Continuous Subsurface Flow Measurements for Solar Cycle 23 from MDI Spherical Harmonic Time Series
Abstract
Subsurface flows play an important role in the flux-transport dynamo models. In particular, the transport of surface poloidal magnetic field to the bottom of the convection zone is governed by the meridional circulation, where the poloidal field is converted into a toroidal field by rotational shear. The past two decades have witnessed rapid advancements in measuring the subsurface flow patterns due to the availability of high-resolution observations from space and ground-based observatories. However, continuous measurement of meridional flow for the entire solar cycle 23 is not available due to the limited high-resolution observations from Michelson Doppler Imager (MDI) instrument on board Solar and Heliospheric Observatory (SoHO). Here we report on a novel method that combines two methods; the image reconstruction from spherical harmonic time series, and the local helioseismic technique of ring diagrams, to produce zonal and meridional flow measurements from May 1996 to December 2010 up to a depth of 40 Mm below the surface. In addition to the temporal variation of the meridional flow, where the flow is faster at solar cycle minimum and slower at maximum, we find several interesting features notably that the meridional flows have a strong depth dependence that differs during the solar minimum and maximum phases. We also find that the meridional flows in the activity belt differs from the flows at higher latitude around 20 Mm below the surface.
This work is partially funded by NASA grants NNH18ZDA0001N-HDEE and NNH18ZDA001N-LWS.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMSH007..06T
- Keywords:
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- 7522 Helioseismology;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY;
- 7524 Magnetic fields;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY;
- 7536 Solar activity cycle;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY;
- 7924 Forecasting;
- SPACE WEATHER