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It has been heretofore understood that patterns of cloudiness are controlled by large scale weather systems. In this video, BJORN STEVENS challenges this orthodoxy, arguing that small and intermediate scales of motion play a key role in determining the Earth’s cloudiness. Using aircraft to measure the vigor of intermediate scales of motion and groups of scientists to examinesmall scale patterning, Stevens identifies distinct patterning of clouds at these smaller scales. He suggests that the role played by small and intermediate scales of motion in cloud patterning is a previously neglected piece of the puzzle which will give us vital insight into how the cloudiness of the Earth might develop in the future.


Bjorn B. Stevens is Director of the Department for the Atmosphere in the Earth System, at Max Planck Institute for Meteorology and teaches at the University of Hamburg. Previously, Stevens was a Professor of Dynamic Meteorology at the University of California, Los Angeles (USA).

Stevens has made major contributions to the research on atmospheric convection in the climate system. He was awarded the Clarence Leroy Meisinger Award of the American Meteorological Society, and is an associate fellow at various institutions, including the Alexander von Humboldt Society.


Max Planck Institute for Meteorology

The Max Planck Institute for Meteorology (MPI-M) is an internationally renowned institute for climate research in Hamburg, Germany.

Our scientists develop advanced models of the Earth system, perform targeted observations, and advance theoretical concepts to support the institute´s chosen mission: 'To understand Earth's changing climate'. The MPI-M comprises two departments: The Atmosphere in the Earth System and The Ocean in the Earth System. We run an international PhD program together with the University of Hamburg and host independent research groups. The institute was founded in 1975 and is part of the Max Planck Society.

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Original publication

Measuring Area-Averaged Vertical Motions with Dropsondes

Stevens Bjorn and Bony Sandrine
Journal of the Atmospheric Sciences
Published in 2019

Sugar, Gravel, Fish, and Flowers: Mesoscale Cloud Patterns in the Tradewinds

others, Stevens Bjorn, Bony Sandrine, Brogniez Hélène, Hentgen Laureline, Hohenegger Cathy, Kiemle Christoph, L'Ecuyer Tristan S., Naumann Ann Kristin, Schulz Hauke and Siebesma Pier A.
Quarterly Journal of the Royal Meteorological Society
Published in 2019

Reading recommendations

EUREC4A: A Field Campaign to Elucidate the Couplings Between Clouds, Convection and Circulation

others, Stevens Bjorn, Bony Sandrine, Ament Felix, Bigorre Sebastien, Chazette Patrick, Crewell Susanne, Delanoë Julien, Emanuel Kerry, Farrell David and Flamant Cyrille
Surveys in Geophysics
Published in 2017

Prospects for Narrowing Bounds on Earth's Equilibrium Climate Sensitivity

Stevens Bjorn, Bony Sandrine, Sherwood Steven C. and Webb Mark J.
Earth's Future
Published in 2016

Clearing Clouds of Uncertainty

Webb Mark J., Zelinka Mark D., Randall David A. and Klein Stephen A.
Nature Climate Change
Published in 2017

The Barbados Cloud Observatory: Anchoring Investigations of Clouds and Circulation on the Edge of the ITCZ

others, Stevens Bjorn, Farrell David, Hirsch Lutz, Jansen Friedhelm, Nuijens Louise, Serikov Ilya, Brügmann Björn, Forde Marvin, Linne Holger and Lonitz Katrin
Bulletin of the American Meteorological Society
Published in 2016
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