1. HMI Science Investigation Overview
Philip Scherrer
HMI Principal Investigator

2. HMI Science Investigation Overview – Agenda
HMI – Investigation Overview - What HMI measures and why.
Investigation Overview
HMI Team and Institutional Roles
Data Product Examples
Science Objectives
Data Products and Objectives
How HMI works at the topmost level
HMI-AIA JSOC Overview
HMI Instrument Requirements

3. Investigation Overview
The primary goal of the Helioseismic and Magnetic Imager (HMI) investigation is to study the origin of solar variability and to characterize and understand the Sun’s interior and the various components of magnetic activity.
HMI makes measurements of the motion of the solar photosphere to study solar oscillations in order to determine the interior sources and mechanisms of solar variability
It also makes measurements of the photospheric magnetic field in order to study how the physical processes inside the Sun are related to surface magnetic field and to enable estimates of the low and far coronal magnetic field for studies of variability in the extended solar atmosphere.

4. HMI Institutional Roles
HMI Instrument
HMI & AIA JSOC
HMI Science Team
SDO Science
LWS Science
HMI
E/PO
Stanford
LMSAL
The HMI Science Team includes 30 Co-Investigators and many Associate Investigators at 21 institutions in the US and abroad

5. HMI Science Objectives – Top Level
HMI science objectives are grouped into five broad categories:
Convection-zone dynamics and the solar dynamo;
How does the solar cycle work?
Origin and evolution of sunspots, active regions and complexes of activity;
What drives the evolution of spots and active regions?
Sources and drivers of solar activity and disturbances;
How and why is magnetic complexity expressed as activity?
Links between the internal processes and dynamics of the corona and
heliosphere;
What are the large scale links between the important domains?
Precursors of solar disturbances for space-weather forecasts.
What are the prospects for predictions?
These objectives are divided into 18 sub-objectives each of which needs data from multiple HMI data products.
Progress requires a science team with experience in multiple disciplines.

6. HMI Data Product Examples
B – Rotation Variations
C – Global Circulation
D – Irradiance Sources
H – Far-side Imaging
F – Solar Subsurface Weather
E – Coronal Magnetic Field
I – Magnetic Connectivity
J – Subsurface flows
G – Magnetic Fields
A – Interior Structure
Sound speed variations relative to a standard solar model.
Solar cycle variations in the sub-photospheric rotation rate.
Solar meridional circulation and differential rotation.
Sunspots and plage contribute to solar irradiance variation.
MHD model of the magnetic structure of the corona.
Synoptic map of the subsurface flows at a depth of 7 Mm.
EIT image and magnetic field lines computed from the photospheric field.
Active regions on the far side of the sun detected with helioseismology.
Vector field image showing the magnetic connectivity in sunspots.
Sound speed variations and flows in an emerging active region.

7. HMI Data Products and Objectives
Global
Helioseismology
Processing
Local
Filtergrams
Line-of-sight
Magnetograms
Vector
Doppler
Velocity
Continuum
Brightness
Brightness Images
Line-of-Sight
Magnetic Field Maps
Coronal magnetic
Field Extrapolations
Coronal and
Solar wind models
Far-side activity index
Deep-focus v and cs
maps (0-200Mm)
High-resolution v and cs
maps (0-30Mm)
Carrington synoptic v and cs
Full-disk velocity, v(r,Θ,Φ),
And sound speed, cs(r,Θ,Φ),
Maps (0-30Mm)
Internal sound speed,
cs(r,Θ) (0<r<R)
Internal rotation Ω(r,Θ)
(0<r<R)
Vector Magnetic
Field Maps
Tachocline
Differential Rotation
Meridional Circulation
Near-Surface Shear Layer
Activity Complexes
Active Regions
Sunspots
Irradiance Variations
Magnetic Shear
Flare Magnetic Config.
Flux Emergence
Magnetic Carpet
Coronal energetics
Large-scale Coronal Fields
Solar Wind
Far-side Activity Evolution
Predicting A-R Emergence
IMF Bs Events
Science Objective
Data Product
Observables
HMI Data
Version 1.0

8. HMI-AIA Joint Science Operations Center
HMI and AIA SOCs have been merged to form a JSOC
Components of the JSOC will be at both Stanford and Lockheed-Martin Solar and Astrophysics Lab (LMSAL)
JSOC-Ops for both HMI and AIA at LMSAL
Data capture, pipeline processing, online archive, tape archive, export functions at Stanford.
HMI Higher level processing at Stanford
AIA Higher level processing at LMSAL
High-speed network connection between the two sites
The JSOC will be discussed in more detail as part of both the SDO CDR and the SDO ground system CDR next year

9. HMI & AIA JSOC Architecture
Catalog
Primary Archive
HMI & AIA
Operations
House-
keeping
Database
MOC
DDS
Redundant Data Capture System
30-Day
Archive
Offsite
Offline
HMI-AIA JSOC Pipeline Processing System
Data
Export
& Web
Service
Stanford
LMSAL
High-Level
Data Import
AIA Analysis
System
Local Archive
Quicklook
Viewing
housekeeping
GSFC
White Sands
World
Science Team
Forecast Centers
EPO
Public

10. Schematic Diagram of HMI
Telescope with polarization analysis
Tunable narrow band filter
Camera system
SDO
MOC
DDS
Computers
Electronics to make it work
Science Investigation
Science Team, NASA, Taxpayers

11. HMI – How It Works
Measure Here
HMI consists of a telescope, tunable filter, camera, and necessary electronics.
HMI repeatedly images the Sun in six polarizations at five wavelengths across a spectral line.
The position of the line tells us the velocity while the shape changes of the line in different polarizations tell us the magnetic field direction and strength in the part of the Sun’s surface seen by each pixel.
Long gap-free sequences of velocity images are needed to enable the techniques of helioseismology.

12. Magnetic Field Sample Profile
HMI measures magnetic fields by sampling the Zeeman split line in multiple polarizations.
The figure shows the five sample positions for a sunspot umbral field (about 3000G) with a 1000 m/s offset.
The green and red curves are Left and Right circular polarized components and allow measurement of the line-of-sight projection of the field.
Analysis of both polarizations is required to infer the Doppler velocity and line-of-sight magnetic flux.
For vector magnetic fields two directions of linear polarization are added to infer the field direction.
One HMI camera is used for velocity and LOS field, the other for vector fields.

13. Sample Dopplergram from SOHO/MDI
MDI velocity image, dark is motion toward the observer, bright is motion away.

14. Sample Dopplergrams from SOHO/MDI
5 hours of MDI Dopplergrams with solar rotation removed

15. Basic Requirements Sources
SDO Level 1 Requirements
SDO Mission Requirements Document (MRD)
Summary of spacecraft and instrument driving requirements
HMI Instrument Functional Specification
Top level instrument requirements – part of the HMI contract statement of work
HMI Instrument Performance Document (IPD)
Detailed HMI science drivers and flowdown to subsystem requirements
HMI Performance Assurance and Implementation Plan (PAIP)
HMI implementation of the SDO Mission Assurance Requirements
HMI to Spacecraft Interface Control Documents (HMI-S/C ICD)
Ground System Interface Control Documents

16. HMI “Level 1” Requirements
To enable accomplishment of the science objectives of the investigation, the HMI instrument will produce measurements in the form of filtergrams in a set of polarizations and spectral line positions at a regular cadence for the duration of the mission that meet these basic requirements:
Full-disk Doppler velocity and line-of-sight magnetic flux images with arc-sec resolution at least every 50 seconds.
Full-disk vector magnetic images of the solar magnetic field with arc-sec resolution at least every 10 minutes.
The HMI data completeness and continuity requirement is to capture 99% of the HMI science observables 95% of the time.

17. Source of HMI Requirements
HMI Science Objectives
Duration of mission
Completeness of coverage
HMI Science Data Products
Roll accuracy
Time accuracy (months)
HMI Observation Sequences
Duration of sequence
Cadence
Completeness data sequence
Noise
Resolution
Time accuracy (days)
HMI Observables
Sensitivity
Linearity
Acceptable measurement noise
Image stability
Time rate (minutes)
Orbit knowledge
HMI Instrument Data
Accuracy
Noise levels
Completeness of filtergrams
Tuning & shutter repeatability
Wavelength knowledge
Image registration
Image orientation jitter
HMI Instrument
Mass
Power
Telemetry
Envelope
Subsystem requirements
CCD: Thermal environment
ISS: pointing drift rate, jitter
Legs: pointing drift range

18. HMI Performance Requirements Summary

19. Summary of Observables Requirements
These are the requirements on the HMI Observables as derived from the HMI science goals. Some of these were included in the SDO MRD.
These imply further requirements on the filtergrams which are the raw data obtained with HMI.
The filtergram requirements in turn impose requirements on the various subsystems.

20. Summary of Filtergram Requirements

21. Summary of Subsystem Requirements
Subsystem requirements for mechanisms (above) and other systems (right). The details are found in the HMI Instrument Performance Document (IPD)