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Morris, Fran; Schwendike, Juliane; Parker, Douglas J.; Bain, Caroline

How Is Synoptic-Scale Circulation Influenced by the Dynamics of Mesoscale Convection in Convection-Permitting Simulations over West Africa?

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  • Medientyp: E-Artikel
  • Titel: How Is Synoptic-Scale Circulation Influenced by the Dynamics of Mesoscale Convection in Convection-Permitting Simulations over West Africa?
  • Beteiligte: Morris, Fran; Schwendike, Juliane; Parker, Douglas J.; Bain, Caroline
  • Erschienen: American Meteorological Society, 2024
  • Erschienen in: Journal of the Atmospheric Sciences, 81 (2024) 4, Seite 765-782
  • Sprache: Nicht zu entscheiden
  • DOI: 10.1175/jas-d-22-0032.1
  • ISSN: 0022-4928; 1520-0469
  • Entstehung:
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  • Beschreibung: AbstractUnderstanding how mesoscale convection interacts with synoptic-scale circulations over West Africa is crucial for improving regional weather forecasts and developing convection parameterizations to address biases in climate models. A 10-yr pan-African convection-permitting simulation and a corresponding parameterized simulation for current-climate conditions are used to calculate the circulation budget around a synoptic region over the diurnal cycle, splitting processes that modulate circulation tendency (vorticity accumulation and vortex tilting) into diurnal mean and anomalous contributions. Dynamical fields are composited around precipitating grid cells during afternoon and overnight convection to understand how the mesoscale convection modulates synoptic-scale processes, and the composites are compared with an observational case. The dominant process modulating circulation tendency was found to be synoptic-scale vorticity accumulation, which is similar in the two simulations. The greatest difference between the simulated budgets was the tilting term. We propose that the tilting term is affected by convective momentum transport associated with precipitating systems crossing the boundary of the region, whereas the stretching term relies on the convergence and divergence induced by storms within the region. The simulation with parameterized convection captures the heating profile similarly to the simulation with explicit convection, but there are marked differences in convective momentum transport. An accurate vertical convergence structure as well as momentum transport must be simulated in parameterizations to correctly represent the impacts of convection on circulation.Significance StatementWe used climate simulations with explicit convection and a convection parameterization to interrogate the relationship between mesoscale convection and synoptic-scale circulation over West Africa. We examined the typical behavior of mesoscale precipitating systems in both simulations and compared this with an observation of a storm. We also investigated how synoptic circulation changed over a diurnal cycle in both simulations. The biggest differences between the simulations were caused by how mesoscale systems in each simulation transport momentum when they cross the boundaries of a circulation, but the greatest impact on synoptic circulation was from the patterns of convergence and divergence induced by mesoscale systems, which are very similar in both simulations. Convection parameterizations should prioritize improving the representation of momentum transport.