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Matt C. Wilbanks, Sandra E. Yuter, Simon P. de Szoeke, W. Alan Brewer, Matthew A. Miller, Andrew M. Hall, and Casey D. Burleyson

context of the evolving mesoscale cloud and precipitation structures. Density currents occur in the atmosphere when cooler, negatively buoyant air descends to the surface, diverges, and propagates radially into the surrounding boundary layer. The dynamics that drive density current flows are very similar throughout a broad spectrum of interactions between fluids of different densities. The kinematic structure and evolution of density currents have been described extensively in both laboratory and

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David L. T. Anderson

Jtr~-1976 DA-ID L. T. ANDERSON 907The Low-Level Jet as a Western Boundary Current DAVID L. T. ANDERSONDepartment of A pptied Mathematics and Theoretical Physics, Cambridge University, Cambridge, England(Manuscript received 23 December 1975, in revised form 12 April 1976)ABSTRACT The low-level jet which flows across the equator and up the Somalf coast is considered as a western

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R. M. Samelson, L. W. O’Neill, D. B. Chelton, E. D. Skyllingstad, P. L. Barbour, and S. M. Durski

boundary layer turbulence, the vertical structure of the atmospheric response, and the factors that control regional variations in coupling strength. One approach to the first of these questions is to consider the dependence of the simulated response on the particular planetary boundary layer (PBL) turbulence scheme used in a given atmospheric model simulation. Perlin et al. (2014) used this method to study SST-stress coupling in the Agulhas Return Current (ARC) region, and found that the strength of

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Alex Schueth, Christopher Weiss, and Johannes M. L. Dahl

the inclusion of surface friction, further substantiating a separate mechanism. Schenkman et al. (2012) also noted a region of boundary layer separation immediately ahead of the nose of the density current ( Fig. 11d ) due to an adverse pressure gradient; Simpson and Britter (1980) share these findings as well ( Fig. 11c ). While both of these authors attributed it to surface friction effects, the simulated RHIs in this study show negative vorticity (oriented away from the updraft) very close

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Hidetaka Hirata, Ryuichi Kawamura, Masaya Kato, and Taro Shinoda

/Kuroshio Extension is always smaller than that of latent heat fluxes during the growth phase of the cyclone, H15 did not consider roles of sensible heat supply from those currents in the CCB–LH feedback process. However, the sensible heat supply from the ocean acts to decrease the static stability in the lower troposphere (e.g., Kuo et al. 1991a ; Neiman and Shapiro 1993 ; Reed et al. 1993 ). Moreover, the increase in temperature in the atmospheric boundary layer by sensible heating may lead to a rise in

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Victoria A. Sinclair, Sami Niemelä, and Matti Leskinen

structure of the boundary layer, and to evaluate the ability of a high-resolution NWP model to correctly forecast the boundary layer structure of the cold front. 2. Data and methods a. Description of numerical models Two NWP models, which are currently run operationally by the Finnish Meteorological Institute, are used to investigate the cold front: the High-Resolution Limited-Area Model (HIRLAM; Undén et al. 2002 ) and Applications of Research to Operations at Mesoscale, (AROME; Seity et al. 2011

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David M. Loveless, Timothy J. Wagner, David D. Turner, Steven A. Ackerman, and Wayne F. Feltz

able to remove from the nocturnal boundary layer. This results in the layer with greatest instability being above the surface. One potential mechanism for initiating and maintaining elevated convection is atmospheric bores ( Parker 2008 ; French and Parker 2010 ). Bores are a type of gravity wave that form from the interaction of a density current with a stable fluid of lesser density. Bores will form in either a partially blocked system ( Rottman and Simpson 1989 ) or a completely blocked system

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Benjamin A. Toms, Jessica M. Tomaszewski, David D. Turner, and Steven E. Koch

nocturnal hours ( Fig. 2b ). As will be shown, the outflow boundary and wavelike features took the form of a bore and soliton induced by a convectively generated density current. Fig . 2. NEXRAD WSR-88D composite reflectivity data at (a) 0700 and (b) 0920 UTC 10 Aug 2014. Reflectivity values below 8 dB Z were filtered out to emphasize the reflectivity returns of the density current and wave packet. The current and wave features are identifiable by the southwest–northeast-arcing bands in low (generally

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Hidetaka Hirata, Ryuichi Kawamura, Masaya Kato, and Taro Shinoda

–O cyclone forecasting errors. Over the northwestern Pacific Ocean and northwestern Atlantic Ocean, the Kuroshio/Kuroshio Extension and the Gulf Stream (i.e., western boundary currents) supply a large amount of heat and moisture to the midlatitude atmosphere (e.g., Kelly et al. 2010 ; Kwon et al. 2010 ). Several previous studies have shown that the supply of heat and moisture contributed to the rapid development of extratropical cyclones through decreased atmospheric stability and increased latent

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Changhai Liu and Mitchell W. Moncrieff

modeling studies of density currents in physically more complex circumstances have been conducted. Thorpe et al. (1980) performed numerical simulations for a typical (daytime) atmospheric situation featuring a neutral boundary layer underneath a progressively enhanced stratification to examine the ambient flow effect on the propagation and structure of density currents. The simulation with a similar atmospheric condition was made by Droegemeier and Wilhelmson (1986) to investigate the

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