|Review of Hagelin et al.|
The manuscript title Evaluating the use of Aeolus satellite observations in the regional
NWP model Harmonie-Arome provides an investigation into the impact of Aeolus HLOS winds assimilation in the 3DVar Harmonie-Arome model over the MetCoOp domain. The paper describes well the datasets used from Aeolus, details about the implementation into the DA system, and impacts both the analysis and forecast. The result suggest that the Aeolus data has a positive impact on wind analysis, with Mie winds providing larger impact, but more neutral impact on the forecast. The reviewer recommends however, that more details be given on the forecast impact, by examining more metrics relevant for regional NWP, especially humidity and precipitation forecast skill which should be influenced by improve wind analysis. Therefore the reviewer recommends publication of the manuscript after major revisions.
Page 1, Line 22: Atmospheric Motion Vectors is already defined- change “Atmospheric Motion Vectors (AMV)” to “AMVs”
Page 1, Line 22-23: AMVs can also be computed by water vapor image sequences as noted earlier in the text, so it is not correct to say wind speed is only measured at cloud top height, but also in layers of the atmosphere where satellite observations are sensitive to water vapor signal. I think the point still remains that vertical coverage with all AMVs is limited.
Page 2, Line 32: Suggest saying the wind measurement is usually near the zonal component of the wind vector rather than east-west since this changes depending on ascending/descending orbit.
Page 3, Paragraph 2: Could you please explicitly mention the horizontal spatial resolution of the Harmonie-Arome model and also the thinning grid resolution for Aeolus observations?
Page 4, Line 110: change “providing to sets of LBC” to “providing two sets of LBC”
Page 4, Line 114: change “All the experiment” to “All the experiments”
Page 4, Line 122: change “first satellite-based lidar mission” to first satellite-based wind lidar mission”
Page 5, Line 141: Can you please define the MetCoOp domain? I do not see any description previously in the text.
Page 5, Line 145: Can you describe the method used to conclude the inflation factor and the rationale for adjusting the observation error limits upward? Is this based on looking at O-A stats from the control, or some other method?
Page 7, Figures 2/3: Is it possible to include plots of observation counts for the Mie and Rayleigh winds used to compute the statistics? And also mention average number of observations assimilated per 3 hour cycle.
Page 7, Figures 2/3 and text: Is there an additional bias correction used to remove the residual bias of the HLOS O-B illustrated for the Rayleigh winds for the laser A data? If not, can you please add text to highlight this point and any impact it might have on the analysis?
Section 4.2: The section on forecast impacts should be expanded to include other metrics, particularly with the application in regional NWP. Realizing that the impacts on the wind forecast are relatively small in terms of speed and wind vector. It may be worth looking at the impact of the u and v wind components (perhaps more wind impact on the u component), and then assess other forecast metrics, especially precipitation or specific humidity as the transport of moisture variables should be impacted by Aeolus information added to forecast initialization.