author = "Grimm, Alice Marlene and Tedeschi, Renata Gon{\c{c}}alves",
          affiliation = "Universidade Federal do Paran{\'a}, Departamento de 
                         F{\'{\i}}sica and Caixa Postal 19044. 81531-990 Curitiba, PR, 
                         Brazil (Grimm and Tedeschi)",
                title = "Mechanisms of the influence of El Niņo and La Niņa episodes on the 
                         frequency of extreme precipitation events in Brazil",
            booktitle = "Proceedings...",
                 year = "2006",
               editor = "Vera, Carolina and Nobre, Carlos",
                pages = "765--773",
         organization = "International Conference on Southern Hemisphere Meteorology and 
                         Oceanography, 8. (ICSHMO).",
            publisher = "American Meteorological Society (AMS)",
              address = "45 Beacon Hill Road, Boston, MA, USA",
             keywords = "Extreme events, precipitation, El Niņo, La Niņa, Brazil.",
             abstract = "This paper examines how El Niņo (EN) e La Niņa (LN) episodes 
                         modify the frequency of extreme precipitation events in Brazil, 
                         and the reason for this modification. Gamma distributions were fit 
                         to precipitation in each day of the year, in the period 1956-2002, 
                         provided by stations all over Brazil. Daily precipitation data are 
                         then replaced by their respective percentiles. Extreme events are 
                         those with a three-day average percentile above 85. The number of 
                         extreme events was computed for each month of each year. Years 
                         were classified as EN, LN and normal years, considering, according 
                         to the EN/LN cycle, that the year starts in August (year 0) and 
                         ends in July (year +1). The mean frequency of extreme events for 
                         each month, within each category of year, and the difference 
                         between these mean frequencies for EN and normal years, and for LN 
                         and normal years show that EN and LN episodes influence 
                         significantly the frequency of extreme events in several regions 
                         in Brazil during certain periods. The relationships between 
                         large-scale atmospheric perturbations and variations in the 
                         frequency of extreme precipitation events are sought through 
                         composites of anomalous atmospheric fields during extreme events 
                         in EN and LN episodes, in three regions in which there is 
                         significant change in the frequency of these events. The general 
                         features of those anomalous fields are similar, no matter if the 
                         extreme events happen during EN or LN episodes or in normal years. 
                         They show the essential ingredients for much precipitation: 
                         moisture convergence and mechanisms for lifting the air to the 
                         condensation level. To understand why the frequency of extreme 
                         events varies significantly between EN and LN episodes, we also 
                         formed composites of monthly atmospheric anomalous fields during 
                         those episodes. In the regions where the frequency of extreme 
                         events increases (decreases) the anomaly composites during extreme 
                         events show similarity (difference) with respect to the mean 
                         anomalies during EN or LN episodes. This indicates that the 
                         frequency of extreme events increases (decreases) when the 
                         large-scale perturbations favor (hamper) the circulation anomalies 
                         associated with them in those regions. This also means that the 
                         behavior of the frequency of extreme events is consistent with 
                         that of the monthly or seasonal total precipitation. The same 
                         conclusion can be reached through the correlation of sea surface 
                         temperature (SST) with the monthly precipitation series or the 
                         frequency of extreme events for two regions in which these events 
                         had their frequency changed during EN and LN episodes. This 
                         correlation analysis was carried out to verify whether there is 
                         another mechanism responsible for extreme events that does not 
                         work during other rainfall events. In general, the relationship 
                         between SST and monthly rainfall is similar to the relationship 
                         between SST and the frequency of extreme events. There are, 
                         however, some differences. For instance, in southern Brazil the 
                         frequency of extreme events is correlated both with SST anomalies 
                         in the Pacific Ocean (associated with EN/LN) and in the Atlantic 
                         Ocean, while the monthly rainfall is more strongly correlated with 
                         SST in the Pacific Ocean..",
  conference-location = "Foz do Igua{\c{c}}u",
      conference-year = "24-28 Apr. 2006",
             language = "en",
         organisation = "American Meteorological Society (AMS)",
                  ibi = "cptec.inpe.br/adm_conf/2005/",
                  url = "http://urlib.net/rep/cptec.inpe.br/adm_conf/2005/",
           targetfile = "765-774.pdf",
                 type = "Hydrological variability and modeling",
        urlaccessdate = "27 jan. 2021"