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.

<p>Ice clouds are challenging because of the high complexity and diversity of their composition  (microphysics) as well as formation and growth processes. As a result, there has been little constraint from observations until recently, resulting in significant limitations in our understanding and representation of ice clouds. A major problem with satellite measurements is the lack of information on the environmental context, which is necessary to identify and understand the formation mechanism and evolution of clouds; these renditions indeed only represent a snapshot of the state of a cloud and its microphysical properties at a given time. This work tackles this issue by providing additional metrics on ice cloud history and origin along with operational satellite products.</p><p>Here, we present a novel framework that combines geostationary satellite observations with Lagrangian transport and ice microphysics models, in order to obtain information on the history and origin of air parcels that contributed to their formation. The trajectory of air parcels encountered along the DARDAR-Nice track has been traced using the air mass transport models CLAMS (Chemical LAgrangian Model of the Stratosphere). CLaMS - Ice model is jointly used to simulate cirrus clouds along trajectories derived by CLaMS. This approach provides information on the cloud regime as well as the ice formation (in-situ vs liquid origin) pathway. For tropical cirrus of convective origin, a Time Since Convection dataset from geostationary observations can also be incorporated into this approach. Preliminary results of this approach obtained on case studies representative of multiple cloud types will be shown here.</p>

<p>The large cirrus outflows that arise from deep convection play a vital role in modulating the energy balance of the Earth’s atmosphere. One important question is how much do the initial conditions of the deep convection influence the subsequent evolution of the detrained cirrus, and if these initial conditions are important, over what timescales do they matter? Characterising how these cirrus outflows evolve over their entire lifetime, and how they might change in response to anthropogenic emissions is important in order to understand their role in the climate system and to constrain past and future climate change.</p> <p>Building on the ‘Time Since Convection’ product used in Horner & Gryspeerdt (2023), this work investigates how the initial conditions of the deep convection influence the subsequent evolution of the detrained cirrus- in particular, how does the timing, location, and meteorological environment of the deep convection alter the detrained cirrus, and for how long are these initial conditions important for the cirrus properties- is there a ‘memory’ of the initial conditions of the deep convection imprinted on the properties of the cirrus hours or days after the initial deep convection has dissipated? To answer this question, data from the DARDAR, ISCCP, and CERES products are used to build a composite picture of the radiative and microphysical properties of the clouds, which is investigated under varying initial conditions.</p> <p>The initial state of the convection is found to have a considerable impact on cirrus development under a variety of conditions. The diurnal cycle, particularly the timing of the convection, is a strong control on the cloud radiative effect, particularly in regions of strong convective activity. The initial aerosol perturbation is also shown to play a role in cirrus development, both in the large scale properties of the cirrus and the microphysical properties.</p> <p>This demonstrates a potential time dependent impact of aerosol and convection on cloud properties and provides a template for future studies of cloud development incorporating diverse sets of measurements.</p>

No abstract

<p>Tropical convective clouds, particularly their large cirrus outflows, play an important role in modulating the energy balance of the Earth’s atmosphere. 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. Previous work has focused on tracking individual convective cores and their evolution into anvil cirrus and subsequent thin cirrus clouds in satellite data.</p><p>In this work we have introduced a novel approach to investigating the evolution of tropical convective clouds by creating a ‘Time Since Convection’ (TSC) dataset. Using reanalysis windspeeds, the time since the air at each location last experienced a convective event (as defined by the presence of a deep convective core) is calculated. Used in conjunction with data from the DARDAR and CERES products, we can build a composite picture of the radiative and microphysical properties of the clouds as a function of their time since convection.</p><p>As with previous studies, we find that cloud properties are a strong function of time since convection, with decreases in the optical thickness, cloud top height, and cloud fraction over time. These changes in in cloud properties also have a significant radiative impacts, with the longwave and shortwave component of the cloud radiative effect also being a strong function of time since convection. In addition, using the DARDAR product, a combination of CloudSat radar and the CALIPSO lidar measurements, we build composite cross sections of convective clouds, characterising their vertical evolution and how it is influenced by external meteorological and initial conditions flagged in the TSC dataset.</p>