150 Day Periodicities in the Voyager 2 Plasma Data

Details 150 Day Periodicities in the Voyager 2 Plasma Data 150 Day Periodicities in the Voyager 2 Plasma Data

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsh21b0151a&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SH21B-0151

Other

2124 Heliopause And Solar Wind Termination, 2162 Solar Cycle Variations (7536), 2164 Solar Wind Plasma

Scientific paper

Launched over 26 years ago, Voyager 2 is now at a radial distance greater than 71 AU and a latitude of -28.7 degrees out of the ecliptic plane. Voyager 2 and the MIT Plasma Spectrometer continue to return measurements daily. Periodicities with T ≈ 150 days have been observed in the solar wind by several authors. Fourier and Lomb-Scargle periodograms of the uniquely long Voyager 2 plasma density and bulk-speed data sets (1978-2003) similarly show a strong component at periods of approximately 150 days. Dividing the data into two (1978.0-1990.5 and 1990.5-2003.0) and taking periodograms of the subsets shows a strong ~150 day component in the earlier data but not the latter. Periodograms of further sub-divisions of the data demonstrate a definite time-variation in the spectral power at periods around 150 days. To give a more quantitative view of time-variation of the periodicities, wavelet-analysis was employed. Initial results showed little or no power in the wavelet power spectra around 150 days. By using unusually (temporally) large wavelets, we demonstrate the existence of episodes of persistent but low-power periodicities in the Voyager plasma data, not detected by the smaller scale wavelets. Using large-scale wavelets reveals two episodes of power at ≈ 150 day periods (both several years long) in the density data and one episode in the bulk-speed data. We compare the bulk-speed and density results and discuss the relationship of the episodes to spacecraft position (radial distance and latitude) as well as to the solar cycle. Results are also compared to measurements of ~150 day periodicities by other authors. Voyager observations are sponsored, in part, by NASA/JPL.

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