As we know, the positive sea surface temperature anomalies during the moderate-to-weak El Nino locate in the central-to-eastern equatorial Pacific, so why do the rainfall anomalies during the moderate-to-weak El Nino locate in the north of the equator?
As shown in Fig. 1 of the attach article, during the developing phase of eastern Pacific (EP) El Nino, which is canonical and always strong, the anomalous rainfall is nearly located on the equator. However, during the developing phase of central Pacific (CP) El Nino, which is a new type and always weak in the amplitude, the anomalous rainfall in the eastern Pacific is almostlly located in the north of the equator. But I just don't know what makes the differences. Can anyone explain this?
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It is tempting to use the poetic description proposed on the NASA website and compare the variability of El Nino's rainfall with a "dance of the atmosphere and the ocean". Figures of this dance are quite complicated and they are not easily recognizable even after analyzing a long experimental record. The example of this variability is presented in the excellent compilation of observations (for the period from 1985 to 2008), which are available at:
https://earthobservatory.nasa.gov/Features/WorldOfChange/enso.php
The pattern is indeed complex. However, I believe that the chaotic behavior of the phenomenon can be easily understood after applying the simple theoretical model described by Garay and Indig in the work: "Chaos in Vallis' asymmetric Lorenz model for El Niño" (Chaos, Solitons & Fractals, vol. 75 June 2015, pp. 253-262). The text is available at:
https://www.sciencedirect.com/science/article/pii/S0960077915000594
The Valis model is very useful to capture the essence of the problem. The situation is similar in many ways to that encountered in meteorological models in the 1960s, when E. Lorenz demonstrated the chaotic nature of weather forecasting systems.
There are much more complicated models that indicate the role of orographic patterns in shaping the asymmetry of precipitation field. One of the best discussions is presented in the following two articles:
https://pdfs.semanticscholar.org/6dd2/6f83800ed3175dcd4ff25a41fe389c86537f.pdf
https://www.gfdl.noaa.gov/bibliography/related_files/knt0702.pdf
The question, how good is their predictive power, is still open.
I have extracted two quotes from the site dedicated to forecasting
http://www1.secam.ex.ac.uk/famous-forecasting-quotes.dhtml
this can justify the constant attempts to forecast despite the obvious limitations:
Quote from Poincare:
"It is far better to foresee even without certainty than not to foresee at all. "
--Henri Poincare in The Foundations of Science, page 129.
Quote from Bohr:
"Prediction is very difficult, especially if it's about the future."
--Nils Bohr, Nobel laureate in Physics
This quote serves as a warning of the importance of testing a forecasting model out-of-sample. It's often easy to find a model that fits the past data well--perhaps too well!--but quite another matter to find a model that correctly identifies those features of the past data which will be replicated in the future.
As commented by Kenneth M Towe and Janusz Pudykiewicz, it is true that the ENSO forecast skill is still not very good, probably due to the unpredictable essence of the natural variability (chaos) or the ineffective forecasting models. What the scientists try their best to do is to improve the understanding, the description and then the prediction of the ENSO phenomenon.
Thank Janusz Pudykiewicz for your answer to the asymmetry of mean Pacific precipitation field, which is useful to understand the anomalous precipitation patterns departured from the mean field. I just wonder if there is some explicit explanation on the anomalous precipitation patterns during the moderate-to-weak El Nino, i.e., the anomalous rainfall in the eastern Pacific is almostlly located in the north of the equator .
Em......Even one can predict the magnitutes of the ENSO events, however, their features can hardly be fully captured. See my small findings:Experiment Findings On the Surface Independent Signals Within the ENSO Events: C...
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