The temperature dependence of ice-nucleating particle concentrations affects the radiative properties of tropical convective cloud systems

Rachel E Hawker,Zhiqiang Cui,Adrian A Hill,Ken S Carslaw,Annette K Miltenberger,Jonathan M Wilkinson,Paul R Field,Benjamin J Murray,Ben J Shipway,Richard J Cotton

doi:10.5194/acp-21-5439-2021

Rachel E Hawker, Zhiqiang Cui + Show 8 more

Open Access

https://doi.org/10.5194/acp-21-5439-2021

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Abstract

Abstract. Convective cloud systems in the maritime tropics play a critical role in global climate, but accurately representing aerosol interactions within these clouds persists as a major challenge for weather and climate modelling. We quantify the effect of ice-nucleating particles (INPs) on the radiative properties of a complex tropical Atlantic deep convective cloud field using a regional model with an advanced double-moment microphysics scheme. Our results show that the domain-mean daylight outgoing radiation varies by up to 18 W m−2 depending on the chosen INP parameterisation. The key distinction between different INP parameterisations is the temperature dependence of ice formation, which alters the vertical distribution of cloud microphysical processes. The controlling effect of the INP temperature dependence is substantial even in the presence of Hallett–Mossop secondary ice production, and the effects of secondary ice formation depend strongly on the chosen INP parameterisation. Our results have implications for climate model simulations of tropical clouds and radiation, which currently do not consider a link between INP particle type and ice water content. The results also provide a challenge to the INP measurement community, as we demonstrate that INP concentration measurements are required over the full mixed-phase temperature regime, which covers around 10 orders of magnitude.

Highlights

Deep convective clouds are important drivers of local, regional and global climate and weather (Arakawa, 2004; Lohmann et al, 2016)
We first examine the effect of icenucleating particles (INPs) parameterisation on the TOA outgoing daytime (10:00–17:00 UTC) radiation relative to the simulation where the only source of primary ice production was through homogeneous freezing (NoINP)
We quantified the effect of the INP parameterisation choice on the radiative properties of a deep convective cloud field using a regional model with advanced double-moment capabilities

Summary

Introduction

Deep convective clouds are important drivers of local, regional and global climate and weather (Arakawa, 2004; Lohmann et al, 2016). The importance and relative contribution of heterogeneous freezing to ice crystal number concentrations (ICNCs) and resultant cloud properties, such as cloud reflectivity, is very uncertain (Cantrell and Heymsfield, 2005; Kanji et al, 2017). This uncertainty stems from the difficulty of predicting INP number concentrations (Kanji et al, 2017; Lacher et al, 2018) as well as the difficulty of quantifying complex interactions between heterogeneous freezing and other ice production mechanisms (Crawford et al, 2012; Huang et al, 2017; Phillips et al, 2005)

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