| 10 Mar 2026
Modifying Windsonds to Improve In-Storm Measurements
Abstract. Obtaining reliable thermodynamic and kinematic profiles from within severe convective storms presents a challenge for radiosondes due to the extreme conditions to which the instrumentation is exposed. The Windsond S1 has emerged as a popular tool for severe storm research; however, exposure to heavy precipitation has been recently documented to cause relative humidity (RH) sensor malfunctions, limiting the reliability of in-storm measurements. We introduce modifications to the Windsond S1 design that limit water ingress and thereby mitigate these issues. The modifications include a redesigned radiation shield that blocks falling raindrops while maintaining adequate ventilation, a stabilizing support arm, and a tether seal. Controlled experiments using irrigation-generated precipitation at approximately 300 mm hr-1 demonstrated that unmodified sondes experienced RH sensor failures, suppressed RH variability, and power failures due to water ingress, while modified sondes remained functional throughout the exposure to the extreme rain rate. Validation profiles comparing modified and unmodified sondes launched under varied atmospheric conditions, including nocturnal flights, showed temperature differences of typically less than 1 °C and RH differences less than 10 %, with no systematic biases introduced by the modifications. These design improvements were applied to an extensive number of Windsonds S1 during the 2025 ICECHIP field campaign for in-storm deployments. Tested modifications to the Windsond S1 require minimal expertise to implement. Further, design files have been made publicly available to support the broader severe storms research community.
Overall Comments:
This is a fantastic and well written paper that highlights a major observational challenge for an actively used instrument. This type of work is critical to ensuring that observations are accurately representing the intended environment. The paper is well reasoned and laid out naturally, showing the process through which the authors identified the problem and solved it. I have only a few monitor comments that should be easily addressable, and I commend the authors on writing an excellent paper.
Specific Comments:
1). The authors provide a figure showing the modifications, but there is little/no description on how the modifications should be attached or if there are specifics to avoid while doing so. More details should be added, even if brief, that describe the process of putting the modifications on so that an average user following this would know how to use the modifications.
2). The authors mention sealing the top lid with a hot glue to prevent water intrusion. Would this not also disable the ability of the sonde to cut the balloon?
3). Lines 123-124 - when describing the second test (the pendulum), there is not that only a single modified sonde was used. Is there justification for not doing this test with both a modified and unmodified sonde? I imagine the thought is that test 1 showed that water intrusion happens, but it's possible that the additional motion of the unmodified sonde could actually reduce water errors in some cases. Potentially not the intrusion, but with holding water on the sensor the added motion could help to dislodge and remove water from the sensor head, thereby reducing errors in this situation.
4). A theme throughout the tests presented that I noticed is that there is no external reference sensor being used. Ideally, a trusted 3rd, non-Windsonde sensor would've been placed in or near the environment to provide a ground truth observation point. As it stands, the experimental setup assumes that the modified windsonde is absolute truth, which may or may not be accurate. If there are still sensor errors being caused even with the modifications, it is impossible to tell without an independent observation. I doubt this information is available at this point, so this is more of a note for future tests and potentially an acknowledgement in the text that this is the assumption being applied.
5). Quick succession launches not on the same instrument train can have wildly different flight trajectories and experience different environments, particularly in convective environments where small spatial changes can result in large thermodynamic changes. The authors do explore the spatial differences between sondes in their analysis, but I think it's worth marking the individual flights as to whether they were on the same instrument train or not.
6). A note on solar radiation corrections - these are typically applied ALL the time. For other radiosonde companies, they cannot tell for example whether you are in cloud or not in cloud and whether the correction should or should not be applied. Generally speaking, I am familiar with one company at least that takes into account altitude, lat/lon position, time of day, time of year, etc. to calculate the solar radiation correction, but that correction is applied even if its going through a thick, sun blocking cloud. This presents problems as applying the solar radiation correction for example when under cloud and not in sunlight, will cause a negative temperature error. This is relevant as the DU1 flight showed a negative temperature bias (in full sun), whereas IPO21 showed a positive temperature bias in partly cloudy conditions. While not consistent between the cloudy vs sunny cases, I do wonder if the modifications made to the sonde have altered the solar radiation behavior and therefore are introducing additional errors when the solar radiation correction is applied. This would presumably manifest differently depending on the conditions.
Technical Corrections:
Line 25 - I would include a reference or point here to link back to Sparv for readers unfamiliar with the product or company, and to reference the company for their work.