On the Sensitivity of a Ground-Based Tropospheric Lidar to Aitken Mode Particles in the Upper Troposphere
, Juan Luis Guerrero-Rascado 2,3, Alexandre L. Correia 1, Diego A. Gouveia 4 and Henrique M. J. Barbosa 1,5,*
Round 1
Reviewer 1 Report
Thank you for your work in this important area of aerosol research using LiDAR instrumentation. Overall, I believe this is great work that can inspire ideas for additional research. I only have a few comments and suggestions, as follows:
- On Table 1, please clarify the meaning and difference in concentrations [cm-3] between the upper troposphere and the PBL. It seems that the N reference is not explicitly explained and it seems there's little difference between PBL and upper tropospheric values.
- On line 131, did you mean to use the word "diode" in there?
- On line 131, "even though the value found looks very small, the number of emitted photons are too high". I'd rephrase this statement. What is small? What is too high? We'd prefer to see values or percentage offsets from a nominal value.
- On Figure 1, I think a good number of researchers would prefer to see LiDAR returns with a range squared corrected view, so that we can see the variation of the actual observation we're making. In addition, error bars in the measurement would be great to see here. It seems that you've done so already on Figure 7.
- On Figure 3, while I understand the desire of the team to post this comparison, it would be useful to indicate errors bars or other related information because the signal values are just too small to make sense of it. Perhaps logarithmic scale?
- On line 249, please write 3,000 instead of 3000
- On line 254, can you express 0.0022 +- 0.0005 in percentage error instead?
- On line 312, can you explain how a spatial resolution of 375 m in the upper troposphere provides a scientifically significant contribution to assessing aerosols in that region?
- Are there plans to conduct intercomparisons with other in-situ instrumentation?
- Can you talk about the calibration of a LiDAR system required for this research?
- On lines 332-334, could you provide a link to the actual data you used in this publication rather than the generic sources. It may help other researchers better understand your approach since they won't have to figure out where the actual data is located.
Author Response
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Author Response.pdf
Reviewer 2 Report
The authors propose a paper discussing the sensitivity of a ground-based lidar for detecting ultrafine particles in the upper troposphere. Overall, the authors have made a good attempt to estimate lidar system parameters for measuring Aitken mode particles in the Amazon upper troposphere. This study is important for understanding the transportation of aerosols, which are cloud condensation nuclei, between the planetary boundary layer and the troposphere.
On the other hand, I think that explanations of simulation models obtained for the lidar measurements still have some problems, as indicated below. In my opinion, a substantial revision is needed to make this manuscript suitable for publication.
* Table 1
Sufficient details of Rg, sg, ℜ, and ℑ are not described in this manuscript, and the data sources of ℜ and ℑ have to be specified. Furthermore, it is not clear where the 10% and 90% quantiles are shown.
The authors explain that a number size distribution in UT is based on Figure 9 in Reference 25. The altitude range of UT in Table 1 is 9 to 15 km, but the maximum altitude in Fig. 9 is 5.8 km. The authors need to explain in detail how you assumed the number size distribution.
*Lines 133-134 and Fig.1
I think the lidar signal is dominant for Rayleigh scattering. If not, the authors need to show the altitude profile of the extinction coefficient αaer in Fig. 1 and clarify that the lidar signal containing aerosol has been reproduced.
* Lines141-142 and Fig.1
In the caption, the authors describe "30 s lidar signal profile", but you also describe "data was collected between 21:00 and 22:00". This is misleading that the observation time is one hour. Moreover, since the observation time per profile is not described in the text, you need to describe "30 seconds". In a discussion in Chapter 5, 30 s/profile and distance resolution 7.5 m are important factors.
The authors describe that the SN ratio in UT is 3. However, the number of photons at an altitude of 11 km or more is 10 or less, that is, the SN ratio is 3 or less. This sentence is not sufficient to explain the quality of the lidar signal.
* Lines 155-156.
"The aerosol number concentration in the PBL was "
-> "The aerosol number concentration in the PBL (N0, pbl) was"
* Lines 160-161.
"where n = 1 represent the aerosol number concentration of 1246 cm-3 at UT,"
-> "where n = 1 represent the aerosol number concentration (N0,ut) of 1246 cm-3 at UT,"
* Lines 183-185.
What do you mean by the "values" you use to evaluate bias in the Laer at UT? Also, please explain in detail why the bias can be evaluated using "above and below mean".
* Line 193-194 and Fig.2.
This manuscript does not give sufficient atmospheric parameters (especially aerosol) for calculation between the PBL and UT (from 2 km to 9 km), and above the UT (15km or more). Is there αaer model profile data used for this calculation? It may be almost the same as the figure in the case of k = 10000. It would be useful to include this information when discussing results in the various k and n.
* Lines 196-197.
What is the mean value of "noise larger than the mean value"? I don't understand the "mean value" and "noise" relationship. The authors need to describe the relations between these.
* Lines 224-245, and Figs. 5-7.
This manuscript investigates lidar system parameters to detect ultrafine particles in the Amazon UT layer. I don't think the discussion of the Linvaer uncertainty will contribute to the decision on lidar system parameters. The authors need to clarify their points and rethink the whole lidar parameter estimation approach.
* Lines 250-251.
The data sources of the SNR=55 and 180 have to be specified.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The manuscript has been revised well. I think this manuscript will be acceptable after some corrections have been done.
* Figs 6 to 8.
I understand that your purpose is to evaluate the impact of the wrong choice of the LR. It is reasonable that the underestimated or overestimated Laer_inv causes AOD bias.
Figs 7 and 8 show that the detection map does not almost depend on Laer_inv, and the detection frequency is achieved in 100% for large ν and/or large κ. However, In Fig. 6, the aerosol layer obtained by underestimated Laer_inv has expanded to a lower range than 9 km altitude. I don't agree that the expanded aerosol layer is included in 100 % detection.
If you want to evaluate whether you can accurately detect the thickness of the AOD and aerosol layer, I think you should reconsider dealing with the extended aerosol layer.
Author Response
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