Ulysses Guest Investigator Programme
One of the recommendations made by the peer review bodies in approving the continued operation of Ulysses beyond its nominal end-of-mission date (October 1995) was that opportunities be created to involve investigators from outside the existing science teams. In addition to the creation and maintenance of user-friendly data archives, both ESA and NASA have established Guest Investigator Programmes to further exploit the excellent data sets obtained by Ulysses. The ESA Announcement of Opportunity was issued in June 1996, and resulted in the selection of nine ESA Guest Investigators who officially joined the Science Working Team in April, 1997.
ESA Guest Investigations
- Investigation of tangential and rotational discontinuities in the solar wind at high latitude
Guest Investigator: F. Neubauer, Univ. Cologne
In the following investigation directional discontinuities in the solar wind, i.e. tangential and rotational discontinuities will be studied using Ulysses magnetic field and SWOOPS plasma data. In conjunction with Helios, Wind and Voyager data the macroscopic properties of the discontinuities and the fine structure of the discontinuity transitions will be investigated. The variation of physical conditions of the sun and in the solar wind as a function of latitude will be particularly effective in the unraveling of the physical processes determining the origin and evolution of discontinuities. The data requested are from the time interval September 94 through March 1996 and are all in the validated data category. We shall first identify appropriate events and then determine their nature, i.e. tangential or rotational discontinuities or other types. This will be followed by a classification according to finestructure of the discontinuity transition. All this will be done for various radial distance intervals and heliographic latitude ranges. Also we shall make sure that the data investigated will be from comparable parts of the past solar cycles. The interpretation of the results will lead to new insights in plasma physics when the discontinuities are used as individual samples from the plasma laboratory.
- The structure and dynamics of interplanetary coronal mass ejections and microstreams observed by Ulysses
Guest Investigator: P. Cargill, Blackett Laboratory, ICSTM
A theoretical and computational investigation of the structure of interplanetary coronal mass ejections (CMEs) and microstreams is proposed. The properties of CMEs at both large heliocentric distances and mid latitude will be contrasted with those expected at the Earth's orbit. Particular emphasis will be placed on how CMEs in low and high speed wind regions differ, and on how portions of the same CME that are in regions of different wind speed evolve relative to each other. The results for mid-latitude will be compared with Ulysses observations obtained between early 1993 and 1994, and as the spacecraft heads to Jupiter and back. It is expected that this work will shed fundamental light on the magnetohydrodynamic processes that govern the motion of CMEs in the solar wind. It is also anticipated that they will contribute to our understanding of the multi-dimensional topology of CMEs, since observations from multiple spacecraft (e.g. Ulysses, Wind and ACE) can be expected to provide data from different locations.
The possible solar origin of microstreams will also be examined. Working from the hypothesis that they are the interplanetary remains of small-scale plasma jets, or magnetic elements, as seen by HRTS and SOHO, the motion of these elements over several AU will be modelled, and the results contrasted with the Ulysses observations. If these structures are to survive from the Sun to the orbit of Ulysses, they must be underdoing a minimal amount of dissipation as they move through the wind. We will assess this possibility in light of current knowledge of dissipative processes. Finally, this study offers an opportunity to compare how large (CMEs) and small (microstreams) solar phenomena behave as they move through the solar wind.
- Kinetic modeling and data analysis of shocks, structures and flow in the 3-D heliosphere
Guest Investigator: D. Burgess, Univ. London
The Space plasma group at QMW has a long record of achievement in the areas of kinetic theory and kinetic computer simulations, specifically in the areas of collisionless shocks, waves and instabilities. In addition, although not experiment builders, we have a wide experience of multi-instrument data analysis. We propose a guest investigator programme, with a number of projects, which brings together these strengths so that we may make a major contribution to the Ulysses mission aims. We propose to (i) investigate the source and acceleration of the solar wind by exploring a coronal jets model, and making predictions about the kinetic features that might be observed; (ii) investigate shocks and CIRs around Solar Maximum, when Ulysses will obtain a unique data set which will give us an insight into the solar cycle modulation of the 3D structure of the heliosphere; (iii) investigate the creation and stability of magnetic holes in the solar wind, as phenomena of nonlinear plasma physics; (iv) investigate the parameter space associated with ion acoustic-like noise in the solar wind, in order to further our knowledge of the plasma physics behind the observed plasma emissions.
- A study of turbulent heliospheric processes
Guest Investigator: T.S. Horbury, Blackett Laboratory, ICSTM
The Ulysses spacecraft, with a mission to explore conditions over the poles of the Sun, has provided the opportunity to study fluctuations in the solar wind and magnetic field in a radically different environment to that at low heliolatitudes. Previous work by the applicant, in conjunction with the Ulysses magnetometer team, has used magnetic field data to demonstrate the character and evolution of turbulent fluctuations at high heliolatitudes and the similarities and differences to those closer to the ecliptic. There is a clear need to extend this analysis to the plasma data and indeed to combine the magnetic feild and plasma data sets to provide more information about the fluctuations. This Proposal is based on such an analysis, which would concentrate on the stream, latitude and distance variations and other properties of turbulent fluctuations, rather than the lower frequency Alfvenic fluctuations which have been studied by other groups. For such an analysis, a variety of techniques would be used, including Fourier-based, structure functions and wavelets. Fourier-based studies of helispheric turbulent fluctuations are common; structure functions have been used more recently, to analyse Ulysses magnetic field data amongst others; while applications of wavelets to helispheric turbulence is an emerging topic which promises advances in the understanding of this important universal process in a magnetohydrodynamic fluid.
- Investigation of Jovian and solar low-frequency radio emissions by using observations from the Unified Radio and Plasma Wave (URAP) experiment on board the Ulysses spacecraft
Guest Investigator: H.P. Ladreiter, SRI Graz
The Unified Radio and Plasma wave (URAP) experiment on board the Ulysses spacecraft allows for different kinds of studies regarding wave phenomena in space: a) the determination of the direction and polarization (and angular size) of radio sources (="direction-finding") in the kilometric/hectometric frequency range associated with the solar- and Jovian environment and b) the study of local wave/particle phenomena in the solar wind and Jovian magnetosphere. Similar observations have already been performed by spaceborne instruments before and after the Ulysses mission. In particular, the Jovian radio emissions down to decametric wavelengths have been observed by the Voyager 1 and 2 spacecraft in 1979 during their periods of close distance to Jupiter. At present time the Galileo spacecraft is observing Jupiter, taking advantage of occultation events created by specific constellations of Jovian moons. Jupiter is also regularly observed using the WAVES experiment on board the Wind spacecraft while orbiting around the earth. Solar radio emissions (in particular type III radio bursts) were observed by all of the mentioned spacecraft as well. All those data sources extended by terrestrial ground-based observations of Jovian emissions at decameter wavelengths give now the possibility to analyze and understand Jovian and also solar radio events using a wide set of independently collected data. The proposed analysis should lead to 1) a comprehensive scenario on the phenomenology (occurrence, source location, size and polarization) of individual radio sources and 2) give clues for theories of plasma processes behind the wave phenomena.
- Search for short- and long-term variability characteristics of quiet-time 0.1 - 100 MeV ion and electron fluxes, in order to gain a better understanding of their origin, energy changes, and propagation
Guest Investigator: P. Kiraly, KFKI Budapest
Energetic particle fluxes in the inner heliosphere are subject to several orders of magnitude variations. Variability in time is most pronounced in the energy region around 1 MeV, where the contribution of modulated galactic cosmic rays to the total ion flux is expected to be small even under the most quiet solar conditions. The origin of the main component of quiet-time fluxes and of their variability is still poorly understood, and its better understanding may shed light on important acceleration and propagation processes. If solar origin predominates, fluctuation studies may provide important clues on the statistical distribution of nanoflare and microflare contributions. Combined with X-ray observations on small flares, spectral comparisons can be made. More or less local turbulence may also be a major contributor. Finally, low-level fluxes may represent diffuse remainders of large fluxes at distant locations, and thus may give good indicators of the global state of the inner heliosphere. The present proposers have already done some statistical work on IMP-8 and VEGA quiet-time data. Ulysses is very well instrumented for such studies, and its orbit allows the extension of previous work to a much larger portion of the inner heliosphere. A thorough analysis of quiet-time data may also provide a better understanding of instrumental backgrounds, thus it may be beneficial for other Ulysses projects as well. Comparison with data of other space missions is also planned.
- Temporal characteristics, directivity and height distribution of solar X-ray/gamma-ray flares from a combined analysis of GRANAT/PHEBUS and ULYSSES/GRB data
Guest Investigator: G. Trottet, Obs. de Paris/DASOP
We propose to perform a joint analysis of solar X-ray/gamma-ray flares observed by the PHEBUS instrument on GRANAT in the 75 keV- 100 MeV energy range and by the GRB experiment on ULYSSES in the 25 - 150 keV energy range. Such a combination of data allows us to observe X-ray/gamma-ray flares from 25 keV up to 100 MeV, i.e. over an energy range which is wider than that observed by each instrument. In particular, this will allow us to study the characteristics and the size distributions of fast X-ray pulses as a function of energy. This has great potential to infer the timescales of electron accelerations in solar flares. Moreover, since GRANAT and ULYSSES have very different orbits, a number of flares will be observed from different angles. This provides information on the height distribution of the X-ray emitting sources at photon energies around 100 keV and slightly above where direct imaging observations are not yet available. The observational results: (i) will be used to study the relative roles of particle acceleration and transport from flare-to-flare and in the course of a given flare; (ii) will provide constraints on flare models in which the energy release process is fragmented.
- Comparison between Ulysses measurements of solar wind proton flux and interplanetary Lyman-alpha measurements
Guest Investigator: T. Summanen, Finnish Meteorological Institute
Ulysses has measured for the first time the latitudinal variation of the solar wind proton flux. According to the Ulysses measurements the solar wind proton flux normalized to 1 AU changed considerably from the descending phase of the solar cycle to the solar minimum. It is also possible that the solar wind proton flux near the poles changes from a solar cycle to another. Inter- planetary (IP) Lyman Alpha observations can offer a tool to study solar wind mass flux averages during a long time period and to separate the spatial and temporal effects. A correct modelling of the ionizing effect of the solar wind on the interplanetary Lyman Alpha data.
SWOOPS solar wind proton flux data offer an opportunity to caclulate a theoretical IP Lyman Alpha intensity more accurately, because the main ionizing effect, the charge exchange between solar wind protons and hydrogen atoms, can be reliably modelled. Then, the comparison with IP Lyman Alpha measurements by SWAN onboard SOHO will reveal possible shortcomings of Lyman Alpha modelling.
- Study of the small-scale and large-scale structures of the heliospheric magnetic field as measured by Ulysses, with particular emphasis on its implications for charged particle transport
Guest Investigator: G. Erdvs, KFKI Budapest
Measurements of energetic particle fluxes onboard Ulysses gave unexpected results, in particular on the latitudinal extent of the recurrent variations associated with corotating interaction regions,a nd on the latitudinal gradients of cosmic rays. These observations stimulated modelling efforts which, however, hinge on many parameters treated by the theories as unknown, free constants. On the other hand, the Ulysses mission is scheduled to provide us with high resolution magnetic field data, extending to high solar latitude, and covering one complete solar cycle. The aim of this guest investigator research program is to study mechanisms of charged particle transport, including the values of the parallel and perpendicular mean free path as can be determined from the actually measured magnetic field. The magnetic field data will also be used to study field line mixing. The program comprises analysis of the magnetic field data as well as theoretical modelling in the context of, and also beyond, the so-called quasi-linear theory. Results obtained in the polar regions will be compared to those in the streamer belt.