R. D. Zwickl

Comet Giacobini-Zinner: Plasma description

A strong interaction between the solar wind and comet Giacobini-Zinner was observed oh 11 September 1985 with the Los Alamos plasma electron experiment on the International Cometary Explorer (ICE) spacecraft. As ICE approached an intercept point 7800 kilometers behind the nucleus from the south and receded to the north, upstream phenomena due to the comet were observed. Periods of enhanced electron heat flux from the comet as well as almost continuous electron density fluctuations were measured. These effects are related to the strong electron heating observed in the cometary interaction region and to cometary ion pickup by the solar wind, respectively. No evidence for a conventional bow shock was found as ICE entered and exited the regions of strongest interaction of the solar wind with the cometary environment. The outer extent of this strong interaction zone was a transition region in which the solar wind plasma was heated, compressed, and slowed. Inside the inner boundary of the transition region was a sheath that enclosed a cold intermediate coma. In the transition region and sheath, small-scale enhancements in density were observed. These density spikes may be due to an instability associated with cometary ion pickup or to the passage of ICE through cometary ray structures. In the center of the cold intermediate coma a narrow, high-density core of plasma, presumably the developing plasma tail was found. In some ways this tail can be compared to the plasma sheet in Earths magnetotail and to the current sheet in the tail at Venus. This type of configuration is expected in the double-lobe magnetic topology detected at the comet, possibly caused by the theoretically expected draping of the interplanetary magnetic field around its ionosphere.

LOW ENERGY IONS IN COROTATING INTERACTION REGIONS AT 1 AU: OBSERVATIONS

Abstract The spacecraft ISEE -3 was launched in August 1978 and subsequently placed in orbit about the Sun-Earth L1 libration point where it continuously monitored the particles and fields in interplanetary space until mid-1982. The ISEE -3 Energetic Proton Anisotropy Spectrometer makes 3-dimensional intensity measurements of 35–1600 keV, Z ⩾ 1 ions. This data is used in conjunction with simultaneous solar wind plasma and magnetic field data from the same spacecraft to study the properties of ions in interaction regions lying at the leading edges of nine corotating high speed solar wind streams observed during October 1978–July 1979. Seven streams have an enhancement of ≲ 300 keV ions in the compressed fast stream plasma between the stream interface and interaction region trailing edge. These enhancements are associated with plasma heating to above 3 × 10 5 K, have soft spectra (spectral index ∼ 4.5−6.0) and in five cases show anti-solar streaming in the solar wind frame.

The CDAW-8 substorm event on 28 January 1983: A detailed global study

Abstract A small, isolated substorm with an expansion phase onset at 0739 UT on 28 January 1983 was well observed by ground-based instrumentation as well as by low- and high-altitude spacecraft. Because of the comprehensive nature of the data coverage, including ISEE-3 identification of plasmoid signatures in the deep tail (∼ 220 R E ) associated with the substorm, we are able to provide a detailed timeline of the growth, expansion, and recovery phases of the substorm. The magnetospheric energy input rates are evaluated using IMP-8 in the upstream solar wind. DE-1 imaging sequences are used to examine auroral features during the growth and expansion phases. Substorm current wedge and expansion onset information is provided by ground-based magnetometer and geostationary orbit (particle and magnetic field) data. The plasma, energetic particle, and field signatures at ISEE-3 are considered within the framework of the near-earth data. Quantitative estimates of substorm energy input and output relationships are made for this case and the timing and physical dimensions of the deep tail disturbance implied are evaluated by the global observations available.

The substorm event of 28 January 1983 - A detailed global study

Abstract A small, isolated substorm with an expansion phase onset at 07:39 U.T. (±1 min) on 28 January 1983 was well observed by ground-based instrumentation as well as by low- and high-altitude spacecraft. This event period was chosen as a detailed analysis interval because of the comprehensive nature of the data coverage, and because ISEE-3 identified signatures within the distant tail (∼220 RE) following the substorm onset which had been interpreted as those of a plasmoid passage. In this paper we provide a comprehensive timeline of the growth, expansion, and recovery phases of the substorm. The magnetospheric energy input rates are evaluated using IMP-8 in the upstream solar wind. For the first time, DE-1 imaging sequences are used to examine auroral features during the growth and expansion phases while ISEE-3 was in the deep tail. Substorm current wedge location and expansion onset information was provided by ground-based magnetometer and geostationary orbit (particle and magnetic field) data. The plasma, energetic particle, and field signatures at ISEE-3 are considered within the framework of the near-Earth data sets. We quantitatively estimate substorm energy input and output relationships for this case and we evaluate the timing and physical dimensions of the distant tail disturbance implied by the global observations available. Overall, the present analysis provides a thorough documentation of a substorm to an unprecedented degree; most of the data support the developing paradigm of the near-Earth neutral line and plasmoid formation model. We also consider the boundary layer dynamics model of substorms as an alternative explanation of the global magnetospheric phenomena in this event, but as presented this model does not provide a superior organization of the available data sets.

Observations of the interactions of heavy ions from Comet P/Giacobini-Zinner with the solar wind

Abstract During the encounter between the ICE spacecraft and Comet Giacobini-Zinner, intense fluxes of energetic heavy ions were observed at distances up to 4 × 10 6 km from the comet. These ions were observed with steep energy spectra and highly anisotropic angular distributions, and are consistent with a composition comprising mainly ions from the water group. The flux versus time profiles have a general fall-off with increasing distance from the comet, but are modulated by both changes in the magnetic field direction and the solar wind velocity, the magnetic field variations being mainly responsible for variations on a time scale of minutes, and the solar wind velocity variations being responsible for much larger time-scale modulations, such as the inbound/outbound asymmetry of the intensity profile. In this paper we present correlated observations of heavy ions, the solar wind velocity and the magnetic field direction, and compare the observations of the ions with the theoretical predictions for their variations with distance from the comet, with the solar wind velocity and with the magnetic field direction.

Dynamic PIC-simulations of charging phenomena related to the ice-spacecraft in both cometary and solar wind environments

Abstract Spacecraft charging phenomena in the cometary environment of Giacobini-Zinner are less dramatic than expected. The potential of the ICE-probe is less than +1V in the vicinity of Giacobini-Zinner, while the potential may rise up to +6V in the solar wind environment. We present results of PIC simulations that show the dominant influence of photoemission (photoelectrons or impact-induced electrons) in the presence of the solar wind core and halo electrons. Secondary electrons are also important in the cometary environment to explain positive potentials.

SPAN: Riding the winds of change

The latest Data Systems Users Working Group (DSUWG, also known as SPAN Users Group) meeting was held October 24–26, 1988, in Anaheim, Calif. While the meeting contained all the normal topics of discussion, this gathering focused its attention on understanding recent changes imposed by NASA Headquarters that affect SPANs current and future operation. The major emphasis of this meeting report is explaining changes that have occurred within NASA and what effect these changes have upon you, the computing network user. Highlights are also included for two other areas that may be of interest: security and European SPAN.