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On the use of a wide-band filter for atmospheric ozone measurements
Research notes
1129
REFERENCES BREKHOVSKIKH
L.M.
1960
BREMMERH.
1958
BUDDENKG.
1961
BURMAN R.andGou~~ R.N. F~RSTERLING K.and W&TER H.O. GALEJS J.
1963 1951 1961
GOULD R.N.~~~BuRMANR. HARRIS F.B. and TANNER R.L. KAMKEE.
1964 1962 1948
RAYLEIGH LORD.
1899
RICHARDS P.I.
1959
W_4IT J. R.
1962
Waves in Layered Media. Academic Press, London and New York. Handbuch der Physik, vol. 16. SpringerVerlag, Berlin. Radio Waves in the Ionosphere. Cambridge University Press, London. J. Atmosph. Terr. Phys. 25, 543. J. Atmosph. Terr. Phys. 2, 22. IRE Trans. on Antennas and Propagation AP-9, 554. J. Atmosph. Terr. Phys. 26, 335. J. Res. N.B.S. 66D, 463. D
Journal of Atmospheric and Terrestrial Physics, 1964, Vol. 26, pp.llZQ-1133.
PergamonPressLtd. Printedin NorthernIreland
On the use of a wide-band filter for atmospheric ozone measurements (Received
12 May
1964)
A calculation has been made to determine the effective transmission of an ultraviolet filter for use in measurements of atmospheric ozone. The effective transmission is a function of height and solar zenith angle; it is dependent also on the solar intensity distribution and on absorption coefficients over the filter range. An experiment is being prepared in which it is planned to measure by optical means the A combination of filter and photocell will vertical distribution of ozone in the atmosphere. monitor from a rocket the intensity of ultraviolet radiation in a select,ed region of moderate ozone absorption. Using the known ozone absorption coefficients, cc, t,he quantity of the gas along the line of sight from the rocket position to the sun can then be deduced from the Lambert Law relation, 1 = 10e-aZ. Here it: is the ozone amount to be determined and I is the intensity of the solar radiation at a given wavelength which has an incident intensity of I, outside the atmosphere. Corrections for rocket aspect, for scattering and for solar zenith angle will be necessary; and the part of the spectrum chosen for monitoring must not only be within the Hartley ozone band but should also be well removed from regions of significant absorption by other atmospheric constituents. Ideally such a measurement would be most accurate if made as nearly as possible at one wavelength only, for which the one value of absorption coefficient would be appropriate. However, in view of the finite width of the transmission region of a practical filter, it is necessary to consider also the variation in absorption over that range. The characteristic of the filter chosen for the initial measurements is shown in Fig. 1, where an indication of the dependence of ozone absorption on wavelength is also given. It is seen that the filter covers an appreciable part of the higher wavelength side of the ozone band and is therefore referred to in this context as a wide-band filter.
Research notes
1130
120 0 ifi x
100 -
/ /
80 -
T
- 0.15
/’
/
E “60-
-0.10
L
/ /
;
/
/
/
’
40-
- 05
20 0
’ 2300
I 2400
2500
2600
2700
2600
‘I_ 2900
+ 3000
0
Wavelength,% Fig. 1 The object of the present calculations was to determine the contributions to the overall filter transmission from radiation at the various wavelengths; and to illustrate the way in which the relative magnitude of such contributions can be expected to change at different altitudes of measurement in the atmosphere. That is, if a certain response is recorded at a given altitude, to what radiation distribution of the filtered region is this to be attributed-and hence what are the appropriate absorption coefficients to be used in calculation of the ozone amount? Data used. For purposes of the calculation, the ozonosphere was divided into twelve layers. These, together with the assumed ozone distribution, are shown in Table 1. Up to 47.8 km the values are those averaged from an Umkehr measurement at 46”N reported by DUTSCR (1960). For the rest of the model, it is supposed that the ozone content decreases linearly from 50 km to reach a value of zero at 80 km. Values for the unattenuated (or 80 km) solar radiation intensity from 2900 d to 2630 A are taken from an article by WILSON et al. (1954). The few lower wavelength values used are those of DETWILER et al. (1961). Ozone absorption coefficients used are those of VIGROUX (1952). Temperature corrections, which are small in the main part of the filter band, were not included. Results of the calculation. A determination was first made of the depth of penetration into the assumed ozonosphere by radiation of various wavelengths incident at four different solar zenith angles. These results are given in Figs. 2 to 5 which show as a function of wavelength the intensity at a given altitude relative to that at 80 km. The whole set of curves is seen to be Table 1. Model ozonosphere adopted Layer
Altitude range (km)
Ozone density (cm 103/km)
Total ozone path (cm lo3 for x = 0”)
1 2 3 4 5 6 7 8 9 10 11 12
80-70 70-60 60-47.8 47.8-42.6 42.6-37.5 37.5-32.7 32.7-28.2 28.2-23.7 23.7-19.2 19.2-14.8 14.8-10.3 10.3-O
0.15 0.5 0.8 1.6 3.2 5.4 9.3 14.7 14.6 8.4 3.8 1.9
1.5 6.5 16.3 24.6 40.9 66.8 108.6 174.7 240.4 277.4 294.5 314.1
1131
Research notes
0.6-
2400
2500
2600
2700
2800
Fig. 2
Wavelength,
i
Fig. 3 80 km.
I.0
0.8 -
0 2400
2500 Wavelength,
Fig. 4
2900
i
Wavelength,
i
3000
Research
1132
notes
steadily displaced towards higher wavelengths as the solar irradiation becomes more oblique. It is interesting to note that the small amount of ozone assumed above 50 km is sufficient to For x = 90”, radiaabsorb virtually all the radiation below 2700 A, even for normal incidence. tion of wavelength as high as 2900 A is unable to penetrate below this altitude.
I.0,
80 km
Wavelength,
Fig. Table
2. Relative
i
5
transmissions
Wavelength interval
80 km
60 km
2640 2700 2750 2800 2850
0.075 0.069 0.023 0.004 0.002
0.054 0.068 0.032 0.008 0.005
+ f f * *
5 if 5A 5A 5A 5A
for x = 0”
Height 42.6 km 0 0.024 0.036 0.024 0.036
37.5 km 0 0 0 0 0.071
For given 10 A intervals, these relative intensities were then multiplied in turn by the absolute solar intensity and by the transmission of the particular filter used. The results illustrate that the greater the depth to which the radiation must penetrate into the ozone layer, the more are the shorter wavelengths subjected to greater attenuation than the higher wavelengths. The effective transmission of the filter is thus moved towards the higher wavelength region of the band. A few typical results (for x = 0”) are listed in Table 2. The change is more rapid with altitude at higher solar zenith angles. The influence of the magnitude of the incident solar radiation is also reflected. Especially apparent is a minimum in the effective transmission near 2800 A which corresponds with a low value of 0.8 ,uW cmP2 ,kml for this interval. Physics Department University of Adelaide South Australia Now at:
Physics Department University of Queensland St. Lucia Brisbane, Queensland Australia
J. R.
CATCHPOOLE
Research
1133
notes
REFERENCES BREWERA. W. and DUTSCHH. U. DETUXLERC. R., GARRETTD. L., PURCELLJ. D. and TOUSEYR. VIGROUXE. WILSONN. L., TOUSEYR., PURCELLJ. D. and JOHNSONF. S.
1960 1961
Ann. Ann.
1952
C.R. Acad. Sci. Paris. 234 (2), 2351. Astr. J. 119,590-612.
1954
Giophy/s. 16, 2, 196. Gkophys. 17,263-272.
Journal ofkmosghericand TerrestrialPhysics, 1964,Vol.26,pp.1133-1138. Pergamon Press Ltd.Printed inNorthern Ireland
Electric fields in the magnetosphere associated with daily geomagnetic variations and their effects on trapped particles (Received
27 April
1964)
IT IS generally accepted now that the lines of geomagnetic force in the magnetosphere are highly conductive electrically and can be regarded as equipotentials. If so, it seems to be possible that electrostatic fields associated with the dynamo currents in the ionosphere propagate into the magnetosphere along the lines of force without significant attenuation, and have an important effect on geomagnetically trapped particles, as has been suggested by DUNGEY (1960). The purpose of this report is to examine in some detail such a possibility on the basis of geomagnetic data. A worldwide distribution of the electrostatic field-E in the ionospheric E-region has been obtained by MAEDA (1955, 1959) for quiet and disturbed days from geomagnetic data during
the Second Polar Year, 1932-1933.
His result may be expressed in a potential form as follows:
‘?(a, 4, ,I) = a22 (Anm cos ma + Bnm sin ml)Pnm(cos 9) nm
(1)
where
P,“(cos
Y a 4 f. #)
= = = = =
electric potential, radius of the ionospheric current colatitude, longitude (or local time reckoned Schmidt’s functions.
Numerical values of typical are shown in Table 1. Table
harmonic
coefficients,
A,”
sheet (=
6.48 x lo* cm),
in angular measure from midnight),
and B nm, for quiet days of mean solstice
1. Spherical harmonic coefficients of the electrostatic potential in the ionospheric E-region (e.m.u.) m
n
1
1
2
3 5 7 2 4 6 8
4%” 613.3 632.7 -123.3 106.4 - 34.0 -222.9 -94.8 27.5
BVlrn 307.4 - -267.5 49.6 11.5 56.6 62.4 13.5 32.2
1129
REFERENCES BREKHOVSKIKH
L.M.
1960
BREMMERH.
1958
BUDDENKG.
1961
BURMAN R.andGou~~ R.N. F~RSTERLING K.and W&TER H.O. GALEJS J.
1963 1951 1961
GOULD R.N.~~~BuRMANR. HARRIS F.B. and TANNER R.L. KAMKEE.
1964 1962 1948
RAYLEIGH LORD.
1899
RICHARDS P.I.
1959
W_4IT J. R.
1962
Waves in Layered Media. Academic Press, London and New York. Handbuch der Physik, vol. 16. SpringerVerlag, Berlin. Radio Waves in the Ionosphere. Cambridge University Press, London. J. Atmosph. Terr. Phys. 25, 543. J. Atmosph. Terr. Phys. 2, 22. IRE Trans. on Antennas and Propagation AP-9, 554. J. Atmosph. Terr. Phys. 26, 335. J. Res. N.B.S. 66D, 463. D
Journal of Atmospheric and Terrestrial Physics, 1964, Vol. 26, pp.llZQ-1133.
PergamonPressLtd. Printedin NorthernIreland
On the use of a wide-band filter for atmospheric ozone measurements (Received
12 May
1964)
A calculation has been made to determine the effective transmission of an ultraviolet filter for use in measurements of atmospheric ozone. The effective transmission is a function of height and solar zenith angle; it is dependent also on the solar intensity distribution and on absorption coefficients over the filter range. An experiment is being prepared in which it is planned to measure by optical means the A combination of filter and photocell will vertical distribution of ozone in the atmosphere. monitor from a rocket the intensity of ultraviolet radiation in a select,ed region of moderate ozone absorption. Using the known ozone absorption coefficients, cc, t,he quantity of the gas along the line of sight from the rocket position to the sun can then be deduced from the Lambert Law relation, 1 = 10e-aZ. Here it: is the ozone amount to be determined and I is the intensity of the solar radiation at a given wavelength which has an incident intensity of I, outside the atmosphere. Corrections for rocket aspect, for scattering and for solar zenith angle will be necessary; and the part of the spectrum chosen for monitoring must not only be within the Hartley ozone band but should also be well removed from regions of significant absorption by other atmospheric constituents. Ideally such a measurement would be most accurate if made as nearly as possible at one wavelength only, for which the one value of absorption coefficient would be appropriate. However, in view of the finite width of the transmission region of a practical filter, it is necessary to consider also the variation in absorption over that range. The characteristic of the filter chosen for the initial measurements is shown in Fig. 1, where an indication of the dependence of ozone absorption on wavelength is also given. It is seen that the filter covers an appreciable part of the higher wavelength side of the ozone band and is therefore referred to in this context as a wide-band filter.
Research notes
1130
120 0 ifi x
100 -
/ /
80 -
T
- 0.15
/’
/
E “60-
-0.10
L
/ /
;
/
/
/
’
40-
- 05
20 0
’ 2300
I 2400
2500
2600
2700
2600
‘I_ 2900
+ 3000
0
Wavelength,% Fig. 1 The object of the present calculations was to determine the contributions to the overall filter transmission from radiation at the various wavelengths; and to illustrate the way in which the relative magnitude of such contributions can be expected to change at different altitudes of measurement in the atmosphere. That is, if a certain response is recorded at a given altitude, to what radiation distribution of the filtered region is this to be attributed-and hence what are the appropriate absorption coefficients to be used in calculation of the ozone amount? Data used. For purposes of the calculation, the ozonosphere was divided into twelve layers. These, together with the assumed ozone distribution, are shown in Table 1. Up to 47.8 km the values are those averaged from an Umkehr measurement at 46”N reported by DUTSCR (1960). For the rest of the model, it is supposed that the ozone content decreases linearly from 50 km to reach a value of zero at 80 km. Values for the unattenuated (or 80 km) solar radiation intensity from 2900 d to 2630 A are taken from an article by WILSON et al. (1954). The few lower wavelength values used are those of DETWILER et al. (1961). Ozone absorption coefficients used are those of VIGROUX (1952). Temperature corrections, which are small in the main part of the filter band, were not included. Results of the calculation. A determination was first made of the depth of penetration into the assumed ozonosphere by radiation of various wavelengths incident at four different solar zenith angles. These results are given in Figs. 2 to 5 which show as a function of wavelength the intensity at a given altitude relative to that at 80 km. The whole set of curves is seen to be Table 1. Model ozonosphere adopted Layer
Altitude range (km)
Ozone density (cm 103/km)
Total ozone path (cm lo3 for x = 0”)
1 2 3 4 5 6 7 8 9 10 11 12
80-70 70-60 60-47.8 47.8-42.6 42.6-37.5 37.5-32.7 32.7-28.2 28.2-23.7 23.7-19.2 19.2-14.8 14.8-10.3 10.3-O
0.15 0.5 0.8 1.6 3.2 5.4 9.3 14.7 14.6 8.4 3.8 1.9
1.5 6.5 16.3 24.6 40.9 66.8 108.6 174.7 240.4 277.4 294.5 314.1
1131
Research notes
0.6-
2400
2500
2600
2700
2800
Fig. 2
Wavelength,
i
Fig. 3 80 km.
I.0
0.8 -
0 2400
2500 Wavelength,
Fig. 4
2900
i
Wavelength,
i
3000
Research
1132
notes
steadily displaced towards higher wavelengths as the solar irradiation becomes more oblique. It is interesting to note that the small amount of ozone assumed above 50 km is sufficient to For x = 90”, radiaabsorb virtually all the radiation below 2700 A, even for normal incidence. tion of wavelength as high as 2900 A is unable to penetrate below this altitude.
I.0,
80 km
Wavelength,
Fig. Table
2. Relative
i
5
transmissions
Wavelength interval
80 km
60 km
2640 2700 2750 2800 2850
0.075 0.069 0.023 0.004 0.002
0.054 0.068 0.032 0.008 0.005
+ f f * *
5 if 5A 5A 5A 5A
for x = 0”
Height 42.6 km 0 0.024 0.036 0.024 0.036
37.5 km 0 0 0 0 0.071
For given 10 A intervals, these relative intensities were then multiplied in turn by the absolute solar intensity and by the transmission of the particular filter used. The results illustrate that the greater the depth to which the radiation must penetrate into the ozone layer, the more are the shorter wavelengths subjected to greater attenuation than the higher wavelengths. The effective transmission of the filter is thus moved towards the higher wavelength region of the band. A few typical results (for x = 0”) are listed in Table 2. The change is more rapid with altitude at higher solar zenith angles. The influence of the magnitude of the incident solar radiation is also reflected. Especially apparent is a minimum in the effective transmission near 2800 A which corresponds with a low value of 0.8 ,uW cmP2 ,kml for this interval. Physics Department University of Adelaide South Australia Now at:
Physics Department University of Queensland St. Lucia Brisbane, Queensland Australia
J. R.
CATCHPOOLE
Research
1133
notes
REFERENCES BREWERA. W. and DUTSCHH. U. DETUXLERC. R., GARRETTD. L., PURCELLJ. D. and TOUSEYR. VIGROUXE. WILSONN. L., TOUSEYR., PURCELLJ. D. and JOHNSONF. S.
1960 1961
Ann. Ann.
1952
C.R. Acad. Sci. Paris. 234 (2), 2351. Astr. J. 119,590-612.
1954
Giophy/s. 16, 2, 196. Gkophys. 17,263-272.
Journal ofkmosghericand TerrestrialPhysics, 1964,Vol.26,pp.1133-1138. Pergamon Press Ltd.Printed inNorthern Ireland
Electric fields in the magnetosphere associated with daily geomagnetic variations and their effects on trapped particles (Received
27 April
1964)
IT IS generally accepted now that the lines of geomagnetic force in the magnetosphere are highly conductive electrically and can be regarded as equipotentials. If so, it seems to be possible that electrostatic fields associated with the dynamo currents in the ionosphere propagate into the magnetosphere along the lines of force without significant attenuation, and have an important effect on geomagnetically trapped particles, as has been suggested by DUNGEY (1960). The purpose of this report is to examine in some detail such a possibility on the basis of geomagnetic data. A worldwide distribution of the electrostatic field-E in the ionospheric E-region has been obtained by MAEDA (1955, 1959) for quiet and disturbed days from geomagnetic data during
the Second Polar Year, 1932-1933.
His result may be expressed in a potential form as follows:
‘?(a, 4, ,I) = a22 (Anm cos ma + Bnm sin ml)Pnm(cos 9) nm
(1)
where
P,“(cos
Y a 4 f. #)
= = = = =
electric potential, radius of the ionospheric current colatitude, longitude (or local time reckoned Schmidt’s functions.
Numerical values of typical are shown in Table 1. Table
harmonic
coefficients,
A,”
sheet (=
6.48 x lo* cm),
in angular measure from midnight),
and B nm, for quiet days of mean solstice
1. Spherical harmonic coefficients of the electrostatic potential in the ionospheric E-region (e.m.u.) m
n
1
1
2
3 5 7 2 4 6 8
4%” 613.3 632.7 -123.3 106.4 - 34.0 -222.9 -94.8 27.5
BVlrn 307.4 - -267.5 49.6 11.5 56.6 62.4 13.5 32.2