Rate of helicity production by solar rotation

In recent years, solar observers have discovered a striking pattern in the distribution of coronal magnetic structures: northern hemisphere structures tend to have negative magnetic helicity, while structures in the south ten d to have positive magnetic helicity. This hemispheric dependence extends f rom photospheric observations to in situ measurements of magnetic clouds in the solar wind. Understanding the source of the hemispheric sign dependenc e, as well as its implications for solar and space physics has become known as the solar chirality problem. Rotation of open fields creates the Parker spiral which carries outward 10(47) Mx(2) of magnetic helicity tin each he misphere) during a solar cycle. In addition, rough estimates suggest that e ach hemisphere sheds on the order 10(45) Mx(2) in coronal mass ejections ea ch cycle. Both the alpha effect (arising from helical turbulence) and the O mega effect (arising from differential rotation) should contribute to the h emispheric chirality. We show that the Omega effect contribution can be cap tured in a surface integral, even though the helicity itself is stored deep in the convection zone. We then evaluate this surface integral using solar magnetogram data and differential rotation curves. Throughout the 22 year cycle studied (1976 -1998) the helicity production in the interior by diffe rential rotation had the correct sign compared to observations of coronal s tructures - negative in the north and positive in the south. The net helici ty flow into each hemisphere over this cycle was approximately 4 x 10(46) M x(2). For comparison, we estimate the ct effect contribution; this may well be as high or higher than the differential rotation contribution. The subs urface helicity can be transported to the corona with buoyant rising flux t ubes. Evidently only a small fraction of the subsurface helicity escapes to the surface to supply coronal mass ejections.