Comment on gmd-2021-32: "Mineral dust cycle in the Multiscale Online Nonhydrostatic AtmospheRe CHemistry model (MONARCH) Version 2.0" by Klose et al.

General comments

This manuscript describes the dust module in the Multiscale Online Non-hydrostatic AtmospheRe CHemistry model (MONARCH) Version 2.0, a state-of-the-art global chemical weather prediction system. The dust module includes a variety of dust emission processes, from conventional, simplified schemes of Marticorena and Bergametti (1995) and Ginoux et al. (2001) to more physically based methods of Shao (2001, 2004), Shao et al. (2011), Kok et al. (2014), and Klose et al. (2014). The processes of the model are well documented, especially for the dust emission processes.

In the experiment and results, the authors conducted a one-year simulation with the four configurations. The model generally shows good representations of the global dust distribution. The evaluation methods are sound, and the presentations are of good quality. However, it is desirable to have a more in-depth evaluation of the characteristics of each dust module (I am curious that which one (or the ensemble of the four ) is the default setting of the dust module for the dust forecasting). Most of the evaulations are global picture of dust emission, deposition, loading and AOD. I would like to see the evaluation of the representation of dust storm events and surface dust concentrations in a future study. Also, I think it is desirable for a multi-year simulation, not just a specific year (2012), to evaluate the model results since the dust aerosol exhibits year-to-year variability.

The authors evaluate the radiative effects of dust aerosol and show the direct radiative effects of the dust. I am not sure that the dust direct radiative forcing interactively affects the meteorological process, but the radiative feedback to the meteorology should be minor because the meteorological fields are re-initialized daily by the ERA reanalysis. I think the evaluation of dust radiative effect can be a reference for the climate models: hence the multi-year evaluation of it is also desirable (in a future study).

In all, I find this manuscript is suitable for publication in the Geoscientific Model Development after a minor revision.

Specific (minor) comments

Line 254: How is the fixed minimal threshold (u_td0 = 5ms⁻¹) determined?

Line 266: How the authors set the "optional constant scaling parameter" c_thr ?

Line 638: "Fig. 7 shows ...": "Fig." should be spelled out as "Figure" at the top of the sentence.

Line 710: A typo: "radition" should be "radiation"

Line 745: “work flow” -> “workflow”

Comment by Yves Balkanski on gmd-2021-32 entitled: ‘Mineral dust cycle in the Multiscale Online Nonhydrostatic AtmospheRe CHemistry model (MONARCH) Version 2.0" by Klose et al.’

This manuscript offers a comprehensive description of how dust modelling is treated in the MONARCH model developed at the Barcelona Supercomputing Center.

The part that treats dust emission flux is very instructive and carefully drafted, it contains all the necessary details for any group to carefully think at how to treat emissions of dust. It is therefore a useful contribution.

After a rather complete model’s description, the authors chose the year 2012 to evaluate the simulated dust against satellite and Aeronet retrieved dust optical depth (DOD). The analysis displays both time series and frequencies of occurrences of dust events for which the DOD exceeds 0.2 at 550nm. For both aspects the model performs rather well compared to other models I am aware of.

Reading the whole paper requires a certain effort since the description is rather complete but the authors were up to the task write it well. In its actual form and with addressing a few minor comments listed below, I find this work worthy of being published in GMD.

Major comment: Aside from the different uses of MONARCH (different scales + assimilation) the authors do not dwell for very long as of why no less than seven different emission schemes can and are used with MONARCH. I encourage them to reflect on it and do a better job at explaining to the reader what guided them to code and adapt such an unusual number of emission schemes.

Minor comments:

You should mention in the abstract that the particle size distribution (PSD) considered in this work extends to 20 mm. By the same token, you could indicate that considering particles larges particles will slightly render more positive both the SW and LW radiative effect of dust.

Page 3, ll 61-73: you should add that simple formulations of dust emissions are unable to be predictive for past periods (mid-Holocene, LGM, rapid transitions…) or for future climate conditions

Page 4 line 88, I wrote in my copy of the ms: ‘Why do you have such a plethoric choice of numerical schemes in MONARCH’ this is link to my major comment above.

Page 5, ll 122-124: ‘The effective and volume radii of each bin in the radiative and sedimentation schemes respectively (see Sec. 3.3, Tab. 6) are time-invariant and based on a lognormal distribution with mass median diameter of 2.524 μm  and geometric standard deviation of 2 (Schulz et al., 1998; Zender et al., 2003).’ This has implications for your results. What I mean is that you probably underestimate the presence of large particles compared to PSDs such as were measured by Ryder et al. (2013 & 2018). You should mention it.

Page 8, l 195: you need a reference regarding the Brittle theory to backup this statement: ‘The K14 dust emission scheme uses the concept of the fragmentation of brittle material.’

Page 11 line 254: How did you come up with chosing the value of 5 m s⁻¹ for utd0? (another reviewer had the same comment)

Page 11 line 260: change ‘the tail of the wind speed distribution’ with ‘the tail of the upper end of the wind speed distribution. Another good illustration of that is the reference Timmreck and Schulz (2014) that I include below.

Bottom of page 11: You present several schemes for moisture correction but you do not discuss their relative merits. Are they observations that would help us favor one scheme rather than another?

Paragraph 3.1.5: I had the remark: Why not use the PSD from Ryder et al. (2013 & 2018)?

Page 19 Figure 3: Some dust specialists argue that Iceland is an important dust source, and having been in Iceland I have witnessed dust uplift there. Why is Iceland not showing up on this map? Is the frequency of events much too small over Iceland?

Page 20 line 449: I find the formulation: ‘For these schemes, the scheme physics …’ rather odd, why not write more simply: ‘The physics of these schemes…’

Page 21 lines 480-482: Indicate from which measurements you inferred the solubility of dust?

Page 32, line 535: you do note explain the low cutoff size for dust size range that you use (1.2 mm). Please explain.

Page 24 last paragraph: a suggestion for future work: the relative patterns of dust emission sources could be challenged with the work of Kok et al (2021) that you coauthored.

Page 25, Table 7: I am uneasy with the large to very large differences between MEEg and MEE, do you have a simple explanation as to why you can have such large differences?

Page 26, line 595-596: as above we have no explanation for this choice of lower boundary of  1.2 mm of the PSD.

Page 27 Figure 6. If you present the following statistics: bias, rmse, correlation for the center and right column, you would be more quantitative than the paragraph of qualitative comparison you wrote. You do present statistics in Fig. 7 which is good.

Figure 10: it would help to have the global mean values of each DRE (LW SFC, LW TOA, SW SFC, SW TOA, total SFC and total TOA) inserted on each panel of this Figure.

Page 34, lines 724 and 728: You misspelled Volz. Please change ‘Voltz’ to ‘Volz’.

Page 36 line 857: I would rephrase ‘multi-physics emission schemes’ to ‘emission schemes with different complexity in the physics’

References:

Ryder, C. L., Highwood, E. J., Rosenberg, P. D., Trembath, J., Brooke, J. K., Bart, M., Dean, A., Crosier, J.,

Dorsey, J., Brindley, H., Banks, J., Marsham, J. H., McQuaid, J. B., Sodemann, H., and Washington, R.: Optical

properties of Saharan dust aerosol and contribution from the coarse mode as measured during the Fennec 2011

aircraft campaign, 13, 303–325, 3, 2013., Atmos Chem Phys, 13(3), 303–325, https://doi.org/10.5194, 2013.

Ryder, C. L., Marenco, F., Brooke, J. K., Estelles, V., Cotton, R., Formenti, P., McQuaid, J. B., Price, H. C., Liu,

D., Ausset, P., Rosenberg, P. D., Taylor, J. W., Choularton, T., Bower, K., Coe, H., Gallagher, M., Crosier, J.,

Lloyd, G., Highwood, E. J. and Murray, B. J.: Coarse-mode mineral dust size distributions, composition and

optical properties from AER-D aircraft measurements over the tropical eastern Atlantic, Atmospheric Chem.

Phys., 18(23), 17225–17257, https://doi.org/10.5194/acp-18-17225-2018, 2018.

Timmreck, C., and M. Schulz (2004), Significant dust simulation differences in nudged and climatological operation mode

of the AGCM ECHAM, J. Geophys. Res., 109, D13202, doi:10.1029/2003JD004381.