Improvement of 6-15 Day Precipitation Forecasts Using a Time-Lagged Ensemble Method

• Published in: Advances in atmospheric sciences Vol. 31; no. 2; pp. 293 - 304
• Main Authors: Jie, Weihua, Wu, Tongwen, Wang, Jun, Li, Weijing, Liu, Xiangwen
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.03.2014; Springer Nature B.V; Beijing Climate Center, China Meteorological Administration, Beijing 100081%Beijing Climate Center, China Meteorological Administration, Beijing 100081%Department of Earth and Atmospheric Sciences, University of Nebraska-Lincoln, NE 68588-0340, USA; University of Chinese Academy of Sciences, Beijing 100049
• Subjects: Atmospheric circulation; Atmospheric Sciences; Earth and Environmental Science; Earth Sciences; Geophysics/Geodesy; Meteorology; Precipitation; Weather forecasting; 大气环流模式; 定性预测; 平均降水量; 时间滞后; 有效时间; 降水预报; 集成方法; 频率偏差; China, People's Rep., Xizang, Tibetan Plateau; China, People's Rep., Beijing; time-lagged ensemble system; precipitation; 6–15 day forecasts; lagged average forecast; 6-15 day forecasts
• ISSN: 0256-1530; 1861-9533
• DOI: 10.1007/s00376-013-3037-8

A time-lagged ensemble method is used to improve 6-15 day precipitation forecasts from the Beijing Climate Center Atmospheric General Circulation Model,version 2.0.1.The approach averages the deterministic predictions of precipitation from the most recent model run and from earlier runs,all at the same forecast valid time.This lagged average forecast （LAF） method assigns equal weight to each ensemble member and produces a forecast by taking the ensemble mean.Our analyses of the Equitable Threat Score,the Hanssen and Kuipers Score,and the frequency bias indicate that the LAF using five members at time-lagged intervals of 6 h improves 6-15 day forecasts of precipitation frequency above 1 mm d-1 and 5 mm d-1 in many regions of China,and is more effective than the LAF method with selection of the time-lagged interval of 12 or 24 h between ensemble members.In particular,significant improvements are seen over regions where the frequencies of rainfall days are higher than about 40％-50％ in the summer season; these regions include northeastern and central to southern China,and the southeastem Tibetan Plateau.