Tropical Atlantic Variability: Observations and Modeling

Abstract

We review the state-of-the-art knowledge of Tropical Atlantic Variability (TAV). A well-developed observing system and sustained effort of the climate modeling community have improved our understanding of TAV. It is dominated by the seasonal cycle, for which some mechanisms have been identified. The interannual TAV presents a marked seasonality with three dominant modes: (i) the Atlantic Zonal Mode (AZM), (ii) the Atlantic Meridional Mode (AMM) and (iii) the variability in the Angola–Benguela Front (ABF). At longer time scales, the AMM is active and low-frequency variations in the strength, periodicity, and spatial structure of the AZM are observed. Also, changes in the mean position of the ABF occur. Climate models still show systematic biases in the simulated TAV. Their causes are model-dependent and relate to drawbacks in the physics of the models and to insufficient resolution of their atmospheric and oceanic components. The identified causes for the biases can have local or remote origin, involving the global ocean and atmospheric circulation. Although there is not a clear consensus regarding the role of model resolution in the representation of the TAV, eddy-resolving ocean models combined with atmospheric models with enhanced horizontal and vertical resolutions simulate smaller biases.

Regional atmospheric response to the Benguela Niñas

“…The SAA is centred at 0 E and 35 S (Figure 2g) and is excited in the case of Benguela Niñas (Figure 3g) by 1.0 hPa. As suggested by previous studies (e.g., Lübbecke et al, 2010;Richter et al, 2010;Cabos et al, 2019), the Benguela variability is connected well with the SAA variability. Interestingly, the SLP seems to be reinforced locally over the ABFZ with a smaller amplitude (about 0.5 hPa, Figure 3g).…”

“…Another characteristic of the ABFZ are its interannual variability in sea surface temperature (SST), socalled Benguela Niño/Niña (e.g., Imbol Koungue et al, 2017Koungue et al, , 2019Rouault et al, 2018). The peak of the amplitude of a Benguela Niño/Niña event occurs usually during February-April (e.g., Cabos et al, 2019;Imbol Koungue et al, 2019). Its horizontal distribution is, in general, limited only in the Angolan and Namibian coast.…”

Why Do Benguela Niños Lead Atlantic Niños?

“…The close connection between Atlantic and Benguela Niño events has been related to their forcing mechanism. While several processes have been shown to contribute to the SSTA in the eastern‐equatorial Atlantic, most studies agree that eastward‐propagating Equatorial Kelvin Waves (EKW) that are forced by interannual wind‐stress fluctuations in the western‐central part of the basin play an important role for the generation of the majority of Atlantic Niño events (see recent reviews by Cabos et al, 2019; Lübbecke et al, 2018). These EKWs are associated with changes in stratification and currents, allowing for less (more) effective vertical entrainment and thus leading to anomalous warm (cold) SST in the cold tongue region (Planton et al, 2018).…”

Can Short and Partial Observations Reduce Model Error and Facilitate Machine Learning Prediction?

“…In fact, the MISO pattern of year 2010 is similar to that of year 1998 with a weak amplitude. Note that the winter of both year 1998 and year 2010 corresponds to a strong positive phase of the Atlantic Zonal Mode (AZM) [ 36 , 37 ]. The results here confirm the negative correlation between the MISO and the AZM as well as the relatively short predictability of the MISO at the positive phase of the AZM.…”