The Westerbork array has recently been adapted and procedures have been developed to observe the sun at cm wavelengths with high time resolution. One dimensional scans are obtained in both circular polarizations every .1 sec.

Optical, radio and X-ray evidence of violent mass motions in the corona has existed for some years but only recently have the form, nature, frequency and implication of the transients become obvious. In this paper I review the observed properties of coronal transients, concentrating on the white-light and radio manifestations. The classification according to speeds seems to be meaningful, with the slow transients having thermal emissions at radio wavelengths and the fast ones non-thermal. I then discuss the possible mechanisms involved in the radio bursts and review the estimates of various forms of energy. It appears that the magnetic energy transported from the Sun by the transient exceeds that of any other form, and that magnetic forces dominate in the dynamics of the motions. The conversion of magnetic energy into mechanical energy, by expansion of the fields, provides a possible driving force for the coronal and interplanetary shock waves.

The soft x-ray (2–54 Å) pictures obtained by the S-054 experiment aboard SKYLAB provide an excellent opportunity to study the association of x-ray loop structures with radio bursts. We report here on the properties of meter-decameter wavelength radio bursts which appear to be associated with two different types of loop structures:

1. a) Relatively short lived small scale loops, which are observed to link magnetic fields of opposite polarity, called x-ray bright points (XBPs); and

2. b) Longer lived loop systems which appear to connect opposite magnetic polarities of an active region and active region complexes as well.

This paper shows the first satellite observations of the Sun's white light corona (2.6 R⊙ −10.0 R⊙) during the active phase of a sunspot cycle. Since March 28, 1979, these observations have been obtained routinely with a spatial resolution of 1.25 arc min and a repetition rate of 10 minutes during the one-hour sunlit portion of each 97-minute satellite orbital period. As an illustration of these new observations, we show the coronal changes associated with the great mass ejection of May 8, 1979.

Radial structure of impulsive hard X-ray and microwave sources in solar flares is not well known at the present time. Measurements of near-the-limb flares with a high spatial and temporal resolution is, of course, the best way to determine the radial structure of these sources. In absence of such measurements, particularly for the hard X-ray emission, behind-the-limb flares provide (through occultation) a means of observing the coronal part of the impulsive source. Here we summarize the characteristics of the impulsive coronal X-ray source deduced from multi-spacecraft observations of a behind-the-limb flare and their implications with respect to impulsive microwave source.

Possibility of a discovery of current sheets in the radioband by using their screening and reflective properties as also their own emission is discussed. It is shown, that the thermal bremsstrahlung of the sheet may be of a sufficiently large intensity on the maximal critical frequency for the plasma in the sheet. In dependence from electron density No and temperature Ts the thickness of the sheet from tens centimetres to hundreds metres is sufficient to provide optical depth Spectral observations with sufficient angular resolution may give such characteristics of the sheet as its temperature, electron density, thickness and height in the solar atmosphere.

Repeated bursts of microwave emission were observed by Slottje (1978) during the solar flares of April 11 and April 28, 1978. The high brightness temperatures which are inferred for these bursts indicate that a coherent mechanism must be responsible for the observed radiation. Slottje suggests that the emission is plasma radiation at the fundamental plasma frequency. We consider here the alternative possibility that the emission is coherent gyrosynchrotron radiation.

In order to study the dynamical burst process we investigated two bursts of 1972 May 18 at 14:05 UT and at 16:16 UT in the microwave (1–15 GHz, Berne and Sagamore Hill), the hard X-ray (28–102 keV, ESRO TD-1A) and the soft X-ray (0.5–20Å, Solrad 11) frequency ranges. For both flares a thermal interpretation was adopted.

An analysis has been carried of the correlation of the occurrence of type III bursts and flares in spotless regions (G-flares) or covering major sunspot umbrae (Z-flares) - i.e. in magnetic conditions presumably opposite - over the past 10 years. A very low correlation of the former flares (8%) and a higher than average value for the latter flares (36% against the normally accepted 25%) shows that the ambient magnetic field of the flaring region is a primary factor for type III burst emission. The presence of a surge and of a rapid brightness rise (“flash-phase”) are recognized to be other important, if secondary, factors for type III burst generation.

We observed short duration, narrow band Type IIIb radio bursts that occur just before the onset of a normal Type III burst. These observations were made with a multichannel radiometer with a center frequency of 25 MHz, time constant of 10 milliseconds and frequency resolution of 100 KHz. The average half power duration of a typical element of a Type III burst was determined. It was found to be very similar to the time profile of a normal Type III burst, i.e., sharp rise and exponential type decay. The duration of the exciter, tE, and the decay time constant, τ, determined from the average time profile were 0.88 and 0.31 seconds, respectively. The corresponding quantities for the associated Type III bursts are 6.0 and 2.1 seconds, respectively. It is interesting to note that the ratios are the same, and equal to 0.98. We found that there is no difference between the time profile of a Type III burst associated with a Type IIIb burst and that of an isolated Type III burst. We also found that the two quantities ‘tE’ and ‘ τ ’ are positively correlated in the case of isolated Type III bursts. The linear correlation coefficient is 0.70. This correlation seems to break down in the case of Type III bursts associated with Type IIIb bursts. We looked for a relation between durations of the elements of the Type IIIb bursts and that of the associated Type III bursts, and found that the two quantities are positively correlated. Lastly, we would like to point out that the elements of Type IIIb bursts observed by us are more intense than the associated Type III burst.