ET Theory 101 USCID Workshop http://biomet.ucdavis.edu PMhr, PMday, PMmon CUP, SIMETAW (DWR link) R.L. Snyder, Biometeorology Specialist Copyright Regents of the University of California
Methods of eat Transfer Conduction- from molecule to molecule Conduction eat Source Convection - by movement of heated air Metal bar Radiation - energy passing from one object to another without a connecting medium Long wave loss from Earth Short wave gained from the sun Earth
1. ow many molecules of air are in a cubic meter? 2.69 x 10 25 Questions 1 and 2 1. If six billion people count 1000 molecules per hour, it would take 511 million years to count the number of molecules in 1 m 3 26,900,000,000,000,000,000,000,000 molecules m -3 2. The air is mostly nitrogen? (T/F)? False 2. Air is mostly empty space. Less than 0.1% of the volume is occupied by molecules orstmeyer, S. 2001. Weatherwise 54:20-27.
Questions 3 and 4 3. Which molecules move faster? A. nitrogen B. oxygen C. carbon dioxide D. water vapor 4. When saturated, the air cannot hold more water vapor (T/F)? 3. At 30 o C, velocities N 2-1709 Km h-1 O 2-1603 Km h -1 CO 2-1366 Km h -1 2 O - 2136 Km h -1 4. False! Less than 0.1% of volume is occupied. Air can hold more water. orstmeyer, S. 2001. Weatherwise 54:20-27.
Questions 5 5. ow many molecule collisions per second occur in a m 3 of air? 5. There are about 595 trillion collisions per second between air molecules in a m 3 of air. 26,900,000,000,000,000,000,000,000 molecules m -3 Occupy < 0.1% volume 595,000,000,000,000 collisions/sec orstmeyer, S. 2001. Weatherwise 54:20-27.
Sensible eat & Temperature Lower temperature Less sensible heat igher temperature More sensible heat
Water Molecules consist of one oxygen and two hydrogen atoms O Water Molecule
Methods of eat Transfer Latent eat - Chemical eat When water molecules evaporate, sensible heat is changed to latent heat and the temperature drops When water molecules condense, latent heat is changed to sensible heat and the temperature rises O O
More Water Vapor More Latent eat Energy breaks our hydrogen bonds and sets us free O O O I am a free water vapor molecule O O O O O O Latent heat
Questions 6 6. Your ice cream will melt faster at 35% R than at 75% R (T/F)? 6. False, there is more total heat in humid than in dry air to melt the ice cream
Which wet towel dries fastest? T a = 30 o C 30 % R 70 % R Adiabatic Process
Questions 7 7. Is there evaporation in a greenhouse with 100% relative humidity? 7. Yes! But both the temperature and vapor pressure must increase following the saturation vapor pressure curve. Diabatic Process
Radiation E = εσt 4 ε = 1.0 for a black body ε < 1.0 for a gray body σ= = 5.67 10-8 W m -2 K -1 T = absolute temperature = o C+273.15
100 Blackbody spectral emittance for Sun and Earth 30 Solar Spectral Emittance (MW m -2 µm -1 ) 80 60 40 20 6000 K 288 K 20 10 Earth Spectral Emittance (W m -2 µm -1 ) 0 73,483,200 W m -2 390 W m -2 0.1 1 10 100 Wavelength (µm) 0
Direct Radiation (Q)( Radiation that comes directly from the sun The amount of energy received per unit area is called Irradiance and the units are commonly W m -2 = J s -1 m -2. The amount of energy received depends on the angle of incidence of the radiation
Direct beam radiation interception (W m -2 ) 0 o 30 o 60 o 60 o 500 433 250 Q s Q s = Q cos(α)
Diffuse Radiation (q)( Solar radiation that is scattered by the sky and comes from all directions. During much of the day, about 10 to 15% of the radiation received on a flat surface is diffuse radiation. The diffuse radiation is nearly the same regardless of the surface orientation. The percentage of diffuse radiation is higher near sunrise and sunset.
Direct and diffuse radiation (W m -2 ) 0 o 30 o 60 o 60 o 500 433 250 Q s 535 468 285 Q s + q R s = Q s + q q 0.15 Q s on a horizontal sfc
30 Albedo Reflection (%) 20 10 0 0.1 1 10 100 Vegetation height (m)
Net solar radiation (W m -2 ) 0 o 30 o 60 o 60 o 500 433 250 Q s 535 468 285 Q s + q 401 351 214 α= 0.25
Net Radiation R n =(1-α)R s +L u +L d R s =Q s +q R s Rs Lu Ld cloudy clear L u + L d = -10 W m -2 to L u + L d = -100 W m -2
Net radiation (W m -2 ) 0 o 30 o 60 o 60 o 500 433 250 Q s 535 468 285 Q s + q 401 351 214 α= 0.25 301 251 114 R Ln =-100
( 1 ) R = R α + R + R n sd Ld Lu Net Radiometer
(b) 2.5 Soil (Ground) eat Flux Thermal Conductivity (W m -1 K -1 ) 2.0 1.5 1.0 0.5 G Sandy Clay Peat = T 2 G C1 C1 z2 z = T 1 1 0.0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Volumetric Water Content
Soil eat Flux Density (G ) T T G G C f i d 2 V t t f i = + C V volumetric heat capacity G Thermocouples d eat Plate G 2
SURFACE ENERGY BUDGETS + + - - + - + - R = G + + LE + n Misc + -
Sensible eat Flux Density Sensible eat Flux Density = 1 2 1 2 z z T T C pκ ρ = h p r T T C 1 2 ρ h h g z z r = = 1 2 1 κ
Latent eat Flux Density Latent eat Flux Density = 1 2 1 2 z z e e C LE p γ ρ κ = w p r e e C LE 1 2 γ ρ w w g z z r = = 1 2 1 κ
Microclimate & ETo Fetch Requirements Shading Wind blocking Marine effects
Fetch Requirements (Indio) ST8_1 ST7_1 and ST8_1 installed on March 24 98 m ST7_1 N Prevailing Wind Direction 83 m CIMIS 162 GRASS
Fetch (98 m Vs 181 m) 15.0 Indio Station ST7_1 13.0 Non Ideal ETo (mm) 11.0 y = 1.00x R 2 = 0.99 9.0 7.0 7.0 9.0 11.0 13.0 15.0 CIMIS ETo (mm)
Empirical ETo El Dorado Country Club Adjustments for Regional effects Wind Blockage Sunrise-Sunset Advection Empirical Equations CIMIS Regional effects
El Dorado Country Club 10.0 El Dorado ETo (mm) 8.0 6.0 4.0 2.0 y = 0.63x R 2 = 0.72 0.0 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 CIMIS ETo (mm)
Torrey Pines Vs Mira Mar 7.0 Torrey Pines ETo (mm) 6.0 5.0 4.0 3.0 2.0 1.0 y = 0.77x R 2 = 0.72 0.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 Mira Mar CIMIS ETo (mm)
Temperature Model 30 Torrey Pines T ( o C) 25 20 15 10 5 y = -0.022x 2 + 1.390x R 2 = 0.885 0 0 5 10 15 20 25 30 35 40 Mira Mar CIMIS T ( o C)
Wind Correction 6.0 Torrey Pines Wind Speed (m s -1 ) 5.0 4.0 3.0 y = 0.915x 2.0 R 2 = 0.667 1.0 0.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 Mira Mar CIMIS Wind Speed (m s -1 )
Torrey Pines ETo Model 5.0 R s & T d from Torry Pines Torrey Pines ETo (mm) 4.0 3.0 2.0 1.0 T = -0.022*T C ^2 + 1.390*T C U = 0.915*U C y = 0.973x R 2 = 0.980 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Mira Mar CIMIS ETo (mm)
Landscape Coefficient K = L ET ET L o ET L - measured ET o - estimated
Dense Canopy Light Interception
Sparse Canopy Light Interception Some light reflected. Increases sensible heat near the surface.
Density Correction 1.20 Fraction of Maximum Kc 0.80 0.40 F C G π = sin 70 2 0.00 0 20 40 60 80 C G Ground Cover (%)
800 700 Sunflowers (Bari, Italy) Rn LE G Energy Flux Density (W m -2 ) 600 500 400 300 200 100 0-100 7 10 13 16 19 8 11 14 17 8 11 14 17 Time
Citrus Energy Balance - Lindsay 2001 800 Rn LE G2 600 Flux Density (W m -2 ) 400 200 0 20-Jun 24-Jun -200 2400 1200 2400 1200 2400 1200 2400 1200 2400 1200 2400
Local Advection 1.6 1400 Transpiration (mm h -1 ) 1.2 0.8 0.4 0.0 Transpiration 23 July 9.76 mm Net Radiation Transpiration 26 July 14.66 mm 1000 600 200-200 0 6 12 18 24 Time (h) Net Radiation (W m -2 )
1.0 0.8 0.6 0.4 0.2 0.0 Time of Drying Fraction of Daily ETc SUNRISE MID AM MID PM NOON SUNSET Fog Contribution
Water Table Contribution ET c ET c No Water Table With Water Table
The End Thanks