albedo (Gray and Landine, 1987)
This module is defined in Classalbedo and estimates the snow albedo throughout the winter and into the melt period. It also estimates the beginning of melt which initiates the snowmelt in the module ebsm. The algorithm developed uses daily values of net radiation, maximum and minimum daily temperatures, snowfall and snow-cover SWE.
Observations
- none
Variables
- albedo () - snowcover albedo. State variable.
- meltflag () - indicates start of melt. 0/1 for false/true. State variable.
- winter () - indicates summer and winter events. 0/1. State variable.
- net_snowD (mm/d) - daily snow fall.
- newsnowcnt (d) - snow age count. Name is confusing as the value is the number of days since the last snow fall.
Parameters
- Albedo_bare () - albedo for bare soil. Advance parameter.
- Albedo_snow () - albedo for fresh snow. Advance parameter.
- hru_lat (°) - latitude. Adjusts empirical Julian constants for Northern/Southern Hemisphere.
Variable Inputs
- hru_tmax (obs)
- hru_tmin (obs)
- hru_newsnow (obs)()
- QdroD (global) (MJ/m^2*d)
- SWE (pbsm)(mm)
- net_snow (intcp)(mm/int)
Notes
winter
The logical flag winter differentiates the major spring melt from fall and late spring snowfalls and associated melt events. Winter is set true between Julian days 300 and 2 when the SWE of the last HRU is greater than 5 mm. Winter is also set true when the daily maximum temperature is less than -6°C and the diagnostic variable Qnc is less than 1.0. Winter is set false when any HRU has no snowcover, i.e. SWE = 0.0.
meltflag
The logical flag meltflag indicates the days when melt is possible. It is always true when there is snowcover and winter is false. Otherwise it is only set when one of the melt criteria is met,
- the daily minimum is greater than -4.0°C
- Qnc > 1.0 AND the daily maximum > 0.0°C
- Qnc > -0.5 AND the daily maximum > MT
where Qnc = -0.371 + 5.22*QdroD[hh]*(1 - A[hh]) and is a measure of incoming short-wave radiation,
and MT = -0.064*jday + 6.69 and is a probabiliy index which increases as the radiative components increase as the year progresses.
newsnowcount
This counter is set to 0 after every snowfall and is incremented every day afterwards until amother snowfall occurs.
Albedo relationships.
At the onset of winter the albedo is set to 0.8. After a snowfall of greater than 5 cm depth (equivalent to a change in SWE of 0.25 mm, assuming a snow density of 0.005 kg/m3)