the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Mar 2021
Evaluation and Impact Factors of Doppler Wind Lidar during Super Typhoon Lekima (2019)
Abstract. Doppler wind lidar (DWL) has been shown to obtain fairly accurate wind speeds in normal wind conditions. However, the evaluation of DWL winds under typhoon conditions is less common. This study evaluated the accuracy of wind data measured by two types of DWLs (WindPrint S4000 and WindCube V2), and investigated the impact of factors (e.g., precipitation and humidity) on the DWL-observed wind speed and direction. Data were collected from joint observations in Baoshan, Zhoushan and Taizhou (China) by the Shanghai Typhoon Institute during the passage of Super Typhoon Lekima in 2019. The DWL observations were compared with measured data from balloon-borne radiosonde released at the same location. The results showed that the 1-min average wind speed and direction of WindPrint S4000 were more consistent with the instantaneous observation data of the sounding balloon than those of WindCube V2. The applicability of DWL was poor when the precipitation intensity was larger than 50 mm · h−1. The DWL wind speed bias significantly increased when the relative humidity exceeded 85 %. When the drift distance of the sounding balloon (ldrift) was less than 1 km, the DWL wind speed bias decreased with an increase of ldrift, whereas it increased with an increase of ldrift when the drift exceeded 1.5 km. Within a radius of 700 km, the root mean square of wind speeds between DWL and sounding balloon measurements showed a trend of increasing as the distance from the typhoon center decreased.
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Interactive discussion
Status: closed
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RC1: 'Comment on amt-2021-42', Anonymous Referee #1, 18 Apr 2021
The paper Evaluation and Impact Factors of Doppler Wind Lidar during Super Typhoon Lekima (2019) is reviewed with the following comments.
General comments
It is an interesting study on Doppler wind lidar data vs. radiosonde data during and near typhoon conditions at three locations in China. The general impression though is that the background for the study, the results and conclusion need much more work to appear in a final form. There appears misinterpretation and lack of focus on the working hypothesis. The fundaments on the theoretical insight is too limited and not presented in a clear and structured way. The paper is rejected.
Specific comments
Lines 16-19 on bias and distance from the typhoon center is not possible to follow in a logical way. This situation also goes for other sections in the paper related such as section 5.3. In case the bias mentioned is shown in Figure 11a and 11b, it does not correspond to the text, and again in lines 472-477 is discrepancy. Overall question is how would you argue that longer distances are giving other results than shorter distances, why and how?
In the introduction several works are cited related to correlation coefficient and RMS but bias is not mentioned. Why is that? It might give a better overview with a table on previous researchers work summarizing their statistics.
Lines 66-74 The text could benefit from more fundamental information on the challenges of Doppler wind lidar and radiosondes in typhoon conditions. It becomes difficult to follow what is the key information and why the measurement techniques is expected to have lower performance than in less windy and rainy conditions. A thought here, is this your hypothesis you are testing? In case so it would be valuable to state this clearly.
Line 81 wording “generally good” is not sufficiently clear
Section 2.1 and 2.2 might be complemented with other auxiliary information if available, e.g. model results of the case and/or local wind speed and direction measurements or from aircraft, to better understand the variability in time and space.
Section 3.1.1. this section would greatly benefit from fundamental knowledge on the two types of lidars. Technical information should appear in the introduction in general terms, so that during the subsequent part of the paper, it is clear what to expect. The specifications on expected accuracy on all the observed parameters from the WindPrint and the WindCubes should be clear. The entire paper is about this topic. Table 2 is included but without further description or explanation (or reference to the values).
Table 1. To clarify, from Bashan there is 43 hours of data, from Zhoushan 24 hours of data and from Taizhou 72 hours of data? It would be valuable to list the number of available valid samples for each. Also in case some samples are invalid, it is relevant to understand this, as it is part of how well given instruments perform.
Section 3.2 is a very basic text and as reader one is left wondering what is the situation when aerosol content, humidity, precipitation, etc. comes into the equations. What effect do you foresee in typhoon conditions. This background would have to be given carefully for both types of lidars, and as well the two radiosonde types. How much more can we expect to trust the various instruments? This remains unclear as is.
Line 191, I do not understand what you mean with “data efficiency”, please clarify
Lines 225-229, this text on aerosol is unclear and not precise. It is difficult to follow what you explain. In case it is fundamental background, it should be presented much earlier in the paper.
Lines 245-250 This text on turbulence and the instruments should be given in background, and corrected, as it is unclear what you are stating. The text is loosely structured, it cause confusion for the reader.
Lines 257-260 This is not correct. Figure 5 shows hardly any DWL data below 100 m height range and in plots a), d) and e) the sonde gives higher values while in plots b) and c) the sonde gives lower values.
Line 285 rephrase “this was due” to e.g. “most likely”. The interpretation of results is not definitive, so you need caution.
Table 3 Would suggestion to include the number of samples and the bias values.
Section 5.1 On precipitation raised a couple of questions. The measurements were taken on the ground (I presume). Do you assume the rain to be homogenous during the entire atmospheric column? Is this valid, or if not always, what may be the case. SNR (signal to noise ratio) explains how good data you have but it appears as you take is as a measure.
Figure 8a and 8b have different scales. Is this intentional, please clarify and note in the text. It would be relevant to related to these plots and at this time revisit why the dB are so different from the two types of lidars, and what we learn from this. If you are comparing the two plots directly between each other (or wish the readers to do so), it is recommended to use the same scale x-axis (rain intensity) and secondary y-axis (sample size) in both plots.
Lines 386-390 on humidity would be place better in the introduction or background section.
Figure 10, why do we hear about bias here for the first time? It is recommended to report on bias throughout the paper, not only for humidity.
Figure 11, would figure b) be a mistake. Is the bias on wind direction around 65 degrees? You have written about a small RMS on wind direction but if there is a very significant bias, that would actually be even more important to report.
Section 5.4 and in particular Figure 12 raises many more question than give answers to the data analysis. Either rework or omit. It is not clear what you wish to present and what can be concluded (also keeping in mind the other uncertainties dealt with earlier).
Technical corrections
Line 29, Cot
Line 34 Kopp would be Köpp 1984?
Line 48 carried out by
Line 55 with the height range (several other places you could add height to clarify your text)
Line 61 Korb? Not in your reference list
Line 189 Goit? Not in your reference list
Line 254 Li et al 2018, you have two references of this, so please add a and b to distinguish
Reference list is not in good shape, as the format changes very much. There is several ‘gray literature” please remove.
There are many more technical corrections (but not listed).
Further English editing is necessary.
Citation: https://doi.org/10.5194/amt-2021-42-RC1 -
RC2: 'Comment on amt-2021-42', Anonymous Referee #2, 09 Aug 2021
General comments:
The paper presents measurements taken during the presence of a typhoon close to Doppler lidar instruments. The paper is dealing with an interesting topic and tries hard to assess the performance of Doppler lidar instruments under extreme weather conditions. However, the typhoon obviously provides too many challenges at once so that no clear picture evolves, how extreme precipitation, humid aerosol and clouds may influence Doppler lidar measurements of horizontal and vertical wind. Observations like this are actually unique and very precious. But it remains unclear in the paper if Doppler lidars can actually provide useful information for analysis and prediction of (super) typhoon properties.
The paper is hence rejected in its current form. Taking into account the highly valuable and unique observations, I encourage the authors to rethink and reshape their work and present a new version of their paper also incorporating the comments below.
Detailed comments:- Quantitative definitions are needed for statements like "fairly accurate" or ambiguous words like "impact factor" (do you mean "co-factor" or "influence factor"?, see Chapter 5).
- Relative humidity of more than 80% doesn’t keep a Doppler lidar from working. Its mostly haze and cloud formation under high relative humidity conditions. The discussion of this effect stays blurry and needs a more detailed approach, separating all potential influence factors.
- Measurement conditions with a typhoon present are very challenging, but in itself very precious. More emphasis should be laid on the evaluation of the basic data from the Doppler lidar, including highly resolved raw profiles of SNR allowing assessment of attenuation by rain, clouds and aerosol.
- The possible presence of clouds is not discussed. The presence of clouds of any size and form can limit the measurement of horizontal wind velocity, because attenutation can affect individual beams during Doppler beam swinging.
- The influence of rain and other factors on Doppler lidar observations can (and should) be studied when more controlled conditions are available. A lot of discussions in the paper are centered around the capabilities of a Doppler lidar under extreme environmental conditions, but this also means that comparison with other methods (e.g. radiosondes) is extremely challenging under such conditions. Heavy rain can also occur without extreme wind, and the other way around. A lot more data taken under more controlled conditions should be available at the given sites which could be used to clearly separate the effects of heavy precipitation, aerosol and clouds individually.
- Scanning angle or the angle of the Doppler lidar window plates need to be discussed here, because it can greatly affect the susceptibility of a system to rainfall, because with a lower scan angle, water runs off more easily from the window.
Technical comments:
L.18: root mean square: This seems to be slang, please specify of you mean root mean square deviation or error...
l.35 "good agreement": please specify
l.93: Please use UTC time or specify the difference of local time to UTC
Table 2: Speed range: Is this the raw velocity range of the detector or the range for a VAD scan?
l.177: "Assumption that the horizontal wind field has a linear distribution": What is meant by "linear distribution"? A linear change within the observation volume?
l.255ff: Horizontal wind below 100m shows other effects that limit the comparability between radiosonde and Doppler lidar (e.g., stronger turbulence close to the ground, exponential increase with height, ...), which should be discussed here)
l.347: The definition "sunny" is misleading, since it there could be no rain and and anyway no sun.
l.355: The analysis of rain impact on the measurements is a bit superficial. There is plenty of information available from the Doppler lidar instrument itself which are not shown. E.g. high-resolution plots of SNR vs. range would be helpful in order to assess the situation in detail. If spectral data is available rain should also turn up in the spectra. Presence of cloud droplets could also easily be identified.
Fi. 11 b: Do you really mean bias? The scale seems to be the actual angle (?)
l.452: It is not clear how the deficiencies of the balloon can be judged if data close to the ground is (a) hardly available and (b) difficult to interprete without additional information (e.g., orography). With a lower scanning elevation (~5° elevation) this height range actually could be accessed with Doppler lidars.
Citation: https://doi.org/10.5194/amt-2021-42-RC2
Interactive discussion
Status: closed
-
RC1: 'Comment on amt-2021-42', Anonymous Referee #1, 18 Apr 2021
The paper Evaluation and Impact Factors of Doppler Wind Lidar during Super Typhoon Lekima (2019) is reviewed with the following comments.
General comments
It is an interesting study on Doppler wind lidar data vs. radiosonde data during and near typhoon conditions at three locations in China. The general impression though is that the background for the study, the results and conclusion need much more work to appear in a final form. There appears misinterpretation and lack of focus on the working hypothesis. The fundaments on the theoretical insight is too limited and not presented in a clear and structured way. The paper is rejected.
Specific comments
Lines 16-19 on bias and distance from the typhoon center is not possible to follow in a logical way. This situation also goes for other sections in the paper related such as section 5.3. In case the bias mentioned is shown in Figure 11a and 11b, it does not correspond to the text, and again in lines 472-477 is discrepancy. Overall question is how would you argue that longer distances are giving other results than shorter distances, why and how?
In the introduction several works are cited related to correlation coefficient and RMS but bias is not mentioned. Why is that? It might give a better overview with a table on previous researchers work summarizing their statistics.
Lines 66-74 The text could benefit from more fundamental information on the challenges of Doppler wind lidar and radiosondes in typhoon conditions. It becomes difficult to follow what is the key information and why the measurement techniques is expected to have lower performance than in less windy and rainy conditions. A thought here, is this your hypothesis you are testing? In case so it would be valuable to state this clearly.
Line 81 wording “generally good” is not sufficiently clear
Section 2.1 and 2.2 might be complemented with other auxiliary information if available, e.g. model results of the case and/or local wind speed and direction measurements or from aircraft, to better understand the variability in time and space.
Section 3.1.1. this section would greatly benefit from fundamental knowledge on the two types of lidars. Technical information should appear in the introduction in general terms, so that during the subsequent part of the paper, it is clear what to expect. The specifications on expected accuracy on all the observed parameters from the WindPrint and the WindCubes should be clear. The entire paper is about this topic. Table 2 is included but without further description or explanation (or reference to the values).
Table 1. To clarify, from Bashan there is 43 hours of data, from Zhoushan 24 hours of data and from Taizhou 72 hours of data? It would be valuable to list the number of available valid samples for each. Also in case some samples are invalid, it is relevant to understand this, as it is part of how well given instruments perform.
Section 3.2 is a very basic text and as reader one is left wondering what is the situation when aerosol content, humidity, precipitation, etc. comes into the equations. What effect do you foresee in typhoon conditions. This background would have to be given carefully for both types of lidars, and as well the two radiosonde types. How much more can we expect to trust the various instruments? This remains unclear as is.
Line 191, I do not understand what you mean with “data efficiency”, please clarify
Lines 225-229, this text on aerosol is unclear and not precise. It is difficult to follow what you explain. In case it is fundamental background, it should be presented much earlier in the paper.
Lines 245-250 This text on turbulence and the instruments should be given in background, and corrected, as it is unclear what you are stating. The text is loosely structured, it cause confusion for the reader.
Lines 257-260 This is not correct. Figure 5 shows hardly any DWL data below 100 m height range and in plots a), d) and e) the sonde gives higher values while in plots b) and c) the sonde gives lower values.
Line 285 rephrase “this was due” to e.g. “most likely”. The interpretation of results is not definitive, so you need caution.
Table 3 Would suggestion to include the number of samples and the bias values.
Section 5.1 On precipitation raised a couple of questions. The measurements were taken on the ground (I presume). Do you assume the rain to be homogenous during the entire atmospheric column? Is this valid, or if not always, what may be the case. SNR (signal to noise ratio) explains how good data you have but it appears as you take is as a measure.
Figure 8a and 8b have different scales. Is this intentional, please clarify and note in the text. It would be relevant to related to these plots and at this time revisit why the dB are so different from the two types of lidars, and what we learn from this. If you are comparing the two plots directly between each other (or wish the readers to do so), it is recommended to use the same scale x-axis (rain intensity) and secondary y-axis (sample size) in both plots.
Lines 386-390 on humidity would be place better in the introduction or background section.
Figure 10, why do we hear about bias here for the first time? It is recommended to report on bias throughout the paper, not only for humidity.
Figure 11, would figure b) be a mistake. Is the bias on wind direction around 65 degrees? You have written about a small RMS on wind direction but if there is a very significant bias, that would actually be even more important to report.
Section 5.4 and in particular Figure 12 raises many more question than give answers to the data analysis. Either rework or omit. It is not clear what you wish to present and what can be concluded (also keeping in mind the other uncertainties dealt with earlier).
Technical corrections
Line 29, Cot
Line 34 Kopp would be Köpp 1984?
Line 48 carried out by
Line 55 with the height range (several other places you could add height to clarify your text)
Line 61 Korb? Not in your reference list
Line 189 Goit? Not in your reference list
Line 254 Li et al 2018, you have two references of this, so please add a and b to distinguish
Reference list is not in good shape, as the format changes very much. There is several ‘gray literature” please remove.
There are many more technical corrections (but not listed).
Further English editing is necessary.
Citation: https://doi.org/10.5194/amt-2021-42-RC1 -
RC2: 'Comment on amt-2021-42', Anonymous Referee #2, 09 Aug 2021
General comments:
The paper presents measurements taken during the presence of a typhoon close to Doppler lidar instruments. The paper is dealing with an interesting topic and tries hard to assess the performance of Doppler lidar instruments under extreme weather conditions. However, the typhoon obviously provides too many challenges at once so that no clear picture evolves, how extreme precipitation, humid aerosol and clouds may influence Doppler lidar measurements of horizontal and vertical wind. Observations like this are actually unique and very precious. But it remains unclear in the paper if Doppler lidars can actually provide useful information for analysis and prediction of (super) typhoon properties.
The paper is hence rejected in its current form. Taking into account the highly valuable and unique observations, I encourage the authors to rethink and reshape their work and present a new version of their paper also incorporating the comments below.
Detailed comments:- Quantitative definitions are needed for statements like "fairly accurate" or ambiguous words like "impact factor" (do you mean "co-factor" or "influence factor"?, see Chapter 5).
- Relative humidity of more than 80% doesn’t keep a Doppler lidar from working. Its mostly haze and cloud formation under high relative humidity conditions. The discussion of this effect stays blurry and needs a more detailed approach, separating all potential influence factors.
- Measurement conditions with a typhoon present are very challenging, but in itself very precious. More emphasis should be laid on the evaluation of the basic data from the Doppler lidar, including highly resolved raw profiles of SNR allowing assessment of attenuation by rain, clouds and aerosol.
- The possible presence of clouds is not discussed. The presence of clouds of any size and form can limit the measurement of horizontal wind velocity, because attenutation can affect individual beams during Doppler beam swinging.
- The influence of rain and other factors on Doppler lidar observations can (and should) be studied when more controlled conditions are available. A lot of discussions in the paper are centered around the capabilities of a Doppler lidar under extreme environmental conditions, but this also means that comparison with other methods (e.g. radiosondes) is extremely challenging under such conditions. Heavy rain can also occur without extreme wind, and the other way around. A lot more data taken under more controlled conditions should be available at the given sites which could be used to clearly separate the effects of heavy precipitation, aerosol and clouds individually.
- Scanning angle or the angle of the Doppler lidar window plates need to be discussed here, because it can greatly affect the susceptibility of a system to rainfall, because with a lower scan angle, water runs off more easily from the window.
Technical comments:
L.18: root mean square: This seems to be slang, please specify of you mean root mean square deviation or error...
l.35 "good agreement": please specify
l.93: Please use UTC time or specify the difference of local time to UTC
Table 2: Speed range: Is this the raw velocity range of the detector or the range for a VAD scan?
l.177: "Assumption that the horizontal wind field has a linear distribution": What is meant by "linear distribution"? A linear change within the observation volume?
l.255ff: Horizontal wind below 100m shows other effects that limit the comparability between radiosonde and Doppler lidar (e.g., stronger turbulence close to the ground, exponential increase with height, ...), which should be discussed here)
l.347: The definition "sunny" is misleading, since it there could be no rain and and anyway no sun.
l.355: The analysis of rain impact on the measurements is a bit superficial. There is plenty of information available from the Doppler lidar instrument itself which are not shown. E.g. high-resolution plots of SNR vs. range would be helpful in order to assess the situation in detail. If spectral data is available rain should also turn up in the spectra. Presence of cloud droplets could also easily be identified.
Fi. 11 b: Do you really mean bias? The scale seems to be the actual angle (?)
l.452: It is not clear how the deficiencies of the balloon can be judged if data close to the ground is (a) hardly available and (b) difficult to interprete without additional information (e.g., orography). With a lower scanning elevation (~5° elevation) this height range actually could be accessed with Doppler lidars.
Citation: https://doi.org/10.5194/amt-2021-42-RC2
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