Abstract
The spatial representativeness of heat fluxes on the basis of single-tower measurements, and the mechanism of the so-called energy imbalance problem, are investigated through numerical experiments using large-eddy simulation (LES). LES experiments are done for the daytime atmospheric boundary layer heated over a flat surface, as a best-case scenario completely free of sensor errors and the uncertainties of field conditions. Imbalance is defined as the deviation of the `turbulent' heat flux at a grid point from the horizontally averaged `total' heat flux. Both the theoretical and numerical results of the present study suggest the limitation of single-tower measurements and the necessity of horizontally-distributed observation networks.
The temporally averaged `turbulent' flux based on a point measurement systematically underestimates the `total' flux (negative imbalance). This is attributed to local advection effects caused by the existence of turbulent organized structures (TOS), whose time scale is much longer than that of thermal plumes. The temporal and spatial change of TOS patterns causes low-frequency trends in the velocity and temperature data resulting in large scatter of the flux estimates. The influences of geostrophic wind speed, averaging time, observation height, computational domain size and resolution on tower-measured fluxes are also discussed. Finally, it is suggested that a weak inhomogenity in surface heating may reduce the negative bias of flux estimates.
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References
Agee, E. and Gluhovsky, A.: 1999, 'LES Model Sensitivities to Domains, Grids, and Large-Eddy Timescales', J. Atmos. Sci. 56, 599–604.
Caramori, P., Schuepp, P., Desjardins, R., and Macpherson, I.: 1994, 'Structural Analysis of Airborne Flux Estimates over a Region', J. Climate 7, 627–640.
Deardorff, J. W.: 1980, 'Stratocumulus-Topped Mixed Layers Derived from a Three-Dimensional Model', Boundary-Layer Meteorol. 18, 495–527.
Desjardins, R. L. and Co-authors: 1997, 'Scaling up Flux Measurements for the Boreal Forest Using Aircraft-Tower Combinations', J. Geophys. Res. 102, 29, 125–129, 133.
Dörnbrack, A.: 1997, 'Broadening of Convective Cells', Quart. J. Roy. Meteorol. Soc. 123, 829–847.
Finnigan, J.: 1999, 'A Comment on the Paper by Lee (1998), “On Micrometeorological Observations of Surface-Air Exchange over Tall Vegetation”', Agric. For. Meteorol. 97, 55–64.
Katul, G., Hsieh, C., Bowling, D., Clark, K., Shurpali, N., Turnipseed, A., Albertson, J., Tu, K., Hollinger, D., Evans, B., Offerle, B., Anderson, D., Ellsworth, D., Vogel, C., and Oren, R.: 1999, 'Spatial Variability of Turbulent Fluxes in the Roughness Sublayer of an Even-Aged Pine Forest', Boundary-Layer Meteorol. 93, 1–28.
Lee, X.: 1998, 'On Micrometeorological Observations of Surface-Air Exchange over Tall Vegetation', Agric. For. Meteorol. 91, 39–49.
Lee, X.: 1999, 'Reply to Comment by Finnigan onMicrometeorological Observations of Surface-Air Exchange over Tall Vegetation', Agric. For. Meteorol. 97, 65–67.
Lee, X. and Black, T. A.: 1993, 'Atmospheric Turbulence within and above a Douglas-Fir Stand, Part 2: Eddy Fluxes of Sensible Heat and Water Vapor', Boundary-Layer Meteorol. 64, 369–390.
Lenshow, D. H., Mann, J., and Kristensen, L.: 1994, 'How Long is Long Enough when Measuring Fluxes and Other Turbulent Statistics', J. Atmos. Oceanic Tech. 11, 661–673.
Letzel, M. O. and Raasch, S.: 2003, 'Large-Eddy Simulation of Thermally Induced Oscillations in the Convective Boundary Layer', J. Atmos. Sci., in press.
Mahrt, L.: 1998, 'Flux Sampling Errors for Aircraft and Towers', J. Atmos. Oceanic Tech. 15, 416–429.
Miura, Y.: 1986, 'Aspect Ratios of Longitudinal Rolls and Convection Cells Observed during Cold Air Outbreaks', J. Atmos. Sci. 43, 26–39.
Moore, K. E., Fitzjarrald, D. R., Sakai, R. K., Goulden, M. L., Munger, J. W., and Wofsy, S. C.: 1996, 'Seasonal Variation in Radiative and Turbulent Exchange at a Deciduous Forest in Central Massachusetts', J. Appl. Meteorol. 35, 122–134.
Müller, G. and Chlond, A.: 1996, 'Three-Dimensional Numerical Study of Cell Broadening during Cold-Air Outbreaks', Boundary-Layer Meteorol. 81, 289–323.
Paw U, T. K., Baldocchi, D. D., Meyers, T. P., and Wilson, K. B.: 2000, 'Correction of Eddy-Covariance Measurements Incorporating both Advective Effects and Density Fluxes', Boundary-Layer Meteorol. 97, 487–511.
Raasch, S. and Schröter, M.: 2001, 'PALM? A Large-Eddy Simulation Model Performing on Massively Parallel Computers', Meteorol. Z. 10, 363–372.
Sakai, R. K., Fitzjarrald, D. R., and Moore, K. E.: 2001, 'Importance of Low-Frequency Contributions to Eddy Fluxes Observed over Rough Surfaces', J. Appl. Meteorol. 40, 2, 178–2, 192.
Schmidt, H. and Schumann, U.: 1989, 'Coherent Structure of the Convective Boundary Layer Derived from Large-Eddy Simulation', J. Fluid Mech. 200, 511–562.
Schröter, M. and Raasch, S.: 2002, 'Broadening of Convective Cells during Cold Air Outbreaks: A High Resolution Study Using a Parallelized LES Model', Extended Abstracts', in 15th Symposium Boundary Layers and Turbulence, Wageningen, The Netherlands, American Meteorological Society, pp. 45–48.
Schröter, M., Bange, J., and Raasch, S.: 2000, 'Simulated Airborne Flux Measurements in a LES Generated Convective Boundary Layer', Boundary-Layer Meteorol. 95, 437–456.
Twine, T. E., Kustas, W. P., Norman, J. M., Cook, D. R., Houser, P. R., Meyers, T. P., Prueger, J. H., Starks, P. J., and Wesley, M. L.: 2000, 'Correcting Eddy-Covariance Flux Underestimates over a Grassland', Agric. For. Meteorol. 103, 279–300.
Weinbrecht, S. and Raasch, S.: 2001, 'High-Resolution Simulations of the Turbulent Flow in the Vicinity of an Arctic Lead', J. Geophys. Res. 106, No. C11, 27, 035-027, 046.
Wyngaard, J. C.: 1973, 'On Surface-Layer Turbulence', in D. A. Haugen (ed.), Workshop on Micrometeorology, American Meteorological Society, pp. 101–149.
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Kanda, M., Inagaki, A., Letzel, M.O. et al. LES Study of the Energy Imbalance Problem with Eddy Covariance Fluxes. Boundary-Layer Meteorology 110, 381–404 (2004). https://doi.org/10.1023/B:BOUN.0000007225.45548.7a
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DOI: https://doi.org/10.1023/B:BOUN.0000007225.45548.7a