Latent heat flux as residual of the surface energy balance — latent_bulk

Calculates latent heat flux as the residual of the available turbulent energy after subtracting sensible heat flux.

Usage

latent_bulk_residual(rad_bal, ...)

# Default S3 method
latent_bulk_residual(rad_bal, soil_flux, sensible, warn_threshold = 600, ...)

# S3 method for class 'weather_station'
latent_bulk_residual(
  rad_bal,
  sensible = NULL,
  rho = 1.225,
  cp = 1005,
  k = 0.41,
  min_wind = 0.1,
  warn_threshold = 600,
  ...
)

Arguments

rad_bal: Net radiation $R_n$ in W m-2.
...: Further arguments passed to methods.
soil_flux: Soil heat flux $G$ in W m-2.
sensible: Sensible heat flux $H$ in W m-2.
warn_threshold: Absolute flux threshold in W m-2 for diagnostic warnings.
rho: Air density in kg m-3, used by the weather-station method when sensible is not supplied and sensible_bulk() is calculated internally.
cp: Specific heat capacity of air in J kg-1 K-1, used by the weather-station method when sensible is not supplied.
k: von Karman constant, used by the weather-station method when sensible is not supplied.
min_wind: Minimum wind speed in m s-1 used by the internal bulk calculation in the weather-station method.

Value

Latent heat flux in W m-2.

Details

The package energy-balance convention is:

$$ R_n = G + H + LE $$

when storage is omitted. Here $R_n$ is net radiation, $G$ is soil heat flux, $H$ is sensible heat flux, and $LE$ is latent heat flux.

The implemented residual is:

$$ LE_{res} = R_n - G - H $$

where $LE_{res}$ is latent heat flux in W m-2, $R_n$ is net radiation in W m-2, $G$ is soil heat flux in W m-2, and $H$ is sensible heat flux in W m-2.

The sign convention is:

$R_n > 0$: radiative energy input at the surface.
$G > 0$: heat flux into the soil.
$H > 0$: sensible heat flux away from the surface.
$LE > 0$: latent heat flux away from the surface.

In the Bulk-Residual workflow, sensible_bulk() first estimates $H_{bulk}$. The latent heat flux is then calculated as:

$$ LE_{res} = R_n - G - H_{bulk} $$

Therefore the Bulk-Residual workflow closes the available energy by construction:

$$ H_{bulk} + LE_{res} = R_n - G $$

This closure is algebraic. It does not prove that $H_{bulk}$ is a physically perfect sensible-heat estimate. Any error in $R_n$, $G$, or $H_{bulk}$ is inherited by the residual latent heat flux.

Large absolute residuals are warned about using warn_threshold, but they are not capped.

Examples

latent_bulk_residual(
  rad_bal = 400,
  soil_flux = 60,
  sensible = 120
)
#> [1] 220

h_bulk <- sensible_bulk(
  t1 = 20,
  t2 = 18,
  v1 = 2,
  v2 = 4,
  z1 = 2,
  z2 = 10
)
#> Warning: sensible_bulk: there are values above the diagnostic threshold of 600 W m-2.

latent_bulk_residual(
  rad_bal = 400,
  soil_flux = 60,
  sensible = h_bulk
)
#> Warning: latent_bulk_residual: there are values above the diagnostic threshold of 600 W m-2.
#> [1] -1541.755