HMI: First results

TL;DR

This paper presents initial results from the Helioseismic and Magnetic Imager (HMI), detailing data acquisition, calibration, inversion techniques to analyze the Sun's magnetic field, and comparisons with Hinode SP data.

Contribution

It introduces the first results from HMI, describing the data processing, inversion methods, and initial validation against Hinode spectro-polarimeter observations.

Findings

HMI provides high-cadence, full-disk solar magnetic data.

The VFISV inversion code effectively infers magnetic field topology.

Initial cross-comparison shows consistency with Hinode SP data.

Abstract

The Helioseismic and Magnetic Imager (HMI) has just started producing data that will help determine what the sources and mechanisms of variability in the Sun's interior are. The instrument measures the Doppler shift and the polarization of the Fe I 6173 A line, on the entire solar disk at a relatively-high cadence, in order to study the oscillations and the evolution of the full vector magnetic field of the solar Photosphere. After the data are properly calibrated, they are given to a Milne-Eddington inversion code (VFISV, Borrero et al. 2010) whose purpose is to infer certain aspects of the physical conditions in the Sun's Photosphere, such as the full 3-D topology of the magnetic field and the line-of-sight velocity at the solar surface. We will briefly describe the characteristics of the inversion code, its advantages and limitations --both in the context of the model atmosphere and the actual nature of the data--, and other aspects of its performance on such a remarkable data load. Also, a cross-comparison with near-simultaneous maps from the Spectro-Polarimeter (SP) onboard Hinode will be made.