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The effects of large eddies on turbulence structures and flux transport were studied using data collected over a flat cotton field during the Energy Balance Experiment 2000 in the San Joaquin Valley of California in August 2000. Flux convergence (FC; larger fluxes at 8.7m than 2.7m) and divergence (FD) in latent heat flux (LE) were observed in a disturbed, unstable atmospheric surface layer, and their magnitudes largely departed from the prediction of Monin-Obukhov similarity theory. From our wavelet analysis, it was identified that large eddies affected turbulence structures, scalar distribution, and flux transport differently at 8.7m and 2.7m under the FC and FD conditions. Using the ensemble empirical mode decomposition, time series data were decomposed into large eddies and small-scale background turbulence, the time-domain characteristics of large eddies were examined, and the flux contribution by large eddies was also determined quantitatively. The results suggest that large eddies over the frequency range of 0.002Hz

[1] Relaxed eddy accumulation (REA) systems that employ one single long inlet tube are prone to measurement uncertainties caused by (a) an imprecisely determined lag time between the change of sign in the vertical wind velocity and the switching of the splitter valves and (b) attenuation of high-frequency concentration fluctuations in the tube flow. However, there is currently no commonly applied procedure to address these uncertainties. In this study, we first evaluated the lag time error of the volume flow, mass flow, and cross-correlation method (online and offline) and experimentally determined the magnitude of high-frequency attenuation for a 21.5 m long inlet tube of an operating REA system. In a second step, we simulated the impact for different artificial lag time errors and low-pass filter strengths on the REA concentration differences and, thus, on the REA flux, using high-frequency time series of temperature, O3, CO2, and H2O. The reduction of scalar fluxes was mainly correlated with increasing switching frequencies and ranged for typical lag time errors of the investigated REA system between

This work investigates the influence of atmospheric temperature and relative humidity profiles obtained from radio soundings, NCEP-I and ERA-Int reanalysis and GFS-FNL analysis data on the simulated evolution of clouds and convection at Nam Co Lake on the Tibetan Plateau. In addition to differences in moisture, the initial atmospheric profiles exhibit considerable differences in near-surface temperatures that affect vertical stability. Our analysis is carried out during 2 days in summer 2012 using a 2-D high-resolution modeling approach with a fully interactive surface model so that surface fluxes react to changes in cloud cover. Modeled convection for the radio-sounding profile compares reasonably well with weather observations for the first day, but less well for the second day, when large-scale synoptic effects, not included in the model, become more important. The choice of vertical profile information leads to strongly differing convection development, translating into modifications of the surface energy balance and of the energy and water cycle for the basin. There are strong differences spanning one order of magnitude in the generated precipitation between the model simulations driven by different vertical profiles. This highlights the importance of correct and high-resolution vertical profiles for model initialization.