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Long-periodic modulations in SKR

Long-periodic modulations in SKR and the near Saturn solar wind plasma environment – Possible planetary and solar effects. Fourier-Wigner-Ville analysis of Cassini data. M.L. Khodachenko 1 , A.G. Kislyakov 2,3 , M. Panchenko 1 , H.O. Rucker 1

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Long-periodic modulations in SKR

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  1. Long-periodic modulations in SKR and the near Saturn solar wind plasma environment – Possible planetary and solar effects. Fourier-Wigner-Ville analysis of Cassini data. M.L. Khodachenko1, A.G. Kislyakov 2,3, M. Panchenko1, H.O. Rucker 1 1 Space Research Institute, Austrian Academy of Sciences, Graz, Austria 2 Institute of Applied Physics, RAS, Nizhny Novgorod, Russia 3Lobachevsky State University, Nizhny Novgorod, Russia EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

  2. Long period (LP) modulations in SKR and MF: Application for monitoring of Saturn system • application to the available data sets of original unique algorithm for data processing: + Wigner E.P., Phys. Rev., 40, 749, 1932; Ville, J., Cables Transm., 2A 61, 1948;Cohen, L., Proc. IEEE, 77, 72, 1989; Shkelev, E.I., Kislyakov, A.G., Lupov, S, Yu., Radiophys. & Quant. Electronics, 45, 433, 2002. • Wigner-Ville (WV) method Advantages of the algorithm: - High sensitivity: detection of the modulating LP signals appeared below the noise level - High spectral and temporal resolution - Ability to detect complex multi-signal modulations(complex dyna- mic processes in source of SKR , external influences, etc.) "sliding window" Fourier (SWF) analysis • Technical requirements: - The length of the analyzed time series should include at least several periods of the LP modulating component; - Sampling cadence of analyzed time series  104 equidistant points per realization; - Input data format: ASCII ► Method Algorithm outcome: Dynamical spectra of the LP signals which modulate SKR data records and parameters of SW: magnetic field; density (?) Analysis of these LP spectra allows to judge about dynamics of the intrinsic physical conditions in the radiation source, including the possibility to detect global quasi-periodic signatures caused by the dynamical processes in the Saturnian environment and/or on the Sun. EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

  3. Wigner-Ville method versus Fourier transform ● Fourier transform allows to perform the analysis of the studied signal in terms of separate frequency components. - gives relative distribution of energy between frequency components. - does not provide the information on the appearance time of particular spectral components. - Possible improvement: Fourier transform within a certain shifting interval of time  t“sliding window” Fourier (SWF) transform. - Wave-let analysis -- further generalization of the SWF method. ● Wigner-Ville (WV) transform – a new method for spectral analysis in astrophysics P(f,t): - distribution of the signal energy over the frequency and time - Fourier image (relative the shifted time) of the local autocorrelation function of the analyzed signal z(t) WV method appears the most efficient for the analysis of cases with the quasi-harmonic modulating signals with a changing frequency and study of pulse sequences. It allows high resolution analysis of frequency-time structures of the modulating signals. z(t) = s(t) + jsG(t)–analytic signal; s(t) and sG(t)– real signal sample and itsGilbert conjugate. EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

  4. Wigner-Ville method versus Fourier transform ► Drawbacksof the WV Method non-local characterof the WV: noise and interferences appeared in a signal during a limited time can influence the WV dynamic spectrum in any its part. I.e. weak components of the signal can be suppressed by the signal intense (or noisy) part. non-linearity of the WV : appearance of artificial intermodulation components (artifacts) at the combination frequencies. Different types of the signal and spectral processing and filtration based on the combination of WV and SWF methods are realized in the algorithmin order to eliminate possible artifacts and provide high spectral and temporal resolution. EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

  5. Long Periodic (LP) modulations in SKR ►Analysis of long - periodic modulations in the SKR data records made by Cassini in 2004 (from 01.01.04 till 01.01.05) ∎ SKRdata file with 20 min sample cadence is analyzed ● Application of Sliding Window Fourier analysis (with different windows) ●Application of Wigner-Ville analysis ●Direct visual analysis of averaged signal curves EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

  6. Long Periodic (LP) modulations in SKR Impulsive modulation activity storms ~0.026 mHz (~10.7 h) modulation ● Direct analysis of data (no averaging) EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

  7. Modulation activity storms in SKR Number of burst (from 1 to 43) ● Modulation bursts repeat quite regularly, with the period ~ 9 days: EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

  8. 10.7 hour modulation in SKR Exact period: 10.75 h (± 0.02 h) , i.e. f0 =0.0258 mHz ● Averaged (over all observation time) spectrum of the 10.7 h line: EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

  9. 10.7 hour modulation in SKR ● Stability of 10.7 h line (10 samples averaged data; digital filter 0.0258 mHz): R – rectangular window; P – Parsen window (~2 times smaller) Possible frequency deviations do not exceed the line width EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

  10. 10.7 hour modulation in SKR ● Filtered 10.7 h line intensity changes: Correlation with SKR pulse activity : (digital filter: f0 =0.0258 mHz ,Δf = 0.001 mHz) EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

  11. Burst character of 10.7 h impulsive modulation of SKR 168-th 51-st 25-th ● Direct analysis of data (no averaging) EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

  12. Burst character of 10.7 h impulsive modulation of SKR ● Modulation burst on 25-th day. Duration: ~ 6.3 days EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

  13. Burst character of 10.7 h impulsive modulation of SKR ● Modulation burst on 51-st day. Duration: ~ 4.7 days EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

  14. Burst character of 10.7 h impulsive modulation of SKR ● Modulation burst on 168-th day. Duration: ~ 5.5 days EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

  15. More Long Periodic (LP) modulations in SKR Interrupted modulation at ~ 0.9 microHz (12.8 days) ~0.0258 mHz (~10.7 h) modulation ● Data averaged over 10 samples(200 min); W=256 EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

  16. More Long Periodic (LP) modulations in SKR ● Variations of 12.8 days line. Averaging over 50 samples (1000 min), W=256 EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

  17. More Long Periodic (LP) modulations in SKR ~ 0.9 microHz (12.8 days) ~ 1.28 microHz (9 days) ● Data averaged over 50 samples (1000 min). “Normalized” signal (divided by module curve)  removing pulses, visibility of sin-type processes Difference between the 12.8 days and 9 days modulations: - 9 days – modulation storms period - 12.8 days – change of the signal amplitude in storms EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

  18. 1.37 – 1.44 days modulations in SKR: Enceladus ??? ~ 8.0 microHz (1.4 days) ~ 7.5 microHz (1.5 days) ● Data averaged over 50 samples (1000 min) - 8.0 microHz line - during the strong emission periods - 7.5 microHz line - when the emission is weaker - Both may be caused by same process (changing velocity of rotation) EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

  19. Long Periodic (LP)modulations in Magnetic field 10.7 h modulation Modulation activity storms ►Analysis of long - periodic modulations in the Magnetic field data records made by Cassini in 2004 (days: 140 - 365) EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

  20. 10.7 h modulations in SKR and Magnetic field ● Comparison of the MF and SKR 10.7 h lines amplitude (intensity) Comon features: - Similar periodicity and morphology;- Similar number of wavelets ( ~23) EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

  21. 10.7 h modulations in SKR and Magnetic field ● Correlation of minima in the MF and SKR 10.7 h lines amplitude (intensity) Line equation:Y = 0.95 X + 0.38 - Delay of SKR reative MF (for the 10.7 h modulation) - Shift between MF and SKR: ~12.8 days ( ! ) Correlation EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

  22. LF modulations in SW density (11 hour line ?) 0.012 mHz (23.2 h) 0.026 mHz (10.7 h) 0.004 mHz (2.9 days) ● Modulation of solar wind density - 11 h line ?: EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

  23. Long Periodic (LP) modulations in SKR ● SKR intensity is modulated in a form of quasi-periodic modulation acti- vity storms or modulation bursts.43 storms/bursts may be distinguish- ed during 2004 ● Modulation activity storms (modulation bursts) repeat almost periodi- cally (~ 9 days) ●Series of periodic pulses: ~10.75 h (0.02585 mHz) (correlated with Saturn rotation) with changing amplitude produce the modulation activity storms ●Amplitude of 10.75 h pulses has complex modulation with well pronoun- ced 1.4-1.5 days and 12.8 days components. ●9 days modulation may be due to propagating periodic compressions in solar wind; 12.8 days may be related to Titan, 1.4 days – to Enceladus (?) ●Magnetic field modulations show presence of 10.7 h, 12.8 days; 20 days and other components ●10.7 h modulations of SKR and MF seem to be connected Further identification of modulation lines to distinguish between solar and planetary effects requires similar analysis of 2005 records, extrapolation of SW data from other space missions EPSC, Europlanet GA – Sep. 18 –22, 2006,Berlin, Germany

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