Simultaneous Prograde And Retrograde Waves Of Solar Magnetic Activity (Sunspots And Photospheric Magnetic Fields) Move Across The Solar Surface With Velocities Of 30 - 75 m/s

Details Simultaneous Prograde And Retrograde Waves Of Solar Magnetic Activity (Sunspots And Photospheric Magnetic Fields) Move Across The Solar Surface With Velocities Of 30 - 75 m/s Simultaneous Prograde And Retrograde Waves Of Solar Magnetic Activity (Sunspots And Photospheric Magnetic Fields) Move Across The Solar Surface With Velocities Of 30 - 75 m/s

May 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...210.9202j&link_type=abstract

American Astronomical Society Meeting 210, #92.02; Bulletin of the American Astronomical Society, Vol. 39, p.208

Astronomy and Astrophysics

Astronomy

Scientific paper

Evidence is presented that slowly moving prograde and retrograde waves (30 - 75 m/s) occur in solar activity patterns during the middle of each 11-year solar cycle. These were detected in sunspot group positions, and more generally, in the intensities of photospheric magnetic fields from Kitt Peak synoptic magnetograms. The waves appeared as diagonal trajectories in modified stackplots, which were restricted in content to activities occurring simultaneously in both hemispheres within the same windows of latitude and longitude. Thus, the waves represent the behavior of features symmetric across the equator. For sunspot group data a convolution method, based on an adaptive kernel, was used to enhance the visualization of trajectories in the stackplots. The dominant features in all stackplots were extracted by spectral filtering that retained only the highest power coefficients in corresponding 2-D FFT analyses. These revealed the broad diagonal lines indicative of waves traveling longitudinally. Examples are provided from various solar cycles to demonstrate the general nature of the phenomenon. The slopes of the stackplot trajectories were extracted and are assumed to represent the velocities of the waves. A linear relationship was observed between this wave velocity and the maximal magnitude of the sunspot index over the last 12 solar cycles. Solitons traveling along a surface or interface could explain this observation. The velocity of solitons increases with amplitude, suggesting higher amplitude waves are associated with greater solar activity. The slow average velocity favors shallow-water-type internal waves traveling along a weak, but definitive, density boundary. Such a region may occur at the interface created by strong horizontal magnetic fields. Since internal waves can exhibit very large amplitudes, these waves could be sufficient to perturb the buoyancy of flux tubes, initiating their rise to the surface. Funded, in part, by the MSU Foundation.

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