Determination of the onset dates of the rainy season in central Amazon with equatorially antisymmetric outgoing longwave radiation

430

369

This paper reviews recent progress made in our understanding of the functioning and variability of the South American Monsoon System (SAMS) on time scales varying from synoptic to long-term variability and climate change. The SAMS contains one of the most prominent summertime climate patterns in South America, featuring a strong seasonal variability in a region lying between the Amazon and the La Plata Basin. Much of the recent progress is derived from complementary international programs, such as the Monsoon Experiment South America (MESA), as well as from ongoing international programs such as the Large Scale Biosphere Atmosphere Experiment in the Amazon Basin (LBA) and the La Plata Basin (LPB) Regional Hydroclimate Project, which includes the CLARIS LPB Europe-South America Network for Climate Change Assessment and Impact Studies in La Plata Basin Project. The latter assesses atmosphere-land surface interactions, the role of land use changes and aerosols from biomass burning considered as sources of variability and change in the SAMS functioning, characteristics and behaviour.The SAMS region is particularly susceptible to variations of climate due to the importance of hydroelectricity generation and the agricultural base of local economies. Also addressed in this report are projections of climate change and extremes, which are important for impact and vulnerability assessments. This discussion includes the need to identify and understand important processes that control the monsoonal climate, how these processes may vary and change, and how they may interact with key societal sectors, including water resource management, hydroelectric generation, agriculture, and agribusiness. This paper reports on the major contributions of MESA to the knowledge of characteristics, functioning and variability of the SAMS, and is based on recent studies and publications, and can be considered as an update of a previous review by C. S. Vera et al. (2006a).

Section: Development Of Sams: Onsetmentioning

confidence: 99%

Section: Development Of Sams: Onsetmentioning

confidence: 99%

Recent developments on the South American monsoon system

Marengo

Liebmann

Grimm

et al. 2010

430

369

“…Garcia and Kayano (2009) (hereinafter referred to as GK09) developed a new method to determine the ONR dates for the SAMS regions which is not based on threshold values. Following Murakami and Nakazawa (1985) who noted that the monsoon systems can be found in the AOLR component, GK09 established the AOLR signal change from positive (reduced convection) to negative (enhanced convection) as the criterion to define the ONR date in the Central Amazon (CAM) area.…”

Section: Introductionmentioning

confidence: 99%

Some considerations on onset dates of the rainy season in Western‐Central Brazil with antisymmetric outgoing longwave radiation relative to the equator

Garcia¹,

Kayano²

2011

Self Cite

ABSTRACT:A new method to determine the onset dates of the rainy season (ONR) in the Central Amazon area using the antisymmetric in relation to the equator outgoing longwave radiation (OLR) data was developed in a previous paper. This method is adjusted and used here to determine the ONR in Western-Central Brazil (WCB). The adjustment is needed because of the northwest-southeast (NW-SE) orientation of the American monsoon-related convection displacement. The area averages of the OLR (AOLR) are used to identify the ONR dates. The ONR dates in WCB based on the precipitation index determined in a previous work are used as reference for comparisons. The differences between the results with the AOLR method and those shown in previous papers, as well as the advantages of this method are discussed, using composite maps of OLR and maps of the Tropical Rainfall Measuring Mission (TRMM) precipitation data for individual years. The results obtained here for the WCB indicate a potential of the new method for monitoring purposes because the OLR data can easily be obtained and the AOLR calculation is very simple.

“…Many studies define the onset and the demise dates of the South American monsoon by applying several criteria. Some criteria are based on outgoing long‐wave radiation (OLR; Kousky, ; Gonzalez et al ., ; Garcia and Kayano, ), some on precipitation (Liebmann and Marengo, ; Marengo et al ., ), while some are based on a combination of wind and precipitation (Gan et al ., ). The onset and the demise of the rainy season are also evaluated by the monsoon indices based on the dynamical aspects of the atmosphere (Gan et al ., ), by the large‐scale index for South American monsoon (LISAM) based on combined empirical orthogonal functions (EOFs) of anomalies of precipitation, specific humidity, air temperature, and zonal and meridional winds at 850 hPa (Silva and Carvalho, ), or by atmospheric humidity flux over an area recognized as the monsoon core, based on zonal wind reversal and changes in humidity in transition seasons (Raia and Cavalcanti, ).…”

Section: Introductionmentioning

confidence: 99%

Seasonal climate and the onset of the rainy season in western‐central Brazil simulated by Global Eta Framework model

Latinovic

Chou

Rančić

et al. 2018

The seasonal cycle of precipitation in tropical South America is determined by the monsoonal system. The transition from dry to wet season occurs in austral spring (September–November, SON) when intense convection from northwestern South America rapidly shifts southwards to the southern Amazon Basin and western‐central Brazil (WCB) in October and further to the southeast of Brazil in November. This study evaluates ability of the global atmospheric model, Global Eta Framework (GEF), at 25‐km horizontal resolution, to simulate the onset of the rainy season in WCB region. The simulations are based on a five‐member ensemble seasonal integrations for the years 2011 and 2013. Evaluation of mean global simulated fields, such as 200‐hPa wind, 500‐hPa geopotential height, 850‐hPa temperature and wind, and MSLP at the surface, for the SON period indicates high level of agreement with reanalyses and observations, both in spatial distribution and intensity for most of the variables. The variable of the lowest skill is precipitation, which is overestimated over some tropical oceanic regions and underestimated over tropical continental regions, including South America. The onset of the rainy season is determined using methods based on precipitation and outgoing long‐wave radiation (OLR). The threshold based on simulated precipitation is also calculated as an alternative method for defining monsoon onset. Comparison of the 5‐day averaged values (pentads) of precipitation and OLR of all members of the ensemble and the ensemble mean against the observed data shows the ability of GEF to reproduce the typical pattern of transition from dry to wet season in WCB, although most of ensemble members tend to underestimate precipitation and overestimate OLR. The onset date is delayed for few pentads in the model simulations.