160-minute solar cycle
Encyclopedia
The 160-minute solar cycle was an apparent periodic oscillation in the solar surface which was observed in a number of early sets of data collected for helioseismology
.
The presence of a 160 minute cycle in the Sun
is not substantiated by contemporary solar observations, and the historical signal is considered by main-stream scientists to occur as the redistribution of power from the diurnal cycle as a result of the observation window and atmospheric extinction.
It was rapidly realised that this frequency corresponded to one-ninth of a day, and therefore the authenticity of this signal was in some doubt. If a non-sinusoidal oscillation is present in a time-series then power will be seen in a periodogram
at not only the frequency of the oscillation, but also harmonics at integer multiples of this frequency. A re-analysis of data obtained over the period of 1974-1976 by Brookes et al. showed that the evidence for a stable, phase-coherent 160 minute oscillation at a constant amplitude was far from conclusive. Although the signal could be detected the amplitude appeared variable and was lower than first reported.
A re-affirmation of the 160 minute signal was obtained by analysis of data from groups in Crimea and Stanford over a long period of time. It was found that the phase showed a steady drift, indicative that the frequency being used in analysis differed slightly from that in the data. This implied that period of 160.01 minutes produced a better fit to the data. Evidence also emerged that multiple sets of observations were phase-coherent. These facts contributed to impressions that the origin of the observed signal was stellar and not terrestrial in origin.
In 1989 as higher-quality multiple-year datasets from a single site became available it was shown by Elsworth et al. that the period of the 160 minute signal was indeed 160.00 minutes, and the amplitude was dependent upon both the length and quality of data obtained in a season, with the signal more prominent at time where atmospheric condition were worse. The group were able to demonstrate that the signal may be simulated by a slightly distorted diurnal sine-wave such as may be obtained by differential atmospheric extinction.
However claims of the presence of a 160 minute period in the Sun were still being presented by Kotov et al. in 1990 , and 1991, however the mainstream scientific establishment had moved on.
and GONG
networks which consist of a global network of stations, as well as space based instruments such as the GOLF instrument aboard the SOHO
spacecraft. These are able keep the Sun under near-continuous observation, and so largely eliminate the influence of diurnal signals. Data from these instruments show no oscillation at 160 minutes.
Helioseismology
Helioseismology is the study of the propagation of wave oscillations, particularly acoustic pressure waves, in the Sun. Unlike seismic waves on Earth, solar waves have practically no shear component . Solar pressure waves are believed to be generated by the turbulence in the convection zone near...
.
The presence of a 160 minute cycle in the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
is not substantiated by contemporary solar observations, and the historical signal is considered by main-stream scientists to occur as the redistribution of power from the diurnal cycle as a result of the observation window and atmospheric extinction.
History
The birth of helioseismology occurred in 1976 with the publications of papers from Brookes, Isaak and van der Raay and Severny, Kotov and Tsap , both of which reported upon the observation of a 160 minute solar oscillation with an amplitude of approximately two metres per second.It was rapidly realised that this frequency corresponded to one-ninth of a day, and therefore the authenticity of this signal was in some doubt. If a non-sinusoidal oscillation is present in a time-series then power will be seen in a periodogram
Periodogram
The periodogram is an estimate of the spectral density of a signal. The term was coined by Arthur Schuster in 1898 as in the following quote:...
at not only the frequency of the oscillation, but also harmonics at integer multiples of this frequency. A re-analysis of data obtained over the period of 1974-1976 by Brookes et al. showed that the evidence for a stable, phase-coherent 160 minute oscillation at a constant amplitude was far from conclusive. Although the signal could be detected the amplitude appeared variable and was lower than first reported.
A re-affirmation of the 160 minute signal was obtained by analysis of data from groups in Crimea and Stanford over a long period of time. It was found that the phase showed a steady drift, indicative that the frequency being used in analysis differed slightly from that in the data. This implied that period of 160.01 minutes produced a better fit to the data. Evidence also emerged that multiple sets of observations were phase-coherent. These facts contributed to impressions that the origin of the observed signal was stellar and not terrestrial in origin.
In 1989 as higher-quality multiple-year datasets from a single site became available it was shown by Elsworth et al. that the period of the 160 minute signal was indeed 160.00 minutes, and the amplitude was dependent upon both the length and quality of data obtained in a season, with the signal more prominent at time where atmospheric condition were worse. The group were able to demonstrate that the signal may be simulated by a slightly distorted diurnal sine-wave such as may be obtained by differential atmospheric extinction.
However claims of the presence of a 160 minute period in the Sun were still being presented by Kotov et al. in 1990 , and 1991, however the mainstream scientific establishment had moved on.
Contemporary Observations
There are currently two solar-observation networks, the BiSONBison
Members of the genus Bison are large, even-toed ungulates within the subfamily Bovinae. Two extant and four extinct species are recognized...
and GONG
Global Oscillations Network Group
The Global Oscillation Network Group is a community-based program to study solar internal structure and dynamics using helioseismology.Six solar observatories are involved, with the intention of achieving almost unbroken observation of the Sun...
networks which consist of a global network of stations, as well as space based instruments such as the GOLF instrument aboard the SOHO
Solar and Heliospheric Observatory
The Solar and Heliospheric Observatory is a spacecraft built by a European industrial consortium led by Matra Marconi Space that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December 2, 1995 to study the Sun, and has discovered over 2100 comets. It began normal operations in May...
spacecraft. These are able keep the Sun under near-continuous observation, and so largely eliminate the influence of diurnal signals. Data from these instruments show no oscillation at 160 minutes.