found to be part of a large-scale teleconnection wave train linked with the subsidence branch of the Walker circulation in the tropical east Pacific, which in turn was generated by an anomalous tropical heat source in north/northeastern Australia. A regional Hadley circulation with an ascending branch to the south of the subsidence branch of the Walker circulation in the tropical east Pacific was identified as an important component connecting the tropical and extratropical circulation. The ascending branch of this Hadley circulation in the south Pacific coincided with an identified Rossby wave source region, which contributed to establishing the extratropical component of the large-scale wave train connecting the south Pacific and the Atlantic region surrounding southeast Brazil. This connection between the Pacific and the Atlantic was confirmed with Rossby ray tracing analyses. The local circulation response was associated to downward air motion (subsidence) over Southeast Brazil, contributing to the expressive negative precipitation anomalies observed during summer 2014, and leading to a major drought event in the historical context. The analysis of atmospheric and oceanic patterns of this event helped defining a schematic framework leading to the observed drought conditions in southeast Brazil, including the involved teleconnections, blocking high pressure, radiative and humidity transport effects.

In mid-2012, the Abdus Salam International Centre for Theoretical Physics (ICTP) released version 4.3 of the Regional Climate Model (RegCM4.3). This version includes a new surface scheme, the Common Land Model (CLM); a new planetary boundary layer (PBL) scheme, the University of Washington PBL (UW-PBL); and new convection schemes including Tiedtke, and Mixed1 and Mixed2 -with Grell (MIT) over the land and MIT (Grell) over the ocean for Mixed1 (Mixed2). These implementations suggest the necessity of an evaluation study to determine the best configuration of RegCM4.3 for simulating the climate of South America (SA). The main motivation is to come up with the best configurations of RegCM4.3 over the SA domain for use in the Coordinated Regional Downscaling Experiment (CORDEX) project. We analyzed 7 simulations for the period 1990−2000. The control simulation used the Biosphere−Atmosphere Transfer Scheme (BATS), Holtslag for the PBL and Mixed1 for cumulus convection. In the other simulations we changed these schemes using the new RegCM4.3 options. The evaluation of the simulations was carried out in 3 groups: (1) sensitivity to convection (Mixed1, MIT and Tiedtke), (2) sensitivity to the PBL (Holtslag and UW-PBL) and (3) sensitivity to surface processes (BATS and CLM). Considering all of SA, the results show that precipitation is better simulated with the schemes of the control simulation, while for air temperature, better results were obtained using the MIT cumulus scheme together with the CLM scheme. In summary, we recommend 2 configurations for the CORDEX project over SA: (1) the schemes used in the control simulation and (2) the MIT scheme for cumulus convection, Holtslag for the PBL, and CLM for surface interaction processes.KEY WORDS: South America · RegCM4.3 · CORDEX · Simulation · Precipitation · Temperature · Evapotranspiration Resale or republication not permitted without written consent of the publisherClim Res 60: [215][216][217][218][219][220][221][222][223][224][225][226][227][228][229][230][231][232][233][234] 2014 lysis (e.g. NCEP, ERA-Interim) to be used as initial and boundary conditions in RCMs, for a range of applications. In particular, for South America (SA), RCMs began to be utilized in the 2000s to simulate the observed features of the present climate (Chou et al. 2000, Menéndez et al. 2001, Nobre et al. 2001. The use of RCMs increased in recent years, encompassing objectives such as: investigation of the RCMs' ability to simulate the climate (Nicolini et al. 2002, Seth & Rojas 2003, Fernandez et al. 2006a; the use of different initial and boundary condition forcing (Seth & Rojas 2003); validation of the simulated diurnal cycle of the precipitation (da Rocha et al. 2009); comparison of the simulated interannual variability of the climate with observations (Misra et al. 2002, Fernandez et al. 2006b); investigation of the ability of RCMs to simulate specific atmospheric systems climatology (Reboita et al. 2010a); and exploration of future climate scenarios (Nuñez et al. 2009, Maren...

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This paper examines the distributions of anomalies of sea surface temperature (SST) and of the moisture sources in the South Atlantic Ocean during extreme dry events in southeastern Brazil in the austral autumn, winter and spring for the period 1982-2009. The extreme dry events were identified based on a combination in which consecutive dry days and variable percentiles were considered in five homogeneous regions in terms of precipitation in southeastern Brazil, as defined through cluster analysis. Composites of anomalies of SST and moisture sources for the dry events selected for the different homogeneous regions show specific characteristics for each region, but some similarities were apparent for the southern and northern parts of southeast Brazil. During spring in all regions, and during autumn and winter in the southern regions, a tripole pattern of SST anomalies was found (negative, positive and negative), together with an anomalous anticyclonic circulation in the Atlantic Ocean transporting moisture to southern Brazil associated with positive SST anomalies. A decrease in the climatological moisture sources in the south of Brazil then ensues, and dry conditions prevail in the regions of interest. In winter and autumn in the northern regions, the same tripole pattern of SST anomalies was also found, but shifted northwards. An anomalous cyclone is associated with the negative SST anomalies, and the climatological moisture sources to the northeast of Brazil reduce their contribution to the region of interest, where negative precipitation anomalies are registered. It seems that the events selected show the results of reductions both in terms of the availability of moisture and in atmospheric instability.

Southeastern Brazil is the most populated and economically developed region of this country. Its climate consists of two distinct seasons: the dry season, extending from April to September, the precipitation is significantly reduced in comparison to that of the wet season, which extends from October to March. However, during nine days of the 2016 dry season, successive convective systems were associated with atypical precipitation events, tornadoes and at least one microburst over the southern part of this region. These events led to flooding, damages to buildings, shortages of electricity and water in several places, many injuries, and two documented deaths. The present study investigates the synoptic and dynamical features related to these anomalous events. The convective systems were embedded in an unstable environment with intense low-level jet flow and strong wind shear and were supported by a sequence of extratropical cyclones occurring over the Southwest Atlantic Ocean. These features were intensified by the Madden–Julian oscillation (MJO) in its phase 8 and by intense negative values of the Pacific South America (PSA) 2 mode.