Earl Scime

Ulysses Solar Wind Plasma Observations at High Southerly Latitudes

Solar wind plasma observations made by the Ulysses spacecraft through –80.2� solar latitude and continuing equatorward to –40.1� are summarized. Recurrent high-speed streams and corotating interaction regions dominated at middle latitudes. The speed of the solar wind was typically 700 to 800 kilometers per second poleward of –35�. Corotating reverse shocks persisted farther south than did forward shocks because of the tilt of the heliomagnetic streamer belt. Sporadic coronal mass ejections were seen as far south as –60.5�. Proton temperature was higher and the electron strahl was broader at higher latitudes. The high-latitude wind contained compressional, pressure-balanced, and Alfv�nic structures.

Ion Acceleration in Plasmas Emerging from a Helicon-heated Magnetic-mirror Device

Using laser-induced fluorescence, measurements have been made of metastable argon-ion, Ar+*(3d4F7/2), velocity distributions on the major axis of an axisymmetric magnetic-mirror device whose plasma is sustained by helicon wave absorption. Within the mirror, these ions have sub-eV temperature and, at most, a subthermal axial drift. In the region outside the mirror coils, conditions are found where these ions have a field-parallel velocity above the acoustic speed, to an axial energy of ∼30 eV, while the field-parallel ion temperature remains low. The supersonic Ar+*(3d4F7/2) are accelerated to one-third of their final energy within a short region in the plasma column, ⩽1 cm, and continue to accelerate over the next 5 cm. Neutral-gas density strongly affects the supersonic Ar+*(3d4F7/2) density.

A forward‐reverse shock pair in the solar wind driven by over‐expansion of a coronal mass ejection: Ulysses observations

A previously unidentified type of solar wind forward-reverse shock pair has been observed by Ulysses at 4.64 AU and S32.5°. In contrast to most solar wind forward-reverse shock pairs, which are driven by the speed difference between fast solar wind plasma and slower plasma ahead, this particular shock pair was driven purely by the over-expansion of a coronal mass ejection, CME, in transit from the Sun. A simple numerical simulation indicates that the overexpansion was a result of a high initial internal plasma and magnetic field pressure within the CME. The CME observed at 4.64 AU had the internal field structure of a magnetic flux rope. This event was associated with a solar disturbance in which new magnetic loops formed in the corona almost directly beneath Ulysses ∼11 days earlier. This association suggests that the flux rope was created as a result of reconnection between the “legs” of neighboring magnetic loops within the rising CME.

The whistler heat flux instability: Threshold conditions in the solar wind

Solar wind electrons are observed often to consist of two components: a core and a halo. The anisotropies and relative average speeds of these two components correspond to a heat flux that has the potential to excite several different electromagnetic instabilities; wave-particle scattering by the resulting enhanced fluctuations can limit this heat flux. This manuscript describes theoretical studies using the linear Vlasov dispersion equation for drifting bi-Maxwellian component distributions in a homogeneous plasma to examine the threshold of the whistler heat flux instability. Expressions for this threshold are obtained from two different parametric baselines: a local model that yields scalings as functions of local dimensionless plasma parameters, and a global model based on average electron properties observed during the in-ecliptic phase of the Ulysses mission. The latter model yields an expression for the heat flux at threshold of the whistler instability as a function of heliospheric radius that scales in the same way as the average heat flux observed from Ulysses and that provides an approximate upper bound for that same quantity. This theoretical scaling is combined with the observational results to yield a semi-empirical closure relation for the average electron heat flux in the solar wind between 1 and 5 AU.

Regulation of the solar wind electron heat flux from 1 to 5 AU: Ulysses observations

In this study the authors use observations from the three-dimensional electron spectrometer and magnetometer aboard the Ulysses spacecraft to examine the solar wind electron heat flux from 1.2 to 5.4 AU in the ecliptic plane. Throughout Ulysses` transit to 5.4 AU, the electron heat flux decreases more rapidly ({approximately}R{sup {minus}3.0}) than simple collisionless expansion along the local magnetic field and is smaller than expected for a thermal gradient heat flux, q{sub {parallel}}e(r)={minus}k{sub {parallel}}{del}{sub {parallel}}T{sub e}(r). The radial gradients and magnitudes expected for a number of electron heat flux regulatory mechanisms are examined and compared to the observations. The best agreement is found for heat flux regulation by the whistler heat flux instability. The upper bound and radial scaling for the electron heat flux predicted for the whistler heat flux instability are consistent with observations.

First medium energy neutral atom (MENA) Images of Earth's magnetosphere during substorm and storm-time

InitialENA images obtained with the MENA imager on the IMAGE observatory show that ENAs ema- nating from Earths magnetosphere at least crudely track both Dst and Kp. Images obtained during the storm of August 12, 2000, clearly show strong ring current asymme- try during storm main phase and early recovery phase, and a high degree of symmetry during the late recovery phase. Thus, these images establish the existence of both partial and complete ring currents during the same storm. Further, they suggest that ring current loss through the day side mag- netopause dominates other loss processes during storm main phase and early recovery phase.

Ulysses observation of a noncoronal mass ejection flux rope: Evidence of interplanetary magnetic reconnection

A well-defined, small-scale (≈0.05 AU) magnetic flux rope was observed by Ulysses at about 5 AU in close proximity to a heat flux dropout (HFD) at the heliospheric current sheet (HCS). This magnetic flux rope is characterized by a rotation of the field in the plane approximately perpendicular to the ecliptic (and containing the Sun and the spacecraft) and with a magnetic field maximum centered near the inflection point of the bipolar signature. The edges of the flux rope are well defined by diamagnetic field minima. A bidirectional electron heat flux signature is coincident with the magnetic flux rope structure. The event occurred during a time of slightly increasing solar wind speed, suggesting that the field and plasma were locally compressed. Unlike most coronal mass ejections/magnetic clouds, this event is characterized by high proton temperatures and densities, high plasma beta, no significant alpha particle abundance increase, and a small radial size. We interpret these observations in terms of multiple magnetic reconnection of previously open field lines in interplanetary space at the HCS. Such reconnection produces a U-shaped structure entirely disconnected from the Sun (which we associate with the HFD), a closed magnetic flux rope (which we associate with the counterstreaming electron event), and a closed magnetic loop or tongue connected back to the Sun at both ends. These observations suggest that magnetic reconnection, and its changes to magnetic field topology, can occur well beyond the solar corona in interplanetary space.

Global confinement and discrete dynamo activity in the MST reversed field pinch

Results obtained on the Madison Symmetric Torus (MST) reversed‐field pinch [Fusion Technol. 19, 131 (1991)] after installation of the design poloidal field winding are presented. Values of βθe0≡2μ0ne0Te0/B2θ(a)∼12% are achieved in low‐current (I=220 kA) operation; here, ne0 and Te0 are central electron density and temperature, and Bθ(a) is the poloidal magnetic field at the plasma edge. An observed decrease in βθe0 with increasing plasma current may be due to inadequate fueling, enhanced wall interaction, and the growth of a radial field error at the vertical cut in the shell at high current. Energy confinement time varies little with plasma current, lying in the range of 0.5–1.0 msec. Strong discrete dynamo activity is present, characterized by the coupling of m=1, n=5–7 modes leading to an m=0, n=0 crash (m and n are poloidal and toroidal mode numbers). The m=0 crash generates toroidal flux and produces a small (2.5%) increase in plasma current.

Effects of spacecraft potential on three‐dimensional electron measurements in the solar wind

Using the three-dimensional, low-energy electron spectrometer aboard the Ulysses spacecraft, we have measured the gyrotropicity of electron distributions in the solar wind. In order to make these observations, we have developed a new technique for correcting spacecraft charging effects in three-dimensional, low-energy particle measurements. Comparisons of ion and electron number and current densities, and the alignment of electron temperature anisotropies with the local magnetic field, are presented as evidence of the improvement in the accuracy of the electron moments resulting from the spacecraft charging corrections. The implications of our charging correction technique go beyond simple scalar corrections to the Ulysses measurements. We discuss the effects of our charging correction upon the measurements of temporal and radial gradients in a plasma environment and for two-dimensionally obtained low-energy particle data.

Parallel velocity and temperature of argon ions in an expanding, helicon source driven plasma

The parallel ion flow in a high-density helicon source plasma expanding into a region of weaker magnetic field is measured as a function of neutral pressure, magnetic field strength, rf power and rf driving frequency. The dependence of the parallel ion flow and parallel ion temperature, measured by laser induced fluorescence, on the plasma density, electron temperature and floating potential, measured with an rf-compensated Langmuir probe, is also examined. At the end of the helicon plasma source, the ion velocity space distribution changes from a single subsonically drifting Maxwellian population to a supersonic ion beam (≈15 eV) plus a cold, subsonically drifting background ion population. At 38 cm into the expansion region beyond the end of the plasma source, the supersonic ion beam is not observed.