GfsEventFilter applies "exponential" filtering to a given variable.
The syntax in parameter files is as follows:
[ GfsEvent ] V TSCALE
V is a variable and
TSCALE is a strictly positive number. At every realisation of the event, variable
V is replaced by
(1 - a)*V + a*VF, where
a = dt/TSCALE,
dt is the timestep and
VF is the filtered variable obtained by corner-value averaging.