Authors should address the following points prior to uploading their paper to ACP:

P. 5, Eq. (2): Please check. I think it should be (H^T)R^-1

P. 11, L. 1-2: Words missing?

P. 18, L. 27: I suggest you remind the reader what “MAD” is.

P. 20, L. 2: I suggest you remind the reader what “STT” is.

P. 26, Table 1: I suggest you mention that the spatial resolution is lat-long (or the reverse).

p. 26, Table 2: I suggest you indicate that B is the background error covariance matrix (and refer to the relevant equation in the text).

P. 31, Fig. 2: Indicate the x-axis is latitude.

P. 33, Fig. 4: I think it would be better to label the x-axis with the month names. Same for Fig. 10.

P. 35, Fig. 6 caption: I suggest you mention the meaning of the colours in the colour-scale range: red/blue, relatively high/low. Same for Fig. 7.

P. 41, Fig. S1 caption: Indicate the temporal range shown in the x-axis. Same for Fig. S3.