EGU General Assembly 2020
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the Creative Commons Attribution 4.0 License.

Response of South and East Asian summer climate to North Atlantic SST anomalies: sensitivity to SST patterns

Satyaban Bishoyi Ratna1, Timothy Osborn1, Manoj Joshi1, and Juerg Luterbacher2,3
Satyaban Bishoyi Ratna et al.
  • 1Climatic Research Unit, School of Environmental Sciences, University of East Anglia, Norwich, United Kingdom (
  • 2Department of Geography and Centre of International Development and Environmental Research, Justus Liebig University of Giessen, Giessen, Germany
  • 3World Meteorological Organization (WMO), Department for Science and Innovation, 7bis Avenue de la Paix, 1211 Geneva, Switzerland

We simulate the response of Asian summer climate to AMO-like (Atlantic Multidecadal Oscillation) sea surface temperature (SST) anomalies using the Intermediate General Circulation Model version 4 (IGCM4). Separate AMO SST patterns are obtained from seven Coupled Model Intercomparison Project phase 5 (CMIP5)/Paleoclimate Model Intercomparison Project phase 3 (PMIP3) global climate models, to explore the sensitivity of the atmospheric response to the SST pattern. Experiments are performed with seven individual and composited AMO SST anomalies globally, and over the North Atlantic Ocean only, for both the positive and negative phases of the AMO. During the positive AMO phase, a Rossby wave train propagates eastward, causing a high pressure anomaly over eastern China/Japan region, associated with a low level anomalous anticyclonic circulation along with warm and dry anomalies. In contrast, the mid-latitude Rossby wave train is less robust in response to the cold phase of the AMO. The circulation response and the associated temperature and precipitation anomalies are sensitive to the AMO SST anomaly patterns. The comparison between global SST and N Atlantic SST experiments indicates that midlatitude East Asian climate anomalies are forced from the North Atlantic region. However, global SST anomaly experiments show that the SST anomalies outside the North Atlantic region, but still associated with AMO, strongly influence South Asian climate as they either strengthen or reduce the precipitation. Experiments with different amplitudes of negative and positive AMO anomalies test the linearity of the response. Over a large region of South and East Asia, temperature has a linear response to the amplitude of North Atlantic SST anomaly associated with both positive and negative AMO conditions, but the precipitation response is nonlinear.

How to cite: Bishoyi Ratna, S., Osborn, T., Joshi, M., and Luterbacher, J.: Response of South and East Asian summer climate to North Atlantic SST anomalies: sensitivity to SST patterns, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2414,, 2020

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Display material version 2 – uploaded on 29 Apr 2020
This is the updated short presentation with some results included in detail for clear understanding.
  • CC1: Comment on EGU2020-2414, Linda van Garderen, 05 May 2020

    Thank you very much for this very interesting presentation.

    I have a question concerning you results plots with the 850hPa wind and precipitation per model. Were these graphs based on averaging over the AMO- and AMO+ days  or are they are results of clustering? Would you be able to elaborate a bit on how you selected the days/timesteps you used for these plots?

    This topic would lend itself very wel for using causal effect networks (Jakob Runger, Marlene Kretschmer) to quantify the effect of te AMO on the temperature in Asia. Is perhaps such a study in the planning?

    Thank you again.



    • AC1: Reply to CC1, Satyaban Bishoyi Ratna, 07 May 2020

      Thanks for your comments on this presentation.

      We have identified the response of 850hPa wind and precipitation anomaly using sets of idealized model experiment with IGCM4. In a perturbed experiment we forced the model with the AMO+ like SST anomaly and compared with a Control experiment to identify the wind and precipitation response over Asia. We have averaged the 850hPa wind and precipitation for each MJJAS mean in the modelling experiment. The difference between the perturbed and control experiment is the response due to the AMO+ phase. Similarly separate modelling experiments were also conducted with AMO- like SST anomaly to study the response due to AMO- phase.

      I am not sure, if the causal effect networks will be useful for the kind of idealized modelling experiments used here. However, we will think more about it.

      Thanks for your interest on our work . Please ask us again if something is not clear.

      Satyaban B. Ratna

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