1. Assessing the diurnal cycle of precipitation in the CSU MMF (T42) Michael S. Pritchard Richard C. J. Somerville John O. Roads Scripps Institution of Oceanography

2. Questions How does the mean daily cycle of JJA precipitation in the MMF compare to CAM, and to satellite retrievals from TRMM? Does the MMF admit the sorts of propagating organized convective systems that in nature cause a nocturnal maximum in summer rainfall over the central U.S.? CMMAP team meeting, Ft. Collins, July 2008

3. Methods CSU MMF & CAM simulations Single-summer with hourly output T42 resolution MMF: 32 (x-z) CRM points per host grid-cell TRMM “3B42” merged rainfall retrieval 3 hourly climatology, 2000-2006 Merged precipitation product using all 3 sensors CMMAP team meeting, Ft. Collins, July 2008

4. Preliminary results 1. Harmonic analysis 2. Broadness of the diurnal maximum 3. Animation: Are there propagating systems connected to nocturnal maxima over the central U.S.? CMMAP team meeting, Ft. Collins, July 2008

5. Harmonic analysis At each grid point Compute “mean summer day” at each grid point Least-squares fit to a 24-hour sinusoid Plot maps of phase, amplitude Only where the fit is reasonable

6. Harmonic analysis % variance, 24-hour harmonic 0%100% Satellite (TRMM 3B42)Standard model Multi-scale model CMMAP team meeting, Ft. Collins, July 2008

7. Harmonic analysis Phase, 24-hour harmonic 1am5am10am3pm8pm12am TRMM 3B42Standard model Multi-scale model CMMAP team meeting, Ft. Collins, July 2008

8. Broadness of diurnal maximum CMMAP team meeting, Ft. Collins, July 2008

10. Broadness of diurnal maximum 6 years of satellite Standard model Multi-scale model 20 years of rain gauge CMMAP team meeting, Ft. Collins, July 2008

11. Nocturnal maxima in the Central U.S.? Satellite Observations Multiscale model Standard model 1a 5a 10a 3p 8p 12a CMMAP team meeting, Ft. Collins, July 2008

13. Preliminary Conclusions Superparameterization improves several aspects of diurnal precipitation at T42 resolution: Phase of the 24-hr harmonic delayed over continents Improved phase variability linked to topography Broadness of diurnal peak shows improved regionally But… Current MMF does not capture the central U.S. propagating precipitation mechanism CMMAP team meeting, Ft. Collins, July 2008

14. Acknowledgements