Aerosol trends as a potential driver of regional climate in the central United States: evidence from observations

Cusworth, Daniel H.; Mickley, Loretta J.; Leibensperger, Eric M.; Iacono, Michael J.

doi:https://doi.org/10.5194/acp-17-13559-2017

Articles | Volume 17, issue 22

https://doi.org/10.5194/acp-17-13559-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-17-13559-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 17, issue 22

Research article

|

15 Nov 2017

Research article |

| 15 Nov 2017

Aerosol trends as a potential driver of regional climate in the central United States: evidence from observations

Daniel H. Cusworth, Loretta J. Mickley, Eric M. Leibensperger, and Michael J. Iacono

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Final revised paper (published on 15 Nov 2017)
Supplement to the final revised paper
Preprint (discussion started on 29 Mar 2017)
Supplement to the preprint

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Comments on acp-2017-208', Anonymous Referee #2, 19 Apr 2017
RC2: 'Peer Review on acp-2017-208', Anonymous Referee #3, 10 Jul 2017
AC1: 'Final Author Comments', Daniel Cusworth, 29 Jul 2017

Peer-review completion

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

AR by Daniel Cusworth on behalf of the Authors (29 Jul 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (12 Aug 2017) by Yun Qian

RR by Anonymous Referee #2 (20 Sep 2017)

Suggestions for revision or reasons for rejection

The authors have attempted to address many of the issues I had raised on the earlier submission. While some of the aspects have been clarified, there still remains some ambiguity in the presentation of the key objectives and conclusions. I believe the manuscript will benefit from these clarifications, as summarized below:

1) In the introduction, the authors make the case that given the uncertainties in previous modeling studies and the confounding interpretations of the causes of the “warming hole”, they turn to observational data sets to reconcile the conflicting hypotheses of prior studies. The authors have confirmed some of the finding of prior studies (e.g., unexpected trends in diffuse SWdn) but have not necessarily provided new explanations for these. It would be useful to list the key conclusions of this analyses as they pertain to warming hole hypotheses.

2) In response to my initial review’s first comment the authors point to the coincident similar magnitude of all-sky SWdn trend across the central U.S. and clear-sky SWdn trends estimated from RRTMG. How does this similarity allow for greater confidence in inferences of meteorological consequences, as stated in the revised manuscript? Is it reasonable to compare modeled clear sky SWdn trends with observed all sky SWdn trends?

3) The authors further point to the above clarification to address the clarification sought in comments 8 and 9 of the previous review, stated again below:

- “the magnitude of the difference in SWdn between sunny and non-sunny summers is compared with magnitude of 2000-2014 change – It is not apparent to me what significance one can draw from this comparison or what it tells us about the variability in SWdn”
- “Similarly, the significance of the magnitude of change in SWdn between PER1 and PER2, relative to the 2000-2004 change is not obvious?”
I do not understand how either of these are clarified?
4) Page 4, line 30-31: the authors state that they exercise caution in interpreting site-specific trends. The statement alone is a bit vague and does not necessarily support the broader generalizations subsequent conclusions convey (e.g., Godwin Creek analysis that is suggested to “casting doubt on role of direct aerosol effects on reversal of warming hole” across the ebtire Southeast.

5) Later in the conclusion section it is stated that the Bondville and Goodwin Creek results demonstrate that caution should be exercised in extrapolating the results to the entire central and southeastern U.S. It is important to maintain consistent messaging through the discussions and acknowledge that many of the conflicting hypotheses still remain. Clearly stating the (site) specific conclusions and any similarities across them would more clearly portray the analyses and the remaining questions. As such it is not readily apparent which aspects of the conflicting hypotheses this analysis has conclusively addressed.

6) Pg 6, line 8-9: I am assuming that monthly simulations imply that monthly mean information was used to drive the RRTMG – please clarify what “monthly simulations” imply.

7) Page 8, line 31: “other meteorological phenomena” are attributed as likely causes for increasing trends in CERES cirrus cloud fraction to rule out possible role of contrails. Some suggestion (qualified as speculative) on these other phenomena would be useful for readers who may want to pursue this further.

8) P 14, line 23-30: I do not fully understand the rationale of this discussion. If RRTMG can reproduce the observed SWdn trend when driven by (observed) aerosol, it implicitly implies co-variability between the aerosol loading (and thus AOD) and SWdn. The discussion is confusing.

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ED: Reconsider after minor revisions (Editor review) (29 Sep 2017) by Yun Qian

AR by Daniel Cusworth on behalf of the Authors (06 Oct 2017) Author's response Manuscript

ED: Publish as is (10 Oct 2017) by Yun Qian

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Short summary

Since 1990, light-scattering pollution known as aerosols have declined as a result of tightening US air quality regulations. Our study finds that US surface solar radiation has increased simultaneously. We establish a link between aerosols and radiation through physical and statistical models. We find the strongest relationship between aerosols, radiation, and climate at a site in the Midwest. Our work underscores the importance of regional pollution on climate in the US and abroad.