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.
1 2 3 4 5 6 7 8 9 10 11 12 | 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)
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