The manuscript by Vishnupriya et al. considers an important topic: the interaction of moist-baroclinic development with the evolving larger-scale midlatitude circulation. The authors phrase this topic in terms of the interaction of warm-conveyor-belt (WCB) outflow with the midaltitude waveguide and examine the climatological behavior over a 43-year period using ERA5 re-analysis data. Four important classes of interaction are (subjectively) classified and WCB outflow and antecedent flow conditions examined. The authors find differences in WCB outflow characteristics that are consistent with the subsequent evolution of the larger-scale flow and document the important insight that the flow evolution following WCB evolution is largely dependent by the preceding large-scale conditions.

This study fits very well in the scope of the journal and improves our understanding of the sensitivity of the midlatitude, larger-scale flow to WCB interactions, which may have important implications for predictability aspects, as noted by the authors. Overall, the manuscript is well written with informative figures. I am critical, however, about a central concept of the study: the definition of the WCB-waveguide interaction, which has implications for causality statements, and which is left implicit in the manuscript. Related, the presentation of WCB as atmospheric features leaves room for the interpretation that WCBs and their outflow have ‘a life of their own’ and can be considered as ‘external perturbations’ to the midlatitude circulation, whereas in fact they are intrinsically tied to moist-baroclinic development embedded within the coupled eddy-driven jet – synoptic eddies system that is the midlatitude storm tracks. While the latter point may be a matter of style and perspective, I think that the manuscript will benefit from de-emphasizing WCBs as independent features and emphasizing the coupling of processes in the storm tracks.

I recommend major revisions before publication.

Best wishes!

Major comments:

Concept of WCB-waveguide interaction

Trajectories, by their very definition, follow the ambient flow. They are invaluable in identifying coherent air streams and processes within these moving air masses. In isolation, however, trajectories do not provide information about *why* the ambient flow evolves as it does, i.e., trajectories provide in this respect limited information about causality.

The term “WCB-waveguide interaction” strongly implies causality: The WCB “acts” on the waveguide (and vice versa). Throughout their manuscript, the authors illustrate that the WCB outflow after the end of ascent follows the upper-tropospheric flow: If there is a ridge, the outflow fills the ridge and “older” outflow air is advected further downstream; if there is a cut-off, the outflow air is trapped in that cut-off, … The authors’ schematic Fig. 11 makes this notion quite explicit. Do the authors consider this advection as the action of the waveguide on the WCB, i.e., as part of the interaction? Or what is the action of the waveguide on the WCB?

The authors define “point-of-interaction” as the start of the backward trajectories, which may be up to 3 days after the end of the ascent, i.e., may have traveled rather passively for up to 3 days. What is the nature of the action of the WCB outflow on the waveguide at this point? I might be wrong, but my answer is: There is no action, except possible due to a modification of the radiative properties of relatively moist and cloudy “young” outflow air. Or do the authors have in mind the (usually small) difference of PV values of “young” outflow air and the ambient low-PV air *equatorward* of the waveguide?

Much previous work, including work in the authors’ group, have argued that a strong action on the waveguide occurs where the outflow is (actually) horizontally divergent. Archambault et al. (2013) explicitly defined an interaction metric based on PV advection by the divergent wind, the divergent wind provides forcing terms in PV budgets of upper-tropospheric PV anomalies (e.g., Teubler and Riemer 2021), and the authors’ group has in previous work indicated on maps the locations where WCB trajectories cross upper-tropospheric isentropic surfaces (cross-isentropic transport relates to horizontal divergence by continuity and approximately vanishing vertical motion at the tropopause). By continuity, horizontal divergence ∂u/∂x + ∂v/∂y = - ∂ omega/∂p. From the authors’ schematic Fig. 3, horizontal divergence is maximized near the end of the ascent, whereas horizontal divergence vanishes for the point of interaction. My specific suggestion is to use the end of ascent as point of interaction, which is physically more justified and should exhibit little sensitivity to reasonable choices of the length of the backward trajectories. In the current manuscript, analyzing the time between end of ascent and “point of interaction” (e.g. in Sect. 4) merely serves to sample the emergent flow pattern without providing a causal link from WCB to flow pattern.In fact, at the end of section 3.2 the authors make a very helpful statement: “This will help us better understand how the properties of the WCB air parcels at the end-of-ascent and the ambient flow conditions together determine the interaction of the WCB outflow with the waveguide.” I recommend that the authors frame the purpose of the study more clearly in this sense already in the introduction.

Archambault, H. M., Bosart, L. F., Keyser, D., & Cordeira, J. M. (2013). A climatological analysis of the extratropical flow response to recurving western North Pacific tropical cyclones. Monthly Weather Review, 141(7), 2325-2346.

Teubler, F., & Riemer, M. (2021). Potential-vorticity dynamics of troughs and ridges within Rossby wave packets during a 40-year reanalysis period. Weather and Climate Dynamics, 2(3), 535-559.

On a related note, the use of the term ‘interaction intensity’ is misleading. While I agree that it is sensible to attribute an ‘intensity’ to the evolving flow patterns – as in ‘strength of the deviation from zonal flow’ – the authors have no metric to assess the action of the WCB outflow on the waveguide (in contrast to Archambault et al.). I suggest revising the terminology to avoid confusion.

Similarly, I am not sure that the term “interaction types” is helpful terminology. Certainly, WCB outflow occurs and follows different types of flow patterns, but in what sense this represents different types of *interaction* is unclear to me.

Implication of causality

In some parts of the manuscript, the authors imply that differences in WCB outflow are causally linked to the representation of the WCB (e.g., in Sect. 6 around lines 599 and 668, also adopting arguments of previous work). As noted above, trajectories follow the ambient flow and causality cannot be inferred. The WCB will be misrepresented if the ambient flow is misrepresented. A recent study by Oertel et al. found that the impact on the larger-scale downstream flow is dominated by the sensitivity of WCBs to ambient conditions rather than to the representation of the microphysics, consistent with the relatively small impact found by Joos and Forbes (2016). Please clarify and revise statements implying causality throughout the manuscript.

Oertel, A., Miltenberger, A. K., Grams, C. M., & Hoose, C. (2025). Sensitivities of warm conveyor belt ascent, associated precipitation characteristics and large‐scale flow pattern: Insights from a perturbed parameter ensemble. Quarterly Journal of the Royal Meteorological Society, e4986.

WCBs as an intrinsic part of midlatitude dynamics

WCBs are an intrinsic part of moist-baroclinic growth in the midlatitudes. A few more specific comments relate to this perspective:

i) From this perspective, “WCBs occur all the time” in the midlatitudes and are not “special events” to which the flow would response in specific ways. The main result of the authors, that the impact of WCB interaction depends mostly on the state of the waveguide and too much lesser extent on WCB characteristics, thereby seems very plausible, yet I fully agree that it is worth documenting and supporting by data. In fact, I recommend extending section 5, in which this main result is presented. To me, section 4 mostly illustrated that WCB trajectories *after* ascent merely sample the upper-level flow conditions (as noted above). I thus believe that this section can be streamlined without much loss at the expense of an extended section 5.

ii) Figure 5: My impression of this figure is that we get most of the signal by multiplying the occurrence frequency of WCBs (Fig. 1d) by occurrence frequency of the respective flow pattern (Fig. 1a-c), i.e., simply by combining the occurrence frequencies of two statistically independent events. This impression seems to be supported by the authors description in 3.1. The interpretation is then that e.g., blocks occur with a certain frequency and ridges occur with a certain frequency, but that WCB occurrence is not a discriminating factor between ridges and blocks, which seems to be in some contrast to statements in the introduction that WCBs play an important role in the evolution of certain events. Can the authors comment and clarify?

iii) PV anomaly associated with WCB outflow: “Young” WCB outflow may have different moist/cloud characteristics as ambient upper-tropospheric air masses *equatorward* of the waveguide and may have somewhat smaller PV values (tenths of PVU). The displacement of the strong PV gradient associated with the waveguide creates very large PV anomalies (several PVU and thus an order of magnitude larger). WCB outflow may flow passively into the region of a large PV anomaly (a ridge) or may actively generate the anomaly by contributing to the displacement of the sharp gradient. Please clarify in the presentation to which type of PV anomaly you refer to and how “passive advection” and “active generation” can be distinguished.

Concept of age of outflow

The significance of this concept not become clear to me.

Minor comments:

• L20 westward of what? within individual basins? Not clear at this point.
• L21, “The preceding ..”: Relating to one of my general comments: This sentence is very important. The previous presentation may otherwise be misunderstood as WCBs being an external actor on the waveguide and not a feature that develops within the synoptic evolution along the waveguide. The latter perspective could still be made more clearly to further improve the manuscript.
• L32 “the dynamics of upper-level extratropical flows is mostly adiabatic and has comparatively high predictability”: The first statement is debatable. Moist-baroclinic as the underlying paradigm of the midlatitude circulation dates back at least to the 1970-80’s (e.g., Gall 1976, Emanuel et al. 1987). More recently, Teubler and Riemer (2021) used the term moist-baroclinic downstream development to emphasize the first-order effect of moist processes. The second statement raises the question: Compared to what? Please clarify this sentence.
• L80ff: I have no doubt about the usefulness of the authors subjective choice. Just out of curiosity (other readers may be curious, too): Did the authors also think about an objective classification, e.g., based on EOF and cluster analysis?
• L139: I do not understand, please clarify; the above flow features are not identified in a Lagrangian sense.
• L152: when --> where
• 319: reveal --> confirm
• L389: I do not follow this argument. Can you clarify? What is meant with „profit“?
• Table 1 and subsection 42.: are described differences in stat sig?
• L410: shift of what?
• L426: Why is this “interestingly”?
• 9: caption inconsistent with labels in plot. please correct
• Pg21, first paragraph: Did you test the sensitivity to your choices?
• L493: I do not follow this speculation. Why would the negative anomaly not simply be the evolving ridge? There is a larger scale positive(!) PV anomaly to the North that may indicate an enhanced large-scale PV gradient, irrespective of WCB activity.
• 5.2: The negative anomaly in Fig. 10 evolves only very little during WCB activity. Why do you refer to it the anomaly as a ridge in the beginning of the sequence and a block at the end. To me, this feature very much looks like a block that pre-exists before WCB activity starts.
• 6 is rather long. I suggest introducing subsections “Final discussion” and “Conclusions”.
• L648: The purpose of this paragraph is not clear to me. Please clarify.
• L670: I believe that it is worth mentioning at some point that there is much analogy to TC interaction (at this point, e.g., Keller et al. 2019). There, the high sensitivity of the downstream flow can be understood in terms of flow bifurcation points, i.e., without reference to uncertainty of model microphysics (which in fact is comparatively small).