Does the threshold representation associated with the autoconversion process matter?
Different ad hoc threshold functions associated with the autoconversion\nprocess have been arbitrarily used in atmospheric models. However,\nit is unclear how these ad hoc functions impact model results. Here\nsystematic investigations of the sensitivities of climatically-important\nproperties: CF (cloud fraction), LWP (liquid water path), and AIE\n(aerosol indirect effect) to threshold functions have been performed\nusing a 3-D cloud-resolving model. It is found that the effect of\nthreshold representations is larger on instantaneous values than\non daily averages; and the effect depends on the percentage of clouds\nin their transitional stages of converting cloud water to rain water.\nFor both the instantaneous values and daily averages, the sensitivity\nto the specification of critical radius is more significant than\nthe sensitivity to the 'smoothness' of the threshold representation\n(as embodied in the relative dispersion of droplet size distribution)\nfor drizzling clouds. Moreover, the impact of threshold representations\non the AIE is stronger than that on CF and LWP.