Engineering topics
Publications and source records attributed to Fisk, L. A..
The purpose of this grant was to develop a theoretical understanding of the processes by which open magnetic flux undergoes large-scale transport in the solar corona, and to use this understanding to develop a predictive model for the heliospheric magnetic field, the configuration for which is determined by such motions.
We present solar wind Fe charge state data measured on the Advanced Composition Explorer (ACE) from early 1998 to the middle of 2000. Average Fe charge states in the solar wind are typically around 9 to 11. However, deviations from these average charge states occur, including intervals with a large fraction of Fe(sup greater or = 16+) which are consistently associated with interplanetary coronal mass ejections (ICMEs). By studying the Fe charge state distribution we are able to extract coronal electron temperatures often exceeding 2 x 10(exp 6) kelvins. We also discuss the temporal trends of these events, indicating the more frequent appearance of periods with high Fe charge states as solar activity increases.
The elemental composition and charge state distributions of heavy ions of the solar wind provide essential information about: (1) atom-ion separation processes in the solar atmosphere leading to the 'FIP effect' (the overabundance of low First Ionization potential (FIP) elements in the solar wind compared to the photosphere); and (2) coronal temperature profiles, as well as mechanisms which heat the corona and accelerate the solar wind. This information is required for solar wind acceleration models. The SWICS instrument on Ulysses measures for all solar wind flow conditions the relative abundance of about 8 elements and 20 charge states of the solar wind. Furthermore, the Ulysses high-latitude orbit provides an unprecedented look at the solar wind from the polar coronal holes near solar minimum conditions. The MASS instrument on the WIND spacecraft is a high-mass resolution solar wind ion mass spectrometer that will provide routinely not only the abundances and charge state of all elements easily measured with SWICS, but also of N, Mg, S. The MASS sensor was fully operational at the end of 1994 and has sampled the in-ecliptic solar wind composition in both the slow and the corotating fast streams. This unique combination of SWICS on Ulysses and MASS on WIND allows us to view for the first time the solar wind from two regions of the large coronal hole. Observations with SWICS in the coronal hole wind: (1) indicate that the FIP effect is small; and (2) allow us determine the altitude of the maximum in the electron temperature profile, and indicate a maximum temperature of approximately 1.5 MK. New results from the SMS instruments on Wind will be compared with results from SWICS on Ulysses.
Variations in the heliospheric magnetic field occur on most scales including those lying intermediate between the gyro-radii of galactic cosmic rays and heliocentric radial distance. It is demonstrated that a correlation exists between these intermediate-scale variations in the magnetic field and the variations in the cosmic ray distribution function that result from the field variations. This correlation will affect the average transport of galactic cosmic rays by significantly altering the patterns of gradient and curvature drifts in the heliosphere. During the current solar cycle, the altered drift patterns can lead to larger radial gradients of the galactic cosmic rays and significantly smaller latitude gradients than is expected only from drifts in the mean magnetic field.
Acceleration of interstellar pickup H(+) and He(+) as well as of solar wind protons and alpha particles has been observed on Ulysses during the passage of a corotating interaction region (CIR) at approximately 4.5 AU. Injection efficiencies for both the high thermal speed interstellar pickup ions (H(+) and He(+)) and the low thermal speed solar wind ions (H(+) and He(++) are derived using velocity distribution functions of protons, pickup He(+) and alpha particles from less than 1 to 60 keV/e and of ions (principally protons) above approximately 60 keV. The observed spatial variations of the few keV and the few hundred keV accelerated pickup protons across the forward shock of CIR indicate a two stage acceleration mechanism. Thermal ions are first accelerated to speeds of 3 to 4 times the solar wind speed inside the CIR, presumably by some statistical mechanism, before reaching higher energies by a shock acceleration process. Our results also indicate that (1) the injection efficiencies for pickup ions are almost 100 times higher than they are for solar wind ions, (2) pickup H(+) and He(+) are the two most abundant suprathermal ion species and they carry a large fraction of the particle thermal pressure, (3) the injection efficiency is highest for protons, lowest for He(+), and intermediate for alpha particles, (4) both H(+) and He(+) have identical spectral shapes above the cutoff speed for pickup ions, and (5) the solar wind frame velocity distribution function of protons has the form F(w) = F(sub o)w(sup -4) for 1 is less than w is less than approximately 5, where w is the ion speed divided by the solar wind speed. Above w approximately 5-10 the proton spectrum becomes steeper. These results have important implications concerning acceleration of ions by shocks and CIRs, acceleration of anomalous cosmic rays, and particle dynamics in the outer heliosphere.
Interstellar hydrogen ionized primarily by the solar wind has been detected by the Solar Wind Ion Composition Spectrometer instrument on the Ulysses spacecraft at a distance of 4.8 AUs from the sun. This 'pick-up' hydrogen is identified by its distinct velocity distribution function, which drops abruptly at twice the local solar wind speed. From the measured fluxes of pick-up protons and singly charged helium, the number densities of neutral hydrogen and helium in the distant regions of the solar system are estimated to be 0.077 +/- 0.015 and 0.013 +/- 0.003 per cu cm, respectively.
The ion composition in the Jovian environment was investigated with the Solar Wind Ion Composition Spectrometer on board Ulysses. A hot tenuous plasma was observed throughout the outer and middle magnetosphere. In some regions two thermally different components were identified. Oxygen and sulfur ions with several different charge states, from the volcanic satellite Io, make the largest contribution to the mass density of the hot plasma, even at high latitude. Solar wind particles were observed in all regions investigated. Ions from Jupiter's ionosphere were abundant in the middle magnetosphere, particularly in the high-latitude region on the dusk side, which was traversed for the first time.
The Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses is designed to determine uniquely the elemental and ionic-charge composition, and the temperatures and mean speeds of all major solar-wind ions, from H through Fe, at solar wind speeds ranging from 175 km/s (protons) to 1280 km/s (Fe(8+)). The instrument, which covers an energy per charge range from 0.16 to 59.6 keV/e in about 13 min, combines an electrostatic analyzer with postacceleration, followed by a time-of-flight and energy measurement. The measurements made by SWICS will have an impact on many areas of solar and heliospheric physics, in particular providing essential and unique information on: (1) conditions and processes in the region of the corona where the solar wind is accelerated; (2) the location of the source regions of the solar wind in the corona; (3) coronal heating processes; (4) the extent and causes of variations in the composition of the solar atmosphere; (5) plasma processes in the solar wind; (6) the acceleration of energetic particles in the solar wind; (7) the thermalization and acceleration of interstellar ions in the solar wind, and their composition; and (8) the composition, charge states, and behavior of the plasma in various regions of the Jovian magnetosphere.
Consideration is given to the origin of the anomalous cosmic ray component as well as to the mechanism and location for the acceleration of these particles. The following three theories for anomalous component acceleration are discussed in detail: (1) transit-time damping, (2) the termination shock over the solar poles, and (3) the termination shock near the equatorial plane. It is noted that observations from Ulysses should provide important constraints on the likely locations for the acceleration, and that acceleration of interstellar H, along with the He, N, O, and Ne could have serious consequences for possible acceleration mechanisms.
Solar wind heating by ionization and assimilation of the interstellar neutral wind is investigated using a numerical model of the interaction. The model is a time-dependent, one-dimensional, spherically symmetric, one-fluid code which includes mass, momentum, and energy sources due to the efficient incorporation of ionized interstellar hydrogen. Solar wind data at 1 AU from October 12, 1978 to February 25, 1980 were input to the inner boundary of the model and propagated out to 10 AU. Then, 52-day averages of proton temperature as functions of radius were produced for three values of the interstellar hydrogen density: 0.0, 0.03, and 0.1 per cu cm. It is concluded that, within the context of the model, the observations of solar wind proton temperatures at Voyager 1 and Pioneer 11 are consistent with heating of the solar wind by an interaction with inflowing interstellar neutral hydrogen. The density of this inflowing gas is near 0.03/cu cm.
The mean ionic charges of nitrogen, neon, magnesium, silicon, and sulfur in solar flare particle events were determined for 12 flares during the time interval from September 1978 to September 1979. The observations were carried out with the MPI/UoMd ULEZEQ Sensor on the ISEE-3 satellite comparing the results with mean charge states established in a hot coronal plasma under equilibrium conditions, different temperatures for different elements are discussed. These range from approx. 2 million K to 7 million K in a single flare. From flare to flare the variation in temperature for each element is less than the variation between different ion species.
The so-called anomalous cosmic ray component, which occurs at energies of about 10 MeV/nucleon and consists only of He, N, O, and Ne, has been a subject of interest for more than a decade. The origin of this component is generally considered to be interstellar neutral gas that is ionized and accelerated in the solar wind. The mechanism and the location for the acceleration, however, remains an unsolved problem. A model is used which includes the effects of gradient and curvature drifts and considers the implications of observed spatial gradients of the anomalous component for the location of the acceleration region. It is concluded that if drifts are important the acceleration region cannot lie at the solar poles. It is also concluded that there is no single region for the acceleration which can account for both the observed intensities and gradients in models which include drift effects.
One of the principal uncertainties in understanding the propagation of cosmic rays in the heliosphere is related to the role of latitudinal transport by gradient and curvature drifts. The steady state distribution of cosmic rays with respect to the heliospheric current sheet or in latitude may possibly provide some information regarding the existing problems. Newkirk and Lockwood (1981) have considered the current sheet with respect to its role as a natural surface of symmetry for the propagation of cosmic rays in the heliosphere. The present investigation represents an extension of this study. Central objectives are related to a determination of the gradient of 5-GeV cosmic rays with respect to the heliospheric current sheet at 1 AU, the possible effect of the solar cycle upon such gradients, and an evaluation of the ability of several theoretical models to explain the gradients.
The first direct measurement of the ionic charge distribution of the helium isotopes and of iron in (He-3)-Fe-rich solar energetic particle events is reported. No significant contribution of singly ionized helium to the events is found. The two-sigma upper limits for the He-3(+)/He-3(2+) and He-4(+)/He-4(2+) ratios are 0.02 and 0.03, respectively. The mean charge state of iron found by averaging five (He-3)-Fe-rich solar energetic particle events is 19 + or -2, significantly larger than the iron charge state for energetic solar particles in normal composition events. These results appear to favor the resonant heating model proposed by Fisk (1978). It is concluded that temperatures in the source region exceed 5 million K in the events under study.
The mean ionic charges and source-region temperatures of flare-accelerated N, Ne, Mg, Si and S in three large solar-energetic-particle events during 1978-1979 are determined from ISEE-3 observations, extending the findings of Hovestadt et al. (1981) and Gloeckler et al. (1981) for C, He, O, and Fe. The results are presented in tables and graphs, and the charge states are shown to correspond to different source temperatures even in the same flare, assuming equilibration in the hot plasma. The electron temperatures range from 2 x 10 to the 6th K for C, N, O, Si, and S, 4 x 10 to the 6th K for Ne and Fe, and 7 x 10 to the 6th K for Mg. The possibility that these temperature inconsistencies reflect different stages in the approach to equilibrium is considered.
A numerical technique is introduced for the solution of the time-dependent equation for the solar modulation of galactic cosmic rays, in which transport in heliographic latitude is ignored. We illustrate this method with a model for the solar cycle variation in cosmic ray intensity. The variation is assumed to result from changes in the number of enhanced cosmic ray scattering regions, which are produced by flare-generated shock waves in the solar wind. The model can account for the observed solar cycle variation in intensity at different energies as well as the observed spatial gradients. This model also provides a natural explanation for the cosmic ray hysteresis effect.
The International Solar Polar Mission (ISPM) Solar-Wind Ion Composition Spectrometer which determines elemental and ionic-charge composition, and the temperatures and mean speeds of all major solar-wind ions, from H through Fe, at solar wind speeds ranging from 145 km/sec (protons) to 1352 km/sec (Fe+8) is described. The instrument, which covers an energy per charge range from 110 eV/q to 66.7 keV/q in 13 min, combines an electrostatic analyzer with postacceleration, followed by a time-of-flight and energy measurement. Conditions and processes in the region of the corona where the solar wind is accelerated; location of the source regions of the solar wind in the corona; coronal heating processes; the extent and causes of variations in the composition of the solar atmosphere; plasma processes in the solar wind; acceleration of energetic particles in the solar wind; the thermalization and acceleration of interstellar ions in the solar wind, and their composition; and the composition and behavior of the plasma in the Jovian magnetosphere are studied.
The apparent distinction between 'V x B' and 'Fermi' mechanisms is clarified in a discussion of the theory of the shock acceleration of energetic particles which restricts attention to those cases where the energetic particles do not themselves influence the given shock structure. The theory is applied to the acceleration of energetic particles in corotating interaction regions (CIR) in the solar wind, where particles are accelerated at either the forward and reverse shocks which bound the CIR by being compressed between the shock fronts and magnetic irregularities upstream of the shocks, or by being compressed between upstream irregularities and those downstream from the shocks. The model is shown to account for the observed exponential spectra at the earth, observed spectra behavior with radial distance and radial intensity gradients, and differences in spectra intensity at the forward and reverse shocks. Energy spectra are also calculated for the shock acceleration of energetic particles in large solar flare events.