24 Nov 2022
24 Nov 2022
Status: this preprint is currently under review for the journal ACP.

The evolution of deep convective systems and their associated cirrus outflows

George Alfred Horner1 and Edward Gryspeerdt1,2 George Alfred Horner and Edward Gryspeerdt
  • 1Space and Atmospheric Physics Group, Imperial College London, London, UK
  • 2Grantham Institute - Climate Change and the Environment, Imperial College London, London, UK

Abstract. Tropical deep convective clouds, particularly their large cirrus outflows, play an important role in modulating the energy balance of the Earth’s atmosphere. Whilst the cores of these deep convective clouds have a significant shortwave (SW) cooling effect, they dissipate quickly. Conversely, the thin cirrus that flow from these cores can persist for days after the core has dissipated, reaching hundreds of kilometers in extent. These thin cirrus have a potential for large warming in the tropics. Understanding the evolution of these clouds and how they change in response to anthropogenic emissions is therefore important to understand past and future climate change.

This work uses a novel approach to investigate the evolution of tropical convective clouds by introducing the concept of ‘Time Since Convection’ (TSC). This is used to build a composite picture of the lifecycle of deep convection, from anvil cirrus to thin detrained cirrus. Cloud properties are a strong function of time since convection, showing decreases in the optical thickness, cloud top height, and cloud fraction over time. After an initial dissipation of the convective core, changes in thin cirrus cloud amount were seen beyond 200 hours from convection.

Finally, in the initial stages of convection there was a large net negative cloud radiative effect (CRE). However, once the convective core had dissipated after 6–12 hours, the sign of the CRE flipped, and there was a sustained net warming CRE beyond 120 hours from the convective event. Changes are present in the cloud properties long after the main convective activities have dissipated, signalling the need to continue further analysis at longer time scales than previously studied.

George Alfred Horner and Edward Gryspeerdt

Status: open (until 05 Jan 2023)

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George Alfred Horner and Edward Gryspeerdt

George Alfred Horner and Edward Gryspeerdt


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Short summary
Tropical deep convective clouds, and the thin cirrus (ice) clouds that flow out from them, are important for modulating the energy budget of the tropical atmosphere. This work uses a new method to track the evolution of the properties of these clouds across their entire lifetimes. We find these clouds cool the atmosphere in the first 6 hours, before switching to a warming regime after the deep convective core has dissipated, which is sustained beyond 120 hours from the initial convective event.