Benguela Niños and Benguela Niñas in Forced Ocean Simulation From 1958 to 2015

Abstract

A systematic study of Benguela Niño and Benguela Niña events during 1958 to 2015 including those that developed before the satellite era (1982) is carried out using an ocean general circulation model in combination with a linear equatorial model. Altogether, 21 strong warm and cold anomalous coastal events are identified among which 6 undocumented extreme coastal events are reported. Results suggest that most of these extreme coastal events including the newly identified ones are linked to remote equatorial forcing via mode 2 equatorial Kelvin waves. The latter propagates after approaching the African coast poleward as coastally trapped waves leading surface temperature anomalies along the Angola‐Benguela current system by one month. One to two months before the peak of Benguela Niños or Niñas usually occurring in March–April, a large‐scale wind stress forcing is observed with both local (variations of alongshore coastal wind stress) and remote forcing developing simultaneously. Results further suggest that surface temperature anomalies off Southern Angola and in the Angola‐Benguela Front are associated with equatorial dynamics and meridional wind stress fluctuations off the southwestern African coast north of 15°S. Similar mechanisms are observed for Northern Namibia in combination with forcing by local meridional wind stress variations.

Why Do Benguela Niños Lead Atlantic Niños?

“…In agreement with a remote forcing mechanism associated with the propagation of downwelling long equatorial waves, the relaxation of the trade winds develops prior to the peak of the event (Figures 4b–4d). These results are also in agreement with Imbol Koungue et al (2019) and Lübbecke et al (2010), who analyzed composites of Benguela Niño events. The zonal wind‐stress anomaly averaged within WCEA is maximum (1.04 × 10 −2 N.m −2 , cf.…”

Regional atmospheric response to the Benguela Niñas

“…According to Imbol Koungue et al . (2019), the extreme Benguela Niñas in boreal spring (February–April) have occurred in 1982, 1985, 1992, and 1997 from 1958 to 2015 period. In this study, the relatively strong cold event in 1983 (see fig.…”

“…April SST anomalies of ERA-interim in the five events defined in Imbol Koungue et al (2019Koungue et al ( ) for 1982Koungue et al ( , 1983Koungue et al ( , 1985Koungue et al ( , 1992Koungue et al ( , and 1997. Black dots denote the significance level of 90% [Colour figure can be viewed at wileyonlinelibrary.com] configuration is employed for the numerical simulations.…”

“…Recently, Imbol Koungue et al . (2019) defined the Benguela Niños/Niñas comprehensively using a combination of observational and satellite data. According to Imbol Koungue et al .…”

“…In this study, the relatively strong cold event in 1983 (see fig. 3 in Imbol Koungue et al ., 2019) is also considered and the composite analysis based on five strong Benguela Niña events is performed for ERA‐Interim and ERA5 reanalyses. To have more robust results, we use the two different reanalysis data set in this study.…”