NASA TECHNICAL 

MEMORANDUM 

Source of Acquisition 

CASI Acquired 

#'IS -~'71" NASA TM X- 62,291 

PIONEER SOLAR PLASMA AND MAGNETIC FIELD MEASUREMENTS 

IN INTERPLANETARY SPACE DURING AUGUST 2-17, 1972 

J_ D_ MihaJov, D. S. Colburn, B. F. Smith, 

C. P. Sonett and J. H. Wolfe 

Ames Research Center 

Moffett Field, Calif. 94035 

May 1973 
r 

_.

Pioneer 

Solar Plasma and Magnetic Field Measurements in Interplanetary Space 

during August 2 - 17 , 1972 

by 

J. D. Mihalov, D. S. Colburn, B. F . Smith, C. P . Sonett and J . H. Wolfe 

NASA Amep Research Center 

Moffett Field , CA 

ABSTRACT 

Solar wind plasma and magnetic field measurements from Pioneers 9 and 

10 during August 2 - 17 , 1972, reveal complex and large- amplitude 

variations on a one- hour time scale and numerous discontinuities . 

During this time period an approximate radial aligmnent of the two 

spacecraft as seen from the Sun occurred with heliocentric distances 

of 0 .8 AU for Pioneer 9 and 2 . 2 AU for Pioneer 10, both at 45 deg east 

of the Earth ' s solar longitude . The peak hourly average solar wind 

proton bulk velocity measured at Pioneer 9 was 990 km sec- l during hour 

o UT of August 5 . The peak hourly average proton number density was 62 

cm- 3 during hour 11 UT of August 3. The peak solar wind speeds are 

generally much r educed at Pioneer 10 compar ed wit h those observed at 

Pioneer 9. The peak 30 minute aver age magnetic field magnitude was 

85 gamma during 1245 - 1315 UT of August 3. The Pioneer 9 data 

i ndicate passage of f our fast forward interplanetary shocks, and one 

slow forward interplanetary shock . 
Introduction 

An unusual period of sol ar flare acti vity i n ear ly August , 1972 , 

Qccurred at McMath Plage Regi on 11976 . During August 2 to 10 , t wo 

3 B and thr ee 2 B flares wer e r epor ted (Solar-Geophysical Data , 1973) . 

Intense and varied geophysical activity (cf. McKinnon , 1972) .and high 

cosmic r ay fluxes (cf . Pomerantz and Duggal , 1973) wer e observed at 

t he Ear t h . Various spacecraft observations which also show unusually 

l ar ge f l uxes of ene r getic solar par ticles and high- speed solar wi nd 

str eams have also been given at the December 1972 and April 1973 

Ame r ican Geophysical Union meetings . This repor t pr esents inter pl anetary 

plasma data from the Ames Resear ch Center solar wind plasma exper iments 

on t he Pioneer 9 and 10 interplanetary spacecraft, as we l l as inter -

pl anetary magnetic field data from the Ames Research Center magnetomete r 

on Pi oneer 9. The solar flares which probably were the source of the 

princ i pal fe atures in the plasma and magnetometer recor ds are l isted in 

Table 1 . Note that the two spacecraft wer e near 45 deg east of the 

Ear th ' s solar longi tude during this time per iod . 

2 
-------

TABLE 1 . Large Solar Flares during Early August 1972 (Solar-Geophysical 

Data> 1973) 

Day, August 1972 Time> UT (onset) Class Approx . Lat. Approx . Long . 

2 0505 2B 13N 35E 

2 1958 2B 14N 2BE 

4 0617 3B 14N BE 

7 1449 3B 14N 37W 

3 
E:x.-p-eriment Details 

The Pioneer 9 Ames solar wind plasma experiment utilizes 120 deg 

electr ostatic deflection for energy per unit charge analysi s , with 

three current collectors connected to elect r ometer amplifiers . 

Proton measurements are made at 30 logarithmically spaced intervals 

ranging fr om 210 to 1 5000 eV, f or a proton energy/plate vol tage differ ence 

r atio of 6. Similarly electron measurements are made at 14 logarithmically spaced intervals ranging from 13 to 1000 eV. The mean r adius 

of the nearly hemispherical analyzer plates is 6 cm and their separation 

is 1/2 cm . The solar wind azimuthal flow direction measurements are 

performed by sampling 2~ deg wide sectors of the spacecr aft rotation . 

The spacecraft spin axis is per pendicular to the eclipti c plane . The 

polar flow direction measurements give the flow vector component 

approximatel y normal to the e cliptic plane , using the r eiative currents 

i n the three collectors. The solar wind proton parameters presented 

here are obtained by a l east- squares fit of the flight data to a convecting 

MaXlyellian velocity dist ribution model with an isotropic temper ature , 

using an instrument model derived from laboratory calibration data . 

This pr ocedure is analogous to that used for the early Pioneer 6 and 

7 Ames plasma probe data (Mihalov and Wolfe, 1971), although linear 

r ather than non- linear least squares fits are done currently . The 

unc er tainties in the plasma parameters for Pioneer 9 have not yet been 

completely evaluated but for similar instrument modes and solar plasma 

conditions they will be much smaller than those given by Mihalov and 

Wolfe (1971) for the Pioneer 6 and 7 data b ecause the l ater instrument 

has significantly improved ene r gy and angular resolution . The Pioneer 

9 plasma experiment is almost i denti.<?al to that on Pioneer 8 which has 

been described by Intr iligator et al . (1969) , and both experiments 

ar e similar in many respects to the Pioneer 6 and 7 plasma probes described 

by Wolfe and McKibbin (1968) . 

4 
The Pioneer 9 Ames magnetometer is a triaxial fluxgate instrument 

with on board signal processing to preclude contrunination of the 

measurement by vector aliasing (Sonett, 1966) . Analog signals from 

the three sensors are prefiltered and then sampled at a high r ate 

(27 sec -

l ) r elative to the 1 Hz spin frequency . Digital spin demodulat i on is performed on the spin plane components by mathematical transformation to a non- rotating coordinate system using the sun angle to 

obtain a high data rate r epr esentation of the field as would be measured 

by a non- spinning spacecraft . Digital filtering is then employed on 

each component to opserve the Nyquist criterion pri or to telemetry 

sampling . The filter constants are automatically adjusted to match 

any of 5 commandable telemetry bit r ates . During the time of the 

magnetometer data presented here, the field sampling interval was 19 sec, 

except for ", 8 hr on August 6-7 when it was 2 .3 sec . The digitization 

window is 0 . 4 gamma (one gamma = 10- 5 G) in each component . 

The Pioneer 10 Ames plasma experiment is similar in many respects 

to the Pioneer 6 and 7 experiments described by Wolfe and McKibbin (1968) . 

Two independent sets of quadrispherical 90 deg electrostatic deflection 

plate s are used in the Pioneer 10 experiment for energy analysis , 

but data from the higher resolution set which uses 26 Bendix conti nuous 

channel multipliers as detectors are not given in this repor t . The 

Pioneer 10 plasma analyzer views along the spacecraft spin axis which 

is directed toward Earth . The lower resolution assembly deflects 

i ncoming par ticles into five current collectors connected to electr ometer amplifiers . The deflection plates have a mean radius of 12 cm 

and a 1 cm separation . The five current collectors provide a total 

angular accept ance of ± 70 deg from the normal to the instrument aper ture . 

The central three collectors each have a 1 5 deg wide angular acceptance . 

The energy analysis for protons may be done at four different sets of 

energy intervals, the maximum number being 64 logarit hmically spaced 

intervals rangi ng from 100 to 18000 eV for a prot on energy/ plate 

5 
I 

f 

vol tage difference ratio of 6. Similarly electr ons are measured 

at 1 5 logar ithmically spaced inter vals that r ange from 2 .1 ~o 500 eV. 

The solar wind flow dir ections are obtained from the combinati on of t he 

r el ative curr ents on the five collectors together with identification 

of the particluar 0 .70 deg wide spacecr af t roll sectors in whi ch the 

sol ar wind is detected . 

The Pioneer 9 spacecraft was launched November 8 , 1968 into a 

heliocentric orbit with a 298 day period . This spacecraft i s spin 

stabilized at 60 r pm. The Pioneer 10 spacecr aft was launched Mar ch 3, 

1972 on a trajectory which, with subsequent corrections, per mi ts 

encounter with the planet Jupiter on December 4, 1973 . This spacecraft 

is spi n stabilized at about 4.7 rpm . The Pioneer 10 mission i s discussed in NASA (1971) , in which some description of the spacecraft and 

exper iments is also given . 

Dur ing the times of these observations the Pi oneer 9 and 10 

spacecraft were at hel iocentric distances of 0 . 8 and 2 . 2 AU r espectively, 

approximately 45 deg east of the Earth ' s solar longitude . Pioneer 9 

was l ocated from 110,000 km to ~ 130 , 000 km north of the "ecliptic 

pl ane during this time, while Pioneer 10 was 11- 12 x 10 6 km south of 

t he ecl iptic plane . 

Description of Observations 

The hourly average solar wind proton bulk velocity, number density 

and temperature observed at Pioneers 9 and 10 are given in Figure 1 . 

These results are presented with an arbitrary delay of the Pi oneer 10 

data by 3 days with respect to the Pioneer 9 data to achieve on the 

figure an approximate alignment of the most prominent features . 

At both Pioneers 9 and 10, features often observed in association with 

interplanetary disturbances are seen, namely , fast velocity increases 

associated with increased proton temp~ratures (Wolfe , 1972) . At the 

shocks in the data discussed here , the abrupt velocity increases are 

f ollowed by peaks in the number density . An exception to this behavior 

6 
is the event seen at Pioneer 9 at the beginning of August 5 which is not 

followed by a large density increase . A r ecent summary of theor etical 

calculations on post- shock conditions may be found in Dryer et al . (1972) . 

Another feature evident at both Pioneers is the gr adual r ecovery 

of number densities over ~ 10 days from l ow values that follow the 

high densi ty peaks seen on August 3 at Pioneer 9 and on August 7 at 

Pioneer 10 assoc i ated wi th the second shock of Table 2 . One also notes 

that during the first few days of these events, a "background" pr oton 

temper ature level which might be ~ 105 K from the Pioneer 9 r ecords 

i s even higher, or ~ 3 x 105 K at Pioneer 10 . If an adi abatic, quiescent 

solar I·lind expansion with an r - 4/3 temper ature gr adient wer e assumed , 

a 10 5 K temper ature at Pioneer 9 at 0 .8 AU would imply a 3 x 104 K 

value at Pioneer 10 at 2 . 2 AU . Her e r refers to heliocentric distance . 

We speculate that convective energy has been t r ansformed into thermal 

energy during this part of the disturbance , as the wind passed between 

0. 8 and 2 . 2 AU , because the Pioneer 9 high vel oci ty peaks of 830 km 

- 1 4 -1 sec at 03h on August and 990 kID sec at Oh and Olh on August 5 

appear to be r eplaced at Pioneer 10 by a single reduc ed amplitude peak 

of 690 km sec -

l at 02h on August 7 . Details of this appar ent heating of 

the solar wind and the heating mechanism i tself ar e topics for furthe r 

study . 

The plasma bulk vel oc i ties of Figure 1 have not been corrected 

for the spacecraft velocities . The Pioneer 9 spacecraft velocity at 

- 1 this t i me is 36 kID sec approximately normal to the solar dir ecti on 

in the direction of planetary motion and in the ecli ptic plane . The 

Pioneer 10 spacecraft velocity at this time is 15 km sec - l in the 

antisolar direction and 17 km secl in the direction of planetary 

motion , parallel to the ecliptic plane . 

Thirty minute aver ages of the Pioneer 9 magnetic field measurements 

during August 2 to 10 are given in Figure 2 . The field latitude and 

l ongi tude are given in the conventional ecliptic coordinate system with 

¢ measured counterclockwise from the solar dir ection, looking from the 

north and G measured from the ecliptic plane to the vector, with 

positive values corresponding t o northward pointing field vec tors . 

7 
There is a peak in the average magnetic field magnitude at 85 gamma during 

1245 to 1315 UT on August 3 . After the early part of August 4 the . 

magnetic field magnitude i s generally much small er than 24 gammas . 

After the early part of August 6 until August 9 the field magnitude is 

at essentially the pr e - disturbance value, less than 10 gammas . 

Pioneer 9 Interplanetary Shock Observations 

Five interplanetary shocks are observed in the Pioneer 9 plasma and 

magnetic fi eld data . The t i mes of t hese events, observed changes in 

magnetic field magni tude and calculated proton bulk velocity, and the 

shock type (Colburn and Sonett , 1966) are given in Table 2 . The times 

are obtained from the magnetometer r ecords and the identification 

to the minute is arbitrary in some of the cases with sl ower t imes on 

the or der of a minute for the change in magnetic field magnHude . 

The shock types are deduced from examination of detailed data that is 

not presented here . 

The best- fit calculation of Lepping and Argentiero (1971) has been 

performed for the August 3, 1117 event , excluding an error cone angle 

calculation . The r esults are given in Table 3 . The notation of Table 

3 follows that of Lepping and Argentiero (1971), with subscripts 1 

and 2 denoting pre - and post- shock quantities. The coordinate system 

used is the convent ional right handed, orthogonal solar ecliptic system 

with +x in the solar direction and +z northward . 

refers to the plasma (proton) bulk velocity . B .. and n refer to the jth lJ 

component of magnetic field and the proton number density, respectively. 

~p = P2- Pl where p r efers to the thermal pressure, in this case due to 

protons and electrons alone . The "solar wind helium is i gnored in 

this calculation . a here is an estimated uncertainty for each measured 

8 
TABLE 2 . I nterplanetary Shocks Obser ved by Pioneer 9 during Early 

August 1972 . 

Sol ar wind Inter planetary 

proton bulk magnetic field 

Day, Spacecraft vel oc i ty change magnitude 

August 1972 t i me , UT (km sec - l ) change (gamma) Type 

3 0440 55 5. 6 Fast Forwar d 

3 1117 --..210 55 Fa st Forwar d 

4 2323 240 14 Fast Forward 

9 0707 ± 10miri ,....,145 ,....,15 Fast For war d 

9 0958 85 "-' - 3 Slow Forwar d 

9 

------ -- --- -------------
TABLE 3 . Best - fit Calculat i on (Leppi ng and Argenti er o, 1971) for 

Pioneer 9 Event of August 3, 1972 , 1117 UT . 

Par ameter Average Value CJ Best Estimate Value 

B

1x(gamma) 3 . 6 1.48 3 . 9 

B

1y - 7 . 3 2 .02 - 6 .1 

B1z -19 . 4 1. 66 -19 . 7 

B2x - 3 . 6 1. 25 - 3 . 6 

B2y -15.0 5.76 -16 . 5 

B2z - 74 . 0 6 . 77 - 73 . 3 

W (kID -1 ) sec -196 11. - 194 

x 

W 52 15. 61 

y 

W - 21 20 . - 26 

z 

n

1 (cm- 3) 19 . 2 2 .7 16 .2 

n2 48 .9 13 . 58 . 4 

( -10 - 2) tJp 10 dynes cm 112 - 55 

10 
parameter, including statistical variance and systematic sources . 

The measur ed pre - and post- shock electr on temperatur es are 7 x 105 "K 

and 9 x 105Krespectively. 

The best- fit shock normal is ~ = (-. 938 , . 341 , .064) , with a 17 

deg change from a shock normal based on average values . This shock normal 

i s within 4 deg of the direction to the f l are location from Pioneer 

9 at the time of the event . An arbitrary preliminary 1 .0 gamma nor thward i nstr umental offset magnetic fi eld has been assumed for these .- calculations . Based on the best- fit shock normal the measured Alfven, 

whistler and sonic shock Mach numbers (Tidroan and Krall , 1971) are 

9 . 5, 1 5 and 2 . 3 r espectively . 

Various estimates of shock speed are possible . The expressi on 

given by Lepping and Argentiero (1971) yields 

645 kID 

n2 - nl 

- 1 

sec 

Evolutionarity (Colburn and Sonett , 1966) yields 754 kID sec -

l < V < 788 

-1 s 

kID sec These two estimates for shock speed are subject to exper imental 

uncertainties that may be as large as ~ 10 percent but a final evaluation has not yet been done . The transit time between Pioneers 9 and 

- 1 10 yields a mean speed of 787 kID sec along the direction between the 

l ocations of the two spacecraft at the times when t his event was observed ; 

this direction is ~ 27 deg west and ~ 7 deg south of the above shock 

normal. An indication of inaccuracy in the above shock normal is the 

negative calculated value for the thermal pressure difference 6p given 

in Table 3 . Perhaps a more corr ect shock normal exists which would 

y ield better agr eement with this measured parameter which is not used 

in the best- fit calculation reported here . Agreement between the 

measured and calculated thermal pressure differences might be supposed 

if a large excess of momentum flux (~ 200 erg cm- 3) due to waves or 

turbulence were present upstream from the shock . This large an amount 

of extra momentum flux would seem unlikely, as no more than 1/30 

this amount was inferred for any of 18 interplanetary shocks studied 

11 
by Chao and Goldstein (1972) , although only two of the 18 shocks they 

studied wer e of comparable Mach number to the event discussed here . 

Also, one would expect excess momentum flux due to waves or turbulence 

downstream r ather than upstream from the shock . 

12 
Chao, J . K. and Goldstein, B. : 1972 , J . Geophys . Res . 77 , 5455 . 

Colburn, D. S. and Sonett , C. P. : 1966, Space Sci . Rev . ~, 439 . 

Dryer, M. , Smith, Z. K., Endrud , G. H., and Wolf e , J. H. : 1972 , Cosmic 

Electrodyn . l, 184 . 

Int riligator, D. S. , Wolfe, J . H. , McKibb in, D. D., and Collard, H. R. 

1969 , Planetary Space Sci . 17, 321 . 

Lepping, R. P. and Argentier o , P . D. : 1971, J . Geophys . Res . 76 , 4349 . 

McKinnon, J . A. : 1972, NOAA Tech . Memo . ERL SEL- 22 , U.S. Depar tment 

of Commerce, N.O.A.A. Environmental Research Laboratories , Boulder, CO . 

Mihalov, J . D. and Wolfe, J . H. : 1971, Cosmic Electrodyn . , 326 . 

N.A. S.A.: 1971, The Pioneer Mission to Jupiter, SP- 268, National Aeronautics and Space Administration, Washington, D.C. 

Pome r antz, M. A. and Duggal , S. P .: 1973 , Nature 241, 331 . 

Solar-Geophysical Data (comprehensive reports) : 1973 , No . 342-part II, 

U. S. Department of Commerce, Boulder, CO , p . 4 . 

Sonett, C. P. : 1966, R. L. Smith-Rose (Ed . ), Space Research , 

Spartan Books, Washington, D.C. , p . 2Bo . 

Tidman , D.A. and Krall, N. A.: 1971, Shock Waves in Collisionless 

Plasmas, Wiley- Interscience, New York . 

Wolfe , J . H. : 1972, i n C. P. Sonett, P. J . Coleman, Jr . , and J . M. 

Wilcox (Eds . ), Solar Wind, SP- 30B , National Aeronautics and Space 

Administration, Washington, D.C., p . 170 . 

Wolfe , J . H. and McKibbin , D. D. : 196B, Planetary Space Sci . 16, 953 . 

1 3 
PN-9 

ISOTROPIC PROTON 

TEMPERATURE (OK) 

PN-9 

PROTON 

NUMBER DENSITY 

(cm- 3 ) 

60 

40 

20 

o 

PN -9 

BULK VELOCITY 

(km/sec) =f 800 

600 

400 

200 2 3 4 

PN -IO 

ISOTROPIC PROTON 

TEMPERATURE (OK) 

PN-IQ 

PROTON 

NUMBER DENSITY 

(cm-3 ) 

PN-IO 

BULK VELOCITY 

(km/sec) 

AUGUST, 1972 

12 

10 

8 

5 6 

300 6 7 8 9 

AUGUST, 1972 

r 

. '-. ....... ..f''\ 

7 8 9 10 II 12 I 13 14 15 I 16 17 

DAY 

10 II 12 13 14 15 16 17 

DAY 

Figure 1. Hourly average plasma paramete rs from Pioneers 9 (top) and 10 (bottom). 

The UT times refer to the Earth , so that a"""'" 6 min correcti on must be applied to 

obtain time s at Pioneer 9, and a /'/ 13 - 15 min correction for Pioneer 10. The 

Pioneer 10 plot i s arbitrarily delayed three days with respect to the Pioneer 9 

plot as indicated by the hori zont al scales . 
100 

~ 

w 75 B 

00 

~E 

z E 50 

(9 0 

« 01 ~ 25 

o -" I ' 

,.~ ~ 

~ 

w 

o 

~ 

1-0'> 

-0) 

(9""0 

Z 

o 

--1 

360 

270 

180 

90 

~~fW f\ ~ 

cp 

o I I 'I 

~ 90 

w 

o 

~O'> 

I- 0) 0 

-""0 

I-

« 

\ vy~~~ "'/ tv 

--1 - 9 0 2 3 4 5 6 7 8 9 10 

---~-- '-.- ---

AUGUST , 1972 DAY 

Figure 2. Thirty-minute average magnetic field measurement s f r om Pioneer 9. 

Th e UT times refe r to the space craft . 

-I