Thunderstorm climatology ofBrazil:ENSOandTropical Atlanticconnections

Abstract

ABSTRACTIn this report monthly thunderstorm days (TD) in 14 large cities of Brazil from 1951 to 2010 are compared with data obtained in the first part of the 20th century in the same cities and correlated with sea surface temperature (SST) of the equatorial Pacific Ocean and Tropical Atlantic Ocean. On average over all cities, 77 TD are reported each year after 1951, against 43 TD in the first part of the 20th century, an increase of 79%. The increase seems to be related to increase in the urbanization in these cities, and not to global warming. A comparative analysis of TD for the whole country with El Niño–Southern Oscillation (ENSO) events suggests that the tendency for El Niño to increase the thunderstorm activity is evident in the South (only in the Spring/Summer), Southeast, Northeast and North (only in the Fall/Winter) regions. Regarding the Tropical Atlantic OceanSST, a similar analysis using the Tropical South Atlantic (TSA) and Tropical North Atlantic (TNA) indices suggests that no significant differences exist between the thunderstorm activity for the two extreme positive and negativeTSAconditions in the South and Southeast regions, while in the Northeast and North regions there is a significant increase in the thunderstorm activity during extreme positiveTSA. Differently, only in the Northeast region there is a significant influence ofTNAon thunderstorm activity. The influence is such that the thunderstorm activity is larger for the extreme negativeTNAthan for extreme positiveTNA. All significant changes were quantified and significant variations were observed. For all parameters investigated (ENSO,TSAandTNA) the Northeast region showed the most significant changes.