Abstract
We extend an existing Born approximation method for calculating the linear sensitivity of helioseismic travel times to flows from Cartesian to spherical geometry. This development is necessary for using the Born approximation for inferring large-scale flows in the deep solar interior. As first sanity check, we compare two f-mode kernels from our spherical method and from an existing Cartesian method. The horizontal and total integrals agree to within 0.3%. As a second consistency test, we consider a uniformly rotating Sun and a travel distance of 42�. The analytical travel-time difference agrees with the forward-modeled travel-time difference to within 2%. In addition, we evaluate the impact of different choices of filter functions on the kernels for a meridional travel distance of 42�. For all filters, the sensitivity is found to be distributed over a large fraction of the convection zone. We show that the kernels depend on the filter function employed in the data analysis process. If modes of higher harmonic degree (90 ≲ l ≲ 170) are permitted, a noisy pattern of a spatial scale corresponding to l ≈ 260 appears near the surface. When mainly low-degree modes are used (l ≲ 70), the sensitivity is concentrated in the deepest regions and it visually resembles a ray-path-like structure. Among the different low-degree filters used, we find the kernel for phase-speed-filtered measurements to be best localized in depth.
| Original language | English (US) |
|---|---|
| Article number | 49 |
| Journal | Astrophysical Journal |
| Volume | 824 |
| Issue number | 1 |
| DOIs | |
| State | Published - Jun 10 2016 |
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Keywords
- scattering
- Sun: helioseismology
- Sun: interior
- Sun: oscillations
- waves
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science
Cite this
SENSITIVITY KERNELS for FLOWS in TIME-DISTANCE HELIOSEISMOLOGY : EXTENSION to SPHERICAL GEOMETRY. / B�ning, Vincent G.A.; Roth, Markus; Zima, Wolfgang; Birch, Aaron C.; Gizon, Laurent.
In: Astrophysical Journal, Vol. 824, No. 1, 49, 10.06.2016.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - SENSITIVITY KERNELS for FLOWS in TIME-DISTANCE HELIOSEISMOLOGY
T2 - EXTENSION to SPHERICAL GEOMETRY
AU - B�ning, Vincent G.A.
AU - Roth, Markus
AU - Zima, Wolfgang
AU - Birch, Aaron C.
AU - Gizon, Laurent
PY - 2016/6/10
Y1 - 2016/6/10
N2 - We extend an existing Born approximation method for calculating the linear sensitivity of helioseismic travel times to flows from Cartesian to spherical geometry. This development is necessary for using the Born approximation for inferring large-scale flows in the deep solar interior. As first sanity check, we compare two f-mode kernels from our spherical method and from an existing Cartesian method. The horizontal and total integrals agree to within 0.3%. As a second consistency test, we consider a uniformly rotating Sun and a travel distance of 42�. The analytical travel-time difference agrees with the forward-modeled travel-time difference to within 2%. In addition, we evaluate the impact of different choices of filter functions on the kernels for a meridional travel distance of 42�. For all filters, the sensitivity is found to be distributed over a large fraction of the convection zone. We show that the kernels depend on the filter function employed in the data analysis process. If modes of higher harmonic degree (90 ≲ l ≲ 170) are permitted, a noisy pattern of a spatial scale corresponding to l ≈ 260 appears near the surface. When mainly low-degree modes are used (l ≲ 70), the sensitivity is concentrated in the deepest regions and it visually resembles a ray-path-like structure. Among the different low-degree filters used, we find the kernel for phase-speed-filtered measurements to be best localized in depth.
AB - We extend an existing Born approximation method for calculating the linear sensitivity of helioseismic travel times to flows from Cartesian to spherical geometry. This development is necessary for using the Born approximation for inferring large-scale flows in the deep solar interior. As first sanity check, we compare two f-mode kernels from our spherical method and from an existing Cartesian method. The horizontal and total integrals agree to within 0.3%. As a second consistency test, we consider a uniformly rotating Sun and a travel distance of 42�. The analytical travel-time difference agrees with the forward-modeled travel-time difference to within 2%. In addition, we evaluate the impact of different choices of filter functions on the kernels for a meridional travel distance of 42�. For all filters, the sensitivity is found to be distributed over a large fraction of the convection zone. We show that the kernels depend on the filter function employed in the data analysis process. If modes of higher harmonic degree (90 ≲ l ≲ 170) are permitted, a noisy pattern of a spatial scale corresponding to l ≈ 260 appears near the surface. When mainly low-degree modes are used (l ≲ 70), the sensitivity is concentrated in the deepest regions and it visually resembles a ray-path-like structure. Among the different low-degree filters used, we find the kernel for phase-speed-filtered measurements to be best localized in depth.
KW - scattering
KW - Sun: helioseismology
KW - Sun: interior
KW - Sun: oscillations
KW - waves
UR - http://www.scopus.com/inward/record.url?scp=84976382138&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84976382138&partnerID=8YFLogxK
U2 - 10.3847/0004-637X/824/1/49
DO - 10.3847/0004-637X/824/1/49
M3 - Article
AN - SCOPUS:84976382138
VL - 824
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 1
M1 - 49
ER -