Ulysses HISCALE Publications and Presentations

 

Measurements of Jupiter's Hot Plasma Population with the Ulysses

HI-SCALE Instrument

 

Authors: T. P. Armstrong, Dept. of Physics and Astronomy, Univ. of Kansas; L. J. Lanzerotti, AT and T Bell Laboratories; R. E. Gold, S. M. Krimigis, and E. C. Roelof, Johns Hopkins Univ. Applied Physics Laboratory; K. A. Anderson and R. P. Lin, Space Science Laboratory, Univ. of Calif.-Berkeley; M. Pick, Observatorie de Paris, Meudon, France; George Simnett, Univ. of Birmingham, U.K.; E. T. Sarris, Democritos Univ. of Thrace, Greece; A. Balogh, Imperial College, London, U.K.; with crucial assistance from: Carol Maclennan, AT and T Bell Laboratories, James Tappin, Univ. of Birmingham, U.K., and T. H. Choo, Dept. of Physics and Astronomy, Univ. of Kansas.

 

Presented at: Goertz-Smith Symposium on the Magnetospheres of the Outer Planets, UCLA, June 22-26, 1992.

 

Outline:

 

• The HISCALE instrument
• Overview - spectrum, anisotropies, time variations
• Comparison of Ulysses and Voyager observations
• Estimate of auroral inputs

  

Figures:

 

	Figure 1. LAN 2A and LAN 2B configurations		Figure 2. Spin plane clock angle (degrees) from spacecraft x-axis
	Figure 3.		Figure 4.
	Figure 5.		Figure 6.
	Figure 7.		Figure 8.
	Figure 9.

 

 

Table 1. Channels used:

 

 

 

	Figure 10 - ions		Figure 11 - electrons
	Figure 12		Figure 13
	Figure 14

 

 

Observe:

  

1. f(μ) for μ=const. decreases with increasing B. Typically, f(μ) µ B-γ where 1~<γ~<3.
2. Ulysses and Voyager 2 have similar profiles for μ=500 and 890 MeV/Gauss ions.
3. Voyager 2 has much larger electron PSDs than Ulysses (despite #2 above).
4. Voyager 1 had much larger ion and electron PSDs than Ulysses.

 

Provisional Conclusion:

 

Ulysses and Voyager ion and electron observations are consistent with lossy radial transport of particles from a time-variable, large radial distance, low-latitude source. Solar wind is an obvious candidate.

  

Table 2 (modified on 4/27/92):

  

 

 

Figure 15. Ulysses trajectory in Jovian dipole coordinates

 

 

 

Data Analyses and Results:

 

The observations show that during almost all the inbound and outbound passes the pitch angle distributions of electrons and ions are either very isotropic or strongly bi-directional (occurring particularly near the closest encounter). To study the energy fluxes and power inputs for the Jovian aurora, we chose two-hour observed data mostly close to Jupiter during the inbound (92:38:19:0 to 92:38:21:0) and outbound (92:40:01:0 to 92:40:03:0) passes. In this study we used:

Loss cone = arcsin (1 / R2)

Flux area ≈ π(Z22 - Z12)

 

where Zi = Ri * sin(Lat.i) for i-th data record.

 

Diff. Flux = Count Rate / G-Factor x Passband

 

Moreover, we assumed that both electrons and ions have a power-law spectrum, and the power index γ was estimated by

 

Diff. Flux = J₀ (E/E0)-γ

 

We found that the assumed power-law spectrum agrees very well with both the Ulysses electron and ion data. For the chosen data set, the average γ is about 2.2 ~ 2.5 for ions and about 1.54 ~ 2.2 for electrons, respectively.

 

With obtained values of γ we can estimate average local energy flux by

 

 

and local power input by

 

Power Input = Energy Flux x Loss Cone x Flux Area

 

Figure 16

Figure 17 - Top: Spin average ions energy spectrum, inbound - LEMS 120 and LEMS 30; Bottom: Spin average electron energy spectrum, inbound - LEFS 60, LEFS 150, and WART 60

 

 

Summary

 

1. Near the closest encounter with Jupiter, the Ulysses data present a good power law spectrum for both electrons and ions within the whole energy band of the HISCALE experiment, and the power index γ slightly increases with decreasing magnetic latitude.
2. The pitch angle distributions of electrons and ions observed by Ulysses at high Jovian magnetic latitudes are basically either isotropic or bi-directional, and the latter indicates strong energetic particle precipitations and Birkeland currents.
3. The observed energy flux at latitude γ ~ 20 deg. is estimated at a level of 1.0 erg cm-2 s-1 for 38-315 keV electrons, and approximately one order less, i.e., 0.1 erg cm-2 s-1, for 56-4752 keV ions. This implies that electron precipitation is the major source of particle precipitation from the Jovian magnetosphere down to the Jovian ionosphere.
4. Assuming the observed electron energy input powered the Jovian aurora, we used a theoretical model of the Jovian atmosphere and ionosphere and calculated that the integrated production rate (0<altitude<2030 km) for H2 Lyman and Werner bands is about 9.67 kR. If the energy efficiency for those bands is 15%, then a total energy flux of 0.4 erg cm-2 s-1 is required.
   

HISCALE observed Jovian particles from as early as Nov. '91 through April. There were abundant and strong field aligned anisotropies--especially dusk outbound with current densities ~1.6 (something) Electrons in HISCALE range (42-300 keV) can provide ~1 erg/cm2 to the atmosphere. (Electrons are about 10x the energy flux of ions in this range.) There are dramatic changes in intensities and angular distributions in times as short as 12 sec. (one s/c rev.). There is evidence for filamentary or laminated structure in hot plasma distributions (there are apparently gradient anisotropies at boundaries).