Deeply Penetrating Banded Zonal Flows in the Solar Convection Zone

Solar rotation patterns have been studied extensively using surface observations. Doppler measurements show bands of varying rotation rates moving toward the equator. These are called torsional oscillations. Prior research has shown they exist near the solar surface. However, their depth and extent below the surface remain unclear. This gap motivated deeper investigation into the solar convection zone. Helioseismology provides a way to probe subsurface structures. The convection zone is about 200 Mm deep, but little is known about the flow patterns within. This study aimed to determine how deep these bands of rotation extend.

The goal was to determine whether torsional oscillations are a surface-only phenomenon or extend deeper. The researchers wanted to assess the depth of these banded flows. They used helioseismic data to investigate the solar convection zone. The study focused on a 4-year period of observations. The aim was to map the vertical extent of the banded flows. Understanding this could improve models of solar dynamics. The researchers sought to confirm the presence of these flows at depth. Their work aimed to provide a clearer picture of solar internal rotation.

The team used helioseismic data from the GONG network and the MDI instrument on SOHO. They analyzed data collected over a 4-year span. The methods involved measuring rotation rate variations below the solar surface. The data was processed to identify patterns of banded flows. The researchers compared results from two independent instruments. This approach helped confirm the consistency of their findings. They focused on the depth range of the convection zone. The study used complementary observations to enhance accuracy.

The banded flows extend downward at least 60 Mm into the solar interior. This depth is approximately 8% of the total solar radius. The flows are not confined to the surface but penetrate deeply. The results show the flows are present over a significant portion of the convection zone. The convection zone is about 200 Mm deep, and the flows cover a large fraction of this. The data from both GONG and MDI instruments supported this finding. The equatorward motion of the bands was confirmed at depth. These results suggest the flows are a subsurface phenomenon.

The study confirms that torsional oscillations extend well below the solar surface. The banded flows are not limited to the surface but reach at least 60 Mm deep. This finding challenges the assumption that these flows are surface-only. The results suggest the flows are a significant feature of the convection zone. The data from two independent instruments supports this conclusion. The study provides new insights into solar internal dynamics. The findings may influence future models of solar rotation. The authors emphasize the importance of helioseismology in probing the solar interior.