SEMIC

SEMIC is a Surface Energy and Mass Balance Model of Intermediate Complexity. It calculates surface temperature and mass balance terms (e.g., accumulation and ablation) over snow- and ice-covered regions, especially over glaciers or large ice sheets. The model is driven by atmospheric forcing like air temperature, downwelling radiation, wind, humidity, surface pressure, snow fall, and rain fall.

SEMIC makes use of derived types. The main ones are surface_param_class for model parameters, surface_state_class for model variables, and boundary_opt_class for flags to check if some variables should be overriding with external fields. surface_state_class includes atmospheric forcing as well as prognostic and diagnostic variables as one-dimensional arrays.

The major subroutine to be called for each time step is surface_energy_and_mass_balance. A proper interface for the model should include the following steps:

1. Allocate all arrays with length N: call surface_alloc(<surface_state_class>,N)
2. Load model parameters, for example using a Fortran Namelist: call surface_physics_par_load(<surface_param_class>,<Fortran Namelist file>)
3. Define the boundary conditions (i.e, the overriding with external fields): call surface_boundary_define(<boundary_opt_class>,<surface_param_class>%boundary)
4. Loop over your time steps: call surface_energy_and_mass_balance(<surface_state_class>,(<surface_param_class>,<boundary_opt_class>,<day>,<year>) Update the forcing variables before and safe model variables after calling surface_energy_and_mass_balance.
5. De-allocate all arrays: call surface_dealloc(<surface_state_class>)

Example

An example on how to setup and run SEMIC is provided in the example directory. Got to that directory and run the example via

make run_example

Optimization

For the optimization of model parameters, I've implemented some algorithms from Jason Brownlee's book Clever Algorithms in Python. Have a look into the optimize directory. Here, you can install the optimization algorithms for Python using setuptools:

python setup.py install

SEMIC as Python module

Thanks to the pretty good f2py wrapper f90wrap 👍, SEMIC can be used as a Python module. Check out f2py/test.py for a quick implementation of SEMIC in Python.

Overview of Derived Types

surface_param_class

    type surface_param_class !< Define all parameters needed for the surface module
        character (len=256) :: name         !< domain name
        character (len=256) :: boundary(30) !< list of vriables names to be overriden by external fields
        character (len=256) :: alb_scheme   !< name of albedo scheme: 'slater', 'isba', 'denby', 'alex', or 'none'
        integer             :: nx        !< number of grid points
        integer             :: n_ksub    !< number of sub-daily time steps
        double precision    :: ceff      !< surface specific heat capacity of snow/ice [J/Km2]
        double precision    :: albi      !< background albedo (bare ice) [no unit]
        double precision    :: albl      !< background albedo (bare land) [no unit]
        double precision    :: alb_smax  !< maximum snow albedo (fresh snow) [no unit]
        double precision    :: alb_smin  !< minimum snow albedo (old, wet snow) [no unit]
        double precision    :: hcrit     !< critical snow height for which grid cell is 50%snow covered [m]
        double precision    :: rcrit     !< critical snow height for which refreezing fraction is 50% [m]
        double precision    :: amp       !< Amplitude of diurnal cycle [K]
        double precision    :: csh       !< sensible heat exchange coefficient [no unit]
        double precision    :: clh       !< latent heat exchange coefficient [no unit]
        double precision    :: tmin      !< minimum temperature for which albedo decline becomes effective ("slater") [K]
        double precision    :: tmax      !< maximum temperature for which albedo decline becomes effective ("slater") [K]
        double precision    :: tstic     !< time step [s]
        double precision    :: tsticsub  !< sub-time step [s]
        double precision    :: tau_a     !< dry albedo decline for "isba" albedo scheme [1/day]
        double precision    :: tau_f     !< wet albedo decline for "isba" albedo scheme [1/day]
        double precision    :: w_crit    !< critical liquid water content for "isba" albedo scheme [kg/m2]
        double precision    :: mcrit     !< critical melt rate for "isba" and "denby" albedo scheme [m/s]
        double precision    :: afac      !< param [no unit]
        double precision    :: tmid      !< param for "alex" albedo parametrization [K]
    end type

surface_state_class

    type surface_state_class !< model variables
        double precision, allocatable, dimension(:) :: t2m         !< 2m air temperature [K]
        double precision, allocatable, dimension(:) :: tsurf       !< surface temperature [K]
        double precision, allocatable, dimension(:) :: hsnow       !< snow pack height (water equivalent) [m]
        double precision, allocatable, dimension(:) :: hice        !< ice thickness (water equivalent) [m]
        double precision, allocatable, dimension(:) :: alb         !< grid-averaged albedo [no unit]
        double precision, allocatable, dimension(:) :: alb_snow    !< snow albedo [no unit]
        double precision, allocatable, dimension(:) :: melt        !< potential surface melt [m/s]
        double precision, allocatable, dimension(:) :: melted_snow !< actual melted snow [m/s]
        double precision, allocatable, dimension(:) :: melted_ice  !< actual melted ice [m/s]
        double precision, allocatable, dimension(:) :: refr        !< refreezing [m/s]
        double precision, allocatable, dimension(:) :: smb         !< surface mass balance [m/s]
        double precision, allocatable, dimension(:) :: acc         !< surface accumulation [m/s]
        double precision, allocatable, dimension(:) :: lhf         !< latent heat flux [W/m2]
        double precision, allocatable, dimension(:) :: shf         !< sensible heat flux [W/m2]
        double precision, allocatable, dimension(:) :: lwu         !< upwelling longwave radiation [W/m2]
        double precision, allocatable, dimension(:) :: subl        !< sublimation [m/s]
        double precision, allocatable, dimension(:) :: evap        !< evaporation [??]
        double precision, allocatable, dimension(:) :: smb_snow    !< surface mass balance of snow [m/s]
        double precision, allocatable, dimension(:) :: smb_ice     !< surface mass balance of ice [m/s]
        double precision, allocatable, dimension(:) :: runoff      !< potential surface runoff [m/s]
        double precision, allocatable, dimension(:) :: qmr         !< heat flux from melting/refreezing [W/m2]
        double precision, allocatable, dimension(:) :: qmr_res     !< residual heat flux from melting/refreezing(at end of time step) [W/m2]
        double precision, allocatable, dimension(:) :: amp         !< diurnal cycle amplitude [K]
        ! Forcing variables
        double precision, allocatable, dimension(:) :: sf          !< snow fall [m/s]
        double precision, allocatable, dimension(:) :: rf          !< rain fall [m/s]
        double precision, allocatable, dimension(:) :: sp          !< surface pressure [Pa]
        double precision, allocatable, dimension(:) :: lwd         !< downwelling longwave radiation [W/m2]
        double precision, allocatable, dimension(:) :: swd         !< downwelling shortwave radiation [W/m2]
        double precision, allocatable, dimension(:) :: wind        !< surface wind speed [m/s]
        double precision, allocatable, dimension(:) :: rhoa        !< air density [kg/m3]
        double precision, allocatable, dimension(:) :: qq          !< air specific humidity [kg/kg]
        integer,          allocatable, dimension(:) :: mask        !< ocean/land/ice mask [0/1/2]
    end type

boundary_opt_class

    type boundary_opt_class !< object to hold flags for overriding with external fields
        logical :: t2m   !< flag for 2m air temperature
        logical :: tsurf !< flag for surface temperature
        logical :: hsnow !< flag for snow height
        logical :: alb   !< flag for albedo
        logical :: melt  !< flag for melting
        logical :: refr  !< flag for refreezing
        logical :: smb   !< flag for surface mass balance
        logical :: acc   !< flag for accumulation
        logical :: lhf   !< flag for latent heat flux
        logical :: shf   !< flag for senible heat flux
        logical :: subl  !< flag for sublimation/refreezing
        logical :: amp   !< flag for diurnal cycle amplitude
    end type