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Volume 9, issue 4 | Copyright
Earth Syst. Dynam., 9, 1191-1215, 2018
https://doi.org/10.5194/esd-9-1191-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 12 Oct 2018

Research article | 12 Oct 2018

The climate of a retrograde rotating Earth

Uwe Mikolajewicz1, Florian Ziemen1, Guido Cioni1,2, Martin Claussen1,3, Klaus Fraedrich1,3, Marvin Heidkamp1,2, Cathy Hohenegger1, Diego Jimenez de la Cuesta1,2, Marie-Luise Kapsch1, Alexander Lemburg1,2, Thorsten Mauritsen1, Katharina Meraner1, Niklas Röber4, Hauke Schmidt1, Katharina D. Six1, Irene Stemmler1, Talia Tamarin-Brodsky5, Alexander Winkler1,2, Xiuhua Zhu3, and Bjorn Stevens1 Uwe Mikolajewicz et al.
  • 1Max Planck Institute for Meteorology, Bundesstr. 53, Hamburg, Germany
  • 2International Max Planck Research School on Earth System Modeling, Bundesstr. 53, Hamburg, Germany
  • 3Universität Hamburg, Meteorologisches Institut, Bundesstr. 55, Hamburg, Germany
  • 4Deutsches Klimarechenzentrum, Bundesstr. 45a, Hamburg, Germany
  • 5Department of Meteorology, University of Reading, Reading, UK

Abstract. To enhance understanding of Earth's climate, numerical experiments are performed contrasting a retrograde and prograde rotating Earth using the Max Planck Institute Earth system model. The experiments show that the sense of rotation has relatively little impact on the globally and zonally averaged energy budgets but leads to large shifts in continental climates, patterns of precipitation, and regions of deep water formation.

Changes in the zonal asymmetries of the continental climates are expected given ideas developed more than a hundred years ago. Unexpected was, however, the switch in the character of the European–African climate with that of the Americas, with a drying of the former and a greening of the latter. Also unexpected was a shift in the storm track activity from the oceans to the land in the Northern Hemisphere. The different patterns of storms and changes in the direction of the trades influence fresh water transport, which may underpin the change of the role of the North Atlantic and the Pacific in terms of deep water formation, overturning and northward oceanic heat transport. These changes greatly influence northern hemispheric climate and atmospheric heat transport by eddies in ways that appear energetically consistent with a southward shift of the zonally and annually averaged tropical rain bands. Differences between the zonally averaged energy budget and the rain band shifts leave the door open, however, for an important role for stationary eddies in determining the position of tropical rains. Changes in ocean biogeochemistry largely follow shifts in ocean circulation, but the emergence of a super oxygen minimum zone in the Indian Ocean is not expected. The upwelling of phosphate-enriched and nitrate-depleted water provokes a dominance of cyanobacteria over bulk phytoplankton over vast areas – a phenomenon not observed in the prograde model.

What would the climate of Earth look like if it would rotate in the reversed (retrograde) direction? Which of the characteristic climate patterns in the ocean, atmosphere, or land that are observed in a present-day climate are the result of the direction of Earth's rotation? Is, for example, the structure of the oceanic meridional overturning circulation (MOC) a consequence of the interplay of basin location and rotation direction? In experiments with the Max Planck Institute Earth system model (MPI-ESM), we investigate the effects of a retrograde rotation in all aspects of the climate system.

The expected consequences of a retrograde rotation are reversals of the zonal wind and ocean circulation patterns. These changes are associated with major shifts in the temperature and precipitation patterns. For example, the temperature gradient between Europe and eastern Siberia is reversed, and the Sahara greens, while large parts of the Americas become deserts. Interestingly, the Intertropical Convergence Zone (ITCZ) shifts southward and the modeled double ITCZ in the Pacific changes to a single ITCZ, a result of zonal asymmetries in the structure of the tropical circulation.

One of the most prominent non-trivial effects of a retrograde rotation is a collapse of the Atlantic MOC, while a strong overturning cell emerges in the Pacific. This clearly shows that the position of the MOC is not controlled by the sizes of the basins or by mountain chains splitting the continents in unequal runoff basins but by the location of the basins relative to the dominant wind directions. As a consequence of the changes in the ocean circulation, a super oxygen minimum zone develops in the Indian Ocean leading to upwelling of phosphate-enriched and nitrate-depleted water. These conditions provoke a dominance of cyanobacteria over bulk phytoplankton over vast areas, a phenomenon not observed in the prograde model.

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Model experiments show that changing the sense of Earth's rotation has relatively little impact on the globally and zonally averaged energy budgets but leads to large shifts in continental climates and patterns of precipitation. The retrograde world is greener as the desert area shrinks. Deep water formation shifts from the North Atlantic to the North Pacific with subsequent changes in ocean overturning. Over large areas of the Indian Ocean, cyanobacteria dominate over bulk phytoplankton.
Model experiments show that changing the sense of Earth's rotation has relatively little impact...
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