E_RyanHarleman: Lake evaporation (Ryan-Harleman method)
In jmerc13/LakeIsodrology: Lake isotope hydrology

Description Usage Arguments Details Examples

E_RyanHarleman returns the daily rate of evaporation, E (mm/day), given the air temperature, lake surface temperature and windspeed 2m above the lake surface.

1 2	E_RyanHarleman(Ta, Tls, U, els, ea, lambda = 2.47, rho = 998, a = 2.7, b = 1/3, c = 3.1, conv = 86.4)

`Ta`	Air temperature, T_{a} (C).
`Tls`	Lake surface temperature, T_{ls} (C).
`U`	Wind speed at 2 m from the lake surface, U (m/s).
`els`	Saturated vapor pressure at the lake surface, e_{ls} (kPa).
`ea`	Atmospheric vapor pressure, e_{a} (kPa).
`lambda`	Latent heat of vaporization, λ_{v} (MJ kg^{-1}). Assumed to be 2.47.
`rho`	Density of water, rho (kg m^{-3}). Assumed to be 998 kg m^{-3}.
`a`	An empirical coefficient modifying the temperature gradient. Assumed to be 2.7.
`b`	Another empirical coefficient modifying the temperature gradient. Assumed to be 1/3.
`c`	An emperical coefficent modifying the influence of wind. Assumed to be 3.1.
`conv`	A multiplier that converts base units to mm/day. It is assumed to be 86.4, but will need to be adjust for alternative units.

Daily evaporation is determined via (Ryan and Harleman 1973, Rasmussen et al. 1995, Rosenberry et al. 2007):

E = \frac{(a \lbrack T_{ls} - T_{a} \rbrack ^{b} + c U)(e_{ls} - e_{a}) }{λ_{v} ρ} 86.4

Rasmussen AH, Hondzo M, Stefan HG. 1995. A test of several evaporation equations for water temperature simulations in lakes. JAWRA Journal of the American Water Resources Association 31 (6): 1023–1028.

Rosenberry DO, Winter TC, Buso DC, Likens GE. 2007. Comparison of 15 evaporation methods applied to a small mountain lake in the northeastern USA. Journal of Hydrology 340 (3–4): 149–166. DOI: 10.1016/j.jhydrol.2007.03.018.

Ryan PJ, Harleman DRF. 1973. An analytical and experimental study of transient cooling pond behavior. Vol. 161. Dept. of Civil Engineering, Massachusetts Institute of Technology.

Ta = 20; Tls = 17; RH = 0.8; U = 4.5
#Calculate the saturation vapor pressure for a given temperature.
es <- sat_vap(Ta)
#Determine the slope of the saturation vapor-pressure curve.
del <- slp_sat_vap(Ta, es)
#Use these data, in addition to the surface temperature of the lake, to determine
# the vapor pressure at the lake's surface.
els <- sat_vap_surf(es, del, Tls, Ta)
#Atmospheric vapor pressure
ea <- atm_vap(RH, es)
#Apply values to the Ryan-Harleman evaporation function:
E_RyanHarleman(Ta, Tls, U, els, ea)