mer remrulks on the absence of very extended ......mer remrulks on the absence of 8 very extended...

M e r Remrulks on the Absence of 8 V e r y Extended Magnetospheric Tsil

J* A- V a A l l - university of Iowa

Iowa city, Iawa 52240

https://ntrs.nasa.gov/search.jsp?R=19660007408 2020-04-22T11:10:45+00:00Z

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Any WOFtby theory of the structure and length of the

magnetospheric tail must be prepared t o deal with questions of

quantitative physical significance. That i s t o say, it must

be subject t o one or more observatiaPal tes ts which can, at

leest i n principle, determine the presence or absence of the

tail at specified points in space.

[Dessler, 19641 [Michel and Dessler, 19651 [I)essler end

Dessler and collaborators

Juday, 19653 [Mchel, 19653 hsve hypothesized that the

magnetospheric t a i l of the earth extends t o sme 20 t o 50 astro-

nomic& units ( - 10 earth radii) in the anti-solar direction. 6

I)ungey [1$5] has contested this hypothesis on grounds of semi-

empirical inplauibil i ty. Nonetheless, it is of interest to

subject the hypothesis of Dessler t o f'wther observational

tests. Dessler et al. have suggested three test questions of

an observational nature:

Test Question I: Is the vector magnetic field due t o the tail observable in the presence of the interplanetary msgnetic f i e l d of the solar wind, the latter being the physical went for the production of the t a i l ? [Dessler, 19641

Test Qpestiaa 11: Is the arrival of l o w energy ( 5 5 MeV) solar protons at the top of earth's atmosphere during the early phase of a FCA event preferentially in the

auroral zones (geomagnetic latitude - 68") and e within the polar caps? [Mtchel and Dessler, 19651

3

Test Question III: Does the effective g-etic &-off for solar protons vanish at the same latitude for a l l

energies less than - 40 MeV and with a "sharpness" in latitude comespollding t o a gyro-radius?

Inasmuch as the generation of super-themud electrons in agitated

planmnn is a well-known, though poorly understood, phemm-m in

the laboratory, in astrophysical systems [Parker, 19651 and more

specifically in the magnetospheric t a i l itself out t o anti-solar

distances at least 88 greet as 32 earth radii [Frank, 19651

[Anderson, 19651, I have proposed a fourth test' question:

Test Question IV: To what anti-solar distance i n the earth's magnetospheric tail are there detectable intensities of super-thermal electrons? 1965 I

[Van Allen,

As described in the hnedfately foregoing reference, I have used

Miner IV data during late Jsnuary--early February 1965 t o pro-

vide a limited answer t o T. &. IV. The answer was a negative

one at an anti-solar distcmce of 3300 esrth radii (0.14 astro-

nomical unit) t o within the carefully specified conditions of the

obsemtions ead characteristics of the epuipment. I have no

deluioas abaut the comprehensive significance of these measure-

ments but I do consider that they contribute t o a rational con-

sideration of the basic hypothesis. ThDLs I do not disagree wtth

the strict substance of Michel's 119661 remarks in the accapnpanying

letter but I do continue t o believe that the Mariner IV particle

D

4

measurements fmx the belief tbat the earth's magnetospheric

tail is pbysically insirmipicaat & 33100 eaxth radii, i n the

Spirit Of T o Q* IV.

With respect t o T. Q. I, Eeppaer et al. [1*3] and

Bess [l965] have ghoM the clew detectability of the magnetic

field of the earth's t a i l out to distances of about 43 earth

radii, but Coleman et ell. 119651 found IY) detectable effect

with the Mariner IV magnetometer & 33100 earth radii.

latter result is ignored by EBchel, possibly again on the gramds

that miner IV c#me 110 closer than a geocentric me of lo t o

the idealized center line of the earth's tail.

view may be vslid but I find it difficult t o believe that a

weak aad extended megnetospheric tail could be attached t o the

earth 86 rigidly sod ideally as Michel maintains.

The

Such a poiat-of-

Turning to l!. Q. II, Michel and Dessler [1%5] cite the

study of Ha&ra 119641 on the 9-12 February 1958 solar cosmic

rag evePt as providing specific support t o their hypothesis.

me papers of [1@1 and m a and ~ ~ a g a ~ [1*3 do

indeed provide a beautiftally detailed study of the caplplex

iopospzIeric phenomena sssociated with the aforementioned evept.

But these effects are almost certainly due t o a cauplex admixture

of csuses--sohr protons, "auroral zone electrons", and electrons

and protons precipitated fkcm the outer radiation belt. The

8

5

portion o f t h e ionospheric effects which is most reasonably

attributable t o solar protons is tbt designated as ( P C A ) ~

by Hakura and B a g d .

pcrttern is exactly contrary t o the& anticipa;ted by Michel and

Dessler, since it appears first near the pole and subsequently

expands toward lower latitudes.

The gFowth of the (FCA)p precipitation

A much more clear-cut response t o T. Q. 11 and t o

T. Q. III is provided by study of the September 1963 solar

proton data of the magnetically oriented satel l i te Injun III

using a combination of particle detectors, especially the solid

state detector of Bostmm for the direct and specific detection

of protons in the narrow energy range 1 t o 2 MeV end within a

narrow angular m e .

exception 8 m n o t o n i c a y increasbg (or constant) intensity

of such protans with increasing lsrtitude mer the range

4

Dessler (T. Q. II). Also contrary t o the expectation of

Michel (T. Q. 111), the principal increase in intensity with

increas- latitude occurs rather gradually mer about 4" in

latitude-that is, over a latitudinal distance of some 450 h

or about 100 gyro-r&. A detaLled paper on these results is in

preparation by Bostrom of the Applied physics Laboratory of Johns

gopkins lbiversity and by Hardiw and Van Allen of the Ihiversity

of Iowa.

A time seqyence of passes s h m without

L < 30, again contrary t o the expectation of Michel and

6

(h the strength of the foregoing discussion, I cohclule

(a) that there is no observatid evidence whatever in favor

of the hypothesis of Dessler et a l c sld (b) tbat there is

indeed substantial obseFvationnl evidence to the contrary.

It is planned to c a t h e the observational exploration

of the mag&?togpheric tail out t o 60 earth radii with the

"lunar-anchoredtl spacecraft, IMP'S I) and E.

7

&kur8, puhio, Wterns of polar c 4 blackout8 dram In geomagnetic cooFdinates wrrected by the higbr terms of spherical hamanlc d-, J. Radio Res. Iaboratorles,

2 3.l. m-@,1964= liakul& m3Ic0, atld mseo Hegas, synthetic study of severe 6olar-

temestrisl disturbances on February 9 - l2,1958, J. Badio -80 Laborstorierr, 11, 197-250, 1w.

m e r , J. P., 10. I. Eess, C. S. Scearce, and T. I,. SkiUmn, Eqhrer 10 mapnetic field messurements, J. Geapby sr Res., 2 68 1-46, 1963.

I

I I I

Hchel, I?. C., Effect of magnetospheric tail on cosmic rey cut- offs, plrrnet. maice ki., Is, 753-760, 1965.

%rker, E. E., Interphn&ary origin of energetic particlee, m s . Rev. Iitrs., 14, 55-57, lg65.

Van Allen, J. A*, Absence of b k e V electrons in the earth*s magnetospheric tail at 3300 earth radii, J. Geophys . Res., ' 70 4731-4739, 1965.

.

In the above paper [Van Allen, 19651, it is possible one rpight g e t the implressian thst the absence of detectable 40 keV electron fluxes has oaaaehow been interpreted bs indicating the absence of e geamsgnctic tail extendine to 3xx> earth radii (%). Eou-, such is evidently not Van Allen's 3.nterprt?t&iOa, for he emphasizes in eonclassion that ' ... the nqnetospheric tail of the earth became6 unobservable by the lxleazls used in this investfgatioa between 32 and 3300

Furthermore, he points aut tbst the avsilebLe dsta on electrons in the t a i l aut to 32 support an expectation of seeing detectable fluxes (3 2 2 dect-/cm2 8ec ster) of 40 keV electrum.

... [Anderson, 19651 would not

Merson observes the flust of magne!toshe&h electrons in the g-tic tsil dropping very rapidly into tlre backgmmd (*folding distances no larger than 1%) in distauces leas tbmn 32 #, wbile the "idands" of high (2 ~l$/am* sec ster) electron fluxes ewe observed with rapidly decreasing frequency at increasing rad ia l distances [Anderson, 1965, -80 1% and 191-

Wortmtely a few t2aments in the paper could be Illis- interpreted, such 88 the one iamCaistely precedin& the c o l l c l u s i ~

Quoted above, which IW&, ' ... it seems qgite unlikely that

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the tail, if M e e d significant at this distance, would not have "waggled" past the spacecraft close amugh t o produce an effect

equivalent t o an average intensity j :2/cm sec ster for 4 hours.* (he must concluie t h i s t o be same sort of error that ha8 slipped by Unnrrticed: Van Allen has irdicated in this saute

paper, that there is no reaison to expect j ?2/cm sec ster at large distsaces even i f the spacecraft were cont-ly in the tail. Furthwre, Van Allem is undoubtedly aware thst (1) no experinv?ntal evidence exist8 that can be uniquely interpreted as of the ta i l and (2) the only pertinent theoretical work indicates either motion essentially in the ecliptic plane (hence, Slmost parallel to the miner 4 trajectory)

[rkssler and Fejer, 19631, or motion in the inmediate vicinity of the earth where the baw shock is strong [Dessler and W e l t e r s , 19641. TJDM there is no reasan t o expect a vehicle 52 % above! the ecliptic plane t o necessarily intersect the tail.

2

2

Similarly t.lO0 disc~u3sicms on detector sensitivity [items (g) and (h) of page 4736, Vaa Allen, 19653, in which it is argued thgt rather large (j 3: 10 /cm sec der) fluxes are

unlikely to escape detection, could be misinterpreted by the casual reader as indicating that Veu Allen stmehow e q e c t s such

fluxes in the vicinity of the magnetospheric tail, even St

3300 BE. Van Allen*s a s s e e d of Anderscm'e data.

2 2

Such an iotc?lpret&ion again s e w inconsistent with

Prom the data presented in the above paper it is evident that no conclusion can be drawn - the length of the

mrmnr?tagnhnric tafl.

c

V

3

hdersan, KO A., Energetic electron fluxes in the tai l of the

geomergnetic field, J. Geaphyp Res., 70, 4741-4763, 1965.

Dessler, A- J., and G- E. Waters, Ebciramagaetic coupling

betwee!n the solar wind and -tosphere, planetary Spac e

sei., 12, 227-234,1@.

V m Allen, J- A., Absence of h-ke? electrons in the earth's

Im8Qetospheric tail. at 3300 earth radii, J. Geophys.

70, 4731-4739, 1965.

I I i I a i i I I II I I I

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Journal of

GEOPHYSICAL RESEARCH VOL- 70 OCTOBER 1,1965 No. 19

Absence of 40-kev Electrons in the Earth's Magnetospheric Tail at 3300 Earth Radii

J. A. VAN ALLOT Department of Physics and Astronomy

Cnicersity of Ioun, lotca City

Abstract. The Marsbound spacecraft Mariner 4 drifted westward through the presumed region of an ea%ended magnetospheric tail of the earth during late January and early Feb- ruary 1965 at a geocentric radial distance of u33ooR~ (earth radii). A pair of thin-window Geiger tubes with wide-angle collimators, which had shown the presence of electrons E. > 40 kev out to 2 3 t h in the morning iringe oi the magnetosphere during the early phase of the flight, failed to detect any effects of a magnetospheric tail during 7 days of flight within a geocentric angle betFeen 1" and 5' from its presumed center h e .

IYIRODUCTION

The ii,t€ril&GE b c t ~ : - i c ~ the so!u ly?::d %Ed the -q i+l<' . n-,3rv-tk f+Ll 1,-2,1]f2 ili tlie nartial conversion of the directed kinetic energy of the solar wind into quasi-thermal energy of the constituent particles. The most direct evidence for this aspect of the interaction phenomena comes from the observation of electrons having kinetic energies E, in the range from about 1 kev to some tens of kev in the transition region on the sunward side of the magnetopause [Free- man et d., 1963; Freeman, 1964; Fan et d., 1964; Frank and Van Allen, 1964~; Anderson et d., 196.51 (see theoretical discussion by Scharf et al. [1965]), in the evening and morning wings of the transition region, and in the magnetospheric tail [Van Allen and Frank, 1959; Grivgauz, 1961; Frank et d., 1963; Frank and van AUen, 19643; Anderson et d., 1965; Frank, 19651. Directional intensities of electrons E. > 40 kev exceeding 10' (em' sec &er)" are com- monly observed. These electrons usually occur in spatial or temporal patches, or both, in the above-mentioned regions. Anderson and Harris E19651 have found (a) that such patches exist

in the magnetospheric tail out to the maximum antisolar distance of their observstions, 3 % ~ (czrt!: mix ) !rnm the czrth's ccrrtcr; ( b ) that t h p y hare a t m n c i m t c-;i*rncc for times of the order of minutes to hours; (c) that the time duration of a giren patch, typically an hour, is more or less independent of radial distance; ( d ) that the apparent spatial dimension of patches, typically 1R, at 25RB radial distance, decreases with increasing radial distance; and ( e ) that the frequency of occurrence of patches (number of patches per unit time of observation) increases with increasing geomagnetic activity but decreases with increa-+g distance in such a way that the effect might be thought to have vanished beyond, perhaps, 100RE.

Desskr [1964] and Michel [1965] have given theoretical arguments which suggest that the magnetospheric tail may be detectable by its influence on the configuration of the interplanetary magnetic field to antisolar distances aa g r a t as 20 to 50 astronomical units (~10%~). The physical plausibility of such a suggestion has been conteated by Duaqey [19sj] on detailed grounds; he regards l@RB as a reasonable outer bound. Other recent theoretical papers

473 1

I 1 I I 1 I I I I I i I I I I 1 I

1733 IBSESCE OF *REV ELECTHOSS AT 3300 E.4HTH RADII

: !TO SUN)

I -5 7

MARINER IV

x,y COORDINATES AT 02 00 UT OF DAY SHOWN

I UNIT = IO6 KM

-10

1

JEARTH

I

I i 1/29 I

Fig. 1. Time-labeled projection of the trajectory of hlnrinrr 4 on the ecliptic. plane a? re- ferred to geocentric solar eeliptic eoordinates.

of 1%". The roll axis of the spacecraft k directed continuouJy at the siin nith an error of less than 1"; rotation of the spacecraft about this ax%+ is controlled in such 3 n-sy :IS to point the axis of a spacecraft-fixed, dirertional an- tenna approxini:ttely toward thc earth. Thus, detector< B. C'. snd D recent. p~rticlec nioving generally ou twrd from the wn and :it angles to the run-to-1irot-w vector of 70" -C 30". The detectors themselves and the complete inner

walls of their collimators are shielded from direct light and X rays from the sun. Detector -4 rerrix-es part ides moring generally inward tomrd the =un a t angle3 to the sun-to-probe Xector of 1%" i 30". The -1de~al1 shieldmg of :ill detector- ha. n miniinurn thickne.ia corre- .lronding to the rmge of w.50 Me1 protons lkrth tli.innels of The wlid-state detector D are quite in-en-itn c l o elect row of anr energy. It ir rq i i ip l~d \\ i t11 411 -.-\m-41 wiirce of -5 4

4734 J. A . VAN ALLEN

TABLE 1. Characteristics of Detectors

Unidirectional Omnidirectional Geometric Geometric Particles to Which Dynamic Range,

Sensitive counts/sec Detector Factor, cm2 ster Factor, cm2

A 0.044 f 0.005 -0.15

B 0.055 f 0.005 -0.15

C 0.050 f 0.005 -0.15

Di 0.065 31 0.003 ...

DS 0.065 f 0.003 ...

Electrons: E, 2 45 kev

Protons: E, > 670 f 30 kev


Protons : E, > 550 f 20 kev


Protons: E, > 3.1 Rlrv

Electrons: None

Protons : 0.50 5 E, 5 11 Mev

Electrons: Iione

Protons: 0.58 5 E p 5 4.0 &lev

From galactic cosmic ray rate of 0.6 to 107

From galactic cosmic ray rate 0f~0.6 to 1 0 7

From galactic cosmic ray rate of 0.6t0107

From in-flight source rate to 106

From in-flight source rate to 106

Mev a particles which provides in-flight back- ground rates of 0.071 and 0.059 (sec)-l on D, and D,, respectively.

Further details about the detectors are given in Table 1.

The five University of Iowa data channels are part of a commutated sequence of eight: E, B, D,, D,, E, B, A, C (where E represents the data channel from another experiment). The basic frame of telemetry during the ‘cruise mode’ (8% bits/sec for entire spacecraft), which was employed throughout the period of the present study, is of 50.4-second duration. Unscaled counts from each of the detectors corresponding to the above eight channels are gated in turn into a shift register of 19 bits plus 2 overflow bits for a 45.0-second period and are read out through the spacecraft telemetry system during the subsequent 5.4 seconds. A complete cycle of eight detectors is completed each 8 x 50.4 = 403.2 swonds. Thus the ‘duty cycle’ of each of the four channels A, C, D,, and D, is 11.2%, and that of channel B is 22.3%.

CHARGED-PARTICLE OBSERVATIONS JANUARY 20 TO FEBRUARY 5,1965

-4s has previously been reported [Van Allen, 19651, the interplnnetary intensity of low-

energy particles (electrons E, 2 40 kev and protons E, 2 0.5 Mev) is strikingly less during early 1965 than during the period of Mariner 2 observations, August 1962 to January 1963 [Van Allen et al., 19641. This fact aids the search for small effects attributable to the earth.

Of the four detectors in the University of Iowa equipment, the low-energy electron detectors A and B are the most sensitive for the detection of a magnetospheric tail. A specific demonstration is provided by the data from RIariner 4 itself during its outbound traversal of the morning fringe of the magnetosphere on November 28-29, 1964. The responses of detectors A, B, and C during this period are shown in Figure 2. The intensity of protons 0.5 5 E, 5 11 Mev (0,) drops to an undetectable level a t a radial distance of 10.5R, [Krimigis and Armstrong, 19651 (not shown in Figure 2) , but electrons E. > 40 kev are clearly detectable out to 23R,, with an apparently significant spike a t 23.7RE. The unidirectional geometric factors of detectors A and B on Mariner 4 (Table 1) are more than 20 times RS great as those of similar low-energy electron detectors used by this laboratory in Ekplorer 14 and Ogo 1 and by -4nderson ct al. in Imp 1, Imp 2, and Imp 3. Their omnidircrtional geomrtric factors, how-

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ABBESCE OF 40-KEV ELECTROXS AT 3300 ESRTH RADII

OODQwm: sQ*R yIQETo?IpI(BIc LAnnDE

I I I 1 r I

I I I I I I

0 -3 -P -1 + I +2 +:*

117 l lb 115 114 113 112 !.2

- m ( y o I I M o s o E )

BmQyllllcluDuL- 1 I I ~ I I l I ~ I I I I ~ i I l

20 R. IS

4735 I I

.

lo-' 19.00 20:OO 2 i O O 22.00 23 00 00'00 01 00 0 2 00 U.T.

28 NOVEMBER 1964- 29 NOVEMBER 1964

Fig. 2. Counting rates of detectors A , B, and C on Manner 4 during traTersa1 of the morning fringe of the earth's magnetosphere.

4736 J. A. VAN ALLEN

ever, are about the same. Hence the detectors on Mariner 4 have a 20-fold increase in signal- to-noise ratio for the detection of electrons having energies of the order of some tens of kev.

Four-hour averaged counting rates of detectors A and B during the period January 20 to February 5, 1965, are shown in Figure 3, to- gether with relevant trajectory parameters.

Both sets of couiiting rates show a noteworthy absence of any effect due to a presumed magnetospheric tail.

A similar result is found for detectors C and D, and D , though the sensitivity of these detectors for the detection of a magnetospheric influence is much less than that of A and B, and their counting rates arc not discussed in detail.

The foregoing impression is made more quantitative as follows:

( a ) The mean rates of A and B with their statistical standard deviations during the entire period shown are 0.689 i 0.002 and 0.5S5 r+ 0.0015 count/sec, respectively.

( b ) Similar rates are observed along seg- ments of the trajectory quite remote from any conceivable terrestrial effects.

(c) The omnidirectional geometric factors of detectors A and B for penetrating particles are not known with precision, but the rates quoted in ( a ) are attributable in a reasonable way to the interplanetary galactic cosmic ray intensity of 4.0 (cm' sec)-l as found by Neher and Ander- son [1965] with a large Geiger tube, also on Mariner 4.

( d ) The empirical and statistically expected standard deviations of 4-hour averages (about one-third of which suffer some loss of telemetry data) are, respectively, for A, 0.025 and 0.024, and for B, 0.016 and 0.016 count/sec.

( e ) Of 94 four-hour averages of the counting rate of A during the period under study, 5 depart from the mean (2 high and 3 low) by more than 2 standard deviations and none by as much as 3. The corresponding departures for B are 4 (2 high and 2 low) by more than 2 standard deviations and none by as much as 3.

( f ) The sensitivity of detectors A and B is as follows: An added unidirectional intensity j = 2 (cm' sec ster)-' of electrons E , 2 40 kev throughout any 4-hour period would produce a departure of more than 3 standard deviations from the long-term 4-hour average. No such departures are observed.

( 9 ) The above-quoted intensity is less by a factor of the order of lo4 than that often observed in the magnetospheric tail out to 30RE. An added unidirectional intensity j = 10' (cm' sec ster)-' for an isolated period as brief as 200 seconds would cause an individual 45-second sample rate of either A or B or both to be in- creased by a factor of -10 over its mean value and would cause the 4-hour average which in- cluded such a burst to depart by more than 3 standard deviations from the long-term 4-hour average. Again, no such event is observed throughout the 17-day period under discussion. It is not possible, of course, to exclude the occurrence of one or more bursts of duration less than 150 seconds, accurately and diabolically located between sampling intervals of both A and B .

(h) If electrons in the magnetospheric tail are streaming outward from the earth a t angles less than 40" or inward a t angles greater than 165' to the sun-probe line they will not enter the collimators of A or B. These possibilities con- stitute a qualification to the failure to observe an effect, but such neat directionality seems quite unlikely, in view of the 'roughness' in direction and magnitude of the B vector as reported by the magnetometer measurements on Mariner 4 during the same period [Coleman et al., 19651.

REMARKS AND CONCLUSIONS The value of (+ - 180') varies from +11"

t o -9" during the period January 20 to Feb- ruary 5. The presumed angle of observation of the center line of the magnetospheric tail is the aberration angle (+ - 180') = -arc tan (earth's orbital velocity/solar-wind velocity) = -arc tan (30/400) = -4.3'. Rtnriner 4 passed slowly through this value of (+ - 180') a t OS00 on February 1, 1965, a t a distance of 52.612, above (north of) the plane of the ecliptic a t a radial distance from the earth of 32SSRE. The useful observational period extends to 1840 on February 5, when a solar cosmic ray event is encountered. At this time (+ - 180') is - g o , the aberration angle corresponding to a solar- wind velocity of 200 km/sec, a value con- siderably lower than has been observed. A slightly positive effect is suggested by the up- ward march of the counting rate of detector A on February 1, but it is not significant statis-

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I I I I i I I I I I I M I I I I

ABSESCE OF 40-KEV ELECTROSS AT 3300 EARTH RADII 4737 m 0

2

. i

:-I

m v a w n

L 2

n-

0 -

n- +

0 -

0 1 3

' * i- 4 .

1 2 5 6 w LL

i

4738 J. A. VAN ALLEN

tically; also, no such trend appears in the data from B.

It may be noted that the 3-hour planetary values of the magnetic index K , are not greater than 3 during the period January 29 through February 5 (Compilations of Solar-Geophysical Data, May 1965, National Bureau of Stand- ards). Hence solar-wind conditions may be presumed to be relatively quite during this period.

The radius of the outer fringe of the magnetosphere is about 20RB in a plane through the earth perpendicular to the sun-earth line (4 = go", 270") and increases in the downstream direction. The 'downstream ratio' 3300RE/20RE = 165 may be compared with the corresponding value of 140 for the lunar wake observations of Ness.

Since Mariner 4 made only a single pass along a somewhat off-center line through the presumed region of the magnetospheric tail, it may be argued that the previously described negative results do not establish the absence of a detectable tail at 3300R2,. But, since the spacecraft spends some 7 days within a geocentric angle between 1" and 5" of the presumed center line of the tail (Figure 3), i t seems quite unlikely that the tail, if indeed significant a t this distance, would not h a w 'waggled' past the spacecraft close enough to produce an effect equivalent to an average intensity j 2 2 (cma sec der)-* for 4 hours.

Hence, I conclude that the magnetospheric tail of the earth becomes unobservable by the means used in this investigation between 32 and .3300RE (at least during conditions of mild geomagnetic activity). I n view of the great interplanetary melee of lower-energy particles and turbulent magnetic fields this conclusion seems palatable.

The corresponding failure of the mngnetome- ter on Mariner 4 t o detect a magnetospheric tail at -3300R, has been reported in a prelimi- nary way by Coleman et al. [1965].

Acknowledgments. I am indebted to Dr. L A Frank and Messrs. H. K. Hills, S. M. Krimigis, T. P. Armstrong, D. L Chinburg, and D. C . Ene- mark of the University of Iowa, and to Dr. H. R. Anderqon and Mews. R. K. Slonn, R. A. Lock- hart, and D. Schofield of the Jet Propulsion Lab- oratory, for various aspects of the work. The flight data used herein are from the JPL prelimi- nary, though subaantially complete, 'users pro-

grams,' which have been received promptly. The fully reduced data will not be available for some months.

The development, construction, and preflight testing of the Univcrsity of Iowa equipment were supported by subcontract 950613 with the Jet Propulsion Laboratory.

REFERENCES Anderson, K. A,, and H. K. Harris, Energetic elec-

tron fluxes in the tail of the earth's magnetic field (title only). Trans. Am. Geophys. Union, - . 46, 119, 1965.

Anderson, K. A,, H. K. Harris, and R. J. Paoli, Energetic electron fluxes in and beyond the earth's outer magnetosphere, J . Geophys. Res., 70, 1039-1050, 1965.

Axford, W. I., H. E. Petschek, and G. L. Siscoe, Tail of the magnetosphere, J . Geophys. Res., 70, 1231-1236, 1965.

Bigg, E. K., Lunar influences on the frequency of magnetic storms, J . Geophys. Res., 69, 4971- 4974, 1964.

Bowen, E. G., Lunar and planetary tails in the solar wind, J . Geophys. Res., 69, 49634970, 1964.

Coleman, P. J., Jr., L. Davis, Jr., D. E. Jones, and E. J. Smith, Mariner 4 magnetometer observations (title only), Trans. Am. Geophys. Union, _ . . .

46, 113, 1965. Davidson, T. W., and D. F. Martyn, A supposed

dependence of geomagnetic storminess on lunar phase, J . Geophys. Res., 69, 3973-3979, 1964.

Dessler, A. J., Length of magnetospheric tail, J . Geophys. Res., 69, 3913-3918, 1964.

Dungey, J. W., The length of the magnetospheric tail, J . Geophys. Res., 70, 1753, 1965.

Fan, C. Y., G. Gloeckler, and J. A. Simpson, Evi- dence for >30 kev electrons accelerated in the shock transition region beyond the earth's magnetospheric boundary, Phys. Rev. Letters, 13, 149-153, 1964.

Frank, L A,, A survev of electronq E > 40 kev beyond 5 earth radii with Explorer 14, J . Geo- phys. Res., 70, 1593-1626, 1965.

Frank, L. A., and J. A. Van Allen, Measurements of energetic electrons in the vicinity of the sunward magnetospheric boundary with Explorer 14, J . Geophys. Res., 69, 49234932, 1 9 6 4 ~ .

Frank, L. A., and J. A. Van Allen, A survey of magnetospheric boundary phenomena, Research in Geophysics, vol. 1, Sun, Upper Atmosphere and Space, edited by H . Odishaw, pp. 161-187, MIT Press, Cambridge, Massachusetts, 1964b.

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(Manuscript received July 12, 1965.)

mer remrulks on the absence of very extended ......mer remrulks on the absence of 8 very extended...

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