Intensities of SATURN KILOMETRIC RADIATION G G. Fischer1 and S.-Y. Ye2 Space Research Institute, Austrian Academy of Sciences, Graz, Austria Department of Physics and Astronomy, The University of Iowa, Iowa City, USA S2nd ISSI team meeting „Rotational phenomena in Saturn‘s magnetosphere“, Bern, Switzerland, March 20-24, 2017 Alexandra Scherr Institut für Weltraumforschung, Österreichische Akademie der Wissenshaften

SKR flux density Normalized to 1 AU Occurrence levels of LH (squares) and RH (triangles) SKR as function of frequency Flux density levels @ 1 AU reached 50%, 10%, 1% of the time Peak flux @ 200 kHz 10-21 W/(m²Hz)=105 Jy Distance normalization by multiplication with (149 597 871/60268*x)² with x being the distance of Cassini to Saturn in RS Lamy et al. (2008)

INTegrated SKR Flux for Periodicity Analysis RPWS HFR measures signals in V²/Hz (1 value for 1 frequency channel every 16 s is typical) Separate signals by polarization (v>0 for LH i.e. S-SKR; v<0 for RH i.e. N-SKR) or in way described in App. B by Fischer et al. (2015) Divide by Z0=120  (impedance of free space) to get W/Hz Divide by antenna effective area (m²) to get W/(m² Hz) No distance normalization here Integrate flux in frequency interval (Shengyi: 80-500 kHz, Georg: 200-800 kHz excluding interferences) to get W/m² and average over 10 minutes (temporal resolution) Text files with integrated N-SKR flux and S- SKR flux in 2 columns on teampage 2005-001T00:00 3.389943e-013 9.197859e-014 2005-001T00:10 5.013889e-014 4.928517e-014 2005-001T00:20 4.883703e-014 2.202277e-014 2005-001T00:30 4.805302e-014 6.180141e-014 2005-001T00:40 8.192228e-014 1.732326e-013 2005-001T00:50 3.849716e-014 7.213932e-013 2005-001T01:00 2.964920e-014 5.463537e-013 2005-001T01:10 2.714829e-014 4.191669e-013 2005-001T01:20 8.593788e-015 4.082689e-014 2005-001T01:30 1.331755e-014 3.941894e-014 2005-001T01:40 1.658909e-014 7.571736e-014 2005-001T01:50 7.960671e-014 2.073140e-013 2005-001T02:00 1.205284e-014 5.043049e-014 2005-001T02:10 3.155642e-015 2.006731e-014 2005-001T02:20 4.867868e-015 3.594250e-014 2005-001T02:30 7.729677e-015 2.810074e-014 2005-001T02:40 2.564268e-014 8.720045e-014 2005-001T02:50 4.647904e-014 2.402210e-013 2005-001T03:00 3.509133e-014 2.084955e-013 2005-001T03:10 7.582632e-015 7.426911e-014 2005-001T03:20 1.937217e-014 1.833823e-013 2005-001T03:30 1.008318e-014 7.013783e-014 2005-001T03:40 1.916473e-014 8.672119e-014 2005-001T03:50 4.673184e-014 1.474847e-013 2005-001T04:00 2.919224e-014 1.122968e-013 2005-001T04:10 3.032302e-014 2.054205e-013 2005-001T04:20 9.169354e-015 5.362015e-014 2005-001T04:30 7.184297e-014 5.567805e-014 2005-001T04:40 2.241784e-013 5.959150e-014 2005-001T04:50 2.365172e-013 1.857084e-013 2005-001T05:00 6.606546e-015 4.498957e-014 2005-001T05:10 8.939642e-016 4.552286e-014 2005-001T05:20 1.219548e-015 4.125929e-014 2005-001T05:30 1.583754e-015 8.344374e-015 2005-001T05:40 5.519982e-015 3.970056e-014

Polarization of SKR

10.7 h periodicity of Int. SKR flux Running average over (2q+1)*10=90 minutes SKR averages calculated as logarithmic (running) averages 4-5 periods within 2 days (48/10.74.5)

25-27 day periodicity of IntEgrated AND Normalized SKR flux Daily averaged integrated SKR flux normalized to 1 AU

Fourier transform of SKR fluxes strong peak at 25-27 days

SKR flux ratio over 1 year (2011) Orbits in 2011 are equatorial Ratio calculated from daily averaged SKR fluxes Vertical dotted lines indicate times of Cassini periapsis passes

SKR flux ratio at inclined orbits (YEAR 2009 chosen Here) Aim is to get “k-values” for SKR (k describes N/S magnetic field amplitude ratio, Provan et al.) Both SKR sources visible only in [-20°,20°] latitude range N/S SKR flux ratio can only be determined in this latitude range N/S flux ratio highly depends on latitude 2 equatorial plane crossings per orbit with high inclination

N/S SKR flux ratio 2004-2017 (LATitude Limit: 20°) 3 regions: S-SKR dominant before mid-2006 Oscillation around 1 for 7 years around equinox N-SKR dominant after mid-2013

N/S SKR flux ratio 2004-2017 (LATitude Limit: 5°) Continuous change of SKR N/S flux ratio superposed by oscillations with a period of ~200 days Smaller amplitudes compared to latitude limit 20° Very similar plot for fluxes of Sheng-yi

LOmB-scargle periodogram of SKR flux ratio Peaks around 130, 200, 300, 420 days with largest peak at 182 days

Comparison with Kasaba et al. Comparison with S/N peak flux ratio from poster of Kasaba et al. (2016, PRE 8 workshop), photo taken with permission Similar results (latitude limit chosen to be 10°) of Kasaba, SKR flux from Georg (right) and from Sheng-yi (left)

Oscillation of N & S Skr fluxes N and S SKR flux (orbital averages) oscillate mainly in phase with each other (except end of 2009 until mid-2011, when they are in anti-phase) N-SKR flux looks constant whereas S-SKR flux decreases over the years

Lomb-scargle periodograms of n-SKR and S-skr fluxes

Comparison of n/S SKR Flux Ratio with k-values of Magnetic Field Time intervals defined by Provan et al. (2013, 2015) by abrupt changes in k, phases or period First interval (k1, days 2025-2597) has subintervals of 210075, 215075, … 255075) No k-values beyond day 3500 (due to high latitude) Determination of 1 k- value over 5 (?) periapsis passes

Comparison of n/S SKR Flux Ratio with k-values of Magnetic Field Time intervals 1-4 show agreement if N or S is dominant (with k1 in interval 1) but different values SKR indicates northern dominance in 5 & 6 (despite medium latitude orbits with long dwell time in southern hemisphere) k-values depend on latitude (Hunt et al., 2015). So do N/S SKR flux ratios. However, only equatorial values are taken. SKR N/S ratios determined over the same intervals as given by Provan et al. (2013, 2015) within 2° latitude

Comparison of n/S SKR Flux Ratio with k-values of Magnetic Field Why do k-values and SKR N/S-ratios not agree? Amplitude of magnetic perturbation field should be proportional to main FAC that cause SKR emission Interval 5 and 6 have medium latitude orbits (periapsis ~30°N) which can influence k-value determination SKR beamed to s/c might not represent overall intensity of radio source Dependence on LT Changes of SKR N/S ratio and of k-values (k) do no agree well at boundaries 1-2, 2-3, 3-4. No abrupt SKR N/S ratio changes at boundaries.

Correlation OF SKR N/S ratio with sun spot number?

Correlation OF SKR N/S ratio with sun spot number? Physical relation between the Sun and SKR intensity Solar EUV increases ionization and therefore higher conductivities and larger currents Solar wind ram pressure influences SKR intensity (Desch & Rucker, 1983) Maxima and minima of sunspot number do not match well to maxima or minima of N-SKR or S-SKR flux alone, only to SKR ratio. Why?

Summary Frequency-integrated SKR flux (N and S values) in W/m² with 10 min. resolution can be found as text files on the team webpage Integrated SKR flux shows 10.7 h periodicity Integrated SKR flux shows 25-27 day periodicity due to Solar rotation (display daily averages, all SKR averages calculated as logarithmic averages) N/S SKR flux ratio highly depends on latitude, restriction to 2°, 5° necessary SKR flux ratio shows southern dominance until mid-2007, an oscillation around 1 from mid-2007 to mid-2012 and northern dominance after mid-2012 SKR flux ratio shows oscillations of ~200 days, what is the cause? Maybe the sunspot number plays a role (external influence) N and S SKR flux mainly oscillate in phase Comparison of N/S SKR flux ratio with k-values from magnetic field shows no good agreement, especially in intervals 5 and 6 (days 3203-3457, i.e. Oct. 2012 until June 2013) when SKR indicates clear northern dominance, but k-values show weak southern dominance