Seasonal Climate Discussion - Summer 2009 -

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

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

Wind 150hPa (total) Geopotential Height 200hPa (anom)

Surface wind (total)

JJA 2009

OLR (anomaly)

Global Summary

Wind 150hPa (anomaly) Geopotential Height 200hPa (anom)

Surface wind (anomaly)

JJA 2009

OLR (anomaly)

Global Summary

Developing El Niño – SST anomalies

Source: NOAA Climate Diagnostics Bulletin

June

July

August

El Niño impacts (northern summer)

NOAA: Climate Prediction Center & ESRL

OLR anomaly (JJA 2009)

Developing El Niño – impacts?

Transition to El Niño

Source: NOAA Climate Diagnostics Bulletin Equatorial anomalies averaged 5N – 5S

Tropics – intraseasonal variability

June

July

August

Source: NOAA Climate Diagnostics Bulletin

June

July

August

Tropics – intraseasonal variability

Source: NOAA Climate Diagnostics Bulletin

x106 m2s-1

June

July

August

= -2D , Vx106 m2s-1

= -2

Tropics – intraseasonal variability

Source: NOAA Climate Diagnostics Bulletin

m s-1 m s-1

June

July

August

June

July

August

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

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

Asian Monsoon – daily dynamical indices

Source: NCEP – CDAS data

Webster-Yang

Wang et al (East Asia)

Goswami (meridional)

Wang & Fan (western index)

Asian Monsoon – dynamical indices

Wang & Fan dynamical monsoon indices

Indian Monsoon – precipitation (IMD)

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

Indian Monsoon – mid-July to Sept.

Daily OLR anomalies + ‘MJO’ modal projection (Mat Wheeler, BMRC)

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{

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)

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)

?

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

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

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

Wind 150hPa (total) Geopotential Height 200hPa (anom)

Surface wind (total)

JJA 2009

OLR (anomaly)

Global Summary

V 250 (total) Z 200 (anomaly)

June

July

August

2009

Z250 Hovmöller, 45-60° latitude

VariableJu

neJu

lyA

ugus

t

Mobile

Persistent

June

Dynamical Tropopause (weekly averages)

July

Aug.

~12 days

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

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!

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

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

1b) Tropics: Asian Summer Monsoon

Observed correlation between 200hPa streamfunction and Arabian Sea precipitation (PI1)

Lin (2009)Model heating and Z 200hPa response

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

- End -