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

mesoscale convection. On the other hand, regional climate model simulations employed over subseasonal or greater time scales are exposed to uncertainty in the linkages among land surface effects, the PBL, and precipitation that arise from the necessary use of cumulus parameterizations, in which closure assumptions that affect convection initiation are quite varied (e.g., Pan et al. 1996 ; Giorgi et al. 1996 ). The current study applies a different approach to analyzing sensitivity of warm

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

Fedorovich (2006) suggest the relationship ≈ −0.2 applies if the shear at PBL top is small. Strassberg et al. (2008) found the shear to be small for the June days, and “small to moderate” for 30 May, with a z i to surface flux ratio less than 0.2, so the relationship should apply reasonably well for the 4 days discussed here. 3 The “regional” fluxes, being based on momentum fluxes computed from fluctuations relative to a 46-km flight-leg linear trend, include the effects of

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Diane Strassberg, Margaret A. LeMone, Thomas T. Warner, and Joseph G. Alfieri

University Press, 289 pp . Kustas , W. P. , J. H. Prueger , J. I. MacPherson , M. Wolde , and F. Li , 2005 : Effects of land use and meteorological conditions on local and regional momentum transport and roughness for midwestern cropping systems. J. Hydrometeor. , 6 , 825 – 839 . LeMone , M. A. , and Coauthors , 2007a : NCAR/CU surface, soil, and vegetation observations during the International H 2 O Project 2002 field campaign. Bull. Amer. Meteor. Soc. , 88 , 65 – 81 . LeMone

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Robin L. Tanamachi, Wayne F. Feltz, and Ming Xue

instruments at the “Homestead” site near Balko, Oklahoma (in the Oklahoma Panhandle), collected data during these events. The RDE–RMEs (denoted A–D) are best illustrated by the time–height plot of water vapor profiles measured by the Atmospheric Emitted Radiance Interferometer (AERI; Fig. 1 ; Feltz et al. 2003a , b ; Knuteson et al. 2004a , b ). High-resolution numerical simulations are performed for this event using the nonhydrostatic Advanced Regional Prediction System (ARPS) model ( Xue et al

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

, and MM5 simulations to look at the role of surface properties, advection, and CBL growth on the horizontal variability, looking at local and regional changes on scales up to hundreds of kilometers. This work complements the earlier work by simultaneously focusing on scales larger than a point but smaller than ∼50 km (defined by the length of the eastern track) and focusing on fair weather, using detailed comparisons of model results to observations. The grid spacing needed for focusing on such

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Monica Górska, Jordi Vilà-Guerau de Arellano, Margaret A. LeMone, and Chiel C. van Heerwaarden

. 2005 ). Closely related to these variations, several studies have attempted to determine the heterogeneity effect on the boundary layer structure by proposing several heterogeneity length scales ( Mahrt 2000 ; Patton et al. 2005 ; Strunin and Hiyama 2005 ). Mahrt (2000) found the strongest effects on the ABL properties if the heterogeneity length scale is between 2 and 20 km. Kang et al. (2007) calculated the minimum heterogeneity length scale that influences the flow through the whole ABL

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John H. Marsham, Stanley B. Trier, Tammy M. Weckwerth, and James W. Wilson

), which is located ahead of the southeastward-moving MCS as it was later weakening, the maximum CAPE was essentially at the surface at both 1106 and 2306 UTC. There was much more CAPE at OUN than MRS. The MRS sounding shows the “onion” structure typical of a profile after deep convection and so this difference between the soundings is consistent with the effects of the preceding MCS B ( Fig. 1 ; Weckwerth et al. 2008 ; Champollion et al. 2009 ) being much larger at MRS. The surface CAPE at OUN would

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

Science. The authors also thank the reviewers for their helpful comments that considerably improved the manuscript. REFERENCES Alapaty , K. , S. Raman , and D. S. Niyogi , 1997 : Uncertainty in the specification of surface characteristics: A study of prediction errors in the boundary layer. Bound.-Layer Meteor. , 82 , 473 – 500 . André , J. C. , P. Bougeault , and J-P. Goutorbe , 1990 : Regional estimates of heat and evaporation fluxes over non-homogeneous terrain. Examples from

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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

turbulent mixing in density currents ( Simpson 1987 ): (i) Kelvin–Helmholtz billows that roll up in the region of speed shear above the head of the current and (ii) lobes and clefts formed by frictional effects on the lower part of the leading edge of the density current. The lobes lead to static instability through an overrunning of the denser fluid in the nose of the current over the lighter fluid. Billows appear to be the primary means by which the air originating from above the inversion is mixed

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