ET Theory 101. USCID Workshop. CUP, SIMETAW (DWR link)

Transcription

1 ET Theory 101 USCID Workshop PMhr, PMday, PMmon CUP, SIMETAW (DWR link) R.L. Snyder, Biometeorology Specialist Copyright Regents of the University of California

2 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

3 1. ow many molecules of air are in a cubic meter? 2.69 x 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 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 Weatherwise 54:20-27.

4 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 Km h-1 O Km h -1 CO Km h -1 2 O Km h False! Less than 0.1% of volume is occupied. Air can hold more water. orstmeyer, S Weatherwise 54:20-27.

5 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 Weatherwise 54:20-27.

6 Sensible eat & Temperature Lower temperature Less sensible heat igher temperature More sensible heat

7 Water Molecules consist of one oxygen and two hydrogen atoms O Water Molecule

8 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

9 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

10 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

11 Which wet towel dries fastest? T a = 30 o C 30 % R 70 % R Adiabatic Process

12 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

13 Radiation E = εσt 4 ε = 1.0 for a black body ε < 1.0 for a gray body σ= = W m -2 K -1 T = absolute temperature = o C

14 100 Blackbody spectral emittance for Sun and Earth 30 Solar Spectral Emittance (MW m -2 µm -1 ) K 288 K Earth Spectral Emittance (W m -2 µm -1 ) 0 73,483,200 W m W m Wavelength (µm) 0

15 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

16 Direct beam radiation interception (W m -2 ) 0 o 30 o 60 o 60 o Q s Q s = Q cos(α)

17 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.

18 Direct and diffuse radiation (W m -2 ) 0 o 30 o 60 o 60 o Q s Q s + q R s = Q s + q q 0.15 Q s on a horizontal sfc

19 30 Albedo Reflection (%) Vegetation height (m)

20 Net solar radiation (W m -2 ) 0 o 30 o 60 o 60 o Q s Q s + q α= 0.25

21 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

22 Net radiation (W m -2 ) 0 o 30 o 60 o 60 o Q s Q s + q α= R Ln =-100

23 ( 1 ) R = R α + R + R n sd Ld Lu Net Radiometer

24 (b) 2.5 Soil (Ground) eat Flux Thermal Conductivity (W m -1 K -1 ) G Sandy Clay Peat = T 2 G C1 C1 z2 z = T Volumetric Water Content

25 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

26 SURFACE ENERGY BUDGETS R = G + + LE + n Misc + -

27 Sensible eat Flux Density Sensible eat Flux Density = z z T T C pκ ρ = h p r T T C 1 2 ρ h h g z z r = = κ

28 Latent eat Flux Density Latent eat Flux Density = 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 = = κ

29 Microclimate & ETo Fetch Requirements Shading Wind blocking Marine effects

30 Fetch Requirements (Indio) ST8_1 ST7_1 and ST8_1 installed on March m ST7_1 N Prevailing Wind Direction 83 m CIMIS 162 GRASS

31 Fetch (98 m Vs 181 m) 15.0 Indio Station ST7_ Non Ideal ETo (mm) 11.0 y = 1.00x R 2 = CIMIS ETo (mm)

32 Empirical ETo El Dorado Country Club Adjustments for Regional effects Wind Blockage Sunrise-Sunset Advection Empirical Equations CIMIS Regional effects

33 El Dorado Country Club 10.0 El Dorado ETo (mm) y = 0.63x R 2 = CIMIS ETo (mm)

34 Torrey Pines Vs Mira Mar 7.0 Torrey Pines ETo (mm) y = 0.77x R 2 = Mira Mar CIMIS ETo (mm)

35 Temperature Model 30 Torrey Pines T ( o C) y = x x R 2 = Mira Mar CIMIS T ( o C)

36 Wind Correction 6.0 Torrey Pines Wind Speed (m s -1 ) y = 0.915x 2.0 R 2 = Mira Mar CIMIS Wind Speed (m s -1 )

37 Torrey Pines ETo Model 5.0 R s & T d from Torry Pines Torrey Pines ETo (mm) T = *T C ^ *T C U = 0.915*U C y = 0.973x R 2 = Mira Mar CIMIS ETo (mm)

38 Landscape Coefficient K = L ET ET L o ET L - measured ET o - estimated

39 Dense Canopy Light Interception

40 Sparse Canopy Light Interception Some light reflected. Increases sensible heat near the surface.

41 Density Correction 1.20 Fraction of Maximum Kc F C G π = sin C G Ground Cover (%)

42 Sunflowers (Bari, Italy) Rn LE G Energy Flux Density (W m -2 ) Time

43 Citrus Energy Balance - Lindsay Rn LE G2 600 Flux Density (W m -2 ) Jun 24-Jun

44 Local Advection Transpiration (mm h -1 ) Transpiration 23 July 9.76 mm Net Radiation Transpiration 26 July mm Time (h) Net Radiation (W m -2 )

45 Time of Drying Fraction of Daily ETc SUNRISE MID AM MID PM NOON SUNSET Fog Contribution

46 Water Table Contribution ET c ET c No Water Table With Water Table

47 The End Thanks