Elementary Atmospheric
Structures and Coronal
Properties
byGeorge Doschek
Presented at the Second Solar-C
Science Definition Meeting
JAXA/ISAS, Japan
9-12 March 2010

Some Plan B Observation and Science Goals•

Fundamental observation goal: trace the flow of energy that powers
solar activity and the solar wind as it propagates from thephotosphere, through the chromosphere and transition region, andinto the corona with objectives such as:– Determine unambiguously the source(s) of coronal heating– Understand the physics of the initiation mechanism of coronal massejections– Observe in detail the physics of magnetic reconnection in initiating solar
flares and its importance in active region heating– Observe the propagation of energy via waves and transient phenomena
from the chromosphere/transition region into the corona and its role indetermining coronal heating and structure– Determine the origin of the slow and fast solar wind•

Science approach: High spatial (0.1-0.3”), spectral (40-60 mÅ), andtemporal (<10s) resolution imaging and spectroscopic observations,covering a temperature range from about 1x104 K (e.g., O I, He I) to20x106 K (e.g., Fe XXIV, Fe XXV).

Key Instrument Characteristics for Tracing the Flow ofEnergy•

Matched spatial resolution from the photosphere into thecorona– Structures and activity in the corona cannot be unambiguously
traced from the corona to possible origins in the photospherewithout matched spatial resolution.

•Continuous temperature coverage (no missing temperatures!)from the photosphere into the corona, including flaretemperatures– Plasma must not be allowed to “escape” observation by heating or
cooling into an unobservable temperature range.
– There must be no ambiguity in temperature determinations (hightemperature resolution is necessary).

•

Ability to measure dynamical properties of plasma (flows,turbulence) over a wide temperature range– Plasma energetics cannot be unambiguously determined without
dynamical measurements.

•No current mission or combination of current missions has allof the above characteristics

Unveiling the Microphysics of the Solar Corona•Particle acceleration•Magnetic reconnection•Ion-cyclotron wave heating•Turbulent cascades•Non-Maxwellian distributions
SOHO/EIT: 2.6” pixels

Seeing the microphysics requires
high spatial and spectral resolution
coupled observations from thephotosphere into the corona

TRACE: 0.5” pixels

5,800 km

Hinode/EIS: 1” pixels

Yohkoh: 2.45” pixels

Elementary heating eventin a polar coronal hole.
This event is clearlyunresolved at ~EIS/TRACE spatial resolution.

TRACE: 0.5” pixels

Plan B Solar-C: 0.1” – 0.3” spatial
resolution will provide an exact
match from the photosphere into
the corona, thus allowing resolutionof elementary heating events andtraceability of footpoint mechanicalenergy into the coronal magnetic
field and into consequent plasmaheating.

coldcoronal holehotsolar limb
coronal holeflare
solar coronahigh density

low density

Unveiling the Microphysics of the Solar Chromosphere/Transition Region•The chromosphere/transition region (CTR) is the interface/connectivity between the corona andthe source of its energy, i.e., the photosphere•The CTR is spatially unresolved with present instrumentation (1.0” at best, with no spectroscopy•The CTR is the site of complex dynamics including heating, waves, and bulk plasma motions•Spectroscopy of the CTR (filling factors/opacity) indicate scale lengths of 70 – 200 km (0.1” – 0.3”)

SUMER spectra showingthat at 2” resolutiondifferent CTR regions
are indistinguishable

S VI 933 Å
200,000 K

H I Ly-ε 937 Å
10,000 K

H I Lyman-α images fromthe VAULT rocket
spectrometer with 0.3”
spatial resolution. The
X-axis is 380” long andthe Y-axis is 250” long.
The large tic marks are20” intervals. Linking
these structures seenin H I to the corona
demands 0.1” – 0.3”
spatial resolution.
The shapes of CTR line profiles
such as O III above show thatCTR path lengths are 0.1” – 0.3”

Some Interesting Wavelength Regions for Consideration

Ne VIIHe I

Very hot active region
and flare EUV lines. Higher
temperatures are moreaccessible in the X-rayregion (1-100 Å)

An Hinodediscovery: achromosphere &coronal loop heatingconnection.
De Pontieu et al.,ApJ, 701, L1 (2009)

Tracking Type II
spicules through thechromosphere/transition region ishighly desirable.

•Type II spicules – a source of heating and mass in the corona?
•What are the properties of the spicules between SOT and EIS Fe XIV
temperatures?

How are coronal loops heated?
Plasma parameters are necessary to find out.
Current instrumentation cannot resolve multi-threaded coronal loops.

from Aschwanden et al., ApJ, 659, 1673 (2007)

A Multi-Thread Loop Model is Needed to Explain
Many Hinode Loop Observations in Active Regions• The overall loop magnetic envelop is assumed tobe composed of sub-resolution magnetic“threads”.
• The threads are modeled as individual flare loops
using a 1D solar flux tube model.
• Heating onset is modeled as a succession ofindependently heated threads.
• The length of the flare loop is determined byobservations of the overall magnetic envelop.
• The energy in each successively heated thread isdetermined such that the total loop EUV flux
matches the light curves such as generated byTRACE.

Hinode/EISFlare loop, missing high temperatures complicates comparisons
to models; models do not agree with observations at high temperatures

Hinode/XRT

Warren, Kim, DeGiorgi, & Urgarte-Urra, ApJ, in press (2010)

Single loop multi-thread
impulsive heating loop
modeling•Difficult to isolate asingle loop
•Hot (3 MK+) loops coolslower than warm (< 2MK) loops•Ensembles of loops,lack of adequate spatial
resolution, andinadequate temperature
coverage makequantitative comparisonswith models difficult

Loops in cores of active
regions are ~ 3 MK & can be
explained by steady heating.
Warm loops outside the corerequire impulsive heating
models.

Warren, Kim, DeGiorgi, & Urgarte-Urra, ApJ, in press (2010)

Warren, Kim, DeGiorgi, & Urgarte-Urra, ApJ, in press (2010)

Multi-thread loop modeling of apost-flare loop. The models
reproduce the “warm” emission
well but fail to reproduce the“hot” emission observed by XRT.
Temperature continuity isinadequate.

Warren, Kim, DeGiorgi, & Urgarte-Urra, ApJ, in press (2010)

Hinode/EIS 40” slot rasters of the “hot” (~3 MK) core of an active region. Light curves
correspond to positions in the active region indicated by boxes. Loops cool from 3 MK
or more to the lowest observable EIS temperatures. What happens when thetemperatures reach lower transition region and chromospheric temperatures? Is theloop plasma visible as “coronal rain”? No one knows.

Ugarte-Urra, Warren, & Brooks, ApJ, 695, 642 (2009)

Hinode Results
Hot 3 MK core active region loopcooling. Steady heating models
can explain the emission.
Impulsive heating models areneeded to explain the “warm”
loops outside the active region
cores. (From Ugarte-Urra, Warren,& Brooks, ApJ, 695, 642 2009)•Spatial resolution and moss
•TRACE/XRT/EIS show steady heating (no intensity variations) in the moss at 1”+•SOT reveals intensity variations within the moss at 0.2” resolution

Active Regions as a Source ofthe Solar Wind• The high speed solar wind (~ 800 km/s) comes fromopen field regions such as coronal holes.
• The sources of the slow solar wind (~400 km/s) are
not known. Both slow and fast wind is relevant forSpace Weather.
• EIS and XRT on Hinode have confirmed that large
outflows occur at the edges of active regions, but it
is not clear that these outflows result in solar wind.
They may be simply confined to very long closed
flux tubes.
• Magnetic field extrapolations out into theheliosphere indicate that active regions might be asignificant source of the slow solar wind.

Active Region Flows – A Sourceof the Solar Wind?

Bryans, Doschek,& Young (2009)

Active Region Flows

Two flow speeds: 20 and 200 km/s
The active region contains unresolved
multiple Gaussian components

FWHM (mA)

Correlation of line width with Doppler
speed suggests unresolved Gaussiancomponents

The First Sign of Multi-million Degree Solar Flare Loops
is in the Corona – Unresolved Magnetic Threads
NRL BCS
spectra: Yohkoh

BCS
onset

Linking the origin of the coronal activity to the energy
sources in the photosphere requires high spatial resolution

Images of Multi-million DegreeFlare Loops• Do flare loops at temperatures of 12-25 MK
look like what we expect?
– No, they don’t, but as they cool to 1-3 MK theylook more and more like respectable 1D loopsshould.
TRACE/Hinode observations confirm the grossflare loop morphology seen by Yohkoh, but thehigher Plan B resolution allows far moredetailed observations of the reconnection
region and current sheet.

Solar Flare Arcade from TRACE
Testing the solar flareStandard Model requires
continuous temperature
coverage from <0.1 MKto >20 MK. Hot spots atthe tops of “reconnected”
loops and non-uniform
intensity distributionsin the multi-million degree
loops are difficult tounderstand with theStandard Model. (SeeReeves et al., ApJ, 668,1210 (2007) for an
explanation of the hotspots).

The First Ionization Potential (FIP) Effect

Ne FIP = 21.6 eV (“high” FIP)
Mg FIP = 7.6 eV (“low” FIP)

Temperature = 4.5 x 105 K
Wavelengths near 400 Å
Mg VI: 2s22p3 4S3/2 – 2s2p4 4P1/2,3/2,5/2
Ne VI: 2s22p 2P1/2,3/2 – 2s2p2 2P1/2,3/2

•Abundances can trace the origins of plasma (e.g., slow solar wind)•Abundance measurements are best with neon and argon in the corona•Abundance measurements require high resolution spectroscopy

Solar-C allows a test of FIP models and uses the FIP effectto, for example, locate sources of the slow solar wind andanswer new questions such as what would abundance
measurements in the moss reveal?

Sheeley, ApJ, 440, 884 (1995)

Conclusions• Hinode is teaching us much about active region
heating and dynamics.
– Loop model tests (e.g., nanoflare models)– Newly discovered coronal flows that might contribute to thesolar wind• However, the work with Hinode raises new questions
that require higher spatial resolution, more spectral
coverage, and higher temporal resolution to answer.
• Plan B, with the combination of high spatial/spectral
resolution and throughput, coupled with large
spectral range, is NOT an incremental advance. It isa quantum leap forward.
• A personal view: To do Plan B properly, there shouldbe equal emphasis on all temperature regions of thesolar atmosphere. Neglect of any temperature
region is unacceptable.