Assimilating Surface Observations in a Four-Dimensional Variational Doppler Radar Data Assimilation System to Improve the Analysis and Forecast of a Squall Line Case

• Published in: Advances in atmospheric sciences 2016-10, Vol.33 (10), p.1106-1119
• Main Authors: Chen, Xingchao, Zhao, Kun, Sun, Juanzhen, Zhou, Bowen, Lee, Wen-Chau
• Format: Article
• Language: English
• Subjects: Atmospheric Sciences; Data assimilation; Data collection; Doppler radar; Earth and Environmental Science; Earth Sciences; Geophysics/Geodesy; Meteorology; Radar; Storms; Surface temperature; Weather forecasting; Wind; 三维变分同化; 地面观测; 多普勒雷达; 系统; 表面观测; 资料同化; 预测能力; 飑线过程
• ISSN: 0256-1530; 1861-9533
• DOI: 10.1007/s00376-016-5290-0

This paper examines how assimilating surface observations can improve the analysis and forecast ability of a four- dimensional Variational Doppler Radar Analysis System （VDRAS）. Observed surface temperature and winds are assimilated together with radar radial velocity and reflectivity into a convection-permitting model using the VDRAS four-dimensional variational （4DVAR） data assimilation system. A squall-line case observed during a field campaign is selected to investigate the performance of the technique. A single observation experiment shows that assimilating surface observations can influence the analyzed fields in both the horizontal and vertical directions. The surface-based cold pool, divergence and gust front of the squall line are all strengthened through the assimilation of the single surface observation. Three experiments--assimilating radar data only, assimilating radar data with surface data blended in a mesoscale background, and assimilating both radar and surface observations with a 4DVAR cost function--are conducted to examine the impact of the surface data assimilation. Independent surface and wind profiler observations are used for verification. The result shows that the analysis and forecast are improved when surface observations are assimilated in addition to radar observations. It is also shown that the additional surface data can help improve the analysis and forecast at low levels. Surface and low-level features of the squall line-- including the surface warm inflow, cold pool, gust front, and low-level wind--are much closer to the observations after assimilating the surface data in VDRAS.