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Preflare Features in Radios and in Hard X-Rays. Ayumi ASAI Nobeyama Solar Radio Observatory, NAOJ collaborated with H. Nakajima, M. Shimojo, H. S. Hudson, R. P. Lin, and S. M. White AOGS 2 nd Annual Meeting, June 22, 2005. Energy Release in Preflare Phase. Impulsive phase:

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Preflare features in radios and in hard x rays

Preflare Features in Radios and in Hard X-Rays

Ayumi ASAI

Nobeyama Solar Radio Observatory, NAOJ

collaborated with

H. Nakajima, M. Shimojo, H. S. Hudson,

R. P. Lin, and S. M. White

AOGS 2nd Annual Meeting, June 22, 2005

Energy release in preflare phase
Energy Release in Preflare Phase

Impulsive phase:

Strong nonthermal emission in HXRs and in microwaves

Fast reconnection, violent energy release

Preflare phase:

Gradual emission in SXRs, start of plasmoid ejection/CME

destabilization of preflare structure

Physical process in preflare phase has a key of flare trigger

Nonthermal emission
Nonthermal Emission

Masuda et al. (1994)

strong energy release 

  • HXR

    thick-target : footpoint

    thin-target : above loop top (nonthermal?/thermal?)

  • microwave

    flare loop

    particle acceleration in preflare phase? (Farnik et al. 2003)

fast shock

flare loop


NOAA 10039


2002/July/23 00:20 UT

NOAA 10039 (SE limb)


Light Curve


microwave(Nobeyama Radioheoigraph)

Divide them into 4 sub-phases, and examine each of them

Phase 1 before the flare
(Phase 1) Before the Flare

  • Large loop-like structure (m-wave)

  • Thin-thermal emission (a~0)

  • Not clear in EUV  high temperature (~5MK)?

  • Like a sigmoid?

Phase 2 preflare phase i
(Phase 2) Preflare Phase I

Rapid temperature increase (SXR, GOES):hotter than 10MK

Low energy HXR emission

thermal emission?


12-25 keV

Phase 2 preflare phase ii
(Phase 2) Preflare Phase II

  • Nonthermal emission (a~-3.0)

  • Above-the-loop-top source (Masuda’s source?)

Phase 3 ejection
(Phase 3) Ejection


  • Faint EUV ejection

  • Associated CME

  • Induce intense energy release

Phase 4 impulsive phase
(Phase 4) Impulsive Phase

  • The physical features are almost the same as in the impulsive phase

    • HXR

      Footpoint (nonthermal)

      Above-the-loop-top (thermal?/nonthermal?)

    • microwave

      Loop / loop top (nonthermal)

Above-the-loop-top source?

Masuda et al. (1994)

Ejections and energy release
Ejections and Energy Release

  • Destabilization of the structure (tether-cutting / breakout)

    • Plasmoids/filaments start to rise

      Induce strong energy release (impulsive phase)

  • Nonthermal emission even in the phase BEFORE the ejection

    Destabilization process is accompanied by particle acceleration




  • We examined the preflare features of 2002 July 23 flare in HXRs and in microwave

  • Faint EUV ejection at 00:24UT

    Induced fast energy release in the impulsive phase

  • We found the thermal and nonthermal features even in the phase before the ejection

    • Nonthermal emission @ footpoin and above the loop top

    • Masuda’s HXR sources?

      Energy release mechanism in the preflare phase is probably accompanied by particle acceleration


Farnik (1996)





gray scale: preflare


Farnik and Savy (1998)

プリフレア相増光の領域の一部は、フレアループと重なっている事が多い。 しかし、2つの領域が完全に一致する物は少ない

gray scale: preflare

contour: flare


Tether cutting model
Tether-Cutting Model

Moore et al. (2001) ApJ




Temperature variation in preflare phase
Temperature Variation in Preflare Phase

Shimojo (1999) Date:20-Sep-1997 09:30UT

Blue con. : 4MK

Green con. : 5MK

Red con. : 6MK

SXT Image



Temp. Map