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  • Author or Editor: J. Liljegren x
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J. M. Hubbe, J. C. Doran, J. C. Liljegren, and W. J. Shaw

Abstract

Results from a field campaign to study the response of the planetary boundary layer to spatially varying surface conditions are presented. Radiosondes released at four locations with contrasting land use characteristics in the U.S. Department of Energy’s Cloud and Radiation Testbed (CART) in Kansas and Oklahoma showed significant variations in mixed-layer depth, temperature, and water vapor mixing ratios over distances of 100–200 km. Using CART and radiosonde data, estimates of the surface sensible and latent heat fluxes are derived; the results from several methods are compared and a discussion of the similarities and differences in the values is given. Although substantial flux differences among the sites account for some of the variations in the boundary layer behavior, other features of the ambient meteorology and initial conditions appear to be equally important. Despite large changes in mixed-layer and surface-layer temperatures over scales of approximately 100 km, no evidence for temperature-induced secondary circulations was found. A simple scaling argument is presented that gives a possible reason for this absence.

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K. Ivanova, E. E. Clothiaux, H. N. Shirer, T. P. Ackerman, J. C. Liljegren, and M. Ausloos

Abstract

Time series both of microwave radiometer brightness temperature measurements at 23.8 and 31.4 GHz and of retrievals of water vapor and liquid water path from these brightness temperatures are evaluated using the detrended fluctuation analysis method. As quantified by the parameter α, this method (i) enables identification of the timescales over which noise dominates the time series and (ii) characterizes the temporal range of correlations in the time series. The more common spectral analysis method is also used to assess the data, and its results are compared with those from the detrended fluctuation analysis method. The assumption that measurements should have certain scaling properties allows the quality of the measurements to be characterized. The additional assumption that the scaling properties of the measurements of an atmospheric quantity are preserved in a useful retrieval provides a means for evaluating the retrieval itself. Applying these two assumptions to microwave radiometer measurements and retrievals demonstrates three points. First, the retrieved water vapor path during cloudy-sky periods can be dominated by noise on shorter-than-30-min timescales (α exponent = 0.1) and exhibits no scaling behavior at longer timescales. However, correlations in the brightness temperatures and liquid water path retrievals are found to be consistent with a power-law behavior for timescales up to 3 h with an α exponent equal to approximately 0.3, as in other geophysical phenomena. Second, clear-sky, moist atmospheres show the expected scaling for both measurements and retrievals of the water vapor path. Third, during clear-sky, dry atmospheric days, instrument noise from the 31.4-GHz channel compromises the quality of the water vapor path retrieval. The detrended fluctuation analysis method is thus proposed as means for assessing the quality of both the instrument data and the retrieved parameters obtained from these data.

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