Atmospheric Optical Turbulence Characteristics over the Ocean Relevant to Astronomy and Atmospheric Physics

Round 1

Reviewer 1 Report

The plot on the right hand side in Figure 2 shows the intensity of optical turbulence as measured by a micro-thermometer from a ship in the coastal area and in the open ocean.  Turbulence measurements of temperature or other characteristics are commonly affected by the flow modification due to the ship itself and of the ship’s wave-driven heave, pitch and roll motion.  Accumulation of salt aerosols on the platinum wires also distorts the temperature measurements. The authors may comment on all these influences on the data shown in  Figure 2.

Commonly astronomical observation from Earth are conducted from telescopes located at high elevation where the atmosphere is calm and the instruments can be stably oriented. The authors may comment on the interest in astronomical observations from the ocean, where the atmosphere contains aerosols and the observational platform is much more difficult to stabilize.  

The word “PROPAGATIAN”     appears in reference 17. 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The Review Comments for “Atmospheric Optical Turbulence Characteristics over the 2

Ocean Relevant to Astronomy and Atmospheric Physics” by Xu et al., 2021.

The manuscript analyzed oceanic intensity of optical turbulence in both offshore areas and open ocean. Authors paid particular attentions to atmospheric refractive index and drew conclusions including: alternating feature near the ocean area. They also identified large variation for near-land area compared to the open ocean. In addition, different temporal profiles for open-ocean turbulence were also depicted. The overall quality of this paper is great, and I found merits by supplementing this paper to the community. The English and organization of the paper need some improvements (detailed below). Therefore, this manuscript may be considered for formal publication with minor modifications after addressing the following issues:

Comments:

1. Figure 1 is shown before mentioning in texts. Please pay attentions to the texts and figures ordering.

2. Line 164-166. “The typical ‘Sombrero’ feature not appears since longer distance offshore. When the scientific research vessel is approaching land, the variation characteristics of C are consistent with the offshore area.” I am not sure if changing the wording from “sombrero” to “seesaw” would work better. Please consider.

3. For 2. Experiment and Methodology, it would be nice if you show the spatial location for two experiments conducted.

4. The presentation of Figure 2 can be improved by describing what are the x and y axis and label color bar with texts. The current form is not reader-friendly and a bit confusing.

5. Same as Figure 4.

6. Equation 5 for potential temperature is very basic, I don’t think listing it here is necessary

7. Same as Equation 7.

8. Line 275-276. “Atmospheric optical turbulence will have a serious impact on the laser beam propagating through the atmosphere and astronomical observation.” This is more like an introductory sentence instead of a summary sentence. To me, it is a bit inappropriate to place it in conclusion section.

9. This paper lacks basic description on how the equipment they used work. Any validations? Any calibrations?

10. Line 202-205 “According to the currently widely used HMNSP99 model, the relationship is investigated between temperature lapse rate and wind shear and turbulence strength profile. Figure 5 shows the C profiles of estimated and measured, as well as the profiles of temperature gradient, wind shear, outer scale, and potential refractive index gradient”. Giving some preliminary introductions to HMNSP99 model would be helpful.

11. Line 170-172. “In order to obtain the variation characteristics of refractive index structure constant profile, eight balloon-borne radiosondes were launched at different moments during the open ocean.” How did you ensure that all balloons ascend at the same speed? Did you measure it?

12. “The integrated parameters (Fried parameter 0 r , seeing  , and isoplanatic angle  , coherence time 0  ) derived from C profiles from offshore and open ocean are considered the main turbulence parameters for astronomy and optical telecommunication. The comparison of integrated parameters between model and radiosonde are shown in Figure 7.” A sentence like this shall come with references

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The authors investigated turbulence over different types of the earth`s surface. The manuscript is interesting enough, but it contains an essential important remark. At least I need sure that the results in the manuscript are valid. Please, pay attention on the result (3) in conclusions. You speak that “the mean r0 from radiosonde measurement at open ocean is lower than offshore” and optical turbulence is stronger in the open ocean than offshore. What are the reasons? The air flow deforms less in the open ocean (the wind speeds are higher) than offshore. So, vertical gradients of mean wind speed may be higher in the open ocean but the strength of turbulence will not increase due to the higher vertical gradients of mean wind speed (air flow may be more laminar although gradients increase). It seems to me that you have not shown this connection reliably, you are only using the method for evaluating optical turbulence, but the coefficients between turbulent and average characteristics should be different if you deal with different underlying surface.

The manuscript is interesting enough but I recommend formulate the results more carefully.

Minor

- Please also discuss and show the profiles of the outer scale of turbulence in the open ocean and offshore;

-I recommend to compare your results associated with the variations of turbulence strength in the open ocean and offshore with the Cn2 statistics estimated in paper (Authors show that the optical turbulence strength decreases when the air flow is directed from the lake to the coastal zone:

- Shikhovtsev, A.; Kovadlo, P.; Lukin, V.; Nosov, V.; Kiselev, A.; Kolobov, D.; Kopylov, E.; Shikhovtsev, M.; Avdeev, F. Statistics of the Optical Turbulence from the Micrometeorological Measurements at the Baykal Astrophysical Observatory Site. Atmosphere 2019, 10, 661. https://doi.org/10.3390/atmos10110661

- Also reccomend compare your results with paper Benjamin Wauer, Qing Wang, Oswaldo Alvarenga, Ryan Yamaguchi, John Kalogiros, Denny P. Alappattu, Galen Cauble Observations of optical turbulence in the marine atmospheric surface layer during CASPER-West. SPIE 2018.

- Figure 2. You should indicate units of Cn2. I may note that right figure shows overestimated values. This is my guess. please check the calculations and confirm it.

-In introduction you may mention the following studies:

- V P Lukin 2021 Phys.-Usp. 64 280

-A. Abahamid, A. Jabiri et al Optical turbulence modeling in the boundary layer and free atmosphere using instrumented meteorological balloons / Astronomy and Astrophysics, 2004.

- Daytime optical turbulence and wind speed distributions at the Baikal Astrophysical Observatory

L A Bolbasova, A Yu Shikhovtsev, E A Kopylov, A A Selin, V P Lukin, P G Kovadlo / Monthly Notices of the Royal Astronomical Society, Volume 482, Issue 2, January 2019, Pages 2619–2626, https://doi.org/10.1093/mnras/sty2706

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Your corrections are good.