Phase Relationship Between Sunspot Number, Flare Index and Solar Radio Flux
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To understand better the variation of solar activity indicators originated at different layers of the solar atmosphere with respect to sunspot cycles, we carried out a study of phase relationship between sunspot number, flare index and solar radio flux at 2800 MHz from January 1966 to May 2008 by using cross-correlation analysis. The main results are as follows: (1) The flare index and sunspot number have synchronous phase for cycles 21 and 22 in the northern hemisphere and for cycle 20 in the southern hemisphere. (2) The flare index has a noticeable time lead with respect to sunspot number for cycles 20 and 23 in the northern hemisphere and for cycles 22 and 23 in the southern hemisphere. (3) For the entire Sun, the flare index has a noticeable time lead for cycles 20 and 23, a time lag for cycle 21, and no time lag or time lead for cycle 22 with respect to sunspot number. (4) The solar radio flux has a time lag for cycles 22 and 23 and no time lag or time lead for cycles 20 and 21 with respect to sunspot number. (5) For the four cycles, the sunspot number and flare index in the northern hemisphere are all leading to the ones in the southern hemisphere. These results may be instructive to the physical processes of flare energy storage and dissipation.
KeywordsSun: sunspot—flare index—solar radio flux—solar cycle
The authors would like to thank the referee for very constructive comments and suggestions. The authors would also like to thank the staff of all the websites that provided the data for public download. Flare Index Data used in this study were calculated by T. Atac and A. Ozguc from Bogazici University Kandilli Observatory, Istanbul, Turkey. This work is sponsored by National Science Foundation of China (NSFC) under grant numbers 10903027, 11078005, 10943002, Yunnan Science Foundation of China under number 2009CD120, China’s 973 project under the grant number G2011CB811400.
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