1. Chromospheric and Transition Region Dynamics
Peter T Gallagher
L-3 Com EER Systems
NASA Goddard Space Flight Center
Taos, October 2003
Peter T Gallagher (NASA/GSFC)

2. Chromospheric and Transition Region Heating
How do nonthermal electrons heat the upper chromosphere and transition region?
Assume a source function of energetic electrons with a spectrum:
F(E) ~ (E/Ec)- electrons cm-2 s-1
Nonthermal electrons supply the necessary energy to heat the plasma and hence cause flows.
Enonthermal = Ethermal + Ekinetic
Taos, October 2003
Peter T Gallagher (NASA/GSFC)

3. Nonthermal Chromospheric Heating
A large overpressure can only be met if the heating time scale is less than the hydrodynamic expansion time scale:
3 kB T / Q < L / cs
Q = heating rate per particle
T = final temperature of the heated plasma
cs = sound speed
L = length of the heated high-pressure region
Resulting pressure gradient will drive mass
flows of hot plasma from the chromosphere to
the corona.
T1: Nonthermal
Electrons
T3: Vup<1000 km/s
T2: Impulsive
Heating
Den
T3: VDOWN<100 km/s
Taos, October 2003
Peter T Gallagher (NASA/GSFC)

4. Gentle Vs. Explosive Evaporation
There is a nonthermal energy flux threshold between gentle and explosive evaporation.
This threshold can be determined by equating the nonthermal thick-target heating rate per particle which the peak radiative loos rate.
Gentle evaporation velocities < 100 km s-1
Explosive evaporation velocities up to 600 km s-1
Taos, October 2003
Peter T Gallagher (NASA/GSFC)

5. Temperature Sensitivities
Ion
 / Å
Te / MK
He I
584.33
0.03
O V
629.27
0.25
Fe IX/X
171
1.0
Mg X
624.95
1.2
Fe XVI
360.76
2.5
Fe XIX
592.16
8.0
GOES-8
/ 1 - 8
10-30
RHESSI -
>10
Taos, October 2003
Peter T Gallagher (NASA/GSFC)

6. Spectral Evolution Soft-hard-soft spectrum Taos, October 2003
Peter T Gallagher (NASA/GSFC)

7. CDS and TRACE: 26 March 2002 Flare
SOHO/CDS
He I (0.03 MK)
O V (0.25 MK)
Mg X (1.1 MK)
Fe XVI (2.5 MK)
Fe XIX (8 MK)
TRACE 17.1 nm
Fe IX/X (1.0 MK)
Taos, October 2003
Peter T Gallagher (NASA/GSFC)

8. RHESSI Imaging Spectroscopy
RHESSI 6-12 keV
CDS Fe XIX (8 MK)
Outflow
Footpoints
Taos, October 2003
Peter T Gallagher (NASA/GSFC)

9. Loop Cooling Curves T* t* Conductive Radiative Taos, October 2003
Peter T Gallagher (NASA/GSFC)

10. C3.0 Flare Properties
Total nonthermal energy: Etot(>10 keV) ~ 5.7 x 109 ergs cm-1 s-1
Spectral index:  ~ 6.6
Maximum upflow velocity: ~250 km/sec
Maximum downflow velocity: < 100 km/sec
Taos, October 2003
Peter T Gallagher (NASA/GSFC)

11. Footpoint Downflows Loops are not static Maximum downflow ~110 km/sec
Loops cool via conduction, radiation, and flows. (SHOW MOVIE)
Taos, October 2003
Peter T Gallagher (NASA/GSFC)

12. Future Work
What is the nonthermal energy flux threshold for explosive evaporation?
Is all the nonthermal energy in a beam lost at a particular height? What is the efficiency?
Study how the chromospheric and TR response varies with low-energy cut-off, spectral index, total flux, etc. using a large sample of data from CDS and RHESSI.
Look at energy balance between nonthermal energy and resulting thermal and kinetic energies.
General question: Impulsive v continuous energy release.
Taos, October 2003
Peter T Gallagher (NASA/GSFC)

13. Prolonged Energy Release
Taos, October 2003
Peter T Gallagher (NASA/GSFC)

14. Loop Cooling Curves T* t* Conductive Radiative Taos, October 2003
Peter T Gallagher (NASA/GSFC)

15. CDS Emission Measure Diagnostics
Assume an isothermal plasma at a temperature T, which corresponds to the maximum of the contribution function.
The integrated intensity of the line can be approximated by:
I = ( 1 / 4  ) A G(T) EM => EM = I 4  / A G( T )
G( T ) from CHIANTI or ADAS.
Elemental abundances of Fludra & Schmeltz (1995)
Taos, October 2003
Peter T Gallagher (NASA/GSFC)

16. CDS Density Diagnostics
Assuming a homogeneous and isothermal plasma:
Ne = SQRT( EM / V )
This approximation does not take into account filamentary plasma.
The fraction of the emitting volume actually contributing to the total emission is termed the filling factor (f).
Estimating the filling factor (0.1-1), the electron density can then be given by:
Ne = SQRT( EM / fV )
Taos, October 2003
Peter T Gallagher (NASA/GSFC)