AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 92. Solar Cycle
Display, Thursday, June 3, 1999, 9:20am-4:00pm, Southeast Exhibit Hall

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[92.02] Evolution of Solar Magnetic Fields in 1996-1998

G. de Toma (LASP, U. of Colorado), O. R. White (High Altitude Obs., NCAR), K. L. Harvey (Solar Physics Research Corp.), G. J. Rottman, T. N. Woods (LASP, U. of Colorado)

NSO/Kitt Peak synoptic charts of magnetic flux in the period from 1996 to 1998 are analyzed together with time series for the 10.7 cm radio flux, sunspot number, and MgII chromospheric index to determine the origin of two times of minimum activity in 1996 and to study the rising phase of the current solar cycle 23 in 1997 and 1998. The two minima between solar cycle 22 and 23 in the Spring and Fall of 1996 are found to correspond to periods of low magnetic activity in the southern and northern solar hemispheres, respectively. The new solar cycle becomes dominant in early 1997, but it is only in the Summer of 1997 that a significant increase in activity can be detected in the magnetic fields observations as well as in irradiance data. By the end of 1998, the activity level has increased to a value that suggests the current cycle is about half way to solar maximum. The number of persistent longitude bands of active nests increases from zero in 1996 to three by 1998. This value seems consistent with numerical simulations which study the dependence with longitudinal wavenumber, m, of magnetic instabilities in concentrated toroidal fields at the tachocline.

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