107
Thermal Radiation and Energy Closure Assessment
high-frequency fluxes superimposed on a longer low-frequency trend. Power spectra for w and u showed the presence of an unsteady low-frequency overhead flow,
resulting in a broadening and substantial variation of the spectral peak for the vertical velocity w. This implies that large-scale motions can manifest themselves in
the surface–boundary layer, resulting in enhanced turbulence affecting the actual
covariance estimates. The power spectra for u showed a major peak at low frequencies (0.001–0.01) and a broad second peak in the higher frequency range (0.03–0.2).
These power spectra results were not atypical for the conditions of this study and also
suggest that the assumptions related to the Monin–Obukhov scaling theory may not
be suited for conditions where the presence of advection is routine and a dominant
feature of the landscape. Cospectra results for H and LE under typical conditions for
this location clearly showed a spectral gap for the heat flux, again underscoring the
clear presence of large low-frequency events that can impact the measurements over
a surface. We concluded by stating that, in spite of the results that we have observed
in the Texas study, EC provides the most physically correct measurement of turbulent fluxes for heat and water vapor. Additional corrections to compensate for or take
into account the additional energy in the form of saturation deficit to ET measurements need to be considered and developed.
REFERENCES
Anderson, M. C., Kustas, W. P., and Norman, J. M. (2007). Upscaling flux observations
from local to continental scales using thermal remote sensing. Agronomy Journal, 99,
240–254.
Baldocchi, D. D., Hicks, B. B., and Meyers, T. P. (1988). Measuring biosphere–atmosphere
exchanges of biologically related gases with micrometeorological methods. Ecology,
69(5), 1331–1340.
Bradshaw, P. (1967). Inactive motion and pressure fluctuations in turbulent boundary layers.
Journal of Fluid Mechanics, 30, 241–258.
Brutsaert, W. (1982). Evaporation into the Atmosphere: Theory, History and Applications.
D. Reidel Publishing Company, Dordrecht.
Desjardins, R. L., Macpherson, I. J., Schuepp, P. H., and Karanja, F. (1989). An evaluation
of aircraft flux measurements of CO 2 , water vapor and sensible heat. Boundary Layer
Meteorology, 47, 55–69.
Foken, T. and Wichura, B. (1996). Tools for the assessment of surface-based flux measurements. Agricultural and Forest Meteorology, 78, 83–105.
Friehe, C. A., Shaw, W. J., Rogers, D. P., Davidson, K. L., Large, W. G., Stage, S. A., Crescenti,
G. H., Khalsa, S. J. S., and Greenhut, G. K. (1991). Air–Sea fluxes and surface layer turbulence around a sea surface temperature front. Journal of Geophysical Research, 96,
8593–8609.
Garratt, J. R. (1975). Limitations of the eddy correlation technique for determination of turbulent fluxes near the surface. Boundary Layer Meteorology, 8, 255–259.
Goulden, M. L., Munger, J. W., Fan, S. M., Daube, B. C., and Wofsy, S. C. (1996). Measurements
of carbon sequestration by long-term eddy covariance: Methods and a critical evaluation
of accuracy. Global Change Biology, 2, 169–182.
Hall, F. G., Huemmrich, K. F., Goetz, S. J., Sellers, P. J., and Nickeson, J. E. (1992). Satellite
remote sensing of surface energy balance: Success, failures, and unresolved issues in
FIFE. Journal of Geophysical Research, 97(D17), 19061–19089.
Thermal Radiation and Energy Closure Assessment
high-frequency fluxes superimposed on a longer low-frequency trend. Power spectra for w and u showed the presence of an unsteady low-frequency overhead flow,
resulting in a broadening and substantial variation of the spectral peak for the vertical velocity w. This implies that large-scale motions can manifest themselves in
the surface–boundary layer, resulting in enhanced turbulence affecting the actual
covariance estimates. The power spectra for u showed a major peak at low frequencies (0.001–0.01) and a broad second peak in the higher frequency range (0.03–0.2).
These power spectra results were not atypical for the conditions of this study and also
suggest that the assumptions related to the Monin–Obukhov scaling theory may not
be suited for conditions where the presence of advection is routine and a dominant
feature of the landscape. Cospectra results for H and LE under typical conditions for
this location clearly showed a spectral gap for the heat flux, again underscoring the
clear presence of large low-frequency events that can impact the measurements over
a surface. We concluded by stating that, in spite of the results that we have observed
in the Texas study, EC provides the most physically correct measurement of turbulent fluxes for heat and water vapor. Additional corrections to compensate for or take
into account the additional energy in the form of saturation deficit to ET measurements need to be considered and developed.
REFERENCES
Anderson, M. C., Kustas, W. P., and Norman, J. M. (2007). Upscaling flux observations
from local to continental scales using thermal remote sensing. Agronomy Journal, 99,
240–254.
Baldocchi, D. D., Hicks, B. B., and Meyers, T. P. (1988). Measuring biosphere–atmosphere
exchanges of biologically related gases with micrometeorological methods. Ecology,
69(5), 1331–1340.
Bradshaw, P. (1967). Inactive motion and pressure fluctuations in turbulent boundary layers.
Journal of Fluid Mechanics, 30, 241–258.
Brutsaert, W. (1982). Evaporation into the Atmosphere: Theory, History and Applications.
D. Reidel Publishing Company, Dordrecht.
Desjardins, R. L., Macpherson, I. J., Schuepp, P. H., and Karanja, F. (1989). An evaluation
of aircraft flux measurements of CO 2 , water vapor and sensible heat. Boundary Layer
Meteorology, 47, 55–69.
Foken, T. and Wichura, B. (1996). Tools for the assessment of surface-based flux measurements. Agricultural and Forest Meteorology, 78, 83–105.
Friehe, C. A., Shaw, W. J., Rogers, D. P., Davidson, K. L., Large, W. G., Stage, S. A., Crescenti,
G. H., Khalsa, S. J. S., and Greenhut, G. K. (1991). Air–Sea fluxes and surface layer turbulence around a sea surface temperature front. Journal of Geophysical Research, 96,
8593–8609.
Garratt, J. R. (1975). Limitations of the eddy correlation technique for determination of turbulent fluxes near the surface. Boundary Layer Meteorology, 8, 255–259.
Goulden, M. L., Munger, J. W., Fan, S. M., Daube, B. C., and Wofsy, S. C. (1996). Measurements
of carbon sequestration by long-term eddy covariance: Methods and a critical evaluation
of accuracy. Global Change Biology, 2, 169–182.
Hall, F. G., Huemmrich, K. F., Goetz, S. J., Sellers, P. J., and Nickeson, J. E. (1992). Satellite
remote sensing of surface energy balance: Success, failures, and unresolved issues in
FIFE. Journal of Geophysical Research, 97(D17), 19061–19089.