Investigation Overview, Scherrer, Page 1SDO Science Writers Workshop – 16 Dec 2009 HMI...

Investigation Overview, Scherrer, SDO Science Writers Workshop – 16 Dec 2009

HMI Investigation Overview

Philip Scherrer

HMI Principal Investigator

[email protected]

This presentation available at

http://hmi.stanford.edu/Presentations


HMI Investigation Overview – Outline

•Investigation Overview

•Science Objectives

•How HMI works

•Helioseismology – What is it?

•Data Products and Objectives

•Inside HMI

•Data Center

•Science Team

•Web Links


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 measures of the motion of the solar photosphere to study solar oscillations

and

HMI measures the polarization in a spectral line to obtain all three components of the photospheric magnetic field.

Investigation Overview - 1



The basic HMI measurements are “filtergrams” – images of the Sun’s photosphere made through a very narrow-band filter tunable to a set of six specific wavelengths across one spectral line.

The raw observations must be processed into higher level data products before analysis can proceed.

HMI produces data products suitable to determine the interior sources and mechanisms of solar variability and how the physical processes inside the Sun are related to surface magnetic field and activity.

It also produces data products to enable estimates of the low and far coronal magnetic field for studies of variability in the extended solar atmosphere.



HMI observations will enable establishing the relationships between the internal dynamics and magnetic activity. This is a prerequisite to understanding possible physics-based solar activity forecasts.

Active participation of the HMI Team in collaboration with the other SDO instrument teams and the LWS community is necessary to achieve the HMI science goals.

HMI data and results will be made available to the scientific community and the public at large through data export, publications, and an Education and Public Outreach program.


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?

HMI Science Objectives


HMI consists of a telescope, tunable filter, camera, and necessary electronics.

HMI images the Sun in four polarizations at six 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 measurements are needed to use the techniques of helioseismology.

HMI – How It Works

6169 6172 6175 6178

Measure Here


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 fields” four states of linear and circular polarization are needed to infer the field strength and direction.

Magnetic Field Sample Profile

HMI measures magnetic fields by sampling the Zeeman split line in multiple polarizations.

The figure shows the six sample positions and polarized spectral components for a 3000G field as found in sunspot umbra.


Helioseismology – What Is It?

These waves are refracted upward by the temperature gradient and reflected inward by the drop in density at the surface

The travel times of these waves depends on the temperature, composition, motion, and magnetic fields in the interior.

The visible surface moves when the waves are reflected enabling their frequency, phase, and amplitude to be measured.

Analysis of travel times over a multitude of paths enables inference of internal conditions.

Helioseismology is the study of solar interior structure and dynamics by analysis of the propagation of waves through the Sun’s interior.

The Sun is filled with acoustic waves with periods near five minutes.


Helioseismology - 2

The wave reflections result in oscillations of the surface.

These motions are a few hundred m/s and are superimposed on the 1500 m/s granulation, 400 m/s supergranulation, 2000 m/s solar rotation and 3500 m/s SDO orbit.

The dynamic range of HMI must accommodate all these motions in addition to the line splitting equivalent to 3000 m/s from sunspot magnetic fields.

Measurements must be often enough to resolve the oscillations (c. 45 seconds).

Sequences must be long enough to resolve phase and frequency yet short enough to sample the evolving structures.


Time-Distance Helioseismology Example

Waves going in all directions are reflected at each point on the surface.

Cross-correlations of the time series observed at pairs of points (A,B) reveal the integrated travel-time along the interior path that “connects” A with B.

Differences between the A→B and B→A directions arise from bulk motion along the path.

Analyses of travel-time maps provide maps of flows and temperatures beneath the surface.


Vector Magnetic Field

Traditional solar magnetic measurements provide only the line-of-sight magnetic flux.

Experience has shown that the full vector field is necessary to understand the connectivity in and between active regions.

Inversions of polarization measurements provide all three components of the field as well as the filling-factor of the unresolved magnetic elements.

Long sequences of vector field data have yet to be measured.

We expect to learn a lot.


Solar Domain of HMI Helioseismology

2

3

4

5

6

7

Sun

Log

Siz

e (k

m)

Zonal flow

AR

spot

SG

dynamo

P-m

odes

Tim

e-D

ista

nce

Rin

gs

Glo

bal H

S1 2 3 4 5 6 7 8 9

min

5min

hour

day

rota

tion

year

cycl

e

Log Time (s)

10

polar field

Earth

HMI resolution

granule


A. Sound speed variations relative to a standard solar model.

B. Solar cycle variations in the sub-photospheric rotation rate.

C. Solar meridional circulation and differential rotation.

D. Sunspots and plage contribute to solar irradiance variation.

E. MHD model of the magnetic structure of the corona.

F. Synoptic map of the subsurface flows at a depth of 7 Mm.

G. EIT image and magnetic field lines computed from the photospheric field.

H. Active regions on the far side of the sun detected with helioseismology.

I. Vector field image showing the magnetic connectivity in sunspots.

J. Sound speed variations and flows in an emerging active region.

B – Rotation VariationsC – 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

HMI Data Product Examples


1. Convection-zone dynamics and solar dynamo– Structure and dynamics of the tachocline– Variations in differential rotation.– Evolution of meridional circulation.– Dynamics in the near-surface shear layer.

2. Origin and evolution of sunspots, active regions and complexes of activity– Formation and deep structure of magnetic complexes.– Active region source and evolution.– Magnetic flux concentration in sunspots.– Sources and mechanisms of solar irradiance variations.

3. Sources and drivers of solar activity and disturbances– Origin and dynamics of magnetic sheared structures and delta-type sunspots.– Magnetic configuration and mechanisms of solar flares and CME.– Emergence of magnetic flux and solar transient events.– Evolution of small-scale structures and magnetic carpet.

4. Links between the internal processes and dynamics of the corona and heliosphere– Complexity and energetics of solar corona.– Large-scale coronal field estimates.– Coronal magnetic structure and solar wind

5. Precursors of solar disturbances for space-weather forecasts– Far-side imaging and activity index.– Predicting emergence of active regions by helioseismic imaging.– Determination of magnetic cloud Bs events.

Primary Science Objectives


HMI Data Products and Objectives

Magnetic Shear

Tachocline

Differential Rotation

Meridional Circulation

Near-Surface Shear Layer

Activity Complexes

Active Regions

Sunspots

Irradiance Variations

Flare Magnetic Configuration

Flux Emergence

Magnetic Carpet

Coronal energetics

Large-scale Coronal Fields

Solar Wind

Far-side Activity Evolution

Predicting A-R Emergence

IMF Bs Events

Brightness Images

Global Helioseismology

Processing

Local Helioseismology

Processing

Version 1.0w

Filtergrams

Line-of-sightMagnetograms

Vector Magnetograms

DopplerVelocity

ContinuumBrightness

Line-of-SightMagnetic Field Maps

Coronal magneticField Extrapolations

Coronal andSolar 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

maps (0-30Mm)

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 MagneticField Maps

Science ObjectiveData ProductProcessing

Observables

HMI Data


Instrument Overview – Optical Path

Optical Characteristics:Focal Length: 495 cmFocal Ration: f/35.2Final Image Scale: 24m/arc-sec

Filter Characteristics:Central Wave Length: 613.7 nmBandwidth: 0.0076 nmTunable Range: 0.05 nmFree Spectral Range: 0.0688 nm

Camera Characteristics:Format: 4096x4096 pixelsPixels: 12Exposure: 150msRead time: 2-sec


HMI Optics Package

OP Structure

Telescope

Front Window

Front Door

Vents

Support Legs (6)

Polarization Selector

Focus/Calibration Wheels

Active Mirror

Limb B/S

Alignment Mech

Oven Structure

Michelson Interf.

Lyot Filter

Shutters

Connector Panel

CameraElectronics

CCD Detector(Vector)

Fold MirrorFocal Plane B/S

Mechanical Characteristics:Box: 0.84 x 0.55 x 0.16 mOver All: 1.19 x 0.83 x 0.29 mMass: 39.25 kg

YX

CCD Detector(Doppler)

Limb Sensor

Z


HMI – Inside the Box

HMI will obtain 32 16-megapixel images each minute


HMI Optics Package

HMI Electronics Box

SDO Spacecraft - HMI Components

Investigation Overview, Scherrer, Page 22SDO Science Writers Workshop – 16 Dec 2009

HMI/AIA JSOC - (Joint Science & Operations Center)

•Data Capture from SDO ground system•Archive of telemetry and processed data•Distribution to team and exports to all users•HMI and AIA processing to “level-1”•HMI higher level science data products

•Expect to archive ~ 1000TB/yr•Metadata stored in PostgreSQL database•Image data is stored online and on tape (LTO-4)•“Pipeline” processing system to generate standard products•Special products computed automatically “on demand”


HMI Co-Investigator Science Team


HMI web page:

http://hmi.stanford.edu

This presentation available at:

http://hmi.stanford.edu/Presentations

Data access:

http://jsoc.stanford.edu

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