Common Community Physics Package (CCPP) Scientific Documentation  Version 2.0
GFDL Cloud Microphysics Scheme

Description

GFDL cloud microphysics (MP) scheme is a six-category MP scheme to replace Zhao-Carr MP scheme, and moves the GFS from a total cloud water variable to five predicted hydrometeors (cloud water, cloud ice, rain, snow and graupel). This scheme utilizes the "bulk water" microphysical parameterization technique in Lin et al. (1983) [60] and has been significantly improved over years at GFDL (Lord et al.(1984) [66], Krueger et al.(1995) [56], Chen and Lin (2011) [11], Chen and Lin (2013) [12]). Physics processes of GFDL cloud MP are described in Figure 1 (also see warm_rain() and icloud()) and are feature with time-split between warm-rain (faster) and ice-phase (slower) processes (see 'conversion time scale' in gfdl_cloud_microphys.F90 for default values).

gfdl_cloud_mp_diagram.png
Figure 1: GFDL MP at a glance (Courtesy of S.J. Lin at GFDL)

Some unique attributes of GFDL cloud microphysics include:

a. Fast Physics

In current fv3gfs, phase-changes are called after the "Lagrangian-to-Eulerian" remapping in FV3 dynamic solver. When GFDL Cloud Fast Physics is activated (fast_sat_adj=.true. in fv_core_nml block), it adjusts cloud water evaporation (cloud water \(\rightarrow\)water vapor), cloud water freezing (cloud water \(\rightarrow\)cloud ice), and cloud ice deposition (water vapor \(\rightarrow\)cloud ice).

b. Horizontal Sub-grid Variability

Horizontal sub-grid variability is a function of cell area:

  • Over land:

    \[ h_{var}=\min \left\{0.2,\max\left[0.01, D_{land}(\frac{A_{r}}{10^{10}})^{0.25}\right]\right\} \]

  • Over Ocean:

    \[ h_{var}=\min \left\{0.2,\max\left[0.01, D_{ocean}(\frac{A_{r}}{10^{10}})^{0.25}\right]\right\} \]

Where \(A_{r}\) is cell area, \(D_{land}\) and \(D_{ocean}\) are base values for sub-grid variability over land and ocean (larger sub-grid variability appears in larger area). Horizontal sub-grid variability is used in cloud fraction, relative humidity calculation, evaporation and condensation processes. Scale-awareness is achieved by this horizontal subgrid variability and a \(2^{nd}\) order FV-type vertical reconstruction (Lin et al.(1994) [61]).

c. Cloud Fraction

Calculation of cloud fraction is based on horizontal sub-grid variability. Cloud fraction calculation includes all hydrometeors:

\[ CF=\max[0,\min(1,\frac{q_{plus}-q_{sat}}{q_{plus}-q_{minus}})] \]

Intraphysics Communication

General Algorithm