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AD A103945 



EVENTS ON VLF/LF PROPAGATION 
PARAMETERS/1978 

John P. Turtle 
John E. Rasmussen 
Wayne I. Kfemetti 


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SEP 9 1981 J 


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4. TiTi.'i~end Subtitle) j 

FFFKCTS OF KNHRGFTIC PARTICLE EVENTS 
ON VLF/LF PROPAGATION PARAMETERS/ 

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is HEY WORDS /Conflnu* on reverae aide if neceaaery end identify bv block number) 


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 


DO 


F ORM 
» JAN 71 


1473 


Unclassified 

SECURITY CLASSIFICATION OP This PAGE W"ben nete^Enrered 


















r 




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 

NTIS GFAScI 
DTIC TAll 
Unannounced 
Justificatlc 

□ 


Bv 

Distr 

Aval 

Dlst 

1 

ibutior 

labilil 

Avail 

Spec 

t/ _ 

,y Codes 

and/or 

ial 



3 








-. ’ * il 

i : ■'];* 

sLitl be Wiitt ft iu u^Ua 


t 








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 

Rome Air Development Center 

RAt>C pla.ni> and executes AeseaAch, development, test and 
A elected acquisition pA.ogA.am In suppoAt orf Command, Control 
Communications and Intelligence (C 3 I) activities. Technical 
and englneeAlng suppoAt uiithln aAeas oi technical competence 
<s pAovlded to ESV ?A.ogAam 0${ices (POs) and otheA BSD 
elements. The pAA.nci.pal technical mission aAeas ane 
communications, electAomagnetic guidance and contAol, sua- 
veiltance o$ gAound and aeAospace objects. Intelligence data 
collection and handling, Incarnation system technology, 
ionosphere pAopagatcon, solid state sciences, micAouxive 
physics and electAo nic Aeliabitity, maintainability and 
compatibility. 




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