Physics
The microphysics scheme includes 5 3D
prognostic variables as
bulk variables; water vapor, cloud water variables (cloud liquid water and ice),
and rainfall and snowfall (solid).
The microphysical prognostic variables are fully coupled with the atmosphere.
The model baseline physics consist in: bulk microphysics
with 5 water species variables, including
evaporation, condensation, depostion, sedimentation, autoconversion, evaporation of cloud
cloud water, sublimation of cloud ice, freezing/melting of
cloud ice/water and rain/snow.
The TKE scheme has 2 source terms (shear and boyancy induced) and a dissipation term. It feeds
back with the atmosphere via the vertical turbulence scheme.
The passive tracer can have one
or multiple sources, and it precipitates based on a user
imposed sedimentation terminal velocity. There is no feedback of the tracer with
the atmosphere.
For radiation, there are
2 longwave radiation schemes with (diagnosed) clouds
(a simple
or "fast" method based on Savijarvi, 1990, or a
broadband longwave method from Chen and Cotton,
1983), 2
shortwave radiation
schemes with clouds (a simple or "fast" code based on Mahrer
and Pielke, 1977, and Savijarvi, 1990, or a 2-stream
multiple band method based on Chen and Cotton, 1983).
A mass-flux moist convection scheme is used for both shallow
(non-precipitating) and deep convection.
enhancement to represent shallow convection.
The vertical
diffusion/turbulence has an option to use Louis-type local K closure
(based on ECMWF model, 2013) but the newer default uses a 1.5 order closure
TKE scheme, and both of these schemes use an additional non-local
mixing in the daytime PBL using an EDMF approach.
Turbulence uses an implicit coupling between the atmosphere and
three sub-grid surface tiles (continental surface, liquid
water surfaces and sea ice).
As a final note, a global
borrowing scheme is used for the water vapor to correct
for any negative values.
An example comparison of the 2-stream model (option)
downwelling longwave flux
(LWdown) at the surface predicted by ASP and the GFS model
can be seen here, where the GFS LWdown is in the
left hand panel. Overall features and order of magnitudes
are quite similar (despite the relative simplicity of the
ASP scheme).
ASP Methods for: | Current Default | Options |
Time Integration | 3rd Order Runge-Kutta
| 4th Order Runge-Kutta (currently not available) |
Dynamics | Hydrostatic, unless using
grid resolutions of less than 10 km...in this case, non-hydrostatic is the default
| Add-on Non-hydrostatic module as a USER option |
Time Stepping (on each RK step) |
Forward-Backward difference (time-split)
(HEVI approach within split for non-hydrostatic part if activated)
| No splitting (but this results in a very small time step) |
Input
Data | Real-time GFS NWP data from NCEP
| Idealized case. |
Initialization Method |
Cold-Start using Short
Forward-Backward adiabatic integrations with a Digital Filter (DF)
method. Then BBDA (Big-Brother Data Assimilation as a nudging of certain
prognostic variables in the dynamics) in the early part of forecast.
| Cold-Start with DF
or initialization with idealized fields
|
Initial and Boundary Winds (derived from:) |
Input u-v wind components
| Geopotential using the balance
equation, vorticity (and divergence), or
using input wind components. *For all non-filtered winds,
the vertically integrated divergence is removed
|
Horizontal Diffusion | 6th order monotonic with constant diffusivity |
4th or 6th (both monotonic) order computational
diffusion with constant (4th, 6th) or spatially variable
diffusivity (4th),
2nd order physically based Smagorinski-closure.
Finally, for high resolutions, one can ise both 6th and 2nd order physically based
methods in tandem.
*All use quasi-horizontal corrections for air temp. and
spec. humidity.
|
Horizontal Advection | Explicit 5th order & 5th order WENO for scalars on last RK step
|
Explicit 2nd, 4th, 5th or 6th order, 5th WENO |
Vertical Advection |
Explicit 3rd order & 3rd order WENO for scalars on last RK step
|
Explicit 2nd, 3rd order, 3rd order WENO, Implicit 2nd
|
Advective Flux Adjustment | Positive definite flux correction
(PDFC) for scalars
|
PDFC on or off |
Divergence Filter/Damping | 4th order (moderate coefficient) |
2nd order (low coefficient), 4th or 6th order (moderate coefficient) |
Horizontal Grid | Arakawa-C,
Lambert Conformal or Mercator Projection (depending on
domain location), or Plate Carree (lat-lon) over the entire globe
| (grid spacing, geographic location, projection and dimensions
are USER specified input parameters) |
Vertical Grid | 28 layers, Hybrid pressure coordinate, Staggered: mass and momentum
variables are centered within vertical layers, vertical
velocities are defined at layer interfaces. Pressure top
at 50 mb | (number of vertical layers and coordinate
level values are USER specified input parameters) |
Lateral Boundaries | Davies type (Newtonian), 9 pts + Exponential fn. 6-hour updates for linear
time tendencies | Davies type
(Newtonian, or both Newtonian and Diffusive), 9 or 5 points |
Vertical Turbulent Diffusion |
TKE 1.5 order closure based closure,
EDMF within the PBL |
Local-K (Louis functions)
above PBL with moist Richarson number in cloudy regions,
1st order mixed in the PBL,
EDMF within the PBL
|
Land Atmosphere Turbulence coupling | Fully implicit
coupling with 3 surface-tiles | Explicit coupling (can lead to numerical instabilities
or jumps for large time step applications)
|
Longwave Atmospheric Radiation | Broadband
longwave radiation with clouds (not every time step)
| Simple "fast" method with clouds
clouds (each time step) |
Shortwave Atmospheric Radiation | Simple "fast" method with clouds (each time step)
| 2-stream shortwave radiation with
clouds (not every time step) |
Shallow Cumulus | Mass-flux
(Tiedtke, Zhang and McFarlane type)
|
Geleyn type Richarson number
modification to turbulence |
Deep
Convection | Mass-flux
(Tiedtke, Zhang and McFarlane type)
| i) Gadd and Keers Moist
Convective Adjustment, ii) Kuo-type Convection, iii) Bougeault
(1985) |
Microphysics |
Bulk cloud liquid water, ice, snowfall and rainfall prognostic variables
(a total of 5).
Multiple microphysical processes are modeled.
|
Dry (adiabatic)...For testing
|
Surface: Land tile |
5-layer fully implicit heat diffusion and
Richard's equation for water transfer, VIC-sub-grid
runoff, soil ice, sub-grid orography roughness.
Single energy budget, composite snow scheme.
Implicit coupling
with atmosphere
| None |
Surface: Ice tile |
3-layer fully implicit heat diffusion. Implicit coupling
with atmosphere
| None |
Surface: Water tile |
Water surface T's uses prognostic skin T, relaxed to prescribed from climatology/Operational NWP input
Charnock surface drag | None |