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Edward I. Tollerud, Fernando Caracena, Steven E. Koch, Brian D. Jamison, R. Michael Hardesty, Brandi J. McCarty, Christoph Kiemle, Randall S. Collander, Diana L. Bartels, Steven Albers, Brent Shaw, Daniel L. Birkenheuer, and W. Alan Brewer

1. Introduction Previous studies of the low-level jet (LLJ) have helped to establish its role as the major conveyor of low-level moisture from the Gulf of Mexico into the central United States ( Stensrud 1996 ; Higgins et al. 1996 ). Higgins et al. (1997) estimate that the contribution of the LLJ to low-level moisture transport over the central plains is almost 50% above average non-LLJ values. A major factor in the LLJ contribution to central plains precipitation is the relationship between

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

organized into large MCSs with high equivalent potential temperature ( θ e ) air that sustains convection embodied within a nocturnal low-level jet (LLJ; e.g., Maddox 1983 ; Cotton et al. 1989 ; Laing and Fritsch 2000 ). Convection associated with this conditionally unstable airstream often occurs north of quasi-stationary east–west-oriented surface fronts ( Kane et al. 1987 ), where mesoscale lifting within or above the frontal surface ( Trier and Parsons 1993 ) helps focus the convection

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Roger M. Wakimoto and Hanne V. Murphey

in a dataset with analogous spatial resolution at the meso- γ scale so that direct comparisons between the case studies could be made. In addition, the kinematic and thermodynamic structure of all of these boundaries was well documented using data from a series of dropsondes deployed by a jet flying at ∼500 mb. The spatial resolution of the sounding data at the meso- β scale was comparable, which facilitated comparisons between the cases. A description of IHOP_2002 and the primary datasets used

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Roger M. Wakimoto and Hanne V. Murphey

. Sounding cross section A series of nine dropsondes were deployed by a jet flying at ∼500 mb in an approximate northwest-to-southeast pattern between 2134:29 and 2156:37 UTC ( Fig. 4b ). The orientation of the cross section resulting from the dropsonde data was nearly perpendicular to the dryline and the frontal boundary. Two air masses can be identified in the vertical cross section shown in Fig. 5 . The frontal and dryline boundaries are approximately delineated by the 317-K isentropes in the

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

section 4 . Possible causes of the RDEs–RMEs are discussed in section 5 . A summary and conclusions are then given in section 6 . 2. Synoptic-scale environment of 12 June 2002 To convey a more complete sense of the atmospheric conditions under which the RDE–RMEs occurred, we briefly discuss the synoptic-scale environment in the region of the Homestead site. At 0000 UTC 12 June 2002, a weak upper-level jet maximum (not shown) extended from eastern Wyoming to western Nebraska. An area of relatively

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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

waves within one hour ( Fig. 21 ), but did not increase in number afterward. The fine-grid simulation predicts that the intensity of mixing (TKE) is strongest within the moist PBL ahead of the bore, directly behind the bore head, and underneath the solitary waves. The first of these three regions is easily understood to be the result of the shear stress related to the strong along-bore flow associated with the low-level jet [the third term on the rhs of (3) ]. This conjecture is supported by an

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

anomalies specific to the 1993 warm season could not account for the precipitation anomaly, but, similar to Beljaars et al. (1996) , they concluded that heavier precipitation was promoted by wetter soil upstream. In contrast, Paegle et al. (1996) found a negative feedback between precipitation and upstream soil wetness for July 1993. They concluded that drier soil upstream resulted in stronger PBL forcing of the nocturnal low-level jet (LLJ), which led to enhanced convergence and water vapor

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Lindsay J. Bennett, Tammy M. Weckwerth, Alan M. Blyth, Bart Geerts, Qun Miao, and Yvette P. Richardson

mixing ratio q decreased with height within and above the NBL to minimum values at approximately z = 120 m at 0415 CST and 175 m at 0530 CST, then increased to maximum values at 230 and 330 m, respectively. This is in contrast to the profiles observed by Mahrt (1979) where q increased with height in the region of the low-level jet and then decreased rapidly above. A deep moist layer ( q > 8 g kg −1 ) extended from the lowest range gate (315 m) of the SRL to an altitude of 1.1 km from the

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