1. The Surface Energy Budget, Part II
COMET Planetary Boundary Layer Symposium
Matt Haugland

2. Generic Examples
How will the following situations affect the components of the Surface Energy Budget?

3. Green crop field
Green crop field

4. Rn S LE G DQ Green crop field
HIGHER
NORMAL
LOWER
Rn S LE G DQ
Result: lower daytime temperature, higher dewpoint

5. Car in the sun
Surface = interior of your car, parked in the sun

6. Rn S LE G DQ Car in the sun Result: very high “surface” temperature!
HIGHER
NORMAL
LOWER
Rn S LE G DQ
Result: very high “surface” temperature!

7. Dead grass
Dead grass, minimal soil moisture

8. Rn S LE G DQ Dead grass HIGHER NORMAL LOWER
Result: higher daytime surface temperature, deeper boundary layer, stronger (& more westerly) wind

9. South-facing slope
South-facing slope

10. Rn S LE G DQ South-facing slope HIGHER NORMAL LOWER
Result: slightly higher surface temperature, slightly lower relative humidity

11. Woodland (nighttime)
Woodland or open-canopy forest (nighttime)

12. Rn S LE G DQ Woodland (nighttime) LESS NEGATIVE NORMAL MORE
Result: lower temperature, higher RH (at night)

13. Hilltop (nighttime)
Hilltop (nighttime)

14. Rn S LE G DQ Hilltop (nighttime)
LESS
NEGATIVE
NORMAL
MORE
Result: higher surface temperature at night

15. Real Example
Consider a mesoscale strip of land in a region with substantially different vegetation

16. Oklahoma’s Winter Wheat Belt
km wide strip in western Oklahoma/Kansas
Winter wheat is primary vegetation type
Cool-season (C3) crop, surrounded by warm-season (C4) grasses
Ideal outdoor laboratory for study of land-surface impact on atmosphere

17. Before Harvest Before harvest (April 2000) – healthy wheat crop
Winter Wheat Belt is greener than adjacent counties
Latent Heat Flux much higher across WWB (sensible heat flux lower)

18. Before Harvest
Average 19Z Temperature (March 2000)

19. Before Harvest
19Z Temperature (8 April 2000)

20. After Harvest
Before harvest (June 2000) – dead wheat stubble, bare soil
Winter Wheat Belt is less green than adjacent counties
Latent Heat Flux much lower across WWB (sensible heat flux higher)

21. After Harvest
Average 21Z Temperature (June 2000)

22. After Harvest
21Z Temperature (8 June 2000)

23. Impact on Air Pressure – Before Harvest
Diurnal Temperature and Surface Pressure Anomalies over the WWB
Before Harvest (March ) - error bars indicate 90% confidence interval
Temperature Pressure
During the afternoon, the low temperature anomaly over the WWB creates a surface high pressure anomaly
Suggests that temperature anomaly is approximately as deep as the PBL

24. Impact on Air Pressure – After Harvest
Diurnal Temperature and Surface Pressure Anomalies over the WWB
After Harvest (June )
Temperature Pressure
During the afternoon, the high temperature anomaly over the WWB creates a surface low pressure anomaly

25. The Diurnal Cycle of Dewpoint
An excellent indicator of land-atmosphere interactions

26. Diurnal Cycle of Dewpoint
4 Stages of the Diurnal Cycle of Dewpoint

27. Diurnal Cycle of Dewpoint – Morning Stage
Dewpoint generally increases
Dew evaporates
Transpiration begins
Shallow boundary layer – moisture builds up
Relatively little dry air entrainment
SEPTEMBER
New Orleans, LA
Phoenix, AZ

28. Evapotranspiration (ET)
Daytime Dewpoint
Evapotranspiration (ET)
Dry Air Entrainment
(Particularly important in western states)
Dry air aloft
Vertical mixing
Moist air near surface

29. Diurnal Cycle of Dewpoint – Daytime Stage
Dewpoint generally decreases
Battle between evapotranspiration and dry air entrainment – D.A.E. usually wins by afternoon, except in highly vegetated areas or in coastal areas where D.A.E. is minimal
AUGUST SEPTEMBER
Mason City, IA
Phoenix, AZ

30. Diurnal Cycle of Dewpoint – Evening Stage
Dewpoint almost always increases
Dry air entrainment shuts off
Dominated by evapotranspiration
Shallow/stable boundary layer – moisture builds up near surface
SEPTEMBER
Grand Island, NE
Los Angeles, CA

31. Diurnal Cycle of Dewpoint – Night. Stage
Dewpoint generally decreases
Dominated by condensation
Largest decreases are in (moist) valleys with plenty of radiational cooling
Can increase at very dry and/or windy locations
FEBRUARY SEPTEMBER
Fresno, CA
Phoenix, AZ

32. Diurnal Cycle of Dewpoint
Oklahoma Mesonet sites representing Winter Wheat Belt (WWB) and adjacent counties (AC)

33. Diurnal Cycle of Dewpoint
Before Harvest (March )

34. Diurnal Cycle of Dewpoint
Average 13Z to 0Z Dewpoint Change (March )

35. Diurnal Cycle of Dewpoint
After Harvest (June )

36. Diurnal Cycle of Dewpoint
Average 11Z to 23Z Dewpoint Change (June )

37. Conclusions
Weather and climate “start” at the ground (surface) and are driven by solar radiation.
Nature of the earth’s surface determines way in which the atmosphere is heated/cooled.
Differences over land surfaces result from contrasts in soil moisture, vegetation type & status, etc.
Local boundary layer conditions strongly depend on local surface characteristics

38. Questions
Any Questions??