Application of Anomalous Variables to Severe Convective System Analyses and Model Evaluation: A Case Study on TornadoProducing Anomalous Systems near Lixia River, Jiangsu Province
During 14:00-15:00 Beijing Time (BT) 23 June 2016, an extremely tornado with the EF4 scale hit the Funing County of Jiangsu Province, causing severe damages. Due to the topographic effect, 11 tornado events were recorded causing more than 10 deaths in nearby region in the past 50 years, and 6 occurred after 1979. By decomposing model initial variables and model predicted outputs into temporal climatic state and anomaly, this paper first analyzed the 6 tornado events using observation data, finding that these tornadoes were associated with lowlevel negative anomalous height trough axes and clashes of anomalous cold and warm air masses. Tornadoes always occur in the anomalous warm air mass. In the second half of the paper, the performances of ECMWF model and NCEP GFS on the tornado process on 23 June 2016 were evaluated using anomalous variables and indices. Analysis results at 14:00 BT illustrated that the tornado occurred at the intersection between a 925 hPa height anomaly trough and a maximum axis of moist vorticity anomaly and moist convergence anomaly at 850 hPa, respectively. The lowlevel moisture convergence and moist vorticity anomalies could well indicate the moisture and unstable condition for tornadogenesis. The ECMWF model well predicted the troughaxis feature for leading 42 h in advance while the NCEP GFS predicted for leading 18 h in advance, respectively. These anomalous variables and indices could help forecasters indicate a potential timespace domain of severe convective systems more quickly.