 Georgian Academy of Sciences  Catalogue
of Unusual Phenomena in the Solar Radio Emission at 210MHz Frequency within
1957-1967 Sh.S.Makandarashvili
The solar radio emission consists of a thermal background and various
bursts of sporadic radio radiation, sometimes very intense. They are usually
localized in active regions of the solar disc. Bursts are considered to be a
basic characteristic of the solar activity, and therefore a significant object
of investigation.
Radioastronomic methods of observation largely supplement the results
of optical investigations and in some occasions they are the only method of
obtaining information on physical conditions of generation and on the way of
propagation of radio waves. Investigations
of the solar radio emission enable one to find out its relation to dynamical
processes in the solar atmosphere and to various geophysical phenomena. The
comparison of results obtained due to observations in different spectral
regions of the solar radiation, is an important method of studying different
events occurring in the solar atmosphere. In the visible region where the Sun
emits most of its energy, time variation of total radiation is very poor. The
radio emission varies significantly: slow variations of the radio emission
level and fast outbursts are superimposed on the weak constant radiation
(constant component). Their intensity in the metre wave band can exceed the
emission of the quiescent Sun by a few thousand times.
Our knowledge of the solar activity has been essentially enlarged due
to development and coordination of optical and radio observations.
Recently measurements of the solar radio emission provided a lot of
information concerning the solar corona. The radio observations have the
advantage of permitting to attain a high resolution for the heights in the
corona as the velocity of propagation of radio waves distinctly depends on the
medium density. Great heights, where the metre wave emission arrives from,
point to the distance from the Sun, at which the solar corona can be studied
by radio methods. At present there is a possibility of continuous observations
of the solar corona and accordingly, registering
of the flux radio emission and bursts. Thus, radio astronomy and optical one
supplement each other.
At present radio emission of the metric wave band is divided into five
types according to spectral properties. radio emission of noise storms belongs
to the first type. It involves irregular increase of the emission with
numerous intensity peaks following one another, the lifetime of which is ten
fractions of a second.
Noise storms, the first type solar radio emission, were registered on
the Earth by J.S. Hey in 1942. Nowadays there exists a considerable amount of
observational data giving possibility to study certain properties of the solar
activity effect. The noise storm bursts are observed earlier and disappear 1-2
days later than the enhanced background radiation.
It is established that the noise storms are connected with large groups
of spots in the photosphere, particularly with those in the central part of
the solar disc. Probability of the radio emission emergence increases with the
area of the whole group as well as with that of the largest spot. Both the
bursts and the background radiation have a high polarisation degree amounting
to 100 per cent with the magnetic field occurring either in the region of the
radio emission generation, or at propagation of the radio waves in the corona.
Duration of noise storms
can vary from a few hours up to a few days in a wide range
of frequencies (50/300 MHz). On the whole, the phenomenon is observable
on metre waves and it represents
the increased emission of the background basic level. The height of the source
region is 0.3 R¤.
Nature of noise storms, however, is not completely clear thus far. High
intensity and variability seem to rule out a thermal origin. The suggested
nonthermal mechanisms are not fully satisfactory. Plasma oscillations
of magnetic brake mechanisms are considered to be the most probable ones.
So far, the following problems remain to be seen finally: relation of
the noise storm radio emission to the magnetic field of an active region and
flares as well as the structure of the coronal sources and its dimensions.
Solution of these problems would allow the radiation mechanism to be refined
,the origin of polarisation to be explained ,the radiation of this type to be
used as an indicator of a state of the local magnetic fields in the corona,
one or another forms of geophysical phenomena depending on them.
Bursts of type II (bursts drifting slowly) involve great disturbances
in the region of the metre waves drifting from high frequencies down to low
ones with a velocity of 1/4 MHz per sec. They are related to the most powerful
flares and last about 10 min.
These bursts were found in the cosmic space at a distance of more than
30 R from the Sun. Bursts of type II are a rather rare phenomenon in the solar
life. At the solar activity maximum no more than about a hundred such bursts
can be observed during the year.
Bursts of type III occur very often. At the period of the solar
activity maximum there are about three bursts per hour on the average.
Duration of bursts of type III is 1-30 sec. There are 4-100 bursts in a group.
In 50\% of cases bursts of type III are related to optical flares and they
mostly occur close to the flare explosion phase.
Bursts of type IV are related to the flare of a long-term radio burst
occupying a wide frequency band and they last a few hours. Bursts of type IV
follow those of type II, often
overlapping them. A full burst of this type has the components corresponding
to the different sources and different radiation mechanisms. Bursts of type V represent wide-band continuous radiation on metre wave-lengths. They last about a minute upon appearing bursts of type III. Prominent
events
The forms, acquired by powerful micro wave bursts in recording at a
fixed frequency, are designated by the symbols as follows:
IS -simple mostly non-metre microwave pulse burst or a decimetre burst.
2S/E -a simple: burst of type I with fluctuations
5S -simple
6S -simple rise and fall of activity, as rule, a moderate burst or that
of low intensity lasting 1-2 min
7C -weak burst in the second part
8S -a short-term outburst
45C -complex:: combination of small or a considerable quantity of
simple bursts
46C -a complex burst with fluctuations
48C -a complex variation of intensity. As a rule, a burst of high
intensity and duration from minutes up to tens of minutes.
40F -fluctuation: small C type burst occasionally superimposing on the
primary burst.
41F -a group of bursts occupying the time interval of the order of
minutes, with peaks separated comparatively.
47GB -a large burst: C type burst of notably high intensity
28PRE -a precursor: preburst activity connected with the primary burst
29PBI -post burst rise: the tail of the primary burst which can be
considered as the enhancement of S-component (a slowly varying component)
21GRF - simple A: index A shows the position of one event superimposed
on the other. In case the superimposed burst is difficult to be separated, it
is designated by type C.
22GRF - burst gradually rising and dropping: a temporary enhancement of
S-component or a similar activity in the burst area. the enhancement sometimes
starts with a sharp rise of the flux similar to a simple burst.
31ABS - absorption: due to the ejected matter mainly appearing after
the burst, occasionally named as a postburst dropping. Such an event is often
observed when the flux drops to the preburst level. A temporary flux dropping,
occasionally called as the burst in absorption or it can simply be a temporary
dropping of radiation.
24R - rising: it can also occur at the beginning of S-component related
with other solar bursts.
26AF - dropping
42 SER - sets of bursts on decimetre, metre and decametre wavelengths;
the majority of events are of type C including burst of types F and G8
43NS-formation of a noise storm
44NS - a noise storm
27RF - rising and dropping: more or less irregular rising and dropping
of the continuum
lasting a few minutes up to an hour; besides, a numerical code is used.
In 1957 a solar radio telescope intended for observations at 210MHz
frequency was put into operation at Abastumani Astrophysical Observatory of
the Academy of Sciences of Georgia (geographical coordinates: latitude 410 8,
longitude 42 08, and altitude 1700m). systematic observations were started in
December 1957. Within 1957-1995 a considerable amount of observational data
are accumulated comprising four solar cycles (maxima in 1957-1958, 1969-1970,
1980-1987 and 1990-1991).
The present Catalogue includes the copies of original records of the
solar radio emission. The records were done by means of the radio telescope
consisting of three units: an antenna feeder system, a radiometer with a
recorder and a power unit.
The antenna consists of 16 active semi-wave dipoles situated in the
plane over the reflecting screen. all the dipoles are interconnected by means
of the equiphase asymmetric feeder and the antenna outlet - with the
radiometer inlet by cable RK -6. The antenna construction permits it to be
pointed to any sky region. The azimuth directional pattern in horizontal and
vertical planes is 120 and 170 respectively.
The method of modulation is used in the radiometer.
It consists in the following: the noise signal received from the Sun
through the antenna applies to the modulator where it is modulated at a
frequency of 100Hz. The modulated signal passes through the high frequency
filter tuned in a frequency of 210 MHz with the passband of 2MHZ . Further, a
square-low detector is located on the path of the high-frequency modulated
signal being detected. At last a low-frequency signal of 1000Hz emerges. The
signal enters into the heterodyne filter, here it is amplified by means of a
low-frequency amplifier with maximum antenna gain 1000 times. It can be
changed using the control knobs on the facade panel of the receiver. The
amplified low-frequency signal enters into a synchronous filter transmitting
the signal of the frequency, by which the high-frequency radio signal is
modulated. Further, the signal in the same heterodyne filter is transformed
into constant current, which is registered with a recorder.
The radiometer is provided with a rough channel switching in case the
signal of a certain value is amplified. On the recorder this signal is
determined as 0.9 of the scale. The signal is brought into the rough channel
from quadratic detector. Maximum enhancement of the rough channel is 100 times
less than that of the accurate one. The rough channel is switched by the
automatic unit at closing the relay contacts connecting the recorder to the
power supply of 220 V. The rough channel is disconnected by pressing the
button on the facade panel of the radiometer.
A noise generator is installed in the radiometer, from which the signal
passes to the modulator by means of the toggle switch on the receiver facade
panel.
All the units of the receiver are supplied with the power from a
stabilised source of supply ±12,6
V. which is located in the radiometer.
The whole receiver is heat settled. The inside temperature is kept 350C
by means of a thermostabilizing unit operating from 220 V alternating current
power supply. Unit Diagram of the
Radiometer At 210 MHz
A - antenna of the radio telescope
M - modulator
NG - semi-conductor noise generator
MA - modulation signal amplifier
V - valve
FA - high frequency amplifier
F - high frequency filter
D - quadratic detector
Gf - generator filter
PS - power supply unit
A - automatic equipment for switching
the rough channel
TR - thermoregulator
RAC - recorder of the accurate channel
RRC- recorder of the rough channel
The value of internal noises is no more than 0.01 of the signal from
the "quiescent Sun". When the solar radio emission is registered the
galaxy background is excluded.
Relative celebration of the receiver is performed by the noise
generator on the diode at the beginning and end of each observation. Absolute
calibration is done by comparison of the signal at the receiver output from
the calibration noise generator and the source of Cassiopeia A approximately
once a year (duration of observation is 4-6 hours a day).
The catalogue covers a cycle of the solar radio emission within
1957-1967. It embodies separate sections of continuous record of the total
flux of the solar radio emission corresponding with those time intervals, when
the bursts of the solar emission, refered to as unusual phenomena in the radio
band, were registered. Out of a considerable number of the registered events,
the unusual phenomena distinctly standing out against the background of total
solar activity of a suitable day, were selected for the catalogue. Bursts,
sets of bursts as well as noise storms are reckoned among such phenomena. In
case a certain day of the solar radiation could be, on the whole,
characterised as a quiescent one, but if, on this background there was a group
of bursts lasting more than a minute with the intensity of the
"quiescent" Sun level, such a group was included in the catalogue.
If there was a noise storm during the whole observational time, not all the
bursts were included, but only the sections of the noise storm, somehow
standing out against the background of total activity. Accordingly, about 900
unusual phenomena have beer processed.
Occasionally at registering of a large solar radiation burst, many
times exceeding the level of the "quiescent"
Sun, sensitivity of the radiometer varied repeatedly. The records were copied
at a special laboratory.
All the bursts of the solar radio emission are represented in the
coordinates of intensity-time. The intensity in the units of 10-22W
M-2Hz-1 and Greenwich time (VT) are plotted along the
axis of ordinates and that of abscissas, respectively. The level of the
receiver internal noise coincides with the time axis. In the catalogue all the records are arranged in chronological order. Each record has an ordinal number. Additional data on the events are listed in the table 1. It contains the ordinal number of the record, date, time interval, beginning and end, type of phenomenon and intensity flux. As it is seem about 1/3 of the events in the solar radio emission occurred in the periods when there were no chromosphere flares. In most cases this can be explained by the fact that single bursts and short-lived groups of bursts often occur both during subflares and other active processes on the Sun (such as short-lived brightening of a flocculus and fast movement of fibres in the magnetic fields of spots), and also that in some periods of registration of the solar radio emission there could be no optical observation of the bursts. Besides, the solar radio emission bursts can be registered during the flares beyond the limb which cannot be observed by optical methods.
References 2.
Bulletin "Solnechnie Dannie" 1957 year N 1-12, 1958 year N 1-12,
1959 year N1-12 3.
Moiseev I.G. Proceedings of Crimea Astrophysical Observatory 1955, 15, 104 4.
Moiseev I.G., Yurobckaja L.I., Yurovski Yu.F. Proceedings of Crimea
Astrophysical Observatory 1969, 39, 325 5.
Makandarashvili Sh.S. Bulletin of Abastumani Astrophysical Observatory 1962
year, N 29 6.
Alimbarashvili A.N., Makandarashvili Sh.S., Parsadanova E.I. Bulletin of Abastumani Astrophysical Observatory 1962 year, N 29
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