Comments on: "Notes on the appropriateness of 'bred modes' for generating initial perturbations"
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We are gratified by Errico and Langland's (EL, 1999) interest in the use of bred vectors (BVs) in ensemble forecasting. Since they offer detailed comments on only 2 of our papers related to breeding, we would like to bring attention to a number of other related papers that are not referenced by EL. In addition to Toth and Kalnay 1997 (TK97), which discussed in detail properties of breeding and its operational implementation at NCEP, these papers cover mathematically-oriented studies (Smith, 1997; Smith and Gilmour, 1998), experiments with low- or intermediate-dimensional models (Houtekamer and Derome, 1994; Swanson et al., 1998; Noone and Simmonds, 1998), and the use and verification of ensemble forecasts with operational numerical weather prediction models (Rennick, 1995; Barker, 1998; Atger, 1999; Zhu et al., 1996; Toth et al., 1996, 1997, 1998). With respect to EL's comments, we agree with many of their points in which they restate important and basic information available form different sources. We read with interest about EL's ideas and experiments regarding the geostrophic balance (or lack of it) of the total energy based (TE) singular vectors (SVs). We are grateful to the authors for helping us find 2 minor inconsistencies in the paper by Szunyogh et al. (SKT, 1997). First, the cross section latitude in Fig. 1b of SKT (45 S) was accidentally omitted from the legend. And second, on page 206, SKT used the wrong phrase 'sign' for distinguishing among the different phases of the leading LLV. At most other places, however, we believe that EL's criticisms are unjustified for 3 reasons. First, at several places EL erroneously attribute statements to us that we have not made in any of our papers. Second, EL make statements, or form conclusions that, based on independent research, are incorrect or very questionable. Finally, at other places, EL make statements that are confusing. We believe that most of the misdirected, incorrect or confusing statements could have been avoided either by reading some of the published references, especially the TK97 paper mentioned above, or by informal discussions. For the sake of brevity, we address only the most relevant issues below, grouped by topic areas.
