Preprints
https://doi.org/10.5194/acp-2021-443
https://doi.org/10.5194/acp-2021-443

  16 Jun 2021

16 Jun 2021

Review status: a revised version of this preprint is currently under review for the journal ACP.

A strong statistical link between aerosol indirect effects and the self-similarity of rainfall distributions

Kalli Furtado and Paul Field Kalli Furtado and Paul Field
  • Met Office, Exeter, UK

Abstract. We use convective-scale simulations of monsoonal clouds to reveal a self-similar probability density function that underpins surface rainfall statistics. This density is independent of cloud-droplet number concentration and is unchanged by aerosol perturbations. It therefore represents an invariant property of our model with respect to cloud-aerosol interactions. For a given aerosol concentration, if the dependence of at least one moment of the rainfall distribution on cloud-droplet number is a known input parameter, then the self-similar density can be used to reconstruct the entire rainfall distribution to a useful degree of accuracy. In particular, we present both single-moment and double-moment reconstructions that are able to predict the responses of the rainfall distributions to changes in aerosol concentration. In doing so we show that the seemingly high-dimensional space of possible aerosol-induced rainfall-distribution transformations can be parametrized by a surprisingly small (at most three) independent “degrees of freedom”: the self-similar density, and auxiliary information about two moments of the rainfall distribution. This suggests that, although aerosol-indirect effects on any specific hydro-meteorological system may be multifarious in terms of rainfall changes and physical mechanisms, there may, nevertheless, be a universal constraint on the number of independent degrees of freedom needed to represent the dependencies of rainfall on aerosols.

Kalli Furtado and Paul Field

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-443', Anonymous Referee #1, 22 Jul 2021
    • AC1: 'Reply on RC1', Kalli Furtado, 06 Oct 2021
  • RC2: 'Comment on acp-2021-443', Anonymous Referee #2, 27 Jul 2021
    • AC2: 'Reply on RC2', Kalli Furtado, 06 Oct 2021

Kalli Furtado and Paul Field

Kalli Furtado and Paul Field

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Short summary
The complex processes involved mean that no simple answer to the question “do aerosols increase or decrease precipitation?” has so far been discovered. Using high-resolution weather simulations we find a fractal property of rainfall that is not affected by aerosols. Using this invariant we can collapse all our simulations to a single “curve”. So, although aerosol effects on rain are many, there may be universal constraint on the number of degrees of freedom needed to represent them.
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