# Observation and Numerical Simulation of a Windshear Case at an Airport in the Qinghai-Tibet Plateau
## 3 Results and Discussion  
### Simulation Result  
The time-height cross section of the simulated wind and EDR at the location of the DWL is shown in Figure 4(a). There are a number of findings:  
Figure 4: The five nested domains G1 to G5.  
1. The easterly jet is reproduced in the simulation, though the maximum wind speed at the jet core is less than actual (only around 35 knots of wind speed has been simulated). There is a veering of the wind above the jet; 2. The intrusion of the westerly jet is also reproduced well, though it occurs later than the actual observation by about 8 h (i.e., 02 local time in actual observations, but around 10 local time in numerical simulation). Moreover, the speed at which the vertical extent of the westerly increases with time is less than actual. The vertical extension of the westerly jet is also lower than actual. By close examination of the data, it is found that these features may be related to the limitation of the global model analysis in this area of complex terrain, as well as the limitation of the amount of data in the Plateau region for more accurate analysis of the wind field, especially in the atmospheric boundary layer; 3. The main features of the EDR distribution is generally reproduced, namely, higher EDR above the jet at the veering of the wind, and the interface between the easterly and the westerly. However, the EDR values appear to be larger than actual observations.  
Another feature of the time-height cross section is the descending of the westerly jet at around 1200 to 1500 m. This is related to the change in the flow regime in the mid-tropospheric westerly in the Plateau region. This is important for en-route stage of the aircraft but is not related to the discussion of windshear, which is the main focus of the present study.  
For better visualization of the airflow, the simulated surface wind (with a height of 10 m above ground level) pattern at the innermost domain is shown in Figure 6. In general, the model simulation shows the weaker easterly wind at first, the setting in of the  
Figure 5: (**a**) is the simulation result of Deardorff scheme, showing the time–height cross section of the simulated wind and EDR. (**b**) is the simulation result of the Smagorinsky scheme.  
easterly jet, the prevailing of stronger easterly winds, and the retreat of the easterly with the replacement by the westerly. Though there are no actual observations in the region to confirm the reliability of the simulated airflow, the changes in the wind appear to be reasonable as compared with the limited observations available from the DWL.  
Figure 6: _Cont._  
Similar to Figure 3b, the time series of the simulated wind speed at the jet core as well above and below the jet is shown in Figure 7a. The simulation appears to reasonably well reproduce the three pulses of the wind speed, which is believed to be the main feature leading to the windshear. Thus, the high resolution numerical simulation seems to be useful in the short-term forecasting of windshear at the Plateau airport under consideration for this particular case.  
Figure 6: The simulated surface wind patterns at four time instances of the simulation. The times of the plots are shown at the top of each sub-figure (**a–d**).  
Figure 7: _Cont._