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Where is Coronal Plasma Heated?. James A. Klimchuk NASA Goddard Space Flight Center, USA Stephen J. Bradshaw Rice University, USA Spiros Patsourakos University of Ionnina , Greece Durgesh Tripathi Inter-University Centre for Astronomy and Astrophysics, India. Three Basic Scenarios.

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slide1

Where is Coronal Plasma Heated?

James A. Klimchuk

NASA Goddard Space Flight Center, USA

Stephen J. Bradshaw

Rice University, USA

Spiros Patsourakos

University of Ionnina, Greece

Durgesh Tripathi

Inter-University Centre for Astronomy and Astrophysics, India

slide2

Three Basic Scenarios

steady

heating

“Steady”

Coronal Heating

v = 0

impulsive

heating

Impulsive

Coronal Heating

thermal cond.

evaporation

Impulsive

Chromospheric Heating

(incl. Type II Spicules)

impulsive

heating

expansion

slide3

ChromosphericNanoflares (inc. Type II Spicules)

impulsive

heating

expansion

  • Test hypothesis that all coronal plasma is heated in the chromosphere
  • Compare predicted and actual observations
  • 1D hydrodynamic approach:
    • Once formed, hot high-pressure plasma expands along the field
    • Expansion dominates;
      • any initial kick (e.g., spicule ejection) is relatively unimportant
    • Basic conclusions not altered by Lorentz forces
euv spectral line profiles e g fe xiv 274
EUV Spectral Line Profiles(e.g., Fe XIV 274Ǻ)

Line profile represents the time-averaged emission from a complete upflow-downflow cycle.

Fast upflow  blue wing component

Slow downflow line core (small red shift)

Observed wing/core intensity ratio ≤ 0.05

(Red-Blue Asymmetry)

(Hara et al. 2008; De Pontieu et al. 2009; McIntosh &

De Pontieu 2009; De Pontieu et al. 2011; Tian et al.

2011; Doschek 2012; Patsourakos et al. 2013;

Tripathi & Klimchuk 2013)

What is expected?

De Pontieu et al. (2009)

blue wing to core intensity ratio
Blue Wing-to-Core Intensity Ratio

* if all coronal plasma comes from chomosphericnanoflares (incl. type II spicules)

nc = coronal density = 3x109 (AR), 109 cm-3 (QS)

hc = coronal scale height = 50,000 km

A = flux tube area expansion factor = 3

l = initial length of heated plasma = 1000 km

v = upflow velocity = 100 km s-1

Klimchuk (2012)

filling factor
Filling Factor

Thehypothesis is incorrect.

Only a small fraction of the observed hot coronal plasma is created by chomosphericnanoflares (incl. type II spicules).

fs < 2% (Active Regions)

< 5% (Quiet Sun)

< 8% (Coronal Holes)

Klimchuk (2012)

slide7

1D Hydro Simulations

(Work with Steve Bradshaw)

HYDRAD Code:

2 fluid (electrons and ions)

Nonequilibrium ionization

Adaptive mesh refinement

  • Initial equilibrium with Tapex = 0.8 MK
  • Impulsively heat the upper 1000 km of the chromosphere in 10 s
  • Evolve for 5000 s
  • Average over space and time

Approximate a l-o-s through an arcade with the integrated emission from a single loop of 50,000 km height

slide8

Icore

IR

IB

The analytical results are confirmed

….also for loops of different length and heating events of different duration

type ii spicules
Type II Spicules
  • Observational discrepancies if all hot plasma comes from Type II spicules:
  • Blue wing-to-line core intensity ratios factor 100 too big (Klimchuk 2012)
  • Coronal-to-LTR emission measure ratios factor 100 too big (K 2012)
  • Blue wing-to-line core density ratios factor 100 too big (Patsourakos, K, & Young 2013)
  • Good news:
  • Type II spicules may explain the bright emission from the LTR (T < 0.1 MK), where traditional coronal heating models fail?
slide10

Emission Measure Distribution

From type II spicules?

Dere & Mason (1993)

slide11

Coronal Heating

Strands

Type-II Spicule

Strand

Composite

(Observed)

Line

Profile

100 x

+

=

Emission

Measure

Distribution

100 x

+

=

conclusions
Conclusions
  • Chromosphericnanoflares (incl. type II spicules) provide only a very small fraction of the hot plasma observed in the corona.
  • Most coronal plasma comes from chromospheric evaporation associated with coronal heating (heating that takes place above the chromosphere).
  • Spicules contribute substantially to the bright emission from the lower transition region, where traditional coronal heating models are inadequate.
  • A better understanding of the origin of spicules requires:
    • Detailed MHD simulations
    • Better observations (e.g., IRIS, Solar-C, LASSO rocket)
slide14

Brightness Decreases with Volume (Expansion)

50,000 km

1000 km

EM0

0.006 xEM0

The total (spatially integrated) emission is dimmer by a factor of 157

type ii spicules1
Type II Spicules

Cool (~104 K) plasma rises

Most heats to ≤ 0.1 MK and falls

Some at the tip heats to ~2 MK and expands to fill the flux tube

Hot plasma slowly cools and drains

Fe XIV (2 MK)

He II (8x104 K)

Ca II (104 K)

v~ 100 km/s

hs~ 10,000 km

d ~ 200 km

d ~ 10%

d hs

hs

d

slide16

Blue Wing (Upflow) Density

Expansion (type II spicules):

Evaporation (coronal nanoflares):

  • Observed densities from the Fe XIV 264/274 ratio are:
    • much smaller than predicted for type II spicules
    • comparable to predicted for coronal nanoflares

Patsourakos, Klimchuk, & Young (2013)

coronal nanoflare frequency
Coronal Nanoflare Frequency
  • All coronal heating is impulsive
  • The response of the plasma depends on the frequency of the nanoflares

Low Frequency

High Frequency

“Impulsive”

“Steady”

trepeat >> tcool

trepeat << tcool

slide18

Type II Spicules

Hinode / SOT

slide19

Quiet Sun

(De Pontieu et al. , 2007)

Ca II (SOT)

He II (AIA)

Coronal Hole

(De Pontieu et al., 2011)

Fe IX (AIA)

ltr to corona emission measure ratio
LTR-to-Corona Emission Measure Ratio

(Lower Transition Region: 4.3 < logT < 5.0)

Ratio of emission measures in the LTR and corona:

Predicted*: > 180

Observed: < 1

Implies a spicule filling factor fs < 1%

* if all coronal plasma comes from type II spicules

adiabatic cooling
Adiabatic Cooling

If the hot spicule plasma cools adiabatically as it expands,

the temperature will drop by a factor

= 28 (Scenario A)

6 (Scenario B)

For initial temperature T0 = 2 MK, the final (coronal) temperature would be

Tc = 7x104 K (Scenario A)

3x105 K (Scenario B)

To have Tc = 2 MK at the end of expansion requires additional coronal heating of the same magnitude that produced the hot spicule plasma in the first place!