@BeginModule
@Name      = EcaId
@Title     = Ice days index per time period
@Section   = ECA indices
@Class     = ECA index
@Arguments = ifile ofile
@Operators = eca_id

@BeginDescription
Let @file{ifile} be a time series of daily maximum temperatures TX,
then counted is the number of days where TX < 0° Celsius. Note
that TX 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_id
@Title     = Ice days index per time period
@EndOperator


@BeginExample
To get the number of ice days for a time series of daily
maximum temperatures, use:
@BeginVerbatim
   cdo eca_id txfile ofile
@EndVerbatim
@EndExample
