Currents in the Jovian middle magnetosphere draw out magnetic field lines radially into a configuration which has high equatorial curvature and weak field strength. Charged particles spiral along field lines into this equatorial region, where, depending on their energies, they may have gyroradii comparable to or larger than the scale length of the field. Magnetic moment violation resulting in a stochastic change in pitch angle may thus occur locally at the equator. Using a linear approximation to the field variation and a mathematical technique for distorting the orbit integration into the complex gyrophase plane, we derive a formula for the nonadiabatic change Δµ in magnetic moment. Δµ varies as cos Ψr where Ψr is particle gyrophase at the equator, so that if a particle traverses the equator several times with different values of Ψr, it suffers randomly correlated values of Δµ. The algebraic formula for Δµ is in excellent agreement with previous numerical computations. The phase space density, averaged over several bounce periods, satisfies a diffusion equation in pitch angle. The diffusion coefficient depends on particle energy, pitch angle, and the field line along which the particles are moving. Energetic sulfur ions (hundreds of keV and higher) are diffused in a few tens of bounce periods beyond 20 RJ, and the behavior of protons is not too dissimilar. Electrons, which at the same energy have much smaller gyroradii, become nonadiabatic and diffusive only near 28 RJ, where the magnetic model predicts a combination of especially weak field and large spatial variation. Pioneer and Voyager particle results are summarized in the light of this diffusion mechanism; while there is evidence for magnetic moment violation, an utter absence of pitch angle structure in the outer magnetodisc region (which should thus follow from the magnetic model) has not been confirmed (or looked for, to a large degree). Implications for other magnetospheric mechanisms are discussed. Finally, the possibility of a similar diffusion in the Saturnian ring current region is addressed, and it is found that only at much higher energies (>100‐MeV protons) is this type of nonadiabatic behavior to be expected.

Electrostatic emissions are often observed by spacecraft in the outer magnetosphere at frequencies between low electron gyroharmonics. The emissions include the well‐known odd half‐harmonic emissions as well as weaker emissions which occur near the electron plasma frequency. We have constructed a scheme for classifying the emissions and have shown that a theoretical model which has been previously used to explain ‘3/2’ emissions can be extended to the other classes of emissions. All of the emissions therefore appear to be generated by the same basic mechanism: an unstable electron plasma distribution consisting of cold electrons (<100 eV) and hot loss cone electrons (∼1 keV). Each emission class is associated with a particular range of model parameters; the wide‐band electric field data can thus be used to infer the density and temperature of the cold plasma component. The model predicts that gyroharmonic emissions near the plasma frequency require large cold plasma densities.

A steady state model of Jupiter's electron radiation belt is developed. The model includes injection from the solar wind, radial diffusion, energy degradation by synchrotron radiation, and absorption at Jupiter's surface. A diffusion coefficient of the form DRR/RJ² = kRm is assumed, and then observed data on synchrotron radiation are used to fit the model. The free parameters determined from this fit are m = 1.95 ± 0.5, k = 1.7 ± 0.5 × 109/s, and μ1 (the magnetic moment of injected particles) = 770 ± 300 MeV/G. The value of m shows quite clearly that the diffusion is not caused by magnetic pumping by a variable solar wind or by a fluctuating convection electric field. The process might be field line exchange driven by atmospheric‐ionospheric winds; our diffusion coefficient has roughly the same radial dependence but is considerably smaller in magnitude than the upper bound diffusion coefficients recently suggested for this process by Brice and McDonough (1973) and S. A. Jacques and L. Davis, Jr. (unpublished manuscript, 1972).

We explore here the possible importance of time‐dependent convection electric fields as an agent for diffusing trapped magnetospheric radiation inward toward the earth. By using a formalism (Birmingham, Northrop, and Fälthammar, 1967) based on first principles, and by adopting a simple model for the magnetosphere and its electric field, we succeed in deriving a one‐dimensional diffusion equation to describe statistically the loss‐free motion of mirroring particles with arbitrary but conserved values of the first two adiabatic invariants M and J. Solution of this equation bears out the fact that reasonable electric field strengths, correlated in time for no longer than the azimuthal drift period of an average particle, move particles toward the earth at a rate at least an order of magnitude faster than electric fields whose source is a fluctuating current on the magnetopause.

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