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@InProceedings{RibeiroSelu:2015:AnSe'c,
               author = "Ribeiro, Bruno Zanetti and Seluchi, Marcelo Enrique",
          affiliation = "{Instituto Nacional de Pesquisas Espaciais (INPE)} and {Instituto 
                         Nacional de Pesquisas Espaciais (INPE)}",
                title = "Analysis of a severe 'comma-shaped' bow echo in southern Brazil",
                 year = "2015",
         organization = "Conference on Mesoscale Processes, 16.",
             abstract = "On 19 October 2014, a squall line with an embedded 'comma-shaped' 
                         bow echo (inverted comma in Southern Hemisphere) impacted Southern 
                         Brazil, causing material damage due to severe straight-line winds. 
                         The damaging-wind path and duration suggest this event was a 
                         derecho. Storm morphology was analyzed using a S-band radar in the 
                         city of Santiago, Southern Brazil. Synoptic and thermodynamic 
                         environments were analyzed through surface stations and sounding 
                         data, as well as the CFSR reanalysis fields preceding the event. 
                         Several intense storms formed along an outflow boundary over 
                         Northern Argentina, where a tornado was reported, and then moved 
                         east toward Brazil organized as a squall line. Most severe wind 
                         gusts were associated with embedded bow echoes, and the most 
                         intense measured gust, of 60 kt, occurred near the head of the 
                         comma-shaped bow echo. Moreover, the damage registered in some 
                         locations lead to estimates of 80-100 kt wind gusts. The squall 
                         line formed under weak forcing, in the left entrance of an 
                         upper-level jet streak and ahead of a surface cold front. A 
                         sounding launched just before the squall line passage showed 
                         intense low-level vertical wind shear (17 m/s 0-1-km and 15 m/s 
                         0-3-km line-perpendicular shear), favoring bowing segments within 
                         the squall line. Below approximately 2.5 km above ground level the 
                         shear was mostly directional, becoming predominantly a speed shear 
                         above this height. Most unstable CAPE was 2100 J/kg, indicating 
                         moderate thermodynamic instability, but precipitable water was 
                         more than 50 mm, which favors heavy precipitation and strong cold 
                         pools. 250-hPa winds of more than 85 kt were observed, coherent 
                         with a leading-line propagation at approximately 50 kt. The 
                         comma-shaped bow echo formed in response to strengthening of the 
                         cyclonic bookend vortex associated with the bow echo. The 
                         high-precipitation supercell responsible for the tornado in 
                         Argentina possibly provided cyclonic vorticity to the bookend 
                         vortex. The supercell formed before the squall-line organization 
                         and may have played an important role in creating the cold pool 
                         responsible for driving the system. Evolution of the comma-shaped 
                         system follows theoretical models for the Northern Hemisphere. The 
                         bowing segment moved faster than other sectors of the squall line, 
                         which might have been caused by acceleration of the Rear-Inflow 
                         Jet. After bookend vortex formation, the northern flank of the 
                         squall line caused wind gusts of more than 50 kt in other 
                         locations, while the southern flank weakened, causing wind gusts 
                         of less than 25 kt. This study describes a classic case of a 
                         strong comma-shaped bow echo embedded in a squall line, and it is 
                         the first of this kind realized in Southern Brazil. Future work on 
                         numerical simulations of bow echoes is required to elucidate the 
                         behavior of these systems in this region.",
  conference-location = "Boston, MA",
      conference-year = "3-6 Aug.",
        urlaccessdate = "29 nov. 2020"
}


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