## Summary: Snow Covered Area Fraction

The article discusses the calculation of the fraction of ground covered by snow, denoted as f_sno, in the Community Land Model (CLM).

Key points:

1. Snow covered area fraction (SCF) is calculated separately for accumulation and depletion processes.

2. During snowfall, the updated SCF (f_sno^(n+1)) is calculated using the equation:
   f_sno^(n+1) = 1 - ((1 - tanh(k_accum * q_sno * Δt))(1 - f_sno^n))
   where k_accum is a constant, q_sno is the amount of new snow, and f_sno^n is the previous SCF.

3. During snow melt, the SCF is calculated from the depletion curve:
   f_sno = 1 - (cos^-1(2*R_sno - 1)/π)^N_melt
   where R_sno is the ratio of the current snow water equivalent (W_sno) to the maximum accumulated snow (W_max), and N_melt is a parameter that depends on the topographic variability within the grid cell.

4. The depletion curve shape parameter N_melt is defined as:
   N_melt = 200 / min(10, σ_topo)
   where σ_topo is the standard deviation of elevation within the grid cell.

5. For "glacier_mec" columns, a flat terrain is assumed, with N_melt = 10.