Library

Notes: [Auszug] Since the beginning of the Interactional Geophysical Year the flare patrol coverage^las been v^ry nearly complete, whereas for radio freqiffeicies 200 and 545 Mc./s. complete radio information is available from the observatory Nera (Holland) and,, associated observing stations at Paramaribo ...

Notes: [Auszug] UNDER this title, in NATURE of April 13, p. 587, Prof. M. Born and K. Fuchs gave some relations between the total and a relative momentum vector of a system of two free particles. They only define the magnitude, not the direction of their relative momentum vector. I believe things become ...

Notes: Conclusion We have got a reasonably clear idea of the various forms under which the type IV continuum emission may appear. Also we can imagine what kind of processes come into play during a type IV event. But the insight gained so far applies to the general case. Individual cases are widely different, and we are still far from understanding why a given event behaves as it does. For instance, why are metric responses lacking at a certain big microwave outburst, or why is the decimetric component particularly strong or prolonged on certain occasions? One can imagine that such questions would receive an answer if one were allowed to “see” the configuration of magnetic lines of force above the activity region ! Does the type IV event tell us a fine story of the interplay of energetic particles and streams of particles with coronal magnetic fields ? Maybe the story would be a fine one if the language could be understood. At present we know only a few words of it; for this reason to us the story is very fragmentary. First of all, however, the message should be recorded far more completely than has been done so far. The number of observations that should be made of one and the same event is tremendous; the program comprises: 1) spectral observations from 1000 Mc/s down to the lowest frequencies; 2) single frequency observations at a great many wavelengths covering the whole radio spectrum; 3) measurements of polarization and 4) determinations of position and angular extent in at least every octave of the whole radio spectrum. Especially as regards the latter two points, the present situation is still very unsatisfactory, though good work has been done already in Japan. The realization of a complete recording of phenomena during a type IV event calls for a combined effort of several observatories. Very encouraging are the established relations between solar type IV events and terrestrial phenomena. From an analysis of solar cosmic ray events as recorded on several places on the earth, interesting inferences have been drawn regarding the travelling conditions of particles in interplanetary space (cf. Carmichael, 1962). Likewise, one may expect interesting information on the behaviour of interplanetary particle clouds of solar origin from (interferometric) observations of decametric radio emission on the occasion of type IV events. The occurrence of a major type IV event enables forecasters to predict successfully geomagnetic and ionospheric storms. Type IV events will determine at what times certain space research experiments will be launched in the next solar cycle. One should like to be able to indicate the probability for the occurrence of type IV solar radio flares themselves. It is known that these flares generally occur in complex sunspot groups; but a complex sunspot group does not of necessity imply the occurrence of a type IV flare. Observations of coronal condensations at microwave frequencies with a high resolution interferometer may help sorting out those centres of activity that are most likely to produce type IV flares.

Notes: Abstract Radiospectrographic observations of some U-like bursts have been employed in combination with a model coronal condensation due to Waldmeier to derive trajectories along which the disturbing agency, which excites the radio emission, may have travelled. Such trajectories as connect regions of opposite magnetic polarity within one centre of activity should have a parachute-like shape in order to account for the observations. Travelling velocities are of the order of 35000 to 55000 km/sec. Moreover, the distribution of U-like bursts in heliographic longitude is investigated and an attempt is made to explain the fact that the second branches of U-like bursts are less developed than the first branches.

Notes: Abstract A microwave magnitude is defined as a logarithmic measure of the energy content of a microwave event. The distributions of microwave magnitudes are derived for collections of bursts that: (1) Occurred during two periods in solar cycle 20, one relatively early and the other relatively late; (2) Occurred in association with optical flares in particular centres of activity. No dependence on the phase in the solar cycle has been found. One centre of activity was found that produced a distribution different from normal. The distribution of microwave magnitudes can be satisfactorily represented by the expression n(m) = const (m/α)e −(m/α) 2. A phenomenological model for the flare build-up process is indicated which leads to a distribution of this very shape.

Notes: Abstract Peak intensities at different frequencies, as reported by several solar radio patrol stations, are used to study the spectrum at the time of maximum intensity of medium-sized solar radio events that cover both the centimetric and metric frequency bands. Two types of spectrum can be distinguished: a V-type of spectrum, where the straight lines, that can be drawn to represent the centimetric and the metric branches, meet each other at a frequency somewhere in the decimetric frequency range and a Jump-type of spectrum, where a discontinuity occurs somewhere in the low-frequency part of the decimetric spectrum. The aspect of the radio response at 600 MHz may have a character which is more ‘centrimetric’ or more ‘metric’. Its character tends to correspond to the spectral branch (metric or centimetric) to which, according to the spectrum, the 600 MHz burst belongs. It is concluded that the centimetric and the metric branch of a cm/m-event are largely independent of each other. It is suggested that a Jump-type of spectrum occurs if some condition relating to the coronal magnetic field is fulfilled.

Notes: Abstract The trajectories of individual electrons of a stream that excites a type III brust may well deviate from a smooth path, for one or both of the following reasons: (1) the magnetic field lines along which the electrons are guided have an irregular course; (2) the pitch angle of an electron is liable to variations. Irregularities of the individual trajectories imply different path lengths and consequently have an effect on the intensity-time profile of the burst. the solution of the ‘gamblers ruin’ problem, known from probability theory, is successfully applied to discuss this effect. It yields model profiles that are very similar to the observed profiles. On the assumption that notably the rise of intensity is to a large extent governed by the effect of the irregularities of electron trajectories, a discussion is made of the parameters that define the stochasticity of these irregularities. Inferences are drawn on th typical shape which an electron path has under the present assumption.

Notes: Abstract Some results on the distribution of polarization characteristics of type III bursts obtained by Chin, Lusignan and Fung (1971) are analysed in terms of the effects of Faraday rotation dispersion on fully polarized signals with small axial ratios of the polarization ellipse.

Notes: Abstract The concept of homology, introduced by Ellison, Mc Kenna, and Rceid (1960) for optical flares, can be extended to flare-associated radio events. Successive flares within the same centre of activity sometimes produce radio events that are remarkably similar. The similarity amounts to the fact that they extend over about the same range(s) in frequency, producing at each frequency responses of comparable intensity and duration. On some occasions the intensity curves at individual frequencies show even detailed resemblance. The occurrence of homologous radio events is commonly restricted to periods of less than 48 hours. Without being homologous, radio events that occur in the same centre of activity may present a common characteristic that is typical for that centre. Two such characteristics are (1) the production of radio responses at centimetric, decimetric and metric frequencies, and (2) the impulsiveness of microwave outbursts. The distribution of time intervals during which such bursts occur is compared with the same distribution for homologous events (Figure 3).

Notes: Abstract The broad band absorptions and emissions in the type IV decimeter continuum are remarkable for the simultaneity of their occurrence at widely different frequencies and for their very short durations. During a given event there is a continuous succession of different patterns of broad band features. It is suggested that the different aspects of the broad band features are variations on a common underlying process. The process would seem to be the screening of a large part of the outgoing beam of radiation, which supposedly is ducted along a tube or channel of relatively low density. As an agency which causes the screening, one may think of shocks or solitons that impinge transversaly on the channel along which the radiation propagates. The various patterns of broad band absorptions and emissions would then be related to structural features of series or trains of passing shocks and/or solitons.