1. The Role of Antecedent Soil Moisture on Variability of the North American Monsoon System Chunmei Zhu a, Yun Qian b, Ruby Leung b, David Gochis c, Tereza Cavazos d, and Dennis P. Lettenmaier a Joint Assembly Acapulco, Mexico May 23, 2007 a Department of Civil and Environmental Engineering, University of Washington, Seattle, WA USA b Pacific Northwest Laboratory, Richland, WA USA c National Center for Atmospheric Research, Boulder, CO USA d CICESE, Ensenada, Mexico

2. 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.

3. 1) The land-surface feedback as inferred through retrospective data analysis

4. Retrospective Land Data Assimilation System (LDAS) dataset 1950 – 1999 ( Maurer et al. 2002 ) ► Monthly precipitation (P) ► surface 2-meter air temperature (Ts) ► Total column soil moisture (Sm) ► snow water equivalent (SWE) Continental U.S.A:Mexico: Long-term climate and derived surface hydrology and energy flux data for Mexico, 1925 – 2004. (Zhu & Lettenmaier 2007) Retrospective Land Surface Dataset

6. 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

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

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

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

10. 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

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

12. 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

13. 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.

14. 2) MM5/VIC Modeling Evaluation of the Influence of Antecedent Soil Moisture on Variability of the North American Monsoon System

15. The PSU/NCAR Mesoscale Model DocumPublicatios Links Precipitation Pressure Radiation Wind Humidity Air temperature Sensible heat flux Latent heat fluxes … First coupled by Drs. Ruby Leung at Pacific Northwest National Laboratory (PNNL) and Xu Liang at University of California, Berkeley

16. Experiment Design Initial soil moisture prescribed at Oct SepAugJulyJune SM free running May 15 Field capacityWilting point Normal (VIC climatology) ► Running on wet, normal and dry monsoon years to represent different atmospheric circulation conditions ► The initial soil wetness condition on May 15 represents winter precipitation condition. Soil Moisture prescribing domain

17. 1984 1987 1995 1979 1993 MSa JJAS Precipitation and Onset MSa and MW JJAS Precipitation 1984 1990 1995 1979 1973 Wet year: 1984 (much earlier onset than 1990) Dry year (after 1980): 1989, 1995 Wet year, dry year??? 1989

18. June Monthly precipitation comparison of 1984 control run with observation July modelObs model Obs

19. August September model Obs model Obs

20. Comparison between Control Run and Observation Onset Date: Control RunObservation June. 12 NAMS precipitation (mm): June July August September 102 142 116 63 93 116 124 52 NAMS NAM

21. Total Column Soil Moisture Comparison with VIC-offline Simulation June July coupled offline coupledoffline

22. August September coupled offline coupledoffline

23. Winter Precipitation - Monsoon Rainfall feedback hypothesis Higher (lower) winter precipitation & spring snowpack More (less) spring & early summer soil moisture Lower (higher) spring & early summer surface temperature Weak (strong) monsoon Hypothesis to be tested by MM5-VIC coupling system:

24. 1984 wet year Experiment: Onset Date: Field CapacityWilting Point Control June 8 June 13 June 12 NAMS Precip (mm): June July August September 107 81 102 139 111 142 137 131 116 91 90 63 The simulation results are unexpected. It seems like the wetter winter leads to earlier onset and heavier monsoon precipitation especially for June and July than drier winter (maybe related to the higher latent heat).

25. Precipitation difference between FC and WP June 1984 July 1984 Aug 1984 Sep 1984

26. Surface Skin Temperature Difference June 1984 July 1984 Aug 1984Sep 1984

27. Latent Heat Difference June 1984 July 1984 Aug 1984 Sep 1984

28. Soil Moisture Fraction Difference June 1984 July 1984 Aug 1984 Sep 1984

29. Pre-monsoon condition (May 15 to June 8) First Layer Soil Moisture Surface Skin TemperatureLatent Heat

30. 1989 dry year simulation Monthly precipitation comparison with observation June July coupledObs coupledObs

31. August September coupledObs coupledObs

32. 1989 Experiment: Onset Date: Field CapacityControl Observation June 11 June 15 June 30 NAMS Precip (mm): June July August Septemeber 86 74 16 130 128 90 109 110 126 104 96 51 It seems like the dry year is less sensitive than wet year. The wet winter condition only causes a little increase of precipitation in June and September.

33. Precipitation difference between FC and Control June 1989July 1989 Aug 1989 Sep 1989

34. Surface Skin Temperature Difference June 1989 July 1989 Aug 1989Sep 1989

35. Latent Heat Difference June 1989 July 1989 Aug 1989 Sep 1989

36. Soil Moisture Fraction Difference June 1989 July 1989 Aug 1989Sep 1989

37. Summary 1) MM5-VIC modeling system could simulate North American Monsoon precipitation realistically well for the wet year 1984, also did a good job for capturing the July, August, September precipitation pattern in Northwestern Mexico for the dry year 1989. More simulation runs need be done across more years to better evaluate the simulation ability of this coupling system. 2) The influence of pre-monsoon soil wetness condition over NAMS onset and precipitation seems the reverse of what we found though the data analysis study for wet year. The wetter winter seems to lead to wetter summer in 1984. But the dry year NAMS precipitation is less sensitive than wet years to the spring soil condition.