A multi-model analysis of the role of the ocean on the African and Indian monsoon during the mid-Holocene |
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Authors: | Y Zhao P Braconnot O Marti SP Harrison C Hewitt A Kitoh Z Liu U Mikolajewicz B Otto-Bliesner SL Weber |
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Institution: | (1) IPSL/Laboratoire de Sciences du climat et de l’environnement, Unité mixte CEA-CNRS, Orme des Merisiers, bat. 712, 91191 Gif-sur-Yvette, France;(2) School of Geographical Sciences, University of Bristol, BS8 1SS Bristol, UK;(3) Hadley Centre Met Office, Exeter, UK;(4) Meteorological Research Institute, Tsukuba, Japan;(5) University of Wisconsin-Madison, Madison, USA;(6) Max Planck Institute für Meteorology, Hamburg, Germany;(7) Climate Change Research, National Center for Atmospheric Research, Boulder, USA;(8) Royal Netherlands Meteorological Institute, De Bilt, The Netherlands |
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Abstract: | We investigate the role of the ocean feedback on the climate in response to insolation forcing during the mid-Holocene (6,000 year
BP) using results from seven coupled ocean–atmosphere general circulation models. We examine how the dipole in late summer
sea-surface temperature (SST) anomalies in the tropical Atlantic increases the length of the African monsoon, how this dipole
structure is created and maintained, and how the late summer SST warming in the northwest Indian Ocean affects the monsoon
retreat in this sector. Similar mechanisms are found in all of the models, including a strong wind evaporation feedback and
changes in the mixed layer depth that enhance the insolation forcing, as well as increased Ekman transport in the Atlantic
that sharpens the Atlantic dipole pattern. We also consider changes in interannual variability over West Africa and the Indian
Ocean. The teleconnection between variations in SST and Sahelian precipitation favor a larger impact of the Atlantic dipole
mode in this region. In the Indian Ocean, the strengthening of the Indian dipole structure in autumn has a damping effect
on the Indian dipole mode at the interannual time scale. |
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