%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Espinoza, J. C.
%A Arias, P. A.
%A Moron, V.
%A Junquas, Clémentine
%A Segura, H.
%A Sierra-Perez, J. P.
%A Wongchuig, S.
%A Condom, Thomas
%T Recent changes in the atmospheric circulation patterns during the dry-to-wet transition season in South Tropical South America (1979-2020) : impacts on precipitation and fire season
%D 2021
%L fdi:010084281
%G ENG
%J Journal of Climate
%@ 0894-8755
%K Amazon region ; SouthAmerica ; Atmospheric circulation ; Interannual variability ; Subseasonal variability ; Trends
%K BRESIL ; AMAZONIE ; ZONE TROPICALE
%M ISI:000752646200013
%N 22
%P 9025-9042
%R 10.1175/jcli-d-21-0303.1
%U https://www.documentation.ird.fr/hor/fdi:010084281
%> https://www.documentation.ird.fr/intranet/publi/2022-03/010084281.pdf
%V 34
%W Horizon (IRD)
%X We analyze the characteristics of atmospheric variations over tropical South America using the pattern recognition framework of weather typing or atmospheric circulation patterns (CPs). During 1979-2020, nine CPs are defined in the region, using a k-means algorithm based on daily unfiltered 850-hPa winds over 10 degrees N-30 degrees S, 90 degrees-30 degrees W. CPs are primarily interpreted as stages of the annual cycle of the low-level circulation. We identified three "winter' CPs (CP7, CP8, and CP9), three "summer' CPs (CP3, CP4, and CP5), and three "transitional' CPs (CP1, CP2, and CP6). Significant long-term changes are detected during the dry-to-wet transition season (July-October) over southern tropical South America (STSA). One of the wintertime patterns (CP9) increases from 20% in the 1980s to 35% in the last decade while the "transitional' CP2 decreases from 13% to 7%. CP9 is characterized by enhancement of the South American low-level jet and increasing atmospheric subsidence over STSA. CP2 is characterized by southerly cold-air incursions and anomalous convective activity over STSA. The years characterized by high frequency of CP9 and low frequency of CP2 during the dry-to-wet transition season are associated with a delayed South American monsoon onset and anomalous dry conditions over STSA. Consistently, a higher frequency of CP9 intensifies the fire season over STSA (1999-2020). Over the Brazilian states of Maranhao, Tocantins, Goias, and Sao Paulo, the seasonal frequency of CP9 explains around 35%-44% of the interannual variations of fire counts.
%$ 021 ; 072