Thermodynamic Processes Driving Thermal Circulations on Slopes: Modeling Anabatic and Katabatic Flows on Reunion Island

• Published in: Journal of geophysical research. Atmospheres 2024-09, Vol.129 (17), p.n/a
• Main Authors: El Gdachi, S., Tulet, P., Réchou, A., Burnet, F., Mouchel‐Vallon, C., Jambert, C., Leriche, M.
• Format: Article
• Language: English
• Subjects: Acceleration; Air; boundary layer; Breezes; Buoyancy; Convergence; Convergence zones; Cooling; Earth Sciences; Flow; Heat budget; heat budgets/fluxes; Heating; high‐resolution simulations; Katabatic winds; Meteorology; Momentum; momentum budgets/fluxes; Regional analysis; Regional development; Return flow; Sciences of the Universe; Simulation; Slope stability; Surface cooling; Thermal circulation; Thermal simulation; thermally driven circulations; Trade winds; Wind
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1029/2023JD040431

This study investigates thermal circulations on Reunion Island (21°07’S 55°32’E), focusing on the complex terrain of the region. Observations from the BIO‐MAÏDO campaign, along with 2 days of high‐resolution simulation using the MesoNH model, were analyzed to understand the thermally‐driven mechanisms. This simulation was conducted with a horizontal resolution of 100 m and employed a vertically stretched grid, achieving a resolution of 1 m at the lowest levels. Two distinct wind regimes were identified, characterized by katabatic flows prevailing within a 30 m thick layer during nighttime, and an anabatic flow manifesting within a layer spanning from 150 to 200 m during the daytime. The simulation was confirmed through validation with surface measurements, and thus enabling a detailed study of thermal breeze circulations. Results reveal that the intensity of trade winds significantly influences the development of thermal circulations. Complex layered structures in the atmosphere were also identified. At an intensity of 7 m s−1, trade winds impede the development of thermal circulations atop the slope, and result in the emergence of a convergence zone between local and regional circulations. The analysis of the breeze establishment period indicates that the katabatic flow stabilizes in 35 min, quicker than the anabatic flow, which takes 110 min. Momentum and heat budget analysis provide insights into the primary drivers of thermal circulations: buoyancy acceleration, influenced by local surface heating during anabatic flow onset, and local surface cooling during katabatic flow onset. Plain Language Summary This research explores thermal circulation in the northwestern region of Reunion Island, an area significantly influenced by the return flow of the trade winds, the trade winds themselves, and breezes. Data from the BIOMAÏDO campaign and simulation using the MesoNH model were employed to analyze the heat‐driven air movements in this specific region. The study identified two distinct wind patterns: a downward katabatic flow within a 30 m layer and a diurnal anabatic flow occurring between elevetions of 150–200 m. Validation through surface measurements corroborated the model simulation, facilitating a detailed analysis of thermal breeze circulations. The results indicate that strong directional winds significantly influence air movement patterns. At a speed of 7 m s−1, these winds inhibit upward air movement along the slopes, creating a convergence zone be