Abramian, Sophie; Muller, Caroline JISTA ; Risi, Camille
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.
Journal of Advances in Modeling Earth Systems
The authors gratefully acknowledge funding from the European Research Council under the European Union's Horizon 2020 research and innovation program (Project CLUSTER, Grant Agreement No. 805041). This work is also supported by a PhD fellowship funded by the Ecole Normale Supérieure de Paris-Saclay. Authors are also grateful to Benjamin Filider, who was of great help and support in the development of ideas. Eventually, we would like to thank Martin Singh, John M. Peters and an anonymous reviewer for their valuable comments and suggestions, which greatly improved the quality of the manuscript.
Abramian S, Muller CJ, Risi C. Extreme precipitation in tropical squall lines. Journal of Advances in Modeling Earth Systems. 2023;15(10). doi:10.1029/2022MS003477
Abramian, S., Muller, C. J., & Risi, C. (2023). Extreme precipitation in tropical squall lines. Journal of Advances in Modeling Earth Systems. Wiley. https://doi.org/10.1029/2022MS003477
Abramian, Sophie, Caroline J Muller, and Camille Risi. “Extreme Precipitation in Tropical Squall Lines.” Journal of Advances in Modeling Earth Systems. Wiley, 2023. https://doi.org/10.1029/2022MS003477.
S. Abramian, C. J. Muller, and C. Risi, “Extreme precipitation in tropical squall lines,” Journal of Advances in Modeling Earth Systems, vol. 15, no. 10. Wiley, 2023.
Abramian S, Muller CJ, Risi C. 2023. Extreme precipitation in tropical squall lines. Journal of Advances in Modeling Earth Systems. 15(10), e2022MS003477.
Abramian, Sophie, et al. “Extreme Precipitation in Tropical Squall Lines.” Journal of Advances in Modeling Earth Systems, vol. 15, no. 10, e2022MS003477, Wiley, 2023, doi:10.1029/2022MS003477.
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