the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 Aug 2021
Investigation of a Saharan dust plume in Western Europe by remote sensing and transport modelling
Abstract. The evolution and the properties of a Saharan dust plume were studied near the city of Karlsruhe in south-west Germany (8.4298° E, 49.0953° N) from April 7 to 9, 2018 combining a scanning LIDAR (90°, 30°), a vertical LIDAR (90°), a sun photometer, and the transport model ICON-ART. The LIDAR measurements show that the dust particles had backscatter coefficients of 0.86 ± 0.14 Mm−1 Sr−1, an extinction coefficient of 40 ± 0.8 Mm−1, a LIDAR ratio of 46 ± 5 sr, and a particle depolarization ratio of 0.33 ± 0.07. These values are in good agreement with those obtained in previous studies of Saharan dust plumes in Western Europe. Compared to the remote sensing measurements, the model simulation predicts the plume arrival time, its layer height, and structure very well but overestimates the backscatter coefficient. In this manuscript, we discuss the complementarity and advantages of the different measurement methods as well model simulations to predict Saharan dust plumes. Main conclusions are that the ICON-ART model can predict the structure of Saharan dust plumes very well but overestimates the backscatter coefficients by a factor of 2.2 ± 0.16 at 355 nm and underestimates the aerosol optical depth (AOD) by a factor of 1.5 ± 0.11 at 340 nm for this Saharan dust plume event. Employing a scanning aerosol LIDAR allows determining backscatter coefficient, particle depolarization ratio and especially LIDAR ratio of Saharan dust both for daytime and nighttime independently. Combining LIDAR with sun photometer data allows constraining aerosol optical depth in different ways and determining column integrated LIDAR ratios. These comprehensive datasets allow for a better understanding of Saharan dust plumes in Western Europe.
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CC1: 'Comment on amt-2021-193', Aristeidis Georgoulias, 04 Aug 2021
Dear authors,
Congratulations on this comprehensive study. Such studies are useful in order to bring out the potential of using different observational datasets and modeling systems to better characterize episodic events over background areas.
I strongly urge you to enrich your reference list and link your study with previous studies in the area combining satellite, model, and observational data. Two such studies are:
Akritidis, D., Katragkou, E., Georgoulias, A. K., Zanis, P., Kartsios, S., Flemming, J., Inness, A., Douros, J., and Eskes, H.: A complex aerosol transport event over Europe during the 2017 Storm Ophelia in CAMS forecast systems: analysis and evaluation, Atmos. Chem. Phys., 20, 13557–13578, https://doi.org/10.5194/acp-20-13557-2020, 2020.
Osborne, M., Malavelle, F. F., Adam, M., Buxmann, J., Sugier, J., Marenco, F., and Haywood, J.: Saharan dust and biomass burning aerosols during ex-hurricane Ophelia: observations from the new UK lidar and sun-photometer network, Atmos. Chem. Phys., 19, 3557–3578, https://doi.org/10.5194/acp-19-3557-2019, 2019.
Specifically, the study from Akritidis et al. (2020) highlights the ability of CAMS to capture the complex aerosol transport event (dust and smoke) over central-western Europe during Storm Ophelia while the second study is mostly ground-based.
Citation: https://doi.org/10.5194/amt-2021-193-CC1 -
AC1: 'Reply on CC1', Hengheng Zhang, 06 Oct 2021
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2021-193/amt-2021-193-AC1-supplement.pdf
-
AC1: 'Reply on CC1', Hengheng Zhang, 06 Oct 2021
-
RC1: 'Comment on amt-2021-193', Anonymous Referee #1, 28 Aug 2021
The study deals with the description of a long-range Saharan dust plume that affected the Central Europe in April 2018 and captured by ground-based instruments (lidars, sunphotometer) operating at Kalrsruhe (Germany). Moreover, an evaluation of the ICON-ART transport model is performed. I think that several modifications on the manuscript are needed in order to be acceptable for publication in AMT. For instance, it has not been clear by the authors which is the added value of the current study with respect to previous similar analyses. Likewise, an intercomparison of the obtained findings with those reported in past studies is missing. A critical point which must be clear to the reader is to highlight the purpose of the current study. There are parts in which different retrieval methods (raman vs klett) are compared, different observational geometries (vertical point vs off-zenith vertical profiles) are discussed, different remote sensing techniques (active vs passive) are employed and dust numerical simulations are evaluated against ground-based measurements. But it is not clear what is the exact proposition from this exercise (e.g., to deploy similar instrumentation for desert dust studies?). Even though the amount of data/techniques sounds impressive, the way that they are presented is confusing to my opinion. As you will see in my comments below it is required a restructure of the paper sections. Finally, please consider to improve the English writing throughout the manuscript.
Comments:
- Lines 12-13: Provide the wavelength
- Lines 34-35: Could you please explain better this sentence? Which are the problems for CALIOP to depict the vertical structure of dust layers?
- Line 47: Replace “Recently, synergy analysis methods…” with “Recently, synergistic approaches/methods…”.
- Lines 54-56: Rephrase and explain better this sentence.
- Lines 74-77: Check also the SDS-WAS in which several regional models provide short-term dust forecasts over the NAMEE domain.
- Lines 90-91: Not only ASD but SSA is also retrieved. Please make the appropriate corrections in this sentence.
- Line 114: It is strange that for the first time in the manuscript you are referring to Figure S3. Also it is missing a short description about this comparison.
- Results and discussion: It would be useful to add a section describing the factors driving the emission and transport of the Saharan dust plume towards central Europe. Such analysis should include model outputs (e.g., meteorology, dust) as well as ground-based observations (these have been already provided but not in an appropriate place) and satellite retrievals thus providing a complete overview.
- Figure 1:
- Which is the off-zenith angle for the KASCAL aerosol profiles?
- Use common colorbar for the three curtain plots in order to facilitate a visual intercomparison among them.
- It would be interesting to make a quantitative comparison (e.g. bias) between the curtain plots. To realize, you have to regrid the altitude-time plots and project them in a common grid.
- I suggest to remove the black curves from the middle plot. I don’t see why they are useful and in some cases it is hard to distinguish them (packing). Moreover, the labels are missing.
- How you have selected the timeframe for the backscatter plot (right figure)?
- How the backscatter coefficient by the model has been calculated?
- Why the modelled backscatter coefficient is so much overestimated?
- Lines 196 – 199: There is a contradiction between these two sentences. Do you mean the extinction coefficients, their uncertainties or both? According to Table S2, the variation of the alpha values is very small among the window types/lengths whereas the uncertainty (standard deviation) decreases for increasing window lengths.
- Figure 2: Please provide a better explanation in the caption.
- Figure 3: Can you provide an explanation for the differences of the lidar ratio (LR) for the dust layer (4-6 km) found between slant and vertical angles?
- Line 226: Replace “retrieved” with “retrieve”.
- Line 231: Why you have used LR=55sr and not 50sr?
- Lines 235-236: Can you provide a short description about the collocation approach that you have followed?
- Line 238: Why the AE is assumed equal to 1?
- Lines 250 – 251: What are we expecting in the case of oriented dust particles? Please provide also some relevant references.
- Lines 261 – 269: I think that this part should be moved to the new section presenting an overview of the studied dust outbreak by means of numerical simulations, satellite observations and ground-based retrievals (see comment 8). Improve also the part of the text between lines 266 and 269.
- Section 3.2: At the end of the main body of the manuscript you are discussing the results of Figure 1 which is quite strange. To my opinion the Results section should be restructured as follows:
- Description of the dust outbreak (lidars, AERONET, model)
- Keep Section 3.1 after removing Figure 4 and the relevant discussion (these should be transferred to the model evaluation)
- Model evaluation discussing also the comparison between lidars and sunphotometer
- Line 284: I would be more cautious with this statement!
- Lines 289 – 290: Why are you ignoring the potential model deficiencies?
- Lines 296 – 297: This sentence needs a better explanation.
- Conclusions: You should rewrite the whole section since it is not appropriate in its current state. You have to mention briefly the overarching goal of your work, then to highlight the main scientific outcomes and finally to propose how the performed analysis can be expanded.
Citation: https://doi.org/10.5194/amt-2021-193-RC1 -
AC2: 'Reply on RC1', Hengheng Zhang, 06 Oct 2021
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2021-193/amt-2021-193-AC2-supplement.pdf
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RC2: 'Comment on amt-2021-193', Anonymous Referee #2, 03 Sep 2021
An intense Saharan dust outbreak was observed with two lidar systems and a sun photometer. The observations are compared to model prediction by ICON-ART model. Arrival time and dust layer heights agreed for the first dust plume, for the second dust plume at higher altitudes the agreement is less good. The backscatter coefficient was overestimated by the model, the AOD underestimated. A lot of work was put into the lidar analysis for one vertical pointing and one slanted (30°) and vertical pointing lidar system. The structure and the language needs improvements.
Comparing a single dust event with the model predictions of a single model is surely a lot of effort, but it is not state of the art anymore. Therefore, major revisions are necessary before publication.
I would consider a single dust event evaluated with different dust transport models more interesting for the community. Doing so, the strengths and weaknesses of the models could be pointed out. At least two or three more dust transport models should be compared.
Or evaluate multiple dust events with the same model to get some statistics when the model predictions are in line with the observations and when not and to look for the reasons. One event evaluated with one model is surely not enough for a publication in 2021.
Already much more complex publications concerning the comparison of ground-based remote sensing (lidar) and dust transport models are present in literature, e.g. for a dust plume across the Atlantic Ocean (e.g., Kanitz et al., 2014), extreme dust events (e.g., Solomos et al., 2017), year-long statistics (e.g., Mona et al., 2014), multi-station statistics (e.g., Soupiona et al., 2020) and fine and coarse dust mass concentrations (e.g., Ansmann et al., 2017). It seems that the present study was performed without the knowledge of the progress made in the past decade.
The list of dust transport models mentioned in the introduction is not complete and should be updated. NMMB/BSC-Dust and SKIRON came immediately into my mind, but certainly there are more.
Literature is full of comparisons of models with observations. A more careful literature research is definitely necessary to place your observations in a broader context and to clearly state the novelty of your study.
Major comments:
- The range limitations of KASCAL (Fig. 1) were not discussed. No data were reported above 6 km. Why?
- Section 3, lines 149-180: The backscatter coefficient itself does not tell you, which layer is dust and which not. Throughout the section, you are writing “dust”. At this point, you haven’t shown the depolarization ratio yet to demonstrate, that your measured backscatter coefficient is really dust.
- Line 171: This statement is true for the first dust layer arriving on 7 April 2018. However, the second dust layer arriving in the evening of 9 April 2018 at around 5-6 km height was predicted by the model around 12 hours too early.
- Lines 176-177: How do you calculate the overestimation of the backscatter coefficient? Please provide more detail on how you get to that value.
- Line 211: Why do you chose lidar ratios of 30 and 50 sr? You measured different ones, reported some lines earlier.
- Line 238: Why do you use an AE of 1? You have measurements of the actual AE.
- The discussion about the single scattering albedo (SSA) and its comparison to literature values could be omitted. You use the standard AERONET output and compare it to literature values. We do not gain additional information out of it.
- Please state at some point, that you are referring to linear depolarization ratio (in contrast to the circular depolarization ratio).
- Your conclusions (lines 282-284) are just qualitative. Please consider some more quantification of the model performance. Therefore, you would need more observations for comparison. Or you would need different models for the same dust event to compare the different model outputs and quantify the agreement.
- If the model could not even reproduce the columnar values such as the AOD (lines 291-297), I am not so confident, that the model compares so well as you stated. To reproduce the arrival time, simply the meteorological fields are correctly predicted. However, if the optical properties such as backscatter coefficient, AOD and AE (see Fig. 7) are not agreeing, the model is probably not the best choice for dust predictions. Here, a comparison to various dust transport models would be nice.
Minor comments:
- The English language has to be checked again, especially in the introduction.
- Keep a uniform format for the dates throughout the paper.
- Line 30: You are not studying dust-cloud interactions in the present study.
- Line 42/43: The sentence could not be understood without the knowledge of the location of SAMUM-1 and SAMUM-2. Please provide the locations and distance from dust source.
- Line 72-74: Why do you mention the results from the North Pacific? There is almost no connection to your work.
- Line 244: The sun photometer works only under clear sky conditions as well.
- Lines 251-252: Please check again Freudenthaler et al., 2009. The values reported at 355 nm are lower than 0.33.
- 1: Is there a special reason to show this specific profile? Please indicate the time of the profile with a vertical bar in the time-height plots on the left. Are the heights reported above ground level or above sea level?
- 2: The figure is too small. Details can’t be spotted. With elastic method, you mean the retrieval using the Klett algorithm? Which filter was applied to the plots shown?
- 4: Which are the uncertainties for the lidar and the model output? Please add error bars to the data points. Caption in not complete, model (green squares) is missing.
- 5: Which smoothing was applied to the data?
References:
Ansmann, A., Rittmeister, F., Engelmann, R., Basart, S., Jorba, O., Spyrou, C., Remy, S., Skupin, A., Baars, H., Seifert, P., Senf, F., and Kanitz, T.: Profiling of Saharan dust from the Caribbean to western Africa – Part 2: Shipborne lidar measurements versus forecasts, Atmos. Chem. Phys., 17, 14987–15006, https://doi.org/10.5194/acp-17-14987-2017, 2017.
Freudenthaler, V.; Esselborn, M.; Wiegner, M.; Heese, B.; Tesche, M.; Ansmann, A.; Müller, D.; Althausen, D.; Wirth, M.; Fix, A.; Ehret, G.; Knippertz, P.; Toledano, C.; Gasteiger, J.; Garhammer, M. & Seefeldner, M.: Depolarization ratio profiling at several wavelengths in pure Saharan dust during SAMUM 2006, Tellus B, Blackwell Publishing Ltd, 2009, 61, 165-179
Kanitz, T.; Engelmann, R.; Heinold, B.; Baars, H.; Skupin, A. & Ansmann, A.: Tracking the Saharan Air Layer with shipborne lidar across the tropical Atlantic, Geophysical Research Letters, 2014, 41, 1044-1050
Mona, L., Papagiannopoulos, N., Basart, S., Baldasano, J., Binietoglou, I., Cornacchia, C., and Pappalardo, G.: EARLINET dust observations vs. BSC-DREAM8b modeled profiles: 12-year-long systematic comparison at Potenza, Italy, Atmos. Chem. Phys., 14, 8781–8793, https://doi.org/10.5194/acp-14-8781-2014, 2014.
Solomos, S., Ansmann, A., Mamouri, R.-E., Binietoglou, I., Patlakas, P., Marinou, E., and Amiridis, V.: Remote sensing and modelling analysis of the extreme dust storm hitting the Middle East and eastern Mediterranean in September 2015, Atmos. Chem. Phys., 17, 4063–4079, https://doi.org/10.5194/acp-17-4063-2017, 2017.
Soupiona, O., Papayannis, A., Kokkalis, P., Foskinis, R., Sánchez Hernández, G., Ortiz-Amezcua, P., Mylonaki, M., Papanikolaou, C.-A., Papagiannopoulos, N., Samaras, S., Groß, S., Mamouri, R.-E., Alados-Arboledas, L., Amodeo, A., and Psiloglou, B.: EARLINET observations of Saharan dust intrusions over the northern Mediterranean region (2014–2017): properties and impact on radiative forcing, Atmos. Chem. Phys., 20, 15147–15166, https://doi.org/10.5194/acp-20-15147-2020, 2020.
Citation: https://doi.org/10.5194/amt-2021-193-RC2 -
AC3: 'Reply on RC2', Hengheng Zhang, 06 Oct 2021
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2021-193/amt-2021-193-AC3-supplement.pdf
Status: closed
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CC1: 'Comment on amt-2021-193', Aristeidis Georgoulias, 04 Aug 2021
Dear authors,
Congratulations on this comprehensive study. Such studies are useful in order to bring out the potential of using different observational datasets and modeling systems to better characterize episodic events over background areas.
I strongly urge you to enrich your reference list and link your study with previous studies in the area combining satellite, model, and observational data. Two such studies are:
Akritidis, D., Katragkou, E., Georgoulias, A. K., Zanis, P., Kartsios, S., Flemming, J., Inness, A., Douros, J., and Eskes, H.: A complex aerosol transport event over Europe during the 2017 Storm Ophelia in CAMS forecast systems: analysis and evaluation, Atmos. Chem. Phys., 20, 13557–13578, https://doi.org/10.5194/acp-20-13557-2020, 2020.
Osborne, M., Malavelle, F. F., Adam, M., Buxmann, J., Sugier, J., Marenco, F., and Haywood, J.: Saharan dust and biomass burning aerosols during ex-hurricane Ophelia: observations from the new UK lidar and sun-photometer network, Atmos. Chem. Phys., 19, 3557–3578, https://doi.org/10.5194/acp-19-3557-2019, 2019.
Specifically, the study from Akritidis et al. (2020) highlights the ability of CAMS to capture the complex aerosol transport event (dust and smoke) over central-western Europe during Storm Ophelia while the second study is mostly ground-based.
Citation: https://doi.org/10.5194/amt-2021-193-CC1 -
AC1: 'Reply on CC1', Hengheng Zhang, 06 Oct 2021
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2021-193/amt-2021-193-AC1-supplement.pdf
-
AC1: 'Reply on CC1', Hengheng Zhang, 06 Oct 2021
-
RC1: 'Comment on amt-2021-193', Anonymous Referee #1, 28 Aug 2021
The study deals with the description of a long-range Saharan dust plume that affected the Central Europe in April 2018 and captured by ground-based instruments (lidars, sunphotometer) operating at Kalrsruhe (Germany). Moreover, an evaluation of the ICON-ART transport model is performed. I think that several modifications on the manuscript are needed in order to be acceptable for publication in AMT. For instance, it has not been clear by the authors which is the added value of the current study with respect to previous similar analyses. Likewise, an intercomparison of the obtained findings with those reported in past studies is missing. A critical point which must be clear to the reader is to highlight the purpose of the current study. There are parts in which different retrieval methods (raman vs klett) are compared, different observational geometries (vertical point vs off-zenith vertical profiles) are discussed, different remote sensing techniques (active vs passive) are employed and dust numerical simulations are evaluated against ground-based measurements. But it is not clear what is the exact proposition from this exercise (e.g., to deploy similar instrumentation for desert dust studies?). Even though the amount of data/techniques sounds impressive, the way that they are presented is confusing to my opinion. As you will see in my comments below it is required a restructure of the paper sections. Finally, please consider to improve the English writing throughout the manuscript.
Comments:
- Lines 12-13: Provide the wavelength
- Lines 34-35: Could you please explain better this sentence? Which are the problems for CALIOP to depict the vertical structure of dust layers?
- Line 47: Replace “Recently, synergy analysis methods…” with “Recently, synergistic approaches/methods…”.
- Lines 54-56: Rephrase and explain better this sentence.
- Lines 74-77: Check also the SDS-WAS in which several regional models provide short-term dust forecasts over the NAMEE domain.
- Lines 90-91: Not only ASD but SSA is also retrieved. Please make the appropriate corrections in this sentence.
- Line 114: It is strange that for the first time in the manuscript you are referring to Figure S3. Also it is missing a short description about this comparison.
- Results and discussion: It would be useful to add a section describing the factors driving the emission and transport of the Saharan dust plume towards central Europe. Such analysis should include model outputs (e.g., meteorology, dust) as well as ground-based observations (these have been already provided but not in an appropriate place) and satellite retrievals thus providing a complete overview.
- Figure 1:
- Which is the off-zenith angle for the KASCAL aerosol profiles?
- Use common colorbar for the three curtain plots in order to facilitate a visual intercomparison among them.
- It would be interesting to make a quantitative comparison (e.g. bias) between the curtain plots. To realize, you have to regrid the altitude-time plots and project them in a common grid.
- I suggest to remove the black curves from the middle plot. I don’t see why they are useful and in some cases it is hard to distinguish them (packing). Moreover, the labels are missing.
- How you have selected the timeframe for the backscatter plot (right figure)?
- How the backscatter coefficient by the model has been calculated?
- Why the modelled backscatter coefficient is so much overestimated?
- Lines 196 – 199: There is a contradiction between these two sentences. Do you mean the extinction coefficients, their uncertainties or both? According to Table S2, the variation of the alpha values is very small among the window types/lengths whereas the uncertainty (standard deviation) decreases for increasing window lengths.
- Figure 2: Please provide a better explanation in the caption.
- Figure 3: Can you provide an explanation for the differences of the lidar ratio (LR) for the dust layer (4-6 km) found between slant and vertical angles?
- Line 226: Replace “retrieved” with “retrieve”.
- Line 231: Why you have used LR=55sr and not 50sr?
- Lines 235-236: Can you provide a short description about the collocation approach that you have followed?
- Line 238: Why the AE is assumed equal to 1?
- Lines 250 – 251: What are we expecting in the case of oriented dust particles? Please provide also some relevant references.
- Lines 261 – 269: I think that this part should be moved to the new section presenting an overview of the studied dust outbreak by means of numerical simulations, satellite observations and ground-based retrievals (see comment 8). Improve also the part of the text between lines 266 and 269.
- Section 3.2: At the end of the main body of the manuscript you are discussing the results of Figure 1 which is quite strange. To my opinion the Results section should be restructured as follows:
- Description of the dust outbreak (lidars, AERONET, model)
- Keep Section 3.1 after removing Figure 4 and the relevant discussion (these should be transferred to the model evaluation)
- Model evaluation discussing also the comparison between lidars and sunphotometer
- Line 284: I would be more cautious with this statement!
- Lines 289 – 290: Why are you ignoring the potential model deficiencies?
- Lines 296 – 297: This sentence needs a better explanation.
- Conclusions: You should rewrite the whole section since it is not appropriate in its current state. You have to mention briefly the overarching goal of your work, then to highlight the main scientific outcomes and finally to propose how the performed analysis can be expanded.
Citation: https://doi.org/10.5194/amt-2021-193-RC1 -
AC2: 'Reply on RC1', Hengheng Zhang, 06 Oct 2021
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2021-193/amt-2021-193-AC2-supplement.pdf
-
RC2: 'Comment on amt-2021-193', Anonymous Referee #2, 03 Sep 2021
An intense Saharan dust outbreak was observed with two lidar systems and a sun photometer. The observations are compared to model prediction by ICON-ART model. Arrival time and dust layer heights agreed for the first dust plume, for the second dust plume at higher altitudes the agreement is less good. The backscatter coefficient was overestimated by the model, the AOD underestimated. A lot of work was put into the lidar analysis for one vertical pointing and one slanted (30°) and vertical pointing lidar system. The structure and the language needs improvements.
Comparing a single dust event with the model predictions of a single model is surely a lot of effort, but it is not state of the art anymore. Therefore, major revisions are necessary before publication.
I would consider a single dust event evaluated with different dust transport models more interesting for the community. Doing so, the strengths and weaknesses of the models could be pointed out. At least two or three more dust transport models should be compared.
Or evaluate multiple dust events with the same model to get some statistics when the model predictions are in line with the observations and when not and to look for the reasons. One event evaluated with one model is surely not enough for a publication in 2021.
Already much more complex publications concerning the comparison of ground-based remote sensing (lidar) and dust transport models are present in literature, e.g. for a dust plume across the Atlantic Ocean (e.g., Kanitz et al., 2014), extreme dust events (e.g., Solomos et al., 2017), year-long statistics (e.g., Mona et al., 2014), multi-station statistics (e.g., Soupiona et al., 2020) and fine and coarse dust mass concentrations (e.g., Ansmann et al., 2017). It seems that the present study was performed without the knowledge of the progress made in the past decade.
The list of dust transport models mentioned in the introduction is not complete and should be updated. NMMB/BSC-Dust and SKIRON came immediately into my mind, but certainly there are more.
Literature is full of comparisons of models with observations. A more careful literature research is definitely necessary to place your observations in a broader context and to clearly state the novelty of your study.
Major comments:
- The range limitations of KASCAL (Fig. 1) were not discussed. No data were reported above 6 km. Why?
- Section 3, lines 149-180: The backscatter coefficient itself does not tell you, which layer is dust and which not. Throughout the section, you are writing “dust”. At this point, you haven’t shown the depolarization ratio yet to demonstrate, that your measured backscatter coefficient is really dust.
- Line 171: This statement is true for the first dust layer arriving on 7 April 2018. However, the second dust layer arriving in the evening of 9 April 2018 at around 5-6 km height was predicted by the model around 12 hours too early.
- Lines 176-177: How do you calculate the overestimation of the backscatter coefficient? Please provide more detail on how you get to that value.
- Line 211: Why do you chose lidar ratios of 30 and 50 sr? You measured different ones, reported some lines earlier.
- Line 238: Why do you use an AE of 1? You have measurements of the actual AE.
- The discussion about the single scattering albedo (SSA) and its comparison to literature values could be omitted. You use the standard AERONET output and compare it to literature values. We do not gain additional information out of it.
- Please state at some point, that you are referring to linear depolarization ratio (in contrast to the circular depolarization ratio).
- Your conclusions (lines 282-284) are just qualitative. Please consider some more quantification of the model performance. Therefore, you would need more observations for comparison. Or you would need different models for the same dust event to compare the different model outputs and quantify the agreement.
- If the model could not even reproduce the columnar values such as the AOD (lines 291-297), I am not so confident, that the model compares so well as you stated. To reproduce the arrival time, simply the meteorological fields are correctly predicted. However, if the optical properties such as backscatter coefficient, AOD and AE (see Fig. 7) are not agreeing, the model is probably not the best choice for dust predictions. Here, a comparison to various dust transport models would be nice.
Minor comments:
- The English language has to be checked again, especially in the introduction.
- Keep a uniform format for the dates throughout the paper.
- Line 30: You are not studying dust-cloud interactions in the present study.
- Line 42/43: The sentence could not be understood without the knowledge of the location of SAMUM-1 and SAMUM-2. Please provide the locations and distance from dust source.
- Line 72-74: Why do you mention the results from the North Pacific? There is almost no connection to your work.
- Line 244: The sun photometer works only under clear sky conditions as well.
- Lines 251-252: Please check again Freudenthaler et al., 2009. The values reported at 355 nm are lower than 0.33.
- 1: Is there a special reason to show this specific profile? Please indicate the time of the profile with a vertical bar in the time-height plots on the left. Are the heights reported above ground level or above sea level?
- 2: The figure is too small. Details can’t be spotted. With elastic method, you mean the retrieval using the Klett algorithm? Which filter was applied to the plots shown?
- 4: Which are the uncertainties for the lidar and the model output? Please add error bars to the data points. Caption in not complete, model (green squares) is missing.
- 5: Which smoothing was applied to the data?
References:
Ansmann, A., Rittmeister, F., Engelmann, R., Basart, S., Jorba, O., Spyrou, C., Remy, S., Skupin, A., Baars, H., Seifert, P., Senf, F., and Kanitz, T.: Profiling of Saharan dust from the Caribbean to western Africa – Part 2: Shipborne lidar measurements versus forecasts, Atmos. Chem. Phys., 17, 14987–15006, https://doi.org/10.5194/acp-17-14987-2017, 2017.
Freudenthaler, V.; Esselborn, M.; Wiegner, M.; Heese, B.; Tesche, M.; Ansmann, A.; Müller, D.; Althausen, D.; Wirth, M.; Fix, A.; Ehret, G.; Knippertz, P.; Toledano, C.; Gasteiger, J.; Garhammer, M. & Seefeldner, M.: Depolarization ratio profiling at several wavelengths in pure Saharan dust during SAMUM 2006, Tellus B, Blackwell Publishing Ltd, 2009, 61, 165-179
Kanitz, T.; Engelmann, R.; Heinold, B.; Baars, H.; Skupin, A. & Ansmann, A.: Tracking the Saharan Air Layer with shipborne lidar across the tropical Atlantic, Geophysical Research Letters, 2014, 41, 1044-1050
Mona, L., Papagiannopoulos, N., Basart, S., Baldasano, J., Binietoglou, I., Cornacchia, C., and Pappalardo, G.: EARLINET dust observations vs. BSC-DREAM8b modeled profiles: 12-year-long systematic comparison at Potenza, Italy, Atmos. Chem. Phys., 14, 8781–8793, https://doi.org/10.5194/acp-14-8781-2014, 2014.
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Citation: https://doi.org/10.5194/amt-2021-193-RC2 -
AC3: 'Reply on RC2', Hengheng Zhang, 06 Oct 2021
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