The magnetic fields of Mercury,Venus and Mars

Just as clearly as Mariner 10 established that Mercury has an intrinsic magnetic field, the Pioneer Venus orbiter has established that Venus has no significant intrinsic field. This is perhaps the opposite of what might be expected. Mercury, a small planet might be expected to cool rapidly and its internal dynamo to cease, while Venus, which is almost as large as the Earth, should not have lost much heat. On the contrary the source of energy of the Mercury dynamo appears to be extant whereas that of Venus appears to be extinct.The existence of a Martian magnetic field is controversial. No unambiguous signature of a Martian magnetic field has been reported. If the field on the nightside of Mars is of planetary rather than solar origin the Russian Mars spacecraft observations indicate the Martian dipole lies near the planetary equator rather than its pole.     

Nonlinear Analysis of a Family of LC Tuned Inverters

four widely used self-oscillating dc-to-square-wave parallel inverters which employ an inductor-capacitor tuned network to determine the oscillation frequency are reduced to a common equivalent RLC network. The techniques of singular-point analysis and state-plane interpretations are employed to describe the steady-state and transient ient behavior of these circuits and to elucidate the three possible modes of operation: quasi-harmonic, relaxation, and discontinuous. Design guidelines are provided through a study of the influence of circuit parameter variations on the characteristics of oscillation and on frequency stability. Several examples are provided to illustrate the usefulness of this analysis when studying such problems as transistor emitter-to-base junction breakdown during oscillations and the design of starting circuits to insure self-excited oscillations in these inverters.     

Radio emissions from Uranus

The Voyager Planetary Radio Astronomy Experiment detected strong 40 kHz to 850 kHz radio emissions from Uranus after closest approach and somewhat weaker emissions, but none above 100 kHz before closest approach, on the dayside of Uranus. The time variations of these emissions closely match Uranus' rotation, in a period of 17.24 h, and are evidently controlled by the strength and shape of its magnetic field. Throughout the entire encounter the polarization of the emission was approximately lefthand, corresponding to extraordinary mode. The emission associated with the nightside pole was a relatively smooth continuum (free of bursts) with a Gaussian-shaped rise and fall at low frequencies, 200 kHz for example, but a Gaussian with a central dip nearly to zero lasting a little less than two hours at frequencies above 400 kHz. Half a rotation later, when Voyager was near the magnetic equator of Uranus and farthest from the nightside dipole tip, the continuum emission was absent, but very strong, narrowband impulsive bursts appeared. Voyager successfully acquired one brief (24 seconds long) record of high time resolution radio observations in the range 500 to 700 kHz. This record, which was made near closest approach, shows a hierarchy of fast variations. Several days after closest approach, at the times of bowshock crossings outbound, the continuum emissions were modulated strongly in a manner suggestive of the presence of waves in the bowshock regions.

The instrument also recorded possible Uranian electrostatic discharges, vertex early arcs occurring in sequences of more than a dozen events with approximately ten-minute period, and, as early as several days before closest approach in the frequency range below 100 kHz, very intense isolated bursts lasting tens of minutes.     

GEOS-1 observations of electrostatic waves,and their relationship with plasma parameters

In this paper we describe and discuss the occurrence of natural wave emissions detected by GEOS-1 at frequencies above the electron gyrofrequency. The bulk of the data presented comes from the first six months of satellite operation and thus concerns mainly dayside phenomena. The paper is arranged as follows:After some general remarks, a classification of the wave phenomena is developed in Section 2, and experimental evidence and morphological information relevant to this classification are contained in Section 3. Section 4 includes some preliminary comments on nightside observations. The results are discussed in Section 5, where it is argued that they can be understood as manifestations of electron cyclotron harmonic (Bernstein) wave emission in a plasma parameter range which has only very recently received any theoretical examinations. This theme is further developed in a comparison paper (Ronnmark et al., 1978).     

Oxygen and Iron Ions at High Heliolatitudes

The fluxes of O and Fe ions at high heliolatitudes measured by the HiScale instrument on Ulysses reflect the dynamical processes that affect the charged particle populations in the heliosphere. Both the O and Fe ions show more latitude dependence in the first (solar minimum) orbit to high southern heliolatitudes than during the second (solar maximum) orbit. The ion fluxes are larger during the solar minimum orbit; the flux levels are influenced by the occurrence of corotating interaction regions. The Fe/O abundance ratios are found to be similar at 1 AU and at high heliolatitudes. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Onset of Long Term Modulation in the Heliosphere in Cycle 23

The combination of Voyager 1 (77.9 AU, 34.4° N) and Voyager 2 (61.2 AU, 24.5° S) at moderate heliolatitudes in the distant heliosphere and Ulysses with its unique latitudinal surveys in the inner heliosphere along with IMP 8 and other satellites at 1 AU constitutes a network of observatories that are ideally suited to study cosmic rays over the solar minimum of cycle 22 and the onset of solar activity and the long term cosmic ray modulation of cycle 23. Through 2000.7 there have been three well-defined step decreases in the cosmic ray intensity at 1 AU with the cumulative effect being in good agreement with the net decrease in cycle 21 at a comparable time in the solar cycle. Over this period the intensity changes at Ulysses are similar to those at 1 AU. In the distant heliosphere the initial decreases appear to be smaller than those at 1 AU. However the full effects of the interplanetary disturbances producing the most recent and largest step decrease in the inner heliosphere have not yet reached V-2. This revised version was published online in August 2006 with corrections to the Cover Date.     

Observations of the profiles of solar UV emission lines and their analysis in terms of the heating and production of the corona

Observations of the solar spectrum have been made between 1200–2200 with high spectral resolution. The results were obtained with an all-reflecting echelle spectrograph carried by a stabilized Skylark rocket launched in April 1970. Measurements of the profiles of a number of emission lines due to Siii, Cii, Siiii and Civ formed in the temperature range 10⁴-10⁵ K, indicate ion energies which are considerably in excess of the electron temperatures derived from the ionization balance. Since the ion/electron relaxation time is very short the observed ion energies cannot correspond to an ion temperature and hence a non-thermal mechanical energy component exists in the transition zone.It is postulated that the non-thermal energy component represents the actual mechanical energy responsible for the heating of the corona, and, that, it is propagated as an acoustic wave. On this basis and with a preliminary estimate of the reflection from the transition zone, a flux of 3 × 10⁵ erg cm ^-2 s ^-1 is established as entering the corona. This value is in agreement with estimates of the total energy loss from the corona due to conduction, radiation and the solar wind, thus establishing a gross energy balance.Theoretical calculations are currently underway to establish the physical nature of the atmosphere which would result from such a propagating flux. At the present time this has been carried out for an atmosphere in hydrostatic equilibrium and the energy balance equation solved. A preliminary temperature structure which results is shown in Figure 1, together with the derived distribution in electron density. This gives a corona of the right temperature and density but the observed structure deviates in detail from those derived from an analysis of the solar XUV spectrum.     

Opacity effects in soft X-ray spectral lines of the solar corona

Current literature suggests that several lines in the soft X-ray portion of the coronal spectrum may not be optically thin. Here, we confirm the results of Schmelz et al. (1996) who find no significant opacity effects for three of the brightest non-iron resonance lines in this part of the spectrum — O VIII at 18.97Å, Ne IX at 13.45Å, and Mg XI at 9.17Å. A comparison is made between each of these lines and an optically thin “reference” line produced by the same element in the same ionization state — O VIII at 15.18Å, Ne IX at 13.55Å, and Mg XI at 9.23Å. In the latter two cases, the comparison line is the intersystem line of the He-like triplet. 33 spectra from the Solar Maximum Mission Flat Crystal Spectrometer are analyzed, all of which were obtained from non-flaring, quasi-stable active regions.