1. Regional climate modelling activities at CSIRO Second AIACC Asia and the Pacific Regional Workshop 2-5 November, Manila John McGregor and Kim Nguyen CSIRO Atmospheric Research Acknowledgements Martin Dix, Jack Katzfey and Eva Kowalczyk

2. Outline  DARLAM limited-area model  features of C-CAM  simulations of present-day Australian climate  simulations of Australian climate change  an artificially-flooded inland lake  simulations over Asia  diurnal rainfall behaviour  new activities

3. DARLAM simulations of tropical cyclones Observed tropical cyclone formation, Jan-March, 1967- 1996 ab 30-year simulated TC formation, Jan- March DARLAM domains: inner 30-km resolution; outer, 125-km resolution; nested in CSIRO Mark2 CGCM Occurrence of TCs, in cyclone-days Walsh, Nguyen and McGregor (2004), Clim. Dyn.

4. January 1982 rainfall from DARLAM 44 km resolution simulation over SARCS region performed in 1999, downscaled from NCEP (and Mk 3) fairly good climatology, but see some spurious lateral boundary effects, due to one-way nesting

5. Conformal-cubic grid Devised by Rancic et al., QJRMS 1996 Grid shows location of mass variables in CSIRO C-CAM model

6. Conformal-cubic C48 grid used for AMIP simulations Resolution is about 220 km

7. · 2-time-level semi-implicit hydrostatic (recently, has non-hydrostatic option) · semi-Lagrangian horizontal advection with bi-cubic spatial interpolation · total variation diminishing (TVD) or semi-Lagrangian vertical advection · unstaggered grid, with winds transformed to/from ·C-staggered positions before/after gravity wave calculations using reversible interpolation · minimal horizontal diffusion needed: ·Smagorinsky style; zero is fine · weak off-centering (in time) used to avoid semi-Lagrangian "mountain resonances" · careful treatment of surface pressure and pressure-gradient terms near terrain · a posteriori conservation of mass and moisture · grid is isotropic Conformal-cubic model features

8. · cumulus convection: -new CSIRO mass-flux scheme, including downdrafts · includes advection of liquid and ice cloud-water · interactive cloud distributions · derived prognostically from liquid water · GFDL parameterization for long and short wave radiation · gravity-wave drag scheme · stability-dependent boundary layer and vertical mixing with non-local option · vegetation/canopy scheme · 6 layers for soil temperatures · 6 layers for soil moisture (Richard's equation) · option for cumulus mixing of trace gases · diurnally varying skin temperatures for SSTs Physical Parameterizations

9. Observed 1979-95 DJF rainfall Observed 1979-95 JJA rainfall CCAM 1979-95 DJF rainfall CCAM 1979-95 JJA rainfall AMIP simulation with quasi-uniform 220 km grid

10. Conformal-cubic C48 grid used for Australian simulations, Schmidt = 0.3 Resolution over Australia is about 60 km

11. Full nudging of far-field winds in the free atmosphere, with e-folding time ~24 h Partial nudging No nudging (only SSTs) Far-field nudging Model uses NCEP/GCM winds only outside the inner red boundary Model uses NCEP/GCM winds (or other fields) at all points. Global nudging Full nudging of fields in the free atmosphere, with e-folding time ~48 h

12. C-CAM/NCEP 1961-1990 IPCC C-CAM/Mk3 “1975-2005” 30-year average annual rainfall total (mm/day) GCM Mk3 “1975-2005”

13. C-CAM/Mk3 “1975-2005” IPCC GCM Mk3 “1975-2005” Annual average maximum daily screen temperature C-CAM/NCEP 1961-1990

14. C-CAM/Mk3 “1975-2005” IPCC C-CAM/NCEP 1961-1990 GCM Mk3 “1975-2005” Annual average minimum daily screen temperature

15. The monthly SST biases are corrected for the latest downscaled C-CAM simulations (using 12 monthly data sets). Mk 3 GCM annual average SST error (degrees C)

16. Mk3 AOGCM C-CAM Xie-Arkin observed DJF rainfall from 30-y CCAM (latest run) driven by Mk3

17. Mk3 AOGCM C-CAM Xie-Arkin observed MAM rainfall from 30-y CCAM (latest run) driven by Mk3

18. Change in annual precipitation (mm/day) for 2xCO2-1xCO2 from the Mk3 OAGCM simulation. Change in annual precipitation (mm/day) for 2xCO2-1xCO2 from the C-CAM simulation, with forcing from the Mk3 OAGCM. For present-day SST distributions, C-CAM produces more accurate simulations of the rainfall patterns. Reasonable to expect that this also applies for the climate-change SST distributions.

19. Regional Model Intercomparison Project RMIP_1: March 1997 - August 1998 RMIP_2: July 1988 - December 1998  on a large Asian domain including India, Indochina, China, Japan, Siberia  60 km resolution  ~10 limited-area models, 1 stretched global model  lateral boundary conditions provided by 6-hourly NCEP reanalyses  organised by Congbin Fu (IAP) with sponsorship from APN

20. Conformal-cubic C63 grid used for RMIP simulations, Schmidt = 0.37 Approx. 60 km resolution Weights used for nudging with far-field winds

21. Xie-Arkin Precip for JJAXie-Arkin Precip for SON 10-y C-CAM/RMIP2 Precip for JJA10-y C-CAM/RMIP2 Precip for SON

22. Xie-Arkin Precip for DJFXie-Arkin Precip for MAM 10-y C-CAM/RMIP2 Precip for DJF 10-y C-CAM/RMIP2 Precip for MAM

23. Xie-Arkin Precip for JJA 10-y C-CAM/RMIP2 Precip for JJA 10-y C-CAM/Mekong Precip for JJA with forcing from Mk3 GCM (instead of NCEP reanalysis)

24. Malaysia Calcutta Obs C-CAM Diurnal rainfall behaviour from 10-y RMIP run

25. Andaman Sea Bay of Bengal Obs C-CAM Diurnal rainfall behaviour from 10-y RMIP run

26. 8 km trial simulation over Fiji C48 grid Model orography For these fine-resolution simulations, “global nudging” from the broad-scale fields is the preferred strategy.

28. In Fiji, Nadi (western division) has a marked seasonality in rainfall as compared to Suva which has year round rainfall under the influence of trade winds (resulting in more number of wet days). The marked differences in rainfall seasonality at these two locations in Fiji has been reproduced in the model. Observed 1975 rainfall Suva May-October ~10 mm/day November-April ~ 12 mm/day Nadi May-October ~3 mm/day November-April ~ 8 mm/day Modelled amounts (next 2 slides) appear similar, but detailed comparison still to be carried out.

29. Fiji rainfall – first 6 months January February April May March June IPCC climatology vs 1975 C-CAM

30. Fiji rainfall – next 6 months July August October November September December

31. Concluding comments  Variable-resolution global models are well-suited to perform the simulations “traditionally” performed by limited-area RCMs, whilst avoiding the usual lateral boundary problems.  The variable-resolution global model C-CAM reproduces well many features of the Australian and East Asian climates  Modelling advances and greater computing power are allowing regional climate simulations down to around 8 km resolution.