Interdecadal Variability of East Asian Summer Monsoon and Precipitation

1. Interdecadal Variability of East Asian Summer Monsoon and Precipitation By Huijun Wang Institute of Atmospheric Physics 2011-07-25

2. EAAM–seasonal migration of the rainbelt Averaged monthly rainfall 1979 through 2006 (http://svs.gsfc.nasa.gov)

3. EAAM–seasonal migration of the rainbelt

4. Changes in observed precipitation, 1951-2000 Courtesy of T. Zhou

5. The East Asian monsoon experienced an interdecadal change at the end of 1970sWang H. J., 2001: The Weakening of the Asian Monsoon Circulation after the End of 1970’s, Adv. Atmos. Sci.,18, 376-386.

6. The East Asian summer monsoon index（Wang, 2001, AAS; Wang, 2002, AAS）

7. Area：110-125E, 20-40N Data：NCEP reanalysis Index of wind speed：

8. Variability of the East Asian winter monsoon index

9. Recent interdecadal Variation of the summer precipitation in eastern China

10. Background • Interdecadal variability: a main contributor to the variation in the summer rainfall in East China; • Late 1970’s change – global scale; southern flood and northern drought (Wang 2001; Wu and Wang 2002; Han and Wang 2007; Ding et al. 2009; ……). • Possible contributors: global SST (Fu et al., 2009); PDO; Indian and Atlantic Ocean SST (Li et al. 2001; Yang and Lau 2004; Dong et al. 2006; Li et al. 2008; Wang et al. 2009; ……); snow cover over the Tibetan Plateau (Ding et al., 2008); Arctic sea ice and Eurasian snow; …… • No consistent conclusion

11. Recent changes in regional and global climate: (Kwon et al. 2007; Cummins et al. 2005; Bratcher and Giese 2002; Peterson and Schwing 2003; Swanson and Tsonis 2009; Easterling and Wehner 2009; ……). • Early 1990’s (south China rainfall increase); • Late 1990’s and beginning of 21st century (other regions China: a new interdecadal period?)

12. Data and the model employed • (1) the 160-station precipitation dataset from the China Meteorological Administration; • (2) the soil moisture, horizontal and vertical wind, specific humidity, geopotential height and air temperature from the NCEP/NCAR reanalysis; • (3) the Hadley Centre sea surface temperature (SST); • (4) the PDO index from the website http://jisao.washington.edu/pdo/ • Model: IAP 9L_AGCM 4° lat × 5°lon (Bi 1993; Wang and Bi 1996)

13. Results of the study • (1) Features of the summer precipitation pattern changes • (2) Regional circulation • (3) Background circulation • (4) Sea Surface Temperature • (5) AGCM experiments

14. (1) Features of the summer precipitation pattern changes percentage of the rainfall departure from the 1951-2008 summer mean (7-year smoothed) HR: 32-36°N, 110-121°E YR: 28-31°N, 110-121°E SC: 22-26°N, 110-121°E

15. difference between 2000-2008 and 1979-1999 (a) station precipitation; (b) soil moisture (reanalysis) + + - - + + Consistent change patterns.

16. (2) Regional circulation (a) 850 hPa omega; (b) vertically integrated water vapor content ; (c) vertically integrated (1000-300 hPa) moisture flux ; (d) climatology of (c). Difference in the moisture flux divergence: HR-(- 0.78); YR-(0.29) (Sun et al., 2010)

17. (3) Background circulation (a) 500 hPa gph; (b) WPSH; (c) 200 hPa jet; (d) Temperature gradient.

18. (4) Sea Surface Temperature SST difference and PDO index

19. Correlation map between the summer-mean PDO index and 500 hPa geopotential height during 1979-2008 Consistent with the Warming center over Lake Baikal

20. (5) AGCM experiments 控制试验：1980-2008年平均的夏季海温 敏感性试验：方框区域内的海温差值叠加控制试验海温

21. 500 hPa hgt Observation Model

22. surface air temperature Observation Model

23. Observation Model Precipitation Transport of water vapor （850 hPa wind）

24. Summary • Two interdecadal variation: one in the end of 1970s, another around 1999 • After 1999, the summer precipitation in eastern China has changed significantly, with reduced rainfall over the middle-and-lower reaches of Yangtze River Basin • The interdecadal change after 1999 is possibly related to variation of PDO, which is supported by the AGCM experiments with prescribed SST anomalies