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The gyro-frequency in the E-layer above Slough, England
Research notes
The gyro-frequency in the E-layer above Slough, England (Received
24 June 1959)
Al&tit-Xw.surements of the gyro-frequency, fa> in the E-layer from the separation of foE and f$ at Slough give fa = 1.236 + 0.015 MC/S. The calculated value is fa = 1.27 MC/S. The difference is consistent with that found by Scott using ffi - fzE measured at high latitudes. THE day-time
ionograms obtained at Slough during June and July 1954 have been analysed to give accurate values of the separation of the ordinary, f,,, and extraordinary, f,, critical frequencies of the E- and Es-layers. This analysis formed part of an investigation of the mode of reflection in the E-layer reported elsewhere (PIGGOTT and BHATTACHARYYA, 1959). The value of the gyro-frequency, ,fH, was deduced using the equation:
f02=fac2_fZfH The observations
(1)
were divided into three groups:
(a) those taken between 2330 and 0730 GMT, (b) those taken between 0730 and 1630 GMT, (c) those taken between 1630 and 2330 GMT. No systematic differences in the average values of fH for the three groups could be detected though the standard deviations were slightly less for group (b) than for the other two groups. In sixty-eight ionograms, all in group (b), both f,E, and f,E, could be read accurately, and the separations found were indistinguishable from that deduced from f,,E and fzE for the same period. In almost all these cases . f,E,? - f,,E was near 0.6 MC/S. The mean and median values off,, in the E-region above Slough found from all 351 pairs of measurements of ordinary and extraordinary wave critical frequencies are l-23, MC/S and l-23, MC/S, respectively. It is unlikely that the probable error, after allowing for systematic experimental error and layer tilts, can exceed &0.015 MC/S. This value may be compared with the ground level value, 1.33 MC/S (adopting F = 0.475) and the value 1.27 MC/S computed from it for a height of 110 km by assuming a mean radius of the earth of 6366 km. A similar slight difference between computed and observed values of fH was found by SCOTT (1951) who ascribed it to the presence of an appreciable ratio of ions to electrons. This explanation involves very serious theoretical difficulties (MASSEY and BATES, 1946) which have not been resolved. The only alternative appears to be that the earth’s magnetic field decreases upwards more rapidly than would be expected from the inverse cube law. Rocket evidence (SINGER et aZ., 1951; CAHILL and VAN ALLEK, 1958), however, shows that the inverse cube law is correct up to about 95 km and that the decrease associated with penetrating the level of the diurnal current system is only of the order 100 *J. Our discrepancy is of the order 1000 y. It is easy to show that, in both sets of data, the apparent value of the magnetic field is smaller than expected by approximately the same amount. * Official communication. 13a-(4 pp.)
197
If we denote the gyro-frequency deduced from equation (1) by fH and that calculated from the dipole field as fH l. the number of ions per electron needed to cause the discrepancy is essentially proport,ional to ,f,, -. ]‘,,I, If there are i ions per electron with mean mass ,u times the electron mass. SCOTT’8 (l!Gl) equation for 21~ can be arranged in the form: 2 =-- AM
(2)
-- .ff,) .fJ(,iff, - fn’)
ddopting, for comparison purposes, t,o ions of mass 24, we get:
fhOTT’S
value ,u m=-&:H *, IO4 corresponding
j, rz: (2.2 Ii_ 0.X) i
10”
The weighted mean of’ SCOTT'S most accurate determinations of A, using the difference f,E - f,E, is ?. -=_ 1.4 x 103. The agreement, is s~lrprisingiy good, indicating t,hat (f,’ - f,) is similar in bot,h cases. Apart from the great theoretical difficulties in accepting values of A of this order, it is improbable that such high ion to electron ratios could be missed in the rocket experiments (ICIIASSEY, 1959). We are, therefore. forced to suspect that there may be an approximation, of t’he order of 3 per cent. in the derivation of equation (1). Further determination off,’ -- ffI using the intensive measurements made during the IGY would appear to be desirable to clear up this outstanding difficulty. ~c~nou)ledge~e~t-The work described in the paper was carried out as part of the programme of the Radio Research Roard and is published by permission of the Director of Radio Research of the Department of Scientific Industrial Research. W. R. PIGGOTT
REFERENCES BATES ID.R. and MASSEYH. S. W. CAHILL, L. J. and VAN A-LLENJ. A. MASSEYH. H. W. PINWTT W.R. and BHATTACHARYYA SCOTT C. w.
SINGER S.F.,MAPLE Eand BOWEN W. A.
J.
1946 1958 1959 1959 1951 1951
198
f’roc. Roy. sot. A 187, 261. ,F. Geophys. Res. 88, 270. Private
communication.
J. Atmosph. Ten-. Phys. J. Geophys. Res. 58, 1. J. Geophys. Rcs. 56, 265.
In press
The gyro-frequency in the E-layer above Slough, England (Received
24 June 1959)
Al&tit-Xw.surements of the gyro-frequency, fa> in the E-layer from the separation of foE and f$ at Slough give fa = 1.236 + 0.015 MC/S. The calculated value is fa = 1.27 MC/S. The difference is consistent with that found by Scott using ffi - fzE measured at high latitudes. THE day-time
ionograms obtained at Slough during June and July 1954 have been analysed to give accurate values of the separation of the ordinary, f,,, and extraordinary, f,, critical frequencies of the E- and Es-layers. This analysis formed part of an investigation of the mode of reflection in the E-layer reported elsewhere (PIGGOTT and BHATTACHARYYA, 1959). The value of the gyro-frequency, ,fH, was deduced using the equation:
f02=fac2_fZfH The observations
(1)
were divided into three groups:
(a) those taken between 2330 and 0730 GMT, (b) those taken between 0730 and 1630 GMT, (c) those taken between 1630 and 2330 GMT. No systematic differences in the average values of fH for the three groups could be detected though the standard deviations were slightly less for group (b) than for the other two groups. In sixty-eight ionograms, all in group (b), both f,E, and f,E, could be read accurately, and the separations found were indistinguishable from that deduced from f,,E and fzE for the same period. In almost all these cases . f,E,? - f,,E was near 0.6 MC/S. The mean and median values off,, in the E-region above Slough found from all 351 pairs of measurements of ordinary and extraordinary wave critical frequencies are l-23, MC/S and l-23, MC/S, respectively. It is unlikely that the probable error, after allowing for systematic experimental error and layer tilts, can exceed &0.015 MC/S. This value may be compared with the ground level value, 1.33 MC/S (adopting F = 0.475) and the value 1.27 MC/S computed from it for a height of 110 km by assuming a mean radius of the earth of 6366 km. A similar slight difference between computed and observed values of fH was found by SCOTT (1951) who ascribed it to the presence of an appreciable ratio of ions to electrons. This explanation involves very serious theoretical difficulties (MASSEY and BATES, 1946) which have not been resolved. The only alternative appears to be that the earth’s magnetic field decreases upwards more rapidly than would be expected from the inverse cube law. Rocket evidence (SINGER et aZ., 1951; CAHILL and VAN ALLEK, 1958), however, shows that the inverse cube law is correct up to about 95 km and that the decrease associated with penetrating the level of the diurnal current system is only of the order 100 *J. Our discrepancy is of the order 1000 y. It is easy to show that, in both sets of data, the apparent value of the magnetic field is smaller than expected by approximately the same amount. * Official communication. 13a-(4 pp.)
197
If we denote the gyro-frequency deduced from equation (1) by fH and that calculated from the dipole field as fH l. the number of ions per electron needed to cause the discrepancy is essentially proport,ional to ,f,, -. ]‘,,I, If there are i ions per electron with mean mass ,u times the electron mass. SCOTT’8 (l!Gl) equation for 21~ can be arranged in the form: 2 =-- AM
(2)
-- .ff,) .fJ(,iff, - fn’)
ddopting, for comparison purposes, t,o ions of mass 24, we get:
fhOTT’S
value ,u m=-&:H *, IO4 corresponding
j, rz: (2.2 Ii_ 0.X) i
10”
The weighted mean of’ SCOTT'S most accurate determinations of A, using the difference f,E - f,E, is ?. -=_ 1.4 x 103. The agreement, is s~lrprisingiy good, indicating t,hat (f,’ - f,) is similar in bot,h cases. Apart from the great theoretical difficulties in accepting values of A of this order, it is improbable that such high ion to electron ratios could be missed in the rocket experiments (ICIIASSEY, 1959). We are, therefore. forced to suspect that there may be an approximation, of t’he order of 3 per cent. in the derivation of equation (1). Further determination off,’ -- ffI using the intensive measurements made during the IGY would appear to be desirable to clear up this outstanding difficulty. ~c~nou)ledge~e~t-The work described in the paper was carried out as part of the programme of the Radio Research Roard and is published by permission of the Director of Radio Research of the Department of Scientific Industrial Research. W. R. PIGGOTT
REFERENCES BATES ID.R. and MASSEYH. S. W. CAHILL, L. J. and VAN A-LLENJ. A. MASSEYH. H. W. PINWTT W.R. and BHATTACHARYYA SCOTT C. w.
SINGER S.F.,MAPLE Eand BOWEN W. A.
J.
1946 1958 1959 1959 1951 1951
198
f’roc. Roy. sot. A 187, 261. ,F. Geophys. Res. 88, 270. Private
communication.
J. Atmosph. Ten-. Phys. J. Geophys. Res. 58, 1. J. Geophys. Rcs. 56, 265.
In press