HR: 0800h
AN: B51A-0934    [Abstracts]
TI: Error Analysis of Estimated Means and Horizontal Gradients of Scalar Variables
AU: * Nakamura, R
EM: reina@coas.oregonstate.edu
AF: Oregon State University, 104 COAS Admin Bldg., Corvallis, OR 97331 United States
AU: Mahrt, L
EM: mahrt@coas.oregonstate.edu
AF: Oregon State University, 104 COAS Admin Bldg., Corvallis, OR 97331 United States
AB: While random sampling errors (RSE) for eddy-correlation fluxes are discussed in the literature, little attention has been paid to RSE for the mean or gradient of scalar variables. Accurate estimates of the mean and the gradient of certain scalar variables are important in evaluating and balancing budgets for these variables. In the present work, we evaluate the RSE for the estimated mean and horizontal gradient of air temperature under various atmospheric stabilities, using data from three field programs. Although air temperature is chosen as an economical scalar variable, our approach is applicable for error analysis of estimated advection and local budgets of CO$_2$. Similarities are expected between the results of the error analysis for air temperature and those for CO$_2$. For all atmospheric stabilities, significant energy occurs at mesoscale frequencies in the spectra of air temperature, which corresponds to significant non-stationarity of air temperature. On the other hand, little energy is present at mesoscale frequencies in the spectra of the horizontal gradient of air temperature, except for highly stable conditions. Low-frequency mesoscale fluctuations result in nonstationary records of horizontal gradient of air temperature, leading to large RSE in the estimated gradient. The nonstationarity effect is found to increase with increasing separation distance between the two air temperature measurements. The evaluated RSE of the horizontal gradient of air temperature is compared to the instrumentation-related uncertainties and the magnitude of the estimated horizontal gradients. An optimum separation distance between two points for air temperature measurements is discussed.
DE: 3379 Turbulence
DE: 3307 Boundary layer processes
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting