|I find it better now that analysis for each model is presented and that more studies are now discussed. However the figure panels should really have been made larger (also some in the supplementary), to make them more legible. Also, when presenting Multi Model Mean, statistical significance must be indicated – this is not yet done in all of the MMM plots. |
Figs. 7 and 8: It is not clear how the “MMM” correlation values are calculated. Are these the average for the seven model correlation values? But in Fig. 7 how can some of the MMM correlation values (e.g., the + sign for the West) be higher than any of the 7 models?
The models certainly show biases, and these should influence the conclusion of this study. That is, if some models show wrong teleconnection between ENSO SST and rainfall (e.g., in the western Pacific) then how can we trust these models in providing useful information as to support paleo proxy reconstructions? What this tells us is that we can only combine proxies and models in regions where teleconnection bias is low. Selecting the best models could also be considered as an avenue. These should be clarified in the conclusion.
Now that the authors have extended the historical period, the spectra in new Fig. 4 are very different from the previous version. Now all models show a peak at 8-yr period. This is a rather striking feature, demonstrating the need to have long time series to resolve low frequency variability particularly when comparing two different long record periods.
The writing can still be improved:
- It is currently still hard to get to the gist of the paper.
For instance, section 3 can be entirely removed. It contains a lot of information that should have been included in figure captions (“A Morlet mother wavelet (Torrence and Compo, 1998) with degree 6”). Some of it can be infused in the other sections, e.g., it would be more useful to say, “A wavelet analysis shows that the frequency and amplitude of Nino3.4 exhibit statistically significant changes….etc.”
- Some are repeated in other sections e.g., “could statistically have been drawn from the same population” is also stated in L281.
- Some statements are general knowledge, e.g., “Wavelet spectral estimates were tested against red noise, represented as a first order autoregressive process” which should rightfully be done; “Wavelet analysis is useful for examining non-stationary signal and provides time and frequency localisation” most readers would know that. Etc….
Also try to express things more concisely, e.g., one sentence in Line 81-85 is too long. Please revise the last section to ensure that things are expressed in a more straightforward manner and concisely.
The referencing with regards to ENSO behaviour response to greenhouse warming (in section 1) is not precise. The Power et al. 2013study is specifically about rainfall response to ENSO SSTs, not the dynamics of the SST changes which are likely to be more apparently relevant to the case of past climatic changes (e.g., Carre et al. 2014). The Power et al. (2013) study is also not about extreme ENSO (Line 43). It is the Cai et al. (2014) study that shows that the rainfall response is attributed to more frequent extreme El Nino. This rainfall response is due to the SST pattern associated with greenhouse warming, rather than changes to the behaviour of El Nino itself. There are actually projected changes in the behaviour of ENSO SST dynamics (not just rainfall), e.g., a study by Santoso et al. (2013, Nature), that links these changes (associated with extreme El Nino) to the projected weakening of the Pacific Ocean circulation. In a separate paper, Cai et al. (2015) found more frequent extreme La Nina (using Nino4 anomalies).
Statement in Line 121 “downloaded from the Project for Model Diagnosis and Intercomparison (PCMDI) through the Australian Earth System Grid (ESG) node.” can perhaps be moved to Acknowledgment.
“This study” in Line 147 should specifically refer to the Bellenger et al. (2013) study.
L192: a missing “we” after “in this study”?
Line 242: “relate” should be “related”
Line 286 “also likely result from external forcings and/or internal ocean-atmosphere dynamics” – how else can they arise from?
L380 – insert “to” between “is be”
L380-382 should simply read: “That is, considering changes only at a singular location does not provide complete information about temporal changes in a large-scale system like ENSO.”
L413 “from multiple…” what