HAO 2010 PROFILES IN SCIENCE: Dr. Mausumi Dikpati

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dikpati@ucar.edu

dikpati@ucar.edu

Dr. Mausumi Dikpati is a Scientist III in the High Altitude Observatory of the National Center for Atmospheric Research. She received her PhD in 1996 from the Indian Institute of Science, Bangalore. She has been at NCAR since the fall of 1996 when she assumed a postdoctoral fellowship in the Advanced Study Program. Her main research interest is in modeling dynamics and MHD of the solar interior and the solar dynamo. Read More »

Professional Web Site(s): http://www.hao.ucar.edu/Public/about/Staff/dikpati/index.html

Impact of Changes in the Sun's Conveyor-belt on Recent Solar Cycles

The Sun goes thorough 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 communication 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 analysis of Mount Wilson Observatory data shows 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° latitude. Furthermore, from mass conservation the return flow was slower in cycle 23 than in previous cycles. Dikpati et al. (2010) used simulations to model how the solar plasma conveyor belt affects the solar cycle. It was found that the longer conveyor belt and the slower return flow during cycle 23 compared to that in cycle 22 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.

Acknowledgements: This work is partially supported by NASA's Living With a Star Program grant NNX08AQ34G.

Team: Mausumi Dikpati (HAO/NCAR), Peter Gilman (HAO/NCAR), Giuliana de Toma (HAO/NCAR), Roger Ulrich (UCLA).

The Sun's characteristic conveyor-belts during cycles 22 (left frame) and23 (middle frame), derived from surface observations and mass-conservation, are shown
Figure 1: The Sun's characteristic conveyor-belts during cycles 22 (left frame) and 23 (middle frame), derived from surface observations and mass-conservation, are shown. The speed associated with the colors is shown in the colorbar. The maximum surface flow-speeds at 25 degree latitude are almost the same in both the conveyor-belts, but the flow turning down towards the equator around 60° latitude during cycle 22 makes the length of the primary conveyor-belt shorter than that during cycle 23 in which flow went all the way to the pole before turning equatorward.
A two-dimensional map of dynamo cycle-period, obtained from the simulations of a flux-transport dynamo, as function of latitude-extent of primary meridional flow-cell and maximum poleward surface-flow speed. Thick continuous white line denotes the contour of an 11-year cycle-period
Figure 2: A two-dimensional map of dynamo cycle-period, obtained from the simulations of a flux-transport dynamo, as function of latitude-extent of primary meridional flow-cell and maximum poleward surface-flow speed. The thick continuous white line denotes the contour of an 11-year cycle-period. Thin white lines denote the contours of other periods in half-year intervals. The horizontal broken line marks the maximum surface-flow speed of 14 meters/sec. The positions of cycles 22 and 23 in this map are shown by semi-transparent gray patches.