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- Title
On the Sensitivity of Convective Cold Pools to Mesh Resolution.
- Authors
Fiévet, Romain; Meyer, Bettina; Haerter, Jan O.
- Abstract
It is well recognized that triggering of convective cells through cold pools (CPs) is key to the organization of convection. Yet, numerous studies have found that both the characterization and parameterization of CP effects in numerical models is cumbersome—in part due to the lack of numerical convergence with respect to the horizontal mesh resolution, Δx, obtained in typical cloud‐resolving simulators. Within a comprehensive numerical convergence study we systematically increase the horizontal resolution in a set of idealized large‐eddy simulations. Our analysis captures key CP processes, namely free propagation, frontal collision and merging of gust fronts. We characterize the numerical convergence of tropospheric moistening rates, gust front vortical strength and propagation speed, and the amplitude of the lobe‐and‐cleft instability. The understanding gained from this analysis may help develop robust subgrid models for CP dynamics. Plain Language Summary: Convective cold pools (CPs) are regions of cool air forming beneath precipitating clouds. As rain droplets evaporate during their fall, they cool down the surrounding air, thereby increasing its weight and causing it to sink down. As the cold sinking airflow hits the ground, it spreads outward in all directions, creating strong wind gusts which are important mediators of the weather system. Indeed, such gust fronts can suppress cloud formation in some locations, by cooling the near‐surface air, while simultaneously triggering cloud formation along their edges by wedging underneath and lifting the ambient air. Numerical weather models should ideally account for these effects. Unfortunately, the models' grid resolution is often too coarse to represent the thin CPs, and it is not yet known what resolution should be used. In this study, high‐resolution simulations of idealized CPs are carried out at different mesh resolutions, allowing a systematic exploration of CPs' sensitivity to grid resolution. Our simulation results may help reveal configuration requirements for high‐resolution simulations and guide climate model development. Key Points: At coarse resolutions, cold pools (CPs) suffer from numerical dissipation, which weakens the mechanical lifting induced by their gust front (GF)At high resolution of ≤100 m, lobe‐and‐cleft instabilities activate, which contributes to weakening the leading GFThe merging of gust fronts not only results in a stronger, longer‐sustained combined front, but is also resilient to mesh coarsening
- Subjects
FRONTS (Meteorology); ATMOSPHERIC models; COOLDOWN; AIR flow
- Publication
Journal of Advances in Modeling Earth Systems, 2023, Vol 15, Issue 8, p1
- ISSN
1942-2466
- Publication type
Article
- DOI
10.1029/2022MS003382