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F. Couvreux, F. Guichard, P. H. Austin, and F. Chen

moisture that are strongly modulated by precipitation ( Chen et al. 2001 ; Trier et al. 2004 ; Holt et al. 2006 ). It has been difficult to assess the impact of either fixed or transient surface heterogeneity because of the scarcity of measurements: local surface flux measurements can suffer from a lack of representativeness that limits their use at the mesoscale ( André et al. 1990 ). Although satellites may provide some estimates at the large scale, it has been more common to use idealized studies

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Margaret A. LeMone, Fei Chen, Mukul Tewari, Jimy Dudhia, Bart Geerts, Qun Miao, Richard L. Coulter, and Robert L. Grossman

1. Introduction This paper the first part of a two-part series that uses a combination of numerical simulations and observations of the fair-weather convective boundary layer (CBL) to explore the relationship of surface heterogeneity and associated fluxes (W m −2 ) of sensible heat H and latent heat LE, to CBL potential temperature Θ (K), mixing ratio Q (g kg −1 ), depth, and circulations on scales from 1 to 100 km. At the same time, we evaluate the numerical simulations and

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Margaret A. LeMone, Mukul Tewari, Fei Chen, Joseph G. Alfieri, and Dev Niyogi

. LeMone , T. T. Warner , and J. G. Alfieri , 2008 : Comparison of observed 10-m wind speeds to those based on Monin–Obukhov similarity theory using IHOP_2002 aircraft and surface data. Mon. Wea. Rev. , 136 , 964 – 972 . Sun , J. , 1999 : Diurnal variations of thermal roughness height over a grassland. Bound.-Layer Meteor. , 70 , 1 – 12 . Sun , J. , and L. Mahrt , 1995 : Determination of surface fluxes from the surface radiative temperature. J. Atmos. Sci. , 52 , 1096

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Margaret A. LeMone, Fei Chen, Mukul Tewari, Jimy Dudhia, Bart Geerts, Qun Miao, Richard L. Coulter, and Robert L. Grossman

surface flux via ≈ −0.2 . Neglecting direct warming by radiative effects, the along-trajectory time rate of change of the virtual potential temperature averaged over z i , 〈Θ υ 〉, is given by Assuming the same z i for both trajectories, and taking the difference between d 〈Θ υ 〉/ dt for air along the “warm” and “cool” trajectories: Integrating (2) and recalling that Δ〈Θ υ 〉 is initially zero (trajectories start at the same 〈Θ υ 〉), we obtain the along

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S. B. Trier, F. Chen, K. W. Manning, M. A. LeMone, and C. A. Davis

point (at 25–30 m AGL) with ∼1-km spacing at the model top near 50 hPa. The PBL scheme ( Janjic 1990 , 1994 ) predicts turbulent kinetic energy and allows vertical mixing between individual layers within the PBL. Other physical parameterizations include a bulk microphysics scheme based on Lin et al. (1983) and the Rapid Radiative Transfer Model (RRTM) longwave ( Mlawer et al. 1997 ) and Dudhia (1989) shortwave radiation schemes. Our choice of domain size and grid spacing reflects a compromise

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Steven E. Koch, Wayne Feltz, Frédéric Fabry, Mariusz Pagowski, Bart Geerts, Kristopher M. Bedka, David O. Miller, and James W. Wilson

length is diagnosed. The other physics used in this simulation consisted of the Blackadar surface flux method ( Zhang and Anthes 1982 ), the Grell and Dévényi (2002) ensemble convective parameterization scheme (only for the 18-km grid), the Reisner et al. (1998) mixed-phase microphysics scheme, the RUC land surface model ( Smirnova et al. 2000 ), and the Mlawer et al. (1997) radiation scheme. An experiment was also performed to examine the sensitivity of the results using the Eta Model PBL

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