Climate Dynamics

, Volume 47, Issue 12, pp 3993–4007 | Cite as

Frontolysis by surface heat flux in the Agulhas Return Current region with a focus on mixed layer processes: observation and a high-resolution CGCM

  • Shun Ohishi
  • Tomoki Tozuka
  • Nobumasa Komori


Detailed mechanisms for frontogenesis/frontolysis of the Agulhas Return Current (ARC) Front, defined as the maximum of the meridional sea surface temperature (SST) gradient at each longitude within the ARC region (40°–50°E, 55°–35°S), are investigated using observational datasets. Due to larger (smaller) latent heat release to the atmosphere on the northern (southern) side of the front, the meridional gradient of surface net heat flux (NHF) is found throughout the year. In austral summer, surface warming is weaker (stronger) on the northern (southern) side, and thus the NHF tends to relax the SST front. The weaker (stronger) surface warming, at the same time, leads to the deeper (shallower) mixed layer on the northern (southern) side. This enhances the frontolysis, because deeper (shallower) mixed layer is less (more) sensitive to surface warming. In austral winter, stronger (weaker) surface cooling on the northern (southern) side contributes to the frontolysis. However, deeper (shallower) mixed layer is induced by stronger (weaker) surface cooling on the northern (southern) side and suppresses the frontolysis, because the deeper (shallower) mixed layer is less (more) sensitive to surface cooling. Therefore, the frontolysis by the NHF becomes stronger (weaker) through the mixed layer processes in austral summer (winter). The cause of the meridional gradient of mixed layer depth is estimated using diagnostic entrainment velocity and the Monin–Obukhov depth. Furthermore, the above mechanisms obtained from the observation are confirmed using outputs from a high-resolution coupled general circulation model. Causes of model biases are also discussed.


Agulhas Return Current Frontogenesis/frontolysis Surface heat flux Mixed layer depth Entrainment velocity High-resolution coupled general circulation model 



We are grateful to two anonymous reviewers for their constructive comments. The CFES simulation was conducted on the Earth Simulator under support of Japan Agency for Marine-Earth Science and Technology (JAMSTEC). This research was supported by the Japan Society for Promotion of Science through Grant-in-Aid for Scientific Research on Innovative Areas 2205. The first author was financially supported by the Sasakawa Scientific Research Grant from The Japan Science Society.


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© Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  1. 1.Department of Earth and Planetary Science, Graduate School of ScienceThe University of TokyoTokyoJapan
  2. 2.Application LaboratoryJapan Agency for Marine-Earth Science and TechnologyYokohamaJapan

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