Low Frequency Signals of Pentad Rainfall Anomaly during Meiyu Season and Its Extended-Range Forecast in Shanghai
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Abstract:
Improving the capability of extendedrange forecast of precipitation during the Meiyu season has become an important research area for operational developments of both weather forecast and climate prediction. By taking the Meiyu season in Shanghai as an example, this paper analyzes the characteristics of intraseasonal pentad anomalies of Meiyu precipitation and its associating key lowfrequency signals on the extendedrange scale through investigating multivariable intraseasonal components extracted by nontraditional filtering. An extendedrange forecast model of pentad precipitation anomalies during the Meiyu season is further established by integrating the multivariable lowfrequency signals, and the performances of the forecast model are evaluated by the hindcasts and forecast experiments. Results show that: (1) The intraseasonal component of pentad precipitation anomaly during the Meiyu season has significant features of 40 to 60 day lowfrequency oscillation, which also has an significant positive correlation and high sign consistency rate with the observed precipitation anomaly. (2) The intraseasonal pentad anomaly of Meiyu precipitation is related to the low frequency signals from both tropics and the middlehigh latitudes, such as the eastward propagation of tropical MJO from the Arabian sea, the northwestward propagation of the western Pacific subtropical high, the intraseasonal phase conversion of PNA (PacificNorth American) teleconnection and the persistent anomaly influences of cold air activities in Northeast Asia. (3) The extendedrange forecast model of the pentad precipitation anomalies by integrating the above multivariable lowfrequency signals is statistically skillful to forecast the intraseasonal component of pentad precipitation anomalies with a leading time of 10 to 35 days. It also shows outstanding capability in predicting the trend of the observed pentad precipitation anomaly.
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Supported by:Beijing E-Tiller Technology Development Co., Ltd.
Supported by:Beijing E-Tiller Technology Development Co., Ltd.