Solar Physics Division Meeting 2000, June 19-22
Session 2. Corona, Solar Wind, Flares, CMEs, Solar-stellar, Instrumentation, Other
Display, Chair: J. Krall, Monday-Thursday, June 19, 2000, 8:00am-6:00pm, Forum Ballroom

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[2.10] What TRACE Observations tell us about Heating of Coronal Loops

M.J. Aschwanden, R.W. Nightingale, D. Alexander (LMSAL), F. Reale, G. Peres (Univ.Palermo)

We analyzed the temperature Te(s) and density structure ne(s) of active region loops in EUV observed with TRACE (see SPD abstract by Nightingale et al.).

The observational data indicate that cool EUV loops with maximum temperatures of Tmax~0.8-1.6 MK cannot be explained with the static steady-state scaling law of Rosner, Tucker, & Vaiana (1978) or Serio et al. (1981), in terms of uniform heating. However, they are fully consistent with Serio's model (which includes gravitation and a heating scale height) in the case of nonuniform heating, with heating scale heights in the range of sH=17 ±6 Mm. This heating function provides almost uniform heating for small loops (L < 20 Mm), but restricts heating to the footpoints of large loops (L~50-300 Mm).

Another observational result of cool EUV loops is that the pressure scale height exceeds the hydrostatic scale height by a factor of ql~1-3. This suggests that the pressure balance of these EUV loops may not be governed by hydrostatic equilibrium, but rather indicates a non-steady state, e.g. caused by dynamic mass flows and/or intermittent heating. Chromospheric upflows may explain the extended scale heights as well as the quasi-isothermal temperature structure of EUV loops.

We review and discuss the differences between cool (T~ 1-2 MK) EUV loops and hot (T~2-8 MK) soft X-ray loops concerning loop scaling laws, radiative equilibrium, hydrostatic equilibrium, and heating function. - This work is supported by the TRACE project at LMSAL (contract NAS5-38099)

Ref.: Aschwanden,M.J., Nightingale,R.W., Alexander,D., Reale,F., and Peres,G. 2000, ApJ, subm., ``Evidence for Nonuniform Heating of Coronal Loops Inferred from Multi-Thread Modeling of TRACE Data''

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