1. 1 Role of Antecedent Land Surface Conditions on North American Monsoon Rainfall Variability Chunmei Zhu Department of Civil and Environmental Engineering University of Washington Sep, 2005

2. 2 North American Monsoon System (NAMS) North American monsoon is experienced as a pronounced increase in rainfall from extremely dry May to rainy June. North American Monsoon Experiment (NAME): Tier 1,2,3. (http://www.cpc.ncep.noaa.gov/products/pr ecip/monsoon/NAME.html) ( Comrie & Glenn, 1998 )

3. 3 The NAMS concept --- thermal contrast between land and adjacent oceanic regions ( http://www.ifm.uni-kiel.de ) The importance to explore possible links between NAMS and antecedent surface conditions.

4. 4 Study Domain Monsoon regions are defined as in Comrie & Glenn (1998) Monsoon West Monsoon South Monsoon North Monsoon East

5. 5 Monsoon West

6. 6 15-year Moving Average Correlation of PI versus MW JJAS rainfall JFM Precipitation Index (PI) JFM PI Winter Precipitation – Monsoon Relationship

7. 7 Winter Precipitation - Monsoon Rainfall feedback hypothesis Higher (lower) winter precipitation & spring snowpack Higher (lower) winter precipitation and spring snowpack More (less) spring or early summer soil moisture lower (higher) spring and early summer surface temperature Weak (strong) monsoon More (less) spring & early summer soil moisture Weak (strong) monsoon Lower (higher) spring & early summer surface temperature

8. 8 JFM Precipitation in extreme monsoon years DRYWET DRY WET Apr-May Soil Moisture in extreme monsoon years Dry MonsoonWet Monsoon

9. 9 Soil moisture anomalies persist from spring until June Correlation of June Sm & JFM PI (1965-1999) Correlation: June Sm & June Ts (No significant relationship in MW ) SW Sm has no significant relationship with Ts

10. 10 Z500 (m) anomaliesJune Ts anomalies High June Low Dry Monsoon Low June High Wet Monsoon

11. 11 Monsoon South

12. 12 Development of a Long-Term Land Surface Data Set for Mexico SMN daily precipitation, surface air temperature data (pre-1940 – 2003 ) produced by SMN (Servicio MeterorolÓgico Nacional), over 5000 stations. SMN daily precipitation data (1995 – near realtime) provided courtesy of Miguel Cortez Vázquez of SMN, around 1,000 stations. NW Mexico NAME Event Raingage Network (NERN) precipitation daily data ( 2002 - ) provided courtesy of David Gochis, 86 station cross Sierra Madre Occidental

13. 13 1 2 3 4 5 6 8 9 10 11 12 13 14 15 7 Comparison of simulated and observed streamflow The streamflow dataset is the Mexico acronym BANDAS (CNA and IMTA).

14. 14 Study Domain The Monsoon South domain is divided into 2 sub-regions (Higgins et al 1998, Hu & Song 2002, Englehart and Douglas, 2001) The long-term mean monthly precipitation 1950-1999 MSa MSb

15. 15 Standardized JJAS Rainfall Wet years Dry years 1951 1969 1973 1979 1987 1995 1958 1966 1984 1986 1990 Monsoon onset date anomaly 1972 1976 1977 1984 1996 Early years Late years 1953 1957 1979 1989 1992 ? monsoon magnitude or onset

16. 16 Winter Precipitation - Monsoon Rainfall feedback hypothesis Higher (lower) winter precipitation & spring snowpack More (less) spring & early summer soil moisture Weak (strong) monsoon Lower (higher) spring & early summer surface temperature From previous study on Southwestern US, we propose a similar …

17. 17 Winter Precipitation – Monsoon Onset 15-year Moving Average Correlation of PI versus monsoon onset Correlation of JFM Precip and Monsoon Onset Date

18. 18 Winter Snow – Monsoon Onset 15-year Moving Average Correlation of JFM SWE index versus monsoon onset The snow – monsoon onset relationship is only significant from 1960 to 1980

19. 19 Late Early LateEarly JFM Precipitation in extreme monsoon years May Soil moisture in extreme monsoon years

20. 20 Winter precipitation – May soil moisture Correlation of JFM Precip and May total column soil moisture Correlation of JFM Precip and May first layer soil moisture

21. 21 May Sm in extreme monsoon years May Ts in extreme monsoon years LateEarly LateEarly

22. 22 Correlation: May first layer Sm & May Ts Correlation: May Ts & monsoon onset May soil moisture plays some role in pre-monsoon seasonal surface thermal condition

23. 23 Late - early Land – sea thermal contrast LateEarly

24. 24 Atmospheric Circulation effect? May Ts anomalies May Z500 anomalies May Ts – Z500 correlation LateEarly

25. 25 Feedback to monsoon magnitude Correlation: May first layer Sm & May Ts Correlation: May Ts & monsoon magnitude

26. 26 Summary ● MW monsoon is negatively related with Southwest winter precipitation. NW Mexico summer monsoon onset date is positively related with Southwest winter precipitation and snow especially for extreme late and early years. ● Spring soil wetness conditions in the SW U.S. and northwestern Mexico are strongly determined by the previous winter’s precipitation, this land memory appears to play some role in the surface thermal condition, then influence the NW Mexico monsoon onset, but seems to contribute little to MW summer monsoon. ● May Z500 anomalies shows strong relationship with May Ts anomaly all over the North America continent, which suggesting that the atmospheric circulation condition may contribute more to the pre-monsoon Ts anomalies than land surface conditions.