A Numerical Study of Downbursts Using the BLASIUS Model

Abstract

Downbursts can produce severe damage in near-ground areas and can also pose serious threats to aircraft in flight. In this study, a high-resolution boundary layer model—the Boundary Layer Above Stationary, Inhomogeneous Uneven Surface (BLASIUS) model—is used to simulate the evolution of a downburst. The observational data collected in Tazhong, China, located in hinterland of the Taklimakan Desert, during the Boundary Layer Comprehensive Observational Experiment on 27 July 2016 are used as the thermodynamic initial field for the BLASIUS model. In addition, the impacts of the terrain on the structure, turbulence intensity, and maximum wind speed of the downburst are also investigated. The results show that the BLASIUS model can simulate the structure and evolution characteristics of downbursts. The cold pool becomes warm if an isolated hill is implanted in the model under the same model conditions. Both the movement speed of the head and the average wind speed of the downburst decrease, while the maximum wind speed increases. The scale of the hill affects the dynamic and thermodynamic structures of the downburst through obstruction and entrainment mixing. The maximum wind speeds occur on the windward slope, and the downburst passes over the hill in the various tests with a hill. The head of the cold pool becomes narrow and tall for larger hill width cases. The Froude number generally decreases as the height of the hill increases, and the downburst can pass over the hill. The results are helpful to improve our understanding of the effects that terrain blocking on downburst structure and near-ground wind shear. Significance Statement Downbursts have the potential to cause significant damage to building structures and agricultural production and to cause unpredictable serious disasters. It is particularly important to understand the structure and evolution of downbursts. In addition, the influence of the topography on the structure and intensity of turbulent vortices during a downburst remain unclear. The results show that the Boundary Layer Above Stationary, Inhomogeneous Uneven Surface (BLASIUS) model can simulate the structure and evolution characteristics of downbursts. The cold pool becomes warm if an isolated hill is implanted in the model. The scale of the hill affects the dynamic and thermodynamic structures of the downburst through obstruction and entrainment mixing. The Froude number generally decreases as the height of the hill increases, and the downburst can pass over the hill.

An incremental analysis update in the framework of the four‐dimensional variational data assimilation: Description and preliminary tests in the operational China Meteorological Administration Global Forecast System

“…Considering the physical parameterization schemes, the rapid radiative transfer model, the common land model, the medium‐range forecast, and the new simplified Arakawa–Schubert are used for the long‐wave and short‐wave radiation schemes, the land surface scheme, the planetary boundary layer scheme, and the deep and shallow cumulus convection parameterization schemes, respectively. Following the non‐hydrostatic atmospheric model, non‐hydrostatic tangent linear and adjoint models are developed (Liu et al, 2017). A series of linear physical processes are applied to the 4DVar assimilation system.…”