J. J. Quenby

The theory of cosmic-ray modulation

The current state of the theory describing cosmic-ray modulation in the interplanetary medium is reviewed. Emphasis is given to the problems of determining the transport coefficient for diffusion in energy and position space and in assessing the importance of particle drift motion in three-dimensional modulation models.

Cosmic ray modulation by expanding, high-latitude streams

As ‘Ulysses’ moved to latitudes above 45°, the regular, recurring series of mid-latitude high-speed streams is no longer observed out to 4 AU. However, the associated, near-relativistic particle modulation persists to at least 70°. We explain this remote shadowing as due to the spread in latitude of the fast streams beyond the ‘Ulysses’ trajectory and show that an estimate of the particle diffusion coefficient within the stream, based on magnetometer data, yields sufficient modulation to make the model plausible.

Ulysses observations of short‐period (≤30 Days) modulation of the galactic cosmic rays

A frequency analysis of the short-period modulation of the GCR as seen by instruments aboard Ulysses shows interesting temporal variations. In particular, during an approximate five-month period from December 1993 to May 1994, the modulation was not the usual 26 days but more than 29 days. The CIR-associated MeV ions did not exhibit this period shift.

Theoretical Studies of Interplanetary Propagation and Acceleration

Studies evaluating the transport coefficients for energetic particles in interplanetary space are described in relation to particle data.

Observations of energetic particles with EPAC on Ulysses in polar latitudes of the heliosphere

SummaryMeasurements with the EPAC energetic-charged-particle instrument aboard Ulysses show between −15° and −65° ions and, to some extent, also electrons apparently accelerated by shocks associated with a cororating interaction region (CIR) operating at low latitudes. Particles could have reached Ulysses along magnetic-field lines which connect to the shocks in the more distant heliosphere. Such connections evidently do not exist above −65°. Between the recurrent streams we find the underlying composition to be similar to that of the anomalous component of cosmic rays (ACR). One channel (ELH), sensitive also to high-energy protons (E>210 MeV), shows that, superimposed to the large-scale heliospheric modulation of galactic ions, a 26-day variation of the flux is observed. Such modulation is also observed for the ACR, in phase with the galactic particle modulation, but anticorrelated to the CIR-related low-energy particles. An estimate of the latitudinal and radial gradients of the galactic cosmic rays at 1 GV gives +0.4%/degree and −11%/AU, respectively.

On the minimum fluxes of low-energy ions (0.5 MeV/nuc-8 MeV/nuc) at high heliospheric latitudes

Abstract The quiet-time fluxes of ions from 0.5 MeV/nuc to 7 MeV/nuc (for oxygen) have been studied for the time period between mid-1993 through the first 104 days of 1994. During this time period Ulysses was below the heliographic current sheet. We find that at the quietest times, the ion population is dominated by the ACR component. For more active times, but still avoiding the most active time periods, the population below 3 MeV/nuc contains a CIR component as well as ACR ions.

Suggestions for magnetospheric experiments

ConclusionThe proposals for a high-inclination satellite and for a satellite to investigate particlewave interactions both seem well within the capabilities of ESRO. However, the two-satellite system, although difficult, seems much more likely to yield additional information on the fundamental acceleration mechanism for the acceleration of auroral and trapped particles; that is the means by which they initially obtain a significantly greater energy than that of solar wind particles. Thus this last proposal is the one most in accord with fundamental aims of much of the work of ION and COS groups.