glacier2
This module is defined in Classglacier and is an energy-budget snowmelt model loosely based on work done by (Gray and Landine, 1987) for the Canadian Prairies. However, it has variations allowing it to input the melt input energy from other CRHM modules.
Use with module "pbsm". Uses external melt model. Internal melt model for "ice" and "firn" is based upun module "ebsm" but by using variations 1 use "Qnsn_Var (variable)", variation 2 use "Qnsn (observation)" and with basic and variation 3 use "QnD (observation)" to operate using other CRHM modules.
Observations
- QnD (MJ/m^2 day) - net radiation. Basic module glacier and glacier#3. Always optional.
- Qnsn (W/m^2 day) - net all-wave at snow surface. Variation #2.
Variables
- firn_h (mm) - depths of snow densification layers.
- firn_dens (1000 kg/m^3) - densities of snow densification layers.
- firn_yr (1000 kg/m^3) - years to 'critical density' and age of firn.
- ice (m) - water equivalent of ice. State variable.
- firn (m) - water equivalent of all firn layers. State variable.
- firn_depth (m) - depth of all firn layers. State variable.
- firn_init (m) - Initial water equivalent of all firn layers.
- nfirn () - number of layers used in firn densification.
- SWE (mm) - snow water equivalent.
- SWEmelt (mm/d) - daily snowmelt.
- SWEmelt_delayed (mm/d) - daily snowmelt delayed by Clark.
- cumSWEmelt (mm/d) - cummulative firn snowmelt.
- firnmelt (mm/d) - daily firn melt.
- firnmelt_delayed (mm/d) - daily firn melt delayed by Clark.
- cumfirnmelt (mm/d) - cummulative firn melt.
- icemelt (mm/d) - daily ice melt.
- icemelt_delayed (mm/d) - daily ice melt delayed by Clark.
- cumicemelt (mm/) - cummulative ice melt.
- infil (mm/int) - depth of infiltration in time step, Dt – expressed as an average depth of water on an HRU.
- cuminfil (mm) - cumulative infiltration - expressed as an average depth of water on an HRU.
- runoff (mm/int) - amount of daily runoff – expressed as an equivalent depth (m3/m2).
- cumrunoff (mm) - cummulative runoff.
- meltrunoff (mm/int) - amount of interval melt runoff. .
- cummeltrunoff (mm) - cumulative interval melt runoff.
- snowinfil (mm/int) - not used. Satisfies module 'Netroute etc.
- LW_ebsm (mm/d) - liquid water in snowpack. State variable.
- u_ebsm (MJ/m^2*d) - snowpack energy deficit. State variable.
- Gmelt (MJ/m^2*d) - Qmelt = Qn+Qh+Qe+Qp..
- Qn_ebsm (MJ/m^2*d) - net radiation.
- Qh_ebsm (MJ/m^2*d) - sensible heat.
- Qe_ebsm (MJ/m^2*d) - latent heat.
- Qp_ebsm (MJ/m^2*d) - input from rainfall.
- SWE_2firn (mm) - end of summer SWE transferred to firn.
- SWE_2firn_dens (mm) - end of summer density of SWE transferred to firn
- cumSWE_2firn (mm) - cummulative SWE added to firn..
- LWmax (mm) -maximum liquid water in snowpack.
- net_rainD (mm/d) - daily net rain calculated from net_rain.
- Qnsn_Acc (W/m^2) - accumulator for Qnsn_Var/Qnsn. Variation glacier#1
Parameters
- delay_melt () - inhibits any melt before this date. Only used when tfactor and nfactor are both zero. Default value not suitable for Southern Hemisphere
- basin_area (km^2) - basin area.
- hru area (km^2) - HRU area.
- firn_h_init (mm) - initial depths of firn densification layers.
- firn_dens_init (1000 kg/m^3) - initial densities of firn densification layers.
- ice_init (mm) - Initial water equivalent of glacier ice.
- firn_Albedo () - Initial glacier firn albedo.
- ice_Albedo () - Initial glacier ice albedo.
- SWEstorage (d) - Storage constant for SWE.
- SWElag (h) - Lag constant for SWE.
- firnstorage (d) - Storage constant for firn.
- firnlag (h) - Lag constant for firn.
- icestorage (d) - Storage constant for ice.
- icelag (h) - Ice constant for SWE.
- TKMA (ºC) - Annual mean annual temperature of glacier.
- SWEAA (mm/yy) - Annual mean accumulation of glacier SWE
- rho0 (kg/m^3) - zero depth intersection of ln(rho/(rhoice-rho)) could equal average density over first one or two meters of snow.
- SWE_to_infilK
- firn_to_infilK
- ice_to_infilK
- rain_to_infilK
- SWE_to_firn_Julian
- tfactor (mm/d*/ºC) - degree day melt factor. Basic module.
- nfactor (mm*m^2/MJ*d) - net radiation factor. Basic module.
- Use_QnD () - Use QnD if available. Basic module.
Variable Inputs
- net_snow (*) (kg/m^2)
- net_rain (*) (kg/m^2)
- net_hru_drift (*) (kg/m^2)
- net_subl (*) (kg/m^2)
- hru_tmean (obs) (ºC)
- hru_tmax (obs) (ºC)
- hru_tmin (obs) (ºC)
- hru_umean (obs) (m/s)
- hru_rhmean (obs) (%)
- hru_Sun_Act (obs) (hr)
- QdroD (global) (MJ/m^2)
- QdfoD (global) (MJ/m^2)
- SunMax (global) (h)
- Albedo (albedo) ()
- meltflag (albedo) ()
- Qnsn_Var (W/m^2 day) - net all-wave at snow surface. Variation glacier#1
Useage.
tfactor and nfactor NOT equal to zero
For comparison there is an option to use the simplified energy budget method proposed by Kustas et al.(1994). In this degree-day algorithm the increased melting later in the season is simulated using a net radiation term.
Melt = tfactor*tmax + nfactor*QnD, where the observation QnD is the net all-wave radiation calculated from a module.
tfactor and nfactor equal to zero
If both parameters tfactor and nfactor are set equal to zero for an HRU, the module uses the original ebsm.f algorithm otherwise the simplified degree-day algorithm is used using the values set in tfactor and nfactor.
Observation QnD is used if available, otherwise Qn is calculated as in the original algorithm.
Over snow during melt;
Qn = -0.53+0.47*(QdroD+QdfoD)*(0.52+0.52*sunact/sunmax)*(1.0-Albedo)
An external observation QnD may be generated using modules long, NeedleLeaf and macro modules Slope_Qsi.mcr and Convert_Qsn_QnD.mcr.