An Energy Storage Process and Energy Budget of Solar Flares

  • K. Tanaka
  • Z. Smith
  • M. Dryer
Part of the International Astronomical Union / Union Astronomique Internationale book series (IAUS, volume 91)

Abstract

The flare energy is generally considered to be stored in stressed (twisted or sheared) magnetic fields. Origin of the stress may be either intrinsic or due to horizontal shear motion (Tanaka and Nakagawa 1973) or due to propagation of twist from below (Piddington 1974). Characteristic magnetic configurations in the great activities (inverted, twisted δ-configuration; Zirin and Tanaka 1973) suggest an inherent shape of fluxtube for these regions: a twisted magnetic knot. Further, evolutionary characteristics such as rapid growths of spots and growth of twist in parallel with apparent shear motion of spot, together with the fact that the shear motion is associated with upward velocity (Tanaka and LaBonte 1979), suggest a continuous emergence of such a twisted knot from below throughout the activity (Tanaka 1979). In this model (Fig. 1) the flare energy may be supplied directly into the corona as the twisted portion of the fluxtube emerges out. The amount of energy supplied between t0 and t may be equated to the energy contained in the twist (ϕ) between z1 and z2,
$$ \rm M(t) = 1/4\pi \int_0^r \ r\phi B_\phi B_Z 2\pi rdr. $$
(1)
Observationally ϕ may be evaluated from the growth of the penumbral twist, which is related empirically to the apparent horizontal shear velocity v by rϕ=1 .5v(t−t0) (Tanaka 1979). Assuming the force-free field we have <BϕB >≌0.22B2 with Bp equal to the peak field strength of the moving spot. Then,
$$ \rm M(t) \simeq \int_{t_0}^t 0.0173 \ B_p^2Av \ dt $$
(2)
where A is area of the moving spot. Eq. (2) is equal to the evaluation of accumulated energy due to the horizontal shear motion except numerical factor (cf. Tanaka and Nakagawa 1973).

Keywords

Convection Flare Boulder 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Dere, K., Horan, D. and Krepline, R.: 1974, J. Atmosph. Terr. Phys. 36, 989.CrossRefADSGoogle Scholar
  2. Piddington, J.: 1974, Solar Phys. 38, 465.CrossRefADSGoogle Scholar
  3. Tanaka, K.: 1979, Publ. Astron. Soc. Japan, in press.Google Scholar
  4. Tanaka, K. and LaBonte, B.: 1979, in preparation.Google Scholar
  5. Tanaka, K. and Nakagawa,Y.: 1973, Solar Phys. 33, 187.CrossRefADSGoogle Scholar
  6. Withbroe, G.: 1978, Astrophys. J. 225, 641.CrossRefADSGoogle Scholar
  7. Zirin, H. and Tanaka, K.: 1973, Solar Phys. 32, 173.CrossRefADSGoogle Scholar

Copyright information

© IAU 1980

Authors and Affiliations

  • K. Tanaka
    • 1
    • 2
  • Z. Smith
    • 1
    • 2
  • M. Dryer
    • 1
    • 2
  1. 1.Tokyo Astronomical ObservatoryUniversity of TokyoJapan
  2. 2.Space Environment LaboratoryNational Oceanic and Atmospheric AdministrationBoulderUSA

Personalised recommendations