A simplified model of precipitation enhancement over a heterogeneous surface

Cioni, Guido; Hohenegger, Cathy

doi:https://doi.org/10.5194/hess-22-3197-2018

Articles | Volume 22, issue 6

https://doi.org/10.5194/hess-22-3197-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/hess-22-3197-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 22, issue 6

Research article

|

07 Jun 2018

Research article |

| 07 Jun 2018

A simplified model of precipitation enhancement over a heterogeneous surface

Guido Cioni and Cathy Hohenegger

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Final revised paper (published on 07 Jun 2018)
Preprint (discussion started on 11 Sep 2017)

Interactive discussion

Status: closed

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

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RC1: 'A Simplified Model of Precipitation Enhancement over a Heterogeneous Surface', Anonymous Referee #1, 12 Oct 2017
- AC1: 'Response to reviewer 1', Guido Cioni, 18 Dec 2017
RC2: 'Review of manuscript (hess-2017-547) by G. Cioni and C. Hohenegger', Anonymous Referee #2, 21 Nov 2017
- AC2: 'Response to reviewer 2', Guido Cioni, 18 Dec 2017

Peer-review completion

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

ED: Reconsider after major revisions (further review by editor and referees) (12 Jan 2018) by Carlo De Michele

AR by Guido Cioni on behalf of the Authors (21 Feb 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (22 Mar 2018) by Carlo De Michele

RR by Anonymous Referee #2 (23 Apr 2018)

Suggestions for revision or reasons for rejection

Review of manuscript (hess-2017-547 Revision): A simplified model of precipitation enhancement over a heterogeneous surface
By: G. Cioni and C. Hohenegger
Recommendation: Minor Revision
Anonymous: Yes

General Comments
I would like to thank the authors for the replies. As described in the following, I am asking for several minor revisions easy to implement and do not need to review this manuscript again for final acceptance.

Major Comments
1. The manuscript is improved after the clarification that the proposed simple model only works if evaporation depends linearly on soil moisture and the propagation speed of the front associated with heterogeneity induced mesoscale circulation does not vary much with surface heterogeneity gradient. Besides in the conclusions, these limitations should be emphasized in the abstract as well, as it is not clear on how much and how often these two conditions are held in nature.

2. As indicated by Fig. 5, soil moisture in the numerical simulations does change strongly with time over the dry patch if not averaged over time. It will be better to explicitly claim the rainfall here refers to accumulation over a diurnal cycle. Otherwise, a basic assumption in the simple model, i.e., soil moisture does not change with time, is invalid. This clear statement about the diurnal time scale will also further clarify the assumption that water vapor from evaporation and advection may not be well-mixed.

3. In the first submission, the author noted that “Our approach in deriving the theoretical model directly neglects the feedback between the land-surface and the atmosphere, as evaporation does not implicitly depend on the near-surface atmospheric specific humidity but only on soil moisture” (Pg. 10, lines 27-29). Although the simple model agrees with the numerical simulations well, probably because evaporation is occasionally linearly dependent on soil moisture under the idealized configuration, it will be informative to have some discussions on the caveats related to this simplification. This can be added in the last section of the manuscript.

Minor Comments
1. Pg. 11, lines 8 - 11: The interpretation on how convective updrafts are less affected by dry air entrainment in the ID cases than in the DA experiments is not sufficient. Besides the impact from moisture difference between the updrafts and the environment, their MSE differences also depend on the vertical profiles of convective mass flux which is associated with entrainment rate.

2. It may be better to switch the two panels in Fig. 7, as the DA cases are discussed before the ID cases in most part of the manuscript.

3. Pg. 14, line 14: Please briefly explain why it is an “upper bound”.

4. Pg. 17, line 13: Remove “absolute”.

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ED: Publish subject to minor revisions (review by editor) (03 May 2018) by Carlo De Michele

AR by Guido Cioni on behalf of the Authors (12 May 2018) Author's response Manuscript

ED: Publish as is (26 May 2018) by Carlo De Michele

AR by Guido Cioni on behalf of the Authors (26 May 2018)

Short summary

Precipitating thunderstorms can occasionally be triggered by the propagation of a front associated with a circulation similar to a land–sea breeze but caused by the contrast of soil patches with different moisture contents. In this study, using an idealized framework, we quantify which fraction of surface rain comes from the contribution of the aforementioned front and which fraction comes from local evaporation. Results show that these two major sources contribute differently.