Time–Distance Helioseismology Data-Analysis Pipeline for Helioseismic and Magnetic Imager Onboard Solar Dynamics Observatory (SDO/HMI) and Its Initial Results

Abstract

The Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory (SDO/HMI) provides continuous full-disk observations of solar oscillations. We develop a data-analysis pipeline based on the time-distance helioseismology method to measure acoustic travel times using HMI Doppler-shift observations, and infer solar interior properties by inverting these measurements. The pipeline is used for routine production of near-real-time full-disk maps of subsurface wave-speed perturbations and horizontal flow velocities for depths ranging from 0 to 20 Mm, every eight hours. In addition, Carrington synoptic maps for the subsurface properties are made from these full-disk maps. The pipeline can also be used for selected target areas and time periods. We explain details of the pipeline organization and procedures, including processing of the HMI Doppler observations, measurements of the travel times, inversions, and constructions of the full-disk and synoptic maps. Some initial results from the pipeline, including full-disk flow maps, sunspot subsurface flow fields, and the interior rotation and meridional flow speeds, are presented.

Analysis of the Helioseismic Power-Spectrum Diagram of a Sunspot

“…Dopplergrams observed by HMI, primarily used for helioseismology studies as recently demonstrated by Zhao et al (2012), are used in this study. The sunspot located inside NOAA AR 11092 is selected for the k-ω power-spectrum analysis.…”

The Helioseismic and Magnetic Imager (HMI) Investigation for the Solar Dynamics Observatory (SDO)

“…Some of the aspects of the instrument and data-analysis pipeline required specific HMI developments and have been detailed in other associated articles. These include detailed discussions of the HMI image quality , the HMI filter characteristics , the instrumental polarization calibration , the vector-field inversion technique , and the time-distance helioseismology travel-time measurement methods , and the time-distance helioseismology processing pipeline (Zhao et al, 2011). The expectation is that there will be additional articles describing the actual on-orbit characteristics of data products.…”

“…Maps of sunspots and other targets, obtained with four-to eight-hour resolution for up to nine days continuously, with the time-distance method can be created on request as described in Zhao et al (2011). Specific active regions or other regions of interest can also be processed through the "rings" pipeline upon request.…”

Meridional Flow in the Solar Convection Zone. Ii. Helioseismic Inversions of Gong Data

“…Presumably, as mentioned above, this is due to an unknown artifact that trends in the CTL direction. After the subtraction of the E − W measurements from the S − N ones, which has been argued will correct for such a trend (Zhao et al 2012b), the S − N travel times show interesting behavior that suggests a signature of the equatorward return flow and possibly multiple cell structures. In the inversion analysis presented here we use the E − W corrected S − N travel-time differences from Paper I and revisit the systematic effect in the discussion section.…”

“…To correct for the center-to-limb (CTL) systematic effect as first presented in Zhao et al (2012b), an identical measurement procedure was carried out to obtain east minus west (E − W) travel-time differences. Essentially, we simply rotate the Doppler images by 90°and use the same data-analysis pipeline.…”