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Enhancing CRCM Performance in the Pacific Ocean: A Model Physics Study

This study evaluates the Canadian Regional Climate Model in the Pacific Ocean, assessing experiment configurations, results, and modifications to enhance model physics for improved accuracy in precipitation, cloud cover, and humidity. The findings highlight areas for improvement and suggest testing strategies for enhanced performance.

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Enhancing CRCM Performance in the Pacific Ocean: A Model Physics Study

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  1. The Performance of the Canadian Regional Climate Model in the Pacific Ocean Yanjun Jiao and Colin Jones University of Quebec at Montreal September 20, 2006

  2. OUTLINE: Experiment configurations Results from original CRCM (precipitation, cloud and relative humidity) Modification to the CRCM model physics Results of CRCMM Summary

  3. CRCM4 domain in PS projection CRCM4 domain in cylindrical projection 1. Experiment configurations Sponge zone (9 grid points) GPCI 2D domain (5ºS-45ºN,160ºE-120ºW) GPCI cross-section (13 points) ISCCP cloud cover (JJA 1998) 180km (60ºN) resolution 11575 grid points 29 Gal-Chen levels 15-min time step Output every 3hrs

  4. CRCM4 Stratiform precipitation 0.25º TRMM Convective precipitation Total precipitation

  5. CRCM4 ISCCP Total cloud

  6. Siebesma et al. (2004)

  7. 3. Modification to the model physics of CRCM4 • The eddy diffusivities calculation of the ECMWF. • A switch to turn off the shallow convection. • The trigger function of shallow convection (DTRH). • The cloud base mass flux closure=f (w*). • Variable cloud radius of the deep convection=f(wLCL). • Variable minimum cloud-depth=f(TLCL). • A dilute updraft ascent. • Xu-Randall cloud scheme. • Evaporation of falling large scale precipitation.

  8. 3.1 Modification to vertical diffusion (ECMWF documentation CY28r1) Revised Louis scheme zpbl 0.1zpbl buofxs > 0 buofxs < 0 • Troen and Mahrt (1986) • Non-local diffusion when eddies have a similar size as the PBL • Explicit entrainment parameterization in the PBL top

  9. CTL LCL 3.2 Modification to shallow convection (BKF) 1) A switch to turn off the shallow convection once deep convection has been detected on the same grid point 2) The trigger function of shallow convection 3) The closure of cloud base mass flux (Grant 2001 and Neggers et al. 2004) CAPE adjustment closure: mass flux at cloud base is totally controlled by the conditions in the cloud layer Subcloud convective velocity scaling closure: links the mass flux at cloud base to the TKE in subcloud layer. Based on the observation that shallow cumulus clouds (visible part because of condensation) often root deeply into the subcloud mixed layer (invisible dry thermal) Deep convection is driven by latent heat release in the convective cloud free convective vertical velocity scale

  10. 3.3 Modification to deep convection Kain (2004) 1) Cloud radius of the deep convection vary with the vertical velocity at lifting condensation level (LCL) 2) The minimum cloud-depth threshold has been parameterized according to the cloud-base temperature rather than remaining constant.

  11. 3.3 Modification to deep convection 3) A dilute updraft ascent has been used to calculate CAPE, which provides a more accurate calculation in convection rainfall and mass flux Equivalent potential temperature in undilute updraft (produces a significant larger CAPE than actual one) Equivalent potential temperature in dilute updraft • Reduces the CAPE value in highly unstable regimes (especially for dry condition) • Reduces the precipitation and the degree of stabilization

  12. is cloud liquid water 3.4 Modification to cloud scheme Xu and Randall (1996)

  13. 3.5 Modification to large scale precipitation (evaporation of falling precipitation from ECMWF) Kessler (1969)

  14. CRCM4 0.25º TRMM CRCMM JJA 1998 precipitation over GPCI 2D domain

  15. CRCM4 CRCMM

  16. CRCM4 CRCMM ISCCP JJA 1998 total cloud over GPCI 2D domain

  17. CRCM4 CRCMM

  18. Vertical profile of the relative humidity

  19. Siebesma et al. (2004) Vertical profile of the cloud cover

  20. Vertical profile of vertical velocity (Pa/s)

  21. 5. Summary Thanks to the GPCI, some deficiencies in the CRCM4 have been found. The CRCMM is better than CRCM4 in the field of: Precipitation Total cloud cover (shallow cumulus region). Vertical profiles of relative humidity, cloud and vertical velocity. Still have some space to improve in convective precipitation (too strong), PBL (too moist and sharp), and LWP (too low in stratocumulus region) …… • Testing the sensitivities to horizontal and vertical resolutions • (180km ~ 90km ~ 45km and L29 ~ L47) • Testing over the North America (AMNO domain) • (CLASS, winter and summer)

  22. Thank you !

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