The IPRC Regional Climate Model (IPRC-RegCM)

    The IPRC-RegCM was developed by Wang t al. (2003). The model has been used in modeling the regional climate over the East Asian monsoon (Wang et al. 2003) and over the eastern Pacific, including the response of the atmosphere to Pacific tropical instability ocean waves (Small et al. 2003), simulation of boundary layer clouds over the Southeast Pacific (Wang et al. 2004a), and the effect of the Andean mountains on eastern Pacific climate (Xu et al. 2004). The latest Version 1.2 includes several modifications and improvements in order to realistically simulate subtropical MBL clouds (Wang et al. 2004a,b, 2005). The key model features of the model are summarized in Table 1 below

    The model uses hydrostatic primitive equations in spherical coordinates in the horizontal and in s (pressure normalized by surface pressure) coordinate in the vertical. It is solved numerically with a fourth-order conservative finite-difference scheme on an unstaggered longitude/latitude grid system and a second-order leapfrog scheme with intermittent use of Euler backward scheme for time integration. The model has 30 vertical levels with high vertical resolution in the lower troposphere (11 levels below 800 hPa) to improve the simulation of boundary layer structure and clouds. Note that in the latest IPRC–RegCM Version 1.2, the third-order upstream advection scheme of Wang (1996) was used for time integration of equations for mixing ratios of water vapor and all hydrometeors, turbulent kinetic energy and its dissipation rate. This scheme has very weak numerical dissipation, small dispersion error, and good shape-conserving properties compared to the fourth-order centered finite-difference scheme that was used in the previous version 1.1.

    The model physics include the cloud microphysics scheme of Wang (1999, 2001); a mass flux parameterization scheme for subgrid shallow convection, midlevel convection, and deep convection developed by Tiedtke (1989) and modified by Nordeng (1995) and Gregory et al. (2000); the radiation package developed by Edwards and Slingo (1996) and further improved later by Sun and Rikus (1999); the Biosphere-Atmosphere Transfer Scheme (BATS) developed by Dickinson et al. (1993) for land surface processes; a modified Monin-Obukhov similarity scheme (Wang 2002; Fairall et al. 2003) for surface flux calculations over the ocean; and a nonlocal E-e turbulence closure scheme for subgrid vertical mixing (Langland and Liou 1996), which was modified to include the effect of cloud buoyancy production (Wang 1999).

    The new Version 1.2 allows an environmental relative humidity dependent detrainment of cloud condensates from convection into grid-resolved cloud water/ice so that immediate and complete evaporation of detrained cloud water/ice takes place only for relatively dry conditions (Wang et al. 2004a). The Version 1.2 also uses the nonlocal E-, turbulence closure scheme documented in Langland and Liou (1996) for subgrid vertical mixing instead of the original local E-, turbulence closure scheme. The threshold cloud water mixing ratio above which the cloud water converts effectively into rainwater/drizzle in the Kessler (1969) type precipitation/drizzle parameterization is increased from 0.4 to 0.5 g kg-1 to reduce drizzle from SCu clouds. In addition, the fraction of the cloud ensemble that penetrates into the inversion layer and detrains there into the environment is set to be 0.3 (b in equation 21, Tiedtke 1989) instead of 0.23 used in Part I (Wang et al. 2004a) for shallow convection. These adjustments in parameters improve the simulation of boundary layer clouds significantly, especially near the coastal region off South America (see Wang et al. 2004b). Other model details are referred to Wang et al. (2003, 2004a,b).

Table 1. List of physical parameterization schemes used in the IPRC-RegCM (Version 1.2). Also included are references and comments where necessary.

 

Physical process

Scheme

Reference

Comments

Grid-resolved moist processes

Bulk mixed-ice phase cloud microphysics

Wang (1999, 2001)

Based mainly on Lin et al. (1983), Rutledge and Hobbs (1983), and Reisner et al. (1998).

Subgrid scale convection

 

Shallow convection, mid-level convection, and deep convection

Tiedtke (1989), Nordeng (1995),

Gregory et al. (2000)

With CAPE closure and organized entrainment and detrainment.

Coupling between subgrid-scale convection and grid-resolved moist processes via cloud-top detrainment (Wang et al. 2003).

Mixing

Vertical: 1.5 level nonlocal turbulence closure

Langland and Liou (1996)

Modified to include cloud buoyancy production of turbulence (Wang 1999).

Horizontal: Fourth-order

Wang et al. (2003)

Deformation and terrain-slope dependent diffusion coefficient.

Surface layer over ocean

Bulk scheme

Fairall et al. (2003)

TOGA COARE v3.0.

Radiation

Multi-band

Edwards and Slingo (1996) updated by

Sun and Rikus (1999)

7 bands for longwave,

4 bands for shortwave,

Full coupling between cloud microphysics and cloud liquid/ice water path.

Cloud optical Properties

 

Longwave radiation

Sun and Shine (1994)

 

Shortwave radiation

Slingo and Schrecker (1982)

Chou et al. (1998)

with specified cloud droplet number concentration (CDNC) of 100 cm-3 over ocean and 300 cm-3 over land.

Cloud amount

Semi-empirical scheme

Xu and Randall (1996)

Dependent on relative humidity and cloud liquid/ice water extent.

Land surface processes

Biosphere-Atmosphere Transfer Scheme (BATS)

Dickenson et al. (1993)

Modified algorithm for solving leaf temperature to ensure a convergent iteration of numerical solution (Wang et al. 2003).

 

Some key references:

Wang, Y. 1996: On the forward-in-time upstream advection scheme for non-uniform and time-dependent flow. Meteor. Atmos. Phys., 61, 27-38.

Wang, Y., 1999: A triply nested movable mesh tropical cyclone model with explicit cloud microphysics–TCM3. BMRC Research Rep. 74, Bureau of         Meteorology Research Centre, Australia, 81 pp.

Wang, Y., 2001: An explicit simulation of tropical cyclones with a triply nested movable mesh primitive equation model-TCM3 Part I: Model description and control experiment.  Mon. Wea. Rev., 129, 1370-1394.

Wang, Y., 2002: An explicit simulation of tropical cyclones with a triply nested movable mesh primitive equation model-TCM3 Part II: Model refinements and sensitivity to cloud microphysics parameterization.  Mon. Wea. Rev., 130, 3022-3036.

Wang, Y., O.L. Sen, and B. Wang, 2003: A highly resolved regional climate model (IPRC–RegCM) and its simulation of the 1998 severe precipitation events over China. Part I: Model description and verification of simulation.  J. Climate, 16, 1721-1738.

Wang, Y., S.-P. Xie, H. Xu, and B. Wang, 2004a: Regional model simulations of boundary layer clouds over the Southeast Pacific off South America. Part I: Control Experiment. Mon. Wea. Rev., 132, 275-296.

Wang, Y., S.-P. Xie, H. Xu, and B. Wang, 2004b: Regional model simulations of boundary layer clouds over the Southeast Pacific off South America. Part II: Sensitivity Experiments. Mon. Wea. Rev., 132, 2650-2668.

Wang, Y., S.-P. Xie, B. Wang, and H. Xu, 2005: Large-scale forcing by Southeast Pacific boundary-layer clouds: A regional model study. J. Climate, 18, 934-951.

Small, R.J., S.-P. Xie, and Y. Wang, 2003: Numerical simulation of atmospheric response to Pacific tropical instability waves. J. Climate, 16, 3722-3737.

Xu, H., Y. Wang, and S.-P. Xie, 2004: Effects of the Andes on Eastern Pacific Climate: A regional atmospheric model study. J. Climate, 17, 589-602.