| Penman Monteith |
| Intermediate Variables |
| maxtemp | : | Max Daily Temp [C] |
| mintemp | : | Min Daily Temp [C] |
| maxhum | : | Max Daily Humidity [%] |
| minthum | : | Min Daily Humidity [%] |
| windspdtmp | : | Avg Wind Speed [mph] |
| solrad | : | Solar Raditation [] |
| pi | : | Pizza Pi [] |
| albedo | : | Albedo of Grass [] |
| avg_wind_mps | : | Average Wind Speed [m/s] |
| meantemp | : | Mean/Avg Daily Temp [C] |
| elevation | : | Elevation [m or km] |
| jday | : | Julian [] |
| dr | : | (inverse relative distance Earth-Sun) [] |
| soldec | : | Solar Declination [] |
| lat | : | Latitude [degrees] |
| radlat | : | Latitude [radians] |
| sunangle | : | Sunset Hour Angle [radians?] |
| eomax | : | E0 Temp Max [C?] |
| eomin | : | E0 Temp Min [C?] |
| es | : | Mean saturation vapour pressure at the air temperature [] |
| ea | : | Actual vapour pressure derived from relative humidity data [] |
| p | : | Atmosphereic Pressure [] |
| lambda | : | Psychrometric constant [] |
| delta | : | Slope vapor pressure [] |
| ra | : | Extraterrestrial radiation [] |
| rso | : | Clear Sky Solar Radiation [] |
| rns | : | Net Solar or Net Shortwave Radiation [] |
| rnl | : | Net Outgoing Longwave Radiation [] |
| rn | : | Net Solar Radiation [] |
| et | : | Extraterrestrial Radiation [mm/day] |
| Equations |
| maxtemp | = | |
| mintemp | = | |
| maxhum | = | |
| minthum | = | |
| windspdtmp | = | |
| solrad | = | |
| pi | = | |
| albedo | = | |
| avg_wind_mps | = | windspdtmp * .44704 |
| meantemp | = | (maxtemp + mintemp)/2 |
| elevation | = | 5342*0.3048 |
| jday | = | |
| dr | = | 1+0.033*cos(2*pi*jday/365) |
| soldec | = | 0.409*sin(2*pi*jday/365-1.39) |
| lat | = | |
| radlat | = | lat*pi/180 |
| sunangle | = | acos(-tan(radlat)*tan(soldec)) |
| eomax | = | 0.6108 * exp(17.27*maxtemp/(maxtemp+237.3)) |
| eomin | = | 0.6108 * exp(17.27*mintemp/(mintemp+237.3)) |
| es | = | (eomax + eomin) / 2 |
| ea | = | (eomax*mintemp/100+eomin*maxtemp/100)/2 |
| p | = | 101.3*((293-0.0065*1628.2416)/293) ** 5.26 |
| lambda | = | 0.000665*p |
| delta | = | 4098*(0.6108*exp(17.27*meantemp/(meantemp+237.3)))/(meantemp+237.3)^2 |
| ra | = | 24*60*0.082/pi*dr*(sunangle*sin(radlat)*sin(soldec)+cos(radlat)*cos(soldec)*sin(sunangle)) |
| rso | = | (0.75+2*10^-5*1628.2416) * ra |
| rns | = | (1-albedo)*solrad |
| rnl | = | 4.903*10^ -9*(((maxtemp+273.16)^4)+(mintemp+273.16)^4) / 2 * (0.34-0.14*ea^0.5) * (1.35*solrad/rso-0.35) |
| rn | = | rns-rnl |
| et | = | (0.408*delta*(rn-0)+lambda*(900/(meantemp+273))*avg_wind_mps*(es-ea))/ (delta+lambda*(1+0.34*avg_wind_mps)) |
| End results |
| maxtemp | ~ | 29.070 [C] |
| mintemp | ~ | 5.990 [C] |
| maxhum | ~ | 20.430 [%] |
| minthum | ~ | 10.620 [%] |
| windspdtmp | ~ | 5.33758333333333 [mph] |
| solrad | ~ | 0.188166666666667 [] |
| pi | ~ | 3.14159265358979 [] |
| albedo | ~ | 0.23 [] |
| avg_wind_mps | ~ | 2.38611325333333 [m/s] |
| meantemp | ~ | 17.53 [C] |
| elevation | ~ | 1628.2416 [m or km] |
| jday | ~ | 240
[] |
| dr | ~ | 0.981888182376604 [] |
| soldec | ~ | 0.159341089421756 [] |
| lat | ~ | 38.7 [degrees] |
| radlat | ~ | 0.675442420521806 [radians] |
| sunangle | ~ | 1.69990244356182 [radians?] |
| eomax | ~ | 4.02191012624216 [C?] |
| eomin | ~ | 0.93446220742991 [C?] |
| es | ~ | 2.47818616683604 [] |
| ea | ~ | 0.309018742192424 [] |
| p | ~ | 83.4770210713801 [] |
| lambda | ~ | 0.0555122190124677 [] |
| delta | ~ | 0.126450439169293 [] |
| ra | ~ | 34.4241817562755 [] |
| rso | ~ | 26.9391540128372 [] |
| rns | ~ | 0.144888333333333 [] |
| rnl | ~ | -3.15550218196602 [] |
| rn | ~ | 3.30039051529935 [] |
| et | ~ | 4.67114559693709 [mm/day] |
Et0 mm/day = 4.67
Et0 in/day = 0.18 |