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Simulating the extratropical response to the Madden-Julian Oscillation
Hai Lin
RPN-A, Environment Canada
International S2S Conference, College Park
February 10-13, 2014
Introduction
o MJO
o Global impact (boreal winter):
NAO (Lin et al 2009); PNA (Mori and Watanabe 2008)
AO (L’Heureux and Higgins 2008)
Canadian temperature (Lin and Brunet 2010)
Canadian precipitation (Lin et al 2010)
• Atmospheric response to MJO forcing:
Matthews et al. (2004)
Lin et al. (2010)
Seo and Son (2012)
Outlines
o Introduction
o Numerical experiments: Dependence on heating location
Nonlinearity
Dependence on initial condition
o Summary
Correlation when PC2 leads PC1 by 2 pentads: 0.66
Lin et al. (2010)
Normalized Z500 regression to PC2
Lin et al. (2010)
Model and experiment
• Primitive equation AGCM (Hall 2000) – similar configuration of model forcing as the Marshall-Molteni model, but not Q-G.
• T31, 10 levels
• Time-independent forcing to maintain the winter climate
• Linear integration, winter basic state
Thermal forcing
Exp1 forcing Exp2 forcing
Lin et al. (2010)
Z500 response
Exp1
Exp2
Lin et al. (2010)
• Linear integration, winter basic state
• with a single center heating source
• Heating at different longitudes along the equator from 60E to 150W at a 10 degree interval, 16 experiments
• Z500 response at day 10
Why the response to a dipole heating is the strongest ?
Day 10 Z500 linear response
80E
110E
150E
Similar pattern for heating 60-100E
Similar pattern for heating 120-150W
• Are the responses to opposite signs of MJO forcing mirror images? (nonlinearity)
• Which response is less sensitive to initial condition and background flow? with less spread?
• How does the response depend on extratropical jet initial condition?
Questions:
• 3 sets of experiments:
1) Control
2) +MJO forcing
3) –MJO forcing
• From 360 different initial conditions
• 30-day nonlinear integrations
Nonlinearity
Thermal forcing
Exp1 forcing Exp2 forcing
Lin et al. (2010)
+MJO thermal forcing
NonlinearityZ500 response
spread
+MJO response has less spread, less sensitive to initial condition
EOF
Downstream shift Intensify
of 360 Z500 day 6-10 responses to the same +MJO
Dependence on initial condition U200
Jet intensifies
Jet moves southward
Summary
• There is significant nonlinearity in response in mean response and spread
• Response to –MJO is more sensitive to initial condition (when the heating is over central Pacific)
• Response sensitive to the strength and position of East Asian jet
• Implication to subseasonal forecasting: MJO phase and jet initial condition