South America Climate During the 1970–2001 Pacific Decadal Oscillation Phases Based on Different Reanalysis Datasets

Abstract

In this paper, circulation and precipitation climate patterns over the South American domain obtained from NCEP-NCAR reanalysis I, JRA-55, and ERA-40 reanalysis datasets were intercompared within the period 1970-2001 in order to verify their climatic association with the Pacific Decadal Oscillation, PDO. Although all three datasets showed similar climatic patterns during each PDO phase, they showed distinct intensities for circulation and precipitation variables. The mean low frequency flow propagation over the South Pacific during negative and positive PDO phases reached central-eastern South America with opposite signals, contributing to the modulation of the local climate. During the negative PDO phases, the northerly flow over South America is intensified, while during the positive phase it is weakened. NCEP-NCAR reanalysis I, in comparison with JRA-55 and ERA-40 values, always indicates the strongest signal for circulation and precipitation variables. NCEP-NCAR reanalysis I meridional wind at the low-level jet area was about 5 and 12% larger than the respective JRA-55 and the ERA-40 values. For the positive and negative PDO phases, only NCEP-NCAR and ERA-40 high-level zonal wind anomalies showed divergent (positive PDO) and convergent (negative PDO) patterns close to 140 • W at equatorial latitudes of the Pacific Ocean, respectively. This one indicated distinct representations of the positioning of Walker cells in the three reanalysis datasets. GPCC dataset, NCEP-NCAR, JRA-55, and ERA-40 reanalysis showed, in general, the dipole precipitation pattern over eastern South America, with signs of changes between the central-eastern and southeastern areas during PDO reversal phases. Over the central-eastern South American region, NCEP-NCAR precipitation is, on average, 57% larger than GPCC values, and 35 and 46% larger than JRA-55 and ERA-40 values, respectively. The observed patterns of anomalies for different PDO phases appeared in all reanalysis datasets, leading us to conclude that the physical meaning is independent from the datasets. Even considering the JRA-55 climate signal over South America associated with the PDO influence as the weakest one, the ability of JRA-55 to calculate monthly precipitation provided the highest linear correlation coefficient values in tropical areas, leading us to consider this dataset as the most reliable for the studied area.

The anomalous wet 2020 southeast Brazil austral summer: Characterization and possible mechanisms

“…Paulo State had similar behavior of the Southern Region of Brazil, i.e., negative precipitation anomalies. These two regions revealed a dipole pattern of anomaly precipitation, also displayed by previous work (e.g., Cunningham and Cavalcanti, 2006;Vasconcellos and Cavalcanti, 2010;Jorgetti, Silva Dias and Freitas, 2014;Bernardino, Vasconcellos and Nunes, 2018;Silva et al, 2020) .…”

“…According toRosso et al (2018) , the positive SAM phase is related with higher frequency, persistence, and total precipitation in SACZ events, which is in agreement with positive precipitation anomalies over SEB, displayed inFigure 1. The influence of lower frequency modes, like PDO, could also be related to this dipole(Silva et al, 2020). It is noteworthy, that despite positive geopotential height anomalies at middle latitude, related by the positive SAM phase, there was a negative anomaly over South Atlantic, reaching SEB coastal.…”

Impacts of teleconnection patterns on South America climate

“…[75][76][77][78] In addition, in a recent study comparing different reanalysis, a dipole pattern over eastern SA during opposite PDO phases was observed: central-eastern SA experiences negative (positive) precipitation anomalies during the cold (warm) PDO phase, while SSA experiences an opposite pattern. 79 In terms of circulation, during the cold (warm) PDO phase the LLJ over SA are intensified (weakened), which is associated with positive (negative) geopotential height anomalies extending vertically through the troposphere over eastern SA. 79 As a novel seasonal analysis regarding the influence of the PDO warm and cold phases on the circulation and precipitation over SA, we present anomalies maps during neutral ENSO periods (Fig.…”

“…79 In terms of circulation, during the cold (warm) PDO phase the LLJ over SA are intensified (weakened), which is associated with positive (negative) geopotential height anomalies extending vertically through the troposphere over eastern SA. 79 As a novel seasonal analysis regarding the influence of the PDO warm and cold phases on the circulation and precipitation over SA, we present anomalies maps during neutral ENSO periods (Fig. 5); previous studies analyzed mainly the PDO impacts on precipitation on different timescales and mainly during ENSO phases.…”

“…5); previous studies analyzed mainly the PDO impacts on precipitation on different timescales and mainly during ENSO phases. 77,[79][80][81] There were fewer cases of the PDO during the austral summer (DJF) and more during the austral autumn (MAM); the austral spring (SON) and winter (JJA) present a similar number of cases. Nevertheless, during DJF there were specific drier regions for both phases (Fig.…”