{"id":"b09567d1-072c-44a8-9bdb-8fc6ea461466","arxiv_id":"2412.06608","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"Ground and satellite data show equatorial plasma bubbles spilled into mid-latitude Europe during the June 2015 storm, producing multi-scale GNSS scintillations over the Iberian Peninsula and Canary Islands.","lead":"This paper uses GNSS receiver data to show that equatorial plasma bubbles spilled over into southern European skies during the June 2015 geomagnetic storm, producing radio scintillations over Portugal, the Canary Islands, and the Mediterranean. It combines ground and satellite measurements to map where small- and medium-scale ionospheric disturbances appeared and moved.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"EPB identification rests on an unvalidated proxy: at the key 01:00 UTC June 23 Swarm pass, the bubble index lies between 0.5-degree TEC-gradient maxima, so gradient/ROTI/S4 co-location alone cannot prove a plasma-bubble source.","rationale":"The reader's weakest assumption matches my main concern: the interpretation of S4, ROTI, and spatial TEC gradients as EPB boundaries is imported from prior low-latitude work, and the Swarm PBI, the only direct bubble indicator, fails to align at the critical 01:00 UTC June 23 pass. Since the paper itself acknowledges that the 0.5-degree maps may be too coarse to resolve the structures identified by Swarm, the central attribution to spilled-over EPBs is less secure than the multi-instrument consistency suggests. This is a gap in independent validation rather than an internal contradiction, so it does not justify rejection. The event is well documented, the data streams are multiple, and the qualitative agreement among S4, ROTI, gradients, and sTEC drops is real. My proposed test would settle the question by using raw Swarm Ne measurements instead of the precomputed PBI product, avoiding circularity, and by checking quantitative consistency with the reported sTEC drops. Until such a test is done, a CONDITIONAL verdict remains appropriate, and my read does not change the reader's verdict.","tokens_in":19037,"tokens_out":5060,"duration_ms":57864,"concrete_test":"Use the raw Swarm A/C Langmuir Probe Ne data for the 23:06 UTC June 22 and 01:00 UTC June 23 descending passes. Identify plasma depletions with a fixed threshold (Ne below a quiet-day median by more than 50% over at least 0.5 degrees of latitude) and compare depletion centroids and widths with the maximum dTEC ridges, ROTI maxima, and the IPPs of the sTEC drops shown in Figures 19-20. Also estimate the sTEC decrease implied by the observed Ne depletion depth and a plausible vertical extent, and check whether it is consistent with the reported 30-50 TECu sTEC drops. If the depletions are not co-located, or if the implied sTEC decrease differs by an order of magnitude, the EPB attribution is unsupported.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim is that the June 22-23, 2015 disturbances over the Iberian/North Atlantic sector were caused by spilled-over equatorial plasma bubbles, not by non-EPB storm-time irregularities. The decisive link is the assertion that high spatial TEC gradients in 0.5x0.5-degree, 5-minute DRAWING-TEC maps mark EPB boundaries. That mapping is imported from a low-latitude Brazil climatology [33] and is not independently validated for this mid-latitude storm event. More importantly, the only direct in-situ bubble detections are sparse and not consistently aligned: of six Swarm PBI events, the authors use two, and Section 4.3 states that on June 23 at 01:00 UTC the Swarm PBI lies between the areas of high TEC gradients and high ROTI, with the authors attributing the mismatch to map resolution. On June 22 at 23:00 UTC the PBI coincides with gradient maxima but not with ROTI-map maxima. Thus, at the only two times an in-situ bubble indicator is available, the proxy and the direct evidence do not align consistently. If the observed S4/ROTI/gradient complex instead reflects storm-time MSTIDs, storm-enhanced density boundaries, or locally generated irregularities, the spill-over interpretation would fail even though every index responds. The paper does not provide an independent check, such as raw Swarm Ne depletion profiles, airglow, or ionosonde observations, that the structures are plasma bubbles advected from low latitudes.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper analyzes the ionospheric response to the June 22-23, 2015 geomagnetic storm over Southern Europe and the Eastern North Atlantic, using 1-minute S4 from three receivers, ROTI from ground receivers and DRAWING-TEC maps, spatial TEC gradients, GIX/NeGIX/TEGIX indices, and the Swarm ionospheric plasma bubble index. It reports scintillations (S4>0.5) at Lisbon, Tenerife, and Lampedusa, with associated ROTI enhancements and steep TEC gradients, and interprets these as the signature of equatorial plasma bubbles (EPBs) spilling over from low latitudes and drifting north-westward. The paper concludes that storm-time mid-latitude irregularity activity in this sector originated from low-latitude plasma structures rather than from local or high-latitude processes alone.","tokens_in":19336,"tokens_out":5319,"duration_ms":50302,"significance":"If the EPB spill-over interpretation is correct, this is a valuable case study of a rare and operationally important phenomenon, with direct implications for GNSS integrity in the EGNOS region. The paper's strengths include the use of multiple independent data streams, the open availability of the S4 data and supplementary animations, and the transparent reporting of mismatches between Swarm PBI and the ground-based proxies. However, the central attribution to EPBs rests on an unvalidated mapping of TEC gradients to EPB boundaries, imported from a low-latitude climatology, and on only two post-hoc selected Swarm detections, one of which is misaligned with the ground-based signatures. These limitations currently leave the spill-over interpretation plausible but not firmly established.","major_comments":[{"comment":"The identification of the observed irregularity structures as EPB boundaries relies on the assumption that high spatial TEC gradients in the 0.5°×0.5°, 5-minute DRAWING-TEC maps mark EPB edges, an assumption imported from the low-latitude Brazil climatology of [33]. This mapping is not independently validated for this mid-latitude storm event. The paper's own data show inconsistent alignments: on June 23 at 01:00 UTC the Swarm PBI lies between the high-gradient/high-ROTI areas, and on June 22 at 23:00 UTC the PBI coincides with gradient maxima but not with ROTI maxima. The authors attribute the June 23 mismatch to map resolution, but they provide no test of this explanation. Please add an independent check (e.g., raw Swarm Ne depletion profiles, airglow, or ionosonde data) or explicitly weaken the EPB-boundary claim.","section":"Section 4.3"},{"comment":"Statements such as \"Spatiotemporal patterns of the variations of the scintillation indices and TEC gradients are very well correlated\" and \"the results agree with the Swarm PBI detections\" are made without any statistical quantification. Since the co-location of S4, ROTI, and TEC gradients is the main evidence for the EPB interpretation, the paper should provide quantitative measures (correlation coefficients, coincidence rates, or significance tests) for these comparisons, including for the two Swarm PBI events.","section":"Sections 4.3 and 5"},{"comment":"The Swarm PBI confirmation is based on only two events selected post-hoc from six detections, with four excluded as too far east or west. One of the two used events (June 23 01:00 UTC) does not align with the ground-based proxies. This selection and the small sample size substantially weaken the claimed confirmation. Please report all six detections with their positions relative to the ground-based disturbance, or discuss explicitly how the selection affects the strength of the confirmation.","section":"Section 2.3"},{"comment":"The resolution of the DRAWING-TEC maps (0.5°×0.5°, 5-minute, further averaged to 15-minute) is coarse compared with the Fresnel-scale irregularities that drive S4 (a few hundred meters) and with the few-kilometer scales associated with ROTI. The authors themselves note in Section 4.3 that the structures may be smaller than the map resolution. It is unclear how gradients computed at this resolution can resolve EPB boundaries, and whether the observed gradient features are robust against the map interpolation. Please provide a resolution analysis or a sensitivity test, and state explicitly what scales the gradient maps can resolve.","section":"Sections 3.2 and 4.3"},{"comment":"The alternative explanation that the observed S4/ROTI/gradient complex reflects storm-time MSTIDs, storm-enhanced density boundaries, or locally generated irregularities is not tested. Given the unvalidated gradient-to-EPB mapping, the paper should at least discuss observable discriminators (e.g., propagation direction, altitude extent, spectral characteristics) and explain why the EPB interpretation is favored over these alternatives.","section":"Sections 4 and 5"}],"minor_comments":[{"comment":"The manuscript contains several typographical errors, including \"sideral\" for \"sidereal\" (Section 3.1.2 and the caption of Figure 2) and \"IPBs\" for \"EPBs\" in Section 4.4.","section":"Throughout"},{"comment":"The figure numbering is inconsistent: Figure 22 appears before Figure 18 in the text, and the text references \"Fig. 18\" after discussing Figure 22; please renumber the figures in order of first appearance.","section":"Figures"},{"comment":"In the reference list, there is a stray text \"Rea2023\" before reference [10], and reference [24] duplicates reference [17]; please clean up the bibliography and check all DOIs.","section":"References"},{"comment":"The caption of Figure 22 contains a typo (\"95=percentile\"), and the units of the GIX component are written inconsistently across the text and figures; please standardize.","section":"Figure 22"},{"comment":"The data availability statement lists the DRAWING-TEC access URL with \"last visited on *** 202*\"; please fill in the actual access dates.","section":"Data Availability"},{"comment":"The title states \"using ground-based data\", but the paper also uses Swarm space-borne data; consider revising the title to reflect the multi-platform nature of the analysis.","section":"Title"}],"recommendation":"major_revision","confidential_remarks":"The manuscript fits the scope of Remote Sensing, and the multi-instrument case study is potentially useful. However, the central spill-over claim needs stronger validation before publication. I would advise the editor to request the supplementary animations or selected still frames for review, as the printed maps alone are difficult to evaluate quantitatively. The post-hoc selection of two Swarm PBI events, one of which is misaligned, deserves particular scrutiny in revision. I do not see concerns about citation integrity; the self-citations provide data and context rather than circular support."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Read this if you work on storm-time irregularities at mid-latitudes. The genuinely new piece is the S4 dataset from Lisbon, Tenerife, and Lampedusa, cleaned with a sensible sidereal mask, and the explicit comparison of S4, ROTI, TEC gradients, sTEC drops, and Swarm indices for this storm. The paper does not overclaim novelty; it builds on earlier ROTI/GIX studies and adds the amplitude-scintillation scale. The multi-instrument consistency is real: S4 > 0.5 clustered between the Canaries and Iberia, ROTI enhancements, sTEC dips of 30–50 TECu co-located, and Swarm NeGIX/TEGIX showing extreme gradients on the two relevant passes. That is credible evidence of a disturbed ionosphere with structure on many scales.\n\nSoft spots. First, the load-bearing step—EPB identification via high spatial TEC gradients—is imported from a Brazilian climatology [33] and not independently verified for this event. The authors are honest that the two Swarm PBI detections do not sit neatly on the gradient maxima: on June 23 at 01:00 UTC the PBI lies between high-gradient/ROTI areas, and on June 22 at 23:00 UTC it coincides with gradients but not ROTI. They blame map resolution, which is plausible, but it weakens the “these are bubbles” conclusion. Second, the Swarm confirmation is a post-hoc subset: six PBI events, four rejected as too far east or west, two used. That is a small sample. Third, there is no statistical quantification or uncertainty analysis; this is a descriptive case study. Some claims about north-westward motion rely on animations that are hard to check in print. None of these is a load-bearing flaw by itself, but together they mean the central claim is plausible rather than airtight. The alternative—storm-time MSTIDs or locally generated irregularities—is not seriously discussed.\n\nOn citation pattern: self-citations are for data sources and prior context, not the argument. No invented entities. The descriptors S4 > 0.5, the 7-day sidereal mask, and the threshold are standard choices, not fitted parameters.\n\nWho benefits: researchers studying the June 2015 storm, EGNOS/GNSS integrity, and mid-latitude irregularity scales. It deserves a serious referee, with requests for an explicit discussion of alternative interpretations and, if possible, one independent bubble check such as ionosonde, airglow, or raw Swarm Ne profiles. I would send it to review rather than desk-reject.","headline":"A solid case-study consolidation of the June 2015 EPB spill-over with genuinely new S4 data, but the EPB attribution is slightly looser than the paper's language suggests.","tokens_in":19923,"tokens_out":1931,"would_cite":true,"duration_ms":21065,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"The June 2015 geomagnetic storm pushed equatorial plasma bubbles from the tropics to mid-latitudes, and ground-based GNSS receivers in southern Europe recorded the resulting multi-scale scintillations.","keywords":["scintillations","S4","ROTI","GIX","equatorial plasma bubbles","equatorial plasma bubbles spill-over","mid-latitudinal ionosphere","ionospheric gradients"],"falsifier":"A decisive check would be to repeat the analysis with higher-resolution TEC maps or in-situ ionospheric density measurements and test whether every S4>0.5 enhancement aligns with a plasma-density depletion whose boundary is the steep gradient zone; a high-gradient, high-S4 region without a corresponding density depletion would falsify the claim that these gradients are EPB boundaries.","tokens_in":18850,"feed_emoji":"📡","tokens_out":11032,"duration_ms":106476,"temperature":0.7,"pith_summary":"This paper aims to show that the severe GNSS disturbances seen across southern Europe and the North Atlantic during the geomagnetic storm of June 22–23, 2015, were caused by a rare northward spill-over of equatorial plasma bubbles, not by high-latitude processes alone. It combines ground-based amplitude scintillation (S4) and ROTI data with spatial TEC-gradient maps and Swarm satellite detections to argue that the same storm-driven structures produced disturbances at multiple spatial scales, from sub-kilometre irregularities to kilometre-scale electron-density depletions. If the interpretation is right, mid-latitude scintillation events can originate in the equatorial ionosphere and travel north-west, which would make monitoring of low-latitude plasma structures relevant for GNSS users in southern Europe. The authors stress that such multi-scale, storm-triggered irregularities are a growing practical concern for navigation and positioning services in the region.","feed_headline":"June 2015 storm pushed equatorial plasma bubbles over southern Europe","feed_subtitle":"S4, ROTI, and TEC-gradient maps trace the same disturbance moving northwest across Lisbon, Tenerife, and Lampedusa.","key_machinery":"The carrying element is the multi-scale coincidence among four independent diagnostics: the amplitude scintillation index S4 (sensitive to sub-kilometre irregularities), the rate-of-TEC index ROTI (sensitive to kilometre-scale structures), spatial TEC gradients computed by finite differences on 0.5-degree-by-0.5-degree gridded TEC maps (sensitive to tens-of-kilometre boundaries), and space-based checks using the Swarm plasma bubble index and sTEC drops. The paper's working identity is that steep spatial TEC gradients mark the edges of plasma depletions, so regions where high S4, high ROTI, and steep gradients coincide can be read as equatorial plasma bubble boundaries; the co-location of all these signatures is the evidence that carries the spill-over interpretation.","core_discovery":"On the night of June 22–23, 2015, all three stations—Lisbon, Tenerife, and Lampedusa—recorded amplitude scintillation S4 above 0.5, with Tenerife showing the earliest and strongest peak and Lampedusa the weakest. ROTI maps and ground-based ROTI show the same disturbance as a band of elevated values moving north-westward between the Canary Islands and the Iberian Peninsula. Spatial TEC-gradient maps reveal elongated north-west–south-east structures whose boundaries coincide with the high S4 and ROTI values, and slant-TEC drops of 30–50 TECu occur at the times of scintillation onset, indicating plasma-depletion boundaries crossing the receiver-satellite lines of sight. Swarm plasma-bubble detections and the GIX, NeGIX, and TEGIX gradient indices place the strongest electron-density and TEC gradients between 20°N and 40°N, over the Strait of Gibraltar and northern Africa. The paper concludes that the storm's mid-latitude perturbations at all these scales were the work of spill-over equatorial plasma bubbles, and that the co-location of S4, ROTI, and spatial TEC gradients can be used to identify such events in this region.","pith_inferences":["If the S4–ROTI–gradient co-location is a reliable EPB-spill-over proxy, then future mid-latitude scintillation climatologies for southern Europe could be built from dense ROTI and TEC-gradient maps alone, without requiring dense S4 networks.","The paper's comparison with the March 2015 storm suggests a diagnostic rule: when storm-time gradients and ROTI are stronger at low-middle latitudes than at middle latitudes, equatorial-origin plasma structures should be suspected rather than high-latitude travelling disturbances.","The authors' own note that the June 23 Swarm-detected bubble falls between gradient maxima implies that 0.5-degree maps may miss smaller spill-over bubbles; combining ground-based gradients with Swarm TEGIX could recover those smaller structures.","A testable extension is to search for the same north-west-moving multi-scale signature in other storms whose prompt penetration electric fields act near local evening at the geomagnetic equator, which would confirm the causal picture the paper outlines."],"forward_implications":["During the night of June 22–23, 2015, S4 exceeded 0.5 at Lisbon, Tenerife, and Lampedusa, with Tenerife showing the strongest and earliest peak and Lampedusa the weakest.","ROTI maps and ground-based receivers locate the disturbance in a band between the Canary Islands and the Iberian Peninsula that moves north-westward over the event.","High S4 values cluster inside the elongated north-west–south-east structures outlined by steep spatial TEC gradients, while slant TEC drops by 30–50 TECu at scintillation onset, marking plasma-depletion boundaries crossing the receiver-satellite lines of sight.","Swarm-based PBI, NeGIX, and TEGIX detections place the strongest gradients between 20°N and 40°N, over the Strait of Gibraltar and northern Africa, in agreement with ground-based GIX maps.","The multi-scale agreement supports using spatial TEC-gradient maps as a proxy for EPB-related scintillation in this region and explains why the June 2015 storm's low-mid-latitude response was stronger than in the March 2015 storm."],"supporting_citations":[{"why":"Reports the first observations of super plasma bubbles in Europe, establishing the spill-over phenomenon that this paper analyses.","marker":"[1]"},{"why":"Multi-instrumental study that identified the June 22–23, 2015 EPB spill-over in the Euro-African sector, providing the ROTI-based detections this paper extends with S4 and gradient data.","marker":"[12]"},{"why":"Shows the co-location of L-band scintillations and calibrated TEC gradients over Brazil, the proxy relation used here to identify EPB boundaries at mid-latitudes.","marker":"[33]"},{"why":"Supplies the interpretation that simultaneous S4 increase and slant-TEC decrease mark an EPB crossing the receiver-satellite line of sight, used to connect the observed sTEC drops to plasma bubbles.","marker":"[18]"},{"why":"Documents the GIX, SIDX, and ROTI behaviour and positioning errors during this storm, providing the large-scale gradient context that the paper cross-validates with GIX and Swarm indices.","marker":"[8]"},{"why":"Defines the ROTI index from GPS observations, the medium-scale irregularity measure used throughout the multi-scale argument.","marker":"[13]"},{"why":"Supplies the finite-difference scheme for computing spatial TEC gradients from gridded TEC maps, the method that defines the structures interpreted as EPB boundaries.","marker":"[31]"}],"fun_headline_variants":["Plasma bubbles spill over southern Europe in June 2015 storm","June 2015 storm pushed plasma bubbles into southern Europe","Equatorial plasma bubbles reached southern Europe in 2015 storm","Ground data trace plasma bubble spill-over over southern Europe","Storm of June 2015 sent plasma bubbles to mid-latitude Europe"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The interpretation depends on treating co-located high S4, high ROTI, and steep TEC gradients as the reliable signature of equatorial plasma bubble boundaries, an identification imported from earlier work and not independently validated for this event, and on the 0.5-degree, 5-minute TEC maps being fine enough to resolve the bubbles.","fun_headline_variants_meta":{"raw":{"variants":["Plasma bubbles spill over southern Europe in June 2015 storm","June 2015 storm pushed plasma bubbles into southern Europe","Equatorial plasma bubbles reached southern Europe in 2015 storm","Ground data trace plasma bubble spill-over over southern Europe","Storm of June 2015 sent plasma bubbles to mid-latitude Europe"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000288,"raw_usage":{"total_tokens":1719,"prompt_tokens":1004,"completion_tokens":715,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":620,"completion_tokens_details":{"reasoning_tokens":629}},"tokens_in":620,"tokens_out":715,"duration_ms":6621,"temperature":1.0,"reasoning_tokens":629,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-11T19:28:12.503299+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A decisive check would be to repeat the analysis with higher-resolution TEC maps or in-situ ionospheric density measurements and test whether every S4>0.5 enhancement aligns with a plasma-density depletion whose boundary is the steep gradient zone; a high-gradient, high-S4 region without a corresponding density depletion would falsify the claim that these gradients are EPB boundaries.","supporting_citations":[{"cited_title":"and Zakharenkova, I., 2016","cited_arxiv_id":null,"evidence_quote":"Reports the first observations of super plasma bubbles in Europe, establishing the spill-over phenomenon that this paper analyses."},{"cited_title":"and Sokolovsky, S., 2019","cited_arxiv_id":null,"evidence_quote":"Multi-instrumental study that identified the June 22–23, 2015 EPB spill-over in the Euro-African sector, providing the ROTI-based detections this paper extends with S4 and gradient data."},{"cited_title":"and Bougard, B., 2015","cited_arxiv_id":null,"evidence_quote":"Shows the co-location of L-band scintillations and calibrated TEC gradients over Brazil, the proxy relation used here to identify EPB boundaries at mid-latitudes."},{"cited_title":"and Radicella, S.M., 2018","cited_arxiv_id":null,"evidence_quote":"Supplies the interpretation that simultaneous S4 increase and slant-TEC decrease mark an EPB crossing the receiver-satellite line of sight, used to connect the observed sTEC drops to plasma bubbles."},{"cited_title":"and Jakowski, N., 2024","cited_arxiv_id":null,"evidence_quote":"Documents the GIX, SIDX, and ROTI behaviour and positioning errors during this storm, providing the large-scale gradient context that the paper cross-validates with GIX and Swarm indices."},{"cited_title":"and Orús‐Pérez, R., 2022","cited_arxiv_id":null,"evidence_quote":"Supplies the finite-difference scheme for computing spatial TEC gradients from gridded TEC maps, the method that defines the structures interpreted as EPB boundaries."}],"review_version":1}