Observation of downburst wind characteristics using the Doppler profiler and near-ground measurements

Abstract

A downburst is a strong downdraft that causes radiating, catastrophic winds at or near the ground. Relevant research conducted in the past decades shows that downbursts not only bring damage to the built environment but also have surprisingly destructive effects on aircraft and other flying objects. However, due to the complexity of atmospheric phenomena and limited measurement datasets, many uncertainties remain to be clarified in the understanding and modelling of the downburst wind field.To further explore the evolution characteristics of thunderstorms, this study uses data recorded during thunderstorms by a Doppler profiler of the Hong Kong Observatory and a near-ground anemometer installed at the Hong Kong International Airport to conduct a detailed feature analysis of the vertical profile and turbulence characteristics of downbursts within the atmospheric boundary layer. Based on long-term field measurements during thunderstorm events, the occurrence of a thunderstorm should be determined by a combination of simultaneous variations in multiple meteorological factors, including wind speed and direction, vertical wind speed, and signal-to-noise ratio (SNR). During thunderstorms, extreme wind speeds occurred in the lower atmosphere and the height of the local peaks seems to be stable in the thunderstorm wind profiles. In addition, both methods, which consider a constant mean component (stationary) and a slowly varying mean component (non-stationary), are used to decompose the measured wind speed and are then compared to investigate the turbulence characteristics of downbursts. It is found that although the gust factor and turbulence intensity show some deviation due to the influence of atmospheric stratification instability, this effect does not appear to be reflected in the turbulence integral scale.