Simulation of Wave Fields to Assess the Sensitivity of Ring-Diagram Analyses to Shearing Flows
Abstract
Ring-diagram analyses of acoustic-wave distortion by flows map horizontal motions within the solar convection beneath the localized regions where the observations are taken. To leading order, the flow field responsible for the advection of waves is taken to be horizontally uniform across the region. Current ring-diagram analyses are only carried out to this order, although in reality the flow is likely to vary across the local patch of the Sun. It is crucial for the interpretation of the results of ring-diagram analyses that the effects of shearing flows be assessed. Furthermore, the present analyses ignore any influence on the ring parameters of flows exterior to the region being studied. We present a progress report on the forward calculation of the modification of ring parameters produced by spatially varying flow fields. We examine effects of flow fields both inside and outside the region of observation. Additionally, we assess the influence of the non-uniform flow on the maps of the velocity field obtained by inverting the ring-parameter data. The effect of the inhomogeneous flow can be studied as a scattering problem. We have developed Green functions connecting an underlying inhomogeneous horizontal flow to the scattered wave field that results when an incident plane wave encounters the flow. By considering an ensemble of such incident waves, ring parameters can be inferred from the wave field. One application is to analyze artificial data sets, computed from models that contain horizontal shear flows. The scattered wave field produced by a prescribed 3-D shearing flow is computed, and the original and scattered wave fields are combined to generate an artificial helioseismic data set. The artificial data so produced should then be passed through a ring-diagram analysis and the deduced velocity field compared to the known imposed flow. Another application is to compute 3-D kernels relating the ring parameters to the underlying flow: these will in the future permit 3-D inversions for the flows within the solar convection zone, using mosaics of many ring-diagram samplings.
- Publication:
-
SOHO-9 Workshop on Helioseismic Diagnostics of Solar Convection and Activity
- Pub Date:
- 1999
- Bibcode:
- 1999soho....9E..64H