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Monte Carlo simulation of a model ionosphere—III. Photoelectron and escape electron spectra
Journalof Atmcapherio andTerre&rMPhyaica, 1974,Vol. 56,PD.188-187.PermmonPrezd.PrIntedInNorthamIreland
SHORT PAPER Monte Carlo simulation of a model ionosphere--III. Photoelectron and escape electron spectra K. Max-Planak-Z
SCELECZEL
fiir Aeronomie, Lindau/Harz, W. Germany
(Received 24 January 1973; in revisedform 4 May 1973) &&&-Photoelectron spectra in different altitudea end escape electron apeatre are calculated from. a Monte Carlo &mnletion of a model ionosphere deearibed in two precediug papere. The reeulta are in good eoaordenee with the data obtained by other authors with experiments or doulatiom3.
of the Monte Carlo simulation of a model ionosphere concerning photoionization yields of 0, 0, and Na (SOHLEQEL, 1971; hereafter referred to ss paper I) and energy flow and energy dissipation (SCHLEGEL, 1973 ; hereafter referred to as paper II), were reported in two preceding publications. In this paper the last part of the Monte Carlo ~v~tigatio~, results of pho~elect~n spectra and escape electron spectra are presented. The results were extracted from the data material which wss stored on magnetic tape in course of the Monte Carlo model ionosphere simulation described in paper I. Com+equently the assumptions and conditions are the same as explained in that paper. The calculations are valid for a day of low a solar activity (IO July 1963, 1000 LT, Fzo., = 73 x lO-Bp of hiih (10 July 1958, 1000 LT, FXo., = 208 x 1O-*g Wm-S Hz-l). As described in paper I, all important steps in the ‘life’ of the photoelectrons travelliug through the atmosphere, were recorded on magnetic tape. For every step the energy and the location of the photoelectron wm characterized by an energy interval number and a height interval number according to Table 1. Thus the electron energy spectra could be easily obtained by counting the number of electrons having a certain set of these numbers. An additional mark indicates whether the electron was travelling upwards or downwards in the atmosphere. As an example, Fig. 1 shows the photoelectron energy spectra for three different height intervals. Since the spatial direction of the electron path was not recorded on the tape, the results of Fig. 1 represent the eIectron flux vduea integrated over the whole solid angle of 4 7r. Besides the scarcity of such data a comparison of these values with others, measured or calculated, is almost impossible beoause of the strong variation with latitude, local time and solar conditions. Nevertheless it seems that the results are within the 8ame order of magnitude &Bthose measured with Bornerocket experiments (e.g. DOERIWU ebal., 1970). More data, experimental a~ well a8 theoretical, exist for escape electron energy spectra. In this mode1 a photoelectron was called an escape electron, if its motion in the last height interval No. 29 (i.e. 900-1000 km) was still directed upwards. The escape electron energy spectrum obtained by counting these electrons is shown in Fig. 2 for the case of low solar activity. For high solar activity the valut?rrexceed those of low solar
R~ULTS
183
184
K. S~OEL Table 1. Height intervals and energy intervals ueed in the Monte Cerlo model Height intervals NO.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 16 16 17 18 19 20 21 22 23 24 25 26 27 28 29
km
<120 126-130 136-140 140-160 150-160 160-170 1’70-180 180-190 lQ@-200 200-220 220-240 240-260 260-280 280-300 300-320 320-340 340-360 360-380 380400 400-450 460-600 500-550 560-600 600-650 666-700 700-750 750-800 800-900 90&l 000
Energy intervals eV
NO.
1 2 3 4 6 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
1 G-1 *26 1.26-l ~68 1.68-2 *OO 2-00-2.51 2-61-3.16 3.16-3.98 3~98-6~01 5.01-6.31 6.31-7-95 7*95-10.0 IO+-12.6 12+16~8 16*8-20~0 [email protected] 25.1-31.6 31+-39.8 39*8-50-l 50.1-63~1 63.1-79.5 79+-100 loo-126 126-168 158-200 206-251 251-316 3X6-398 398-501 801-631 631-795 795-l 000 1000-l 260
activity by a factor 2 in the energy range of about l-30 eV, and by a factor 3 in the range of aboub 30-1000 eV. A comparison with results of other authors, both theoretical and experimental, show a good accordance in the general shape of the spectrum aa well as in the absolute values (CICERONE and BOWHILL,1971; HEIKKILA, 1970; NISBET, 1968; RAO and MAIER, 1970; YI-TGVESSON and P-s, 1968). A more convenient comparison of those results with those of other authors is possible by comparing the escape electron fluxes integrated over a certain energy range aa shown in Table 2. The values obtained with this model are 5.7 x lo* electrons/cm* set and 3-O x lo8 electrons/cm2 set for high and low solar activity, respectively. In p~ic~ar the results obtained with theoretioal models are in quite good accordance, if one takes into account the different solar EUV spectra, solar activities and solar zenith angles which are applied in the calculations. A comparison of Figs. 1 and 2 shows that there are no remarkable differences between the photoelectron energy spectrum in the height range of 400-450 km
Monte t!ebrlo simulation of B model ionosphere-111
ELECTRON ENERGY 6-d Fig. 1. Differential energy spectra of photoelectrons for different height intervals and low solar activity. ‘125 km’ stands for height interval NO. 2 (120-130 km). ‘210 km’ stands for height interval No. 10 (200-220 km). ‘425 km stands for height interval No. 20 (400450 km). ,oeE-..
.--
ESCAPE
-
ELECTRON
___--
ENERGY
[ev]
Fig. 2. Difkential energy spectra of photoelectrons escaping from the ionosphere (Error bars indicate the statistical error of the in the case of low solar activity. Monte Carlo calc~ation.)
186
180
K. Table
2. Comparieon
of different escape electron flux calculations and measurementi.
Integrated escape electron flux Energy range Solar aotivityF1,., (amma a~-‘) (lo-= Wrnms Hz-l) (eV)
Author CICERONE and BO~EILL (1971) HE~KKILA (1970)
NIBBET (1968)
RAO
itkE.LEGEL
and MAIEIS
7.1 x 108 2.6 x 108
Solar zenith angle
O-30 O-30
226 144
O0 63’
Monte Carlo calculation8
8-100
133
4o”
ISIS-I experimental data (particle epectrometer)
7.3 x 108 6.2 x 108
O-40 O-40
226 76
O0
Calculations from traneport equationa
1.6 x 108
>3*7
81
86O
Explorer 31 experimental data (ret. pot. analyzer)
l-32 1-32
208 73
29.4’ 29.4’
Monte Carlo
7+-17.2* 7*1-22.48 7+-17.2*
166 146 141
61’= 46’ 72’
Radar Thomson scatter stud&
7 x 108
O0
(1970)
Sol!U.JZQEL (this work) YNIXESSON PERKINS (1968)
and
Remarka
6.7 x l@ 3.0 x 108 3 x 108 9 x 108 4 x 108
calculation8
(* These energies are not the total electron energies but only the energy of the vertical component of the particle’s motion.)
and the escape electron spectrum. Since about 400,000 primary photoelectrons with an energy between 12-l and 1240 eV were traced through the atmosphere, the statistical errors of the Monte Carlo calculations are relatively low. They are about 6-10 per cent near the maximum of the energy spectra and increase up to 60 per cent with increasing energy. An error in the absolute values of the energy spectra may be caused by the linear scaling process, based on the sunspot number which was applied to obtain the high solar activity EUV spectrum from the low solar activity EW spectrum. Although this procedure is quite doubtful, it was applied because of the lack of data at the time of the beginning of this work. The other limitations due to imperfections of the model and uncertainties of the input parameters are discussed in paper II. With the hope of reducing these uncertainties and of providing more experimental data to compare with the theoretical results discussed here, the author is participating in a sounding rocket campaign in the early spring of 1973. The experiments on that rocket measure simultaneously not only the electron spectra but also all the important input parameters of the model, such as solar EUV radiation, atmospheric composition and electron density. If all the experiments work satisfactory this will be a step towards a more comprehensive understanding of the various processes taking place in the atmosphere.
Monte C&lo simul8tion of a model ionosphe_IU
187
Acknowledgemen&-This paper is published by permissionof Prof. DIEHINQER,the director of the Max-Planck-1nBtitut fti Aeronomie. REFERENCES CICEBONER. J. and Born S. A. DOERXNOJ. P., FASTIE W. G. end FELDMANP. D. HJXKK- W. J. NISBET J. 5. RAO B. C. N. and MAIER E. J. R. 8-GEL K. SoE.LEoELK. YNQVESSONK. 0. and PERKINS F. E.
1971 1970
J. gwphyye.Rea. 76, 8299. J. geophys. Rea. 76, 4787.
1970 1968 1970 1971 1973 1968
J. geophys. Rea. 75, 4877. J. otnwe. ten-. Whys. 30, 1267. J. geophys. Rec. 75, 816. J. d??W8.terr. Phye. B, 1923. J. d??lO8. tew. Phy8. a, 416. J. geophy8. Rea. 73, 97.
SHORT PAPER Monte Carlo simulation of a model ionosphere--III. Photoelectron and escape electron spectra K. Max-Planak-Z
SCELECZEL
fiir Aeronomie, Lindau/Harz, W. Germany
(Received 24 January 1973; in revisedform 4 May 1973) &&&-Photoelectron spectra in different altitudea end escape electron apeatre are calculated from. a Monte Carlo &mnletion of a model ionosphere deearibed in two precediug papere. The reeulta are in good eoaordenee with the data obtained by other authors with experiments or doulatiom3.
of the Monte Carlo simulation of a model ionosphere concerning photoionization yields of 0, 0, and Na (SOHLEQEL, 1971; hereafter referred to ss paper I) and energy flow and energy dissipation (SCHLEGEL, 1973 ; hereafter referred to as paper II), were reported in two preceding publications. In this paper the last part of the Monte Carlo ~v~tigatio~, results of pho~elect~n spectra and escape electron spectra are presented. The results were extracted from the data material which wss stored on magnetic tape in course of the Monte Carlo model ionosphere simulation described in paper I. Com+equently the assumptions and conditions are the same as explained in that paper. The calculations are valid for a day of low a solar activity (IO July 1963, 1000 LT, Fzo., = 73 x lO-Bp of hiih (10 July 1958, 1000 LT, FXo., = 208 x 1O-*g Wm-S Hz-l). As described in paper I, all important steps in the ‘life’ of the photoelectrons travelliug through the atmosphere, were recorded on magnetic tape. For every step the energy and the location of the photoelectron wm characterized by an energy interval number and a height interval number according to Table 1. Thus the electron energy spectra could be easily obtained by counting the number of electrons having a certain set of these numbers. An additional mark indicates whether the electron was travelling upwards or downwards in the atmosphere. As an example, Fig. 1 shows the photoelectron energy spectra for three different height intervals. Since the spatial direction of the electron path was not recorded on the tape, the results of Fig. 1 represent the eIectron flux vduea integrated over the whole solid angle of 4 7r. Besides the scarcity of such data a comparison of these values with others, measured or calculated, is almost impossible beoause of the strong variation with latitude, local time and solar conditions. Nevertheless it seems that the results are within the 8ame order of magnitude &Bthose measured with Bornerocket experiments (e.g. DOERIWU ebal., 1970). More data, experimental a~ well a8 theoretical, exist for escape electron energy spectra. In this mode1 a photoelectron was called an escape electron, if its motion in the last height interval No. 29 (i.e. 900-1000 km) was still directed upwards. The escape electron energy spectrum obtained by counting these electrons is shown in Fig. 2 for the case of low solar activity. For high solar activity the valut?rrexceed those of low solar
R~ULTS
183
184
K. S~OEL Table 1. Height intervals and energy intervals ueed in the Monte Cerlo model Height intervals NO.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 16 16 17 18 19 20 21 22 23 24 25 26 27 28 29
km
<120 126-130 136-140 140-160 150-160 160-170 1’70-180 180-190 lQ@-200 200-220 220-240 240-260 260-280 280-300 300-320 320-340 340-360 360-380 380400 400-450 460-600 500-550 560-600 600-650 666-700 700-750 750-800 800-900 90&l 000
Energy intervals eV
NO.
1 2 3 4 6 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
1 G-1 *26 1.26-l ~68 1.68-2 *OO 2-00-2.51 2-61-3.16 3.16-3.98 3~98-6~01 5.01-6.31 6.31-7-95 7*95-10.0 IO+-12.6 12+16~8 16*8-20~0 [email protected] 25.1-31.6 31+-39.8 39*8-50-l 50.1-63~1 63.1-79.5 79+-100 loo-126 126-168 158-200 206-251 251-316 3X6-398 398-501 801-631 631-795 795-l 000 1000-l 260
activity by a factor 2 in the energy range of about l-30 eV, and by a factor 3 in the range of aboub 30-1000 eV. A comparison with results of other authors, both theoretical and experimental, show a good accordance in the general shape of the spectrum aa well as in the absolute values (CICERONE and BOWHILL,1971; HEIKKILA, 1970; NISBET, 1968; RAO and MAIER, 1970; YI-TGVESSON and P-s, 1968). A more convenient comparison of those results with those of other authors is possible by comparing the escape electron fluxes integrated over a certain energy range aa shown in Table 2. The values obtained with this model are 5.7 x lo* electrons/cm* set and 3-O x lo8 electrons/cm2 set for high and low solar activity, respectively. In p~ic~ar the results obtained with theoretioal models are in quite good accordance, if one takes into account the different solar EUV spectra, solar activities and solar zenith angles which are applied in the calculations. A comparison of Figs. 1 and 2 shows that there are no remarkable differences between the photoelectron energy spectrum in the height range of 400-450 km
Monte t!ebrlo simulation of B model ionosphere-111
ELECTRON ENERGY 6-d Fig. 1. Differential energy spectra of photoelectrons for different height intervals and low solar activity. ‘125 km’ stands for height interval NO. 2 (120-130 km). ‘210 km’ stands for height interval No. 10 (200-220 km). ‘425 km stands for height interval No. 20 (400450 km). ,oeE-..
.--
ESCAPE
-
ELECTRON
___--
ENERGY
[ev]
Fig. 2. Difkential energy spectra of photoelectrons escaping from the ionosphere (Error bars indicate the statistical error of the in the case of low solar activity. Monte Carlo calc~ation.)
186
180
K. Table
2. Comparieon
of different escape electron flux calculations and measurementi.
Integrated escape electron flux Energy range Solar aotivityF1,., (amma a~-‘) (lo-= Wrnms Hz-l) (eV)
Author CICERONE and BO~EILL (1971) HE~KKILA (1970)
NIBBET (1968)
RAO
itkE.LEGEL
and MAIEIS
7.1 x 108 2.6 x 108
Solar zenith angle
O-30 O-30
226 144
O0 63’
Monte Carlo calculation8
8-100
133
4o”
ISIS-I experimental data (particle epectrometer)
7.3 x 108 6.2 x 108
O-40 O-40
226 76
O0
Calculations from traneport equationa
1.6 x 108
>3*7
81
86O
Explorer 31 experimental data (ret. pot. analyzer)
l-32 1-32
208 73
29.4’ 29.4’
Monte Carlo
7+-17.2* 7*1-22.48 7+-17.2*
166 146 141
61’= 46’ 72’
Radar Thomson scatter stud&
7 x 108
O0
(1970)
Sol!U.JZQEL (this work) YNIXESSON PERKINS (1968)
and
Remarka
6.7 x l@ 3.0 x 108 3 x 108 9 x 108 4 x 108
calculation8
(* These energies are not the total electron energies but only the energy of the vertical component of the particle’s motion.)
and the escape electron spectrum. Since about 400,000 primary photoelectrons with an energy between 12-l and 1240 eV were traced through the atmosphere, the statistical errors of the Monte Carlo calculations are relatively low. They are about 6-10 per cent near the maximum of the energy spectra and increase up to 60 per cent with increasing energy. An error in the absolute values of the energy spectra may be caused by the linear scaling process, based on the sunspot number which was applied to obtain the high solar activity EUV spectrum from the low solar activity EW spectrum. Although this procedure is quite doubtful, it was applied because of the lack of data at the time of the beginning of this work. The other limitations due to imperfections of the model and uncertainties of the input parameters are discussed in paper II. With the hope of reducing these uncertainties and of providing more experimental data to compare with the theoretical results discussed here, the author is participating in a sounding rocket campaign in the early spring of 1973. The experiments on that rocket measure simultaneously not only the electron spectra but also all the important input parameters of the model, such as solar EUV radiation, atmospheric composition and electron density. If all the experiments work satisfactory this will be a step towards a more comprehensive understanding of the various processes taking place in the atmosphere.
Monte C&lo simul8tion of a model ionosphe_IU
187
Acknowledgemen&-This paper is published by permissionof Prof. DIEHINQER,the director of the Max-Planck-1nBtitut fti Aeronomie. REFERENCES CICEBONER. J. and Born S. A. DOERXNOJ. P., FASTIE W. G. end FELDMANP. D. HJXKK- W. J. NISBET J. 5. RAO B. C. N. and MAIER E. J. R. 8-GEL K. SoE.LEoELK. YNQVESSONK. 0. and PERKINS F. E.
1971 1970
J. gwphyye.Rea. 76, 8299. J. geophys. Rea. 76, 4787.
1970 1968 1970 1971 1973 1968
J. geophys. Rea. 75, 4877. J. otnwe. ten-. Whys. 30, 1267. J. geophys. Rec. 75, 816. J. d??W8.terr. Phye. B, 1923. J. d??lO8. tew. Phy8. a, 416. J. geophy8. Rea. 73, 97.