Helioseismic observations from my HMI (Helioseismic and Magnetic Imager) instrument revealed that meridional circulation in the solar interior has a double-cell structure with an equatorward flow located in the middle of the convection zone about 60,000 miles beneath the visible surface of the Sun. Meridional circulation, which transports solar materials between low and high latitudes inside the Sun, is a fundamental property of the Sun, but was poorly known. It is widely believed that the circulation plays an important role in redistributing solar angular momentum and transporting magnetic flux, setting up 11-year solar activity cycles. Previously it was thought that the circulation had a single-cell structure with a poleward flow near the surface and an equatorward flow located near the bottom of the convection zone. Through analyzing the unprecedented high-quality helioseismic data obtained fromHMI by using a helioseismic analysis technique called time-distance helioseismology, the solar physicists found that the solar meridional currents have at least two circulation cells in each hemisphere, with an equatorward flow located between about 40,000 and 80,000 miles below the surface. That is, the equatorward flow is roughly in the middle of the convection zone. This result provides a new insight into the dynamics of the solar interior hidden from direct observations, and requires a reexamination of the theories of solar magnetic cycles. Credit: NASA SDO / Stanford HMI

• published: 29 Aug 2013
• views: 448