### Abstract

Context. The cross-covariance of solar oscillations observed at pairs of points on the solar surface is a fundamental ingredient in time-distance helioseismology. Wave travel times are extracted from the cross-covariance function and are used to infer the physical conditions in the solar interior. Aims. Understanding the statistics of the two-point cross-covariance function is a necessary step towards optimizing the measurement of travel times. Methods. By modeling stochastic solar oscillations, we evaluate the variance of the cross-covariance function as function of time-lag and distance between the two points. Results. We show that the variance of the cross-covariance is independent of both time-lag and distance in the far field, that is, when they are large compared to the coherence scales of the solar oscillations. Conclusions. The constant noise level for the cross-covariance means that the signal-to-noise ratio for the cross-covariance is proportional to the amplitude of the expectation value of the cross-covariance. This observation is important for planning data analysis efforts.

Original language | English (US) |
---|---|

Article number | A41 |

Journal | Astronomy and Astrophysics |

Volume | 593 |

DOIs | |

State | Published - Sep 1 2016 |

### Fingerprint

### Keywords

- Methods: data analysis
- Sun: helioseismology
- Sun: oscillations

### ASJC Scopus subject areas

- Astronomy and Astrophysics
- Space and Planetary Science

### Cite this

*Astronomy and Astrophysics*,

*593*, [A41]. https://doi.org/10.1051/0004-6361/201628129

**Statistics of the two-point cross-covariance function of solar oscillations.** / Nagashima, Kaori; Sekii, Takashi; Gizon, Laurent; Birch, Aaron C.

Research output: Contribution to journal › Article

*Astronomy and Astrophysics*, vol. 593, A41. https://doi.org/10.1051/0004-6361/201628129

}

TY - JOUR

T1 - Statistics of the two-point cross-covariance function of solar oscillations

AU - Nagashima, Kaori

AU - Sekii, Takashi

AU - Gizon, Laurent

AU - Birch, Aaron C.

PY - 2016/9/1

Y1 - 2016/9/1

N2 - Context. The cross-covariance of solar oscillations observed at pairs of points on the solar surface is a fundamental ingredient in time-distance helioseismology. Wave travel times are extracted from the cross-covariance function and are used to infer the physical conditions in the solar interior. Aims. Understanding the statistics of the two-point cross-covariance function is a necessary step towards optimizing the measurement of travel times. Methods. By modeling stochastic solar oscillations, we evaluate the variance of the cross-covariance function as function of time-lag and distance between the two points. Results. We show that the variance of the cross-covariance is independent of both time-lag and distance in the far field, that is, when they are large compared to the coherence scales of the solar oscillations. Conclusions. The constant noise level for the cross-covariance means that the signal-to-noise ratio for the cross-covariance is proportional to the amplitude of the expectation value of the cross-covariance. This observation is important for planning data analysis efforts.

AB - Context. The cross-covariance of solar oscillations observed at pairs of points on the solar surface is a fundamental ingredient in time-distance helioseismology. Wave travel times are extracted from the cross-covariance function and are used to infer the physical conditions in the solar interior. Aims. Understanding the statistics of the two-point cross-covariance function is a necessary step towards optimizing the measurement of travel times. Methods. By modeling stochastic solar oscillations, we evaluate the variance of the cross-covariance function as function of time-lag and distance between the two points. Results. We show that the variance of the cross-covariance is independent of both time-lag and distance in the far field, that is, when they are large compared to the coherence scales of the solar oscillations. Conclusions. The constant noise level for the cross-covariance means that the signal-to-noise ratio for the cross-covariance is proportional to the amplitude of the expectation value of the cross-covariance. This observation is important for planning data analysis efforts.

KW - Methods: data analysis

KW - Sun: helioseismology

KW - Sun: oscillations

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U2 - 10.1051/0004-6361/201628129

DO - 10.1051/0004-6361/201628129

M3 - Article

VL - 593

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

SN - 0004-6361

M1 - A41

ER -