The evolution of cirrus clouds from deep convection
File(s)
Author(s)
Horner, George
Type
Thesis
Abstract
Aerosols significantly impact the climate through their interactions with clouds, where the magnitude and uncertainty of the radiative forcing of aerosol-cloud interactions vary by cloud type. This uncertainty is particularly pronounced for deep convective clouds. Tropical deep convection and its associated cirrus outflows have a near-zero net cloud radiative effect (CRE) due to the offset between shortwave cooling and longwave warming. Therefore, minor changes in the properties of deep convection or associated anvil cirrus, such as those caused by aerosols, could impact the net CRE. Understanding what controls the radiative evolution of deep convection is vital to better constrain aerosol-cloud interactions. This thesis introduces a novel method to examine the evolution of deep convective clouds, from the short-lived, optically-thick convective cores to the thin detrained cirrus that can persist for days after the initial convection has dissipated. The radiative evolution of clouds along trajectories from deep convection is investigated, revealing a positive total high cloud CRE. The anvil cirrus lifetime is calculated, with longer lifetimes observed for detrained cirrus from oceanic rather than terrestrial convection. Longer lifetimes increase the total high cloud CRE. It is found that stronger convection produces detrained cirrus with greater warming over their entire lifetime, primarily driven by changes in the SW CRE due to diurnal variability in convection. Finally, the sensitivity of the detrained cirrus CRE to the convective strength is linked to the sensitivity of the high cloud top pressure to the aerosol optical depth, accounting for the non-local impact aerosols may have on detrained cirrus some distance away from the initial convection. This thesis provides an upper bound on aerosol impacts on tropical high cloud CRE. By introducing a novel equation to quantify non-local aerosol effects, it provides a framework for assessing such impacts under various scenarios, enhancing our understanding of aerosol-cloud interactions.
Version
Open Access
Date Issued
2024-08-07
Date Awarded
01/02/2025
License URL
Advisor
Gryspeerdt, Edward
Sponsor
Royal Society (Great Britain)
Grant Number
URF/R1/191602
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)