|My sincere gratitude to Clark, Marsh and Harle for addressing comments from the other reviewer and myself. I appreciate the effort that has gone in to improve the manuscript and consider in greater detail in considering the forcing mechanisms, but I still consider some of my comments have been insufficiently addressed. Furthermore, while reviewing this MS a second time, I still consider the following comments outstanding. |
1) GODAS Description
In my opinion, it is incorrect to call GODAS an “observational dataset” (section title, line 116). It is an ocean reanalysis product, and should be termed as such. Apologies for not noticing in the initial submission. My not noticing in the initial submission led me to make some comments which were not necessary. However, I believe it’s critical to acknowledge ocean reanalysis correctly. Line 111-112 needs revision to reflect that they are using “an ocean reanalysis product and an eddy-resolving global ocean model hindcast”.
At the start of this description, the authors refer to “measurements of…” This is not strictly true, as the measurements have been assimilated into a numerical model (the GFDL Modular Ocean Model). Therefore the output of the reanalysis is not a measurement. I suggest replacing with “values of …” when referring to the GODAS outputs (sentence line 118-119). On line 119-121, the correct verb in this sentence should be “assimilates”. Line 126-127: GODAS does not interpolate, it is a reanalysis product, using a data assimilation scheme (according to the documentation a 3DVAR one), it is not an interpolation scheme.
On lines 183-184, the authors refer to GODAS “altimetry data”. This is not strictly correct, while GODAS assimilates the satellite altimetry data after 2007, this is not altimetry data. Even after 2007, the GODAS SSH field will be a numerical solution that balances all input data in the data assimilation scheme. The GODAS product refers to a “sea surface height relative to the geoid”, and the description should refer to this.
Finally, further suggested changes relating to this comment are: line 186-187, line 384-386, line 423; where the authors refer to “observational data”. On line 409, the authors use “observations” to mean “results”. I suggest replacing; “observations” as it is a loaded word in our subject area (I hope my comments above sufficiently illustrate), particularly where comparisons with numerical model outputs are made.
2) NCEP wind fields.
The authors have now also applied a new data source, wind fields from NCEP. It is unclear whether they use this to refer to wind fields which may be included as part of the GODAS data distribution, or whether they have sourced this elsewhere. Suitable reference/acknowledgement to the underlying data and its provider should be made, as well as a short description (a meteorological reanalysis, or an observational dataset?).
3) Lines 146-167 / Transport calculation
The authors have much improved this section, however, I still found it implicit as to how they have calculated the total transport. Based on the description and equations (1) and (2), it is implied that the total eastward volume transport is the integral in equation (2) through the section from the eastward velocities from the GODAS reanalysis product, and the geostrophic eastward volume transport is based on thermal wind. It was my own error in not realising the reanalysis product is a model which also provides the absolute velocities, and therefore my comments in the initial review referring to no mention of the geostrophic referencing were due to not realising this.
4) The choice of sections for calculation of transports
The choices of sections are at times difficult to interpret based in knowledge from the circulation of the region. At 30 W, the authors define transports between 45 N and 60 N, over 0 to 1000 m. This will include some of the recirculating branches in the sub-polar North Atlantic, and will include some transport which does not contribute to the ECS. Based on the histograms in Figures 12 & 13, 55 N as the northern boundary would have been a more considered choice in terms of how circulation at 30W feeds the ECS transport.
It is also not clear to me why the authors decided to define the slope current transport as solely the northward transport component. In my opinion, it make it less meaningful to compare to established calculations of slope current transport in the published literature (Porter, Hopkins, Huthnance and others).
5) Other minor comments
Lines 196-237. The description of particle tracking is much improved. However, it would still be helpful to have a range of the number of particles released in each experiment.
Lines 248-249: I am presuming TEOS10, but this choice of words leaves that open for interpretation. I suggest omitting “… using the equation of state of seawater” and referring back to the methodology “(Section 2.2)”
Line 67-69: Grammatically not correct use of “to effect” as a verb. I would suggest using “to affect” or make the sentence “The NAO has also been shown to effect surface temperature change along the eastern boundary: …”
Line 175: "subpolar range" - typo
Figure 1. Previous comments relating to this figure have not been adequately addressed. The image quality in the PDF file was still poor. I would suggest improving the scaling of the quiver to make arrows more obvious. There is no indication on months used for summer/winter. The caption states “relative velocity” but not what to; the text states the figure shows “quiver plots of velocity”.
Figure 8. Caption states that transects are both ~100 km (first sentence) and 50 km (second sentence) long. Please clarify.