The Sun goes through cycles lasting approximately 11 years that include phases with increased magnetic activity, more sunspots, and more solar flares, and phases with less activity. The level of activity on the Sun can affect navigation and communications systems on Earth. Puzzlingly, solar cycle 23, which ended recently, lasted longer than previous cycles, with a prolonged phase of low activity that scientists had difficulty explaining.

A new analysis suggests that one reason for the long cycle could be changes in the Sun’s conveyor belt. Just as Earth’s global ocean circulation transports water and heat around the planet, the Sun has a conveyor belt in which plasma flows along the surface toward the poles, sinks, and returns toward the equator, transporting magnetic flux along the way. Recent measurements show that in solar cycle 23, the poleward flow extended all the way to the poles, while in previous solar cycles the flow turned back toward the equator at about 60 degrees latitude. Furthermore, from mass conservation, the return flow was slower in cycle 23 than in previous cycles.

Dikpati et al. use simulations to model how the solar plasma conveyor belt affects the solar cycle. The authors find that the longer conveyor belt and the slower return flow could have caused the longer duration of cycle 23. The results should help scientists better understand the factors controlling the timing of the solar cycles and could lead to better predictions.


Title: Impact of changes in the Sun’s conveyor-belt on recent solar cycles

Authors: Mausumi Dikpati, Peter A. Gilman, and Giuliana De Toma: High Altitude Observatory, National Center for Atmospheric Research, Boulder, Colorado, USA; Roger K. Ulrich: Department of Physics and Astronomy, University of California at Los Angeles, Los Angeles, California, USA.

Source: Geophysical Research Letters (GRL) paper 10.1029/2010GL044143, 2010,