Assessment of 20th-century reanalysis circulation patterns associated with El Nino-Southern Oscillation impacts on the tropical Atlantic and northeastern Brazil rainy season

摘要

The present study investigates how the 20th-century atmospheric reanalyses (ERA-20C and NOAA-20CR) reproduce the known impacts of El Nino-Southern Oscillation (ENSO) on the tropical North Atlantic (TNA) atmospheric circulation from the boreal winter to spring and the consequences on northeastern Brazil (NEB) precipitation during its rainy season (boreal spring). For the period 1979-2010, comparisons of atmospheric patterns associated with ENSO events are made through the use of anomaly composites of variables provided by ERA-20C, NOAA-20CR and satellite-era reanalyses (ERA-Interim and NCEP-Reanalysis 2). We also evaluate the ability of the reanalyses to reproduce the interannual variability of precipitation during the boreal spring over Ceara state (located in NEB) by statistically comparing them with Funceme rain-gauge and Global Precipitation Climatology Center (GPCC) datasets. As the main result, both 20th-century reanalyses capture the major features in the tropical Pacific representing the climatic system during ENSO years as well as its impacts on the tropical Atlantic, in agreement with previous studies. However, some differences are noted, such as (a) NOAA-20CR differs from the other reanalyses since it indicates stronger (weaker) near-surface (upper levels) wind anomalies over the central-western equatorial Pacific in both El Nino and La Nina composites; (b) over the tropical Atlantic, all reanalyses indicate the existence of an omega anomalies dipole between 10 degrees N and 10 degrees S for both ENSO phases although a weaker signal is seen in NOAA-20CR; (c) NOAA-20CR underestimates the intensity of the precipitation anomalies over the NEB during El Nino and La Nina years, and this is associated with the weaker vertical velocity anomalies. These results indicate that ERA-20C is the most appropriate 20th-century reanalysis to study the long-term interannual variability in the tropical Atlantic associated with ENSO and its impacts on precipitation in northeastern Brazil.