Giant Cell Signal Extracted from GONG Data

An analysis of velocity data from the GONG instruments reveals the existence of Giant Cell Convection. These large-scale convection cells were proposed more than 30 years ago to help explain the structure and evolution of solar active regions. Although the flows are weak ( less than 20 m/s), the long lifetime of the flow pattern should have an accumulative effect on the movement of solar magnetic features.

The discovery of these cells is due to advances in both instruments (see The Global Oscillations Network Group ) and analysis techniques (Hathaway 1992 Solar Phys. 137,15). A spectrum (8 kb) of the convective motions shows the presence of a velocity signal at low wavenumbers (large wavelengths). An image (28 kb) constructed from the spectral components with wavenumbers between 1 and 16 shows features that are weak at disk center and stronger near the limb. This is an important feature expected for horizontal flows on the surface of the sun. An MPEG movie (125 kb) covering 10 hours on June 25th 1994 shows that these features persist over the course of a day. Another MPEG movie (480 kb) covering 4 days shows that many of the features rotate from day-to-day at about the solar rotation rate (14 degrees/day).

Some noise due to scattered light still persists in these images and efforts are underway to remove it. Future efforts will involve studies of how these velocity features affect the evolution of the sun's magnetic field pattern. This discovery may provide solar astronomers with an important tool for predicting future solar activity.