Reconstruction of the Heliospheric Current Sheet Tilts Using Sunspot Numbers

Abstract

We have investigated the correlation between the relative sunspot number and tilt of the heliospheric current sheet (HCS) in solar cycles 21-23. Strong and highly significant positive correlation (r > 0.8, P < 0.001) was found for corresponding data in the time interval from May 1976 through December 2004. Cross-correlation analysis does not reveal any time shift between the data sets. Reconstructed values of the HCS tilt, for the time interval before 1976, are found using sunspot numbers. To take different amplitude of solar cycles into account they were then normalized to zero in the minima of the solar activity and to average in solar cycles 21-23 maximal calculated HCS tilt in the maxima. These normalized reconstructed HCS data are compared with the angular positions of the brightest coronal streamers observed during total solar eclipses in 1870-2002, and their agreement is better for the minima of the solar activity than for the maxima.

An empirical model of heliospheric cosmic ray modulation on long-term time scale

“…The HCS tilt angle model depends only on the solar cycle phase and describes the cyclic behaviour of the HCS tilt angle, reflecting its asymmetric shape, with short length and fast ascending phase in contrast to the gradual descending phase. The reconstructed series agree well with the observations by WSO as well as with sparse estimates from image analysis of solar eclipses (Pishkalo 2006). Due to observational constraints there is an upper limit in the tilt angle maximum at 70°, but this has no effect on the application of the reconstructed tilt angle in studying the heliospheric modulation of GCRs.…”

“…4). Some indirect sparse tilt angle estimates, based on image analysis of solar eclipses from 1870 through 2002, are done by Pishkalo (2006). We also show them in the same figure for comparison.…”

Solar Cycle in the Heliosphere and Cosmic Rays

“…4). Direct computations of the tilt angle started in mid-1970s but indirect estimates (Pishkalo 2006) can be done even before that based on observations of solar eclipses since 1870 (Fig. 4).…”

“…The red dots represent the HCS tilt angle (radial model) averaged over cycles 21-23 (Wilcox Solar Observatory http://wso.stanford. edu/Tilts.html), the blue stars depict the tilt angle reconstructed from solar eclipses since 1870 (Pishkalo 2006), and the blue curve is a 7-point running mean over the blue stars (cf. Alanko-Huotari et al 2007a) with almost no sunspots on the solar surface (Eddy 1976).…”

Astrophysics in 2006

“…Also the solar wind speed at 1 AU was found to vary with the solar cycle (Watari et al 2005). Of geophysical importance may also be that the tilt of the heliospheric current sheet is strongly correlated with the sunspot number (Pishkalo 2006), that is, the "ballerina skirt" is flat during the solar minimum and highly warped during the solar maximum, as you expect for slower and faster pirouettes.…”