| 10 Mar 2026
Persistent episodes of the Euro-Atlantic upper-level jets in summer: precursors, maintainers and impacts
Abstract. Recent studies have highlighted the link between upper-level jet stream dynamics, especially the persistence of certain jet configurations, and extreme summer weather in Europe. In this work, we use a recently developed toolbox for the detection and study of jet core features in wind speed fields to define persistent episodes of the subtropical or of the eddy-driven jet over the Euro-Atlantic sector and focusing on summer. During these events, we analyse the state of the jets themselves, as well as of the atmosphere directly surrounding the jet, using jet-centred composites. We study the role of these quantities as potential precursors to, or maintainers of persistent episodes. Fields used to quantify the state of the atmosphere before or during persistent episodes include events of high variability or high persistence like Rossby wave breaking or blocks, and potential sources or sinks of momentum such as temperature gradient, diabatic processes or eddy activity. We also systematically study the link between these episodes and severe weather events in Europe.
We show that the two jet categories have different persistence properties and persistent episode temporal distribution. The precursors, maintainers and impacts of these events are also vastly different, although commonalities exist. Both jets are, on average over their persistent episodes, stronger and shifted equatorward compared to their summer mean state. Looking into each individual episode reveals that each jet's persistence can be explained using a combination mechanisms, which include both remote, large-scale drivers as well as local effects. We a significant increase in hot and dry spells during persistent episodes of the STJ, and of wet spells during persistent episodes of the EDJ.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Weather and Climate Dynamics.
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Review of ‘Persistent episodes of the Euro-Atlantic upper-level jets in summer: precursors, maintainers and impacts.’ Submitted to Weather and Climate Dynamics.
This study applies a novel, rather detailed identification method of different jet types to identify persistent (>5 day) episodes of the subtropical and eddy-driven jets STJ and EDJ, respectively. Many synoptic features such as Rossby wavebreaking, waviness, EKE, and 2-meter temperature and precipitation are considered relative to the first three days of persistent episode onset. There are some notable shifts in temperature and precipitation, and indeed hot, wet, and dry spells, associated with persistent jet episodes. However, many of the results are interpreted, though statistically insignificant. Some figures examine shifts during the first three days of persistent episode onset (Figure 4, 6, 8, 9), while Figure 5 and Table 1 examine 3-day hot/wet/dry spells during the entire episode. These two views do not always provide consistent results. Some shifts are considered geographically while others are jet-centered, which seems to provide different takeaways regarding shifts in temperature and precipitation. Statistical significance seems to less common than one would hope. I suggest reducing the number of metrics considered and focusing on one perspective – shifts during onset or shifts of spells throughout their duration.
While the analysis presented is reliably interpreted in the text, and the discussion section is well-written, it is difficult to follow a clear picture of how the conclusions are drawn from the figures, which seem to mainly emphasize high event-to-event variability over consistent synoptic shifts. It almost leads the reader to draw the conclusion there there isn’t much that is consistent across the events captured, so why are they grouped together? Are the jet events causing the associated temperature and precipitation impacts, or are they merely coincident? Though this study acknowledges both options are possible, one does wonder why these jet events are important if there isn’t a systematic lead-lag relationship with temperature / precipitation demonstrated. Do persistent jet episodes shift the impacts of focus if more than just the first three days are considered? It seems Table 1 and Figure 4 show these shifts most clearly, while Figure 5 suggests these shifts might be occurring prior to the beginning of a persistent episode. Given the need to tighten up the perspectives taken on jet-relevant shifts in weather extremes, this paper can only be accepted pending major revisions.
Other major comments
While the refined approach taken to study persistent jet episodes and their link to Euro-Atlantic summer extremes is appreciated, the introduction is often terse and lacking reference to prior literature studying persistent extratropical patterns, such as the seminal paper by Dole and Gordon 1983, among others. Since some of the introduction addresses concepts such as persistence broadly, instead of just for Euro-Atlantic summertime, the literature referenced should be much more complete and just as broad, and not limited to more recent studies.
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2024GL109788
https://journals.ametsoc.org/view/journals/atsc/60/16/1520-0469_2003_060_1941_ptdowr_2.0.co_2.xml
https://www.science.org/doi/10.1126/sciadv.aat3272
While the analysis examines several perspectives on the composite shifts associated with persistent STJ and EDJ episodes, revealing some interesting features, the approach would greatly benefit from some streamlining. Figures 4 and 6 consider the first three days after a persistent episode begins, which, given the emphasis on persistence (>5 days), seems a bit odd and appears to miss the impacts on hot/dry/wet spells (Table 1). Why were only the first three days considered? Why is this approach so different from the focus on spells during the entire persistent episode as discuss in Figure 5 and Table 1? The description of Figure 6 is rather confusing as most shifts are not statistically significant, and I think there’s a typo in the caption about significance which made verifying the text a bit confusing also.
Section 3.5 covering the individual event shifts is rather confusing and hard to follow, given the many partitions and jet-relative areas that are described without any spatial visuals. While I support considering event-specific shifts and the general spirit of quantifying how many cases have similar features, it’s very hard to find the main message of these results and figures 8-9, particularly regarding the 'mechanism' groupings introduced.
Specific Comments
Line 10 ‘persistent episode temporal distribution’ unclear what is meant, please rephrase.
Line 14 ‘we a significant increase’ typo in abstract.
Line 26 ‘Persistence is not uniquely defined and the term is used in different contexts in large scale dynamics and extreme events
research Tuel and Martius (2023)’ could write (Tuel and Martius 2023) I think? At first I thought research was a verb without the () around the reference (maybe just a personal problem).
Line 70 Q3 – somewhat awkwardly phrased.
Line 76 ‘We focus our analysis on the Euro-Atlantic sector and the northern
hemisphere extended summer.’ – since this regionality and seasonality is not mentioned in the list of research questions, I suggest moving this statement to be before the research questions so it is implicit.
Line 78 ‘yet the bulk of the research on jet dynamics focuses on winter, when the jets are stronger and more separated from each other.’ – it may be helpful to mention this earlier because otherwise the literature review is rather sparse. Arguably the wealth of literature on ‘persistent flow anomalies’ going back to at least Dole and Gordon 1983 applies as persistent episodes of the jet even if the episodes are identified with geopotential height anomalies. However, as stated, past research on summer Euro-Atlantic jet episodes is less extensive.
Line 84 – why June 15?
Line 98 ‘the four weather regimes’ – these haven’t been mentioned before, a description in the introduction explaining what these are is needed.
Line 101 – the z500’ field is defined using a 15-day running mean, these fields us 10 day filter. Why are the methods different when they are all indicated with the same notation? Is there any concern regarding the mismatch between the 15-day and 10-day fields?
Line 109 - since this method is described in detail in the 2025 paper, I suggest mentioning that fact earlier than line 114 so that the reader knows this is a quick summary of prior published methods.
Line 136 “The persistence metric shows a similar distribution for both jets, with a slight shift to higher persistence values for the STJ. The EDJ has more longer episodes then the STJ although
the longest episode, lasting 56 days, is of the STJ.” If EDJ has longer episodes how does that not correspond to a higher persistence metric? Some interpretation of what the persistence metric means, given this counterintuitive comparison, is needed.
Line 171 – by 7 August not 4 August right?
Line 184 – heating… would add this is reflected by the heavy precipitation located on the anticyclonic shear side of the entrance region since that’s the only evidence in the figure.
Line 187 ‘Selecting periods only by jet persistence has highlighted two interesting situations where jet dynamics and extreme events
were connected’ – well at this point in the results, there isn’t any evidence it was specifically jet dynamics that produced the extremes in these two cases, there’s simply a coincidence of features. I suggest removing this sentence. A robust link between jet dynamics and extremes is the hypothesis that has yet to be tested.
Line 191 ‘slightly more tilted’ – I see mainly indistinguishable tilt differences at almost all lags. For the EDJ events there are more meaningful shifts it seems.
Line 196 ‘persistent in average windspeed’ – well, the shift isn’t even outside the 90th percentile confidence range, so there’s limited evidence for this being significant.
Figure 5 – it doesn’t seem that the European heat wave regions necessarily align with the significant shifts associated with the persistent jet events. Particularly the application to precipitation which is only significant in the UK for EDJ events and at no other times. If kept in the results, the statistical significance needs to be tested for the temperature and precipitation shifts. I realize that makes the figure less interpretable if all 5 regions are compared, though again, considering shifts in all of these five regions seems minimally justified based on Figure 4.
Table 1 – this considers spells of hot/wet/dry extremes *during* persistent jet episodes, while Figure 5 considers a [weakly justified] lead-lag relationship. I suggest focusing on the Table 1 results which seem more salient than the lead/lag evolution in Figure 5. As Figure 4 only considers the figure three days after a persistent episode begins, there seems to be a discrepancy between it and Table 1 that would benefit from better alignment (example: no precip signal in west/east regions in Figure 4d but one suggested from Table 1). Can a spatial representation of the hot/wet/dry spell results in Table 1 be presented?
Figure 6 – grey hatching is *insignificant* in this plot? With 90 or 95% confidence (both have been used in prior plots). I would’ve though the hatching showed significant points, not insignificant? The text about AWB and CWB is confusing, as both look either significant or insignificant depending on if the caption has a typo.
Line 276 ‘On the cold flank…’ – Are these statistically significant? The offset between the positive/negative PV anomalies and the jet core is really confusing – I appreciate this is acknowledged but it’s pretty glaring here.
289 – 297: it’s hard to follow how the choices here reflect the prior results or are motivated specifically by jet/extreme linkages. Can they be linked to what we see in prior figures?
Figures 8-9 It is quite difficult to digest the information in these figures, for me. But as a reference for those interested in particular cases, they may be of use (assuming there are statistically significant shifts..). Were the weather regimes shown in the top row ever defined in the text? From Figure 9 caption “ Orange: lower-lower, magenta: higher-lower, green: lower-higher, pink: higher-higher.” This is very confusing.
Line 365 – I’m not convinced that it’s a mechanism to just be starting out southward shifted at the beginning of the summer period. A mechanism to me is something like maintenance due to nonlinear PV flux convergence due to a certain PV configuration, for instance a series of positively-tilted waves north of the jet axis.
Discussion – which figures are used to support which statements would greatly help the reader follow the arguments presented.