Decadal Variation of Atmosphere-Ocean Interaction in the Tropical Atlantic and its Relationship to the Northeast Brazil Rainfall

Rao, V. Brahmananda; Chapa, Srinivasa Rao; Franchito, Sérgio H.

doi:10.2151/jmsj1965.77.1_63

Cited by 15 publications

(14 citation statements)

References 44 publications

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“…Normalized rainfall departures for Nordeste were obtained for 61 stations given in Rao et al (1995) and updated in Rao et al (1999). Initially, means and standard deviations were determined for each station.…”

Section: Methodsmentioning

confidence: 99%

“…Normalized annual rainfall departures for sub-Sahara were obtained from Nicholson (1994). The procedure to obtain the annual rainfall departures for sub-Sahara is the same as the one used by Rao et al (1995Rao et al ( , 1999. In this study, we used 11-yr running averages to remove interannual and decadal fluctuations.…”

Section: Methodsmentioning

confidence: 99%

“…Zonally averaged motions in the meridional plane are the pure Hadley circulations. Deviations from these zonally averaged motions are associated with pure Walker circulations (Rao et al 2004). However, local vertical motions, which cause rainfall variations, have both the Walker and Hadley modes.…”

Section: Introductionmentioning

confidence: 99%

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Is the Recent Increasing Trend of Rainfall over Northeast Brazil Related to Sub-Saharan Drought?

et al. 2006

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In recent years, there has been an increase in rainfall over northeast Brazil (Nordeste), while over the sub-Saharan region there has been a drought. The correlation coefficients between the II 1 vr running means of the rainfall series over the two regions are significant (at the 95% confidence level by a two-sided t test), suggesting that both trends are related. The rainfall variations over the two regions are connected to the position of the intertropical convergence zone (ITCZ) over the Atlantic. A more southward (northward) position of the ITCZ is favorable for higher than normal rainfall over Nordeste (sub-Sahara). The correlation coefficient between the position of the ITCZ over the Atlantic and the rainfall over Nordeste (sub-Sahara) is negative (positive) and highly significant, reaching values over 0.9. Thus, this study suggests that a more southward than normal location of the ITCZ in the Atlantic may be the cause for the recent increasing (decreasing) trend of rainfall over Nordeste (sub-Sahara).

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Is the Recent Increasing Trend of Rainfall over Northeast Brazil Related to Sub-Saharan Drought?

et al. 2006

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“…Where Q v is the meridional moisture flux, Q u is the zonal moisture flux, g is gravity, q is the specific humidity, u and v are the zonal and meridional components of the wind, and pt and po represent the pressure at 700 hPa and the surface, respectively (Rao et al, 1999). Marengo et al, 2004 show that the impact of the SALLJ on moisture transport on the east side of the Andes is more strongly felt below the 700 hPa level, where most of the moisture is concentrated.…”

Section: Quantification Of the Moisture Flux And Horizontal Moisture mentioning

confidence: 99%

Assessments of moisture fluxes east of the Andes in South America in a global warming scenario

Soares

Marengo

2008

Intl Journal of Climatology

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The HadRM3P regional model from the UK Hadley Centre has been used to assess the moisture flux and the low-level jet (LLJ) east of the Andes in South America over two time periods: the first can be understood as the current climate and covers the period from 1980 to 1989; the second covers the period from 2080 to 2089 under a future global warming climate as projected by the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A2 high-emission scenario. The results are analyzed considering the vertically integrated moisture transport in the lower atmosphere and the moisture flux between the two core areas of South America -the Amazon Basin and the La Plata River Basin. In order to analyze the moisture transport east of the Andes, composites of South American LLJs were built based on the wind speed and vertical wind shear following the modified Bonner criteria 1 used to define LLJs. Integrations along the lateral boundaries of the two basins show that there could be a more intense moisture transport from tropical regions available to feed the mesoscale convective systems in the subtropical La Plata Basin in the IPCC A2 scenario, as compared to the present. This is because of the intense flow to the south associated with a faster LLJ bringing more moisture from the Amazon Basin southwards. It was also observed that the presence of the LLJ affects moisture convergence in the Amazon Basin in the current climate as well as in the warmer climate. In the future high-emission scenario A2, a more intense LLJ in a global warming climate suggests increased moisture transport from north to south east of the Andes as compared to the present.

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“…Over the southwest Atlantic, interannual intensifications of the SACZ have also been linked to SST anomalies (Nogués-Paegle et al 2002). Furthermore, the decadal rainfall variation presents a pattern of meridional shift of the ITCZ on both the eastern Pacific and western Atlantic Ocean, which is closely related to the decadal change of the cross-equatorial SST gradient (Nobre and Shukla 1996;Rao et al 1999).…”

Section: Introductionmentioning

confidence: 99%

Role of Land Surface Processes in South American Monsoon Development

Xue

Sales

et al. 2006

Journal of Climate

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This study explores the role of vegetation biophysical processes (VBPs) in the structure and evolution of the South American monsoon system (SAMS) with an emphasis on the precipitation field. The approach is based on comparing ensemble simulations by the National Centers for Environmental Prediction general circulation model (GCM) in which the land surface parameterization in one ensemble includes an explicit representation of vegetation processes in the calculation of surface fluxes while the other does not [GCM/ Simplified Simple Biosphere Model (SSiB) and GCM/Soil, respectively], but with similar monthly mean surface albedo and initial soil moisture. The ensembles consist of five pairs of 1-yr integrations differing in the initial conditions for the atmosphere. The results show that, during the austral summer, consideration of explicit vegetation processes does not alter the monthly mean precipitation at the planetary scale. However, at continental scales, GCM/SSiB produces a more successful simulation of SAMS than GCM/Soil. The improvement is particularly clear in reference to the seasonal southward displacement of precipitation during the onset of the SAMS and its northward merging with the intertropical convergence zone during the monsoon mature stage, as well as better monthly mean austral summer precipitation over the South American continent.The changes in surface water and energy balances and circulation in October (monsoon onset) and December (the start of the monsoon mature stage) were analyzed for a better understanding of the results and mechanisms involved. It was found that the major difference between the simulations is in the partitioning of latent heat and sensible heat fluxes (i.e., different Bowen ratio), which produced different latitudinal and longitudinal thermal gradients at the surface. A stronger sensible heat flux gradient between continent and ocean in the GCM/SSiB simulation helped generate an enhanced ventilation effect, which lowered moist static energy (MSE) over the northeast coast of South America leading to stronger counterclockwise turning of the low-level wind from the Atlantic Ocean toward the continent during the premonsoon and early monsoon stages, modifying moisture flux convergence (MFC). It was further iden-* Current affiliation: National Climate Center, Beijing, China. tified that the seasonality of savanna and shrublands to the south and east of the Amazon rain forest contributed to the variability of heating gradients and influenced the SAMS onset and its northward merge with the ITCZ at the early monsoon mature stage. The comparison of the differences between precipitation, evaporation, advection of MSE, and MFC based on simulations using two different land parameterizations suggested that the VBP modulated the surface water budget, but its impact on precipitation was determined by the changes in circulation via changes in heat gradient and MSE.

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Decadal Variation of Atmosphere-Ocean Interaction in the Tropical Atlantic and its Relationship to the Northeast Brazil Rainfall

Cited by 15 publications

References 44 publications

Is the Recent Increasing Trend of Rainfall over Northeast Brazil Related to Sub-Saharan Drought?

Is the Recent Increasing Trend of Rainfall over Northeast Brazil Related to Sub-Saharan Drought?

Assessments of moisture fluxes east of the Andes in South America in a global warming scenario

Role of Land Surface Processes in South American Monsoon Development

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