03 Feb 2021

03 Feb 2021

Review status: this preprint is currently under review for the journal ACP.

On the Contribution of Fast and Slow Responses to Precipitation Changes Caused by Aerosol Perturbations

Shipeng Zhang, Philip Stier, and Duncan Watson-Parris Shipeng Zhang et al.
  • Atmospheric, Oceanic and Planetary Physics, Department of Physics, University of Oxford, UK

Abstract. Changes in global-mean precipitation are strongly constrained by global radiative cooling, while regional rainfall changes are less constrained because energy can be transported. Absorbing and non-absorbing aerosols have different effects on both global-mean and regional precipitation, due to the distinct effects on energetics. This study analyses the precipitation responses to large perturbations in black carbon (BC) and sulphate (SUL) respectively by examining the changes in atmospheric energy budget terms on global and regional scales, in terms of fast (independent of changes in sea surface temperature (SST)) and slow responses (mediated by changes in SST). Changes in atmospheric radiative cooling/heating are further decomposed into contributions from clouds, aerosols, and clear-clean sky (without clouds or aerosols).

Both cases show a decrease in global-mean precipitation, dominated by fast responses in the BC case while slow responses in the SUL case. The geographical patterns are distinct too. The intertropical convergence zone (ITCZ), accompanied with tropical rainfall, shifts northward in the BC case, while southward in the SUL case. For both cases, energy transport terms from the slow response dominates the changes in tropical rainfall, which are associated with the northward (southward) shift of Hadley cell in response to the enhanced southward (northward) cross-equatorial energy flux caused by increased BC (SUL) emission. The extra-tropical precipitation decreases in both cases. For the BC case, fast responses to increased atmospheric radiative heating contribute most to the reduced rainfall, in which absorbing aerosols directly heat the mid-troposphere, stabilise the column, and suppress precipitation. Unlike BC, non-absorbing aerosols decrease surface temperatures through slow processes, cool the whole atmospheric column, and reduce specific humidity, which leads to decreased radiative cooling from the clean-clear sky, and is consistent with the reduced rainfall. Examining the changes in large-scale circulation and local thermodynamics qualitatively explains the responses of precipitation to aerosol perturbations, whereas the energetic perspective provides a method to quantify their contributions.

Shipeng Zhang et al.

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-2020-1317', Anonymous Referee #1, 18 Feb 2021
  • RC2: 'Comment on acp-2020-1317', Anonymous Referee #2, 02 Mar 2021
  • RC3: 'Comment on acp-2020-1317', Anonymous Referee #3, 25 Mar 2021

Shipeng Zhang et al.

Data sets

On the Contribution of Fast and Slow Responses to Precipitation Changes Caused by Aerosol Perturbations Shipeng Zhang

Shipeng Zhang et al.


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Short summary
The relationship between aerosol-induced changes in atmospheric energetics and precipitation responses across different scales are studied in terms of fast (radiatively or microphysically mediated) and slow (temperature mediated) responses. We introduced a method to decompose rainfall changes into contributions from clouds, aerosols, and clear-clean sky from an energetic perspective. It provides a way to better interpret and quantify the precipitation changes caused by aerosol perturbations.