@InProceedings{MachadoChabRibeFrei:2019:EvNeCo,
               author = "Machado, Luiz Augusto Toledo and Chaboureau, Jean-Pierre and 
                         Ribeiro, Bruno Zanetti and Freitas, Edmilson Dias de",
          affiliation = "{Instituto Nacional de Pesquisas Espaciais (INPE)} and {University 
                         Paul Sabatier Toulouse III} and {Instituto Nacional de Pesquisas 
                         Espaciais (INPE)} and {Universidade de S{\~a}o Paulo (USP)}",
                title = "The S{\~a}o Borja Downburst Observed During RELAMPAGO: Evidences 
                         and a New Conceptual Model",
                 year = "2019",
         organization = "AGU Fall Meeting",
             abstract = "During the RELAMPAGO campaign, a downburst was observed at 
                         S{\~a}o Borja, a Brazilian city close to Argentina. A mesoscale 
                         convective system, formed over the south of Paraguay during the 
                         night of the 27 November 2018, split in two supercells. Its 
                         anticyclonic circulation moved toward the southeast reaching 
                         S{\~a}o Borja, the downburst occurred at around 1400 UTC. The 
                         measured Vertically Integrated Liquid (VIL) changed from 235 kg/m2 
                         to 105 kg/m2 in 10 minutes. This 130 kg/m2 of water corresponds to 
                         around 1.5 million tons of water falling in 10 minutes over 2000 
                         km radius area. Data from the X band Dual Pol radar describes the 
                         processes leading to the downburst, which are associated with the 
                         formation of a mesocyclone and its collapse in few minutes. Based 
                         on these measurements, a new conceptual model is presented. The 
                         mesocyclone is located at 6000 m height, just above the maximum 
                         vertical velocity, the Bounded Weak Echo Region (BWER), and 
                         captured hydrometeors in its circulation. This explains the 
                         highest reflectivity observed there. In this circulation, hail can 
                         grow because constantly fed by the strong updrafts which bring air 
                         mixed with supercooled liquid water and ice as shown by the lower 
                         polar cross correlation inside the BWER. This conceptual model can 
                         also explain how large hydrometeors can grow, because staying for 
                         longer time confined to the mesocyclone circulation. Hydrometeors 
                         are caught in the rotation and sustained by the meso-region of 
                         upward field. The region where the downdraft begins inhibits the 
                         upward motion. Ice evaporates and downdraft increases. The 
                         downdraft in this part of the mesocyclone creates convergence of 
                         ice that stimulates aggregation, increasing hail size, and thus 
                         precipitating. Consequently, precipitation reaches the lower level 
                         and overcomes the surface convergence reducing the updraft. The 
                         BWER is the updraft pillar of the mesocyclone: if it collapses or 
                         moves away from the mesocyclone, the mesocyclone collapses 
                         reaching the surface. This hypothesis was tested using the MESO-NH 
                         model. The presentation will describe the observations and some 
                         preliminary results from the simulations. The RELAMPAGO campaign 
                         in S{\~a}o Borja was supported by FAPESP grant 2015/14497-0.",
  conference-location = "San Francisco, CA",
      conference-year = "09-13 dec.",
             language = "en",
           targetfile = "machado-sao.pdf",
        urlaccessdate = "01 maio 2024"
}