see attached file

REVIEW of „WCD Ideas: Teleconnections through weather rather than stationary waves" by C. Spensberger

Review by D. Domeisen

SUMMARY and OVERALL ASSESSMENT:

This study challenges the use of “teleconnections” as stationary wave patterns, and suggests that Rossby wave train patterns are brought about by smaller-scale non-stationary patterns.

The study is well written and clearly structured. Given that this is an “Ideas” paper based on a viewpoint, I allow myself to add my own view here: I fully agree with the overall message of the manuscript that there is a clear connection between stationary waves and smaller-scale processes. I am less convinced that the teleconnections community is not aware of this point, but I agree that this topic deserves further investigation. I have a range of major comments and questions for the revision that I hope will strengthen the manuscript.

MAJOR COMMENTS

1. In my opinion the use of the term “teleconnection” for quasi-stationary patterns such as e.g. the North Atlantic Oscillation is incorrect. The term should be used for what was originally defined in Wallace & Gutzler 1981 (also cited in this study), which defines teleconnections as correlations between time variations in meteorological parameters at separated points on the globe. Note that this is my personal opinion, and I am aware that patterns such as the NAO are often referred to as “teleconnection patterns”. However, the views of “local” and “global” teleconnections sometimes appear mixed in the manuscript, and this should be clarified (see detailed comments below).
2. Stationary wave patterns, such as e.g. the Aleutian low, are clearly made up of smaller-scale processes on shorter timescales – this is well known (e.g. Orlanski, 2005). I don’t think there is much debate of this point, but of course in the sub-seasonal to seasonal literature this question is not discussed, as it is the average state or persistence of these large-scale patterns that matters for long-range teleconnections.
3. “idealized reanalysis”: This is an interesting idea. It’s however not clear how such a reanalysis would look. Would e.g. other types of waves (gravity waves, Kelvin waves, mixed Rossby-gravity waves, etc) also be part of the dataset? Which variables would be part of the reanalysis?
4. Step IV: “Predictability through teleconnections.”: currently, predictability and causality are generally evaluated in models using large ensembles that either contain a specific precursor event or not, and hence the causality can easily be established. Another method involved nudging of the atmosphere to a certain state to establish causality. It would be helpful to clarify what the approach through the idealized reanalysis would add to understand the relevant mechanisms.
5. Step IV: what about precursor processes that are crucial for causing an event that do not involve Rossby waves? For example, tropical convection is crucial for ENSO and MJO teleconnections, but if I understand correctly they would not be represented in the idealized reanalysis.
6. Following up on point 5, and more generally (beyond step IV described in the manuscript), I think the author may be talking not about teleconnections, but about Rossby wave trains. Teleconnections involve a much wider range of processes than just Rossby waves, including processes in both the atmosphere and the ocean (see e.g. Liu and Alexander, 2007). For the concrete example of ENSO and MJO teleconnections to the North Atlantic that is extensively used in the manuscript, this teleconnection includes a myriad of other processes beyond Rossby waves, see specific point below (lines 116 -121). Given the use of this teleconnection for illustration throughout the manuscript I would encourage the author to refer to the literature covering this teleconnection in more depth (see detailed comment below).

DETAILED MINOR COMMENTS:

Line 11: “Teleconnections can be comparatively local” is not something I would agree with, see major point 1 above.

Line 22: “Teleconnections to ENSO and the MJO”: not clear, do you mean “teleconnections originating from ENSO or the MJO”?

LINES 61-62: the manuscript sometimes goes back and forth between the two definitions of “local” teleconnections and “global” teleconnections. Although the manuscript is said to focus on the global definition, sometimes it falls back to the local definition, e.g. “exchange […] within teleconnections”. See major point 1 above.

Line 54: Hypothesis 3 is formulated much less general than the first two hypotheses. It might be beneficial for the paper to stay at a conceptual level.

Line 73: “they are an expression of their existence”: I assume “they” refers to “stationary waves” and “their” refers to “teleconnections”, is this correct? Please clarify.

Line 96: “potential and limits for predictability through these teleconnections”: yes, indeed. See e.g. Gonzalez-Aleman et al, 2021

Lines 97-100: I don’t agree here. Even for considering teleconnections from a global perspective, and in particular for the example used here for the MJO teleconnection to the North Atlantic, each step is usually considered in isolation, see also point below for lines 116-121 and major point 6.

Lines 101-106: note that this “paradox” is only a paradox for some models. It would be helpful to understand how the approach here can “solve” the paradox.

Lines 105-106: could you elaborate how this is different from the storyline approach?

Lines 116-121: Rossby waves communicating effects of ENSO and the MJO to the North Atlantic have a myriad of roles. It seems from the manuscript, e.g. also lines 144-145, that the author suggests that there is a single process acting all the way from the Indo-Pacific to the North Atlantic through Rossby wave propagation that communicates the effects of ENSO and the MJO to the North Atlantic. First of all, Rossby waves are not the only process that communicates these effects, e.g. for the pathway through the tropical North Atlantic, where the Walker circulation plays a major role. For the pathways that are communicated at least in part by Rossby waves, there is a very wide range of processes. For example, for the pathway of ENSO to the North Atlantic (this pathway has been shown to be the dominant pathway), there are the following processes involved:

• Communication of SST anomalies to tropical convection
• Tropical convection to North Pacific storm track and Aleutian low (e.g. Deng, Y., and T. Jiang, 2011)
• Rossby wave propagation to upper stratosphere
• Wave-mean flow interaction from upper stratosphere to lower stratosphere
• Lower stratospheric mean temperature anomaly to tropospheric synoptic eddies in the North Atlantic

This is just an example showing how many different processes beyond Rossby waves are involved. Given the message of the manuscript, it would make sense to reduce the analysis to Rossby wave trains rather than teleconnections (see major point 6 above).

TECHNICAL COMMENTS

Line 50: typo: “is global, first step could”

Line 51: typo: “the North Atlantic is storm track is”

Line 57: sentence missing verb

Line 69: check grammar

Line 132: typo: “diagnostic, a I would propose”

Line 136: “similar” to what?

Throughout paper: check grammar for use of “allow”

REFERENCES USED IN THIS REVIEW

Deng, Y., and T. Jiang, 2011: Intraseasonal Modulation of the North Pacific Storm Track by Tropical Convection in Boreal Winter. Journal of Climate, 24, 1122-1137.

González-Alemán et al (2021): Tropospheric role in the predictability of the surface impact of the 2018 sudden stratospheric warming event, Geophysical Research Letters, https://doi.org/10.1029/2021GL095464

Liu, Z, and M. Alexander. "Atmospheric bridge, oceanic tunnel, and global climatic teleconnections." Reviews of Geophysics 45.2 (2007).

Orlanski, I. (2005). A New Look at the Pacific Storm Track Variability: Sensitivity to Tropical SSTs and to Upstream Seeding, Journal of the atmospheric sciences