Daily Interpolation

Forcing variable

Since the version 196, you can now use daily meteorological forcing files. The following new variables are now requested:

• Tmin: minimal daily near-surface temperature (K)
• Tmax: maximal daily near-surface temperature (K)
• precip: daily mean precipitation (kg m-2 s-1)

The other variables requested as previously are:

• Psurf: daily mean surface pressure (hPa)
• Qair: daily mean near-surface specific humidity (kg/kg)
• LWdown: daily mean long-wave incomming radiation (W m-2)
• SWdown: daily mean short-wave incomming radiation (W m-2)
• Wind (or Wind_N and Wind_E): daily mean near-surface wind speed (m s-1)

Interpolation principles

• The temperature is varying within the day using a sinusoïdal function, maximal (Tmax value) at 2pm (local time) and minimal (Tmin value) at 2pm - daylength/2. The daylength is calculated and based on the solar angle calculation.
• The specific humidity is also varying within the day using a sinusoïdal function with qair_max and qair_min values calculated from the weathgen_qsat_2d function.
• The precipitation variable (precip) is split into rain and snow based on 0°C threshold. This split is done at each model time step (30 min usually) using the Tair interpolated value.
• The daily short-wave incomming radiation is distributed over the day using a the solar angle value at each time step as weight.
• Surface pressure, Long-wave radiation and Wind variables are linearly interpolated from day to day.