Comments on "Effects of the terdiurnal tide on the Sporadic-E layers (Es) development at low latitudes over the Brazilian sector" by Fontes et al.,



Using the ionosonde and meteor radar observations and the MIRE model, this study investigated the effects of terdiurnal tide on the Es layers at low latitudes in the Southern Hemisphere. The paper suggested that the terdiurnal tide could help in the formation of the Es layers in the Brazilian sector. The results could improve our understanding of the formation of Es layers in the lower latitudes. However, they are major issues that need to be clarified first. 

Comments

1. The production and loss terms used in the model should be given.

2. The paper mentioned that the wind data used in MIRE were obtained by the meteor radar. The altitude range for the meteor radar is from 80 to 100 km while the height range of interest in this study is between 86 and 140 km. The authors mentioned that they expanded the wind equation to 120 km. It is not clear to me how the authors obtain the neutral wind data from 100 to 140 km and the accuracy of the wind data in this altitude range. The neural wind data is very important in simulating the formation of the Es layers.
3. I think that to study the seasonal variation, multiple years of data are needed. This paper only used one year of data. I suggest that the authors use a larger dataset.
4. Figures 1 to 5 are not new to me. At least, the authors should make comparisons with previous studies.
5. Figure 8: the comparisons should be made among observations, simulation1 (D+S), and simulation2 (D+S+T).
6. Terdiurnal tides in the low latitudes have been widely studied. The literature research could be done better.

The topic of this paper is the observation of sporadic E (Es) layers with a low-latitude ionosonde station in Brazil. The authors focus on the terdiurnal tidal component that they extract from Es occurrence and other related parameters provided by the ionosonde. The topic is interesting and important to the community since until today there is still a lack of understand the iono-neutral coupling processes and the exact contribution of the tidal species to Es formation.  However, I feel the presentation has to be improved before the paper can be published in Annales Geophysicae. Please find my detailed comments below:

Major points:

1. It is interesting to see that different types of Es layers appear during different times of the day. However, from my point of view Fig. 1,2 and Fig.3 contain almost the same information. Only from figure 3 the reader can get a rough estimation on how frequent each Es type appears. Of course, it is also beneficial to present absolute numbers. I recommend to combine these Figures but keep Figure 3 and adjust the text accordingly.
2.  Same applies for Figure 4 and Figure 5. The information both plots contain are redundant and I recommend to delete Figure 4 because all necessary information are presented already in Fig. 5. You may think of adding a 4th line to Fig 5 representing the seasonal mean from Figure 4. 
3. Starting from line 126: You identified a 8-h structure in the Es data. But the rates during the night are very low and it is almost impossible to see a 3rd maximum in the morning hours (refers to Fig 1,2,3). In best case there a weak enhancement best visible in autumn. Therefore, I recommend not to call it "peak" in the text. 
4. I have one question concerning Fig.6. Is there a special reason why you choose the ftEs parameter? Do other parameters like fbEs or foEs show similar results?
5. In Fig. 8, you present model results showing the electron concentration over the course of the day. When inspecting the right hand side plots,I see a large discrepancy to your Es observations from the ionosonde that I don't understand. E.g., during December conditions (upper right plot) there are two obvious ion concentration modes travelling downward. These two modes appear slightly higher and steeper compared to the upper left plot containing the dirunal and semidiurnal tidal component only which coincides with the Esh observations in Fig 2, 3. But: Especially for December the morning mode of observed Esh in Fig 3 is much stronger compared to the afternoon mode. This is totally opposite to the model outputs of electron concentration.
   
   Is this a problem from the model? Or is it a problem in the determination of the Es type? Please explain this contrary behaviour. 
   
      

Minor comments:

- Please let the reader know  in the text that you seasons refer to Southern Hemispheric conditions (sorry in case I missed it) only in order to avoid any misunderstanding.

- line 40: development of the sporadic E layers