Plan A:Helioseismology
Requirements
Laurent Gizon
Max Planck Institute for Solar System Research
Katlenburg-Lindau, Germany

Outline
The key scientific questions addressed by Plan A andhelioseismology have been presented.
In short, we need to measure flows and otherinhomogeneities deep in the convection zone and athigh latitudes (unknown territory).
Topics:1. Measurable flows
2. How large should the inclination of the orbit be?
3. Stereoscopic helioseismology
4. Telemetry rate?
5. Some other basic requirements for helioseismology

MDI medium-l data (256x256 pixels)
One local helioseismology measurement every 3 months

Latitude (deg)Latitude (deg)Random noise ~1-2 m/s, systematic errors <?
Zonal flow residuals

Meridional flow residuals

Plots of residuals ofrotation and meridional
circulation after
subtraction of a longterm average.
About 50 Mm deep.
Valid up to 50 deg
latitude. Beck et al.
(2002) find +/- 5 m/s
temporal changes.
High latitudes??

Year (19962002)

MDI medium-lGizon et al. 2005

Detectable flow in one monthof observations using
deep focusing time-distance
helioseismology(10 x 12 deg^2 resolution)

How inclined should the orbit be?
Inclination is needed
1.To beat foreshortening, projection effects, andconvection noise. 30 deg.
2.To probe the deep convection zone in thepolar regions. Prolate tachocline? 45/2 deg.
(Less stringent requirement from T. Sekii.)

30 + 45/2 = 45 + 7.5 deg
Inclination wrt Ecliptic > 45 deg

Dopplergram

Frequency (mHz)(30min avg)

P modes

Foreshortening
LOS projection

SOHO/MDI pixel number (along equator)
Supergranulation
noise

MDI velocity POWER

P mode power

S/N=2Background noise60
ANGLE from center of disk (deg)Several vantage points:‘Stereoscopic’ helioseismology• SDO/HMI, Solar Orbiter, GONG
• Out-of-Ecliptic views and/or large Earth-Sun-S/C angles• New possibilities for helioseismology
Non-overlapping regions:Global helioseismology: At high frequencies, spatial leaks are reduced whatever the degree.
Error reduction for certain mode frequencies. At low frequencies, SNR is the issue, not theleaks.
Local helioseismology: A new game! New single-skip ray paths can be considered, even raypaths that go through the core. Regions on the Sun can be tracked over a longer time.
Noise reduction for larger target depths.
Same region seen from two or several viewing angles:
Reduction of random noise.
In principle, with three observations of the los Doppler velocity, it should be possible toreconstruct the velocity vector. Since oscillations and convection have different
geometrical properties, it may be possible to partially decoupled the two. This may lead toa large increase in the oscillation S/N at low frequencies (can be tested using numericalsimulations). Implications for g-mode searches?

SOLAR C
Solar Orbiter

SDO/HMIGONG

Solar Orbiter

Sun-S/C-Earth Angle(not the latest plan)

SO orbit inclination:
progressively increases to 37 deg at
the end of the extended mission.
Sun-S/C distance varies a lot.

The choice of orbit is very important:•High inclination to the Ecliptic (>45 deg) during
at least one/two months per orbit for severalorbits.
• Launch time (overlap with SDO and SO, andsome observations near solar minimum).
•Smoothly varying S/C-Sun distance.
•Large S/C-Sun-Earth angles if possible…

Object

Spatial resolution *Observation timeCore~0.01 R

As much as possible

Meridional circulation,rotation~0.01 R

Months to years

Tachocline **(flows 20-100 m/s)

~0.01 Ryears

Farside calibration **~0.01 Rmonths to years

High resolution local
helioseismology

0.002 R

days to weeks*A resolution of 0.01 R means a pixel spacing of 0.005 R = 3 Mm  512^2 pixels** Courtesy of C. Lindsey
256x256 pixels may be enoughA lot more than helioseismology can bedone with high-resolution Dopplergrams
Flows can be measured from direct
Doppler measurements, and from themotion of supergranules or small
magnetic features.
And much much more.
Requires high resolution, but not at full
temporal cadence.
Thus it is useful to have a big CCD andto also transmit high-resolution images
at low cadence.
MDI Doppler image showing
view of South pole

Basic requirements for helioseismology•

Observables:– LOS velocity (or possibly intensity for several lines)– LOS magnetic field, continuum intensity•

Field of view: full disk••

Camera: say 2000^2 pixels
Cadence and spatial resolution:– 60 sec for LOS velocity images ‘binned’ down to 512^2 pixels– Less often (every hour?), V, B and I at full resolution•Data coverage:– As long as possible (years)– As continuous as possible (>90% duty cycle)•Telemetry >20 kb/s, all the time.
(12 b)*512^2/(4/pi)/(60 s)/2.2=18.7 kb/s
12 kb/s if only Fourier coefficients of interest+ telemetry for high-resolution low-cadence images.

••

Clock precision and image stabilisation system must be
excellent for stereoscopy.
Orbit inclination >45 deg