# Wind Characteristics in Mountainous Valleys Obtained through Field Measurement
## 1 Introduction  
Wind engineering is a discipline that studies the impact of wind on human engineering and social activities [1]. The research on wind-induced vibrations of bridges is becoming more important with the continuous emergence of bridges with continually record-breaking span lengths. Wind load is now the main control load for the design of long-span bridges. The complex topography of mountainous areas significantly changes the vertical distribution of wind speed and the turbulence structure of the near-surface flowing wind, producing an extremely complicated effect of wind on the structure of the bridge. To study the aerodynamic performance of a bridge structure under wind load and ensure the safety of the bridge, the wind field characteristics at the bridge site must be accurately determined. Due to the peculiarities of the terrain within which mountain bridges are located, it is difficult to construct a unified quantitative guiding standard for the wind field characteristics of mountain terrain, although some research results have been obtained. Many studies [2; 3; 4] focused on wind flow over the low, gently sloping terrain where there is no significant separation [5]. The current research on the characteristics of mountain topography and wind fields is focusing on the acceleration effect of top mountain wind speed and the characteristics of turbulence in leeward mountain areas under the effect of inflow [6]. Others examined the effects of multiple mountain wind fields [7]. At present, there are three main analytical methods used to study wind characteristics: field measurement, numerical simulation, and terrain model wind tunnel tests. The conditions of the model wind tunnel test are easy to control, and the test data are reliable. [PERSON] et al. used the terrain model wind tunnel test method to study the spatial distribution characteristics of a wind field at a bridge site located within complex valley terrain [8]. [PERSON] et al. conducted wind tunnel tests on two-dimensional mountains and three-dimensional symmetrical mountains [9]. [PERSON] et al. studied the influence of ground and mountain surface roughness on the flow separation characteristics of the leeward surface of a mountain in a wind tunnel [10]. [PERSON] et al. studied the influence of six different configurations of ribs on the surface wind pressure on high-rise buildings using wind tunnel experiments [11]. However, limited by the wind tunnel test conditions, the geographical range expressed by the terrain model and the scale adopted are generally small. Therefore, the accuracy of these test results needs to be further studied. The use of numerical simulation methods to study wind characteristics is also a hot topic. [PERSON] et al. conducted a numerical simulation study on a valley wind environment in Northern Portugal [12]. [PERSON] et al. analyzed the long-term wind observation data from multiple observation stations of complex terrain in a coastal area and obtained the correlation between the wind speed of each observation station and the target point using numerical simulation methods [13]. [PERSON] et al. numerically simulated the wind field of urban terrain [14]. [PERSON] et al. used numerical simulation to study the characteristics of the wind field in a location and, based on this, proposed a new spatial wind field prediction model for complex terrain [15]. [PERSON] et al. also used numerical simulation to study the characteristics of a wind field in a larger area and conducted a topographic test [16]. [PERSON] et al. conducted large eddy simulations (LESs) to study the effect of windward-face-mounted ribs on the flow fields, wind pressure distribution, and aerodynamic forces of different high-rise building models, and finally proposed an empirical configuration equation for the ribs [17].