The Bjerknes feedback in the tropical Atlantic in CMIP5 models

Abstract

for the error in seasonality. The third component of the BF, the impact of HC' on SST' in the eastern part of the basin, deviates from what we find in reanalysis. We find an influence of HC anomalies on overlying SSTs in the eastern equatorial TA, but it is weaker than in the reanalysis and it is not strongly confined to the equator. Longitude-depth cross sections of equatorial temperature variance and correlation between subsurface temperature anomalies and SST' in the cold tongue region show that flawed simulation and slow adjustment of the subsurface ocean are responsible for this.

On the relationship between Atlantic Niño variability and ocean dynamics

“…Our results agree with the observations-based part of Deppenmeier et al (2016)'s analysis of the Bjerknes feedback in the tropical Atlantic. However, while Deppenmeier et al (2016) point out that it is mainly the relationship between upper ocean heat content (approximated by our SSH) and SST that is too weak in CMIP5-simulations, the KCM's problems are mainly related to the SST-u10 relationship, possibly due to the low atmospheric vertical resolution.…”

“…In agreement with Keenlyside and Latif (2007) and Deppenmeier et al (2016), all observed feedback elements are generally strongest in early boreal summer, establishing a closed Bjerknes feedback loop in May-July (Fig. 10a).…”

“…In a positive feedback, it relates SST and thermocline variability in the eastern ocean basin to zonal surface wind variability in the western ocean basin (u10) and lends growth to the Pacific (Bjerknes 1969) and Atlantic Niños (e.g. Keenlyside and Latif 2007;Burls et al 2012;Lübbecke and McPhaden 2013;Deppenmeier et al 2016). Traditionally, three elements of the Bjerknes feedback are considered when assessing the overall strength of the feedback: (1) Eastern ocean basin SST anomalies force u10 anomalies in the western ocean basin, (2) u10 anomalies trigger a thermocline response across the basin that can be measured via thermocline variability in the eastern ocean basin, and (3) eastern basin thermocline anomalies amplify the initial SST anomaly.…”

Symmetry of the Atlantic Niño mode

“…Several studies have demonstrated that even though weaker than in the Pacific, the Bjerknes feedback is active in the equatorial Atlantic [e.g., Zebiak, 1993;Keenlyside and Latif, 2007;Lübbecke and McPhaden, 2013;Deppenmeier et al, 2016]. Other mechanisms that have been discussed involve meridional advection of temperature anomalies [Richter et al, 2013], forcing from equatorial deep jets [Brandt et al, 2011b], and heat flux forcing [Nnamchi et al, 2015].…”

An Equatorial–Extratropical Dipole Structure of the Atlantic Niño

“…On the other hand, the Atlantic Niño is widely believed to be dynamically driven because of the Bjerknes feedback (Zebiak 1993;Keenlyside and Latif 2007;Lübbecke and McPhaden 2013;Deppenmeier et al 2016), equatorial Kelvin waves (Brandt et al 2011), and meridional temperature advection from the tropical North Atlantic Ocean (Richter et al 2013).…”