Indian summer monsoon and ENSO (Wu and Kirtman 2003, 2004) Daehyun Kim, Yoo-geun Ham Climate Dynamics Laboratory 2005. 3. 30
Method in these papers - Composite • Wu and Kirtman 2003 • In reality, ENSO and the monsoon are integral parts of the coupled system and interact with each other • The monsoon anomalies include both ENSO-related and –unrelated variations. Similarly, the Pacific SST anomalies likely have monsoon signals. • This leads to difficulty in separating the wind anomalies induced by either ENSO or monsoon alone. • Because of the tendency for a warm(cold) event to concur with a dry(wet) monsoon (Meehl 1987; Webster and Yang 1992), the obtained anomalous circulation features display a high degree of similarity for these two types of composite. • Thus the composites cannot separate the anomalies induced by the monsoon from those induced by ENSO.
AGCM AGCM Atmosphere Ocean OGCM Monsoon and ENSO – Signal or Noise? CGCM (Interactive ensemble) Real world CGCM AGCM OGCM Continuous, totally coupled Discontinuous, coupled with few variables • What we want to see? • How can we interpret the result of model?
Statistical appearance of monsoon-ENSO relationship Observation • It is hard to analyze with OBS data because the period is short • (for the many essential variables) • In the model result, we can see that there is similar appearance of monsoon – ENSO relationship CGCM
zonal advection mean upwelling How the monsoon affect to ENSO? In the weak monsoon period anomalous depression low level divergence wind forcing to Ocean Sea surface Oceanic Kelvin wave propagation ThermoclineDepth Indian Ocean Maritime continent Pacific Ocean
The effect of monsoon on ENSO – 1. to warm phase (model) SSTA Heat contents Wind Warm-normal(SSTA) Warm-dry minus Warm-normal Warm-wet minus Warm-normal
The effect of monsoon on ENSO – 2. to cold phase (model) SSTA Heat contents Wind Cold-normal(SSTA) Cold-dry minus Cold-normal Cold-wet minus Cold-normal
The effect of monsoon on ENSO – 3. to normal phase Heat contents Wind SSTA Normal -Dry • Even in the normal years, the monsoon effect is similar with in the warm and cold years Normal -Wet
The effect of monsoon on ENSO – 4. observation normal dry-normal wet-normal Warm • the amplitude is small • but same sign with model Cold
Statistical appearance of monsoon-ENSO relationship 2 ENSO transition Monsoon transition
Composite anomalies Warm Dry Cold Wet Warm Dry Cold Wet Wet Cold Warm Dry
Divergence Moisture divergence caused by anomalous Walker circulation Wet Cold Dry
Conclusion • Indian monsoon can affect to the ENSO evolution • a strong or weak monsoon has significant effects on an ongoing warm event through surface zonal wind-stress anomalies in the equatorial western central Pacific • ENSO can affect to the Indian monsoon transition • through modulating tropical east-west circulation over the tropical Indian and Pacific Oceans • -> low-level anomalous moisture convergence : precondition of following monsoon
Indian monsoon and ENSO relationship • AnomalousSurface • Easterly • Air-seaInteraction Cold Central Pacific Strong monsoon • Modulation • of Walker • Circulation • Enhanced • Moisture • Convergence • Reduced • Moisture • Convergence • Modulation • of Walker • Circulation Warm Central Pacific Weak monsoon • Anomalous • Surface • Westerly • Air-seaInteraction Thank you!