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Saturation vapor pressure (t2es)

Source: R/metutils.R
sat_vapor_pressure.Rd

Compute saturation vapor pressure from temperature using one of the following methods:

  • (Default) Clausius–Clapeyron (FAO-56 style) — Recommended for most applications. Commonly used approximation for terrestrial ecosystem models, consistent with Penman-Monteith and FAO-56 (Allen et al, 1998).

  • Magnus — More accurate in the range −40 to +50 C. Coefficients as in Alduchov & Eskridge (1996).

  • Goff–Gratch - Highest accuracy; use when following WMO-style recommendations. Goff–Gratch 1946; WMO, 2014.

Usage

sat_vapor_pressure(
  temp,
  temp_units = "degC",
  out_units = "kPa",
  method = c("ClausiusClapeyron", "Magnus", "GoffGratch")
)

get.es(temp)

t2es(
  temp,
  temp_units = "degC",
  out_units = "kPa",
  method = "ClausiusClapeyron"
)

Arguments

temp

numeric vector of temperatures

temp_units

input temperature units ("degC","K","degF"), default "degC"

out_units

output pressure units ("kPa","hPa","Pa","mb"), default "kPa"

method

one of "Magnus","ClausiusClapeyron" (default), or "GoffGratch". See details for references.

Value

numeric vector in out_units

Details

Each method uses different units internally, users can specify units for both inputs and outputs, with defaults "degC" and "kPa", respectively.

References

Alduchov, O. A., & Eskridge, R. E. (1996). Improved Magnus Form Approximation of Saturation Vapor Pressure. J. Appl. Meteor.*, 35(4), 601–609. <doi:10.1175/1520-0450(1996)035<0601:IMFAOS>2.0.CO;2>

Allen, R. G., Pereira, L. S., Raes, D., & Smith, M. (1998). Crop evapotranspiration – Guidelines for computing crop water requirements. FAO Irrigation and Drainage Paper 56.

Goff, J. A., & Gratch, S. (1946). Low-pressure properties of water from −160 to 212F. Trans. ASHVE, 52, 95–122.

WMO (2014) Guide to Instruments and Methods of Observation (WMO-No. 8), ch. 4.

Author

David LeBauer

Examples

# Calculate saturation vapor pressure at 20°C
sat_vapor_pressure(20)
#> [1] 2.370916
t2es(20)
#> [1] 2.370916

# Using different methods
t2es(c(10, 20, 30), method = "Magnus")
#> [1] 1.227922 2.338205 4.242926
t2es(283.15, temp_units = "K", method = "GoffGratch")
#> [1] 1.22703

# Different output units
t2es(20, out_units = "hPa")
#> [1] 23.70916