Upload
luis-atkinson
View
218
Download
0
Tags:
Embed Size (px)
Citation preview
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 -