Transition to El Niño Source: NOAA Climate Diagnostics BulletinEquatorial anomalies averaged 5N – 5S

8. Tropics – intraseasonal variability June July August Source: NOAA Climate Diagnostics Bulletin June July August

9. Tropics – intraseasonal variability Source: NOAA Climate Diagnostics Bulletin x10 6 m 2 s -1 June July August = -2 D, V x10 6 m 2 s -1 = -2

10. Tropics – intraseasonal variability Source: NOAA Climate Diagnostics Bulletin m s -1 June July August June July August

11. Summary Global overview Tropics, with focus on Asia Indian Monsoon very weak Strong East Asian monsoon circulation? Consistent with warm west/central Pacific SSTs Tropical cyclone activity – (contrast active W + E Pacific with quiet Atlantic) Extra-tropics & global teleconnections Monsoon / Mediterranean link Northern Hemisphere extra-tropics – (circulation, impact on UK) Met Office seasonal forecast Hemispheric wave patterns: observational + modelling studies

12. Dynamical seasonal mean indices JUN Monthly-mean ERA-Interim data JUL AUG JJA Webster-Yang index U850-U200 40-110E, 5-20N Goswami - Meridional Hadley index V850-V200 70-110E, 10-30N Wang & Fan western index U850 south -U850 north All dynamical indices show considerable weakening in 2009 19892009

13. Asian Monsoon – daily dynamical indices Source: NCEP – CDAS data Webster-Yang Wang et al (East Asia) Goswami (meridional) Wang & Fan (western index)

14. Asian Monsoon – dynamical indices Wang & Fan dynamical monsoon indices

15. Indian Monsoon – precipitation (IMD)

16. Indian Monsoon – onset to August Daily OLR anomalies + MJO modal projection (Mat Wheeler, BMRC) MJO mode by filtering in the zonal wavenumber / frequency domain, Wheeler & Weickmann (2001) SymmetricAnti-symmetric

17. Indian Monsoon – mid-July to Sept. Daily OLR anomalies + MJO modal projection (Mat Wheeler, BMRC)

18. BMRC filtered OLR data shows clear evidence of eastward propagating MJO-type anomalies in the northern tropics (2.5N – 17.5N). JUN JUL AUG SEP OCT INDIA {

19. The Wheeler-Hendon multivariate MJO index Based on U850, U200, OLR data in near-real time. Near-equatorial. Little evidence for (equatorial) MJO at onset time or during August, unlike OLR index. Strong MJO activity during November (blue)

20. Northward propagations seen in daily OLR / precip Early onset MAY JUNE JULY AUG SEP OCT MAY JUN JUL AUG 70-90E average. Source: NOAA/ESRL OLR (anomaly) ?

21. North Indian Ocean Basin (No official bounds, most form May-Nov) Trop Storm CatLifetime BIJLI TS 15-17 Apr AILA 1 24-25 May # 3 TS 5-5 Sept First system start: 15 April 3 depressions; 2 tropical storms All three made landfall Aila caused over $40million damage, 330 fatalities (deadliest storm this year) Aila, 25 May, well-defined eye visible (NASA/TRMM) Tropical Cyclone activity

22. Summary Global overview Tropics, with focus on Asia Indian Monsoon very weak Strong East Asian monsoon circulation? Consistent with warm west/central Pacific SSTs Tropical cyclone activity – (contrast active W + E Pacific with quiet Atlantic) Extra-tropics & global teleconnections Monsoon / Mediterranean link Northern Hemisphere extra-tropics – (circulation, impact on UK) Met Office seasonal forecast Hemispheric wave patterns: observational + modelling studies

23. Indian Monsoon impact on Mediterranean? Rodwell & Hoskins (1996): monsoon influence on Mediterranean summer descent

24. Wind 150hPa (total)Geopotential Height 200hPa (anom) Surface wind (total) JJA 2009 OLR (anomaly) Global Summary

25. V 250 (total)Z 200 (anomaly) June July August 2009

26. Z250 Hovmöller, 45-60° latitude Variable June July August Mobile Persistent

27. June Dynamical Tropopause (weekly averages) July Aug. ~12 days

28. JJA09 Met Office Seasonal Forecasts from April / May Ensemble mean – April f/cAnalyses (NCEP/NCAR)Ensemble mean – May f/c Z500 Pmsl SST

29. JJA09 Met Office Seasonal Forecasts from April / May Ensemble mean – April f/cAnalyses (NCEP/NCAR)Ensemble mean – May f/c SST T2m Precip !model estimate!

30. Origin of the 2009 extra-tropical anomalies? Similarity of N.Hem wavetrain pattern in summer 2007/8/9 Is the observed pattern likely to recur? Is it related to a particular forcing? If so, what timescale? Hypotheses & evidence 1) Tropics – (a) ENSO; (b) Asian Monsoon 2) AMO – decadal variability of Atlantic SSTs (Sutton & Hodson, Knight et al) 3) Arctic sea-ice loss (Balmaseda et al, 2009) Idealised experiments for 2007 (Hoskins, Fonseca, Blackburn) Direct Rossby wave response to tropical heating Diagnosis of anomalous forcing – importance of eddy feedback Comparison with ECMWF relaxed seasonal hindcasts

31. 1b) Tropics: Asian Summer Monsoon Observational evidence of circum-global wavetrain associated with Asian/Indian monsoon (Ding & Wang, 2005) Idealised modelling, including transient eddy feedbacks (Lin, 2009) Observed Z200 composite differences

32. 1b) Tropics: Asian Summer Monsoon Observed correlation between 200hPa streamfunction and Arabian Sea precipitation (PI1) Lin (2009) Model heating and Z 200hPa response

33. Origin of the 2007/8/9 anomalies? Remains an open question: Possibility of quasi-resonance, triggered by a number of forcings Hypotheses & evidence: 1) Tropics – (a) ENSO; (b) Asian Monsoon 2) AMO – decadal variability of Atlantic SSTs 3) Arctic sea-ice loss Idealised experiments for 2007: Direct Rossby wave response to tropical heating Diagnosis of anomalous forcing – eddy feedback? Comparison with ECMWF relaxed seasonal hindcasts

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