Reply to G. Visconti

The authors wish to thank G. Visconti for the attention he paid to their work. It gives us an opportunity to come back to it. The comments are actually all on points we had discussed in our paper giving the reader a warning on how a particular assumption was related to reality and what limitations and drawbacks it had. Thus, the comments should be considered as numerical illustrations of the points, but in several cases the illustrations “are incorrect”, using his words, including one arithmetical error. The first comment is about single atmospheric temperature Ta for both upward and downward IR fluxes. On p. 175 on the upper right, we discuss the limitations of the assumption and note that it can give underestimations in the sought values of Ta and in the surface temperature T,. On page 176, in the middle left, we had given T, = 282K and said that “to obtain T, = 288K, one must significantly decrease D (the transmission, as G. Visconti is demonstating) or a (the atmospheric absorption), or both”. We may comment on this, by saying that with D = 0.14, albedo 0.3 and surface absorption of the solar radiation a,=0.45, from our formula (2.7), one should obtain T,= 279.4K, not 282.6K he is presenting. We rounded numbers up to three significant digits, so our 282K, which was obtained for L, = 0.5 is actually 282.38 because for the solar constant 1370 Wm-2, T, = 278.78K z279K. We said quite clearly that the single value of Ta is defective for normal conditions, but with a situation approaching the isothermy, because of the atmospheric heating and surface cooling, the model should work better. Actually, it has the correct asymptote for large optical depth T and gives results for intermediate T comparable to Turco et al. (1983) and several others. The second comment concerns the application of our model to C 0 2 , dust storms and smoke. We do not prove our formula, because a model cannot be proven, but needs to be tested to see how it works. The testing grounds are the temperatures for the normal earth; we got some underestimations for T, and T,, the temperatures for the normal Mars; the results obtained were about right; the changes in T, for doubling Cot in the earth’s atmosphere which are 6 = 1.4K are again somewhat underestimated; the changes in Ta and T, for the dusty Martian atmosphere are in good agreement with observations; changes in T, and T, for the Earth’s atmosphere with dust compare well (with some underestimation) with the Pollack et al. (1983) multi-layer radiative convective model. Our philosophy was that if the model does not work too badly at such widely different conditions, it should be reasonable in predicting effects of large amounts of smoke. Commenting about C 0 2 , Visconti has some grounds: we should here not use T, = 288K because it is not consistent with optical properties of the model at normal conditions, but using T, = 282K gives S(2C0, ) = 1 S K , improving only slightly the performance of the model. Now, about the ratios of the optical thicknesses in solar, 7s, and IR, 7, Visconti says that we assumed incorrect ratios of 5, and 7. Actually, we did not, at this point, assume anything, but after review of a substantial amount of the literature for optical properties of smoke, we took