Rafei et al. (2025) Downdrafts and Convective Gusts in High‐Resolution Simulations: An Australian Case Study

⚠️ Warning: This summary was generated from the abstract only, as the full text was not available.

Identification

• Journal: Journal of Geophysical Research Atmospheres
• Year: 2025
• Date: 2025-12-19
• Authors: Moutassem El Rafei, Alejandra Isaza, Steven C. Sherwood, Jason Evans, Andrew Brown, Fei Ji, Andrew Dowdy
• DOI: 10.1029/2025jd044151

Research Groups

Not specified in the abstract.

Short Summary

This study investigates the forcing mechanisms of strong convective downdrafts and surface gusts using high-resolution Weather Research and Forecasting (WRF) model simulations. It finds that very high spatial resolutions (down to 200 m) are crucial for accurately representing these phenomena, revealing that perturbation pressure and thermal buoyancy are primary drivers, which are significantly underestimated by coarser models.

Objective

• To study the forcing mechanisms behind strong convective downdrafts and associated surface gusts using cloud-resolving simulations.
• To understand why coarser grid spacings fail to adequately capture realistic downdrafts and their dynamics.

Study Configuration

• Spatial Scale: Nested downscaling approach with grid spacings down to 200 m (also 1 km and 5 km resolutions were used).
• Temporal Scale: Short-duration regional simulations.

Methodology and Data

• Models used: Weather Research and Forecasting (WRF) model.
• Data sources: Numerical simulations (WRF model output).

Main Results

• A 200-m resolution simulation successfully generated a strong gust event characterized by a pronounced, coherent downdraft.
• The 1-km simulation underestimated the downdraft, and the 5-km simulation failed to represent it at all.
• The vertical momentum budget in weaker downdrafts simulated at 1 km differed from that at 200 m.
• In the 200-m simulation, the perturbation pressure vertical gradient and thermal buoyancy were the main contributors to downdraft acceleration, with condensate loading playing a less significant role at mid and low levels.
• Coarser resolutions (e.g., 1 km) underestimated the role of perturbation pressure, resulting in a smaller contribution to downward acceleration compared to thermal buoyancy and condensate loading.
• The spatial distribution of downdraft forcing mechanisms is a key factor explaining why coarser grid spacings fail to capture realistic downdrafts.

Contributions

• Demonstrates the critical importance of very high spatial resolution (large-eddy simulations, LES) for accurately simulating strong convective downdrafts and surface wind hazards.
• Identifies the perturbation pressure vertical gradient and thermal buoyancy as primary drivers of downdraft acceleration at cloud-resolving scales, clarifying their relative importance compared to condensate loading.
• Provides insights into the limitations of coarser atmospheric models in representing downdraft dynamics, attributing failures to the misrepresentation of spatial distribution of forcing mechanisms.
• Offers findings relevant for improving risk assessment applications and the parameterization of downdrafts in numerical weather prediction models.

Funding

Not specified in the abstract.

Citation

@article{Rafei2025Downdrafts,
  author = {Rafei, Moutassem El and Isaza, Alejandra and Sherwood, Steven C. and Evans, Jason and Brown, Andrew and Ji, Fei and Dowdy, Andrew},
  title = {Downdrafts and Convective Gusts in High‐Resolution Simulations: An Australian Case Study},
  journal = {Journal of Geophysical Research Atmospheres},
  year = {2025},
  doi = {10.1029/2025jd044151},
  url = {https://doi.org/10.1029/2025jd044151}
}