Geomagnetic micropulsation measurements for magnetosphere and solar wind diagnostic

Gulelmi, A. V.

Shchepetnov, R. V.

Troitskaya, V. A.

English

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National Aeronautics and Space Administration 
Goddard Space Flight Center 
Contract No.NAS-5-12487 
ST-GM-PF-1076 
DETERMINATION OF THE DIMENSIONS OF THE MAGNETOSPHERE, AS 
MEASURED BY THE SUBSOLAR DISTANCE,FROM THE DATA OF 
TERRESTRIAL OBSERVATIONS OF GEOMAGNETIC 
MICROPULSATIONS 
V.A. Troitskaya 
R.V. Shchepetnov 
A.V. Gul'el'mi 
(USSR) 
7 NOVEMBER 1968 
https://ntrs.nasa.gov/search.jsp?R=19690000995 2020-03-12T05:27:18+00:00Z
ST-GM-PF-10769 
DETEREIIINATION OF THE DIMENSIONS OF THE MAGNETOSPHERE, AS 
MEASURED BY THE SUBSOLAR DISTANCE,FROM THE DATA OF 
TERRESTRIAL OBSERVATIONS OF GEOMAGNETIC 
MICROPULSATIONS 
Doklady Aktldemii Nauk SSSR 
Tom 182, No.5, pp 1063-1066 
Izd-vo "NAUKA", MOSCOW 1968. 
S L W Y  
by 
V . A .  Troitskaya, 
R.V. Shchepetnov and 
A.V. Gul'el'mi. 
The geomagnetic micropulsations of the type Pc 2-4, are used for the 
determinations of the dimension of the magnetosphere as measured by the 
subsolar distance, since they are, in fact,the magnetosphere's proper 
hydromagnetic oscillations excited at its periphery by solar corpuscular 
streams. 
in a wide range of magnetic field sudden impulses at the equator. 
This method is considerably improved by simultaneous measurements 
* 
* * 
One of the promising directions of the investigation of micropulsations, 
is the study of the possibility of their use for the diagnostics of the mag- 
netosphere and solar wind parameters. Inasmuch as up to the present time, 
only the general principles of physical interpretations of the micropulsations 
were contemplated, so the various empirical and semi empirical methods (1,3) 
are being widely used alongside with the theoretical approach to the diagnostics 
problem (2).  
Amid the diversity of the geomagnetic micropulsations the oscillations of 
the type Pe 2-4 with periods T = 10-150 sec., stand out; they are practically 
continuously observed on the Earth's surface facing the Sun. 
contemporary representations they are the magnetosphere's proper hydromagnetic 
oscillations, excited on its periphery by solar corpuscular streams. 
lation period naturally depends on the dimensions of the resonator, the "walls" 
of which are the Earth's surface and the shock-wave front, which occurs during 
solar wind flow,past the magnetosphere, and limits the geomagnetic field from 
the subsolar side at an average distance of about ten Earth's radii. 
According to 
The oscil- 
The direct measurements of the magnetic field and of fluxes of particles 
on satellites and rockets show that the magnetosphere boundary is in a conti- 
nuous motion, approaching the Earth's surface with the increase of solar wind 
and receding, when the wind weakens and the normal pressure on the magneto- 
sphere's surface decreases. Consequently the periods of Pc 2-4 micropulsations 
2 
vary. may be considered as a simple 
ground indicator, which allows to observe continuously the position of mag- 
netosphere boundary. 
Thus the micropulsations of this type 
If we represent the dependence of the micropulsation period T on the 
magnetosphere dimensions on the line of Earth-Sun in the form T = const-RV, 
the basic problem will consist in determining the exponent V. 
lity factor is estimated from the condition, that to the average magnetosphere 
dimension R, % 10 (in the units of Earth's radius) correspond the typical 
periods To RJ 30 sec. 
The proportiona- 
Thus 
T = T~(R/R~)v, (1 1 
where To and R, are assumed to be known, while v is a quantity subject to deter- 
minat ion. 
In the work [l], the exponent v n, 4.8 was found by direct comparison of 
satellite data about the dimensions of the magnetosphere with periods of Pc 2-4 
micropulsations. 
means of ground data. 
variation of Pc 2-4 micropulsation period during a sudden magnetosphere defor- 
mations, taking place under the action of solar wind's inhomogeneities. 
den contraction'or expansion of the magnetosphere, the superficial currents 
flowing along its boundary correspondingly increase or weaken and a positive 
. (negative) impulse of magnetic field Si (Fig.1-a) is observed on the Earth's 
surface. 
the micropulsations disappear completely (Fig.1-b,c). 
In the proposed work attempt is made to determine v only by 
For this purpose we shall make use of cases of sharp 
At sud- 
It is interesting to note that sometimes following a negative impulse, 
The evaluation method of the exponent v is based on the comparison of the 
sudden impulse's magnitude AB with the micropulsation periods T and T', which 
were observed before and after 
According 
the equator is 
manner 
to Mead [ 4 ]  the 
linked with the 
where B, 5 25.000~ (1 y = 10'
the sudden impulse. 
magnitude of the sudden impulse Si*, recorded at 
dimensions of magnetosphere in the following 
gauss). Eliminating from ( 2 )  by means of (1) 
the quantities R and R' we find 
_- lg ($) = 
(3) 
* It should be noted that at the investigation of Earth's surface, the value 
of Si will be somewhat higher owing to the induction effect in Earth's crust. 
As is well known, this effect is approximately accounted for by multiplication 
of the measured values Si by coefficient 2/3.  
3 
This formula allows us to determine by combination of experimental data on T, 
T' and AB the exponent V. The results of the preliminary measurements, accor- 
ding to 20 cases of micropulsation period variation during the time Si, lead t o  
the value V 2 4.6. This is rather close to the value, found by means of direct 
comparison of T and R. 
b 
Fig. 1 
Examples of micropulsation registration 
from top to bottom are: 
St. Borok (4 = 52', A x: 123'20'), Petropavlovsk (@' = 44'24',A = 218"14') 
Soroa (CUBA) (@ = 33'; A = 345') 2 August 1964; 
b) from top to bottom: 
Borok, Petropablovsk, Soroa (CUBA), Dallas (USA) 2 May, 1965; 
c )  St. Borok, 14 December 1958. 
It is Intsresthg t o  note,.that for well known V, there is a possibility 
to determine the magnetosphere dimensions before and after Si with a precision, 
independent of the exact choice of parameters RP and To. 
(R'/R) from (2) by means of (l), we obtain 
In reality, eliminating 
4 
The formula for the determination of R' has quite an analogous form. 
A very specific peculiarity of the described measurement is the fact 
that the shift of micropulsation periods was analyzed by a net of obsevatories 
situated along the Earth's globe perimeter such as, for example, Borok, Petro- 
pavlovsk-on-Kamchatka (USSR), Soroa (CUBA), and by special experiments, conducted 
at antipode points (Borok, Hayt, Dallas). 
The quantity v will be defined more exactly by both methods. Therefore, 
let us take note that formula (3)  rewritten in the form 
could be used for the experimental determination of the quantity B,. 
The formation of magnetosphere boundary takes place under the action of 
solar corpuscular streams filling the interplanetary space. Therefore the data 
on the position and displacements of the boundary contain an indirect information 
about the properties of the interplanetary medium in the vicinity of the Earth. 
Ffg .2 
.---- 
Fig. 3 
Dependence of type Pc 2-4 
- micropulsation.period on the 
dimensions of magnetosphere. 
Dependence of micropulsations period 
and the magnitude of the impulse AB on 
the magnetosphere's dimensions and the 
solar wind velocity (upper curve at the 
contraction of magnetosphere, lower at 
expansion). 
If we are to employ the ratio R = 1.068 (~/4nnbp17V2)'Ir,  which links the 
magnetosphere's dimensions with solar wind pressure on magnetosphere at the 
5 
subsolar point ( 4 ) ,  then by taking into account (1) we obtain: 
Here M is the Eatth's magnetic moment, mp is the proton mass, V is the wind's 
velocity, N is the proton concentration. The utilization of formula (6)  for 
the evaluation of solar wind velocity according to data on the periods of 
micropulsations is hampered by the variability of particle concentration in 
the interplanetary medium. If, however, we assume that NV = const (5) ,  then 
V = const T-6/v. The value v = 4 . 6  has been defined above, and the proportiona- 
lity factor may be estimated from the condition that to the mean solar wind 
velocity V % 500 km/sec corresponds a typical period To % 30 sec. 
admissions the values of solar wind corresponding to various periods of steady 
micropulsations (Table 1) were calculated. Naturally, the results of computation 
should be considered as preliminary. In the direct comparisons of data on the 
corpuscular stream parameters with the observed periods of micropulsations will 
allow to make more precise the character of the relationship between T and V. 
With these 
TABLE I 
We have mentloned above the cases of cessation of micropulsations after 
negative Si (Fig.1-c). In Fig.3 (the lower curve) the values of negative 
impulses are plotted along the vertical axis, and the magnetosphere dimensions 
R to Si corresponding to them and computed by formula (1) with v = 4.6 are 
plotted along the horizontal axis. 
the same method, since after the considered negative Si, oscillations cease. 
However, inasmuch as R and AR are well known, it is possible to find R' by 
formula (2). It is interesting to note, that in all the cases of micropulsation 
cessation, after Si, the magnetosphere boundary drifted away to substantial dis- 
tances R' a 13-15. If the relation V % 1/T6/v, obtained at the condition NV = 
= const is correct, this will lead to rather small values of solar wind velocity: 
The value of R' cannot be determined by 
6 
V 2 150 km/sec. Besides, it is not exluded that the cessation of micro- 
pulsations takes place with a sharp drop of solar wind velocity, as well 
as with the decrease in the particle concentration.* 
The dependence between R and the value of AB is shown on the upper 
curve in Fig.3. In general case this dependence is not single-valued. There- 
fore, in the sorting of cases shown on the graph, a complementary link in the 
form of T = 2T', was superimposed. 
Thus concomitant analysis of micropulsations in a wide range of periods 
and sudden impulses of the magnetic field on equator, greatly improves the 
reliability of ground observation of the geomagnetic effects. 
The authors express their gratitude to E.RI Mustel', V.P. Shabanskiy 
and K.G. Ivanov, for the discussion of the investigated serto-s of problems. 
Institute of Physics in the 
name of 0. Yu. Schmidt 
Akademy of Sciences SSSR 
Manuscript received 
26 January 1968. 
* * * THE END * * * 
R E F E R E N C E S  
1. 
2. 
3. 
4. 
5. 
6. 
7. 
8 .  
V.A. TROITSKAYA, 'O.V. BOL'SHAKOVA, E.T. MATVEEVA, Geomagnetizm i Aeronomiya 
6, No.3, 533 (966). 
A.V. GUL'EL'MI, Geomagnetiz i Aeronomiya, 6, No.1, 135 (1966). 
T. HIRASAWA, A. NISHIDA, T. NAGATA, Rep. Ionosph. and Space Res. Japan, 
20, No.1, 51 (1966). 
G.D. MEAD, J. Geophys. Res., 69, No.7, 1184 (1964). 
M. NEUGEBAUER, C.W. SNYDER, J. Geophys. Res., 71, No.19, 4469 (1966). 
R.R. HEACOCK, V.P. HESSLER, J. Geophys. Res., 70, No.5, 1103 (1965). 
B.A. TVERSKOY, Geomagnetizm i Aeronomiya, 7, No.2, 226 (1967). 
A.V. GUL'EL'MI, (Fizicheskaya interpretatsiya mikropul'satsiy) Physical 
interpretation of Micropulsations. Report at All-Union 
conference according to MGSS, M., results, 1967. 
CONTRACT NO. NAS-5-12487 
Volt Information Sciences, Inc., 
1145 19th Street, N.W. 
Washington, D.C. 20036 
Telephone: [202] 223-6700 X 36,37. 
Translated by 
Ludmilla D. Fedine 
4-5 November 1968 
Revised by 
Dr. Andre L. Brichant 
6 Xovember 1968 
* Furthermore, we do not consrder in present case, the influence of inter- 
planetary field orientation on the Pc excitation. 


Determination of the dimensions of the magnetosphere, as measured by the subsolar distance, from the data of terrestrial observations of geomagnetic micropulsations

Determination of the dimensions of the magnetosphere, as measured by the subsolar distance, from the data of terrestrial observations of geomagnetic micropulsations

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