Polarimetric Backscatter Sonde Observations of Southern Ocean Clouds and Aerosols
Round 1
Reviewer 1 Report
This study demonstrates a new way to obtain cloud and aerosol information in remote oceans, namely, polarimetric backscatter sonde measurements. The measurements are validated against ground-based cloud radar and lidar. In addition, backward trajectory analyses have been conducted to shed light on the origin of the observed aerosols. Overall, this study has a great potential to be important for the community because aerosol measurements, in particular their vertical profiles, are most needed, but have been lacking, in Southern Ocean.
However, there are two serious issues that must be addressed before I recommend it to be accepted. First of all, all the cited works are shown as "?" in the manuscript. So are the figure and table numbers. This makes the manuscript extremely difficult to read. Second, the description of the background knowledge is inadequate. Many important background knowledge lacks citation (e.g. Southern Ocean clouds are poorly modeled and cloud cover is underestimated). Those information are critical and must have citations. Also, one of the most important reasons why Southern Ocean clouds and aerosols are important is that aerosol cloud-mediated effect is non-linear (more sensitive in pristine conditions) and only in pristine environments can we stand a chance to accurately quantify the aerosol indirect radiative forcing (the Ken Carslaw's 2013 Nature paper). This point, however, is not even mentioned. Also, some recent important Southern Ocean field campaigns (i.e. MARCUS and SOCRATES) are not even mentioned, which makes the background introduction inadequate.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
The authors present what appear to be the first radiosonde-mounted measurements from their new Polarsonde instrument to be reported in the literature. The Polarsonde consists of a single-wavelength blinking LED source and detectors for linearly co- and cross-polarized returns. Returns are proportional to aerosol and hydrometeor loading, and degree of depolarization is dependent on contributions from non-spherical scatters, generally speaking. The manuscript describes three profiles obtained from launches at Macquarie Island, and seeks to attribute features to aerosol and cloud conditions, supported by the colocated radiosonde measurements, as well as radar, ceilometer and satellite data and backtrajectories from reanalyses. Carrying such an instrument on a radiosonde seems novel and useful. The manuscript is not overreaching and I recommend publication after minor revisions.
Major comment:
The manuscript frequently describes instrument response signatures in terms of depolarization, but then never shows us depolarization from the instrument. Prior to publication, I would require that the figures which currently show the co- and cross-polar signals independently also show calculated depolarization. The reader now has to infer by mentally trying to divide one line by another in every case.
Minor comments:
line 90: Can you please briefly explain intuitively why "for large plate-like crystals δ90 ≃ 0, similarly to spheres"? Does this assume a population of entirely randomly oriented plates?
line 133: It would be more precise to refer to 0°C as the melting level or specify the temperature.
line 231: What is the uncertainty in the radiosonde RH at –42°C?
Is it possible for the Polarsonde to become wet or rimed? If so, would that influence the instrument performance?
Figure 7-9: Panel b x-axis label appears to be incorrect. Please add units and indicate what each line color refers to (black versus green).
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
General comments
This paper describes very interesting experiment using polarimetric backscatter sonde. However, there is serious problems in the interpretation of the observed data. The authors attribute the large background seen in Fig. 3 to aerosol scattering, but it cannot be aerosol scattering. Firstly, the scattering is too strong for aerosols. (The authors should give rough estimates of the backscattering coefficient and compare with typical aerosol backscattering coefficient values.) Such background is not seen in the second and third launches after three and six hours later. Aerosol distribution cannot change that quickly in the far downwind region from the source areas. The cloud radar plot in Fig. 7 indicates cloud signal from 1000 to 5500m height, and it is natural to think the signal is from cloud. The data should be analyzed again, and the manuscript should be rewritten completely. Most of the descriptions on aerosols does not make sense.
Specific comments
The sensor optical system should be described in more details, including dimensions of the instrument, distance to the scattering volume, and optical elements or shade for restricting receiver FOV. Also, the direction of polarization should be illustrated clearly like that in Fig. 2 of Ref. 8, for both 90deg and 45 deg units. The “depolarization ratio” should be defined explicitly. It is not actually the depolarization ratio for the 45deg unit. The term “co-polarized” and “cross-polarized” is also confusing for the 45deg unit.
Figures: “Temp (degC)” should be removed from the footnote of Fig.7(b), Fig.8(b), and Fig.9(b). The label of Fig.9 (c) (time period) is wrong.
The unit for the ceilometer time-height indications must be written. The color scale is probably in logarithmic scale, and it can be seen that the contract between cloud and aerosol is very high.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
My comments have been well addressed. I am now fine with the current version.
Reviewer 3 Report
The revised version is greatly improved.
