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Jake P. Mulholland, Stephen W. Nesbitt, Robert J. Trapp, and John M. Peters

forcing owing to the stronger deep-layer wind shear in the higher-terrain supercell inflow may have also resulted in the stronger upward vertical velocities, especially in the low to midlevels (e.g., Weisman and Rotunno 2000 ; Peters et al. 2019b , 2020b ). Overall, these results suggest that terrain-induced variations to vertical wind profiles were mainly responsible for the differences noted in convective morphology as compared to terrain induced thermodynamic variations, in line with conclusions

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Zachary S. Bruick, Kristen L. Rasmussen, Angela K. Rowe, and Lynn A. McMurdie

. 2009 ). In subtropical South America, correlations between rainfall and ENSO have been demonstrated, especially for the La Plata basin encompassing northeast Argentina, Paraguay, and southeastern Brazil. Rainfall tends to be maximized in this area during El Niño, leading to flooding within the basin ( Camilloni and Barros 2003 ; Cavalcanti et al. 2015 ). Synoptic forcing for enhanced rainfall in the La Plata basin may be provided by a stronger subtropical jet with increased cyclonic vorticity

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James N. Marquis, Adam C. Varble, Paul Robinson, T. Connor Nelson, and Katja Friedrich

horizontal flow convergence frequently aids convection initiation processes by forcing low-level air parcels upward, locally reducing CIN, deepening boundary layer moisture below cloud base, and providing a focal area for moist updrafts to detrain into the overlying free troposphere, reducing the negative entrainment effect ( Ziegler et al. 1997 ; Markowski and Richardson 2010 ; Moser and Lasher-Trapp 2017 ). Common mesoscale convergence features that trigger deep convection initiation (hereafter CI

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Jake P. Mulholland, Stephen W. Nesbitt, and Robert J. Trapp

(LLJ), and upper-level negative geostrophic potential vorticity (weak ambient inertial instability) all favored the most rapid transition of discrete convective cells into an MCS. Furthermore, Dial et al. (2010) found that for cases of convection initiation (CI) along a frontal or similar boundary, the potential for UCG increased when the cloud-layer wind and deep-layer vertical wind shear vectors were nearly parallel to the initiating boundary. Additionally, as the magnitude of low-level forcing

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Zachary S. Bruick, Kristen L. Rasmussen, and Daniel J. Cecil

, 2016 ) because of the impingement of the SALLJ on the topography. The orographic forcing helps to overcome any mechanical capping produced by subsiding upper-level air in the lee of the Andes. Additionally, the SDC and the plains immediately to their east were the focus of the RELAMPAGO and CACTI field campaigns. To understand the life cycle of intense convection, the TRMM PR data were separated into three categories, including deep, deep and wide, and wide convective cores (DCCs, DWCCs, and WCCs

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Hernán Bechis, Paola Salio, and Juan José Ruiz

moist tropical air mass to the north of the line and dry, warm air, which moves leeward of the Andes slopes in a zone of prevailing westerly flow. The regional circulation that leads to this airmass contrast is linked to the characteristics of the topography. North of 35°S the Andes block the low-level flow, forcing a mainly meridional displacement of air masses. In particular, the channeling of warm, moist air masses from low latitudes leads to the formation of the South American low-level jet

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Stephen W. Nesbitt, Paola V. Salio, Eldo Ávila, Phillip Bitzer, Lawrence Carey, V. Chandrasekar, Wiebke Deierling, Francina Dominguez, Maria Eugenia Dillon, C. Marcelo Garcia, David Gochis, Steven Goodman, Deanna A. Hence, Karen A. Kosiba, Matthew R. Kumjian, Timothy Lang, Lorena Medina Luna, James Marquis, Robert Marshall, Lynn A. McMurdie, Ernani de Lima Nascimento, Kristen L. Rasmussen, Rita Roberts, Angela K. Rowe, Juan José Ruiz, Eliah F.M.T. São Sabbas, A. Celeste Saulo, Russ S. Schumacher, Yanina Garcia Skabar, Luiz Augusto Toledo Machado, Robert J. Trapp, Adam C. Varble, James Wilson, Joshua Wurman, Edward J. Zipser, Ivan Arias, Hernán Bechis, and Maxwell A. Grover

; Salio et al. 2007 ; Rasmussen and Houze 2016 ). This poleward penetration often coincides with the deepening of a lee trough called the northern Argentinean low (NAL; Seluchi et al. 2003 ; Saulo et al. 2004 , 2007 ). The NAL enhances the local pressure gradient force, leading to poleward SALLJ penetration near the Andes, with a wind speed maxima (up to 25 m s −1 ) at 1–1.5-km altitudes as far south as 35°S ( Nicolini and Saulo 2006 ), typically maximizing at night ( Nicolini and García Skabar

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Jake P. Mulholland, Stephen W. Nesbitt, Robert J. Trapp, Kristen L. Rasmussen, and Paola V. Salio

northwesterly flow pattern aloft across the tracking domain ( Fig. 12b ), whereas MCS events display a more westerly component across the tracking domain ( Fig. 12a ). MUN events also tend to have a slightly more amplified upper-level trough off the west coast of South America, potentially resulting in greater quasigeostrophic (QG) forcing for synoptic-scale ascent or supporting frontal intrusions in some events, favoring more widespread CI. The largest differences in the upper-level patterns exist between

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Adam C. Varble, Stephen W. Nesbitt, Paola Salio, Joseph C. Hardin, Nitin Bharadwaj, Paloma Borque, Paul J. DeMott, Zhe Feng, Thomas C. J. Hill, James N. Marquis, Alyssa Matthews, Fan Mei, Rusen Öktem, Vagner Castro, Lexie Goldberger, Alexis Hunzinger, Kevin R. Barry, Sonia M. Kreidenweis, Greg M. McFarquhar, Lynn A. McMurdie, Mikhail Pekour, Heath Powers, David M. Romps, Celeste Saulo, Beat Schmid, Jason M. Tomlinson, Susan C. van den Heever, Alla Zelenyuk, Zhixiao Zhang, and Edward J. Zipser

boundary layer height estimates from soundings (PBLHT), microwave radiometer retrieved precipitable water (MWRRET), Doppler lidar retrieved horizontal and vertical winds (DLPROF), atmospheric emitted radiance interferometer (AERI)-estimated lower-tropospheric temperature and humidity (AERIOE), interpolated soundings (INTERPSONDE), and variational analysis retrieved large-scale forcing (VARANAL). Cloud products include cloud optical depth (MFRSRCLDOD), combined lidar–radar time–height cloud boundaries

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