Re: GRL MS# 12580 Anne Marie MacInnes, Editor's Assistant Geophysical Research Letters American Geophysical Union 2000 Florida Ave., NW Washington, DC 20009-1277 Dear Ms. MacInnes: We have incorporated the referees comments in the revised paper in the files sent. The title of our paper is "Earthshine Observations of the Earth's Reflectance". In the Readme.txt file, the referees' comments that require a response are denoted by by "Comment" and each is followed by a "Reply". Those parts of the reports that require no reply have been deleted. The Latex file is named goodejgr.tex, and goodejgr.ps can be printed out as a camera ready version. The three figure for the paper are goodefig1a.eps, goodefig2a.eps and goodefig3a.eps. I have also enclosed a picture and caption (cover.eps) that I think would be appropriate for highlighting our paper. Sincerely, Phil Goode ***********************REFEREE REPORTS******************* 12580 - Referee #1 Review GRL MS # 12580 Comments to EARTHSHINE OBSERVATIONS OF THE EARTH's REFLECTANCE submitted to GRL by Goode et al. Comments 1 &2: 1. Publication of the coronograph's description and of the details of corrections applied to get the earth's albedo. It is not sufficient to write "Details will be described in a separate paper". 2. Quoting of the formula used and not of a geocentric one for simplicity. The publication of the description of the equipment and the full methodology might be in "grey" literature but readers should be able to retrieve it if setting up similar investigations. If the authors prefer inclusion in this paper I propose to give the paper to one of the reviewers again. Reply to 1&2: We now quote the exact formula. In addition, we have changed changed the text to refer to a website at which the reader can find details about most aspects of our project. Minor Comments: Abstract: useful monitor of global albedo First page: vonder Haar (also in reference list) First page: instantaneous and large scale Sub-headings would help to clarify Page 5: at least square fit Svensmark and Friis-Christensen put forward a hypothesis, which is not proven. Last page with text: scene models used. Citation Rougier is incomplete. Reply to Minor Comments: We have made all the suggested changes, except we did not add sub-headings because the paper is short. Also, we eliminated the reference to Rougier because he measured the lunar phase function and not the earthshine. ------------------------------------------------------------------------------- ---- 12580 - Referee #2 Referees report for GRL MS# 12580: "Earthshine Observations of the Earth's Reflectance" (P.R. Goode et al.) 2. Detailed comments ___________________ Comment 1: 1) The text should be modified in several places to improve clarity. For example, in the abstract the sentence "Separately, we find comparable hourly variations during the course of many nights due to the earth's rotation." is unclear and can be interpreted several ways. It would be better written as "Separately, we find comparable hourly variations during the course of many nights due to new clouds entering the field of view as the Earth rotates." (I assume clouds are the major cause of this variation). I would suggest the authors ask a colleague who is unfamiliar with their paper to read it and point out where the text is unclear or provides too little explanation. Reply 1: Sentence changed. Comment 2: 2) The phrase "global climate system" appears several times. If the authors mean "global cloud cover", they should say it. If not, they should say whatever this phrase means. Reply 2: We have changed the text to "earth's albedo" in the first place "global climate system" appears (as per the first referee). In the second place the phrase appears, we changed it to "global climate". Comment 3: 3) The typical variation in the atmospheric extinction coefficient during the nights of experimental measurements should be quoted and how well it is calibrated and corrected-for (only a global value of "an order of magnitude less than 5%" is quoted). Reply 3: We now quote the range of typical extinction coefficients and errors in the fit for the earthshine and moonshine for typical nights. With the quoted range of extinction coefficients, the reader can easily calculate the range of extinctions, as exp(\alpha z). Comment 4: 4) Fig.1 could be improved for the non-expert by including a small cartoon along the x axis at the top showing sketches of the moon's bright and dark sections corresponding to the different phase angles. This will show the reader the limiting measurable views of the moon corresponding to insufficient dark region (low phase) or insufficient bright region (high phase). Reply 4: Done. Comments 5-7: 5) The reason for the large spread in the observed A*'s in Fig.1 should be given where it first appears in the text. 6) I have a similar comment for Fig.2: when it is first described in the text, the reason for the discrepancy between the data and curve in the right hand panel (the 5% discrepancy) should be explained at that time, and not left for the reader to deduce later. 7) The reason for the discrepancy in Fig.3 between the amplitude of the observed and simulated seasonal variations should be explained or commented on in more detail. Is the albedo of vegetation included in the model and could this contribute? Reply 5-7: The resaons for the spread in Figure 1 and the offset in Figure 2 are not clear until Figure 3 is interpreted. The logic of the paper would be difficult if we were to make changes suggested in 5) and 6). Instead, we changed the text around Figure 3 to explain those questions raised both in 5) and 6). The albedo of the vegetation is included in the model, but not its seasonal variation which would seem to be much less significant here than the binning. Comment 8: 8) A typical value(s) and precision(s) should be quoted for the earlier results of Danjon et al. where this reference first appears in the paper. Are Danjon's measurements sufficiently precise to infer quantitative estimates of (or limits on) the long-term change in the Earth's albedo over the last 50-75 years (this is commented on at the end of the paper, but should be quantified)? Reply 8: The results of Danjon et al. suffer from an incorrect lunar phase function which is the source of a sizeable systematic error yielding an albedo which is far too large. In addition, we don't have his data, but we hear of errors of about 5%. All of this makes a tie-back problematic, so rather than getting into this secondary issue in detail, we decided to drop the remarks about making a tie-back to 70 years ago. Comment 9: 9)The authors are encouraged to add a further paragraph near the end of their paper on the future prospects for improving and developing this technique. The prospects appear to be very interesting. The shortwave albedo is about 100 W/m2, with about 70 W/m2 reflected from the atmosphere (clouds and aerosol) and about 30 W/m2 from the surface. At present their experimental precision is 1.7%, or about 1.7 W/m2. This precision is comparable to the estimated radiative forcing from CO2 last century (1.5 W/m2), and to the peak-to-trough amplitude of the observed solar modulation of cloud cover (about 1.2 W/m2). In other words, if this technique can be developed and the precision improved by modest amount, it can provide a monitor of long term shifts in cloud cover and aerosols at a sufficient level of precision to be of direct interest to climate change. Reply 9: We added text specifying that the network would give us the additional precision to enable us to test at a "sufficient level of precision to be of direct interest to climate change. "