Melt Routine Features.
This description of melt routine features will help to clarify the differences in operation of the modules, ebsm, MSM and Kevin.
Temperature Index and Simplified Energy Budget Method.
If either tfactor or nfactor is non zero this mode is selected.
Temperature Index.
Units of tfactor are (mm/d*°C).
- ebsm - Daily calculation. Melt = tmax[0]*tfactor (mm/day). Uses daily maximum temperature.
- Kevin - Interval calculation. Melt = hru_t[hh]*tfactor/Freq (mm/int). Is set to zero unless hru_t is > 0°C. Where Freq is the number of intervals in a day.
Simplified Energy Budget Method proposed by Kustas et al. (1994).
Units of nfactor are mm/(MJ/m^2)/day. This converts the energy input to mm (kg/m2) of melt.
- ebsm - Daily calculation. Melt = QnD*nfactor (mm/day).
- Kevin - Interval calculation. Melt = hru_Qn *WtoMJ*nfactor/Freq (mm Dt).
nfactor converts energy to melt. It is the latent heat of fusion, 0.3336 MJ/kg. However, it may be adjusted by the thermal quality B = 0.95.
Simplified Energy Budget Sources.
- QnD (W/m^2) - may be calculated using modules slope_Qsi, long, albedo, NeedleLeaf and Convert_Qnsn_QnD.
- hru_Qn (MJ/d) - may be calculated using modules slope_Qsi, long, albedo, NeedleLeaf and Convert_Qnsn_hru_Qn.
Adjusting for Cloud Cover.
Hours of bright sunshine used to be measured at meteorology stations. Today that is rarely done. Earlier algorithms for calculating short wave and long wave radiation used the ratio of actual sunshine hours to the maximum possible in the day (n/N). The module ebsm uses this ratio. When the sunshine hours are not measured the module calcsun can estimate (n/N) from the measured incoming short-wave Qsi and the clear sky Qsi calculated by the module global.
Adjusting Calculated Incoming Short-wave on a Slope for Cloud Cover.
Since radiation measurements are not normally made on a slope, it is necessary to calculated the incoming short-wave using the module global and then reducing the value for cloud cover. This is done by adjusting the value using the ratio of Qsi measured on the level divided by the calculated Qsi for the level. The module MSM uses these inputs.
ebsm (tfactor and nfactor both zero).
Qm = Qsn + Qnl + Qh + Qe + Qg + Qp - du/dt
During melt Qn = Qsn + Qsl is a linear function of the daily net short-wave radiation.
Qn = -0.53+0.47*(QdroD + QdfoD)*(0.52+0.52*sunact/sunmax)*(1.0-Albedo).
MSM (tfactor and nfactor both zero).
to be completed.
Kevin (tfactor and nfactor both zero).
to be completed.