1. Dept. of Earth and Atmospheric Sciences
Examining the Influence of Antecedent Soil Moisture in Numerical Simulations of the July 2007 Rainfall Event in Pennsylvania and New York
Stephen Jessup
Stephen Colucci
Dept. of Earth and Atmospheric Sciences
Cornell University

2. Presentation Overview
Synoptic conditions
Model validation
Altered initial soil moisture experiments
Boundary layer effects
Precipitation results
Summary

3. Project Objectives
Simulate a precipitation event with reasonable accuracy using WRF
Run simulations with altered initial soil moisture
Better understand role of surface-atmospheric coupling and resulting influence on precipitation

4. Synoptic Conditions on 27-28 July 2007

5. HPC Surface Analysis 12Z 27 July

6. Surface Analysis 00Z 27 July

7. 850 mb Analysis 00Z 28 July

8. 700 mb Analysis 00Z 28 July

9. 500 mb Analysis 00Z 28 July

10. 300 mb Analysis 00Z 28 July

11. HPC Surface Analysis 12Z 28 July

12. Radar-estimated Storm Total Precipitation

13. Rain Gauge Totals

14. Comparison of Rain Gauge and Radar Estimated Precipitation

15. Simulations of 27-28 July Rainfall Event

16. 27-28 July 07 Model Results

17. Model Storm Total Precipitation

18. Radar-estimated Storm Total Precipitation

19. Altered Initial Soil Moisture Experiments

20. Simple Hypothesis 1
Altering soil moisture affects evaporation, which in turn affects atmospheric boundary layer moisture
Increased soil moisture → increased lower atmospheric moisture
Decreased soil moisture → decreased lower atmospheric moisture

21. Differences in total surface moisture flux

22. Differences in specific humidity, 3 hours into model run (925 mb)‏
July07qdiff00Z925mb.gif

23. Differences in specific humidity, 9 hours into model run
July07qdiff00Z925mb.gif

24. Simple Hypothesis 2
Changing soil moisture affects the Bowen ratio, which modifies boundary layer heating processes
In runs with altered initial soil moisture, boundary layer temperature differences between runs should be negative for increased soil moisture and positive for decreased soil moisture

25. Differences in T, 3 hours into model run
July07qdiff00Z925mb.gif

26. Differences in T, 6 hours into model run
July07Tdiff21Z925mb.gif

27. Differences in T, 9 hours into model run
July07Tdiff00Z925mb.gif

28. Simple Hypothesis 3
Altering soil moisture alters atmospheric conditions from the lower boundary
In model runs with altered initial soil moisture, atmospheric moisture and temperature differences between runs should be greatest in lower atmosphere and decrease with height

29. Profile of differences in q, 00Z SoilM 1.5 -1.0
July07qdiff00ZSoilM1.5profile.gif

30. Profile of T difference between 1.5 and 1.0 Soil Moisture runs at 03Z
July07tempdiffprofile03Z

31. Influence of Altered Initial Soil Moisture on Precipitation

32. Radar Estimated Precipitation 06Z

33. Model Simulated Precipitation 06Z
July07Run9precip.gif

34. Precipitation from Altered Initial Soil Moisture Runs 06Z
July0706ZPrecipSoilM.gif
July07PrecipSoilM.gif

35. Precipitation Differences Compared to 1.0 Soil Moisture Run

36. Summary
WRF simulates precipitation field from July rainfall event reasonably well
Boundary layer effects of modeled changes in initial soil moisture match simple predictions
Changes in initial soil moisture modify the mesoscale environment, which in turn affects precipitation generation
Earlier initiation of heavy precipitation with enhanced soil moisture
More widespread region of moderate to heavy precipitation with enhanced soil moisture

37. Future Work
Observational study (using NARR) to examine flash flood events in Northeast U.S
Do synoptic/mesoscale conditions differ from those of Central U.S. heavy precipitation events?
Analysis of basin-averaged rainfall estimates using AMBER