Review of paper egusphere-2024-2395.

General comments

The paper is interesting and shows a theoretical explanation of passive microwave time series collected over aquifers in Greenland and Antarctica. The text is well written and easy to understand. It opens by introducing the scientific problem, the test sites and relative geophysical parameters, the electromagnetic models used for the analysis. Then it keep on with a suitable description of the results along with a fair discussion about these achievements and the uncertainties in the process. The workflow is fine although I found some major issues in the many assumptions made due to the lack of ground data. Assumption that often are unreferred and somewhat strong. In my opinion this point must be stressed clearly both in the abstract and in the introduction, in order to provide the reader with a clear overview of what will follow. Provided this, the paper is not a breakthrough but a first attempt to understand the relationship between aquifers evolution and microwave signatures although the many assumptions made can weak the reach of the work.

Specific comments

• The main issue of the paper is the lack of ground measurements to be used both in the modelling phase and in the verification of results. This lack has led to many assumptions and has weakened the work. For instance, density and temperature profiles at site 2 are not known and assumed as site FA-13 (line 59), temperature profile and liquid water content are not known for the Antarctic test site (line 64). The aquifer’s liquid water content is let range from 5% to 25% but no reference is provided (line 188, it seems that these values comes from other papers or simulations, not from ground measurements). Also, temperature profile at Wilkins Ice Shelf test site is derived from a model but no references are given (lines 213-215 and 219-223).

The depletion trend of the aquifers is just assumed, and no ground truth is available but the one on April (lines 258-259 and 297) for Greenland and December for Antarctica. Given the work found that the water table level is one of the main drivers of Tb timeseries trend, the water table level must be derived in a more robust way. Maybe from a geophysical model.

The snow temperature profile changes in time due to changes in water level and thermal forcing from above, no details are provided about its modelling (at line 261 is cited just a “squeezed”). For FA-13 the firn permittivity is set to a fixed value corresponding to a given liquid water content (line 279), however no references are provided to justify this geophysical value.

For the second Greenland site, the assumptions are similar to FA-13 but in this case the liquid water content of the aquifer is set to 10% (line 303). No justification is provided for this value.

For the Antarctic test site, the water table level is “adjusted as shown in figure 10” (lines 315-316).

Overall, it seems that the work relies on too many assumptions, in several cases without proper reference.

• In Fig.4 and 5 it is possible to see two temperature profiles, but nothing is said about the day of the year on which they were collected. Considering that the paper analyze a time series of 4 months, the temperature swing in the snow/firn is appreciable and not considered.
• Ice permittivity models from Mätzler 1996 and Tiuri 1984 are appreciably different (line 191). More details should be provided about the use of these models.
• In the simulations it is not cited the inclusion of the temporal temperature swing in the upper layers that, given the shallow thickness of the snow (about 10m) can have an impact on the Tb. And maybe contribute to the “cooling” trend of SMAP Tb.
• Having the model parameterized in section 3.1, a sensitivity analysis is provided in section 3.2. However, given the many assumptions often not referenced, the representativeness of the trends found seems at least questionable.
• At line 397 the paper says “This model eliminates the ambiguities…..where different parameters ae needed to explain ….”. Actually, given the number of assumptions made, this sentence sounds too optimistic.

Minor points

• line 26, there is a red “s” in aquifers.
• line 56, here the second test site is 5km far from FA-13 while at line 298 is 6km. It is better to use a single value for coherency.
• What is the Tb reduction? It is not a common parameter and should be described in the text, not in a table (line 289).
• section 2.1. This section is redundant and the formulation can be found in many books and papers. I strongly suggest removing this section that adds nothing to the discussion and leave just some proper references.
• Figure 3 must be improved, for instance by using inset with large-scale maps, a clearer (lat, lon) grid, etc.
• section 3.1.2 seems misplaced and should be moved close to the model description.
• in line 332 the first “H pol” should be “V pol”
• the panels in figures 10 and 11 should be represented in a unique figure each to ease the comparison of the curves.
• In figure 12, the different limits of y-axes makes the comparison of the two different cases difficult. Better to merge the two panels into one.
• What “the increased water content contributes constructively to the decreased water table depth” means at line 367?
• lines 388-394 are redundant and can be shortened or deleted at all.