Interplanetary type III radio bursts observed simultaneously by ICE

We analyze two solar type III radio bursts that were observed simultaneously by the ICE and Ulysses spacecraft. Both bursts originated behind the solar limb as viewed from either spacecraft. At the time of these events, ICE was in the ecliptic plane at 1 AU and Ulysses was 35° south of the ecliptic plane at 4 AU. For one event on 931117, the ratios of the peak flux densities measured at each spacecraft, at each observing frequency, were consistent with the most probable source locations relative to ICE and Ulysses. The second event on 931004 was a complex burst consisting of two distinct components at high frequencies. At low frequencies, the intensity of the first component decreased rapidly at each spacecraft. The second component, however, dominated the low frequency emission observed at Ulysses but not at ICE. These differences in the observed radiation must be related to the different viewing geometries of the two spacecraft. The measured onset times as a function of observing frequency were consistent with a constant exciter speed through the interplanetary medium and suggest that there are significant propagation delays, especially for the radiation propagating within the ecliptic plane.     

Ulysses/Galileo observations of type III radio bursts and associated in-situ electrons and Langmuir waves

Both the Ulysses and Galileo spacecraft detected energetic electrons and Langmuir waves that were associated with a type III radio burst on 10 December 1990. At the time of these observations, these spacecraft were in the ecliptic plane and separated by 0.4 AU, with Galileo near the Earth at 1 AU and Ulysses at 1.36 AU. From the measured electron arrival times, the propagation path lengths of the electrons to both Ulysses and Galileo were estimated to be significantly longer than the length of the Parker spiral. These long path lengths are interpreted as due to draping of the interplanetary magnetic field lines around a CME. The onset times of the Langmuir waves at Ulysses and Galileo coincided with the estimated arrival time of the 9 keV and 14 keV electrons, respectively.     

Ground-based solar radio observations of the August 1972 events

Ground-based observations of the variable solar radio emission ranging from few millimetres to decametres have been used here as a diagnostic tool to gain coherent phenomenological understanding of the great 2, 4 and 7 August, 1972 solar events in terms of dominant physical processes like generation and propagation of shock waves in the solar atmosphere, particle acceleration and trapping.The basic data used in this review have been collected by many workers throughout the world utilizing a variety of instruments such as fixed frequency radiometers, multi-element interferometers, dynamic spectrum analysers and polarimeters. Four major flares are selected for detailed analysis on the basis of their ability to produce energetic protons, shock waves, polar cap absorptions (PCA) and sudden commencement (SC) geomagnetic storms. A comparative study of their radio characteristics is made. Evidence is seen for the pulsations during microwave bursts by the mechanism similar to that proposed by McLean et al. (1971), to explain the pulsations in the metre wavelength continuum radiation. It is suggested that the multiple peaks observed in some microwave bursts may be attributable to individual flares occurring sequentially due to a single initiating flare. Attempts have been made to establish identification of Type II bursts with the interplanetary shock waves and SC geomagnetic storms. Furthermore, it is suggested that it is the mass behind the shock front which is the deciding factor for the detection of shock waves in the interplanetary space. It appears to us that more work is necessary in order to identify which of the three moving Type IV bursts (Wild and Smerd, 1972), namely, advancing shock front, expanding magnetic arch and ejected plasma blob serves as the piston-driver behind the interplanetary shocks. The existing criteria for proton flare prediction have been summarized and two new criteria have been proposed. Observational limitations of the current ground-based experimental techniques have been pointed out and a suggestion has been made to evolve appropriate observational facilities for solar work before the next Solar Maximum Year (SMY).     

Evidence for a common source of fragmented decimeter emission and meter wave type II bursts in some solar type IV bursts

The paper presents facts of relevance for flare particle acceleration and shock wave excitation in the solar corona from a detailed analysis of meter wave (40–800 MHz OSRA Tremsdorf spectrograms) and microwave data (3.1–50 GHz polarimeter records Bern University) of several type IV bursts. We argue for a slowly uprising (about 0.1 of the local Alfvén speed) quasi-periodically acting (1...3 min period) accelerator in the 10¹¹...10⁹ cm^–3 density region. It produces particles emitting patches of fragmented decimetric/metric radio emission. One of the quasi-periodically appearing patches is associated with the microwave burst emission, the same (or a later, lower frequency one) immediately preceeds the meter wave type II burst lanes. Therefore the onset of the patch source seems to induce also the MHD-like disturbance which can steepen to the type II burst emitting shock. In some events the fragmented patches in the frequency-time plane show a linear spreading toward lower and higher frequencies. This can be a signature of an accelerated movement. Our interpretation of the data allows to understand some of the timing and location problems between the type II shockfront and other CME or flare components.     

Abnormal changes of dynamic derivatives at low reduced frequencies

A number of studies have found that abnormal changes of dynamic derivatives occurred at very low reduced frequencies, but its inducement mechanism is not very clear. This paper has researched the abnormal changes and analyzed the influence on some parameters by solving the unsteady flow around forced oscillation airfoils based on Navier-Stokes equations. Results indicate that when the reduced frequency approaches to zero, the dynamic derivatives obtained by the numerical method will diverge. We have also proven it in theory that this phenomenon is not physical but completely caused by numerical singularity. Furthermore, the abnormal phenomenon can be effectively mitigated by using the time spectral method to solve the aerodynamic forces and the integral method to obtain the dynamic derivatives. When the reduced frequency is in the range of 0.001–0.01, the dynamic derivative maintains nearly unchanged for the whole speed region. This study can provide a reference for the reasonable choice of the reduced frequency in calculations and experiments of dynamic derivatives.     

Satellite observations of power line harmonic radiation

In-situ spectral observations of power-line harmonic radiation (PLHR) are still quite rare and almost all the detailed characteristics have been derived from studies at Antarctic stations such as Siple and Halley, and their conjugates in North America. Because of the lack of more direct satellite evidence of PLHR and the difficulties in interpretation of morphological studies, such as those of Ariel 3 and 4, there is considerable controversy concerning the relative importance of PLHR and its contribution to wave-particle interactions (WPI) in the magnetosphere. The early Ariel 3 and 4 global surveys indicated that, in terms of true mean wave energy, there is no longitudinal localisation, the contribution of world-wide intense VLF emissions, associated with magnetic storms, being dominant. Also, the most intense wave emission, that of plasmaspheric hiss at ELF (< 1 kHz) exhibits little evidence of localisation. The PLHR phenomenon is most conspicuous by its persistence in quiet times (Kp ≤ 2+) at 45° < Λ < 55° over North America and its conjugate region, even though the less frequent strongest emissions, to which it gives rise in the summer, are located polewards at 3 < L < 5. In the northern winter, when spheric activity over both North America and its conjugate are low, there is a high occurrence of strong discrete emissions, which are more sharply localised than in the summer, on the NE industrial U.S.A. field line. The most recent Ariel 4 studies, particularly on the spheric wavefield over North America (using data from the Appleton Laboratory impulse counters) and on the character of the wavefield over the mainland and over the Atlantic immediately to the east (where the spheric contribution is similar) throw new light on the problem. It appears that the principal role of the PLHR may be to sustain duct structure and multihop propagation which is relatively much rarer over the Atlantic. Typical industrial PLHR consists of a series of narrow pulses at twice the mains frequency. It is suggested that these ‘artificial spherics’ may help to sustain the WPI and multihop duct structure. At L = 4, Yoshida et al. (1980) have shown that there is a strong, sharp maximum for WPIs originating in spherics, at f ? 3 kHz, in good agreement with Siple observations.     

Exploration of the solar corona by high resolution solar decametric observations

In this review, current state of knowledge of high resolution observations at decameter wavelengths of the quiet Sun, the slowly varying component (SVC), type I to V bursts and noise storms is summarized. These observations have been interpreted to yield important physical parameters of the solar corona and the dynamical processes around 2R from the photosphere where transition from closed to open field lines takes places and the solar wind builds up. The decametric noise bursts have been classified into (i) BF type bursts which show variation of intensity with frequency and time and (ii) decametric type III bursts. The angular sizes of noise storm sources taking into account refraction and scattering effects are discussed. An attempt has been made to give phenomenology of all the known varieties of decametric bursts in this review. Available polarization information of decametric continuum and bursts has been summarized. Recent simultaneous satellite and ground-based observations of decametric solar bursts show that their intensities are deeply modulated by scintillations in the Earth's ionosphere. Salient features of various models and theories of the metric and decametric noise storms proposed so far are examined and a more satisfactory model is suggested which explains the BF type bursts as well as conventional noise storm bursts at decametric wavelengths invoking induced scattering process for 1 t conversion. Some suggestions for further solar decametric studies from the ground-based and satellite-borne experiments have been made.     

EXOSAT observations of bursts from 2S1636-536: Burst morphology

In two observations with the EXOSAT ME a total of 11 bursts were detected; 7 in July and 4 in May 1984. In terms of rise time and peak count rate there are only 2 kinds, those with a sharp rise and peak count rate of 500 cts/sec/detector and those with a slow rise and a peak count rate of 200 cts/sec/detector. The spectral analysis of these bursts shows a similar situation: for the sharp bright bursts the black body radius increases rapidly to > 20 km and the temperature lags. For the slow dim bursts the temperature rises ahead of the black body radius expansion which is small and slow. The time t _1/2 at which half the total burst energy has been released is 3.5 seconds for bright bursts and 8 seconds for dim ones. These gross differences may be related to the predominance of helium or hydrogen in the thermonuclear flash.     

Interplanetary scintillation observations of the high-latitude solar wind

Until the ULYSSES spacecraft reached the polar regions of the solar wind, the only high-latitude measurements available were from indirect techniques. The most productive observations in regions of the solar wind between 5R and 200R have been the family of radio scattering techniques loosely referred to as Interplanetary Scintillation (IPS) (Coles, 1978). Useful observations can be obtained using a variety of radio sources, for example spacecraft beacons, planetary radar echoes and compact cosmic sources (quasars, active galactic nuclei, pulsars, galactic masers, etc.). However for measurement of the high-latitude solar wind cosmic sources provide the widest coverage and this review will be confined to such observations. IPS observations played a very important role in establishing that polar coronal holes (first observed in soft x-ray emission) were sources of fast solar wind streams which occasionally extend down to the equatorial region and are observed by spacecraft. Here I will review the IPS technique and show the variation of both the velocity and the turbulence level with latitude over the last solar cycle. I will also outline recent work and discuss comparisons that we hope to make between IPS and ULYSSES observations.     

Radial profile measurements of the solar wind speed using radio sounding techniques

Velocity measurements of the solar wind in the region of its acceleration were carried out in 1984 with Venera Orbiters using the following specific radio sounding techniques: (i) phase and frequency correlations from two or three widely-spaced ground stations; (ii) phase and frequency correlations from two spacecraft and two widely-spaced ground stations; (iii) two station two-way coherent Doppler measurements; (iv) determination of the break frequency in power spectra of intensity fluctuations. Our results are substantially lower than those derived from direct Doppler shift measurements of transition region and lower coronal resonance lines and those from measurements applying the Doppler dimming technique.     

Analysis of solar panel orientation in low altitude satellites

The computation of the optimal orientation of solar panels which are fixed to the body of the satellite, from the point of view of average power, is presented. In practical cases, some of the parameters which determine the optimal orientation vary during the lifetime of the satellite. In these cases we compute a worst case optimum, which maximizes the average power in the worst case situation. Finally, an application of these procedures to an Earth observation satellite is performed     

The analysis of energy release in solar flares based on X-ray observations

Extended review of selected papers which deal with the problem of flare heating in solar coronal loops is presented. Discussed methods of the analysis of flare heating based on the X-ray observations have been worked out using the Palermo-Harvard hydrodynamic code. The case is presented when the assumption of the uniform heating across the loop is made. The existence of multiple elementary heating episodes is postulated as well. Next the possibility of the non-uniform heating across the loop is assumed and its manifestation in the X-ray observations is investigated. The application of proposed methods of the analysis to the observations of solar flares in X-rays is presented.     

Natural and man-made noise in the Earth-ionosphere cavity at extremely low frequencies (Schumann resonances and man-made ‘interference’)

The equations for the Earth-ionosphere cavity resonance fields are given and some of the approximations used in their derivation are indicated. Typical electric and magnetic 5 to 20 Hz Schumann resonance field intensities are listed and compared with the level of other natural and man-made electromagnetic noise. Applications of Schumann resonances to thunderstorm location and measurement of global lightning activity are reviewed briefly. Ionospheric conductivity profiles appropriate for this frequency range are discussed and the importance of atmospheric conductivity below 60 km is pointed out.     

Variability of BL Lac objects at X-ray and other frequencies

EXOSAT observations reveal that daily X-ray variability appears to be a common property of high luminosity BL Lac objects. Results are reported for PKS0735+178, OM280(=1147+245), OQ530(=1418+546), OV-236 (=1921-293) and OJ287(=0851+202). In OJ287, for which we have the most extensive coverage, the amplitude of variability at X-ray frequencies appears to be a factor of a few larger than at longer wavelengths.     

Pioneer and Voyager observations of large-scale spatial and temporal variations in the solar wind

The Pioneer 10, Pioneer 11, and Voyager 2 spacecraft were launched in 1972, 1974, and 1977, respectively. While these three spacecraft are all at compartively low heliographic latitudes compared with Ulysses, their observation span almost two solar cycles, a range of heliocentric distances from 1 to 57 AU, and provide a unique insight into the long-term variability of the global structure of the solar wind. We examine the spatial and temporal variation of average solar wind parameters and fluxes. Our obsevations suggest that the global structure of the outer heliosphere during the declining phase of the solar cycle at heliographic latitudes up to 17.5°N was charaterized by two competing phenomena: 1) a large-scale increase of solar wind density, temperature, mass flux, dynamic pressure, kinetic energy flux, and thermal enery flux with heliographic latitude, similar to the large-scale latitudinal gradient of velocity seen in IPS observations, 2) a small-scale decrease in velocity and temperature, and increase in density near the heliospheric current sheet, which is associated with a band of low speed, low temperature, and high density solar wind similar to that observed in the inner heliosphere.     

Measurements of low energy electrons and ions during long-lived solar particle events

Following a solar flare in April 1979, a stream of ions and electrons appeared in interplanetary space for about 8 days. The ions follow a classic ESP pattern. Large fluxes of low energy (2–11 keV) electrons are also present throughout the event. Several distinct populations of these electrons can be identified in association with filaments of interplanetary magnetic field. The electron energy spectrum is remarkably well fit by a power law exponent -2.7 during most of the event.The pitch angle distribution of the low energy electrons are complex and undergo many changes. Weak pitch angle scattering and adiabatic effects play a role in shaping these distributions. The low energy electron fluxes increase following the strong interplanetary shock on 5 April 1979.An invited paper presented at STIP Workshop on Shock Waves in the Solar Corona and Interplanetary Space, 15–19 June, 1980, Smolenice, Czechoslovakia.Physics Department and Space Sciences Laboratory.Space Sciences Laboratory.     

Dynamic analysis of spinning solar sails at deployment process

The spinning deployment process of solar sails is analyzed in this study.A simplified model is established by considering the out-of-plane and in-plane motions of solar sails.The influences of structure parameters,initial conditions,and feedback control parameters are also analyzed.A method to build the geometric model of a solar sail is presented by analyzing the folding process of solar sails.The finite element model of solar sails is then established,which contains continuous cables and sail membranes.The dynamics of the second-stage deployment of solar sails are simulated by using ABAQUS software.The influences of the rotational speed and out-of-plane movement of the hub are analyzed by different tip masses,initial velocities,and control parameters.Compared with the results from theoretical models,simulation results show good agreements.     

Characteristics of shocks in the solar corona,as inferred from radio,optical, and theoretical investigations

Solar radio bursts of spectral type II provide one of the chief diagnostics for the propagation of shocks through the solar corona. Radio data on the shocks are compared with computer models for propagation of fast-mode MHD shocks through the solar corona. Data on coronal shocks and high-velocity ejecta from solar flares are then discussed in terms of a general model consisting of three main velocity regimes.An invited paper presented at STIP Workshop on Shock Waves in the Solar Corona and Interplanetary Space, 15–19 June, 1980, Smolenice, Czechoslovakia.