Physics
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995soph..156...17k&link_type=abstract
Solar Physics (ISSN 0038-0938), vol. 156, no. 1, p. 17-28
Physics
17
Exponents, Solar Cycles, Solar Physics, Solar Rotation, Sun, Time Dependence, Legendre Functions, Random Noise, Random Processes, Sunspots
Scientific paper
I study the temporal variation of the solar rotation on time scales shorter than the 11-year cycle, by analyzing the daily Mt. Wilson Doppler measurements from 1967 to 1992. The differential rotation is represented by the three coefficients, A, B, and C, of the following expansion: omega = A + B sin2 (theta) + C sin4 (theta). The A, B, and C time series show clearly the 11-year solar cycle and they also show high-frequency fluctuations. The Hurst analysis of these time series shows that a Gaussian random process such as observational noise can only account for fluctuations on time scales shorter than 20 days. For time scales from 20 days to 11 years, the variations of A give rise to a Hurst exponsent of H = 0.83, i.e., the variations of A are `persistent'. The temporal variations of B show the same behavior as C, which is different from A. From one to 11 years, the B and C variations are dominated by the 11-year cycle, while for time lags shorter than about 250 days, the B and C fluctuations give rise to a Hurst exponent of H = 0.66, which lies between H = 1/2 of a Gaussian random process, and the exponent of the persistent process shown by A. An analysis of the equivalent coefficients of the first three even Legendre polynomials, computed using A, B, and C, provides additional information. For time scales between 100 and 1000 days, the ranges, R/S, of Legendre polynomial coefficients decrease with increasing order of the polynomials which suggests that the persistent process operates mainly on large spatial scales. The Hurst exponent of H = 0.83 for variations in A is the same as H for monthly sunspot numbers with time scales between 6 months and 200 years and for C-14 radiocarbon data with time scales between 120 years and 3000 years, previously analyzed by other authors. The combined results imply that the underlying solar process shows the same persistent behavior for time scales as short as about 20 days up to time scales of a few thousand years.
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