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Relative intensities of Na lines in the emission of sodium ejected from rockets
Ftaner, &mce ,!kf. Fergamon Press 1959. Vol. 2, pp. 71-77. Printed in Great Britain.
RESEARCH
~~~~~~ (Received 7 Jury 1959) In 1950. D, R. Bates’” detailed the possibilities offered by an artificial sodium cloud to get inf~rmatian concerning the high atmosphere. Since that time, experiments have been perfmm~d in the United States by Manring, Bedinger and othersfg~s~*J. ReccntIy we have undertaken a series of experiments with French missiles with a view to study the emission of the ultraviolet doublet 3303 (4P-3s) aud the intensity ratio of the lines 5893 and 3303. The first experiments were made duriug last March in French Sahara, where two “V&on* ique” rockets were fired, the first at 1840 hr GMT on 10 March and the second at 0544 hr GMT on 12 March; the first reached an &i~ tude of 126 km and the second 180 km. The experimental details have been given in a previous publication[“‘. Since our problem was the comparison of the intensities of the two lines, yellow and ultraviolet, it was of the utmost importance to get the two lines on the same spectrum. Hence the spectrograph was adjusted for focus in the two spectral regions and we used Kodak OaF plates, sensitive from 6800 A to the ultraviolet. One spectrum was obtained for each firing; on 10 March the exposure time was 30 min, and on 12 March 15 min only, owing to the increasing light of the dawn The plates and spectrograph were then calibrated at the laboratory with a Philips sodium lamp which emits both lines with an intensity ratio which has been carefully measured. We found Zs8g3/Z,,,, = 1277. The first speeulua obtained in the ever&g twilight, gives no evidence of the 3303 line; the second, at the morning twilight, gives a weak line at 3303; we must note that the exposure time was shorter and that the yellow
NOTES
line was less than half the intensity obtained in the first case. Hence we may immediately deduce that the intensity ratio of these two lines is variable, but so far we are not in a position to say whether the difference comes from the different altitudes, or from the time of firing or from the atmospheric conditions. In spite of the mculty of the comparison, due to the weakness of the ultraviolet line, we could determine the ratio of the energy intensities received at ground level: the intensity of the yellow line was l-5 times the intensity of the ultraviolet line. We are conscious of the avoidable sources of error of this measurement, and the figures given above are only a rough estimate of the intensity ratio; but it is of interest to compare this value to the similar measurement made by Cooper et CZZ.‘~), who have found a ratio of more than 1:lOO. We find that, in out experiment, the ultraviolet line was far more intense than I /lOOth of the yellow line, while the ratio I:100 is in agreement with the theory of resonance scattering. A ratio of, say, 1:2 or 1:3 would indicate a quite different excitation. This means that different mechanisms are a~~~no~ly or sue cessively present in the mesosphere. Furthes, if we contemplate the fact that in the iirst experiment 3303 line was not visible, we are brought to the conclusion that further investigations are necessary. We must remem+ ber that Redingcr & aL(Q have not observed the ultraviolet line at night nor in the evening, and also that it is m the evening that the 3303 line is missing in our own experiments. In further experiments we intend to replace the ultraviolet spectrograph by a quartz spew+ trograph, to increase the transmission for 3303 line and to vary the conditions of the &it@ in order to examine the possibility of di.@erent kinds of excitation of the sodium ejected from the rockets. We intend also to find the spatial region where 3303 line is excited.
RESEARCH
12
Such information may be of importance for a better knowledge of the state of the upper atmosphere, which is substantially variable with altitude as was already noted in the U.S. experiments. A. AND E. VASSY Physique de I’Atmosph2re Facultb des Sciences de Pm-is References 1. 2. 3. 4. 5.
D. R. BATES, J. Geophys. Res. 55, 347 (1950). J. F. BEDINGERand E. MNWNG, J. Geophsy. Res. 62, 170 (1957). C. D. COOPER, E. MANRIN~ and J. F. BEDINGER J. Geophys. Res. 63,369 (1958). J. F. BEDINGER,E. R. MANRINGand S. N. GHOSH, J. Geophys. Res. 63, 19 (1958). A. and E. VASSY, C.R. Acad. Sci.. Paris 248,223s (1959).
The came&jet
hypothesis of whistler generation
(Received
10 August 1959)
The paper of H. Norinder and E. Knudsen, on “The relations between lightning discharges and whistlers”(‘), is of considerable interest from the standpoint of generation of whistlers. This part of the phenomenon has received little attention up to now, apart from the fact that the whistler is associated in time with a spheric, though it is known that not every spheric gives rise to a whistler. Only the high-energy sferics appear to be capable of generating whistlers, and of these only those with “slow tails” (which, as Norinder points out in his paper, apparently correspond to multiple discharges). The time lags involved in the “slow tails” are of the order of tens or hundreds of milliseconds, and the spheric energy peaks at around 5 kc/s, rather than near 10 kc/s as in the ordinary strong spheric. The insertion and passage of the extraordinary component of the spheric signal through the lower ionosphere, with the high values of collision frequency encountered there, appears to be the least understood part of whistler propagation. It is difficult to understand how upon occasions, long echo trains of twenty to
NOTES
thirty round trips can be achieved under such circumstances, nor how occasional amplification of whistler echoes can occur. (This phenomenon has been attributed to “polar creep”, but either polar or equatorial creeps would be inconsistent with the widely accepted current belief in ducts of field-aligned ionization.) The diurnal variation in frequency of occurrence of whistlers is also consistent with strong absorption in the lower ionosphere. It is the purpose of this letter to outline what might be termed the current-jet theory of whistler generation and to review the evidence for such a hypothesis. In this theory, the penetration of the lower ionosphere is accomplished by a high-energy current jet which is emitted from the top of the thundercloud shortly after the spheric discharge occurs. Until it enters the ionosphere, the current jet is accelerated by the electrostatic field of the thunderstorm, and also interacts with one or more of the slow-tail portions of the spheric in such a way as to either amplify the spheric signal or be accelerated by it. During the passage through the lower part of the ionosphere the current jet becomes fieldaligned and undergoes synchronous acceleration by a later spheric. During this phase, additional acceleration along the field line takes place due to the acceleration by collisions at the “magnetic mirrors” at each end of the path. Meanwhile a travelling-wave-type interaction is taking place between the high-energy electrons launched in the current jet and the electromagnetic wave of the spheric signal. These high-energy electrons are trapped in the geomagnetic field and are reflected back and forth by the “magnetic mirror” in the lower ionosphere. The result is that the thunderstorm creates its own duct of field-aligned ionization, which guides and interacts with the spheric signal either to amplify or damp it out depending upon the relative velocities of electrons and electromagnetic waves. Such accelerated current-jet electrons could also contribute in thunderstorm latitudes to the inner radiation belt, a slow tail of 1 set duration corresponding to energies (for electrons) of 20 keV or more. Let us now review the evidence for such a hypothesis. Although the existence of upward
RESEARCH
~~~~~~ (Received 7 Jury 1959) In 1950. D, R. Bates’” detailed the possibilities offered by an artificial sodium cloud to get inf~rmatian concerning the high atmosphere. Since that time, experiments have been perfmm~d in the United States by Manring, Bedinger and othersfg~s~*J. ReccntIy we have undertaken a series of experiments with French missiles with a view to study the emission of the ultraviolet doublet 3303 (4P-3s) aud the intensity ratio of the lines 5893 and 3303. The first experiments were made duriug last March in French Sahara, where two “V&on* ique” rockets were fired, the first at 1840 hr GMT on 10 March and the second at 0544 hr GMT on 12 March; the first reached an &i~ tude of 126 km and the second 180 km. The experimental details have been given in a previous publication[“‘. Since our problem was the comparison of the intensities of the two lines, yellow and ultraviolet, it was of the utmost importance to get the two lines on the same spectrum. Hence the spectrograph was adjusted for focus in the two spectral regions and we used Kodak OaF plates, sensitive from 6800 A to the ultraviolet. One spectrum was obtained for each firing; on 10 March the exposure time was 30 min, and on 12 March 15 min only, owing to the increasing light of the dawn The plates and spectrograph were then calibrated at the laboratory with a Philips sodium lamp which emits both lines with an intensity ratio which has been carefully measured. We found Zs8g3/Z,,,, = 1277. The first speeulua obtained in the ever&g twilight, gives no evidence of the 3303 line; the second, at the morning twilight, gives a weak line at 3303; we must note that the exposure time was shorter and that the yellow
NOTES
line was less than half the intensity obtained in the first case. Hence we may immediately deduce that the intensity ratio of these two lines is variable, but so far we are not in a position to say whether the difference comes from the different altitudes, or from the time of firing or from the atmospheric conditions. In spite of the mculty of the comparison, due to the weakness of the ultraviolet line, we could determine the ratio of the energy intensities received at ground level: the intensity of the yellow line was l-5 times the intensity of the ultraviolet line. We are conscious of the avoidable sources of error of this measurement, and the figures given above are only a rough estimate of the intensity ratio; but it is of interest to compare this value to the similar measurement made by Cooper et CZZ.‘~), who have found a ratio of more than 1:lOO. We find that, in out experiment, the ultraviolet line was far more intense than I /lOOth of the yellow line, while the ratio I:100 is in agreement with the theory of resonance scattering. A ratio of, say, 1:2 or 1:3 would indicate a quite different excitation. This means that different mechanisms are a~~~no~ly or sue cessively present in the mesosphere. Furthes, if we contemplate the fact that in the iirst experiment 3303 line was not visible, we are brought to the conclusion that further investigations are necessary. We must remem+ ber that Redingcr & aL(Q have not observed the ultraviolet line at night nor in the evening, and also that it is m the evening that the 3303 line is missing in our own experiments. In further experiments we intend to replace the ultraviolet spectrograph by a quartz spew+ trograph, to increase the transmission for 3303 line and to vary the conditions of the &it@ in order to examine the possibility of di.@erent kinds of excitation of the sodium ejected from the rockets. We intend also to find the spatial region where 3303 line is excited.
RESEARCH
12
Such information may be of importance for a better knowledge of the state of the upper atmosphere, which is substantially variable with altitude as was already noted in the U.S. experiments. A. AND E. VASSY Physique de I’Atmosph2re Facultb des Sciences de Pm-is References 1. 2. 3. 4. 5.
D. R. BATES, J. Geophys. Res. 55, 347 (1950). J. F. BEDINGERand E. MNWNG, J. Geophsy. Res. 62, 170 (1957). C. D. COOPER, E. MANRIN~ and J. F. BEDINGER J. Geophys. Res. 63,369 (1958). J. F. BEDINGER,E. R. MANRINGand S. N. GHOSH, J. Geophys. Res. 63, 19 (1958). A. and E. VASSY, C.R. Acad. Sci.. Paris 248,223s (1959).
The came&jet
hypothesis of whistler generation
(Received
10 August 1959)
The paper of H. Norinder and E. Knudsen, on “The relations between lightning discharges and whistlers”(‘), is of considerable interest from the standpoint of generation of whistlers. This part of the phenomenon has received little attention up to now, apart from the fact that the whistler is associated in time with a spheric, though it is known that not every spheric gives rise to a whistler. Only the high-energy sferics appear to be capable of generating whistlers, and of these only those with “slow tails” (which, as Norinder points out in his paper, apparently correspond to multiple discharges). The time lags involved in the “slow tails” are of the order of tens or hundreds of milliseconds, and the spheric energy peaks at around 5 kc/s, rather than near 10 kc/s as in the ordinary strong spheric. The insertion and passage of the extraordinary component of the spheric signal through the lower ionosphere, with the high values of collision frequency encountered there, appears to be the least understood part of whistler propagation. It is difficult to understand how upon occasions, long echo trains of twenty to
NOTES
thirty round trips can be achieved under such circumstances, nor how occasional amplification of whistler echoes can occur. (This phenomenon has been attributed to “polar creep”, but either polar or equatorial creeps would be inconsistent with the widely accepted current belief in ducts of field-aligned ionization.) The diurnal variation in frequency of occurrence of whistlers is also consistent with strong absorption in the lower ionosphere. It is the purpose of this letter to outline what might be termed the current-jet theory of whistler generation and to review the evidence for such a hypothesis. In this theory, the penetration of the lower ionosphere is accomplished by a high-energy current jet which is emitted from the top of the thundercloud shortly after the spheric discharge occurs. Until it enters the ionosphere, the current jet is accelerated by the electrostatic field of the thunderstorm, and also interacts with one or more of the slow-tail portions of the spheric in such a way as to either amplify the spheric signal or be accelerated by it. During the passage through the lower part of the ionosphere the current jet becomes fieldaligned and undergoes synchronous acceleration by a later spheric. During this phase, additional acceleration along the field line takes place due to the acceleration by collisions at the “magnetic mirrors” at each end of the path. Meanwhile a travelling-wave-type interaction is taking place between the high-energy electrons launched in the current jet and the electromagnetic wave of the spheric signal. These high-energy electrons are trapped in the geomagnetic field and are reflected back and forth by the “magnetic mirror” in the lower ionosphere. The result is that the thunderstorm creates its own duct of field-aligned ionization, which guides and interacts with the spheric signal either to amplify or damp it out depending upon the relative velocities of electrons and electromagnetic waves. Such accelerated current-jet electrons could also contribute in thunderstorm latitudes to the inner radiation belt, a slow tail of 1 set duration corresponding to energies (for electrons) of 20 keV or more. Let us now review the evidence for such a hypothesis. Although the existence of upward