Climatology of Planetary Boundary Layer Height-Controlling Meteorological Parameters Over the Korean Peninsula

Round 1

Reviewer 1 Report

The authors have well addressed my comments. 

Reviewer 2 Report

Dear Authors,

I do not have any additional comment on the paper. You have modified it according to previous comments. In my opinion it can be published.

 

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments on “Climatology of planetary boundary layer height- controlling meteorological parameters over the Korean peninsula”

This study examines the planetary boundary layer (PBL) height in the Korean peninsula using ERA-Interim reanalysis data and sounding and Global Positioning System Radio Occultation (GPSRO) datasets. This work provides some evidences for us to understand the atmospheric boundary layer. However, I have some major and minor concerns on this study.

1. The study used ERA-Interim reanalysis data to calculate the PBL height using the bulk Richardson number. Because a higher-quality product ERA-5 has been released, I would suggest the authors to use ERA-5, which provides hourly product and a spatial resolution of 0.25 degree.
2. It is desirable to examine the PBL height in different surface features. For instance, what would be the differences in PBL height between urban and rural areas? If so, why? Is it because of urban heat island effect?
3. The authors analyze the linear trend in PBL height during 2008-2017. This is a way too short period to examine trend in time series. Because the ERA-5 data can date back to 1979, can the authors examine the linear trend during 1979 to present, rather than 2008-2017?
4. Lines 21-24: “The variability of the PBLH with respect to temperature, relative humidity, surface pressure, wind speed, lower tropospheric stability, and surface fluxes was also examined. The growth of the PBL was high in spring and southern region due to the low soil moisture content of the surface.” Please add more discussions on how low soil moisture content of the surface can increase the PBL height. It is really important for us to understand the mechanisms. Instead of using time series, could the authors plot the spatial patterns of temperature, relative humidity, surface pressure, wind speed, lower tropospheric stability, and surface fluxes?

Minor comments:

Line 24-26: “The increasing trends of the surface temperature and PBLH were observed from 2008 to 2017 that may due to climate change.” This sentence is grammatically wrong. Moreover, this argument is not supported by any evidence. I would suggest the authors to remove this sentence.

Line 62: De Wekkere et al. [18]

Lines 104-105: “to describe the variability of PBLH and surface temperature due to climate change for the 10 years period” It doesn’t make any sense to examine any impacts of climate change during a ten-year period.

Author Response

Thank you for your thoughtful comments.

Please see the attachment for detailed response.

Author Response File: Author Response.pdf

Reviewer 2 Report

This study presents the spatial and temporal variability of the planetary boundary layer height (PBLH) over the Korean peninsula from 2008 to 2017 by using ERA-Interim dataset and investigated the correlation between PBLH and several climatology variables (e.g., temperature, relative humidity, pressure and wind speed). The authors comprehensively examine the characteristics of the PBLH in their study area. However, several major points listed below should be addressed to make a thorough revision.

1. The authors validated the PBLH derived from ERA with sounding datasets over four different geographical locations, and then presented the spatial and temporal variation of PBLH over Korean peninsula. The authors should carefully evaluate the bias of terrain height and pressure levels of ERA-Interim datasets with four sites, which largely influence the validation results of PBLH. Orographic correction is necessary. Since the ERA5 datasets have been proposed with finer spatial resolution (0.2525) and hourly temporal resolution, I suggest the authors replace the ERA-Interim datasets by ERA5 datasets.
2. It is quite misleading that the authors validated the ERA PBLH calculated by bulk Richardson number against the PBLH derived from GPSRO measurements with different algorithm (the minimum gradient of the refractivity). Henncmuth et al. (2006) had reported that using the minimum gradient of the refractivity methodology would have large bias when inversion layer exists. I wonder whether the authors considered different thermo-dynamics stabilities when comparing ERA with GPSRO and the accuracy of GPSRO PBLH over Korean peninsula or other regions with similar characteristics should also be shown in this study.
3. There should be some details (number of soundings, elevation, data period) and some statistics for the timing and height of PBL at different sounding sites. Did the authors eliminate erroneous and rainy cases for quality-control of the sounding data?
4. Air pollutants is very important for the development of the PBL. Some discussions about this issue is missing.
5. The authors explained the Bowen ratio influence soil moisture. However, they did not explain the mechanism on how soil moisture influence PBLH.
6. The authors analysis the relationship between PBLH and the surface temperature, relative humidity, wind speed, lower tropospheric stability (LTS), Bowen ratio, surface sensible heat, latent heat. The contribution of different controlling factors should be given, and the most dominant factors should be pointed out.
7. For figure 9 and 10, statistical significance at 95% or 99% confidence level should be added. The Spearman rank-order correlation method can be used for the statistical test.
8. I suggest the authors combine Figure 6 and 7, where the PBLH is set to the left y-axis. Surface sensible heat flux, latent heat flux T, RH, wind speed, LTS and ozone mixing ratio are set to right y-axis, respectively.
9. Tables 1-4 should be re-organized.
10. Why there are white blank at the right side in Figures 2, 4 and 8, since ERA and GPSRO datasets cover the entire globe.

Author Response

Thank you for your thoughtful comments.

Please see the attachment for detailed response.

Author Response File: Author Response.pdf

Reviewer 3 Report

The paper is well written with figures sufficient to illustrate the conclusions. Suggest acceptance in present form.

Author Response

Thank you for your thoughtful comments.

Please see the attachment for detailed response.

Author Response File: Author Response.pdf

Reviewer 4 Report

General comments

The authors analyzed the height of the planetary boundary layer (PBL) over the Korean peninsula using the ERA-Interim dataset of the ECMWF. They compared the PBLH determined with the ERA data with those obtained with the GPSRO data and with the bulk Richardson number applied to vertical soundings, finding a satisfactory agreement. Then they estimated the PBLH for the decade 2008-2017 in order to get climatological information and understand typical trends.

The topic of the paper is important, but I believe that additional work is needed on the manuscript before its possible publication.

I’m not an English mother tongue, but I would suggest checking the English language because some parts of the manuscript are not easily readable. Some sentences seem to be incomplete.

My comments are detailed below.

Detailed comments

• Line 64 and line 66: It is caused or causes?
• Lines 62 and 69: De Wekkere or De Wekker?
• Line 97: approximately
• Line 126: All the variables are well known, but LTS. Please introduce LTS. How is it defined and measured? This also helps interpreting figure S4.
• Line 142: "were" not needed.
• Line 144: PBLH in title 2.2, not PBL.
• Line 150: provides.
• Lines 146:157: The various methods could be presented as a bullet list. Also, the sentences explaining some methods are too synthetic, few words should be added to improve the explanations.
• Line 158: I do not fully understand this sentence. Typically, cloudy conditions are associated to low solar radiation and stable situations (e.g., E and F Pasquill Gifford classes, or large values of the Monin Obukhov length L). Therefore, why the authors associate "turbulent" and "cloudy conditions"?
• Line 159: "it is" or "it has been"?
• Lines 162-163: Please check the sentence "The Ri ... estimation". It does not seem complete. A verb is probably missing.
• Lines 167-168: 1) Add "that" after "level". 2) Use "represents" in place of "represent".
• Lines 168-170: Do the authors mean that they evaluated Ri for all the z values within the range from 10 m to 4 km in order to find PBLH?
• Line 170: Add a comma after Davy. As an alternative, use the corresponding reference number.
• Lines 171, 174, 176: Please use always "6-hour"
• Line 172: computed
• Line 175: Seasons names should not require capitalization. Please use small initial letter for summer, as done for the other seasons.
• Lines 174-175: Please remove the article ("the") before "winter" and "spring".
• Line 179: No need to specify that the PBLH is not above the msl, it is typically above ground level.
• Lines 180-182: My impression is that the approach would be more clear using this sentence: "We validated the PBLH values estimated from the ERA data with those derived from the sounding measurements using the bulk Richardson number". The sentence "The similar Ri ... PBLH estimation" could be deleted.
• Line 184: consists
• Lines 185-187: Please review the sentence. "showed that" or just "showed"? Moreover it should be "observations,", not "observations;"
• Line 188: "were matching reasonably well" or "has given satisfactory results"?
• Line 191: "that" should be deleted.
• Line 192: produces
• Lines 195-196: a correlation of 0.74
• Line 197: Is "determined" the correct word here?
• Figure 2a: Would it be possible to add the number of points in each plot?
• Figure 2b. Is "continued" needed ?
• Lines 209-210: Sentence not clear. "that" should be deleted. Moreover, Figure 3 shows the seasonal variability, where do we see PBLH at 15 LT in such a figure?
• Line 214: "The reason ... the mountains". Please re-write the sentence because it is not clear.
• Figure 3 shows that PBLH is never lower than 1 km, in fact the lowest outlier in Pohang is about 1 km. It seems strange to me because in my experience PBLH could be as low as 100 m, or lower, in strong stability conditions (for example during the night).
• Line 221: Figure 4, not figures.
• Line 234: created
• Lines 237-238: Actually, it is the low solar radiation that causes low temperatures, not the opposite. Do you mean "produced by low insolation"?
• Line 248: produces
• Line 249: given
• Line 259: High wind speeds cause intense mechanical turbulence, not intense convection. Intense convection is present when there is high solar radiation. Consider for example the definition of the Monin Obukhov length.
• Line 260: Please review the sentence.
• Line 261: How is this instability defined? Is it the atmospheric stability used in dispersion modeling?
• Line 275: "at>2 km" should be "at heights greater than 2 km".
• Lines 280-281: "(figure not shown) represent the moisture content of the soil": this part of the sentence is not clear.
• Figure 5: Values lower than 500 m are shown in this figure. Shouldn't these values appear also in figure 3 for the summer trend?
• Line 287: Please add at least a reference for this statement ("It is known ...").
• Line 288: "are presented" should be "present"; "causes" should be "cause"
• Line 296: Figure 7 shows higher wind speeds at low latitudes, while the mountains are at high latitudes. So, probably I do not understand the second part of the sentence.
• Line 299: Why aerosol layer used for ozone layer? (ozone is a gas).
• Figure 7: Why the WS values higher than 6 m/s in winter are not shown for latitudes 32-34?
• Figure 7: Why there are no fluxes below 34N ?
• Line 321: "... insolation, then it gradually decreases ...".
• Line 324: Define the PBLH grow rate (for example, PBLH variation over time variation?). Also specify its units (m/h?).
• Lines 326-327: Please review the sentence (The surface ... on the surface).
• Line 327: "supports" --> "support"
• Lines 329.330: Please review the sentence.
• Line 331: "high growth" or "highest growth"?
• Line 331: "is higher" --> "are higher"
• Line 332: Check the sentence: it seems to me that we need something between "region" and "that".
• Figure 8: Add the units of the grow rate.
• Line 338: Please modify in "... correlation (R) and standard deviation (SD) ...", so that R and SD in Tables 1-4 are defined.
• Lines 344-345: "These ... enhancement". This sentence is not clear to me. I agree that high wind speed generate mechanical turbulence and high solar radiation generate convective turbulence. Both the two types of turbulence have the effect to increase the PBLH. Also, a high PBLH favors the atmospheric dispersion of pollutants. I do not understand why the authors have reversed the logic: it is not the pollutant transport caused by winds that increases the PBLH.
• Line 347: As already written, please define LTS and its physical meaning. The atmospheric stability may be indicated with the Pasquill Gifford stability classes, or with the Monin Obukhov length. Is LTS related to one of these two variables?
• Tables 1-4: They should be formatted differently, otherwise numbers are not clearly readable.
• Lines 360-361: Those factors actually control the PBLH evolution, not "may control". Also please use a small initial letter for temperature.
• Lines 362-363: "The ... PBLH", sentence not clear.
• Lines 363-365: "Further ... enhancement", as already written, as far as I know, it is the mixing layer height that influences the pollution levels, not the opposite.
• Lines 365-368: The sentence is not clear.
• Lines 376-377: "The strong ... Figure S2)", this sentence seems not complete.
• The whole paragraph 3.5 must be rewritten because there are many unclear sentences.
• Lines 394-395: "The ... winter", the sentence must be reviewed.
• Lines 400-401: Please review the sentence.

Author Response

Thank you for your thoughtful comments.

Please see the attachment for detailed response.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I appreciate the authors to address my comments. However, I am really not satisfied with the revision in terms of reanalysis data. We have a new product (ERA5) freely available and with higher quality in many aspects (e.g., boundary-layer dynamics). Why don't we use new product to replace the old and out-of-date products? In addition, there is high-quality MERRA2 reanalysis products that cover the study period. Please be more critical about the research findings. I don't think there is really a time frame in performing high-quality and cutting-edge research.

Reviewer 2 Report

This

This study presents the spatial and temporal variability of the planetary boundary layer height (PBLH) over the Korean peninsula from 2008 to 2017 by using ERA-Interim dataset and investigated the correlation between PBLH and several climatology variables (e.g., temperature, relative humidity, pressure and wind speed). The authors comprehensively examine the characteristics of the PBLH in their study area. However, several major points listed below should be addressed to make a thorough revision.

1. The authors validated the PBLH derived from ERA with sounding datasets over four different geographical locations, and then presented the spatial and temporal variation of PBLH over Korean peninsula. The authors should carefully evaluate the bias of terrain height and pressure levels of ERA-Interim datasets with four sites, which largely influence the validation results of PBLH. Orographic correction is necessary. Since the ERA5 datasets have been proposed with finer spatial resolution (0.2525) and hourly temporal resolution, I suggest the authors replace the ERA-Interim datasets by ERA5 datasets.
2. It is quite misleading that the authors validated the ERA PBLH calculated by bulk Richardson number against the PBLH derived from GPSRO measurements with different algorithm (the minimum gradient of the refractivity). Henncmuth et al. (2006) had reported that using the minimum gradient of the refractivity methodology would have large bias when inversion layer exists. I wonder whether the authors considered different thermo-dynamics stabilities when comparing ERA with GPSRO and the accuracy of GPSRO PBLH over Korean peninsula or other regions with similar characteristics should also be shown in this study.
3. There should be some details (number of soundings, elevation, data period) and some statistics for the timing and height of PBL at different sounding sites. Did the authors eliminate erroneous and rainy cases for quality-control of the sounding data?
4. Air pollutants is very important for the development of the PBL. Some discussions about this issue is missing.
5. The authors explained the Bowen ratio influence soil moisture. However, they did not explain the mechanism on how soil moisture influence PBLH.
6. The authors analysis the relationship between PBLH and the surface temperature, relative humidity, wind speed, lower tropospheric stability (LTS), Bowen ratio, surface sensible heat, latent heat. The contribution of different controlling factors should be given, and the most dominant factors should be pointed out.
7. For figure 9 and 10, statistical significance at 95% or 99% confidence level should be added. The Spearman rank-order correlation method can be used for the statistical test.
8. I suggest the authors combine Figure 6 and 7, where the PBLH is set to the left y-axis. Surface sensible heat flux, latent heat flux T, RH, wind speed, LTS and ozone mixing ratio are set to right y-axis, respectively.
9. Tables 1-4 should be re-organized.
10. Why there are white blank at the right side in Figures 2, 4 and 8, since ERA and GPSRO datasets cover the entire globe.

Reviewer 4 Report

General comments

The English language of the paper has been improved, and it is now more easily readable.

I still have some observations:

• Space between words is sometimes missing (e.g. Line 19 “inPBLH”, line 99 “approximately1”, line 240 “between1.4”, line 244 “percentilesof”, line 248 “4also”, …). The authors should check the whole manuscript and separate words when needed.
• Lines 33-34: The authors write: “PBL patterns are also influenced by atmospheric conditions, topographic features, and agricultural practices”. Is “agricultural practice” the correct term or do the authors mean “land use” or “land cover”. For example, PBLH may be different over water, over urban surfaces, and over desert surfaces, but these surfaces have nothing to do with agricultural practices. (The sentence was present in the original version of the paper, I’m sorry I did not notice it before).
• Line 66: I still do not agree with the sentence “high PBLH over mountains is caused by dispersion of air pollutants…”. Actually, high PBLH values favor the dispersion of air pollutants. I also checked the Lieman and Alper paper, and they write (soon after their figure 11) “Another point to mention is the major effect that changes in PBL height may have on the dispersion of air-pollution”. Again, few lines later “Fig. 13 … shows how the mixing layer aloft generated by the mountain strongly influences the PBL height and consequently the dispersion of air pollutants…”. Therefore it is not the PBLH which is caused by air pollutants, on the contrary, it is the PBLH which has effects on pollution levels.
• Line 302: Separate the two numbers within the parenthesis.
• Lines 338-342: It seems to me that there is a mixing between causes and effects. The presence of complex orography creates upward forcing which, together with convective turbulence, increases the PBLH. Then, pollutants may mix within this increased PBLH.
• Line 349: OZ has been defined as the ozone mass mixing ratio (lines 333-334), and ozone is a gas, not an aerosol. Not clear why the authors use “aerosol layer (OZ)” now.
• Figure 7, bottom part. The authors should mention somewhere in the text that flux data below 34N are not reported because MERRA 2 provide them only for land regions.
• Lines 365-366: The last sentence of figure 7 caption (“However … LT”) is not clear.
• Lines 375-376: High wind speed is responsible for surface forcing (i.e., mechanical turbulence), it does not support convection, which is due to solar radiation.
• Lines 412-413: If emissions remain constant, an increase in PBLH causes a decrease in pollution levels. In fact, a PBLH increase has the effect to increase the volume where the pollutants can be mixed, then, with the same mass of pollutant emitted, the concentration decreases. Therefore, the increased pollution described in the KMA reports may be due to increased emissions or to other reasons, not to increased PBLH.
• Table 5: A single decimal would be enough for PBLH and T.