Local circulation characteristics and mechanism analysis of Haituo mountain in Beijing during winter 2019

Abstract

<p>The Haituo mountain, one of the main outdoor venues of the Winter Olympic (Paralympic) Games, presents a severe challenge for refined prediction of wind field due to its complex terrain. Therefore, it is imperative to carry out intensive wind field observations to improve our understanding of local circulation  characteristics  and  influence  mechanism  of  complex  terrain,  and provide data support for the improvement of refined prediction and service in the competition area. Based on data obtained in the observational experiment at Haituo mountain in 2019, the horizontal distribution, vertical structure, mountain-valley wind conversion time and local circulation characteristics under the influences of different background wind fields are statistically analyzed using multi-source data, such as data collected by automatic weather stations, doppler wind lidars, eddy covariance systems, ceilometer and cloud radars, etc. The influence mechanism for local circulation in the Haituo mountain is discussed from three perspectives, i.e., topographic dynamic and thermodynamic impacts and background wind field influences. The results show that the local circulation characteristics in the Haituo mountain are significant under calm weather conditions when the background winds are weak. The local circulation is dominated by thermally-driven valley wind circulation superimposed by the influence of background airflow passing over the mountain. At low-altitude (＜1650 m) stations, mountain and valley winds show opposite directions; at mid- (1650—1800 m) and high- (＞1800 m) altitude stations located near the mountain ridges and peaks, mountain and valley winds both are dominated by westerly winds. Valley wind is significantly stronger than mountain wind at the low- and mid-altitude stations, while the opposite is true at high-altitude stations. In contrast, under the influence of strong background winds, local circulation characteristics disappear and the wind direction in the whole valley tends to be consistent with the background wind, while the difference in wind direction between the daytime and nighttime is small and wind speed decreases with increasing height.</p>