Implications of solar p-mode frequency shifts
Goldreich, Peter and Murray, Norman and Willette, Gregory and Kumar, Pawan (1991) Implications of solar p-mode frequency shifts. Astrophysical Journal, 370 (2). pp. 752-762. ISSN 0004-637X. doi:10.1086/169858. https://resolver.caltech.edu/CaltechAUTHORS:20130313-114003503
We relate entropy and magnetic field perturbations to variations of solar p-mode eigenfrequencies. The frequency variations result from changes in path length and propagation speed. These produce shifts of opposite sign. Path length changes dominate for entropy perturbations, and propagation speed changes dominate for most types of magnetic field perturbations. The p-mode frequencies increased along with solar activity between 1986 and 1989. The frequency shifts exhibit a rapid rise with increasing frequency followed by a precipitous drop. The positive component signals a strengthening of the photospheric magnetic field to an rms value of order 200 G. The sudden drop at high frequency is due to a combination of a resonance and an increase in temperature in the chromospheric cavity. The magnetic stress perturbation decays above the top of the convection zone on a length scale comparable to the pressure scale height and grows gradually with depth below. The former characteristic implies that the stress is mainly due to small magnetic elements of the enhanced network, a conclusion supported by our analysis of Kitt Peak magnetograms. The latter property suggests that the flux tubes which pierce the photosphere strengthen with depth, at least to a pressure level of 10^8 dynes cm^(-2). The presence of a resonance in the chromospheric cavity means that the transition layer maintains enough coherence to partially reflect acoustic waves even near cycle maximum. The fractional chromospheric temperature rise implies a much larger fractional increase in the rate of mechanical heating, as indicated by the variation of the Ca II H and K lines.
http://dx.doi.org/10.1086/169858 DOI UNSPECIFIED
http://adsabs.harvard.edu/doi/10.1086/169858 ADS UNSPECIFIED
© 1991 American Astronomical Society. Received 1990 July 9; accepted 1990 September 18. The authors thank J. Harvey, K. Libbrecht, C. Thompson, H. Wang, and M. Woodard for enlightening discussions. They are indebted to J. Christensen-Dalsgaard for providing them with programs that generate his solar models and the equation of state on which they are based, and for helpful suggestions on improving the manuscript. This research was supported by NSF grant AST 89-13664 and NASA grant NAGW 1303. Part of it was performed while P. G. was visiting the Harvard Smithsonian Center for Astrophysics, and P. K. was visiting the Institute for Theoretical Physics at Santa Barbara. P. G. thanks the Smithsonian Institution of Washington for the award of a Regents Fellowship.
NSF AST 89-13664
NASA NAGW 1303
Smithsonian Institution of Washington Regents Fellowship UNSPECIFIED
hydromagnetics - Sun: oscillations
Implications of solar p-mode frequency shifts Goldreich, Peter; Murray, Norman; Willette, Gregory; Kumar, Pawan Astrophysical Journal, Part 1, vol. 370, April 1, 1991, p. 752-762.