ASPECT EFFECTS

1. ASPECT EFFECTS

3. Photosynthetically-active radiation (spectral portion,0.3-0.4 CI) 0400-0500h 0500-0600h 0600-0700h 0700-0800h 0800-0900h 0900-1000h 1000-1100h 1100-1200h

5. TERRESTRIAL RADIATION

6. Longwave Radiative Exchange The atmosphere absorbs long-wave radiation (L) from the Earth, clouds and gases at all altitudes Absorption greatest in lower portion of the atmosphere, where H20 and CO2 concentrations are highest The atmosphere absorbs effectively from 3-100 m, except in the atmospheric window (8-11 m) Most longwave loss to space occurs through this window, but clouds can partially close it

7. NET RADIATION BALANCE

8. L is greater in magnitude and more variable than L L = 0 (T0)4 + (1 - 0) L Amount of L reflected (slight adjustment) L* = L - L (usually negative) NET ALL_WAVE RADIATION DAYTIME: Q* = K - K + L - L Q* = K* + L* NIGHT: Q* = L*

9. Radiation Measurements PAR L K UV-A K (not visible) L

10. More radiation sensors… Source: University of Colorado

11. K in tropical forests of Colombia/Ecuador

12. Radiation Balance Components Negative in Oke

13. Clouds Reduce K because of absorption and reflection from cloud tops (may eliminate S) Increase D by scattering incoming solar radiation Strongest K  under partly cloudy skies with sun in clear patch Absorb much of L and re-emit it as L (low cloud emits more) Reduce diurnal temperature variation

14. Global Energy Balance (SIMPLIFIED) Source: NOAA

15. SURFACE ENERGY BALANCE

16. Q* - positive in daytime - almost always negative at night Any Q* imbalance is accounted for by convective exchange or conduction Q* = QH + QE + QG + S where QH = sensible heat flux QE = latent heat flux QG = conduction to or from ground (See Figure 1.10)

18. Recall the First Law of Thermodynamics ENERGY IN = ENERGY OUT Qin > Qout (flux convergence) Net storage gain leads to warming Qout > Qin (flux divergence) Net storage energy loss leads to cooling Qin = Qout No net change in energy storage

20. WATER BALANCE & LATENT HEAT

21. Water: H2O • High heat capacity • Exists in all states at Earth’s • temperatures • Heat required/released during phase changes: • Latent heat of fusion (Lf = 0.334 MJ kg-1) • Latent heat of vaporization (Lv = 2.45 MJ kg-1) • Latent heat of sublimation (Ls = Lf + Lv)

22. Water Balance p = E + r + s Where p isprecipitation E is evapotranspiration r is net runoff s is soil moisture storage content QE = Lv E QM = Lf M Where E and M are in kg m-2 s-1 See Fig. 1.13

23. Sensible and Latent Heat Fluxes • Eddy correlation (later) • Sonic anemometer • measurements of vertical • velocity and temperature • Krypton hygrometer • measurements of water • vapour density

26. Advection and Winds Air flow at local scale can affect energy balance as can air flow at scales larger than boundary layer At the micro-scale, horizontal temperature variation causes horizontal pressure differences Why ? Warm air is lighter than cold air This leads to winds (kinetic energy) Energy transferred to smaller and smaller scales before being dissipated as heat

27. DIURNAL PATTERNS OF SENSIBLE AND LATENT HEAT FLUXES

28. DAYTIME: • Both sides of equation are positive: • surface radiative surplus • Surplus partitioned into ground and • atmosphere • Convection is the most important means of • daytime heat transport from surface • QE is greater when soil moisture is high • QH is greater when water is more restricted

29. NIGHT: • Both sides of equation are negative: • surface radiative deficit • Deficit partitioned into heat gain from ground • and atmosphere • Q* loss is partially replenished by QG • QE and QH of less importance as convective • exchange is dampened by the night-time • temperature stratification