Filters

Overview

Filters are a mechanism whereby the input forcing data can be modified in some way prior to the model run. For example, this could be use to apply a gauge undercatch to precip. Filters modify the data of a virtual station in situ.

Warning

Filters run in the order defined in the configuration file.

Please see config:forcing for how to attach a filter to an input forcing file.

Available filters

Longwave

debias_lw

class debias_lw : public filter_base

Debias an incoming longwave radiation using an additive constant factor.

Requires:

Incoming longwave radiation \([W \cdot m^{-2}\)]

Modifies:

Input longwave

Configuration keys:

{
   "variable": "lw",
   "factor": 3.5
}

variable: Name of the variable to modify that coincides with the input met file.

factor: The amount to add to the input longwave by: lw = lw + factor

Type:: string
Type:: double
Units:: \([W \cdot m^{-2}]\)

Precipitation

goodison_undercatch

class goodison_undercatch : public filter_base

Undercatch correction for a Nipher shielded guage via Goodison 1998 for solid precipitation

Requires:

Precipitation [ \( mm\) ]
Windspeed at gauge height [ \(m \cdot s^{-1} \) ]

Modifies:

Input precipitation

Configuration keys:

{
   "precip_var": "ppt",
   "wind_var": "u"
}

precip_var: Name of the precipitation variable in the met file.

wind_var: Name of the wind speed variable in the met file.

References:

Goodison, B. E. (1998), WMO Solid Solid Precipitiation Measurement Intercomparison. https://globalcryospherewatch.org/bestpractices/docs/WMOtd872.pdf

Type:: string
Type:: string

macdonald_undercatch

class macdonald_undercatch : public filter_base

Undercatch correction for a Alter shielded Geonor and tipping bucket via Macdonald, et al. 2007

Requires:

Precipitation [ \( mm\) ]
Windspeed at gauge height [ \(m \cdot s^{-1} \) ]

Modifies:

Input precipitation

Configuration keys:

{
   "precip_var": "ppt",
   "wind_var": "u"
}

precip_var: Name of the precipitation variable in the met file.

wind_var: Name of the wind speed variable in the met file.

References:

Macdonald, J., & Pomeroy, J. (2007). Gauge Undercatch of Two Common Snowfall Gauges in a Prairie Environment. Proceedings of the 64th Eastern Snow Conference, St. John‘s, Canada., 119–126.

Type:: string
Type:: string

Wind

scale_wind_speed

class scale_wind_speed : public filter_base

Scales a wind speed from a given height to the standard reference height in CHM, 50 m Uses a snow roughness z0, but assumes no snow depth (can be corrected for later).

Requires:

Windspeed [ \(m \cdot s^{-1} \) ]

Modifies:

None

Provides:

Reference windspeed at reference height - “U_R” [ \(m \cdot s^{-1} \) ]

Configuration keys:

{
    "variable":"u",
    "Z_F":10
}

variable: Name of the wind variable in the met file

Z_F: Wind observation height

Type:: string
Type:: double
Units:: [\(m\)]