@BeginModule
@Name      = EcaFd
@Title     = Frost days index per time period
@Section   = Climate indices
@Class     = Climate index
@Arguments = ifile ofile
@Operators = eca_fd

@BeginDescription
Let @file{ifile} be a time series of daily minimum temperatures TN,
then counted is the number of days where TN < 0° Celsius. Note
that TN must be given in units of Kelvin.
The date information for a time step in @file{ofile} is the date of
the last contributing time step in @file{ifile}.
@EndDescription
@EndModule


@BeginOperator_eca_fd
@Title     = Frost days index per time period
@EndOperator


@BeginExample
To get the number of frost days for a time series of daily
minimum temperatures, use:
@BeginVerbatim
   cdo eca_fd tnfile ofile
@EndVerbatim
@EndExample
