Abstract
Doppler wind lidar has played an important role in alerting low-level wind shear (LLW). However, these high-resolution observations are underused in the model-based analysis and forecasting of LLW. In this regard, we employed the Weather Research and Forecasting (WRF) model and its three-dimensional variational (3D-VAR) system to investigate the impact of lidar data assimilation (DA) on LLW simulations. Eight experiments (including six assimilation experiments) were designed for an LLW process as reported by pilots, in which different assimilation intervals, assimilation timespans, and model vertical resolutions were examined. Verified against observations from Doppler wind lidar and an automated weather observing system (AWOS), the introduction of lidar data is helpful for describing the LLW event, which can represent the temporal and spatial features of LLW, whereas experiments without lidar DA have no ability to capture LLW. While lidar DA has an obviously positive role in simulating LLW in the 10–20 min after the assimilation time, this advantage cannot be maintained over a longer time. Therefore, a smaller assimilation interval is favorable for improving the simulated effect of LLW. In addition, increasing the vertical resolution does not evidently improve the experimental results, either with or without assimilation.
Highlights
Low-level wind shear (LLW), which is a known aviation safety hazard, is receiving more attention as the number of flights increases [1,2,3]
The physics schemes used in all domains include the Rapid Radiative the simulation results with 1 km and 200 m resolutions against observations from the lidar and automated weather observing system (AWOS), Transfer Model longwave radiation [24], Dudhia shortwave radiation [25], the Yonsei University we found that the simulation with a 200 m resolution performed slightly worse than that with a 1 km (YSU) planetary boundary layer scheme [26], the Purdue–Lin microphysics scheme [27,28], and the resolution
The lidar data assimilation (DA) can effectively absorb lidar observations, and improve the simulation ability of the Weather Research and Forecasting (WRF) model on LLW; Assimilation experiments with a small interval (e.g., 10 min) are beneficial for the simulation of LLW, whereas experiments with a large interval are unfavorable for maintaining the development of the wind field
Summary
Low-level wind shear (LLW), which is a known aviation safety hazard, is receiving more attention as the number of flights increases [1,2,3]. When flights encounter LLW during takeoff or landing, the small temporal–spatial range of LLW occurrence makes pilots’ response difficult. It is necessary to determine the timings and positions of LLW by numerical models or other effective methods. Numerical weather prediction (NWP) technology is an effective tool for providing future weather information, and successful predictions on severe weather phenomena can reduce the damage to human lives and social resources [6]. Considering the small temporal–spatial scale and high variability of LLW, model-based simulation or forecasting should be performed at a high resolution (e.g., several kilometers or less). Some related studies that have been documented at present include ideal simulation experiments of terrain-induced turbulence [7], large-eddy simulation of the turbulent
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