Search Publications
Temporal changes in the frequencies and widths of the solar p-mode oscillations
Schou, J.; Rodriguez, J.; Scherrer, P. +7 more
We present a study of the temporal changes in the sensitivities of the frequencies and widths of the solar p-mode oscillations to corresponding changes in the levels of solar activity during Solar Cycle 23. From MDI and GONG++ full-disk Dopplergram three-day time series obtained between 1996 and 2008 we have computed a total of 221 sets of m-avera…
Local helioseismology of sunspot regions: Comparison of ring-diagram and time-distance results
Kosovichev, A. G.; Howe, R.; Komm, R. +10 more
Local helioseismology provides unique information about the subsurface structure and dynamics of sunspots and active regions. However, because of complexity of sunspot regions local helioseismology diagnostics require careful analysis of systematic uncertainties and physical interpretation of the inversion results. We present new results of compar…
Characterization of solar-cycle induced frequency shift of medium- and high-degree acoustic modes
Rabello-Soares, M. Cristina
Although it is well known that the solar acoustic mode frequency increases as the solar activity increases, the mechanism behind it is still unknown. Mode frequencies with 20 < l < 900 obtained by applying spherical harmonic decomposition to MDI full-disk observations were used. First, the dependence of solar acoustic mode frequency with sol…
Properties of Near-surface Flows around Active Regions from Helioseismic Holography
Braun, D. C.; Wan, K.
A variety of local-helioseismic analyses have shown ~50 m/s flows converging on active regions (ARs). We have examined the average properties of both the 75 strongest converging and 75 strongest diverging flows present in Carrington rotation CR1988 within the uppermost 3 Mm of the Sun. The flows, averaged over 5 days, were deduced from calibrated …
Stochastic Seismic Emission from Acoustic Glories in Solar Active Regions
Donea, Alina; Newington, Marie
Helioseismic images of active regions show enhanced seismic emission in 5 mHz oscillations in a halo surrounding the active region called the "acoustic glory". In this paper we analyse the high-frequency power excess surrounding two active regions that occurred during the "shy" ascending phase of the solar cycle 24, at the beginning of 2010. This …
Meridional Flow Observations: Implications for the current Flux Transport Models
Howe, Rachel; Komm, Rudolf; Hill, Frank +2 more
Meridional circulation has become a key element in the solar dynamo flux transport models. Available helioseismic observations from several instruments, Taiwan Oscillation Network (TON), Global Oscillation Network Group (GONG) and Michelson Doppler Imager (MDI), have made possible a continuous monitoring of the solar meridional flow in the subphot…
Ring-diagram parameter comparisons for GONG, MDI and HMI
Howe, R.; Komm, R.; Hill, F. +4 more
We examine the differences between ring-diagram mode frequency estimates from samples of Global Oscillation Network Group [GONG], Michelson Doppler Imager [MDI] and Helioseismic and Magnetic Imager [HMI] data, and find that different instruments and analysis pipelines do result in small systematic differences which may not be uniform across the so…
The rotation rate and its evolution derived from improved mode fitting and inversion methodology
Eff-Darwich, A.; Korzennik, S. G.
We present inferences of the internal solar rotation rate and its evolution during solar cycle 23. A full solar cycle of MDI observations have been analyzed using an improved fitting methodology and using time series of various lengths, up to a single 4,608 day long epoch (64 times 72 days or 12.6 yr). We used time series of spherical harmonic coe…
Properties of Supergranulation During the Solar Minima of Cycles 22/23 and 23/24
Williams, Peter E.; Pesnell, W. Dean
The solar minimum at the transition from cycle 23 to 24 was notable for its low level of activity and its extended duration. Among the various fields of study, the evolution of the solar convection zone may provide insight into the causes and consequences of this recent minimum. This study continues previous investigations of the characteristics o…
The thermal structure of sunspots from ring diagram analysis
Basu, Sarbani; Baldner, Charles S.; Bogart, Richard S.
We present a large sample of 264 active regions from solar cycle 23, analysed using ring diagrams. The frequencies of these rings are inverted to determine the thermal structure (sound speed and adiabatic index) of these regions as a function of radius. The large sample allows us to describe in a statistically significant way how the thermal prope…