author = "Marengo, Jos{\'e} Antonio and Liebmann, Brant and Kousky, Vernon 
                         E. and Filizola, Naziano P. and Wainer, Ilana C.",
          affiliation = "{CPTEC-INPE-Cachoeira Paulista-12630-000-SP- Brasil}",
                title = "Onset and end of the rainy season in the Brazilian Amazon Basin",
              journal = "Journal of Climate",
                 year = "2001",
               volume = "14",
               number = "5",
                pages = "833--852",
                month = "Mar.",
             keywords = "South-Ameriacan, outgoing longwave radiation, Australian summer 
                         monsoon, sector, interannual variability, annual cycle, surface 
                         temperature, convective activity, SST anomalies, circulation, 
             abstract = "Onset and end of the rainy season in the Amazon Basin are examined 
                         for the period 1979- 96. The onset and end dates are determined by 
                         averaging daily rainfall data from many stations, and then 
                         constructing 5- day averages (pentads). Onset (end)is defined as 
                         the pentad in which rainfall exceeds (falls below)a given 
                         threshold, provided that average rainfall was well below 
                         (above)the threshold for several pentads preceding onset (end), 
                         and well above (below)the threshold for several pentads after 
                         onset (end). For the criteria chosen, the climatological onset 
                         progresses toward the southeast, arriving in mid- October, and 
                         then toward the mouth of the Amazon, arriving near the end of the 
                         year. The end dates are earliest in the southeast and progress 
                         toward the north, but withdrawal is slower than onset. The onset 
                         dates, however, are quite sensitive to changes in the threshold. 
                         If the threshold is doubled, for example, the sense of onset is 
                         reversed, with onset occurring toward the northwest. Changes in 
                         threshold do not change the direction of the progression of the 
                         end of the rainy season. The central Amazon shows the largest 
                         variation in the date of onset. In several years, onset in the 
                         southeast occurs before that in the central Amazon, but onset near 
                         the mouth is always latest. There is an unexpectedly low 
                         relationship between the length of the rainy season and total 
                         accumulation. Likewise, there is little relationship between the 
                         onset (and end)date and the total accumulation. Composites of 
                         outgoing longwave radiation and the low- level wind field show 
                         that in the central Amazon, onset is associated with an anomalous 
                         anticyclone and enhanced trade winds in the Atlantic. Near the 
                         mouth of the Amazon, however, onset is associated with large- 
                         scale northerly anomalies, and the zonal component of the trade 
                         winds is reduced. There is an apparent association between sea 
                         surface temperature anomalies in the tropical Atlantic and Pacific 
                         and the pentads of onset and end of the rainy season in the 
                         northern and central Amazon, and near its mouth. The sense is that 
                         a warm Pacific and cold Atlantic result in a delayed onset and 
                         early withdrawal. Although the strong El Nino of 1982/ 83 and La 
                         Nina 1988/ 89 were examples of a delayed and early onset, 
                         respectively, the relationships it still holds these years are not 
           copyholder = "SID/SCD",
                 issn = "0894-8755",
             language = "en",
           targetfile = "Marengo_Onset and end of the rainy.pdf",
        urlaccessdate = "25 jan. 2021"