On the Annual and Semi-Annual Components of Variations in Extent of Arctic and Antarctic Sea-Ice

Round 1

Reviewer 1 Report

Dear Editor,

I believe that the work by Lopes et al. is sufficiently interesting for publication. The authors study the relations among the harmonics found in records of sea ice extent by comparing the Arctic and Antarctic regions. They found that the annual cycles are negatively correlated (which is obvious), but the semi-annual cycles present an interesting relation which is in quadrature and there is a phase shift. Other harmonics referring to the LOD and the polar position are analyzed as well. 

I have only a few suggestions

1) many figures use a light grey color which is hardly seen. I suggest using two colors such as red and blue that can be easily differentiated.

2) The abstract may be rewritten and reduced. The authors should try to summarize their findings better.

3) the adoption of the SSA analysis is fine, however, it is very likely that just using a simple Fourier bandpass filter around the frequencies of interest may be good as well.

4) Figure 10 and its relation with the analysis carried out earlier should be better explained

Author Response

Please find our answers to the reviewers in the uploaded pdf file. 

Author Response File: Author Response.pdf

Reviewer 2 Report

There are some suggestions for authors to consider in the discussion.

 

The difference between Antarctic and Arctic ice, among other factors, is due to the fact that the Arctic ice is mostly in the Ocean (the height can vary between 2 to 5 meters), while the Antarctic ice is on the continent (the average height is 2.5 km). This factor has not been addressed by the authors. Additionally, the authors have not discussed internal factors, such as temperature variability. I suggest that the authors discuss this factor since climatic variations are due to factors internal and external to the ocean-atmosphere system. There are satellite data covering the same period as that analyzed Arctic and Antarctic ice (https://www.nsstc.uah.edu/data/msu/v6.0/)

 

Discussion of ice periodicities has focused on annual periodicity and its harmonics (The annual periodicity, is a gravitational periodicity, i.e., the Earth's orbital period. In fact, the Earth orbital period is the most important component, at annual scale, in the analytical expansion of the Sun's position around the Solar System barycenter). But, after four decades of recording, there are multi-annual periodicities in the Arctic and Antarctic ice variations. For example, in the Arctic and Antarctic ice time series there are quasi-five-yearly and decadal periodicities. The quasi-five-year periodicity has been recorded for both external and internal factors of the ocean-atmosphere system (for a broad discussion on this periodicity, the authors can consult the following reference and citations: https://doi.org/10.1016/j. asr.2021.03.023). These multiannual periodicities can be clearly seen in the envelope of the two time series of the analyzed ice.

Author Response

Please find our answers to the reviewers in the uploaded pdf file. 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear editor

I think that the authors have edited the paper as suggested.