A Composite Approach of Radar Echo Extrapolation Based on TREC Vectors in Combination with Model-Predicted Winds |
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| Authors: | LIANG Qiaoqian FENG Yerong DENG Wenjian HU Sheng HUANG Yanyan ZENG Qin and CHEN Zitong |
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| Institution: | Guangdong Meteorological Observatory, Guangzhou 510080,Guangdong Meteorological Observatory, Guangzhou 510080,Guangdong Meteorological Observatory, Guangzhou 510080,Guangdong Meteorological Observatory, Guangzhou 510080,Guangzhou Institute of Tropical and Marine Meteorology, Guangzhou 510080,Guangdong Meteorological Observatory, Guangzhou 510080,Guangzhou Institute of Tropical and Marine Meteorology, Guangzhou 510080 |
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| Abstract: | Extending the lead time of precipitation nowcasts is vital to improvements
in heavy rainfall warning, flood mitigation, and water resource management.
Because the TREC vector (tracking radar echo by correlation) represents only
the instantaneous trend of precipitation echo motion, the approach using
derived echo motion vectors to extrapolate radar reflectivity as a rainfall
forecast is not satisfactory if the lead time is beyond 30 minutes. For
longer lead times, the effect of ambient winds on echo movement should be
considered. In this paper, an extrapolation algorithm that extends forecast
lead times up to 3 hours was developed to blend TREC vectors with
model-predicted winds. The TREC vectors were derived from radar reflectivity
patterns in 3 km height CAPPI (constant altitude plan position indicator)
mosaics through a cross-correlation technique. The background steering winds
were provided by predictions of the rapid update assimilation model CHAF
(cycle of hourly assimilation and forecast). A similarity index was designed
to determine the vertical level at which model winds were applied in the
extrapolation process, which occurs via a comparison between model winds and
radar vectors. Based on a summer rainfall case study, it is found that the
new algorithm provides a better forecast. |
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| Keywords: | radar motion vector rapid update assimilation model extrapolation nowcast |
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