Using the high time resolution of 1 ms, the data of solar microwave millisecond spike (MMS) event was recorded more than two hundred times at the frequency of 2.84 GHz at Beijing (Peking) Observatory since May 1981. A preliminary analysis was made. It can be seen from the data that the MMS-events have a variety of the fast activities such as the dispersed and isolated spikes, the clusters of the crowded spikes, the weak spikes superimposed on the noise background, and the phenomena of absorption. The marked differences from that observed with lower time resolution are presented. Using the data, a valuable statistical analysis was made. There are close correlations between MMS-events and hard X-ray bursts, and fast drifting bursts. The MMS events are highly dependent on the type of active regions and the magnetic field configuration. It seems to be crucial to find out the accurate positions on the active region where the MMS-events happen and to make co-operative observations at different bands during the special period when specific active regions appear on the solar disk

Chen, Zhi-Jun

Fu, Qi-Jun

Hu, Chu-Min

Jin, Sheng-Zhen

Li, Xiao-Cong

Liu, Yu-Ying

Wang, Shu-Lan

Zhao, Ren-Yang

Zheng, Le-Ping

English

NASA Technical Reports Server

N87-21809
SOLAR MICROWAVE MILLISECOND SPIKE AT 2.84 GHZ
Qi-jun Fu*
Astronomy Program
University of Maryland
College Park, MD 20742
Sheng-zhen Jin, Ren-yang Zhao, Le-ping Zheng, Yu-ying Liu, Xiao-cong Li,
Shu-lan Wang, Zhi-jun Chen, and Chu-min Hu
Beijing Observatory
Academia Sinia
Beijing, China
ABSTRACT
Using the high time resolution of 1 ms, the data of solar microwave
millisecond spike (MMS) event more than two hundred times at the
frequency of 2.84 GHz have been recorded at Beijing (Peking) Observatory
since May 1981. The present paper has made a preliminary analysis. It
can be seen from these data that the MMS-events have a variety of the
fast activities such as the dispersed and isolated spikes, the clusters
of the crowded spikes, the weak spikes superimposed on the noise
background, and the phenomena of absorption. The marked differences
from that observed with lower time resolution are presented. Using
these data, a valuable statistical analysis has been made. There are
close correlation between MMS-events and hard X-ray bursts, and fast
drifting radio bursts. The MMS-events are highly dependent with the
type of active regions and the magnetic field configuration. It seems
to be crucial to find out the accurate positions on the active region
where the MMS-events happen and to make co-operative observations at
different band during the special period when specific active regions
appear on solar disk.
I. INTRODUCTION
At Beijing Observatory, a fast sampling recorder with time constant
of I ms for solar observation at 2.84 GHz was devised in 1981 (Jin, Zhao
and Fu). From April 1981 to June 1983, these systems worked in 480
days, about 250 events have been recorded. These results have given us
a clue to the researching on the physical process of microwave
millisecond spike (MMS) emission linked with its associated phenomena.
*Permanent address: Beijing Observatory, Academia Sinica, Beijing, China
237
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II. ANALYSIS OF FEATURES OF THE MMS-EVENTS
There are many and varied structures of the spikes in the MMS-
events. They may be classified as follows:
i) Dispersed or isolated spike clusters:
Among all MMS-events recorded spike bursts grouped in isolated
clusters occur most frequently. The duration of the clusters is often
10-100 ms and the time interval between clusters is about I00-i000 ms.
Each single spike generally last about 3-10 ms, sometimes longer, with
peak flux density higher
than 2000 sfu.,
sometimes higher than
i000 sfu.
Generally, the
isolated spike clusters
correspond with
subflares and/or
impulsive radio bursts
(type 3s, 5s and 8s).
Fig. i shows the record
of MMS-event occurring
at 0544 UT on Feb. 3,
1982. The duration of
the largest spike is 19
ms, with the amplitude
of 2.2 x 104 sfu. Most
MMS-events contained
isolated spike clusters,
while about I/3 of the
events were completely
composed of isolated
spike clusters.
2) Crowded
spike clusters
Such clusters
are composed of a 2.5
number of crowded
spike pulses.
Duration of each _
cluster amounts to >
tens to hundreds of
ms, even more than 10
s. Individual spike x
in the cluster has
short duration (not 0
more than a few ms)
and high flux density
(about ten thousands
sfu.). About half of
6s --TIME
(a)
v
>-
k=
Z 2.5
uJ
¢3
X
..J
EL
_lOOms_
_TIME
(b)
Fig. 2 a) A part of the crowded spike cluster occurring at 0839 UT.
on May 16, 1981.
b) The details indicated by an arrow in Fig 2a.
238
the MMS-event recorded contained crowded spike clusters. About I0 events
of such clusters occurred without other types of clusters during the
period mentioned above. Fig. 2 indicates a part of the crow spike
clusters contained in the May 16, 1981 event. It is the biggest event
among the whole record we obtained. There were 37 spikes in the I00 ms
time interval. The average duration of individual Spike is 2-3 ms. Some
of them has a duration of less than 1 ms, the time resolution of the
radio telescope. Th_ amplitude of the largest spikes in the time
interval is 4.8 x I0_ sfu., with the duration of less than 4 ms. The
most crowded cluster recorded had 430 spike each minute.
3) Long lasting weak spike clusters
They display as some small spike on the noise background. The
spikes sometimes are isolated, sometimes crowded in groups. Their flux
density is generally of the order
of i000 sfu. The clusters have a
duration of several minutes to
tens minutes, even a couple of
hours. They look like a "noise
storm" at microwave band.
Generally, the long-lasting weak
spike clusters correspond to weak
radio burst or flares. About a
half of all MMS-events recorded
belong to this type, which gener-
ally happens when some specific
active region appears. Fig. 3
shows the long-lasting weak spike
cluster recorded on July 15, 1981.
4) Absorption phenomena
Besides the upward spike pulses,
we have recorded a number of downward
negative ones, namely absorption
phenomena. Their flux density is
obviously lower than that of slow burst
level. Of all the MMS events analyzed
about 10 events contained such
absorption phenomena. Fig. 4, Fig. 5
shows a part of the MMS recorded at
0901UT. on July 30, 1981 and at 0403
UT on July 21, 1981, respectively . It
can be seen that there are at least two
kinds of aborption phenomena in the
MMS-events.
Figs. 6, 7, 8, and 9 show four
typical MMS-events recorded on May 16,
1981 (Zhao, R., and Jin, S. 1982), July
31, 1981 (Fu, Q. and et al. 1982) Feb.
3, 1982 and Mar. 30, 1982.
0.75
=.1
u. -- ls _
_ TIME
Fig. 3 Weak spike cluster in the noise background
occurring at 0910 UT. on July 15, 1981.
_t
O
T.-
>
I--
z
W
x
..I
i1
2
n!
.._!
145msl
500ms
TIME
Fig.4 Absorption phenomenon occurring at 0901
UT. on July 30, 1981
239
>.
x
,.e, t
ls --
TIME
Fig. 5 Absorption phenomenon occurring at 0403 UT.
on July 21, 1981.
¢O
460 MHz
B 2840 MHz
C 3650 MHz
D 9395 MHz
0830 0900 UT ' ' '
0805 0815 0825 UT.
(a) (b)
Fig. 6 Microwave outburst associated MMS-event (Figures 2, 10) occurred on
May 16, 1981
a) slow record at 2.84 GHz
b) impulsive structures during initial rising phase at 460, 2840, 3650, and 9395
MHz
240
NA(102)
3
I
h Ut
= • •
0200 0300
I I I I
0400 0500
0
- ' UT.
_ • "= HARD X-RAY BURSTS
Z_:_'Z_.'z,,,.. H FLARES
AZ_==, /% /% A /_ /_ BURSTS AT 2.84 GHz
Fig. 7 Spike's number per minute (NA) and X-ray bursts, flares, and radio bursts
at 2.84 GHz associated on the event of July 31, 1981.
NA(IO 2)
0100 0200
L
i _ ! I I
0300 0400 0500 0600
&
IT/
(a)
| , |
0700 0800 UT.
A,_ HARD X-RAY BURSTS
/_ H FLARES
& BURSTS AT 2.84 GHz
JZ .
CONT. RADIO SPECTRAL EVENT
1.5 s
(b)
Fig. 8 The event of Feb 2, 1982.
a) spike's number per minute (NA) and other solar activities associated.
b) the details of flux density at the time indicated by an arrow in Fig. 8a.
241
16s
(a)
] 'ii
500 ms
(b)
Fig. 9 The event of Mar. 30, 1982
a) a part of record of 16 seconds
b) the details indicated by an arrow in a).
242
III. CHARACTERS OF OUR OBSERVATIONS
Owing to the time resolution obtained by us is higher than those
obtained by Slottje, C. (1980) and Drago, F. (1977), the morphology of
events observed by us is markedly different from that by them and
reflect MMS emission more accurately. It has been found that:
I) The amplitude of the largest spike is more than 5 x 104 sfu.
(possibly larger than 105 sfu.).
2) The duratioan of most spikes in great events is less than 4
ms. Some are less than 1 ms (Fig. I).
3) The ratio of the amplitude of individual spike to the slow burst
background in the event of May 16, 1981 is I00 to 500.
4) Some spikes which
cannot be resolved with lower
time resolution have been
resolved. Fig. lOa show a
recorded group of spikes. Fig.
lOb shows the same groups of
spikes with a time constant of
I0 ms. It can be clearly seen
that the group of spikes has
become a noise pattern with
random fluctuations. The
amplitude has decreased to less
than one half of the original
pattern, while the continuous
background has increased
greatly.
5)Because of the many
records with high temporal
resolution, its seems likely
that the basic unit of MMS
structure is a spike having a
duration from less than i ms to
tens or hundreds of ms. Spikes
appear individually to form a
sparse cluster as a "noise
storm" (Fig. 3), or in groups
with a group duration of tens
or hundreds of ms and even tens
of seconds. There are a number
of groups in an event. With a
lack of temporal resolution,
these groups become noise
pattern with random
fluctuation. Some "swltch-on
and switch off structures"
(Slottje, C. 1980) recorded
with a lower time resolution
I
I k ,IiilLT
I
m
_j
i
0.1s(a)
!
• / 0.1s
(b) "-_ TIME
Fig. 10 A part of spikes occurring at 0815 UT. on May 16, 1981
a) with time constant of 1 ms
b) with time constant of 10 ms
243
are possibly an assembly of a large number of unresolved spikes. The
first spike marks the begining of the assembly, and the last spike the
end. Its rising time or falling time amounts to only I _ 2 ms (Fig. i0).
6) Owing to continuous patrolling and maintaining a record of NA,
spike's number each minute, a valuable statistical analysis was made with
using the events recorded.
IV. CORRELATION BETWEEN MMS-EVENTS AND OTHER SOLAR ACTIVITIES:
i) The correlation between MMS event at I0 cm and solar activity
period:
Table i and Fig. II show the number of MMS-events recorded at
different periods of solar activity. It indicates that the appearance of
MMS-events decreases as solar activity decends.
Table i
May-Dec. Jan.-Mar. Mar.-Sept. Jan.-June
1981 1982 1982 1983
No. of MMS events/100 h 11.2 10.8 4.6 2.3
2) From Oct. 1981 to July 1982,
the MMS-events were recorded in 142
days, in these days, 299 hard x-ray
bursts recorded ("NASA Technical _ 10
Memorandum 84998", and "Listing of x- z
ray flares on HINOTORI") 94 of them >
•
are found to be co-occurrence with the
MMS events. This amounts to a
percentage of 31.4%, which is much
higher than those for the radio bursts _ 5
and optical flares with only 17.5% and =
8.6% respectively are associated MMS-
z
events. If taken the "satellite
nights" into consideration, the
significance of x-ray burst and MMS-
event association may even be
enhanced.
3) Table 2 gives the statistics
of the percentage of _MS events that
I I I I
"_
I I I I
81 82 83 84
YEAR
Fig. 11 The correlation between MMS-evcnt at
t0 cm and solar activity period
were associated with the radio bursts, optical flares, hard x-ray burst
and radio spectral events. It should be pointed out that the most of
radio burst assocaited with MMS events contain impulsive structure (Fig.
6). Some of the impulsive structure has been proved that they are
integrated with a great number of spikes (Fu, Q°, Li, C., and Jin, S.
1985), and the most of radio spectral events associated with MMS-events
are type III.
244
Table 2
radio optical hard x-ray radio spectral
bursts flare bursts events
MMS-events 82% 59% 34.6% 61.5%
Peaks* in MMS-events 64% 59.6% 49.2%
*The amount of peaks in the plot of spike's number per minute via time.
4) Relation between MMS-events and solar active regions:
For those MMS-events associated with solar flares, we can relate
former with the active regions where the flares located. 149 such cases
have been found for statistical study. Results are listed in Table 3.
We notice that 87.3% of such MMS events occurred in the regions
with magnetic field more than 2000 Gauss, while in 6 and BY magnetic
configurations, which are rather rare as a whole, concentrated 54.6% of
the MMS-events generation. When referring to sunspot group, we find
that 84.8% of the events are associated with type D, E and F. These
lead to the conclusion that strong and complex magnetic field is an
important indicator for the happening of MMS-events.
Table 3
Relation Between MMS-Events and Solar Active Regions
Type of Percentage of Magnetic Percentage of Type of
Magnetic MMS-events field MMS-events Sunspot
Structure associated strength associated group
(Gauss)
Percentage of
MMS-events
associated
4.2 > 2000 87.3 E 34.8
41.2 > 2500 62.0 F 24.6
_y 17.5 D 25.4
6 37.1 other 15.2
5) The closeness of association between the MMS-events and hard x-
ray bursts differs significantly at different periods. The period Oct.
8-24, 1981 is a noticeable example. Duringjthis period 24 MMS-events
(with 28 peaks) and 62 hard x-ray events were registered when the time
intervals of our radiometer's working. 93% of the peaks of events has x-
ray association and for all the x-ray events, 41% are co-occurrence with
MMS-events. These correlations are much higher than the average values
over all periods (49.2% and 31.4% respectively as stated before). Almost
245
whole of them were located on
active regions 17906 and
17923. This means that for
some particular solar active
regions, the probability of
co-occurrence of MMS-events
and x-ray events can be very
high.
6) The longitude distri-
bution of the flares
associated with MMS-events:
Fig. 12 and Fig. 13 show the
distribution of these flares
in longitude of solar disk and
in Carrington longitude,
respectively. As one may
expect, there is obvious
directivity of the emission of
these events. The "half-
power" beamwidth of emission
is estimated to be 450 to
5_. The distribution is
somewhat asymmetric, in favor
of the west part of the
disk. There are some active
longitude (as 30_) on solar
disk for the flares associated
with MMS-events as the normal
flares, from the Fig. 13. It
means that, similarly to
normal flares, MMS-flares
correlate to certain active
places wiht long living on the
solar disk.
NUMBER OF FLARES
30" i
I
I
20'
E 90 60 30
I
0 30
i
60 90 W
Fig. 12 The distribution of the flares associated with MMS-events in
longitude of solar disk
(/)
I'-
Z
w
I
_10
o
n. 5
w
m
Z
i!! ;
i. i
• ! i
.... ZI![,l111,,lili, l
6'0 120 - 180 2_0 300
i......
. i
360
Fig. 13 The distribution of the flares associated with MMS-events in
Carrington longitude
V. DISCUSSION:
Owing to the systematic observation with equipment of high time
resolution (I ms), some interesting new features of fast fine structure
of solar microwave bursts have been revealed. For example, the MMS
emission has shorter duration and higher flux density than were
previously known, and the basic units of such fast activities are single
spike crowded together forming separate clusters. Observation shows
that many spikes are not yet resolved. Therefore, it is of importance
to have the time resolution further improved.
With the observational data accumulated so far, the following
results are worth noticing: the MMS events are closely correlated with
hard x-ray bursts and with fast drifting dm bursts. Some MMS-events
found no correspondence with the bursts at the same frequency on slow
speed record but corresponded to the bursts occurring in other
wavelengths. It is likely that the contribution of the spike clusters
246
were smoothed out on the slow speed record, it seems that they originate
from different physical processes. Thus, such fast activity may be a
fundamental process different from the flares and normal radio bursts.
The MMS events are highly dependent with the type of active regions and
the magnetic configuration of the active regions. Possibly, it is
crucial to find out the accurate positions on the active region where
the MMS-events happen and the position relative to the places where
other solar activities associated occur, for judging what is better
mechanism for MMS emission.
Since the discovery of solar microwave spike emission with high
time resolution observations at cm wavelengths, much theoretical work on
the interpretation of its high brightness temperature and polarized
characteristics has been proposed. The mechanisms for generating MMS
emission have been reviewed in more detail by the authors (Holma, G.D.,
1982; Melrose, D.B., and Dulk, G.A., 1982). There is another type of
cyclotron maser instability with a "hollow beam" distribution of
electrons (Li, H°, Li, C., and Fu, Q., 1985) seems to be more important
than that associated with a loss-cone distribution. Possibly, different
kinds of MMS emission have different mechanisms. It is important to
make co-operative observations at different radio wavelengths, optical
wavelengths, x-ray and others during the special period when specific,
as mentioned in section IV, active region appear on solar disk for
clarifying the essence of the fast fine structure emission.
REFERENCES
DrSge, F. 1977, Astro. Astrophys., 57, 285.
Fu, Q., et al. 1982, Astronomical Circular No. 13, March 25.
Fu, Q., Li, C., and Jin, S. "Microwave Millisecond Spike Groups Super-
imposed on Solar Microwave Bursts", 1983, Kunming International
Workshop of Solar Physics, China (submitted to Acta Astrophysica
Sinica).
Holman, G.D., 1982, Advanced Space Research, vol. 2, 181.
Jin, S., Zhao, R., and Fu, Q., "Solar Microwave Bursts Recorded at 2.84
GHz with Millisecond Time Resolution", (submitted to Solar Physics).
Li, H.W., Li, C.S., and Fu, Q.J., 1985, Acta Astrophysica Sinica, (in
Chinese) Vol. 5, No. 4, 300.
Melrose, D.B. and Dulk, G.A., 1982, Ap.J., 259, 844.
Slottje, C., 1980, Radio Physics of the Sun, M.R. Kundu and T.E. Gergely
(eds.) p. 195.
Zhao, R., and Jin, S., 1982, Scientia Sinica, 25, 422.
247


Solar microwave millisecond spike at 2.84 GHz

Solar microwave millisecond spike at 2.84 GHz

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