1. Intensities of SATURN KILOMETRIC RADIATIONG
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

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

3. 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: kHz, Georg: 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
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4. Polarization of SKR

5. 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)

6. 25-27 day periodicity of IntEgrated AND Normalized SKR flux
Daily averaged integrated SKR flux normalized to 1 AU

7. Fourier transform of SKR fluxes
strong peak at days

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

9. 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

10. 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

11. 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

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

13. 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)

14. 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

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

16. 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 ) 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

17. 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

18. 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.

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

20. 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?

21. 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 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 , i.e. Oct until June 2013) when SKR indicates clear northern dominance, but k-values show weak southern dominance