simulating the extratropical response to the madden-julian oscillation

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