the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 29 Aug 2024
Solar cycle impacts on North Atlantic climate
Abstract. The North Atlantic sector has been identified as a region where the 11-year solar cycle has small but non-negligible impacts on near-surface climate. Nonetheless, debate persists about the robustness of such impacts and the mechanisms that explain them. The limited length of historical records, together with the complexity of separating the solar cycle influence from other forcings and from internal variability explain, at least partially, the discrepancies in published results. This work explores the signatures of the 11-yr solar cycle over the North Atlantic in 20th Century reanalysis datasets, which provide longer reconstructions of climate by assimilating only long-record surface observations. The signatures are compared with those detected in long reconstructed observational datasets, modern reanalysis and previous studies. The results confirm previous studies and reveal a robust lagged boreal winter response in mean sea level pressure north of the Azores, peaking 2–3 years after solar maxima. The response is however non-stationary, varying both within the season and on multi-decadal scales. An assessment of the impacts on sub-surface ocean temperatures using an ocean reanalysis dataset supports the hypothesis that thermal inertia of the ocean could explain the lag in the response and amplification of the response. A re-emergence of warm anomalies in the years following solar maxima is observed over the central North Atlantic and is consistent with the observed solar response in sea level pressure north of the Azores.
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Status: closed (peer review stopped)
- RC1: 'Comment on egusphere-2024-2487', Anonymous Referee #1, 20 Sep 2024
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RC2: 'Comment on egusphere-2024-2487', Anonymous Referee #2, 27 Sep 2024
The paper explores the effects of the 11-yr sunspot cycle on climate over the North Atlantic region. It uses a variety of data sets, analysed with standard methods, to address lead-lag relations between solar activity and responses in sea-level pressure and eventually in the Atlantic ocean. The topic itself is interesting and fits with the journal’s scope. However, although the paper is well written, I struggled to find much novelty in this paper. There are interesting avenues, as commented below, but they need more work. Therefore I recommend a major revision of the paper.Main commentTo address the sunspot cycle imprint in a diverse set of datasets has been done in many other studies. The methods used (especially MLR) are standard and their flaws are also well known and discussed in the lierature. Eventually, what the authors find mostly confirms what other people have already found. What I did find interesting, though, was the last part on the ocean heat re-emergence. However, it is not so easy to grasp the re-emergence process from the figure and separate it from other processes. I am not an oceanographer, but would like to see more evidence for this process and a cleaner separation from other processes such as advection, upwelling etc.Also, I liked that the authors use the CERA20C and ORA20C data sets for this purpose (complementing studies from other authors that use coupled simulations). CERA20C is an ensemble of 10 so-called “weakly coupled” assimilations of a coupled model system with an outer loop-coupling (with two iterations). ORA20C is an ocean reanalysis driven with ERA20C input with the main aim to generate initial conditions for the different streams of CERA20C. This implies some important differences between them in the way surface fluxes are calculated, which would have to be addressed, but using these semi-coupled data sets is an important asset. That said, I think the products should be better explained, especially the features that might be relevant here. For instance, the solar forcing in the products needs to be explained (20CRv3 and CERA20C both use a forcing that has the 11-yr solar cycle) and likewise the ozone forcing (20CRv3 and CERA20C both use the CMIP5 standard forcing, which has the 11-yr cycle). Both the top-down and the bottom-up forcing are already presrcibed in the reanalyses. There would be another ocean data set that would be interesting to study in this context, namely the Simple Ocean Data Assimilation with sparse input SODAsi, which in some ways is a bit similar to 20CRv3 as ORA20C is to ERA20C and CERA20C.Other commentsThe authors write that they use "a detrended TSI predictor (DTSI hereafter) using a band-pass Butterworth filter to retain periodicity between 7-15 years, as described in Misios et al. (2016)." But what is the source of the TSI data?Why do the authors use the AMO as a predictor? Since they are later focusing on ocean temperatures, this seems dangerous. At least, this should be tested and reported.Why using Dec-Feb? The monthly analysis shows that this gives the best response, but it should be discussed in the context of the literature.Citation: https://doi.org/
10.5194/egusphere-2024-2487-RC2 -
EC1: 'Editor comment on egusphere-2024-2487', Stephan Pfahl, 10 Oct 2024
Dear authors,
As you can see, both reviewers provide several constructive and important suggestions how to improve various aspects of your manuscript. However, both also state that there is not much novel material in your paper, which I consider a very critical point. I would only take a revised manuscript into consideration in which, in addition to addressing the specific points raised by the referees, you introduce additional original material and make much clearer what the novel aspects of your study are, also accounting for the critical discussion in the literature (see comments by referee #1) in a more explicit way. Alternatively, you may consider to withdraw your manuscript and submit a new version if the required revisions appear to be too comprehensive and result in a largely new paper. In any case, I’d invite you to provide final author comments addressing the concerns raised by the referees.
Best regards,
Stephan Pfahl
Citation: https://doi.org/10.5194/egusphere-2024-2487-EC1
Status: closed (peer review stopped)
- RC1: 'Comment on egusphere-2024-2487', Anonymous Referee #1, 20 Sep 2024
-
RC2: 'Comment on egusphere-2024-2487', Anonymous Referee #2, 27 Sep 2024
The paper explores the effects of the 11-yr sunspot cycle on climate over the North Atlantic region. It uses a variety of data sets, analysed with standard methods, to address lead-lag relations between solar activity and responses in sea-level pressure and eventually in the Atlantic ocean. The topic itself is interesting and fits with the journal’s scope. However, although the paper is well written, I struggled to find much novelty in this paper. There are interesting avenues, as commented below, but they need more work. Therefore I recommend a major revision of the paper.Main commentTo address the sunspot cycle imprint in a diverse set of datasets has been done in many other studies. The methods used (especially MLR) are standard and their flaws are also well known and discussed in the lierature. Eventually, what the authors find mostly confirms what other people have already found. What I did find interesting, though, was the last part on the ocean heat re-emergence. However, it is not so easy to grasp the re-emergence process from the figure and separate it from other processes. I am not an oceanographer, but would like to see more evidence for this process and a cleaner separation from other processes such as advection, upwelling etc.Also, I liked that the authors use the CERA20C and ORA20C data sets for this purpose (complementing studies from other authors that use coupled simulations). CERA20C is an ensemble of 10 so-called “weakly coupled” assimilations of a coupled model system with an outer loop-coupling (with two iterations). ORA20C is an ocean reanalysis driven with ERA20C input with the main aim to generate initial conditions for the different streams of CERA20C. This implies some important differences between them in the way surface fluxes are calculated, which would have to be addressed, but using these semi-coupled data sets is an important asset. That said, I think the products should be better explained, especially the features that might be relevant here. For instance, the solar forcing in the products needs to be explained (20CRv3 and CERA20C both use a forcing that has the 11-yr solar cycle) and likewise the ozone forcing (20CRv3 and CERA20C both use the CMIP5 standard forcing, which has the 11-yr cycle). Both the top-down and the bottom-up forcing are already presrcibed in the reanalyses. There would be another ocean data set that would be interesting to study in this context, namely the Simple Ocean Data Assimilation with sparse input SODAsi, which in some ways is a bit similar to 20CRv3 as ORA20C is to ERA20C and CERA20C.Other commentsThe authors write that they use "a detrended TSI predictor (DTSI hereafter) using a band-pass Butterworth filter to retain periodicity between 7-15 years, as described in Misios et al. (2016)." But what is the source of the TSI data?Why do the authors use the AMO as a predictor? Since they are later focusing on ocean temperatures, this seems dangerous. At least, this should be tested and reported.Why using Dec-Feb? The monthly analysis shows that this gives the best response, but it should be discussed in the context of the literature.Citation: https://doi.org/
10.5194/egusphere-2024-2487-RC2 -
EC1: 'Editor comment on egusphere-2024-2487', Stephan Pfahl, 10 Oct 2024
Dear authors,
As you can see, both reviewers provide several constructive and important suggestions how to improve various aspects of your manuscript. However, both also state that there is not much novel material in your paper, which I consider a very critical point. I would only take a revised manuscript into consideration in which, in addition to addressing the specific points raised by the referees, you introduce additional original material and make much clearer what the novel aspects of your study are, also accounting for the critical discussion in the literature (see comments by referee #1) in a more explicit way. Alternatively, you may consider to withdraw your manuscript and submit a new version if the required revisions appear to be too comprehensive and result in a largely new paper. In any case, I’d invite you to provide final author comments addressing the concerns raised by the referees.
Best regards,
Stephan Pfahl
Citation: https://doi.org/10.5194/egusphere-2024-2487-EC1
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