the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Aug 2026
Measurement report: Geostationary satellite and ground-based video observations of cloud brightness variations triggered by the 2022 Hunga Lamb wave
Abstract. The eruption of the Hunga volcano on 15 January 2022 generated a Lamb wave, an atmospheric pressure perturbation propagating horizontally at the speed of sound. A recent regional study uncovered variations in the reflectance of liquid clouds triggered by the wave’s temperature perturbations, most notably a transient darkening during the first minor-arc wave passage across the Caribbean. The present expanded analysis—combining ground-based video footage, surface pressure records, and geostationary satellite imagery—reveals that the Lamb wave-induced cloud reflectance variations were globally detectable for ~6 days. Reflectance anomalies traced temperature anomalies on timescales as short as a few seconds to 1 min and persisted at the 2 % level even after 3 days of propagation. The relative magnitudes of cloud darkening and brightening changed upon each crossing of the antipode or the epicenter due to the caustic phase shift. Brightening dominated during the second minor-arc wave passage because of a polarity inversion. The observed lifetime of the Lamb wave compares well with early theoretical estimates.
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Status: final response (author comments only)
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RC1: 'Comment on manuscript by Horváth et al. (egusphere-2026-3997)', Anonymous Referee #1, 30 Aug 2026
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AC1: 'Reply on RC1', Akos Horvath, 07 Oct 2026
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-3997/egusphere-2026-3997-AC1-supplement.pdf
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AC1: 'Reply on RC1', Akos Horvath, 07 Oct 2026
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RC2: 'Comment on egusphere-2026-3997', Shingo Watada, 21 Sep 2026
Review of “Measurement report: Geostationary satellite and ground-based video observations of cloud brightness variations triggered by the 2022 Hunga Lamb wave” by Horváth et al. submitted to EGUsphere
The authors extended the work of Horváth et al. (2025) which studied the Lamb waves from the 2022 Hunga Tonga eruption using geostationary weather satellite multiband imagery. This manuscript includes near source and far-field regional image scans for L1 and up to L4 Lamb wave arrivals, near-field and far-field surface pressure records, and ground-based videos near the source.
The brightness temperature (BT) and reflectance (R) consistently correlated with the local pressure variations positively and negatively, respectively. Second time derivatives of BT and R are always remarkably anti-correlated. This manuscript collectively documents the Lamb waves captured by the geostationary weather satellites.
One thing I would like to emphasize is the cause of the asymmetry of L1 (and all following L-waves). The Green’s function of a point source in a 2D space, either on the plane or on the sphere, has a tail, unlike Green’s functions in 1D and 3D spaces which lack this feature. I agree that there is a tail caused by nonlinear gas dynamics as described in Appendix A, but the tail here is a different origin. The origin of tail is \pi/4 phase advance of the 2D Green’s function, i.e., in all frequencies, at one wavelength away or more from the source, the wave phase advanced by \pi/4 compared to the phase of waves traveling over a source-station distance with a constant phase speed of the wave. The phase shift typically appears as far-field asymptotic forms of the Bessel function (or the Hankel function) as \sqrt{2/\pi k r}\cos{(kr - \pi/4)} on a plane and Legendre function as \sqrt{2/\pi (n+1/2)\sin \theta}\cos{((n+1/2)\theta -\pi/4)}. The polar phase shift \pi/2 is added to this initial phase \pi/4 at every passage of the poles (at source and antipode). L1 wave is advanced by \pi/4, L2 wave 3\pi/4, L3 wave 5\pi/4, L4 wave 7\pi/4, so on. These phase advances are the same for all frequencies and change the waveforms to be asymmetric in time.
Specific comments
1) L 96 I cannot access Data S1 in the Supplement. Where is Data S1?
2) L 108-115 This paragraph requires corrections and the description of the initial phase shift of \pi/4, which I wrote in the general comment above.
3) Figure 2, Line 185-188 The pressure peak and the energy peak of L1 wave are marked at the same timing. Because the phase of L1 wave advanced by \pi/4, the pressure peak and the energy peak (or envelope of the entire L1 wave) arrive at different times. The difference reflects the \pi/4 phase advance. If you compute the envelope of entire L1 pressure wave, you will see the envelope peak is behind the pressure peak. Please label the P_peak and E_peak of L1 wave at different times reflecting the \pi/4 phase advance. Also, timing of L4 P_trough, E_peak labels should reflect the 7\pi/4 phase advance.
4) L 258 paroxysmal means something to start and stop abruptly and repeatedly. Do you really mean the Hunga Tonga explosion to be paroxysmal? If not, please think moving or rephrasing paroxysmal.
5) L 261 Tongatapu is not a point but a finite area. The interchangeable use of "Tongatapu" and "Nuku’alofa" confuses readers. We know"Nuku’alofa" means a video in Tongatapu. But "Tongatapu" means an island with a width of 20 km. All "Tongatapu"s at L79, L261, L283, L238, L264, L354, L356, and L938, refer to the video recorded at Nuku’alofa. Can you useNuku’alofa instead of Tongatapu at these lines?
6) L 340 What are the "project times"? What does HH:MM:SS mean? since when? Does it different from video frame times in Figure 4?
7) L348 How does Figure 5 depict the blue (B) remain constant? I do not see blue plot in Figure 5.
8) L353-354 "which reached Tongatapu a few minutes later at ~04:33 UTC" confused me. The Figure 4 caption says that "camera in Nuku'alofa Tongatapu" indicating Nuku'alofa and Tongatapu are at the same location. Please describe the detailed location information of Nuku'alofa within the Tongatapu Island to avoid confusion among readers.
9) L355 “at 05:07–05:08 UTC (Fig 2) Considering a ~45 min travel time to Nu’uuli (assuming a phase speed of 315 m/s)” In this traveltime estimate, do you consider the phase advance of \pi/4? at Nu'uuli? If the wave period is short, less that one minutes, we can ignore the phase advance.
10) L429 Where is Supplement Animation 1?
11) L429 “channel 2 reflectances” What is the wavelength of channel 2 of GEOS-17 ?
12) L495 Again where is Supplement Animation 2?
13) L798-799 “trough–peak–trough sequence“ L4 wave has a 3\pi/2 wave advance relative to the L1 wave. Please remember that the L1 wave has a \pi/4 advance in all frequencies so the shape of L1 wave not time symmetric, even for a simple point source. Therefore, L4 wave phase advanced 7\pi/4 which makes the waveform “trough–peak–trough sequence“ asymmetric in time.
14) Figure 14. Current timing of P_trough and P_peak labels are as if the waveforms are symmetric in time. These L4 wave should reflect 7\pi/4 phase advance so the waveforms are not symmetric in time, but the phase advance 7\pi/4 is difficult to be noticed in the Figure 14.
15) L881 The climatic eruption phase of the 1991 Pinatubo volcano unrest continued for at least a few hours (e.g. Watada and Kanamori 2010). The prolonged source time function with a lower source intensity makes the detection of L2 and L3 waves difficult compared to the 2022 impulsive Hunga Tonga source.
Citation: https://doi.org/10.5194/egusphere-2026-3997-RC2 -
AC2: 'Reply on RC2', Akos Horvath, 07 Oct 2026
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-3997/egusphere-2026-3997-AC2-supplement.pdf
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AC2: 'Reply on RC2', Akos Horvath, 07 Oct 2026
Data sets
NOAA GOES-R Series Advanced Baseline Imager (ABI) Level 1 Data NOAA https://registry.opendata.aws/noaa-goes/
High Rate SEVIRI Level 1.5 Image Data - MSG - 0 degree EUMETSAT https://user.eumetsat.int/catalogue/EO:EUM:DAT:MSG:HRSEVIRI
Geo-KOMPSAT-2A (GK2A) Advanced Meteorological Imager (AMI) Meteorological Satellite Data Korea Meteorological Administration https://data.kma.go.kr/data/rmt/rmtList.do?code=21&pgmNo=683
National Centers for Environmental Information (NCEI) ASOS https://www.ncei.noaa.gov/data/automated-surface-observing-system-one-minute-pg2/
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In a single sentence, the manuscript provides a thorough characterization of the atmospheric waves that kept circling the Earth for a few days after an unusually powerful volcano eruption.
I found the paper not only informative, scientifically sound and valuable, but, at parts, outright fascinating to read. I appreciated the well-presented results and the clear explanations, and even the highly relevant and helpful YouTube videos referenced in the paper.
A key strength of the study is its comprehensive, integrated approach: It combines observations from multiple sources (ranging from ground-based cameras and barometers to imagers on multiple satellites) and examines multiple effects of the atmospheric waves (their impacts on atmospheric pressure, and on the reflectance and brightness temperature of clouds). It also includes clear and reasonable physical explanations for the observed behaviors.
While I have a high opinion of the manuscript and I believe it is worthy of publication, I still recommend a few minor refinements. Please find my specific comments below.
Line 90: It would be helpful to explain in a few words what minor arc and major arc passages are (e.g., waves reaching a point along the short or the long way, covering less than or more than 180°, etc.).
Line 103: I recommend deleting the comma after “method”.
Line 111: It would help to explain briefly how exactly the frequency of a Lamb wave is calculated. Is it perhaps 1 over the time difference between the two minimums (before and after the main peak) in Figure 2, or is it something else?
Line 289: I recommend inserting the word “white” in front of “arrow”, as the arrow in the figure is white (and not black, as the illustration in Line 289 suggests).
Figure 3: The times after 05:07 UTC mentioned in the caption don’t appear in the figure. Perhaps some figure panels are missing, or some time values are mistaken? Also, it would help to change the color and/or the pattern for two of the three ovals that are shown with a dotted red line (1st and 2nd peaks and recovery), just to avoid confusion and to make the identification easier. For example, using green or orange colors and/or using dashed lines could work. (Of course, the main text should be updated accordingly, for example in Line 337.)
Lines 964-965: Clicking on the links to the supplements does not seem to work for me.