Intensity Measurements of a Landfalling Tropical Cyclone Using Conventional Coastal Weather Radar

Round 1

Reviewer 1 Report

Comments on the manuscript entitled "Intensity measurements of a landfalling tropical cyclone using conventional coastal weather radar" by Yurchak B. S. submitted to Meteorology.

 

Recommendation: Minor revision

To evaluate the support for the change in tropical cyclone (TC) intensity identified by HLS-approximation of SCRBs of recorded TC radar images, this study estimates the temporal variability of the intensity of TC Irving which was obtained from the data of a conventional weather radar.

Overall, the topic is important for the understanding of intensity measurements of landfalling TC, the results can support their main conclusions, the paper is well written. As I have only one comment on the understanding of intensity measurements, I recommend “Minor revision”. The detailed comment is listed below.

 

Minor comment:

1. I fully agree with the author that, with the help of coastal weather radar, the accuracy of the measurements of both TC track and its intensity can be improved greatly. I would like to know whether the inconsistency of TC measurements affects the changes of TC intensity during the landfalling period. Namely, only when TC is close to the coastal weather radar, the TC intensity can be improved by the radar. During the TC approaching period, the TC intensity measurements are different when TC is far away or close to the radar.

 

Author Response

Indeed, as follows from Fig. 2, the measured TC intensity increased as the cyclone approached the coast. However, this phenomenon (initial intensification) is not due to the peculiarities of the method, but to the actual change in the physical state of the TC, which is confirmed by the increase in the maximum wind speed in the center of the TC (Fig. 3) at this time (0:14 -02:15 LT). This is probably due to the warmer water in the gulf compared to the open sea. At the same time, the influence of refraction on the parameters of radar sounding, which really affects the sounding of TCs, has not yet been studied enough. Considerations on this subject are given in Appendix B.

Reviewer 2 Report

Review report for meteorology-1603328

 

Brief Description of the Work

The aim of this work is to study the intensity of tropical cyclone, wherein the maximum wind speed is calculated by the Hyperbolic-Logarithmic approximation of spiral cloud-rain bands of recorded radar images. 

Main Results Obtained

This study illustrates the restoration of tropical cyclone intensity changes from archived data, which was in the surveillance zone of the conventional coastal weather radar. This study demonstrates the feasibility of using the HLS-approximation technique for retrieving the tropical cyclone intensity variation from conventional weather radar data.

General Considerations 

 

The topic treated in this work is interesting. However, the author's English language description is not very clear and understandable. 

 

Questions/Suggestions

 

I don't know what the author is trying to say in this sentence in,  

1. 1) Line 6:  

“The continious measuring to support the forecasting is especially important for landfalling cyclones.”

1. 2) Line 8:

“Estimates of the temporal variability of the intensity of TC Irving, which was in the Gulf of Tonkin of the South China Sea on July 23-24, 1989, were obtained from the data of a conventional weather radar installed at the Phu Lien Observatory in northern Vietnam.” 

………

And so on.

 

Conclusions

 

As mentioned, the work is interesting, but it is not yet suitable published in the present from. The authors are strongly encouraged to take into account the extensive editing of English language.

 

Comments for author File: Comments.pdf

Author Response

1. The phrase in line 6 is reworded:

It is especially to continuously measure TC intensity for landfalling cyclones to improve their forecast.

2. The phrase in line 8 is reworded:

 For example, TC Irving, which operated in the Gulf of Tonkin, South China Sea, on July 23-24, 1989,  was observed by a conventional weather radar installed at the Phu Lien Observatory in North Vietnam.

3. All text has been extensively edited with  MDPI English Editing Services.

Reviewer 3 Report

In this manuscript, the conventional (non-doppler) coastal weather radar image data is used for the estimation of tropical cyclone intensity. Specifically, The maximum wind speed is estimated by using hyperbolic-logarithmic spiral (HLS) to approximate the radar images of spiral cloud-rain bands.  This study is valuable as it provides an alternative way to estimate the intensity of tropical cyclones with existing equipment in a low-cost manner. The structure of this manuscript is intact, and the discussion is comprehensive. 

Following are my comments:

Lines 152-155. The simplification of the HLS approximation is introduced without mentioning its potential effects. It is necessary to add some justification/reference to support this simplification. 

Lines 172-173. Add reference.

Content between Eqs. 12 and 13: 10 is an interesting value. It is necessary to elaborate on why there is a 10-times relation. In the case the existence of the number 10 can be explained, it is suggested to combine Eqs. 12 and 13.

 

Author Response

1. Lines 152-155.

The simplification of the approximation procedure, which consists in using fixed values ​​of the friction coefficient and the hyperbolicity index instead of using a range of their values, is insignificant in most cases, but sometimes leads to noticeable deviations.To eliminate any ambiguity, the data were recalculated according to the usual procedure already tried, which used a range of friction coefficient and hyperbolicity index.Accordingly, Figure 2 has been updated. The main features of the change in intensity remain the same, with some changes in values, primarily related to extreme values. On the updated figure, the curve by points is represented by a solid red line, the moving average is represented  by a blue dashed line. Accordingly, the description of the change in intensity has been slightly updated in Sections 2.2 and 4.

 

 

 

2. Lines 172-173.

 

References 12, 16 and 17 are added in the phrase:

Earlier, in the above-mentioned works of the author [12, 16, 17], such a comparison, as a rule, was carried out with the data of the aircraft sounding of the TC.

 

 

3. 10 times value and combination of equations (12) and (13).

Let us consider the dimension of the term in formula (12)  .

β and other terms in round brackets (…) are dimensionless.

As per the source [18] of this formula, the pressure P is in hPa  and the density ρ is in      kg m^-3.

Therefore, one can write:

;

 

The following relationships in SI base units are used:

 

 

 

Pa is pascal, N is newton, s is second, m is meter, kg is kilogram. 

 

 

Therefore,  , and  .

 

Equations (12) and (13) are combined in the revised text into one equation (12). 

PS. Since equations cannot be displayed, the full response please see attached.

Author Response File: Author Response.doc

Reviewer 4 Report

Basically, the paper by Yurchak, B.S. is very well written with a good command of English.

I have only meta-comments:

1/ It should be better to add some statistics about the cyclones hitting this area: frequency, intensity, in order to place TC Irving in the right context. Why this particular one was chosen for the study?

2/ The author is not giving any physical explanation to the variations in intensity, except of course the landfall. A sketch of possible explanations, I would say just ideas, would be better.

Again, a very good paper.

Author Response

1. TC Irving was selected for radar tracking based on the following: MRL-5 radar was installed at the Phu Lien Observatory only in the autumn of 1988. Until that time, the possibility of radar tracking of cyclones approaching the coast of northern Vietnam did not exist. In the period from 1989 to 1991, 13 TCs entered the coast of northern Vietnam (including Irving). All of them were detected by radar, but the period of their tracking for various reasons was much shorter compared to the period of tracking of the TC Irving. Additionally, TC Irving was the strongest among them and in this respect was a unique object for research by the radar method. Approximately 60% of all TCs that hit the coast of Vietnam fall into the radar surveillance zone. The corresponding wording is placed in the Introduction section.

 

2. This work has the main goal of demonstrating the possibility of the radar method to register changes in the intensity of TCs. For a correct interpretation of the recorded changes in intensity, additional physical data on the atmospheric and hydrological parameters of the waters of the Gulf of Tonkin are required. In the opinion of the author, hydrological data are of great importance, since the TC is fed by energy coming from the near-surface layer of the sea. It seems that for a practically important prediction of the change in intensity, it is necessary to analyze two competing factors affecting the behavior of TC in the process of reaching the coast, when part of the TC is still above the sea and is fed by well-heated water in shallow water, and the part that is already on land, loses energy due to friction on a hard surface. It is also possible that the influence of pollution with surfactants on the overheating of the coastal waters. The reason for this conclusion is a noticeable fluctuation in the TC intensity during landfall (please see updated Fig. 2). However, the author is not an expert in these matters and therefore refrained from giving an extended physical interpretation of the results obtained in the article, but concentrated on confirming the radar data with independent meteorological measurements at coastal weather stations. So, a very preliminary short note on this has been added to the Discussion section (p.14). One can only express the hope that the results obtained will be useful in further studies of the behavior of TCs during landfall in order to improve the reliability of the operational forecast under these conditions.

 

P.S. Thank you for your kind words about the submitted paper.