Authors should address the following points:

Page/line numbers refer to text in the authors’ reponse (manuscript starts at p. 5)

P. 5 (1 of manuscript)

L. 13: I suggest you start sentences with a word and not a number.

P. 7

L. 4: Do you need “in order”? Same elsewhere in the paper.

L. 16: But could you construct an initial B that has tracer-wind correlations?

L. 26: I think you need to provide some references here for the hybrid approach, at least for NWP. I suggest:

ECMWF: Buizza et al. (2008), Isaksen et al. (2010), Bonavita et al. (2012)

Met Office, UK: Clayton et al. (2013)

Environment Canada: Buehner et al. (2010)

P.10

L. 9: Is the assimilation at the beginning, middle or end of the analysis step? Please clarify.

P. 11

L. 8: I presume the difference between the background vector and the mean background vector is scaled by the inflation factor. Perhaps state this.

P. 14

L. 28: Do you need “dramatic”? I suggest you avoid subjective statements.

P. 15

L. 17: Perhaps explain further this concept of the “restarts”? 1-2 lines would suffice.

P. 17

L. 16: What do you mean by “centered”? Centered in time? Or something else? Please clarify.

L. 17: Identify the background fields – are they the short-term forecast?

P. 18

L. 7: Identify the term with the superscript “TR” (presumably the true wind).

P. 19

L. 5: Write out in full “10 day”, and then identify the acronym 10-d.

P. 21

L. 4: I suggest “do not”.

L. 7: I suggest d-> days.

L. 14, 15: Use “overweigh” and “underweigh”.

L. 25: Remind the reader what is “L”. You could do this in L. 21 (I assume L is the localization length).

P.23

L. 20: Perhaps indicate that National Centers for Prediction is NCEP (the acronym is well known in the field).

L. 23: Do you need “most striking”? Would ”biggest” be better, as less subjective?

P. 24

L. 15: Why is this not surprising?

P. 25

L. 20: Do you need “further”?

L. 25: To help the reader, I suggest you remind them what is “SWM”. Same for “WEP” in L. 28, and “NMI” in L. 29, and “DA” in L. 6 of P. 26.

P. 26

L. 1: I suggest you start the sentence with: “The NMI…”.

P. 27

L. 19: Manuscript.

P. 33

Table 1 caption: For completeness you could identify the acronyms RMSE, WEP and NMI.

P. 37

Fig. 3 caption: Perhaps the authors could indicate there are no rotational modes for positive m by referring to p. 13 of the text.

P. 39

Fig. 5 caption: Suggest you indicate what the ends of the colour scale indicate, as you do for other figures.

References:

Bonavita, M., Isaksen, L., and Hólm, E. (2012). “On the use of EDA background error variances in the ECMWF 4D-Var,” in ECMWF TechMemo664. Available online at:http://www.ecmwf.int

Buehner, M., Houtekamer, P.L., Charette, C., Mitchell, H.L., and He, B. (2010). Intercomparison of variational data assimilation and the ensemble kalman filter for global deterministic NWP. Part I: description and single-observation experiments. Mon. Weather Rev. 138, 1550–1566. doi:10.1175/2009 MWR3157.1

Buizza, R., Leutbecher, M., and Isaksen, L. (2008). Potential use of an ensemble of analyses in the ECMWF Ensemble Prediction System. Q. J. R. Meteorol. Soc. 134, 2051–2066. doi:10.1002/qj.346

Clayton, A.M., Lorenc,A.C., and Barker, D.M. (2013). Operational implementation of a hybrid ensemble/4D-Var global data assimilation system at the Met Office. Q. J. R. Meteorol. Soc. 139, 1445–1461. doi:10.1002/qj.2054

Isaksen, L., Bonavita, M., Buizza,R., Fisher, M., Haseler, J., Leutbecher, M., et al. (2010). “Ensemble of data assimilations at ECMWF,” in ECMWF Tech Memo 636. Available online at: http://www.ecmwf.int