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GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L18710, doi:10.1029/2006GL026384, 2006

Indian Ocean zonal mode activity in a multicentury integration of a coupled AOGCM consistent with climate proxy data

Thomas Mölg

Tropical Glaciology Group, Department of Earth and Atmospheric Sciences, University of Innsbruck, Innsbruck, Austria


Manuel Renold

Climate and Environmental Physics, Physics Institute, University of Berne, Berne, Switzerland


Mathias Vuille

Climate System Research Center, Department of Geosciences, University of Massachusetts, Amherst, Massachusetts, USA


Nicolas J. Cullen

Tropical Glaciology Group, Department of Earth and Atmospheric Sciences, University of Innsbruck, Innsbruck, Austria


Thomas F. Stocker

Climate and Environmental Physics, Physics Institute, University of Berne, Berne, Switzerland


Georg Kaser

Tropical Glaciology Group, Department of Earth and Atmospheric Sciences, University of Innsbruck, Innsbruck, Austria


Abstract

The coupled atmosphere-ocean system over the Indian Ocean (termed Indian Ocean Zonal Mode, IOZM) and its activity over the past 200 years is analyzed in a paleoclimate simulation from a coupled atmosphere-ocean general circulation model (AOGCM). Validation shows that the AOGCM captures spatio-temporal patterns of sea surface temperature anomalies as well as the seasonal phase-locking feature of the IOZM. The period 1820–1880 exhibits a high frequency of climatically significant IOZM events, compared to a relatively low frequency in the 20th century. This shift in frequency provides a climate dynamics background for the interpretation of proxy data from East Africa, a region subjected to anomalously strong October–December precipitation during IOZM events. In the late 19th century, East African lakes had highstands (e.g., Lake Victoria) and its glaciers stable extents (e.g., Kilimanjaro), consistent with a wetter climate due to the higher frequency of IOZM events.

Received 22 March 2006; accepted 21 August 2006; published 30 September 2006.

Index Terms: 3344 Atmospheric Processes: Paleoclimatology (0473, 4900); 3339 Atmospheric Processes: Ocean/atmosphere interactions (0312, 4504); 3305 Atmospheric Processes: Climate change and variability (1616, 1635, 3309, 4215, 4513); 3337 Atmospheric Processes: Global climate models (1626, 4928).

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Citation: Mölg, T., M. Renold, M. Vuille, N. J. Cullen, T. F. Stocker, and G. Kaser (2006), Indian Ocean zonal mode activity in a multicentury integration of a coupled AOGCM consistent with climate proxy data, Geophys. Res. Lett., 33, L18710, doi:10.1029/2006GL026384.