Review of "China Coastal GNSS Network: Advancing Precipitable Water Vapor Monitoring and Applications in Climate Analysis" by Zhilu Wu et al. April 2025

David K. Adams - dave.k.adams@gmail.com

General Commnents.

I think, in general, this article is very straightforward and should be accepted after some minor corrections. There are a few issues I raise in the paper and I have made lots of small corrections to the English. One thing I would recommend, is to include some yearly timeseries distributions of a couple of sites of PWV from different stations, as in Figure 12, but just for one year so that the reader can have a better idea of the accuracy and general climate in terms of humidity. Also, I thought your limits of PWV maximum and minimum values are a bit extreme (see below)

Specific Comments.

Line 25. You should probably be a bit more precise here instead of just referring to "water vapor". With respect to water vapor as a variable, what is typically most valuable for modeling, weather prediction, global climate studies is its vertical distribution and the total column water vapor or "precipitable water vapor".

Line 32. There have also been numerous field campaigns around the world employing GNSS meteorology, you should mention some from different regions of the world. I will let you choose and make no specific recommendation.

Line 47. Write "Recent research has utilized GNSS ..."

Line 48. What do you mean " project proposing water vapor products from ..." ? This idea is unclear.

Line 74. Write " ...providing reference positions for coastal research..."

Line 87 Write " At the outset, only observations from the GPS and GLONASS satellite constellations were available."

Line 87 Write " In recent years, with the advancement of the Galileo..."

Line 99 Write" ...University (Shi et al., 2008; Liu and Ge, 2003) using the static precise point position ..."

Line 102 Write " and an elevation-dependent weighting function was applied."

Line 110 Write "...ZTD consists of a hydrostatic part..."

Line 111 Write " ...(pressure and temperature) provided by Global Pressure and Temperature...,"

Line 114 This idea is a bit unclear. What do you mean by " Batch least-squares estimator" ?

Line 127 c. Validation of GNSS ZTDs based on ERA5 products

You do not have any local surface meteorological stations collocated or near the GNSS antennas?

You could use these surface met. stations for the surface pressure and to derive Tm with a simple model and then calcuate PWV. This would be good to compare against ERA5 since these ERA5 data are very smoothed in some respect (~ 25km x 25km grid

Line 164 Your PWV limiting values for outliers are very strange (0.72 mm and 86.21mm)

It is not physically possible to have PWV values near 0 nor near 90mm. Even under typhoon/hurricane conditions, the maximum PWV should be near 80mm at the highest. And PWV can never be near 0mm in these region under any conditions.

Line 166 " In addition, a station-specific outlier detection method was employed."

Line 167 " the median PWV value was calculated within a 15-day moving window centered on the specific day." Why do you employ such a long moving window? It is typically hourly or daily change in PWV that is of interest.

Line 182 I would not call ERA5 Numerical Weather model data. It is reanalysis data which include both observations and model output.

Line 240 " Additionally, the quality of the RS profiles may contribute to the larger biases observed."

Another thing to consider is that the RS can be biased if they rise through cloud/rainy conditions leading to higher PWV values than the GNSS PWV which has a large cone of observation ( ~20km diameter) can may contain clear skies in addition to the cloudy/rainy skies. These "saturated" soundings can be easily identified visually,

Line 325 Write "In addition, the spatiotemporal characteristics of coastal PWV in China were analyzed" And again, 0mm PWV values are not possible, there should always be a couple of mm of PWV even in very cold, dry weather in this region.

The manuscript „China Coastal GNSS Network …” submitted by Wu et al. described PWV determination and results for a network of GNSS stations located along the Chinese coastlines. The paper is well written and supported by figures and numbers. Nevertheless, I have some general questions and suggest modifications to improve the draft before submission.

Major questions:

1. The authors processed GNSS data from 55 stations; however, the PVW results are available, but the data and metadata are not. It would be beneficial to get access to the GNSS data and to know whether there are plans to release this important dataset. In any case, I recommend updating the station table in the dataset with more accurate locations (currently roughly at the 10km level), start/end dates, and equipment for the stations.
2. The title contains “climate,” but the authors processed only the years 2009-2019. At least 20-30 years of data are required to derive climate trends. I expect the authors to extend the dataset to 2024 (at least 15 years) or provide a profound explanation if this is impossible.
3. I suggest adding more information to the PWV records in the dataset. Why not provide the inputs taken from ERA4 (Eqn. 3 and 4)? Furthermore, I miss the uncertainty information. This is a minor detail, but I wonder about the different spacing of the PWV values in the dataset (+/—3s). Is there a reason for this?

Minor comments:

1. Is there a particular reason for using the ESA GNSS products?
2. Is there a public source for the radiosonde data? Same for the sea surface temperatures.
3. Provide a consistent description for the GNSS processing with suitable references. A reference to ESA products is missing. The reference for antenna information is outdated. Add the length of the troposphere interval (1h) [l115].
4. I somehow miss the climate aspect of the discussion - the trend estimation against SST covers, to my understanding, seasonal variations.