Unveiling Convective Momentum Transport at different scales during EUREC4A

Savazzi, Alessandro; Nuijens, Louise; Rooy, Wim de; Siebesma, A. Pier

doi:10.5194/egusphere-egu22-8166

Cited by 4 publications

(8 citation statements)

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“…Another use of the ensemble is as a benchmark for convective parameterizations for GCMs, since the task of such parameterizations is to compute cloud properties from vertical profiles of the model's prognostic variables. Finally, we see Cloud Botany as sitting on the abstract side of a spectrum of modeling approaches, which include simulation setups under time‐varying forcings derived from a numerical weather prediction model (Savazzi, Nuijens, de Rooy, & Siebesma, 2022), on the lateral boundaries of open domains (Dauhut et al., 2022), Lagrangian LES (Narenpitak et al., 2021), mesoscale models with parameterized convection (Beucher et al., 2022) and regional and global models with partially resolved convection (Schulz & Stevens, 2023; Stevens et al., 2019). All these will be needed to fully elucidate the subtleties that govern the interactions between clouds, their environment and climate at the trade‐wind mesoscales.…”

Section: Discussionmentioning

confidence: 99%

Cloud Botany: Shallow Cumulus Clouds in an Ensemble of Idealized Large‐Domain Large‐Eddy Simulations of the Trades

Jansson,

Janssens,

Grönqvist

et al. 2023

J Adv Model Earth Syst

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Small shallow cumulus clouds (<1 km) over the tropical oceans appear to possess the ability to self‐organize into mesoscale (10–100 km) patterns. To better understand the processes leading to such self‐organized convection, we present Cloud Botany, an ensemble of 103 large‐eddy simulations on domains of 150 km, produced by the Dutch Atmospheric Large Eddy Simulation model on supercomputer Fugaku. Each simulation is run in an idealized, fixed, larger‐scale environment, controlled by six free parameters. We vary these over characteristic ranges for the winter trades, including parameter combinations observed during the EUREC4A (Elucidating the role of clouds–circulation coupling in climate) field campaign. In contrast to simulation setups striving for maximum realism, Cloud Botany provides a platform for studying idealized, and therefore more clearly interpretable causal relationships between conditions in the larger‐scale environment and patterns in mesoscale, self‐organized shallow convection. We find that any simulation that supports cumulus clouds eventually develops mesoscale patterns in their cloud fields. We also find a rich variety in these patterns as our control parameters change, including cold pools lined by cloudy arcs, bands of cross‐wind clouds and aggregated patches, sometimes topped by thin anvils. Many of these features are similar to cloud patterns found in nature. The published data set consists of raw simulation output on full 3D grids and 2D cross‐sections, as well as post‐processed quantities aggregated over the vertical (2D), horizontal (1D) and all spatial dimensions (time‐series). The data set is directly accessible from Python through the use of the EUREC4A intake catalog.

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Section: Discussionmentioning

confidence: 99%

Cloud Botany: Shallow Cumulus Clouds in an Ensemble of Idealized Large‐Domain Large‐Eddy Simulations of the Trades

Jansson,

Janssens,

Grönqvist

et al. 2023

J Adv Model Earth Syst

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“…Their subcloud layer divergence under a cloud cluster opposes the subcloud-layer convergence otherwise observed (e.g. fig.12 ofSavazzi et al, 2024), perhaps disabling subcloud layer thermals from reaching cloud base and sustaining the convective heating pattern(Narenpitak et al, 2023). Such a mechanism, which relies on unconstrained warm rain microphysics schemes(Van Zanten et al, 2011), deserves further study.…”

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confidence: 86%

Shallow convective heating in weak temperature gradient balance explains mesoscale vertical motions in the trades

Janssens,

George,

Schulz

et al. 2024

Preprint

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Earth’s climate sensitivity depends on how shallow clouds in the trades respond to changes in the large-scale tropical circulation with warming. In all theory for this cloud-circulation coupling, it is assumed that the clouds are controlled by the field of vertical motion on horizontal scales larger than the convection’s depth (~1 km). Yet this assumption has been challenged both by recent in-situ observations, and idealised large-eddy simulations (LESs). Here, we therefore bring together the recent observations, new analysis from satellite data, and a forty-day, large-domain (1600 x 900 km2) LES of the North Atlantic from the 2020 EUREC4A field campaign, in search of new explanations for the interaction between shallow convection and vertical motions, on scales between 10-1000 km (mesoscales). Across all datasets, the shallow mesoscale vertical motions are consistently represented, ubiquitous, frequently organised into circulations, and formed without imprinting themselves on the mesoscale buoyancy field. This allows us to employ the weak-temperature gradient approximation, which shows that between at least 12.5-400 km scales, the vertical motion balances heating fluctuations in groups of precipitating shallow cumuli. That is, across the mesoscales, shallow convection controls the vertical motion in the trades, and does not simply adjust to it. In turn, the mesoscale convective heating patterns appear to consistently grow through moisture-convection feedback. Therefore, to represent and understand the cloud-circulation coupling of trade cumuli, the full range of scales between the synoptics and the hectometre must be included in our conceptual and numerical models.

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“…If nothing else, the difference emphasises that also other processes that can generate deeper, precipitating convection, such as aerosol concentrations, or dynamics associated with rain evaporation (Radtke et al, 2023), deserve consideration in explanations for SMOCs. More broadly, while we have here found that rain can help to create SMOCs, we have not studied rain evaporation dynamics, which might break them (Narenpitak et al, 2023), or even reverse their direction (Savazzi et al, 2023). Understanding what governs the lifetimes of SMOCs, and the shallow convective systems to which they couple, is a worthwhile topic of future research.…”

Section: Three Other Areas Of Focusmentioning

confidence: 90%

“…From the suite of realistically forced LESs of EUREC 4 A that are emerging (e.g. Dauhut et al, 2023;Saffin et al, 2023;Savazzi et al, 2023), we will focus on the regional simulations presented by Schulz and Stevens (2023). Run with the Icosahedral Nonhydrostatic (ICON) model in its large-eddy simulation configuration (Dipankar et al, 2015;Heinze 5.2 Observations & simulations 125 et al, 2017), these simulations represent the spatio-temporal extent of the campaign as realistically as possible.…”

Section: Icon Large-eddy Simulationsmentioning

confidence: 99%

“…It also serves as a point of departure for using parameter ensembles to study variability in convective clouds in other regions of the world, or in warmer climates. Finally, we see Cloud Botany as sitting on the abstract side of a spectrum of modelling approaches, which include simulation setups under time-varying forcings derived from a numerical weather prediction model (Savazzi et al, 2023), on the lateral boundaries of open domains (Dauhut et al, 2023), Lagrangian LES (Narenpitak et al, 2021), mesoscale models with parameterised convection (Beucher et al, 2022) and regional and global models with partially resolved convection (Schulz & Stevens, 2023;Stevens et al, 2019). All these will be needed to fully elucidate the subtleties that govern the interactions between clouds, their environment and climate at the trade-wind mesoscales.…”

Section: Conclusion 185 Conclusionmentioning

confidence: 99%

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Mesoscale cloud patterns in the trade-wind boundary layer

Janssens

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As we will discuss momentarily, such thinking lies at the heart of another recent observational effort that explains the difference between the variable, positive trade-cumulus feedback simulated by GCMs, and the small feedback that is observed and simulated by At the end of this thesis, we will see that much work still remains to be done in refining, validating and systematising our thinking of mesoscale trade-cumulus patterns. Chapter 8 offers a discussion of the central conclusions (presented in concise form in the Summary), and outlines several perspectives based on the ideas presented in the coming chapters.

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Unveiling Convective Momentum Transport at different scales during EUREC4A

Cited by 4 publications

References 0 publications

Cloud Botany: Shallow Cumulus Clouds in an Ensemble of Idealized Large‐Domain Large‐Eddy Simulations of the Trades

Cloud Botany: Shallow Cumulus Clouds in an Ensemble of Idealized Large‐Domain Large‐Eddy Simulations of the Trades

Shallow convective heating in weak temperature gradient balance explains mesoscale vertical motions in the trades

Mesoscale cloud patterns in the trade-wind boundary layer

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