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Assessing the diurnal cycle of precipitation in the CSU MMF (T42)

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. Questions. How does the mean daily cycle of JJA precipitation in the MMF compare to CAM, and to satellite retrievals from TRMM?

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Assessing the diurnal cycle of precipitation in the CSU MMF (T42)

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  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 Satellite (TRMM 3B42) Standard model 0% 100% Multi-scale model CMMAP team meeting, Ft. Collins, July 2008

  7. Harmonic analysisPhase, 24-hour harmonic TRMM 3B42 Standard model 1am 5am 10am 3pm 8pm 12am Multi-scale model CMMAP team meeting, Ft. Collins, July 2008

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

  9. CMMAP team meeting, Ft. Collins, July 2008

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

  11. Nocturnal maxima in theCentral U.S.? SatelliteObservations 12a 8p Multiscalemodel 3p 10a Standardmodel 5a 1a CMMAP team meeting, Ft. Collins, July 2008

  12. 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

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