Impact of Ice Nucleating Particles and Secondary Ice Production on the Radiative Properties of a Large Tropical Atlantic Deep Convective Cloud Field.

Deep convective clouds in the maritime tropics play a critical role in atmospheric circulation and global climate. We present results highlighting the influence on INP number concentration at all mixed phase temperatures on the radiative properties of a large and complex Tropical Atlantic cloud field. The combined effects of heterogeneous and secondary ice production on cloud field structure are determined using the Met Office Unified Model and the advanced double moment capabilities of the Cloud Aerosol Interacting Microphysics Module. We find that the slope of the applied INP parameterisation (i.e. dINP/dT) significantly alters the cloud field micro- and macrophysical structure. Changes to dINP/dT cause differences in domain-average outgoing shortwave of up to 20 W m^-2. We find that the effect of dINP/dT is substantial regardless of whether ice multiplication (the Hallett Mossop process) occurs or not. Additionally, the impact of secondary ice multiplication on domain cloud fraction and outgoing radiation is dependent on dINP/dT. We further investigate the interaction between heterogeneous ice production by dust and secondary ice multiplication using statistical emulation of an idealised deep convective cloud. We quantify the response of total outgoing shortwave and longwave radiation to the interacting influences of INP parameterisation slope, total dust concentration and secondary ice multiplication rates. Our work highlights the importance of correctly representing INP number concentrations at all mixed-phase temperatures for the accurate quantification of climate forcing by deep convective clouds.