U. of Iowa 67-39
MICROBURST PHEXOMETJA
3. An Association Between Electron Mlcrobursts and VLF Chorus*
Me N. OlivenJmc and D. A. Gurnett
Department of Physics and Astronomy University of Iowa
Iowa City, Iowa
September 1967
*Research supported i n par t by the Office of Naval Research under Contract 1509(06) and NASA G r a n t NGR-16-001-043
=NASA Graduate Trainee
2
ABSTRACT
Observations m a d e with t h e Injun 3 s a t e l l i t e of pre-
c ip i t a t ing Ee 2 40 keV electron microbursts and of VLF chorus
emission have revealed t h e i r simultaneous occurrence. Observed
electron microbursts a re a l w a y s accompanied by a group of VLF
chorus emissions; chorus i s not necessmily accompanied by
microbursts. The maximum region of microburst occurrence from
0400 I magnetic l oca l time s 1300 and 65" I invariant l a t i t ude
s 70" l i e s well within t he maximum region of chorus emissions
from 0300 s magnetic local time 5 1500 and 55" s; invariant l a t i -
tude I; 75". It i s not generally possible t o f ind a one t o one
(burst t o burst) correspondence between individual electron
microbursts aad VLF chorus burs ts .
3
INTRODUCTION
Much theore t ica l and experimental e f fo r t has recently been
concentrated on the investigation of wave-particle interact ions
i n the magnetosphere (Kennel and Petschek ~19661; and o thers ) .
Experiments aboard the low-altitude, magnetically-oriented Injun 3
s a t e l l i t e fo r t he period from January to October 1963 provided the
opportunity t o simultaneously invest igate VLF radio noises and
energetic charged p a r t i c l e fluxes. I n t h i s paper we discuss an
association found i n the Injun 3 data between electron microbursts
and VLF emissions cal led chorus.
A detai led description of the detectors and VLF equipment
used i n t h i s study i s given by O'Brien e t al. [1964]; Gurnett
and O'Brien [1$4]; and i n a companion paper by Oliven e t al.
[1967].
sensi t ive to electrons of energies E
mated t o detect pa r t i c l e s moving approximately perpendicular
(90" detector) and p a r a l l e l (180" detector) t o the geomag-
ne t i c f i e l d i n the northern hemisphere.
The two p a r t i c l e detectors used i n t h i s study were
2 40 keV and were co l l i - e
The VLF experiment
used a loop antenna, oriented so t h a t the geomagnetic f i e l d
was i n the plane of the loop, and detected t h e VLF magnetic
f i e ld .
mitted t o the ground v i a the s a t e l l i t e telemetry t ransmit ter .
The wide-band VLF signal (200 Hz - 7 KHz) i s t rans-
4
This study was limited to t he investigation of VLF
phenomena which are associated with impulsive precipi ta t ion of
large fluxes of electrons in to the auroral zone and called elec-
t ron microbursts (Oliven e t a l . [l967]). Electron microbursts
itre characterized by t h e i r short time scale ( e 1 second i n
duration), energies E
precipi ta ted electron fluxes above background of 2 10 electrons
2 40 keV (as observed by Injun 3 ) , peak e 4
-2 -1 em sec sterad-' for E 2 40 keV, and a maximum occurrence
during loca l morning at about 65 to 70 degrees invaziant
l a t i tude . Electron microbursts are responsible for x-ray
bremsstrahlung bursts observed a t a l t i tudes < 100 km by Ander-
son [1965], Venkatesan e t al. [1967] and others, and cal led
x-ray microbursts.
e
Fv
5
STATISTICAL STUDY OF VLF CHORUS OC-CE
A study of Injun 3 VLF records during periods of electron
microburst ac t iv i ty revealed the simultaneous occurrence of VLF
chorus. Chorus consists of closely spaced, often overlapping,
randomly occurring discrete bursts, usually r i s ing i n frequency
i n the range of - 0.5 t o 6 KHz, with the individual bursts
typica l ly having a duration of a few tenths of a second (Allcock
L-19571 and Helliwell C196.51) . satell i te-observed chorus are shown i n Figures 1 and 2. The
Bequency-time spectrograms of
broad-band in t ens i ty of chorus bursts detected by Injun 3 varied
from approximately 1.0 milligammas (the receiver noise l eve l ) t o
a m a x i m u m of about 30 milligammas. Positive ident i f ica t ion of
chorus observed by Injun 3 was made by visual. observation o f high
time resolution frequency-time spectrograms.
To determine the regions of occurrence of chorus, data
from the ent i re l i fe t ime of Injun 3 were investigated, covering
24 hours i n local. time and invariant la t i tudes from 35" t o 80".
This region was divided in to blocks 5" i n invariant l a t i tude and
one hour i n magnetic loca l time. I n the region between 65" and
74" invariant l a t i tude where ground-based observations of VLF
emissions have established a maximum of chorus ac t iv i ty the
blocks were made smaller t o provide greater de ta i l . In these
n
1
B c
6
regions the blocks were 3" i n invariant l a t i t u d e by one hour of
magnetic loca l time.
Data samples were chosen t o be 8 seconds i n length. A t
When- l e a s t t e n such data samples were investigated per block.
ever possible ( in most cases) t en d i f ferent passes were used per
block, thus each s a t e l l i t e pass was permitted t o contribute only
one sample per block.
studied t o determine the presence of chorus.
occurrence were computed by taking t h e r a t i o of the number of
Approximately 2400 individual samples were
Percentages of
samples per block containing chorus t o the t o t a l number of
samples studied per block.
investigation.
Figure 3 gives t h e r e su l t s of t h i s
Chorus i s seen t o occur primarily i n the region from
55" - 75" invariant l a t i tude and from 0300 - 1500 magnetic l o c a l
time. The most intense region of occurrence, between 0600 and
1200 magnetic l o c a l time, contains many blocks where the per-
centage of occurrence exceeds 50%.
the frequency of occurrence exceed 80%.
Table 1.
In no block, however, does
This i s seen i n
These s t a t i s t i ca l . r e su l t s appear t o be i n reasonably
good agreement with the s t a t i s t i c s accumulated from ground-based
observations (Laaspere [1964]).
7
COKRELATION OF ELECTRON MICROBURSTS WITH CHORUS
A n investigation of about 400 satell i te-observed micro-
'burst episodes (segments of data i n which one or more clear ly
ident i f iab le microbursts were found) was undertaken.
episodes varied i n length from about 8 seconds t o several
minutes, depending upon the duration of microburst ac t iv i ty ;
sanrples were chosen from all regions of inva.ri.ant l a t i t ude and
magnetic loca l time i n which electron microbursts existed. VLF
These
spectrograms of these periods of time were produced and v isua l ly
inspected f o r VLF emissions ac t iv i ty i n t h e frequency of - 200
Hz t o 7 KHz.
I n dl these microburst episodes it w a s found t h a t when-
ever electron microbursts were present they were always accom-
panied by VLF chorus emissions; no exceptions were found i n
any of the cases investigated. O f par t icu lar in t e res t are the
blocks i n the regions from 2000- 0200 hours magnetic l o c a l time
where the probabi l i ty of finding electron microbursts or chorus
i s very s m a l l .
electron microbursts are always accompanied by chorus. A typi-
ca l example of an electron microburst episode accompanied by
VLF chorus i s seen i n Figure 4.
Even i n these regions the r u l e i s unviolated;
The converse re la t ion was not
found t o hold; namely the occurrence of chorus i s not always
accompanied by microbursts .
"
8
The probabi l i ty of electron microbursts always occurring
accompanied by chorus can be found by studying t he occurrence
frequency probabi l i t ies of each phenomenon. Figure 5, reproduced
from and discussed i n t h e companion paper (Oliven e t a l . [1967]),
represents t he occurrence frequency of electron microbursts.
Each block covered 5" invariant l a t i t ude (3" between 65" and 74")
by one hour magnetic l oca l time. Where possible, different san-
ples of data were used i n t h i s study from those used t o compile
Figure 3 .
The dependence of chorus on t he occurrence of microbursts
can be established by comparing t he conditional probabi l i ty of
chorus occurring when microbursts are occurring, P(C/M), with
t he probabil i ty of chorus occurrence, P(C). Our resu l t s show
t h a t P(C/M) = 100%. Comparing Figures 3 and 5 and Table 1, it
can be seen t h a t P(C) i n t he region where microbursts occur i s
typ ica l ly about 60%, but never greater than 80%.
i s substant ia l ly greater than P(C) we can conclude t h a t the re
i s a def in i t e association between t he occurrence of chorus and
Since P(C/M)
t he occurrence of electron microbursts.
The region of maximum occurrence of electron microbursts,
In which are always accompanied by chorus, i s seen i n Figure 6.
t h e blackened regions, the probabi l i ty o f observing microbursts
I'
9
with chorus i s greater than 10%. Within these blackened areas
the probabi l i ty o f chorus occurrence i s always greater than t h a t
of electron microburst occurrence. Outside t h i s region where
microbursts are l e s s common, l e s s than lo%, the regions of maxi-
mum VLF chorus occurrence, greater than 20%, are indicated by
dotted areas. From Figure 6 the region of maximum microburst
occurrence i s seen t o l i e within the region of maximum chorus
occurrence.
It should be noted t h a t the absolute frequencies of occur-
rence i n Figures 3, 5, and 6 may depend on the noise l e v e l of the
detectors, the antenna noise i n the case of the VLF receiver and
the background counting r a t e i n the case of the 40 keV electron
detectors. Addttionally, t he occurrence frequencies i n the case
of the electron microbursts i s affected by the c r i t e r i a used fo r
the ident i f ica t ion of microburst events, as discussed i n the
companion paper (Oliven e t al. [1967]).
shape and locations o f t he two regions of maximum occurrence
would be expected t o be re l a t ive ly insensi t ive t o changes i n the
detection threshold.
However, the general
It i s usually not possible t o ascribe a given burst i n
the electron data with a spec i f ic chorus burst i n the VLF data;
Figure 7 i l l u s t r a t e s t h i s point. It can be seen i n Figure 7
10
t h a t t he duration of burs ts i n both records i s similar but t3at
it i s not possible t o uniquely associate a given microburst with
a given chorus .burst.
Greater t h e resolution of electron microbursts can be
achieved by viewing t h e daughter bremsstrahlung x-ray micro-
burs ts with high-time resolution equipment i n balloon-borne
detectors.
passed within approximately 400 km of a University o f C a l i f o r n i a
balloon-borne x-ray experiment (Milton and Oliven [1967]). Fig-
ure 8 presents t he Injun 3 precipi ta ted and trapped electron
flux, E
30 keV I; Ex ray 5 60 keV, when t he subsa te l l i t e point was approx-
imately 400 km f rom t h e balloon.
x-ray data indicate the presence of microbursts.
burst correspondence of electron microbursts t o x-ray micro-
burs ts i s t o be expected because of the l imited spakial extent
(about 100 km) fo r such bursts .
t o be present during t h i s i n t e rva l but again, a one to one
matching of chorus burs ts with electron or x-ray microbursts i s
During one pass t he Injun 3 subsa te l l i t e posit ion
2 40 keV, and t he balloon x-ray f lux measurements, e
- Both t h e electron data and t he
No burs t t o
Chorus burs ts are also seen
not possible. I n general, there are usually several chorus
bursts for each electron microburst.
J
11
DISCUSSION
It has been found t h a t satell i te-observed electron micro-
bursts axe a.lways accompanied by VLF chorus bursts and t h a t the
region of maximum occurrence for electron microbursts l i e s within
the region of m a x i m u m occurrence fo r VLF chorus.
are not, however, always accompanied by electron microbursts . Also, it i s not generally possible to f ind a one to one, burst to
burst, association between electron microbursts and VLF chorus.
The general time scale fo r both chorus bursts and electron micro-
bursts i s very similar, generally a few tenths of a second.
Chorus bursts
These associations between chorus and microbursts suggest
a cornon origin fo r both phenomena.
from energetic charged paxtieles (cyclotron radiat ion from indi-
vidual pa.rticles) cannot explain the in t ens i t i e s of VLF emissions
such as chorus, ( E l l i s [1957]; Santirocco [1$0]; Liemohn [1$5]),
it i s generally believed t h a t VLF emissions are generated by plasma
i n s t a b i l i t i e s within the magnetosphere. A plasma i n s t a b i l i t y
acts to coherently bunch or organize the charged paxt icles so
t h a t large in t ens i t i e s can be obtained. On very general grounds
Brice [1964a] and Kennel and Petschek ~19661 show t h a t the
generation of whistler mode wave energy by in terac t ion with elec-
trons gives r i s e to a decrease i n the p i tch angle of t he resonant
Since incoherent radiat ion
12
electrons and t o precipi ta t ion i f t he mirror a l t i tude i s suf-
f i c i en t l y decreased. Thus, the plasma i n s t a b i l i t y which produces
VLF chorus may also cause precipi ta t ion of t h e 40 keV electrons
which a re observed as electron microbursts.
The deta i led plasma i n s t a b i l i t y mechanism which produces
chorus emissions i s not known, although several possible mech-
anisms have been considered (Brice [1964a and 1964b1; Kennel
and Petschek [1966]).
I n considering t he region of occurrence of chorus and
electron microbursts it i s important t o note tha t , whereas the
guiding center of t he electrons i s constrained t o follow a geo-
magnetic f i e l d l ine , t he VLF chorus energy i s guided only ap-
proximately along t h e geomagnetic f i e ld l ine , t o within f 19".
Thus, i f chorus and electron microbursts a re produced together
at high la t i tudes i n t he magnetosphere then at lower a l t i tudes
t h e region illuminated by the chorus should be generally l a rger
and roughly symmetric i n l a t i t ude with t h e region where electron
microbursts a re observed. This relat ionship i s i n agreement
with t he observed regions of occurrence for chorus and micro-
burs ts shown i n Figure 6. Also, s ince chorus and microbursts
do not follow t h e same path from the region of generation one
would not necessari ly expect a burs t by burs t correspondence
between chorus burs ts and electron microbursts.
13
ACKNOWLEDGEMENTS
The authors wish t o express t h e i r thanks for
t he advice and support offered i n t h i s project by
Professor J. A. V a n Allen of the University of Iowa.
This work was supported at the University of Iowa
by t he Office of Naval Research Contract 1509(06)
and NASA Grant NGR-16-001-043.
14
T a b l e 1
PERCENTAGE OCCURRFNCE OF CHORUS DETECTED BY INJUN 3 WIT- THE HEART OF THE CHORUS W G I O N OF OC-CE
Magnetic L o c a l Time Invariant L a t i t u d e
0900 60 70 70 60 50
1000 30 60 70 60 40
1100 20 70 70 60 50
1200 20 70 70 80 70
15
Allcock, G. McK., "A Study of the Audio-Frequency Radio Phenomenon xi?own as 'Dawn Chorus', " Australian J. of Physics - 10, 286- 298 (1957).
Allcock, G. McK. and L. H. Martin, "Simultaneous Occurrence of 'Dam Chorus' a t Places 600 km Apart, '' Nature - 178, 938-939 (1956).
Anderson, K. A., "Balloon Measurements of X-Rays i n the Aurora Zone," Auroral Phenomena, ed. M. W a l t (Stanford University Press, Stanford, California, 1965) .
Brice, N. M., "An Explanation of Triggered VLF Emissions," J. Geophys. Res. 68, 4626-4628 (1963).
Brice, N. M., "Fundamentals of Very Low Frequency Emission Gen- erat ion Mechanisms, (1964a) . 5. Geophys. Res. - 69, 4515-4522
Brice, N. M., "A Qual i ta t ive Explanation of t h e Diurnal Varia- t i o n o f Chorus, J. Geophys. Res. 9, 4701-4703 (1964b) .
E l l i s , G. R., "Low-Frequency Radio Einission from Aurorae, J. Atmos. and Terr. Phys . - 10, 303-306 (1957).
Gurnett, D. A. and B. J. O'Brien, "High Latitude Geophysical Studies with S a t e l l i t e Injun 3. 5. Very-Low-Frequency Electro- magnetic Radiation, " J. Geophys. Res. - 69, 65-84 (1964).
Helliwell, Robert A., Whistlers and Related Ionospheric Phenomena, (Stanford University Press, Stanford, California, 1965) .
Kennel, C. F. and H. E. Petschek, "Limit on Stably Trapped Pa r t i c l e Fluxes, I' J. Geophys. Res. - 71, 1-28 (1966).
Laaspere, T., M. G. Morgan, and W. 6. Johnson, "Chorus, Hiss, and Other Audio-Frequency W s s i o n s a t Stations of the Whistlers- E a s t Network, '' Proc. IEm - 52, 1331-1349 (1964).
16
Liemohn, H. B., "Radiation from Electrons i n Magnetoplasma, Radio Science @, 741-766 (1965).
Maeda, K. and I. Ximura, "Origin and Mechanism of VLF m s s i o n s , " Space Science Res. 111, ed. W. P r ies te r (John Wiley and Sons, Inc., New York, 1962).
Milton, D. W. and M. N. Oliven, "Simultaneous S a t e l l i t e and Balloon Observations of t he Same Auroral Zone Precipi ta t ion Event," J . Geophys. Res. - 7'2 (1967).
O'Brien, B. J., C. D. Laughlin, and D. A. Gurnett, "High Latitude Geophysical Studies with S a t e l l i t e Injun 3 . of the Sa te l l i t e , " J. Geophys . Res. - 69, 1-12 (1964) . 1. Description
Oliven, M. N. and D. A. Gurnett, " S ta t i s t i ca l Studies Concerning t he Connection between 40 keV Electron Microbursts and VLF Chorus ESnissions," T r a n s . Am. Geophys. Union - 48, 74 (1967).
Oliven, M. N., D. Venkatesan, and K. G. McCracken, "Microburst Phenomena. (submitted t o J. Geophys . Res. for publication) . 2. Auroral Zone Electrons," U. of Iowa 67-19
Santirocco, R. A,, "Ehergy Fluxes from t h e Cyclotron Radiation Model of VLF Radio E3.nission, I' Proc. IRE - 48, 1650 (1960).
Venkatesan, D., M. N. Oliven, P. J. Edwards, K. G. McCracken, and M. Steinbock, Wicroburst Phenomena. 1. Auroral Zone X-Rays, ' I U. of Iowa 67-18 (submitted t o J. Geophys. Res. fo r publication).
J
FIGURE CAPTIONS
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Examples of spectrograms of VLF chorus. these chorus bursts a re so closely spaced t h a t t h e i r individual iden t i ty i s l o s t . however, ve r i f i e s t h e i r individual r i s i n g tones.
Some of
Aural ident if icat ion,
Additional samples of VLF chorus. The middle s t r i p shows t h e f i r s t 30 seconds o f t h e top s t r i p seen on a compressed v e r t i c a l scale.
The occurrence frequency i n invariant l a t i tude and magnetic loca l time of VLF chorus emissions detected by Injun 3 . Each sample block contains a t l e a s t 10 samples
Simultaneous measurements of electron microbursts and VLF chorus made by Injun 3 detectors. f luctuations of electrons of time scale c 1 second are electron microbursts.
The l a g e
The occurrence frequency i n invariant l a t i t u d e and magnetic loca l time of precipi ta t ing electron micro- burs ts detected by the Ee 2 40 keV detector aboazd Injun 3. ' samples.
Each sample block contains a t l e a s t 10
Region of maximum jo in t occurrence of electron micro- bursts and VLF chorus. The black area indicates a region i n which the occurrence probabi l i ty of elec- t ron microbursts (accompanied by VLF chorus) exceeds 10%. Dotted areas represent regions of maximum VLF chorus occurrence ( > 20% occurrence probabili ty) which is, i n general, not accompanied by electron microbursts.
High-time resolution appearance of simultaneous per- iods of electron microburst and VLF chorus records. No one-to-one correspondence between bursts can be established.
Injun 3 observed electron microbursts and VLF records, and x-ray bremsstrahlung records of balloon-observed pulsation and microburst events seen a t a longitudinal separation from the subsa te l l i t e point of - 400 km. (Milton and Oliven [l967]).
18
Figure 1
c
v) Q
0 0 w v)
m 0 P Q 62 w
0 I In m - - 0
,--
Figure 2
/ i
20
0 I 2 3 4
5 6 7 8 9 IO I I 12 13
14 15 16
17 18 19
20 21 22 23
INVARIANT LATITUDE
35" 40" 45" 50" 55" 60" 65" 70" 75" 80" I I 1 I I I I i ' I I ' I
..... ..... ..... 11 J J JiZi ..... ..... .....
...... *.., .* ...... ......
.... .... .... .... .... ............ ............ ............
...... ...... ...... ...... I I I I
...... ...... ...... ...... 0% u
o< ::s 10%
10% < I I I s 20%
Figure 3
21
G 67 -769 INJUN 3 JAN. 1,1963 14:55:00 U.T. ALTITUDE 838 KM
Lz6.32-7.52 LOCAL TlME=7:43
VLF EXPERIMENT
- k v, I -
I
2 2.5 .o I I .5
I .o
0
N
180" 213 PARTICLE DETECTOR ELECTRONS E 140 KeV
I4 : 55 : 30
U.T.
Figure 4
22
G 66 - 808
INVARIANT LATITUDE
35O 40" 45" 50° 55" 60° 6 5 O 70" 75" 80° I I I I I I I I ' I I ' I ...... ...... ...... 0 ......
. . . . . e ..... .... . ..... ..... ..... . .. . : ::::,\ . .e . . . * ..... ..... ...e. , .... \
\
... . ... .
.e..
.... . .. . . .. . . . . . . . . .... .. .. .. .. 19 20 21 22 23
... . .. * ... ...
...e ... . . . . . . . 0% a 20% 530% 50% < I 60%
o< ::s 10% 30% < # 5 4 0 %
10% < I I I s 20% 40% < 50%
Figure 5
23
G 67-774
MAGN ETlC LOCAL TIME
I MAX~MUM MICROBURSTS AND CHORUS El MAXIMUM CHORUS
Figure 6
24
G 66-53
INJUN 3 JAN. 17,1963
08 : 27 : 14 U.T. ALTITUDE 561 KM L = 6.53 LOCAL TI ME = 5:Oi
VLF EXPERIMENT
3- 180" 213 PARTICLE DETECTOR
-
08:27: I4 08:27: 15 08:27:16 U.T. TI ME
Figure 7
x r n N - 0 S/3Y 831s - 335 *-
03 s
Figure 8
9 UNCLASSIFIED Security Classification
(Security c lass i f icat ion o f t i t le body o f abstract and indexing annotatron must be entered when the overall report i s c las s i f r ed ]
1 ORIGINATIN G ACTIV ITY (Corporate author) 126 R E P O R T S E C U R I T Y C L A S S I F I C A T I O N
University of Iowa Department of Physics and Astronomy
- I UNCLASSIFIED
I Z b I
3 REPORT T I T L E
MICROBURST PKENOMECJA 3 . A n Association Between Electron f icroburs ts and VLF Chorus
4 DESCRIPT IVE NO'ES (Type o f report and inclus ive da t e s )
Progress September 1967 5 AUTHORf.7) (Last name. f i rs t name, ini t iaf )
Oliven, M e N. and Gurnett, D . A.
7 6 . N O O F R E F S 5 R E P O R T DATE 7 6 T O T A L N O O F P A G E S
September 1967 24 19 4 I
s a . C O N T R A C T O R G R A N T N O 9 6 O R I G I N A T O R * S R E P O R T NUMBERfS) Nonr 1509 (06)
b. P R O J E C T NO.
C .
U. of Iowa 67-39
9 6 O T H E R R E P O R T NO(S) ( A n y othernumbers &hat may be aasigned this report)
d b
I O A V A I L A B I L I T Y / L I M I T A T I O N NOTICES
Distribution of t h i s document i s unlimited.
11. SUPPLEMENTARY NOTES 12 SPONSORING MIL ITARY A C T I V I T Y
Office of Naval. Research
13 ABSTRACT
Observations made with t he Injun 3 sate l l i te of precipi ta t ing Ea 2 40 keV
electron microbursts and of VLF chorus emission have revealed t h e i r simultaneous
occurrence. Observed electron microbursts are always accompanied by a group of
VLF chorus emissions; chorus i s not necessari ly accompanied by microbursts.
maximum region of microburst occurrence from 0400 I magnetic l oca l time I 1300
and 65" 5 invariant l a t i t ude 5 70" l i e s well within t h e maximum region of chorus
emissions from 0300 2 magnetic l oca l time i; 1500 and 55" i; invariant l a t i t ude i;
75". pondence between individual electron microbursts and VLF chorus bursts.
b
The
It i s not generally possible t o f ind a one t o one (burst t o burs t ) corres-
Security Classification 1
Security Classification 14.
K E Y WORDS
VLF Chorus
Mi crobur s t Phenomena
Microburst Phenomena 3 . An Association Between
S a t e l l i t e Observed Auroral Zone Precipi ta t ing
S a t e l l i t e Observed VLF Chorus
Auroral Zone Precipi ta t ion
Electron Microbursts and VLF Chorus
Electrons
INSTRUCTIONS 1. ORIGINATING ACTIVITY Enter the name and address of the contractor, subcontractor, grantee, Department of De- fense activity or other organization (corporate author) issuing the report. 2a. REPORT SECURITY CLASSIFICATION Enter the over- all security classification of the report. Indicate wliether “Restricted Data” is included Marking is to b e in accord- ance with appropriate security regulations. 26. GROUP Automatic downgrading is specified i n DoD Di- rec t ive 5200.10 and Armed Forces Industrial Manual. Enter the group number. Also, when applicable, show that optional markings have been used for Group 3 and Group 4 as author- ized. 3. REPORT T I T L E Enter the complete report title i n all capital letters. Titles in all cases should b e unclassified. If a meaningful t i t le cannot be selected without classifica- tion, show title classification i n all cap i t a l s i n parenthesis immediately following the title. 4. DESCRIF’TIVE NOTES If appropriate, enter the type of report, e. g., interim, progress, summary, annual, or final. Give the inclusive dates when a specific reporting period is covered. 5. AUTHOR(S): Enter the name(s) of author(s) as shown on or in the report. If military, show rank and branch of service. The name of the principal arithor is an absolute minimum requirement. 6. REPORT DATE: Enter the date of the report as day, month, year; or month, year. on the report, u se da te of publication. 7a. TOTAL NUMBER O F PAGES T h e total page count should follow normal pagination procedures, Le., enter t h e number of pages containing information 76. NUMBER OF REFERENCES Enter the total number of references cited in the report. 8a. CONTRACT OR GRANT NUMBER If appropriate, enter the applicable number of the contract or grant under which the report was written 86, &, & 8d. PROJECT NUMBER: Enter the appropriate military department identification, such as project number, subproject number, system numbers, task number, etc. 9a. ORIGINATOR’S REPORT NUMBER@): Enter the offi- cial report number by which the document will b e identified and controlled by the originating activity. b e unique to this report. 96. OTHER REPORT NUMBER(S): If t he report has been assigned any other report numbers (either b y the originator or b y the sponsor), also enter t h i s number(s). 10. AVAILABILITY/LIMITATION NOTICES Enter any lim- itations on further dissemination of the report, other than thosi
Enter l a s t name, first name, middle initial.
I If more than one date appears
I This number must
L INK B L I N K C
T
imposed by security classification. using standard statements such as:
(1)
(2)
(3)
“Qualified requesters may obtain copies of t h i s report from D D C ” “Foreign announcement and dissemination of this report by DDC is not author ized” “U. S. Government agencies may obtain copies of t h i s report directly from DDC. Other qualified DDC use r s shal l request through
“U. S. military agencies may obtain copies of this report directly from D D C Other qualified use r s shal l request through
11
(4)
(5) “All distribution of th i s report is controlled Qual- ified DDC users shall request through
I S
If the report h a s beep furnished to the Office of Technical Services, Department of Commerce, for sale to the public, indi- cate this fact and enter the price, i f known. 11. SUPPLEMENTARY NOTES: Use for additional explana- tory notes. 12. SPONSORING MILITARY ACTIVITY: Enter the name of the departmental project office or laboratory sponsoring (pay- ing for) t he research and development. Include address. 13. ABSTRACT: Enter an abs t rac t giving a brief and factual summary of the document indicative of t he report, even though it may a l so appear elsewhere in the body of the technical re- port. If additional s p a c e is required, a continuation shee t sha l l be attached.
It is highly desirable that the abstract of c lass i f ied reports be unclassified. Each paragraph of the abstract shall end with a n indication of the military security classification of the in- formation in the paragraph, represented as (TS), (Sj. ( C ) , or (U).
There is no limitation on the length of the abstract. How- ever, the suggested length is from 150 to 225 words.
14. KEY WORDS: Key words a re technically meaningful terms or short phrases that characterize a report and may be used as index entries for cataloging the report. Key words must be se lec ted so that no security classification is required. Identi- fiers, such as equipment model designation, trade name, mili taq project code name, geographic location, may be used a s key words but will b e followed by an indication of technical con- text. The assignment of links, rales, and weights is optional.
b
DD 1473 (BAG,K) Security Classification
