1. A. J. Kopf 1,2 and D. A. Gurnett 1 1 University of Iowa 2 University of Florida Special thanks to J. D. Menietti, R. L. Mutel, and W. M. Farrell

2. Striations  What Are Kilometric Striations? Fine-structure features found in kHz-band, generally overlapping kilometric radiation Appear as narrow, discrete stripes on a frequency-time spectrogram, nicknamed “rain” for appearance With Cassini, can only be resolved in wideband spectrograms due to resolution Caused by cyclotron maser instability Seem to be best explained by upward-traveling ion solitary structures (ion holes)  Why Study These Features? Test the conclusions from Earth ○ First time these features have been observed elsewhere Remote study of source region characteristics ○ Striations visible 10s-100s of radii from planets

3. Striations at Earth Menietti et al., JGR, 2000

4. The Study  Jupiter data from 100-day period during Cassini flyby, distance <1000 R J  Saturn data since approach, distance <100 R S  Follows the model of Menietti et al. (2000)  Focused on key characteristics, including: Probability of observation (11.5%) Frequency range of observations (40-215 kHz) Duration of striations (0.8 s) Frequency drift (-3.5 kHz) Drift rate (-4.4 kHz/s)

5. Striations at Jupiter

6. By the Numbers: Jupiter  Observation Frequency: 9.1%  Frequency Range: 25 – 75 kHz  Average Duration: 12.6 s  Average Frequency Drift: -14.6 kHz  Average Drift Rate: -1.2 kHz/s

7. Striations at Saturn

8. By the Numbers: Saturn  Observation Frequency: 10.8%  Frequency Range: 30 – 80 kHz  Average Duration: 6.8 s  Average Frequency Drift: -9.9 kHz  Average Drift Rate: -1.6 kHz/s

9. Striation Duration Menietti et al., JGR, 2000

10. Negative Drift Rates Menietti et al., JGR, 2000

11.  Assuming and Approximating: These planets have a dipole magnetic field The source radiates at the local electron cyclotron frequency The source moves upward along the field line at the magnetic latitude of the spacecraft  Average Source Speeds and Locations: Earth = 213 km/s @ 1.5 R E (Mutel et al., 2006) Jupiter = 3000 km/s @ 5.9 ± 0.3 R J (Io) Saturn = 2000 km/s @ 2.2 ± 0.2 R S (Encel. torus) An Upward-Moving, Constant-Velocity Source

12. Mutel et al., JGR, 2006

13. Why 2.2 R S ?  The region around 2.2 R S, the inner edge of the Enceladus plasma torus, is a very active zone.  Narrowband Z-mode tones detected near the inner edge of the Enceladus torus [Farrell et al., 2005]  Mass unloading directly observed at 2.2 R S [Farrell et al., 2008]

14. Positive-Drifting Striations

16. Summary and Comparison EarthJupiterSaturn Observation Rate 11.5%9.1%10.8% Frequency Range (kHz) 40 – 21525 – 7530 – 80 Avg. Duration (s) 0.812.66.8 Avg. Frequency Drift (kHz) -3.5-14.6-9.9 Avg. Drift Rate (kHz/s) -4.4-1.2-1.6 Avg. Source Speed (km/s) 21330002000 Estimated Source Location 1.5 R E 5.9 ± 0.3 R J 2.2 ± 0.2 R S