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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
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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
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Wind 150hPa (total) Geopotential Height 200hPa (anom)
Surface wind (total)
JJA 2009
OLR (anomaly)
Global Summary
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Wind 150hPa (anomaly) Geopotential Height 200hPa (anom)
Surface wind (anomaly)
JJA 2009
OLR (anomaly)
Global Summary
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Developing El Niño – SST anomalies
Source: NOAA Climate Diagnostics Bulletin
June
July
August
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El Niño impacts (northern summer)
NOAA: Climate Prediction Center & ESRL
OLR anomaly (JJA 2009)
Developing El Niño – impacts?
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Transition to El Niño
Source: NOAA Climate Diagnostics Bulletin Equatorial anomalies averaged 5N – 5S
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Tropics – intraseasonal variability
June
July
August
Source: NOAA Climate Diagnostics Bulletin
June
July
August
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Tropics – intraseasonal variability
Source: NOAA Climate Diagnostics Bulletin
x106 m2s-1
June
July
August
= -2D , Vx106 m2s-1
= -2
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Tropics – intraseasonal variability
Source: NOAA Climate Diagnostics Bulletin
m s-1 m s-1
June
July
August
June
July
August
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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
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Dynamical seasonal mean indices
JUN
Monthly-mean ERA-Interim data
JUL
AUG
JJAWebster-Yang indexU850’-U200’40-110E, 5-20N
Goswami - Meridional Hadley index V850’-V200’70-110E, 10-30N
Wang & Fan western indexU850south-U850north
All dynamical indices show considerable weakening in 2009
1989 2009
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Asian Monsoon – daily dynamical indices
Source: NCEP – CDAS data
Webster-Yang
Wang et al (East Asia)
Goswami (meridional)
Wang & Fan (western index)
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Asian Monsoon – dynamical indices
Wang & Fan dynamical monsoon indices
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Indian Monsoon – precipitation (IMD)
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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)
Symmetric Anti-symmetric
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Indian Monsoon – mid-July to Sept.
Daily OLR anomalies + ‘MJO’ modal projection (Mat Wheeler, BMRC)
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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
IND
IA{
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The Wheeler-Hendon multivariate MJO indexBased 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)
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Northward propagations seen in daily OLR / precipEarly onset
MAY
JUNE
JULY
AUG
SEP
OCT
MAY
JUN
JUL
AUG
70-90E average. Source: NOAA/ESRL
OLR (anomaly)
?
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North Indian Ocean Basin (No official bounds, most form May-Nov)
Trop Storm Cat Lifetime
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
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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
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Indian Monsoon impact on Mediterranean?Rodwell & Hoskins (1996): monsoon influence on Mediterranean summer descent
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Wind 150hPa (total) Geopotential Height 200hPa (anom)
Surface wind (total)
JJA 2009
OLR (anomaly)
Global Summary
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V 250 (total) Z 200 (anomaly)
June
July
August
2009
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Z250 Hovmöller, 45-60° latitude
VariableJu
neJu
lyA
ugus
t
Mobile
Persistent
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June
Dynamical Tropopause (weekly averages)
July
Aug.
~12 days
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JJA09 Met Office Seasonal Forecasts from April / May
Ensemble mean – April f/c Analyses (NCEP/NCAR)Ensemble mean – May f/c
Z50
0P
msl
SS
T
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JJA09 Met Office Seasonal Forecasts from April / May
Ensemble mean – April f/c Analyses (NCEP/NCAR)Ensemble mean – May f/c
SS
TT
2mP
reci
p
!model estimate!
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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
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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
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1b) Tropics: Asian Summer Monsoon
Observed correlation between 200hPa streamfunction and Arabian Sea precipitation (PI1)
Lin (2009)Model heating and Z 200hPa response
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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