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Chunmei Zhu a , Yun Qian b , Ruby Leung b , David Gochis c , and Dennis P. Lettenmaier a

MM5/VIC Modeling Evaluation of the Influence of Antecedent Soil Moisture on Variability of the North American Monsoon System. Chunmei Zhu a , Yun Qian b , Ruby Leung b , David Gochis c , and Dennis P. Lettenmaier a.

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Chunmei Zhu a , Yun Qian b , Ruby Leung b , David Gochis c , and Dennis P. Lettenmaier a

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  1. MM5/VIC Modeling Evaluation of the Influence of Antecedent Soil Moisture on Variability of the North American Monsoon System Chunmei Zhua, Yun Qianb, Ruby Leungb, David Gochisc, and Dennis P. Lettenmaiera aDepartment of Civil and Environmental Engineering Box 352700, University of Washington, Seattle, WA 98195 bPacific Northwest National Laboratory, Richland WA 99352 cNational Center for Atmospheric Research, PO Box 3000, Boulder, CO 80307

  2. Hypothesis to be tested by: (Zhu et al., J. Climate, 2005, 2007) 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

  3. Links Docum Publicatios PNNLUW vegetation type:Single Multiple elevation band: Single Multiple Parameters: Soil, veg type dependent cell dependent initialization: Spin up 3 months Offline VIC First coupled by Drs. Ruby Leung at PNNL and Xu Liang at University of California, Berkeley MM5-VIC coupled model system Precipitation Pressure Radiation Wind Humidity Air temperature Sensible heat flux Latent heat fluxes … Modification of coupled MM5/VIC modeling system by UW

  4. Soil Moisture prescribing domain Late Early Domain Regions for which winter precipitation are related to summer monsoon in MW and MSa in Zhu et al 2005, 2007. 150*178 grid cells at 30km resolution in a Lambert-Conformal projection MW (eastern AZ and western NM) 1 NAMS (1) MS (2) (northwestern Mexico) MM5/VIC model setup: ●Kain-Fritsch (KF) scheme ● Rapid Radiative Transfer Model (RRTM) long-wave scheme ● simple ice-explicit microphysics ● medium-range forecast (MRF) boundary layer scheme ●NCEP/NCAR Reanalysis LBC

  5. 2 May 15 SM free running June July Aug Sep Oct Experimental Design ►The initial soil wetness condition on May 15 is a surrogate for previous winter precipitation condition. ►Control simulation s. moisture prescribed from offline VIC LDAS (3 mo spin-up, Mar-Apr-May). Initial soil moisture prescribed at Field capacity Wilting point ► Simulations performed on wet and dry monsoon years to represent different atmospheric circulation conditions

  6. MW JJAS Precipitation 1984 1990 1995 1973 1979 1989 1995 1979 1993 1984 Selection of wet/dry years: 1989 Wet year: 1984 Dry year:1989 MSa JJAS Precipitation (dark) and Onset (gray)

  7. June July July June Aug Sep Aug Sep Validation of coupled MM5/VIC modeling system 1984 wet year:Mean monthly daily precipitation Control Simulation Observation

  8. 1989 dry year:Mean monthly daily precipitation Control Simulation Observation June July June July Aug Sep Aug Sep MM5/VIC more aggressive in precipitating during ‘dry’ year

  9. June July June July Aug Sep Aug Sep PositiveSoil Moisture-Monsoon Rainfall Feedback ? mean monthly precipitation difference 1984-wet minus 1984-dry 1989-wet minus 1989-dry

  10. The reverse of the proposed negative -- Winter Precipitation - Monsoon Rainfall feedback hypothesis 1 Higher (lower) winter precipitation & spring snowpack More (less) spring & early summer soil moisture 2 3 Lower (higher) spring & early summer surface temperature Weak (strong) monsoon Begin to examine 3 links……

  11. June July June July Aug Sep Aug Sep June July July June Aug Sep Aug Sep Soil moisture differences between the wet and dry runs persist until mid-summer First Layer Third Layer 1984 1989

  12. Land surface memory – surface thermal conditions (1984) Difference maps between 1984-wet and 1984-dry runs June July First layer soil moisture Aug Sep June July + Aug Sep Latent heat June July -- Surface skin temperature Aug Sep

  13. Difference maps between 1989-wet and 1989-dry runs June July First layer soil moisture June July Aug Sep + Aug Sep June July Latent heat -- Surface skin temperature Aug Sep

  14. ? June July Aug Sep June July Aug Sep Larger Thermal contrast– stronger monsoon Difference map between 1984-wet and 1984-dry runs: Monthly mean surface skin temperature Monthly mean precipitation

  15. ? Southwest surface heat low– monsoon strength Difference maps between 1984-wet and 1984-dry runs 925mb Geopotential Height Surface Skin Temperature June July Aug Sep June July Aug Sep June July In MM5-VIC increased local surface pressure weakens the Southwest surface heat low, but is related to the stronger monsoon? 500mb Geopotential Height Aug Sep

  16. Monthly mean 925 mb meridional moisture flux (QV) averaged over longitude (107-113 oW) at 32 oN Weakening of the thermal low in MM5/Vic sims results in greater moisture flux into the interior of the NAMS region, likely from increased moisture availability due to increased regional evaporation instead of increased low level winds

  17. Shallower Boundary Layer Boundary layer height difference between 1984-wet and 1984-dry runs Wet soil moisture conditions reduce the depth of the boundary layer, therefore increase the boundary layer moist static energy and the frequency and magnitude of rainfall from local convective storms. June July Aug Aug Monthly mean planetary boundary layer height (PBL) in the NAMS domain local land-atmosphere interaction

  18. Summary and Conclusions ●The MM5-VIC control sims reproduce reasonable monsoon precipitation for 1984 and 1989 over northwestern Mexico (1989 somewhat wet vs. obs) ●The model land surface has memory of the initial soil wetness that lasts for several months (until August). This land memory has a negative relationship with surface thermal conditions over the NAMS domain and its larger adjacent area. ●In contrast to the original hypothesis, the wet year 1984 and dry year 1989 experiments exhibit similar positive soil moisture – rainfall feedbacks over the NAMS domain. In essence, it appears that local-regional recycling of moisture dominates in sustaining increased precipitation in the model. However magnitude of imposed anomaly likely imparts excessive influence. ● In nature, both the large-scale circulation changes and local land-atmospheric interactions in response to soil moisture conditions likely play important roles in the soil moisture – monsoon precipitation feedback. The symbiosis of these features needs to be studied in more detail.

  19. Limitations of the experiments Extreme wet and dry soil conditions in the sensitivity experiments extreme surface temperature anomalies exaggerated surface low (not the optimal strength and location to start monsoon) very intense local evaporation Contribute to apparent positive soil moisture – rainfall feedback Future Work Explore the relationship between antecedent soil moisture and monsoon rainfall under less extreme soil conditions, and to identify the relative importance of large-scale circulation and local evaporation.

  20. Changes the surface pressure and the flow field Changes moisture convergence and precipitation. Large-scale circulation or local land-atmosphere interaction ? Meehl G. A., 1994: J. Climate shallower boundary layer Increased convective instability and potential for precipitation Schar C et al. 1999: J.Climate Mo K. C. and H. H. Juang, 2003: J. Geophy. Res

  21. NAMS (1) (2) Monthly means of energy components in the NAMS region Wet soil raises the latent heat and reduces the sensible heat by nearly equal amounts, resulting in decreased surface skin temperature

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