Influence of low-level blocking and turbulence on the microphysics of a mixed-phase cloud in an inner-Alpine valley

Ramelli, Fabiola; Henneberger, Jan; David, Robert O.; Lauber, Annika; Pasquier, Julie T.; Wieder, Jörg; Bühl, Johannes; Seifert, Patric; Engelmann, Ronny; Hervo, Maxime; Lohmann, Ulrike

doi:https://doi.org/10.5194/acp-21-5151-2021

Articles | Volume 21, issue 6

https://doi.org/10.5194/acp-21-5151-2021

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

https://doi.org/10.5194/acp-21-5151-2021

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

Articles | Volume 21, issue 6

Research article

|

01 Apr 2021

Research article |

| 01 Apr 2021

Influence of low-level blocking and turbulence on the microphysics of a mixed-phase cloud in an inner-Alpine valley

Fabiola Ramelli, Jan Henneberger, Robert O. David, Annika Lauber, Julie T. Pasquier, Jörg Wieder, Johannes Bühl, Patric Seifert, Ronny Engelmann, Maxime Hervo, and Ulrike Lohmann

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Final revised paper (published on 01 Apr 2021)
Preprint (discussion started on 01 Sep 2020)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of Ramelli et al.', Dmitri Moisseev, 09 Nov 2020
- AC1: 'Authors’ Response to Dmitri Moisseev', Fabiola Ramelli, 23 Dec 2020
RC2: 'Review for ACP-2020-774', Anonymous Referee #2, 16 Nov 2020
- AC2: 'Authors’ Response to RC2', Fabiola Ramelli, 23 Dec 2020

Peer-review completion

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

AR by Fabiola Ramelli on behalf of the Authors (23 Dec 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (12 Jan 2021) by Ari Laaksonen

RR by Dmitri Moisseev (20 Jan 2021)

RR by Anonymous Referee #2 (04 Feb 2021)

Suggestions for revision or reasons for rejection

The authors have responded to all review comments satisfactorily. The only issue noted is the wording with respect to the description of what physical process is responsible for the shear layer, and what physical processes the shear layer is responsible for. There are also have some minor comments (mostly technical) which should also be possible to resolve rapidly without need for a further review.

Specific (mostly technical) comments

Line 17: Suggest you rephrase this to '.. in this particular case (since the majority of the precipitation evaporated when falling through the subsaturated layer above), ..'

Line 47: Suggest you rephrase this to 'In this study ..'

Line 63: Suggest you rephrase this to 'This work ..'

Line 96: Suggest you rephrase this to 'During the case study presented here, the large-scale flow was from the
south-western direction..'

Line 121: The radar wind profiler also uses DBS to obtain the horizontal wind so is not vertically-pointing only. Typical operation may be 3-5 beams, and the elevation angle is usually between 66 and 76 degrees from horizontal.

Line 124: DBS is short for Doppler Beam Swinging.

Line 125: I assume 'an elevation angle of 75 degrees from horizontal'?

Line 138: Suggest you rephrase this to 'The observations presented in this case study were measured in a ..'.

Line 166: You state the dielectric factor here |K|^2, which is 0.93 for liquid water drops at 0 C at X-band. However, it is not quite constant with radar frequency (0.934 at S-band, 0.881 at Ka-band, and 0.686 at W-band).

Line 176: There is unlikely to be any liquid water droplets below the top liquid layer during the period when the low-level cloud was not present (17:45-18:40 UTC) as this would be visible in the lidar backscatter and depolarization fields during this time period. It is likely that there is a liquid layer at the top of the mid-level cloud throughout the time period but this is difficult to state definitively. There may be liquid water present within (rather than only at the top of) the mid-level cloud at other periods but there is no evidence for this. The LWP measurement values cannot easily be used to diagnose whether there are multiple layers either. I suggest removing the sentences starting on line 176.

Figures 5 and 7. Suggest stating '.. horizontal wind speed and ..'

Line 228: Suggest 'The observations presented here ..'

Lines 266-267 and 384: The shear is very unlikely to be responsible for creating an ice supersaturated environment. The difference in relative humidity is likely to be due to there being two atmospheric layers with different air motion and the shear results from the difference in the wind speeds for these two atmospheric layers.

Line 327: The seeder-feeder mechanism was not seen to operate here at all, because there was so little precipitation falling through from above.

Line 328: Suggest 'We assume that in the case study presented here ..'

Line 388: Suggest 'The observations presented here were obtained within a region ..'

Line 397: The shear layer is not really a 'separate' layer, it describes the boundary between the in-valley blocked flow and the stronger cross-barrier flow aloft. I.e. enhanced turbulence is present due to there being a strong gradient (shear) in the vertical profile of the horizontal wind. Suggest '.. and the presence of enhanced turbulence in the region of strong vertical wind shear in the boundary between the blocked layer in the valley and the stronger cross-barrier flow aloft.

Line 411: This statement is the wrong way round. The sublimation layer arises because the upper cross-barrier flow and lower in-valley flow have different humidities, together with the presence of shear because the horizontal winds also differ.

Line 412: As in the statement above, precipitation reaches the surface when the subsaturated layer is shallower, not because the shear layer extends to lower altitudes.

Line 416: It is unlikely that it is the altitude of the shear layer that is the major physical reason responsible, rather it is the altitude at which the subsaturated layer begins. The correlation you suggest arises because the altitude of the shear layer corresponds to the altitude of the top of the subsaturated layer.

Line 424: Do you mean a 'dry layer aloft' here? It's unlikely to be a 'boundary layer aloft'.

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ED: Publish subject to minor revisions (review by editor) (13 Feb 2021) by Ari Laaksonen

AR by Fabiola Ramelli on behalf of the Authors (18 Feb 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (19 Feb 2021) by Ari Laaksonen

AR by Fabiola Ramelli on behalf of the Authors (01 Mar 2021) Manuscript

Short summary

Interactions between dynamics, microphysics and orography can enhance precipitation. Yet the exact role of these interactions is still uncertain. Here we investigate the role of low-level blocking and turbulence for precipitation by combining remote sensing and in situ observations. The observations show that blocked flow can induce the formation of feeder clouds and that turbulence can enhance hydrometeor growth, demonstrating the importance of local flow effects for orographic precipitation.