Relationship between preceding winter Asia-Pacific Oscillation (APO) and summer precipitation over the middle and lower reaches of the Yangtze River Mingzhu YANG1, Ge LIU2*, Xiaying ZHU1, Sulan NAN2, Linhai SUN1, Xiaolong JIA1, Ping ZHAO2 1 Beijing Climate Center, CMA, Beijing 100081, China 2 Chinese Academy of Meteorological Sciences, Beijing 100081, China 9th May, 2019 Nanning, Guangxi, China Sponsored by the National Key R&D Program of China (Grant 2018YFC1501706)
OUTLINE • 1. What is Asia-Pacific Oscillation (APO) ? • It's definition and physical implication. • Link between the APO and summer rainfall anomalies over eastern China. • 2. Implicationof preceding winter APOon summer rainfall anomalies over eastern China • 3. 2019 summer rainfall predicted by the APO and its uncertainty
1.What is the APO ? T' is defined as the deviation of temperature from the global zonal mean. The Asian Pacific Oscillation (APO) is defined as a zonal seesaw of the tropospheric eddytemperature in the mid-latitudes of the Asian-Pacific region. (Zhao et al., 2007,Clim Dyn )
Physical significance of the APO The anomalous Tibetan Plateau heating affects the interannual variability of APO during summer. (G. Liu, et al. 2017, J.Cli) Spatial structure of anomalous vertical circulation (red vector lines) and T’ (oC; contours and shading) obtained by regression against the summer Tibetan Plateau thermal index, in which the cross sections are along 85oE, 55oN, and 175oW. The regression is based on NCEP reanalysis data during 1948–2015. Positive (negative) T' anomalies significant at the 95% confidence level are shaded yellow (blue). The black shaded area denotes the terrain. The APO reflects an anomalous zonal land-sea thermal contrast at the middle-upper troposphere. As an extratropical large-scale teleconnection pattern, the APO links atmospheric circulation anomalies on the hemispheric scale and measures the variability of summer monsoon rainfall over South Asia, East Asia, and extratropical North America.
1.What's APO ? The link of the APO with summer rainfall anomalies. The May APO is also significantly correlated with June rainfall over the MLRYR region The summer APO is closely related to simultaneous rainfall over eastern China, especially over the mid and lower reaches of the Yangtze River (MLRYR) (Zhao et al., 2007) (Liu et al., 2015)
2. Implication of preceding winter APO on summer rainfall anomalies over eastern China The summer rainfall of MLRYRhas very significant correlation with preceding winter APO. • Distribution of coefficients of correlation betwen the time series of summer MLRYR rainfall and preceding winter T’300-200hPa field during 1959-2014, in which the correlation coefficients significant at the 95% and 99% confidence levels are shaded.
Distribution of correlation coefficients of winter IAPO with (a) winter, (b) subsequent spring and (c) summer T’300-200hPa during 1958-2014 , in which the correlation coefficients significant at the 95% and 99% confidence levels are shaded.
preceding winter IAPO normalized MLRYR summer rainfall Accompanying the increase the APO's standard deviation (σ), the reliability that the preceding winter APO predicts summer MLRYR precipitation becomes higher. When the preceding winter APO index is higher (lower) than 1.0 (–1.0) σ, it can qualitatively predict the MLRYR summer precipitation, with an accuracy of 87% during the period 1958–2018. Distribution of correlation coefficients between preceding winter IAPO and summer (JJA) precipitation in gauge stations of China during 1958-2018. (Shaded areas denotes coefficients significant at 95% or 99% confidence levels). The preceding winter APO should be considered as an important precursory signal in predicting summer precipitation over the MLRYR.
3. 2019 summer rainfall prediction by APO and uncertainty analysis preceding winter APO MLRYR summer precipitation The normalized APO index in winter of 2018/2019 is -1.40, which indicates that there might be more rainfall over the middle and lower reaches of the Yangtze River during the upcoming summer. Prediction of percentage of anomalous precipitation in summer, 2019, which is obtained by using the preceding winter APO signal. Black dots denote prediction reliability exceeding the 95% confidence level.
uncertainty analysis in recent years Prediction Observation
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