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Variations in the relation between sunspot number and IF2
Research
notes
547
LITERATUR BLACKBAND W. T. KOCH H. und SCHMINDER R. KOCH H. und SCHMINDER R. LAUTER E. A. LAUTER E. A., ENTZIAN G. und KNUTR
R.
1962 1960a 1961b 1960 1960
Nature, Lond. 193,863. 2. Geophys. 26, 285. Geofis. Pur. Appl. Im Druck. T’ortr. Ber. Kleinheubach, 75. 2. Meteor. 14,275.
Variations in the relation between sunspot number and IF2 (Received
7 February
1962)
IT HAS been shown by NAISMITH et al. (1961) that the E-region character figure (Ch,) corresponding to a given value of the relative sunspot number (R) progressively decreased over the five half sunspot cycles from 1933 to 1957. It is of interest to consider whether a similar effect has been observed in higher parts of the ionosphere. The behaviour of the FZ-region of the ionosphere is considerably more complex than at lower levels. An index of FZ-region ionization is thus required which eliminates both geographical and temporal variations. Such an index (1~2) has been devised by MINNIS and BAZZARD (1960) and is based on data from a number of observing stations in various parts of the world. The index is available for each month since 1938.
IF2
Fig.
1. The relation between annual mean values of sunspot number, I”-layer index, 1~2, for the 23 years 1938-1960.
R, and the
Fig. 1 shows the relation between annual mean values of IF2 and R during the 23 years (rather more than two sunspot cycles) 1938-1960. There is clearly a well-defined but non-linear relation between the two variables. The best quadratic expression has been fitted to the observations by the method of least squares; the curve is shown in the Figure and is given by the expression R = 11.44 + 0.478 TBZ + 0.00278 (1P2)2
(1)
The expected values of R, Rx, calculated using equation (1) and the observed values of 1~2, have been compared with the observed values of R, R,. The difference, RE - R,, is plotted against time in Fig. 2. During the 12 year period 1938-1949 Rz - R, was usually positive while during the subsequent 11 years the difference was usually negative. These two halves of the period have
548
Research notes
been compared using “Student’s” t-test. The result, t = 5.5, indicates that the probability of the two halves having the same mean value is much less than 0.1 per cent. Conclusions based on this test must, however, be treated with reserve since a 10 year periodic term may still be discerned in the minima of Fig. 2.
20 r
-to-
I940
1950
1960
Fig. 2. The difference between expected and observed sunspot numbers during the 23 years 1938-1960.
_
.X
x \
?
Fig. 3. The difference between the annual mean values of 1p,0 and R plotted against 1~2 for the descending parts of the sunspot cycles since 1938. From an examination of the monthly data, MINNIS (private communication) has established that the relation between R and I p2 is linear up to about Ipa = 120 and is curved for higher Ipg values. He gives the expression for the linear part as R = 5 + 0.88 IF
(up to Ip2
= 120).
(2)
A quadratic expression was fitted to the observed annual mean values in years when IF2 exceeded 120 and to the ordinate and slope of equation (2) at I 32 = 120. The expected sunspot numbers from this new composite relation were incorporated in a modification of Fig. 2. The trend was still apparent but a 10 year cyclic component became more obvious, mainly due to increased differences, R, - R,, in years of high sunspot number.
Research
notes
549
The straight line of best fit to the data in Fig. 2 has been calculated for the 20 years 1938-1957 (two sunspot cycles) which are contemporary with the E-region discussion of NAISMITH et al. (1961). This line is also shown in the Figure. The smoothed value of R, decreased by 16 from 1938 to 1955: two occasions when I p2 was 112, and hence when R, was 100. Adopting a zero flux level at 1~~ = - 160 as suggested by MINNIS and BAZZARD (1960), this corresponds to a decrease in ionizing flux of 6 per cent. The E-region character figure decreased by 8.5 per cent over the same period. Since this work was done a further paper by NAISMITH and SMITH (1961) has been published. This paper examines the relation between monthly values of 1~~ and R for the four half sunspot cycles between 1938 and 1957 and the best fit straight lines are calculated for each half cycle. It is shown, from a discussion of the intercept and slope of the regression lines, that the value of 1~2 corresponding to a fixed value of R progressively decreased over the period. This present note confirms that conclusion but the work differs from NAISMITH and SMITH in the treatment of the data and particularly in the use of a parabolic rather than a linear fit to the IFZ-R relation. Although there is yet but little data available, there are some indications that the trend apparent in the years up to 1957 has not continued. This may best be demonst’rated in Fig. 3. Here the difference 1~s - R is plotted against Ip, 0 for the available portions of the three descending half cycles. The two half cycles 193881944 and 1947-1954 are roughly similar except that the latter cycle has smaller values of Ip - R and a slightly smaller gradient, (13, - R)/Ipp The most recent observations, since the exceptional peak of 1957-1958, suggest a reversal of sign in the gradient. Despite the small amount of data, it may be noted that in neither of the preceding cycles would it have been possible to draw a best fit line through any three such widely spaced Future variations will be followed with interest as d&a become points with a negative gradient. available. dcknowledgements-This note is published by permission of the Director of Research, Marconi’s Wireless Telegraph Co. Ltd. Thanks are due to Dr. C. M. MINNIR and to colleagues at the Baddow Research Laboratories for helpful comments on methods of presentation. IMarconi’s Wireless Telegraph Baddow Research Laboratories Great Baddow, Essex
L. W. BARCLAY
Co. Ltd.
REFERENCES MINNIS C. M. and BAZZARD G. H. NAISMITH R., BEVAN H. C. and SMITH P. A. NAISMITH R. and SMITH P. A.
1960 1961
J. dtmosph. J. Atmosph.
Terr. Phys. Terr. Phys.
18, 297. 21, 167.
1961
J. Atmosph.
Terr.
22, 270.
Phys.
Total ionospheric electron content by Doppler integral of the satellite signal (Received
22 January
1962)
SEVERAL methods have been proposed and utilized to measure total ionospheric electron content. The method using the Faraday polarization rotation of the satellite signal as described for instance by BLACKBA.ND et al. (1959) and by GARRIOTT (1960), has given interesting results as published by YEH and SWENSON (1961). Another method using the differential Doppler effect between two harmonic frequencies transmitted by a satellite had been proposed by AITCHINSON and WEEKES (1959) and Ross (1960). Results were given for the same period using the same satellite as with the Faraday method.
notes
547
LITERATUR BLACKBAND W. T. KOCH H. und SCHMINDER R. KOCH H. und SCHMINDER R. LAUTER E. A. LAUTER E. A., ENTZIAN G. und KNUTR
R.
1962 1960a 1961b 1960 1960
Nature, Lond. 193,863. 2. Geophys. 26, 285. Geofis. Pur. Appl. Im Druck. T’ortr. Ber. Kleinheubach, 75. 2. Meteor. 14,275.
Variations in the relation between sunspot number and IF2 (Received
7 February
1962)
IT HAS been shown by NAISMITH et al. (1961) that the E-region character figure (Ch,) corresponding to a given value of the relative sunspot number (R) progressively decreased over the five half sunspot cycles from 1933 to 1957. It is of interest to consider whether a similar effect has been observed in higher parts of the ionosphere. The behaviour of the FZ-region of the ionosphere is considerably more complex than at lower levels. An index of FZ-region ionization is thus required which eliminates both geographical and temporal variations. Such an index (1~2) has been devised by MINNIS and BAZZARD (1960) and is based on data from a number of observing stations in various parts of the world. The index is available for each month since 1938.
IF2
Fig.
1. The relation between annual mean values of sunspot number, I”-layer index, 1~2, for the 23 years 1938-1960.
R, and the
Fig. 1 shows the relation between annual mean values of IF2 and R during the 23 years (rather more than two sunspot cycles) 1938-1960. There is clearly a well-defined but non-linear relation between the two variables. The best quadratic expression has been fitted to the observations by the method of least squares; the curve is shown in the Figure and is given by the expression R = 11.44 + 0.478 TBZ + 0.00278 (1P2)2
(1)
The expected values of R, Rx, calculated using equation (1) and the observed values of 1~2, have been compared with the observed values of R, R,. The difference, RE - R,, is plotted against time in Fig. 2. During the 12 year period 1938-1949 Rz - R, was usually positive while during the subsequent 11 years the difference was usually negative. These two halves of the period have
548
Research notes
been compared using “Student’s” t-test. The result, t = 5.5, indicates that the probability of the two halves having the same mean value is much less than 0.1 per cent. Conclusions based on this test must, however, be treated with reserve since a 10 year periodic term may still be discerned in the minima of Fig. 2.
20 r
-to-
I940
1950
1960
Fig. 2. The difference between expected and observed sunspot numbers during the 23 years 1938-1960.
_
.X
x \
?
Fig. 3. The difference between the annual mean values of 1p,0 and R plotted against 1~2 for the descending parts of the sunspot cycles since 1938. From an examination of the monthly data, MINNIS (private communication) has established that the relation between R and I p2 is linear up to about Ipa = 120 and is curved for higher Ipg values. He gives the expression for the linear part as R = 5 + 0.88 IF
(up to Ip2
= 120).
(2)
A quadratic expression was fitted to the observed annual mean values in years when IF2 exceeded 120 and to the ordinate and slope of equation (2) at I 32 = 120. The expected sunspot numbers from this new composite relation were incorporated in a modification of Fig. 2. The trend was still apparent but a 10 year cyclic component became more obvious, mainly due to increased differences, R, - R,, in years of high sunspot number.
Research
notes
549
The straight line of best fit to the data in Fig. 2 has been calculated for the 20 years 1938-1957 (two sunspot cycles) which are contemporary with the E-region discussion of NAISMITH et al. (1961). This line is also shown in the Figure. The smoothed value of R, decreased by 16 from 1938 to 1955: two occasions when I p2 was 112, and hence when R, was 100. Adopting a zero flux level at 1~~ = - 160 as suggested by MINNIS and BAZZARD (1960), this corresponds to a decrease in ionizing flux of 6 per cent. The E-region character figure decreased by 8.5 per cent over the same period. Since this work was done a further paper by NAISMITH and SMITH (1961) has been published. This paper examines the relation between monthly values of 1~~ and R for the four half sunspot cycles between 1938 and 1957 and the best fit straight lines are calculated for each half cycle. It is shown, from a discussion of the intercept and slope of the regression lines, that the value of 1~2 corresponding to a fixed value of R progressively decreased over the period. This present note confirms that conclusion but the work differs from NAISMITH and SMITH in the treatment of the data and particularly in the use of a parabolic rather than a linear fit to the IFZ-R relation. Although there is yet but little data available, there are some indications that the trend apparent in the years up to 1957 has not continued. This may best be demonst’rated in Fig. 3. Here the difference 1~s - R is plotted against Ip, 0 for the available portions of the three descending half cycles. The two half cycles 193881944 and 1947-1954 are roughly similar except that the latter cycle has smaller values of Ip - R and a slightly smaller gradient, (13, - R)/Ipp The most recent observations, since the exceptional peak of 1957-1958, suggest a reversal of sign in the gradient. Despite the small amount of data, it may be noted that in neither of the preceding cycles would it have been possible to draw a best fit line through any three such widely spaced Future variations will be followed with interest as d&a become points with a negative gradient. available. dcknowledgements-This note is published by permission of the Director of Research, Marconi’s Wireless Telegraph Co. Ltd. Thanks are due to Dr. C. M. MINNIR and to colleagues at the Baddow Research Laboratories for helpful comments on methods of presentation. IMarconi’s Wireless Telegraph Baddow Research Laboratories Great Baddow, Essex
L. W. BARCLAY
Co. Ltd.
REFERENCES MINNIS C. M. and BAZZARD G. H. NAISMITH R., BEVAN H. C. and SMITH P. A. NAISMITH R. and SMITH P. A.
1960 1961
J. dtmosph. J. Atmosph.
Terr. Phys. Terr. Phys.
18, 297. 21, 167.
1961
J. Atmosph.
Terr.
22, 270.
Phys.
Total ionospheric electron content by Doppler integral of the satellite signal (Received
22 January
1962)
SEVERAL methods have been proposed and utilized to measure total ionospheric electron content. The method using the Faraday polarization rotation of the satellite signal as described for instance by BLACKBA.ND et al. (1959) and by GARRIOTT (1960), has given interesting results as published by YEH and SWENSON (1961). Another method using the differential Doppler effect between two harmonic frequencies transmitted by a satellite had been proposed by AITCHINSON and WEEKES (1959) and Ross (1960). Results were given for the same period using the same satellite as with the Faraday method.