Very long-period oscillations in the atmosphere (0–110&thinsp;km)

Offermann, Dirk; Kalicinsky, Christoph; Koppmann, Ralf; Wintel, Johannes

doi:https://doi.org/10.5194/acp-21-1593-2021

Articles | Volume 21, issue 3

https://doi.org/10.5194/acp-21-1593-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-21-1593-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 21, issue 3

Research article

|

05 Feb 2021

Research article |

| 05 Feb 2021

Very long-period oscillations in the atmosphere (0–110 km)

Dirk Offermann, Christoph Kalicinsky, Ralf Koppmann, and Johannes Wintel

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Final revised paper (published on 05 Feb 2021)
Preprint (discussion started on 20 May 2020)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Atmospheric physics. Very long-period oscillatory structures in the middle atmosphere.', Anonymous Referee #1, 04 Jun 2020
AC1: 'acp-2020-89', Dirk Offermann, 29 Jun 2020
RC2: 'Review of amt-2020-89', Anonymous Referee #2, 08 Jul 2020
- AC2: 'acp-2020-89', Dirk Offermann, 27 Jul 2020
RC3: 'Review of "Self-sustained Oscillations in the Atmosphere (0 – 110 km) at Long Periods" by Offermann et al.', Anonymous Referee #3, 30 Jul 2020

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Dirk Offermann on behalf of the Authors (20 Aug 2020) Manuscript

ED: Referee Nomination & Report Request started (27 Aug 2020) by Heini Wernli

RR by Christian von Savigny (08 Sep 2020)

Suggestions for revision or reasons for rejection

General comments:

The authors generally adequately responded to the points raised in my earlier review and I’m happy with most of the changes. I still think that an analysis on pressure levels rather than geometric altitude may shed some light on the underlying processes, but OK! I would recommend to look at this in the future.

There is, however, one major point that questions part of the results in my opinion. The periods listed in Table 2a are based on the harmonic fit approach as described in the text. The authors write in line 477: „The clusters are separated by major gaps, as is indicated by vertical dashed lines (black).“
Looking at the right parts of Fig. 9 and also Fig. 10 it’s not really obvious what qualifies as a gap and what doesn’t. Based on Figs. 9 and 10, the choice of gaps appears quite arbitrary. In turn, the derived „mean periods“ within these clusters are also arbitrary. I argue that some of the periods determined are not really robust or may not be robust, because they depend on the choice of cluster bounds, which was done by you and not based on an objective approach. This does not appear to affect all identified periods, but probably a substantial part of them.

Specific comments:

Lines 278 and 282: the standard deviations are given with +-. Standard deviations cannot, however, be negative by definition.

Line 305: ´the significance is much better for ECHAM6).´

Please show the 95% lines for ECHAM as well.

Line 351: ´multiplied by 2)´

I suggest mentioning briefly, why the values were multiplied by 2 (to improve clarity)

Line 390 – 394: Did you scale the Gaussian noise in any way, e.g. to match the standard deviation of the temperature data?

Fig. 6: Period labels at top ´34 YR´ and ´4 YR´ not well placed.

Line 425: ´This was done by stepping through the period domain in steps 10% apart.´

I wonder, how this assumptions affects the identified periods. How would the periods look like, if you had used 15% or 20% steps. Would you identify different periods?

Fig. 7: Period labels at top ´400 YR´ and ´10 YR´ not well placed.

Fig. 8: Please mention briefly in Fig. caption, what the red line shows.

Line 477: ´The clusters are separated by major gaps, as is indicated by vertical dashed lines (black).´

As mentioned above, this seems to be a very arbitrary approach and the resulting main or mean periods will directly depend on you subjective choice of gaps.

Fig. 12: Please explain, what ´W´ means.

Fig. 13: The occurrence of the lower maxima (near 40 km) in the correlations is certainly not surprising, because at 42 km the correlation is an autocorrelation and the coefficient is 1. This means that you can directly choose the altitude, where a value of 1 occurs, but adjusting the reference altitude. It would be interesting to see how the Fig. changes if a different height is used as reference. Perhaps the 2 curves agree much better, if z = 35 km is used as a reference? I suggest showing 2 or 3 curves with different reference altitudes.

Line 667: ´ This is a relative change, only.´

I don't really understand this statement. This is an absolute change in mixing ratio, not a relative change (in %), right?

Line 788: ´The periods are robust, i.e. they are found with similar values in different models.´

As pointed out above, I don’t think all the periods are robust.

Line 798: ´Maxima of oscillation amplitudes appear to be associated with westerly (eastward) winds together with large temperature gradients (positive or negative). Amplitude minima are associated with either easterly (westward) winds or with near zero temperature gradients.´

This could be directly related to the propagation of planetary waves in a westerly wind regime (Charney-Drazin-criterion). I suggest discussing this briefly. PW are also associated with vertical displacments, which could explain some of the observed effects.

Line 849: ´ (b) The periods given in Table 2a were all calculated by means of harmonic analyses´

There's a logical error here. The use of the LM-algorithm and the potential occurrence of a common-mode failure cannot be used as an argument for non-spurious results, right!

Typos etc.:

Line 175: ´.The´ -> ´. The´

Line 198: ´,2006´ -> ´, 2006´

Line 216: ´Fig.2´ -> ´Fig. 2´

Line 241: misplaced period.

Line 301: ´( black´ -> ´(black´

Line 359: ´Fig.6´ -> ´Fig. 6´

Line 384: ´Scargle 1984´ -> ´Scargle, 1984´

Line 497: ´Fig.9´ -> ´Fig. 9´

Line 509: ´Fig.11´ -> ´Fig. 11´

Line 623: ´,1995´ -> ´, 1995´

Line 703: ´Fig.6´ -> ´Fig. 6´

Line 744: ´Fig.7´ -> ´Fig. 7´

Line 786: ´etc´ -> ´etc.´

Line 812: ´etc..´

Line 823: ´period- space´ -> ´period-space´

Line 854: ´al.,(1995)´ -> ´al. (1995)´

Line 909: ´and even where´ -> ´and even when´ ?

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RR by Anonymous Referee #3 (24 Sep 2020)

ED: Reconsider after major revisions (25 Sep 2020) by Heini Wernli

AR by Dirk Offermann on behalf of the Authors (12 Oct 2020) Author's response Manuscript

ED: Reconsider after major revisions (30 Oct 2020) by Heini Wernli

AR by Dirk Offermann on behalf of the Authors (17 Nov 2020) Author's response Manuscript

ED: Publish subject to minor revisions (review by editor) (14 Dec 2020) by Heini Wernli

AR by Dirk Offermann on behalf of the Authors (18 Dec 2020) Author's response Manuscript

ED: Publish as is (18 Dec 2020) by Heini Wernli

AR by Dirk Offermann on behalf of the Authors (23 Dec 2020)

Short summary

Atmospheric oscillations with periods of up to several 100 years exist at altitudes up to 110 km. They are also seen in computer models (GCMs) of the atmospheric. They are often attributed to external influences from the sun, from the oceans, or from atmospheric constituents. This is difficult to verify as the atmosphere cannot be manipulated in an experiment. However, a GCM can be changed arbitrarily. Doing so, we find that long-period oscillations may be excited internally in the atmosphere.