William Jones (he/him)

Abstract:

The anvil clouds of tropical deep convection have large radiative effects in both the shortwave (SW) and longwave (LW) spectra with the average magnitudes of both over 100 Wm−2 . Despite this, due to the opposite sign of these fluxes, the net average of the anvil cloud radiative effect (CRE) over the tropics is observed to be neutral. Research into the response of the anvil CRE to climate change has primarily focused on the feedbacks of anvil cloud height and anvil cloud area, in particular regarding the LW feedback. However, tropical deep convection over land has a strong diurnal cycle which may couple with the shortwave component of the anvil cloud radiative effect. As this diurnal cycle is poorly represented in climate models it is vital to gain a better understanding of how its changes impact the anvil CRE. To study the connection between the deep convective cloud (DCC) lifecycle and CRE, we investigate the behaviour of both isolated and organised DCCs in a 4-month case study over sub-Saharan Africa (May–August 2016). Using a novel cloud tracking algorithm, we detect and track growing convective cores and their associated anvil clouds using geostationary satellite observations from the Meteosat Spinning Enhanced Visible and Infrared Imager (SEVIRI). Retrieved cloud properties and derived broadband radiative fluxes are provided by the Community Cloud retrieval for CLimate (CC4CL) algorithm. By collecting the cloud properties of the tracked DCCs, we produce a dataset of anvil cloud properties along their lifetimes. While the majority of DCCs tracked in this dataset are isolated, with only a single core, the overall coverage of anvil clouds is dominated by those of clustered, multi-core anvils due to their larger areas and lifetimes. We find that the anvil cloud CRE of our tracked DCCs has a bimodal distribution. The interaction between the lifecycles of DCCs and the diurnal cycle of insolation results in a wide range of the SW anvil CRE, while the LW component remains in a comparatively narrow range of values. The CRE of individual anvil clouds varies widely, with isolated DCCs tending to have large negative or positive CREs, while larger, organised systems tend to have a CRE closer to 0. Despite this, we find that the net anvil cloud CRE across all tracked DCCs is close to neutral (−0.94 ± 0.91 Wm−2 ). Changes in the lifecycle of DCCs, such as shifts in the time of triggering, or the length of the dissipating phase, could have large impacts on the SW anvil CRE and lead to complex responses that are not considered by theories of LW anvil CRE feedbacks. </jats:p>

Abstract:

<jats:p>Abstract. Deep convective clouds substantially modify the balance of shortwave and longwave radiative energy at the top of the atmosphere. Although in the present-day these effects approximately balance out, projected changes in deep convective clouds could alter the future top-of-atmosphere energy balance. Past studies have found relationships between convection and anvil clouds, but our understanding of how convection typically controls the properties and evolution of anvil clouds that determine anvil radiative effects remains incomplete, limiting our ability to explain or justify projected changes in cloud optical properties. This manuscript presents a new method to track the lifecycle of deep convective clouds and their convective cores in three-dimensional space in km-scale global climate models. An analysis of how convective organisation, intensity and area relate to anvil properties in the ICOsahedral Non-hydrostatic (ICON) model is then presented. Approximately 1000 deep convective clouds are tracked over one simulation week in the tropical Amazon region. We find that while both updraft intensity and area correspond to larger anvils, the correlation between convective area and anvil size is stronger than that between anvil size and updraft intensity. Updraft intensity was associated with a 4-fold increase in anvil extent when convective cores were larger, compared to when they were in the bottom 50th size percentile. This result could not be explained by associated changes in peak convective mass flux or organisation. These results indicate how changes in the frequency or typical size of convective updrafts may link to changes in anvil development, extent and, ultimately, radiative effects.</jats:p>

Abstract:

The top-of-atmosphere net radiative effect of convective anvils is estimated to be close to zero and arises from a balance of significant short-wave cooling and long-wave warming over a complex diurnal cycle. When anvils are optically thick, the cooling due to daytime scattering of shortwave solar radiation dominates. In contrast, optically thin anvils have weaker scattering of solar radiation, so longwave warming becomes the dominant effect. Hence, it is essential to understand the controls of anvil radiative properties over the convective lifecycle, which arises from a complex interplay of convective cloud dynamics and microphysics. The convective mass flux modulates anvil extent, and changes in ice crystal size and morphology affect anvil lifetime and radiative properties. Convective anvils have been proposed to respond to global warming (cloud feedbacks) and anthropogenic aerosols (aerosol-cloud interactions). However, the associated uncertainties remain large and key relevant processes are not represented in the current generation of climate models. Emerging kilometre-scale climate models present new opportunities to examine these effects at the process level.In this work we bring together multiple research strands to quantify the controls of convective anvil clouds and associated radiative effects over the convective lifecycle towards understanding its sensitivity to climate and air pollution changes. We use the tobac cloud tracking framework to track convective cores and associated anvils in 4D across regional and global km-scale ICON model simulations which allows us to quantify the link between convective mass flux, anvil extent and anvil radiative properties. We apply this framework to regional high-resolution simulation of ICON coupled to HAM-lite, our reduced complexity aerosol model derived from the microphysical aerosol scheme HAM [Weiss et al., GMD, 2025], to explore the sensitivity of anvils and their radiative effects to aerosol perturbations in the context of the ORCHESTRA/EarthCARE Model Intercomparison Project (ECOMIP) as well as the TRACER campaign MIP. We find that an increase in aerosol increases cloud droplet numbers, suppresses warm rain formation, increases convective mass flux and thereby upper tropospheric ice water content and will discuss how these changes translate into anvil cloud radiative effects. Prototype next generation km-scale climate models are implicitly already including such anvil radiative effects; however, these currently remain unconstrained by observations. We develop novel observational constraints on the convective anvil cloud lifecycle through consistent tracking of convection using the tobac-flow cloud tracking framework [Jones et al., 2024] between MSG SEVIRI observations and forward simulated geostationary satellite radiances from ICON model output.  This reveals that deep convective systems in ICON grow too fast and show a faster dissipation of thick to thin anvils than observations, which affects their radiative effects. Our work provides novel approaches to improve our understanding of aerosol effects on convective clouds and climate.

Abstract:

The top-of-atmosphere radiative effect of tropical anvil clouds varies with cloud opacity, and can range from substantially negative to largely positive. Recent climate model assessments have found a decrease in the proportion of thick, or opaque, anvil cloud with warming, resulting in a positive climate feedback. However, the mechanism for this change remains obscure.Lifecycle analysis of deep convective clouds tracked using tobac in the convection-permitting global ICOsahedral Non-hydrostatic model (ICON) shows how anvil area and opacity respond to convection. We find that both properties increase in response to increased convective intensity and convective area, but that their sensitivity to each is not equal. To interpret these results, we independently develop a simple analytical model that links anvil expansion and opacity to convective mass flux (CMF). The model predicts that higher CMF leads to greater anvil expansion, increasing the area of thick anvil cloud. But when anvil opacity also depends on convective intensity, we find a strong, non-linear increase in thick anvil amount in response to increasing CMF, consistent with the response observed in ICON. This implies a strong sensitivity of thick anvil amount to changes in the upper tail of the distribution of CMF and illustrates a possible mechanism by which changes in the distribution of cloud CMF could drive anvil thinning in a warming climate.

Abstract:

Earth system modeling is currently undergoing an exciting transformation, thanks to new technical capabilities that allow for significant spatial refinement. For the first time, these capabilities allow us to explicitly simulate extreme precipitation and its effects on climate-relevant timescales on a global scale. Thus, new Earth system data from high-resolution modeling approaches offer an exciting foundation for new analyses and research. In our study, we examine the distribution and changes in extreme precipitation from global simulations. We obtained this data from the ICON Earth system model simulations conducted within the nextGEMS project, which aims to create future projections up to the year 2050 with a grid spacing of approximately 5 km. Our analysis focuses on the portion of precipitation contributing to the top ten percent of globally accumulated precipitation. Using the open-source tool tobac we identify and track the resulting precipitation cells over time. Our analysis reveals that warming causes the most extreme precipitation cells to become more intense. At the same time, the data shows a significant decrease in the total number of cells, resulting in fewer, more intense extremes. Finally, we discuss these findings in relation to changes in the spatial distribution of the cells and changed environmental conditions.