# Observation and Numerical Simulation of a Windshear Case at an Airport in the Qinghai-Tibet Plateau
## 1 Introduction  
An airport located in an area of complex terrain may be susceptible to the low-level windshear and turbulence due to terrain disruption of the airflow in favorable meteorological conditions ([PERSON] and [PERSON] (2013) [1], [PERSON] and [PERSON] (2022) [2]). The Hong Kong International Airport is an example of a busy airport located near mountainous terrain. Significant windshear occurs at a rate of about once in every 500 movements. Real-time alerting of windshear and turbulence, particularly for clear air situations for terrain-disrupted airflow, is now made possible with the advancement of remote-sensing meteorological instruments such as the more common usage of Doppler Light Detection And Ranging (LIDAR) systems ([PERSON] and [PERSON], 2008) [3]. At the same time, short-term forecasting of low-level windshear has also been explored. In a recent study ([PERSON] et al., 2021) [4], a numerical modeling system with a horizontal resolution of 40 m is found to show positive skills in capturing low-level windshear using pilot reports of windshear as the sky truth. Significant windshear refers to a change in headwind of 15 knots or more, over a distance of several hundreds of meters up to several kilometers, resulting from changes in wind speed and/or wind direction. It may cause the aircraft to deviate from its intended flight path. Significant windshear near the ground could be hazardous because of the limited space left from the ground for the maneuvering of the aircraft. Timely alerting of windshear, by detection and/or by forecasting by numerical weather prediction models, would be crucial in the assurance of aviation safety. In China, there are a number of airports located in the mountainous area of the Qinghai-Tibet Plateau. Windshear and turbulence have often been reported at the airports in this region ([PERSON] et al., 2021) [5]. In the international meteorological and air traffic journals, thereis rather limited documentation of windshear and turbulence for airports in the Plateau, especially the mechanism of windshear. To the knowledge of the authors, there does not seem to be high-resolution numerical simulation of the terrain-disrupted airflow in aviation applications for this region as well, though there are studies about high-resolution numerical simulations for other airports (e.g., [6; 7; 8]). The applicability of the method, e.g., as described in [PERSON] et al. (2021) [4] for the airports in that region, would be an interesting topic scientifically with practical application values. Moreover, in the previous results reported in the literature, the airport is close to isolated high-rising terrain only. For the Qinghai-Tibet Plateau, it consists of very extensive terrain with highly varying heights. It would be interesting to study the terrain-induced windshear over there, to explore the usefulness of high-resolution numerical weather prediction models in forecasting abrupt wind changes. Large eddy simulation (LES) studies for meteorological applications have been considered in a number of studies in the literature. [PERSON] (2020) [9] and [PERSON] (2013) [10] have considered applications for LES for a couple of airports in Japan. [PERSON] et al. (2010) [11] have considered the LES simulation of the eddy dissipation rate (EDR), which is an internationally adopted metric for turbulence, for a complex terrain for T-REX experiment in the US. The verification of LES has also been conducted for a long period of time in a relatively flat area in the Netherlands ([PERSON] et al., 2015) [12]. This short letter documents a case of windshear at an airport at the Plateau. For the first time, a high spatial resolution (40 m) numerical weather prediction model is used to explore the feasibility of reproducing the main features of the wind that may be related to the windshear. A key element in the simulation of the wind at high spatial resolution is the choice of turbulence parameterization scheme, as discussed in [PERSON] et al. (2022) [13].