Abstract

AbstractHistorical changes of global precipitation in the 20th century simulated by a climate model are investigated. The results simulated with alternate configurations of cloud microphysics are analyzed in the context of energy balance controls on global precipitation, where the latent heat changes associated with the precipitation change is nearly balanced with changes to atmospheric radiative cooling. The atmospheric radiative cooling is dominated by its clear‐sky component, which is found to correlate with changes to both column water vapor and aerosol optical depth (AOD). The water vapor‐dependent component of the clear‐sky radiative cooling is then found to scale with global temperature change through the Clausius–Clapeyron relationship. This component results in a tendency of global precipitation increase with increasing temperature at a rate of approximately 2%K−1. Another component of the clear‐sky radiative cooling, which is well correlated with changes to AOD, is also found to vary in magnitude among different scenarios with alternate configurations of cloud microphysics that controls the precipitation efficiency, a major factor influencing the aerosol scavenging process that can lead to different aerosol loadings. These results propose how different characteristics of cloud microphysics can cause different aerosol loadings that in turn perturb global energy balance to significantly change global precipitation. This implies a possible coupling of aerosol–cloud interaction with aerosol–radiation interaction in the context of global energy balance.

Highlights

  • Climatic change of global-mean precipitation has yet to be fully understood as illustrated by a substantial diversity in the hydrologic sensitivity, defined as the global-mean precipitation increase per increase in global-mean surface air temperature, among state-of-the-art global climate models (Pendergrass and Hartmann, 2012, 2014) in the context of historical climate change (Fläschner et al, 2016; Salzmann, 2016).It is well understood that global-mean precipitation change is constrained by energy balance controls where the change to the latent heat released by precipitation is nearly balanced with change to atmospheric radiative cooling (e.g. Allen and Ingram, 2002)

  • The results simulated with alternate configurations of cloud microphysics are analyzed in the context of energy balance controls on global precipitation, where the latent heat changes associated with the precipitation change is nearly balanced with changes to atmospheric radiative cooling

  • Another component of the clear-sky radiative cooling, which is well correlated with changes to aerosol optical depth (AOD), is found to vary in magnitude among different scenarios with alternate configurations of cloud microphysics that controls the precipitation efficiency, a major factor influencing the aerosol scavenging process that can lead to different aerosol loadings

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Summary

Introduction

Climatic change of global-mean precipitation has yet to be fully understood as illustrated by a substantial diversity in the hydrologic sensitivity, defined as the global-mean precipitation increase per increase in global-mean surface air temperature, among state-of-the-art global climate models (Pendergrass and Hartmann, 2012, 2014) in the context of historical climate change (Fläschner et al, 2016; Salzmann, 2016). 2014), which is further broken down to different factors such as aerosol absorption (Pendergrass and Hartmann, 2012) and water vapor heating in the SW (DeAngelis et al, 2015) These uncertainties of factors influencing the atmospheric radiative cooling impose substantial uncertainties on historical changes of the global precipitation simulated by climate models. Due to a lack of reliable, long-term precipitation measurements covering a whole globe, simulated historical changes of the global-mean precipitation are much less constrained with observations compared to those of the global-mean surface air temperature Another uncertainty arises from ambiguous definition of the hydrologic sensitivity, which mixes up the rapid adjustment and slow response of the energy balance perturbation (Fläschner et al, 2016). The latter is found to significantly vary in magnitude among scenarios with different configurations of cloud microphysics, illustrating a significance of aerosol radiative effect and its modulation by cloud microphysics on historical change of global precipitation

Model data
Radiative-convective equilibrium
Clear-sky radiative cooling
Cloud radiative effect
Total change of global precipitation
CM3w CM3
Conclusion
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