@article{15047,
  abstract     = {Tropical precipitation extremes and their changes with surface warming are investigated using global storm resolving simulations and high-resolution observations. The simulations demonstrate that the mesoscale organization of convection, a process that cannot be physically represented by conventional global climate models, is important for the variations of tropical daily accumulated precipitation extremes. In both the simulations and observations, daily precipitation extremes increase in a more organized state, in association with larger, but less frequent, storms. Repeating the simulations for a warmer climate results in a robust increase in monthly-mean daily precipitation extremes. Higher precipitation percentiles have a greater sensitivity to convective organization, which is predicted to increase with warming. Without changes in organization, the strongest daily precipitation extremes over the tropical oceans increase at a rate close to Clausius-Clapeyron (CC) scaling. Thus, in a future warmer state with increased organization, the strongest daily precipitation extremes over oceans increase at a faster rate than CC scaling.},
  author       = {Bao, Jiawei and Stevens, Bjorn and Kluft, Lukas and Muller, Caroline J},
  issn         = {2375-2548},
  journal      = {Science Advances},
  number       = {8},
  publisher    = {American Association for the Advancement of Science},
  title        = {{Intensification of daily tropical precipitation extremes from more organized convection}},
  doi          = {10.1126/sciadv.adj6801},
  volume       = {10},
  year         = {2024},
}

@article{14453,
  abstract     = {Squall lines are substantially influenced by the interaction of low-level shear with cold pools associated with convective downdrafts. Beyond an optimal shear amplitude, squall lines tend to orient themselves at an angle with respect to the low-level shear. While the mechanisms behind squall line orientation seem to be increasingly well understood, uncertainties remain on the implications of this orientation. Roca and Fiolleau (2020, https://doi.org/10.1038/s43247-020-00015-4) show that long lived mesoscale convective systems, including squall lines, are disproportionately involved in rainfall extremes in the tropics. This article investigates the influence of the interaction between low-level shear and squall line outflow on squall line generated precipitation extrema in the tropics. Using a cloud resolving model, simulated squall lines in radiative convective equilibrium amid a shear-dominated regime (super optimal), a balanced regime (optimal), and an outflow dominated regime (suboptimal). Our results show that precipitation extremes in squall lines are 40% more intense in the case of optimal shear and remain 30% superior in the superoptimal regime relative to a disorganized case. With a theoretical scaling of precipitation extremes (C. Muller & Takayabu, 2020, https://doi.org/10.1088/1748-9326/ab7130), we show that the condensation rates control the amplification of precipitation extremes in tropical squall lines, mainly due to its change in vertical mass flux (dynamic component). The reduction of dilution by entrainment explains half of this change, consistent with Mulholland et al. (2021, https://doi.org/10.1175/jas-d-20-0299.1). The other half is explained by increased cloud-base velocity intensity in optimal and superoptimal squall lines.},
  author       = {Abramian, Sophie and Muller, Caroline J and Risi, Camille},
  issn         = {1942-2466},
  journal      = {Journal of Advances in Modeling Earth Systems},
  number       = {10},
  publisher    = {Wiley},
  title        = {{Extreme precipitation in tropical squall lines}},
  doi          = {10.1029/2022MS003477},
  volume       = {15},
  year         = {2023},
}

@article{14654,
  abstract     = {Two assumptions commonly applied in convection schemes—the diagnostic and quasi-equilibrium assumptions—imply that convective activity (e.g., convective precipitation) is controlled only by the large-scale (macrostate) environment at the time. In contrast, numerical experiments indicate a “memory” or dependence of convection also on its own previous activity whereby subgrid-scale (microstate) structures boost but are also boosted by convection. In this study we investigated this memory by comparing single-column model behavior in two idealized tests previously executed by a cloud-resolving model (CRM). Conventional convection schemes that employ the diagnostic assumption fail to reproduce the CRM behavior. The memory-capable org and Laboratoire de Météorologie Dynamique Zoom cold pool schemes partially capture the behavior, but fail to fully exhibit the strong reinforcing feedbacks implied by the CRM. Analysis of this failure suggests that it is because the CRM supports a linear (or superlinear) dependence of the subgrid structure growth rate on the precipitation rate, while the org scheme assumes a sublinear dependence. Among varying versions of the org scheme, the growth rate of the org variable representing subgrid structure is strongly associated with memory strength. These results demonstrate the importance of parameterizing convective memory, and the ability of idealized tests to reveal shortcomings of convection schemes and constrain model structural assumptions.},
  author       = {Hwong, Yi-Ling and Colin, M. and Aglas, Philipp and Muller, Caroline J and Sherwood, S. C.},
  issn         = {1942-2466},
  journal      = {Journal of Advances in Modeling Earth Systems},
  number       = {12},
  publisher    = {Wiley},
  title        = {{Assessing memory in convection schemes using idealized tests}},
  doi          = {10.1029/2023MS003726},
  volume       = {15},
  year         = {2023},
}

@article{14752,
  abstract     = {Radiative cooling of the lowest atmospheric levels is of strong importance for modulating atmospheric circulations and organizing convection, but detailed observations and a robust theoretical understanding are lacking. Here we use unprecedented observational constraints from subsidence regimes in the tropical Atlantic to develop a theory for the shape and magnitude of low‐level longwave radiative cooling in clear‐sky, showing peaks larger than 5–10 K/day at the top of the boundary layer. A suite of novel scaling approximations is first developed from simplified spectral theory, in close agreement with the measurements. The radiative cooling peak height is set by the maximum lapse rate in water vapor path, and its magnitude is mainly controlled by the ratio of column relative humidity above and below the peak. We emphasize how elevated intrusions of moist air can reduce low‐level cooling, by sporadically shading the spectral range which effectively cools to space. The efficiency of this spectral shading depends both on water content and altitude of moist intrusions; its height dependence cannot be explained by the temperature difference between the emitting and absorbing layers, but by the decrease of water vapor extinction with altitude. This analytical work can help to narrow the search for low‐level cloud patterns sensitive to radiative‐convective feedbacks: the most organized patterns with largest cloud fractions occur in atmospheres below 10% relative humidity and feel the strongest low‐level cooling. This motivates further assessment of favorable conditions for radiative‐convective feedbacks and a robust quantification of corresponding shallow cloud dynamics in current and warmer climates.},
  author       = {Fildier, B. and Muller, Caroline J and Pincus, R. and Fueglistaler, S.},
  issn         = {2576-604X},
  journal      = {AGU Advances},
  keywords     = {General Earth and Planetary Sciences},
  number       = {3},
  publisher    = {American Geophysical Union},
  title        = {{How moisture shapes low‐level radiative cooling in subsidence regimes}},
  doi          = {10.1029/2023av000880},
  volume       = {4},
  year         = {2023},
}

@article{10656,
  abstract     = {Idealized simulations of the tropical atmosphere have predicted that clouds can spontaneously clump together in space, despite perfectly homogeneous settings. This phenomenon has been called self-aggregation, and it results in a state where a moist cloudy region with intense deep convective storms is surrounded by extremely dry subsiding air devoid of deep clouds. We review here the main findings from theoretical work and idealized models of this phenomenon, highlighting the physical processes believed to play a key role in convective self-aggregation. We also review the growing literature on the importance and implications of this phenomenon for the tropical atmosphere, notably, for the hydrological cycle and for precipitation extremes, in our current and in a warming climate.},
  author       = {Muller, Caroline J and Yang, Da and Craig, George and Cronin, Timothy and Fildier, Benjamin and Haerter, Jan O. and Hohenegger, Cathy and Mapes, Brian and Randall, David and Shamekh, Sara and Sherwood, Steven C.},
  issn         = {1545-4479},
  journal      = {Annual Review of Fluid Mechanics},
  pages        = {133--157},
  publisher    = {Annual Reviews},
  title        = {{Spontaneous aggregation of convective storms}},
  doi          = {10.1146/annurev-fluid-022421-011319},
  volume       = {54},
  year         = {2022},
}

@article{10653,
  abstract     = {Squall lines are known to be the consequence of the interaction of low-level shear with cold pools associated with convective downdrafts. Also, as the magnitude of the shear increases beyond a critical shear, squall lines tend to orient themselves. The existing literature suggests that this orientation reduces incoming wind shear to the squall line, and maintains equilibrium between wind shear and cold pool spreading. Although this theory is widely accepted, very few quantitative studies have been conducted on supercritical regime especially. Here, we test this hypothesis with tropical squall lines obtained by imposing a vertical wind shear in cloud resolving simulations in radiative convective equilibrium. In the sub-critical regime, squall lines are perpendicular to the shear. In the super-critical regime, their orientation maintain the equilibrium, supporting existing theories. We also find that as shear increases, cold pools become more intense. However, this intensification has little impact on squall line orientation.},
  author       = {Abramian, Sophie and Muller, Caroline J and Risi, Camille},
  issn         = {1944-8007},
  journal      = {Geophysical Research Letters},
  number       = {1},
  publisher    = {Wiley},
  title        = {{Shear-convection interactions and orientation of tropical squall lines}},
  doi          = {10.1029/2021GL095184},
  volume       = {49},
  year         = {2022},
}