Modeling stratospheric intrusion and trans-Pacific transport on tropospheric ozone using hemispheric CMAQ during April 2010 – Part 1: Model evaluation and air mass characterization for stratosphere–troposphere transport

Itahashi, Syuichi; Mathur, Rohit; Hogrefe, Christian; Zhang, Yang

doi:https://doi.org/10.5194/acp-20-3373-2020

Articles | Volume 20, issue 6

https://doi.org/10.5194/acp-20-3373-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-20-3373-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 20, issue 6

Research article

|

23 Mar 2020

Research article |

| 23 Mar 2020

Modeling stratospheric intrusion and trans-Pacific transport on tropospheric ozone using hemispheric CMAQ during April 2010 – Part 1: Model evaluation and air mass characterization for stratosphere–troposphere transport

Syuichi Itahashi, Rohit Mathur, Christian Hogrefe, and Yang Zhang

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Final revised paper (published on 23 Mar 2020)
Supplement to the final revised paper
Preprint (discussion started on 07 May 2019)
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: 'Review comments', Anonymous Referee #1, 03 Jun 2019
- AC1: 'Response to Referee Comment 1 (RC1) by Anonymous Referee #1', Syuichi Itahashi, 20 Aug 2019
RC2: 'Reviewer comment', Anonymous Referee #3, 11 Jun 2019
- AC2: 'Response to Referee Comment 2 (RC2) by Anonymous Referee #3', Syuichi Itahashi, 20 Aug 2019
RC3: 'Review on "Modeling Trans-Pacific Transport using Hemispheric CMAQ during April 2010: Part 1. Model Evaluation and Air Mass Characterization for the Estimation of Stratospheric Intrusion on Tropospheric Ozone"', Anonymous Referee #2, 12 Jun 2019
- AC3: 'Response to Referee Comment 3 (RC3) by Anonymous Referee #2', Syuichi Itahashi, 20 Aug 2019
SC1: 'Using PV to identify air of stratospheric origin', Heini Wernli, 19 Jun 2019
- AC4: 'Response to Short Comment by Heini Wernli', Syuichi Itahashi, 20 Aug 2019

Peer-review completion

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

AR by Syuichi Itahashi on behalf of the Authors (20 Aug 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (28 Aug 2019) by Pedro Jimenez-Guerrero

RR by Anonymous Referee #1 (08 Sep 2019)

RR by Anonymous Referee #2 (27 Sep 2019)

Suggestions for revision or reasons for rejection

The manuscript improved a lot, thanks for that!

Nevertheless, the issue with the
horizontal resolution is still a major weakness of this article. As detailed below (item 2+3),
both articles cited in my first review do not, at least from my point of view, support the
hypothesis of this article (top page 5), that the CMAQ model with 108 km grid spacing is
able to capture SSTevents sufficiently. Additionally, I am not convinced that the provided evaluation
shows that the SST events are captured correctly: the averaged SST maybe, but not the
events. As the result can change considerably simply due to employingby decreasing the horizontal
resolution, the scientific gain from this study is very, very limited. I understand, that it is
an issue of computer resources, nevertheless, some studies can simply not be performed,
if the resources are not available.

There are some remaining issues I’d like to point to:
1. Title: the title sounds a little bit weird. Leaving out the first words it reads “stra-
tospheric intrusion of tropospheric ozone [...]”. This seems wrong. I suggested to
delete the word “tropospheric” from the title, as “trans-pacific transport” includes,
at least for me, that it is a tropospheric process.
2. p. 4 ll. 27-30: In my opinion the results of Cristofanelli et al. are summarized in
a wrong way. The important outcome is, that the models with lagrangian transport scheme
were able to capture SST, but the Eulerians were not. Unfortunately, the models
with lagrangian transport schemes had a resolution of 1x1 degree and the Eulerian
models had a much coarser resolution. But the Cristofanelli publication does not
provide any evidence, that an Eulerian model in 1x1 degree would be able to capture
SST.
3. p. 4 ll. 30-32: The study of Gery (2003), as pointed out explicitly within the article,
is only valid for the Unified model of the UK Met Office (UM). Gery (2003) explicitly points
out that the results very much depend on the convection and diffusion parametrisation used in
the respective model. Therefore one can not simply assume that all models are able to capture SST
events in a horizontal resolution, just because the UM is able to do so. In principle each model
needs to be evaluated from which horizontal resolution on it is able to capture SST
resonable. I do not know such an evaluation for CMAQ driven by WRF.
4. p. 9 ll. 19-30: Instead of mentioning the biomass burning as the first and thus most
important reason, I would guess, that the underrepesentation of the STT events due
to the coarse resolution is the major reason.
5. p. 11 ll. 11-13: As above, I opt that a higher resolution in the horizontal would be
much more promising than increasing vertical layering. (By the way, Gery (2003)
points out, that increasing vertical resolution in his simulations decreased the vertical
transport, which is contrary to the statement in the present article.)
6. Section 3.2: SST events are connected with PV streamers and the stratospheric
air mass is transported downward in the wake of the front, thus there is a non-
negligible horizontal motion involved. I would expect that a high amount
of stratospheric influenced air is discarded, just be characterizing the air column-wise from top
to bottom.
7. Fig.8: This flow-chart is not really a flow-chart. Somehow the
information that the flowchart "cycles" over all columns or for one
column only (and that the analysis is columnwise) needs to be included. More importantly it should
be indicated that, if the above grid box is denoting a stratospheric air mass, the vertical
index is decrease (one box down in the column) and the analysis is continued for the
next lower box. Currently, the same analysis would be repeated over and over again
for the same grid box, as no index change is depicted in the flowchart. Last
but not least, an outcome for each grid box, indicating stratospheric
or not, should be explicitly shown.

Minor Issues
• p. 4 last sentence: what is the “tracer amount across tropopause”? Are you omitting
the word transport here somehow?
• p. 5, ll. 20-22: This is not a sentence.
• p. 13, ll. 3/4: “The flowchart the air mass ...” ??? Is not a sentence.

Hide

ED: Reconsider after major revisions (27 Sep 2019) by Pedro Jimenez-Guerrero

AR by Syuichi Itahashi on behalf of the Authors (05 Nov 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (07 Nov 2019) by Pedro Jimenez-Guerrero

RR by Anonymous Referee #2 (20 Nov 2019)

ED: Reconsider after major revisions (15 Dec 2019) by Pedro Jimenez-Guerrero

AR by Syuichi Itahashi on behalf of the Authors (14 Jan 2020) Author's response Manuscript

ED: Publish as is (24 Jan 2020) by Pedro Jimenez-Guerrero

Short summary

The state-of-the-science Community Multiscale Air Quality model extended for hemispheric applications (H-CMAQ) is used to model the trans-Pacific transport which has been recognized as a potential source of air pollutants over the US. In Part 1, modeled ozone is evaluated with observations at surface, by ozonesonde and airplane, and by satellite across the Northern Hemisphere. In addition, a newly developed air mass characterization method to estimate stratospheric intrusion is presented.