the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Convective updrafts near sea-breeze fronts
- 1Key Laboratory for Humid Subtropical Eco-Geographical Processes of the Ministry of Education, Fujian Normal University, Fuzhou, China
- 2School of Geographical Sciences, Fujian Normal University, Fuzhou, China
- 3National Center for Atmospheric Research, Boulder, Colorado
- 4Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing, China
- 1Key Laboratory for Humid Subtropical Eco-Geographical Processes of the Ministry of Education, Fujian Normal University, Fuzhou, China
- 2School of Geographical Sciences, Fujian Normal University, Fuzhou, China
- 3National Center for Atmospheric Research, Boulder, Colorado
- 4Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing, China
Abstract. Sea-breeze fronts (SBFs) are frequently found to trigger deep convection. The convective updrafts near the SBF are critical in this triggering process. Here, the size and strength of the updrafts near an idealized SBF are investigated with large-eddy simulations. A central focus of this study is to compare the updrafts near the SBF, which are substantially affected by the SBF, to the updrafts ahead of the SBF, which develop in a typical convective boundary layer. It is found that the updrafts near the SBF are larger than, but have similar strength to, the updrafts ahead of the SBF. The larger updrafts near the SBF are produced through the merger between the postfrontal streaky structures and the updrafts originating near the SBF. Lagrangian budget analysis of vertical momentum reveals that the dynamics experienced by the parcels constituting the updrafts near the SBF is almost the same as that ahead of the SBF, so that the strength of the updrafts near the SBF is similar to that ahead of the SBF. It is also found that the size and strength of the updrafts near the SBF scale with the boundary-layer height and the convective velocity scale, respectively, like those in the typical convective boundary layer. The present results should also apply to other boundary-layer convergence lines similar to the SBF.
Shizuo Fu et al.
Status: final response (author comments only)
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RC1: 'Comment on acp-2022-49', Anonymous Referee #1, 23 Feb 2022
The manuscript examines the updraught strengths along and ahead the sea breeze front in an idealised LES setup with varying surfcae sensible heat flux over land and demonstrates why the updraughts are of dimilar strength but wider along the sea breeze front. It is a compnion paper of anotehr paper by Fu et al.
While the manuscript is well written and concise, the Figures are of good quality and it is reasonably convincing, it is still somewhat thing concerning parameter sampling and given that there is already a companion paper.
I found the discussion of older literature relatively thin, you can find more on it e.g. in Bechtold et al 1991, where also the effect on the background wind is discussed. In your results you simply dropped all discussion and experimentation on background wind and Coriolus scaling and I would ask at least for additional experimentation with varying background winds.
Also I found the discussion of boundary-layer rolls/streaks streaks l165-169 very thin, there is more literature on it including e.g on inflection point instability etc. So these streaks or rolls depend on the surface fluxes over sea (set to zero in your experiment) , more complicated in a moist problem, and the wind shear and will necessarily effect the updraughts. So you might also expand a bit more on this, possibly experimentally -
RC2: 'Comment on acp-2022-49', Anonymous Referee #2, 11 Apr 2022
This study is looking at updrafts around Sea Breeze fronts. I find the topic interesting, but much of the work here could do with a little bit more in-depth analysis. Some of the figures seem to have little added value over some of the others, and as a result the paper seems to mostly get stuck in a qualitative description of SBFs that has been known for a while. I would hope that the authors could sharpen the paper up a bit, with some suggestions below. Most importantly, I would be interested to see where a different updraft definition could lead, especially for a more robust statistical sampling. I would therefore recommend major revisions to this paper.
Methodological questions:
*) Lagrangian particles without a subgrid scale model. As suggested by L104, this would be not necessary for “large collections”, but then the authors start tracing particles in a small single updraft
*) Only a small subset of the domain is initialized with particles, resulting in a depletion of the particle concentration and the need for a reset (together with the lack of subgrid model). Thus, particles end up being inhomogenously distributed across the updraft, and may cause biases.
*) The selection of updrafts purely based on their mid-BL w is a noisy way of doing it, with arbitrary tuning parameters, and assuming that a thermal extends through the boundary layer without tilt in this highly sheared environment (let alone a bubble vs plume discussion). What are the sensitivities to those parameters? And why not use buoyancy, or better yet an emitting/decaying scalar like Couvreux et al (2010 or so)?
Content:
*) Fig 4: Not entirely sure what I am supposed to get out of this that isn’t in Fig 3. Same for Fig 6: This seems to be the same information already in Fig 3 ?
*) Fig 5: I’m not sure how the separation in 4 different groups happens exactly. Is this by 25%ile initial location along the x axis? Please describe this better. Also, the most important conclusion of Fig 5 seems obvious if only qualitative. ( Near SBF parcels have the SB circulation superimposed on them). Is there a way to quantify this, in a statistical approach over many different plumes?
*) Fig 7: What is the added value of the Lagrangian approach here? The buoyancy and pressure gradient terms are also possible to calculate over a conditional average of the plume – with the bonus that it could cover all plumes in the entire Near/Far region. Or are the particles necessary to offset the challenges in the updraft definition above?
*) Fig 9: If this is all dependent on very classical parameters, but not on the difference between those parameters (see for instance van Heerwaarden et al, JAS 2014)? Surely that should break at extreme values? Or is it because there simply was no ocean heat flux in this case?
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AC1: 'Comment on acp-2022-49', Shizuo Fu, 06 May 2022
The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-49/acp-2022-49-AC1-supplement.pdf
Shizuo Fu et al.
Data sets
Updrafts near SBF Shizuo Fu https://doi.org/10.17605/OSF.IO/3HYPS
Shizuo Fu et al.
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