@Article{MarengoLieKouFilWai:2001:OnEnRa,
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,
rainfall.",
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
considered.",
copyholder = "SID/SCD",
issn = "0894-8755",
language = "en",
targetfile = "Marengo_Onset and end of the rainy.pdf",
urlaccessdate = "03 maio 2024"
}