AD A103945
EVENTS ON VLF/LF PROPAGATION
PARAMETERS/1978
John P. Turtle
John E. Rasmussen
Wayne I. Kfemetti
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4. TiTi.'i~end Subtitle) j
FFFKCTS OF KNHRGFTIC PARTICLE EVENTS
ON VLF/LF PROPAGATION PARAMETERS/
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VLF propagation
LF propagation
Ionospheric disturbances
Polar cap absorption events
'STRACT (Continue on reverae aide II
neceaaery end Identify by block number)
| This report provides a summary of disturbance effects of energetic
particle events on YLF/LF propagation parameters as observed by the USAF
High Resolution VLF/LF Ionosounder in northern Greenland. Disturbance
effects on ionospheric reflectivity parameters, including reflection heights and
coefficients, are presented along with data from a riometer, a magnetometer,
and satellite particle detectors.
Fv
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Preface
The authors thank Royce C. Kahler and Duane Marshall for help with the in¬
strumentation which made the measurements possible, and Jens Ostergaard and
Ujarne Hbbesen for the outstanding operation in Qanaq, Greenland.
Appreciation is also extended to the Danish Commission for Scientific Research
in Greenland for allowing these measurements to be conducted, and to Jorgen
Taagholt and V. Neble Jensen of the Danish Meteorological Institute's Ionospheric
Laboratory for their continued cooperation in this program.
Accession F^f
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Contents
1. INTRODUCTION 7
2. KVKNT DATA U
2. 1 Observed Waveforms 12
2.2 Quantitative Reflection Parameters 12
2.2. 1 Reflection Heights 12
2. 2. 2 Reflection Coefficients 14
2.2 Polarization Ellipses for the Down-Coming Skvwaves 14
2. SI PPI.EMKNTARY DATA 15
■4. DISTURBANCE CHARACTERISTICS Hi
RKKKRENCKS 14;
Illustrations
1. Ionosoundrr Propagation Path, Thule AH— Qanaq, Greenland 8
2a. Transmit! iilg Antenna - Thule AH, Greenland !<
2b. Orthogonal Receiving Antennas—Qanaq, Greenland HI
i. Hasic lonosounding Experiment 10
i. Example of Parallel and Perpendicular Waveforms 11
5. I-'mirier Amplitude Spectrum of Transmitted Pulses II
ti. Conversion Curve Cl roundwave—Skvwave Arrival Time Difference
to Reflection Height 12
S
Illustrations
7. IH. 7 - 25.2 MoY Proton Flux vs the Minimum 16 kHz || Reflection
17
19
27
25
4 2
51
5 9
67
7 5
62
91
99
107
115
122
121
129
Tables
1. 1978 Solar Particle Kvents 10
Heights
8. YLF/LF Ionospheric- Reflectivity Data for 12 February 1978
(DAY 04.4) Solar Particle Kvent
9. YLF/LF Ionospheric Reflectivity Data for 25 February 1978
(DAY 056) Solar Particle Kvent
10. YLF/LF Ionospheric Reflectivity Data for 7 March 197 8
(DAY 066) Solar Particle Kvent
11. YLF/LF Ionospheric Reflectivity Data for 8 April 1978
(DAY 098) Solar Particle Kvent
12. YLF/LF Ionospheric Reflectivity Data for 11 April 1978
(DAY 101) Solar Particle Kvent
13. Y LF/L.F Ionospheric Reflectivity Data for 17 April 1978
(DAY 107) Solar Particle Kvent
14. YLF/LF Ionospheric Reflectivity Data for 28 April 1978
(DAY 118) Solar Particle Kvent
15. \ LF/l.F Ionospheric Reflectivity Data for 7 May 1978
(DAY 127) Solar Particle Kvent
16. \ l.l'/l.F Ionospheric Reflectivity Data for 11 May 1978
(DAY 121) Solar Particle Kvent
17. YLF/LF Ionospheric Reflectivity Data for 2 1 May 1978
(DAY 151) Solar Particle Kvent
18. \ LF/l.F Ionospheric Reflectivity Data for 11 .July 1978
(DAY 192) Solar Particle Kvent
19. YLF/LF Ionospheric Reflectivity Data for 8 September 1978
(DAY 251) Solar Particle Kvent
20. \ LI 'Ll' Ionospheric Reflectivity Data for 22 September 1978
(DAY 266) Solar Particle Kvent
21. \ LF/l.F Ionospheric Reflectivity Data for 8-17 October 1978
(DAYS 281-290) Solar Particle Kvent
22. \ LF'LF Ionospheric Reflectivity Data for 10 November 1978
(DAY 9 14) Solar Particle Kvent
29. \ 1.1 /LI- Ionospheric Reflectivity Data for 11 December 1978
(DAY 245) Solar Particle Kvent
Effects of Energetic Particle Events on
VLF/LF Propagation Parameters /1978
I. INTRODUCTION
A compilation of data on the VLF/LF reflectivity of the polar ionosphere during
1978 has been published in previous technical reports. ! In this report, the data
for specific periods are expanded in order to give a more detailed presentation of
the effects of energetic particle events on VLF/LF propagation parameters. These
periods have been chosen to show disturbance effects for events in which the 13.7
to 25.2 MeV proton flux recorded by the IMP 7/8 satellites exceeded 10
particles / cm^ sec sr MeV. The propagation data were obtained bv the L'SAF High
4 5
Resolution VLF/LF fonosounder ’ which provides direct measurements of ionos¬
pheric reflection height and the reflection coefficient matrix elements ||R|| and||R^.
Also included are data on particle flux density. HF riometer absorption, and geo¬
magnetic field intensity.
The VLF/LF Ionosounding Transmitter (F'igure 1) is located at Thule Air Base
Greenland (76° 33' N l.at., 68 3 40' VV Long.), and the receiving site is 106 km north
at the Danish Meteorological Institute's Ionospheric Observatory in Qanaq, Green¬
land (77° 24' N l.at., 69 ’ 20' \V Long., Geomagnetic Lat. 89^ 06' N). The iono¬
sounding transmissions consist of a scries of extremely short (approximately
(Received for publication 20 March 1981)
(Due to the large number of references cited above, they will not bo listed here.
■See References, page 147.)
WEST LONGITUDE
90 80 70 60 SO 40
Figure 1. lonosounder Propagation Path,
Thule AB-Qanaq, (ireenland
100 yst’c) VI.F |)ulsos, procisolv controlled in timr, and rad ia tod from I ho 130-m
vortical antenna (Figure 2a). Orthogonal loop antennas (Figure 2b) arc used to
receive the two polarization components of the ionospherieall.v reflected sky wave
signal. One loop, oriented in the plane of propagation, senses the groundwave and
the unconverted or "parallel” (II ) component of the down-coming skywave; the
second loop, nulled on the groundwave, senses the converted or perpendicular (jO
skywave component. The signal from each of the antennas is digitally averaged to
improve the signal-to-noise ratio of the individual received waveforms before they
are recorded on magnetic tape. At the receiver, the radiated signal arrives first
by groundwave propagation (Figure 3). Due to the extremely short pulse length,
this signal has passed the receiver before the arrival of the ionosphericallv re¬
flected skywave pulse, providing independent groundwave and skywave data. An
example of the observed waveforms is given in Figure -1, where the parallel wave¬
form (a) consists of a groundwave propagated pulse, a quiet interval containing low
level, off path groundwave reflections, followed by the first-hop parallel skywave
component; the perpendicular waveform (b) is also shown. Fa eh of these waveforms
8
Figure 2b. Orthogonal Receiving Antennas —Qanaq, Greenland
Figure d. Basir Ionosoumting Kscporiment
10
CROUNDWAVE
Figure 4. Example of Parallel and Perpendicular Waveforms
LU
a ♦
D
Ct ‘
Figure 5. Fourier Amplitude Spectrum
of Transmitted Pulses
s'RET’FNf v
2. EVENT DATA
The data are presented for each disturbance event in three general formats:
first, the observed waveforms are shown in a synthetic three-dimensional display
which starts approximately two days prior to the event and covers a fourteen-rlav
period; second, the data are presented in the frequency domain with reflection
heights and coefficients plotted as a function of frequency over the range from
approximately 5 to 30 kHz; third, the data are presented as a function of time-of-
day. In addition to reflection information, this section contains data on ionospheric
absorption, geomagnetic field activity, and solar proton fluxes.
2.1 Observed Waveforms
A three-dimensional waveform display is presented for a 2-week period con¬
taining each disturbance event, together with a display of the same 2-week period
from a year in which it was not disturbed. For each display, the waveforms were
stacked one behind the other in linear time, progressing from bottom to top. Each
individual waveform is a 30-min average of approximately 10, 000 pulses. The
horizontal scale for these plots is linear in time (microseconds), measured from
the start of the groundwave. This scale can be used to calculate an effective
height of reflection bv attributing the time delay between the start of the ground-
wave and the start of the skvwave to a difference in travel distance, assuming a
sharplv bounded, mirror-like ionosphere. Figure 6 gives a conversion curve for
this calculation based on simple geometry anti the specific Thule AB—Qanaq,
Greenland separation of 106 km. For the O'sturbance periods, fixed local ground
clutter, amounting to only 2"'i, of die ground -ve amplitude, was removed to avoid
interference with the skvwave and improve the appearance of the waveforms.
The three-dimensional displays of the disturbed and normal parallel wave¬
forms are given for each event in Parts A and B of f igures 8 through 23. A plot
of the diurnal variation in solar zenith angle for the midpoint of the path apnears
in Part C. The perpendicular waveform displays are shown in Parts l) and E. The
time of maximum particle flux is indicated on the disturbance plots.
2.2 Quantitative Keflertion Parameters
For each event individual \ | and _L waveforms were selected in order to show the
effects of the disturbance on the ionospheric reflection height and reflection coeffi¬
cients as a function of frequency. The selected waveforms from the disturbance
period are shown in Part F of the data figures, whereas the corresponding un¬
disturbed waveforms are shown in Part G.
2.2. 1 K K PI. KG T ION (FIGHTS
The group mirror height (GMH) of reflection was obtained bv determining the
group delav of the skvwave relative to ihe groundwave and attributing this differ¬
ence to a difference in the propagation distance. The group delav can be defined as
4
tne rate of change of phase with frequency as discussed in Lewis et al. For the
GROUNDWAVE-SKYWAVE ARRIVAL TIME DIFFERENCE - nSEC
F'gum 6. Conversion Curve Groundwave —Skvwave
Arrival Time I>ifference to Reflection IK■ i l; lit
CiMH data presented in this report, a finite frequency difference of 1.0 k 11v was
used, and the corresponding phase difference as a function of frequence tor the
groundwave and both skvwave signals was obtained be Fourier analysis of the re¬
spective pulses. The CIMH calculations took into account around conductivity
(10 ’ mho/m is assumed), with the Wait and Howo' corrections applied. Group
mirror heights for the parallel and perpendicular waveforms are plotted as a func
tion of frequency in Farts H and I of Figures 8 through 28 for both normal and
disturbed conditions. The CIMti's are also presented as a function of time-of-dav
for the average frequency of 16. 5 kHz. In Figures 8 through 22, Farts I. and O,
parallel and perpendicular reflection height information is given based on two-hou
averaged data for the two-week period; Parts V and W show the 24-hour period of
the event onset in greater detail, based on 5-min averaged data. These parts
7. Wait, J.R., and Howe, H. H. (1956) Amplitude and Phase Curves for Ground-
wave Propagation in the Band 200 Cycles per Second to 500 Kilocycles .
Nat'l Bureau of Standards, U. S. Circ. Mo. 5?4.
18
include a normal reflection height curve for reference purposes. Each point of
the reference height curve is an average, by two-hour time blocks, for the 14-dav
normal period indicated.
2.2. 2 REFLECTION COEFFICIENTS
Assuming that the ionosphere acts as a "mirror" at the GHM, we obtained
7
plane wave reflection eoeliieients bv comparing the ratio of the skvwave Fourier
amplitude at a specific frequency to that of the groundw'ave, taking into account the
wave spreading, earth curvature, ground conductivity, path lengths, and antenna
patterns including ground image effects.
The reflection coefficient uH ( j , obtained from analysis of the parallel skywavo
component, is plotted as a function of frequency for both normal and disturbed
renditions in Part H. From the corresponding perpendicular skvwave pulses, the
coefficient ||Rj^ was obtained; it appears as a function of frequency in Part 1. The
ll K II coefficient for 16 kHz is plotted as a function of time-of-dav in Part M along
with the averaged normal coefficient. As with the reflection heights, a more de¬
tailed ,|K,. coefficient plot, based on 5-min averaged data is shown in Part V, To
show the variation in reflectivity as a function of frequency during the event, the
reflection coefficients were calculated at 8 kHz, 16 kHz. and 22 kHz and are plotted
in Part N as a function of time for the 14-dav period. The corresponding reflection
coefficient plots for ||Hj_ are given in Parts P, Q, and W.
For certain coefficient data points, plotted as asterisks, the reflection coeffi¬
cient appears without a corresponding GMH. For these particular data, only the
skywave-groundwave ratios could be obtained since the skvwaves were too weak to
provide reliable group delay information. The reflection coefficients were esti¬
mated, therefore, using a nominal GMH of 80 km in the calculations. These esti¬
mated coefficient values are included in the averages presented in Parts M, N, P
and Q. but the assumed heights are not used in the GMH averages.
2.3 Polarization Ellipses for the Down-Coming Skvwaves
g
As described by Pasmussen et al, the polarization ellipse of the skvwave can
be determined from the amplitudes of the parallel and perpendicular components
and their phase difference. Each ellipse represents the locus of the tip of the
rotation field vector as seen when looking in the direction of propagation of the
down-coming skywave, and x-axes being horizontal. The ellipses are drawn to a
scale in which the incident wave amplitude is unity, and each division on the axis
is 0. 1. The direction of rotation is indicated by an arrow. Parts .1 and K of
8 . Rasmussen, J.K., et al (197 5) Low Frequency Wave-Reflection Properties of
the Equatorial Ionosphere , AFCRL-TR-75-06l5, ADA0251 11.
14
Figures 8 through 23 present polarization ellipse data as a function of frequency at
5 kHz intervals based on the selected disturbed and normal waveforms of Parts }•'
and G, respectively.
3. SUPPLEMENTARY DATA
In order to interpret the effects of ionospheric disturbances on the VLF/LF
ionosounding data, information from several geophysical sensors are included.
Parts K and S of Figures 8 through 23 present data from a magnetometer and a
30 AlHz riometer operated bv HA DC at Thule AB, Greenland. The riometer, the
conventional monitor of ionospheric disturbances, measures the signal level of
cosmic noise passing through the ionosphere, A decrease in the received noise
level results from increased absorption caused by enhanced ionization from ener¬
getic particles. The riometer data in this report have been normalized to remove
the quiet dav curve. The data plotted in Part H of each figure give riometer
absorption levels. A zero level represents normal undisturbed conditions, a posi¬
tive deflection shows increased absorption while a negative deflection results from
a noise increase as would be associated with a solar radio burst. The effects of
energetic particle events are seen as an abrupt increase in the absorption level
followed by a gradual recovery to normal levels over a period of several days. The
magnetometer data plotted are the horizontal (H) component of the polar magnetic
field determined by a 3-axis fluxgate magnetometer at Thule AB. The magnetometer
responds to the effects of polar ionosphere current systems related to disturbance
events.
In addition to the information from the ground-based monitors, particle flux
data are presented from the Applied Physics Laboratory of Johns Hopkins University
*
experiments aboard the IMP 7 and 8 satellites. These satellites are in roughly
circular orbits at about 35 earth radii. The data presented in Parts T and U are
hourly averages of differential flux levels for protons in two energy ranges: 0. 97
to 1.85 MeV and 13.7 to 25.2 MeV. These particle data are most important for
relating the VLF/LF ionosounder effects to the size of a particular disturbance.
Particle data obtained from the National Space Science Data Center,
Greenbelt, Maryland.
15
4. DISTURBANCE CHARACTERISTICS
Table 1 gives a summary of the data presented lor each event covered in this
report. In addition, data are included for 6 events which occurred front 1974-1977.
i)
These events were described in a previous report.
Table 1. Solar Particle Events
Event
Pate
Figure
Point
No.
Maximum
, 13.7-25. 2 MeV
Proton Flux
■)
No. /cm“ see sr Mo\
Minimum
16 kHz II
11 e flection
Height
km
30 MHz
Kiorneter
Absorption
dll
Hluminat ion
Conditions
13 Fob
(044)
8
60. 0
56
6 . 0
day-night
25 Feb
(056)
0. 05
64
<0. 5
day -night
7 Mar
(066)
10
0 . 02
70
<•0.5
dav-night
8 Apr
(098)
11
0 . 1
65
v. 0. 5
dav -night
11 Apr
( 101 )
12
3. 0
5B
3. 0
das time
17 Apr
(107)
13
0 . 2
60
0. 5
davt ime
28 Apr
(118)
14
no data
no data
i'. 8
das’! itc
7 May
(127)
15
10 . 0
57
1.0
davt inn
1 1 Ma.v
(131)
16
0 . 1
63
■- < 1 . 6
dav' ire
3 1 May
(15 1)
17
0. 4
63
1.0
davt ime
1 1 duly
(19 2)
18
0. 3
64
1.0
d a v 11 r: 1 < ■
8 Sept
(25 1)
lit
0 . 18
63
■ 0. 5
dav - night
2 3 S^pl
(266)
20
100 . 0
5 1
10 . 0
las - night
8 Oct
(281)
21
0 . 8
65
• 0. 5
a.tv night
10 Nov
(314)
22
0. 3
65
1.0
lav -n:g:.'
12 Pec
(345)
23
Point
No.
0. 1 74
1974-1977 Events 1 ’
<0. 5
nightt tine
5 Nov 74
(309)
24
1. 3
63
• 0. 5
lav mjht
30 Apr 7 6
( 121 )
25
6 . 0
58
3. 0
}.t\ He r
22 Aug 76
(235)
26
0 . 6
60
1.7
davt ime
26 .lu l 77
(207
27
0 . 02
70
■ 0. 5
davt i e ; e
24 Sept 77
(267)
28
2 . 0
57
2 , 0
lav
22 Nov 77
(326)
14. 0
64
0 . 7 5
nig-ht tin *•
9. Turtle. .1.
, Rasmussen, 3.K. , Klemetti, W. 1. (1980) Effects of
Energei ic
Particle
Event s
on Vl.F/I.F Propagation
Paratnete
*s , 11*74 - rnTT,
'1771 nr
Tir-w^rr-
16
1978 was a very active year; ionospheric disturbance effects of 16 energetic
particle events are given in this report. The characteristics of the effects of
energetic particles on the VI.J-7l.l-' propagation parameters are a function of event
size and solar illumination conditions. The reflection heights for both parallel
and perpendicular components drop coincident with the influx of energetic particles.
The level to wiiich the height drops depends upon the magnitude of the particle flux
and the solar illumination conditions during the event.
Data giving 16 kHz |j reflection heights and particle flux levels from Table 1
are plotted in Figure 7. The maximum of the 13-25 MeY particle flux is plotted
as a function of the lowest reflection height during the event. A "best fit" straight
line drawn through the points indicates a roughly exponential relationship betivcen
the particle flux and the resulting reflection height. Two points, 23 and 29, art-
separated from the rest and were not used in calculating the "best fit" line.
Figure 7. 13.7 - 25.2 MeY Proton Flux vs the
Minimum 16 kHz II Reflection Height
17
r
These were both nighttime events and suggest the probability of two curves, one for
sunlit events and the other for events where there is no solar illumination. During
event recovery various patterns are seen in the data depending on the solar illumina¬
tion. There is no diurnal height variation during continuous daytime (Figure 18) or
continuous nighttime (Figure 23) events. However, a diurnal height variation is
seen during day-night events resulting front changing solar illumination conditions
(Figure 20).
A more complex behavior is shown bv the YDF/I.F reflection coefficients during
energetic particle events. During daytime events the reflection coefficients can
show an increase with respect to normal conditions. There is less diurnal varia¬
tion during disturbed daytime conditions than during normal conditions, the effects
of particle ionization appear to override the effects of varying solar zenith angle.
During the recovery the reflection coefficients gradually drop and go through a null.
A typical daytime disturbance is seen in Figure 15. Reflection coefficients during
nighttime events show effects similar to the reflection heights; a drop followed bv
a gradual recovery. During day-night events the interaction between varying solar-
ionization with particle ionization produce a more complex disturbance pattern.
1R
1 February 1978 Solar Particle Fvent
Date: 13 February
Report Figure: 8
Related Solar Flare:
Start of Ionospheric Disturbance;
Time of Maximum 13-25 MeY Proton Flux:
Maximum Flux:
Length of Particle Event:
Lowest 16 kHz Reflection Height:
30 MHz Riometer Absorption:
Solar Zenith Angle Range:
Illumination Conditions:
Day: 44
0255 FT X-ray class: M7
195 0 UT
14 February 0600 1 I
60 particles/cm sec sr Me\
7 days
56 km
6 dB
SS-' - 1 17°
Day-Night
This strong event occurred at the transition between nighttime and day-night con¬
ditions. The undisturbed (normal) 3-dimensional waveform plots (parts B and E)
show that during the period covered bv this event there is insufficient solar radia¬
tion to cause a diurnal height variation in the reflection parameters. During the
first days of the event the depressed 16 kHz II reflection height curves (parts L
and O) also showed little diurnal change; however, during the event recovery a
diurnal variation is noted. As particle ionization decreased diurnal variations in
solar radiation were sufficient to cause a difference in the day and night reflection
heights. The nighttime portion of the daily curve recovered more rapidly than Ihe
daytime. The reflection coefficient curves (parts N and Q) show a drop in signal
strength at event maximum followed by a gradual recovery. A strong diurnal
variation appeared suddenly during the latter part of the recovery.
19
Figure 8. VLF/I.K Ionospheric Reflectivity Data for 13 February 1978 (DAY 044) Solar Particle Kvent (font)
VLF/LF Ionospheric Reflectivity Data for 13 February 1978 (DAY 0-14) Solar Particle Kvent (font)
' ■% N
25 February 1978 Solar Particle Event
Date: 25 February
Report Figure: 9
Related Solar Flare:
Start of Ionospheric Disturbance:
Time of Maximum 13-25 MeV Proton Flux:
Maximum Flux:
Length of Particle Event:
Lowest 16 kHz Reflection Height:
30 MHz Riometer Absorption:
Solar Zenith Angle Range:
Illumination Conditions:
Day: 56
1453 FT X-rav class: M4
1555 FT
2000 FT
0.05 particles/cm^ sec sr MeV
1 day
64 km
<0.5 dU
85° - 113-
Day - Night
This was a short-lived low energy event. The satellite particle data (parts T
and L) indicate that the 1. 85 MeY low energy protons were first recorded at about
0800 FT, this was eight hours earlier than the 25-MoY protons. According to the
5-min time average ionosounding data (parts V and VV), the change in reflection
heights and coefficients did not occur until the arrival of the high energy protons
at about 1555 FT. The low energy particles did not produce enough ionization to
disturb the reflection parameters.
30
Figure 9. V LF/L.F Ionospheric Reflectivity Data for 25 February 1978 (DAY 056) Solar Particl
GROUP MlR«0« HttGMlS tROM PAR»uEl S«»WAvF DATA
;ure 9. v LW LF Ionospheric Reflectivity Data for* 25 February 1978 (DAY 056) Solar Particle Kvent (Cont)
7 March 1978 Solar Proton Event
Date: 7 March
Report Figure: 10
Related Solar Flare:
Start of Ionospheric Disturbance:
Time of Maximum 13-25 MeV Proton Flux:
Maximum Flux:
Length of Particle Event:
Lowest 16 kllz Reflection Height:
30 MHz Riometer Absorption:
Solar Zenith Angle Range:
Illumination Conditions:
Day; 6 6
1213 UX X-rav class: .M2
8 March 0100 UT
8 March 1700 UT
0. 02 Particles/cm" sec sr JlleV
1 day
70 km
< 0. 5 dB
80° - 180°
Day - Night
This was the smallest particle event to be covered in this report. The 25 Mo\
■>
proton flux reached onlv 0.02 particles/cm “ sec sr MeV and the 16 kllz il reflec¬
tion height dropped to 70 km. In spite of the low particle flux the combination of
particle ionization and solar radiation were enough to produce lower reflection
heights than were recorded during the 12 December l!)i8 nighttime event which had
a five times greater 25 MeV particle flux (see Table 1).
Figure 10. VLF/LF Ionospheric Reflectivity Data for 7 March 1!)78 (DA7' 006) Solar Particle Kvont (Font)
10. VLF/L.F Ionospheric Reflectivity Data for 7 March 1978
tivily Data lor 7 March 197fi (DAY 0(56) Solar Particle i vcnt (Cont)
March 1978 (DAY 066) Solar Particle l'vent (Cont)
8 April 1978 Solar Particle Fvent
Date: 8 April
Keport Figure: 11
Kelated Solar Flare:
Start of Ionospheric Disturbance:
Time of Maximum 13-25 MeV Proton Flux:
Maximum Flux:
Length of Particle Kvent:
Lowest 16 kHz Reflection Height:
30 MHz Riometer Absorption:
Solar Zenith Angle Range:
Illumination Conditions:
Day: 98
0201 UT X-ray class: XI
0300 UT
0700 UT
0. 1 particles/cm^ sec sr MeV
3 days
65 km
< 0. 5 dB
68° - 96°
Day-Night
This was the first in a series of eight energetic particle events which occurred
during the period from 8 April (DAY 098) through 13 May (DAY 133) Figures 11
through 16 give the data for each separate event. Some of the events occurred
only a couple of days apart so that the recovery effects of one event overlapped with
the onset of another. The 25 MeV proton flux, seen in part U of Figures 11 through
16. remained above the disturbance threshold (0.01 particles/cm sec sr MeV) for
the entire period from 17 April (DAY 107) to 12 May (DAY 132). Doth reflection
heights and coefficients were continuously disturbed during the period.
VLF/LF Ionospher
11 April l«i,« Solar I’artirli l.vm'
Date: 11 April
Report Figure: 12
Related Solar Flare:
Start of Ionospheric Disturbance:
Time of Maximum 12-25 MeV Proton
Maximum Flux:
Length of Pa-tide Event:
Lowest 16 kHz Reflection Height:
20 MHz Riometer Absorption:
Solar Zenith Angle Range;
Illumination Conditions:
Day: 101
1:H0 11 X-ray . lass; X
1:155 I T
• lux: 2200 L I
2 particles / cm^ sec sr ,Mc\
-l <tavs
58 km
:i (IB
67 5 - 05°
Davtime
51
12. VLF/LF Ionospheric Reflectivity Data for 11 April 1978 (DAY 101) Solar Particle Event (Cont)
Figure 12. \ I.F'/LF Ionospheric: Reflectivity Data for 11 April 1078 (DAY 101) Solar Particle Event (Cont)
17 April 1978 Solar Particle Event
Date: 17 April
Report Figure: 13
Related Solar Flare:
Start of Ionospheric Disturbance
Time of Maximum 13-25 MeV Proton Flux:
Maximum Flux:
Length of Particle Event:
Lowest 16 kHz Reflection Height:
30 MHz Riometer Absorption:
Solar Zenith Angle Range:
Illumination Conditions:
Day: 107
No data X-ray class:
0100 UT
1400 UT
2
0.2 particles/cm sec sr MeV
Continuing
60 km
< 0. 5 dB
65“ - 93“
Daytime
59
£»DU«> »>»*{# WHICH!* WO WHfCTtDN cafHtUVJJ »»£>*• HBffNDICUtJW SKf#AV* DATA
Apr il 11178 (DAY 107) Sols
28 April 1978 Solar Particle Kvent
Date: 28 April
Report Figure: 14
Related Solar Flare:
Start of Ionospheric Disturbance:
Time of Maximum 12-25 MeV Proton Flux:
Maximum Flux:
Length of Particle Kvent:
Lowest 16 kHz Reflection Height:
30 MHz Riometer Absorption:
Solar Zenith Angle Range:
Illumination Conditions:
Day: 118
1320 L'l X-rav class: X
21) April 1025 FT X
30 April 1508 FT X
No data
2000 UT 30 April
No data
5 days
About 57 km
9. 8 dB
60° - 88°
Daytime
67
Figure 14. VLF/LF Ionospheric Reflectivity Data for 28 April 197 8 (DAY 118) Solar Particle Fvent (Cont)
14. VLF/LF Ionospheric Reflectiv
Ionospheric Reflectivity Data for 28 April 1978 (DAY 118) Solar Parti, to Kvent (C'ont)
7 May 1978 Solar Particle Fvent
llate: 7 Mas
Report 1 mure: 15
Relate l Solar Flare;
Start <>! Ionospheric Disturbance;
Time <>t Maximum 15-25 Met Pn
Maximum Flux:
Length of Particle Kvent:
Lowest 16 kHz Reflection Height;
20 MHz Riometer Absorption;
Solar Zenith Angle Range;
Illumination Conditions;
Das; 127
0221 I 1 A-lav
0240 11
Flux 0500 t 1
10 particles / cm' a
Continuing
57 km
1 dH
59 0 - 87 0
Daytime
The reflection parameters during this event were typical of those seen during
davtime conditions. The reflection heights showed a drop followed by a gradual
return to normal. In contrast with the undisturbed conditions there was no diurnal
height variation during the event. The effects of particle ionization override the
small variation in solar ionizing radiation during the day. As' is typical of davtime
events reflection coefficients at event maximum were stronger than before the
event. The maximum was followed by a gradual decrease, the 16 and 22 kHz I!
and coefficients dropped below pre-event levels several days after event maxi¬
mum. The final recovery of 7 Mav event merged bv another event which occurred
on 11 May (DAY 121).
75
\V<I>
Figure 15. V FF/i.F Ionospheric Reflectivity Data lor 7 Mav l!'71i (l)A\ 127).Solar Particle Fvrnl (Conti
Figure 15. VLF/LF lonospheri
11 May 1978 Solar Particle Event
Date: 11 May
Report Figure: 16
Related Solar Flare:
Start of Ionospheric Disturbance;
Time of Maximum 13-25 MeV Proton
Maximum Flux:
Length of Particle Event:
Lowest 16 kHz Reflection Height:
30 MHz Riometer Absorption:
Solar Zenith Angle Range;
Illumination Conditions:
Day: 131
No data X-ray class:
0800 UT
Flux: 0900 UT
2
0. 1 particle/cm sec sr MeV
1 day
63 km
<0.5 dB
58° - 86°
Daytime
I
86
Figure 16. YLF/'I.F Ionospheric Reflectivity Data for II Wav 1978 (DAY 131) Solar Particle Kvent (Cont)
lectivity Data lor 11 May 1978 (DAY 131) Solar Particle Event (Cont)
Reflectivity Data for 11 May 1978 (DAY 131) Solar Particle Event (Cont
31 May 1978 Solar Particle Event
Date: 31 May
Report Figure: 17
Related Solar Flare;
Start of Ionospheric Disturbance:
Time of Maximum 13-25 MeV Proton
Maximum Flux;
Length of Particle Event:
Lowest 16 kHz Reflection Height:
30 MHz Riometer Absorption;
Solar Zenith Angle Range;
Illumination Conditions:
Day: 151
No data X-ray class:
1000 UT
Flux: 1400 UT
2
0.4 particles/cm sec sr MeV
3 days
63 km
1 dB
53° - 81“
Daytime
91
Mm i
V 1.1-7 I,K Ionospheric Kcllect ivity Data lor 31 May 1!)78 (DAY 151) Solar Particle Kvont (Cont)
Ionospheric Reflectivity Data
11 July 1 !• i 8 Sola r Pa id it le 1'vt-ilt
Date: 11 July
Report Figure: 18
Related Solar Flare:
Start of Ionospheric Disturbance:
Time of Maximum 13-25 MeY Proton Flux:
Maximum Flux:
Length of Particle Event:
Lowest 16 kHz Reflection Height:
30 MHz Hiomoter Absorption:
Solar Zenith Angle Range:
Illumination Conditions:
Du\: 1!'2
0625 FT X-ra\ class; X3
1058 FT X 15
About 1000 FT
13 Julv 0600 FT
0.2 Parti lies / rm^ see si Me\
7 days
64 km
1 <1R
53’ - 81 ’
Daytime
This was a daytime event. Unlike most events in this report the particle flux seen
in parts 1. and 1 showed a slow rise to maximum level requiring about 2 days. As
is often seen in daytime events the ;; reflection coefficients (parts N and Q) were
stronger during the time of particle maximum than before the disturbance onset.
This maximum was followed bv a period of several days with fairly steady reflec¬
tion coefficients. Towards the end of the event the 22 kHz reflection coefficients
gradually dropped to a low level before returning to normal. As with other day¬
time events the reflection heights showed a decrease followed by a gradual recovery
with very little diurnal variation.
99
102
Figure 18. VLK/LK Ionospheric Reflectivity Data for 11 July 1978 (DAY 192) Solar Particle Event (Cont)
LF Ionospheric Reflectivity Data for 11 July 1978 (DAY 192) Solar Particle Event (Cont)
Figure 19. VLF/LF Ionospheric Reflectivity Data for 8 September 1978 (DAY 251) Solar Particle Event (Cont)
\I)AY J:> 1 1 Solar I'arth !<■ Dvi'iH K'ont)
1
23 September 1978 Solar Particle Event
Date: 23 September
Report Figure: 20
Related Solar Flare:
Start of Ionospheric Disturbance;
Time of Maximum 13-25 MeV Proton Flux:
Maximum Flux:
Length of Particle Event:
Lowest 16 kHz Reflection Height:
30 MHz Riometer Absorption:
Solar Zenith Angle Range:
Illumination Conditions:
Day: 266
1021 UT X-rav .lass: \1
1030 UT
24 September 1500 l"i
2
100 particles/cm see sr MeV
12 days
5 1 km
10 dli
77° - 103°
Day-Night
This was the strongest energetic particle event which has occurred since the
VLF/LF ionosounding program began in 1974. Record low reflection heights were
recorded; 51 km for the 16 kHz || polarization and 47 km for the X component.
During the event the reflection height curves showed a diurnal variation, the ampti
tude of this variation increased as the particle flux decreased. The nighttime
reflection heights recovered towards normal more rapidly than the daytime (sunlit)
reflection heights. The reflection coefficients showed less diurnal amplitude varia
tion during the event than before or afterwards. The sharp nulls seen in the reflec
tion coefficient data (parts N and Q) at about 0900 UT and 0000 UT are caused by
the 2-hr average window used in data reduction. A 5-min average plot of the data
at these sunrise and sunset times does not show these nulls.
115
ire 20. VLF/LF Ionospheric Reflectivity Data for 23 September 1978 (DAY 266) Solar Particle Event
Reflectivity Data for 23 September 1!>78 (DAY 266) Solar Particle
8-17 October 1978 Solar Particle Events
Date: 8 October Day: 281
Report Figure: 21
Related Solar Flare: 1937 UT X-ray class: -\14
Start of Ionospheric Disturbance: 2215 UT
Time of Maximum 13-25 MeV Proton Flux: 9 October 2300 UT
Maximum Flux:
Length of Particle Event:
Lowest 16 kHz Reflection Height:
30 MHz Riometer Absorption:
Solar Zenith Angle Range:
Illumination Conditions:
Subsequent Fvents:
2
0. 8 particles/cm sec sr MeV
3 days
65 km
<0.5 dB
81° - 107°
Day-Night
13 October (DAY 286)
Maximum Flux: 0.02 particles
0900 UT
14 October
17 October (DAY 290)
Maximum Flux: no data
A series of four energetic particle events occurred during October 1978. The last
two occurred on consecutive days (8 and 9 October) and are treated here as one
event. The other events which occurred on 13 October and 17 October barely
reached threshold. The 8 and 9 October events were day-night disturbances which
typicallv produced enhanced diurnal reflection parameter variations.
123
Ionospheric Hcl'lcctivitv Uata for 8-17 October ]!>7fJ
1
10 November 1978 Solar Particle Event
Date: 10 November
Report Figure: 22
Related Solar Flare:
Start of Ionospheric Disturbance:
Time of Maximum 13-25 MeV Proton Flux:
Maximum Flux:
Length of Particle Event:
Lowest 16 kHz Reflection Height:
30 MHz Riometer Absorption:
Solar Zenith Angle Range
Illumination Conditions:
Day: 314
0122 UT X-ray class: M4
0200 UT
11 November 0000 UT
2
0.3 Particles/cm sec sr MeV
4 days
65 km
1 dB
93° - 121°
Day - Night
This event occurred during the period when under normal conditions there was
insufficient daytime solar radiation to produce a diurnal variation in either reflec¬
tion parameter. However, as was the case in the 13 February event, during the
disturbance the combination of particle ionization and varying solar radiation
produced a day-night change in both the reflection heights and coefficient
(parts L, M, O, and P).
131
»«»»» mi nu€c
RECEIVEO PERPENDICULAR WAVffORMS
Figure 22. VLF/LF Ionospheric Reflectivity Data for
11 December 1978 Solar Particle Event
Date: 11 December
Keport Figure: 23
Related Solar Flare:
Start of Ionospheric Disturbance:
Time of Maximum 13-25 MeV Proton Flux:
Maximum Flux:
Length of Particle Event:
Lowest 16 kHz Reflection Height:
30 MHz Riometer Absorption:
Solar Zenith Angle Range;
Illumination Conditions:
Day: 345
1807 UT X-ray class: M7
1833 UT X2
12 December 0130 UT
No data
2
About 0. 1 particle/cm sec sr MeV
5 days
7 4 km
<0.5 dB
98° - 126°
Nighttime
Because this was a polar nighttime event the effects on the propagation parameters
were less than would have occurred had this been a daytime event. The minimum
16 kHz II reflection height during the event was 74 km (part L). The 8 April dav-
2
night event with a similar particle flux (0. 1 particle=/cm sec sr MeV) produced
a 65-km reflection due to the combined effects of solar and particle ionization.
Neither reflection parameter showed a diurnal variation during the 12 December
event due to lack of solar illumination.
139
ttOCEDUB mm tUM-MOT
nim>
Figure 23. VLF/LF Ionospheric Reflectivity Data for 11 December 1978 (DAY 345) Solar Particle Event (Cont)
1
References
I. Pagliurulo, It. 1'. , Turtle, .1. P. . Rasmussen, .1. F. . and Klemelti, U . 1. (1!'78)
\ l.F/I.K Reflectivity of the Polar Ionosphere, 1 .Ian - 22 Apr IS*7H,
TTXl K 1 - TR-78-186. A I) A062524. "
Pagliarulo, H. P. . Turtle, .1. P. . Kasimissen, .1. E. , Klemetti, U.I., and
I’oolov, It. I.. (P'^8) \ 1.1'/ 1.1- Refloetivitv of llio Polar Ionosphere,
28 Apr - 2 Sept l i' 78, H7\.I)C' -1'fi-7P -100. AH A074762.
8. Pagliarulo, K. P. . Turtle, .1. P. , Kasmussen, .1. F. , Coolev, K.I.. . and
Klenietti, \V. I. (P'78) \ l.P/l.T' Refloetivitv of tho Polar Ionosphere,
8 Se pt - 80 Dee li>78. H AI )C' -TR-7!> -178, Al) A074475. ~
4. Lewis, F. A. . Kasmussen, .1. F. , and Kossev, P. A. ( P'78) Measurements of
ionospherie refleetivitv from 6 to 85 kHz, ,1. Cleophvs. Res. TIPP*.
5. Kossev. P. A. , Kasmussen, .1. F. , and I.ewis, K. A. (P'74) \ I.K pulse iono-
sounder measurements of the refleetion properties of ihi' lower ionosphere,
Akademie \ ei laq, I'OSPAK, .lulv.
6. Hudden, K.CL (l!*61) Radio Haves in the Ionosphere, p. 85, Cambridge
Puiversitv Press, London.
7. Wait. .1. K. , and Howe, 11,11. (11)56) Amplitud e and Phase Curves for Cl round-
wave Propagation in the Hand 200 Cveles per Second to 500 Kilo cycles,
Nat'l Hureau of Standards, P. S. Circ. No. 574.
8. Kasmussen, .1. K. , et al (P'75) Low Frequency V* 've-Refleetion Properties of
the Kquat o rial Ionosphere . A PC Kl.-TR -75 -0615, Al) A 0 S5 ITT!
0. Turtle, .1. P. , Kasmussen, K. , Klemetti, W . I. (li)80) Pfleets of Fnergetie
Particle Fvents on Vl.K/LK Propagation Parameters, l!'7 4 - P'77 , It A DC -
T K -80-807.
147
I
MISSION
of
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RAt>C pla.ni> and executes AeseaAch, development, test and
A elected acquisition pA.ogA.am In suppoAt orf Command, Control
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and englneeAlng suppoAt uiithln aAeas oi technical competence
<s pAovlded to ESV ?A.ogAam 0${ices (POs) and otheA BSD
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