THE UNIVERSITY OF MICHIGAN COLLEGE OF ENGINEERING Department of Aerospace Engineering High Altitude Engineering Laboratory Scientific Report IONOSPHERIC CHARACTERISTICS FROM ALTITUDE VARIATIONS OF POSITIVE ION DENSITIES AT NIGHT S. N. Ghosh ORA Project 05627 under contract with: NATIONAL AERONAUTICS AND SPACE ADMINISTRATION CONTRACT NO. NASr-54(05) WASHINGTON, D. C. administered through: OFFICE OF RESEARCH ADMINISTRATION ANN ARBOR March 1968

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Table of Contents Page List of Tables v List of Figures vii Abstract ix 1. Introduction 1 2. Altitude Distributions of Positive Ions at Different Times of the Day. 2 3. Nighttime Ionic Processes. 4 4. Calculated Rate Coefficients of Ionospheric Reactions. 6 5. Lifetimes and Effective Recombination Coefficients of Positive Ions at Night. 8 6. Conclusions 8 References 11 iii

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List of Tables Table Page 1. Characteristics of Positive Ion Distributions for 100-280 Km at Different Times of the Day. 3 2. Nighttime Ionic Processes for 100-280 Km. 5 3. Effective Recombination Coefficients and Lifetimes of Positive Ions at Night. 7 v

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List of Figures Page Fig. 1. Day and nighttime altitude variations of positive ions during the last solar minimum activity period averaged from observations made by different investigators. 12 Fig. 2. Production and loss rates of O ions at night. For comparison the total production and loss rates of O+ during daytime are drawn. 13 Fig. 3. Production and loss rates of 02 ions at night. The total production and loss rates of O0 during daytime are also drawn. 14 Fig. 4. Loss rates of N2 ions at night. For comparison the total 2 + production and loss rates of N2 during daytime are drawn. Fig. 5. Production and loss rates of NO ions at night. The total production and loss rates of NO during daytime are also drawn. 16 Fig. 6. Production and loss rates of N ions at night. For comparison the total production and loss rates of N+ during daytime are drawn. 17 vii

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Abstract Altitude variations of different types of positive ions in the ionosphere at night obtained from rocket-borne experiments, have been utilized to obtain ionospheric characteristics. Major nighttime ionic processes and rate coefficients of certain reactions involving positive ion - neutral atoms or molecules are obtained. Lifetimes and effective recombination coefficients of positive ions at night are also obtained. It was further shown that at night the ionosphere is not in equilibrium. Only at localized regions, there is equilibrium between the production and loss rates. ix

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1. Introduction In a previous report (Ghosh, 1967), the ionospheric characteristics from altitude variations of positive ion densities during daytime obtained from rocket-borne experiments, have been obtained. At night also, the altitude distributions of ion densities were obtained. Although ion densities decrease to a great extent at night, and that the number of nocturnal rocket firings are comparatively few, certain ionospheric characteristics can be drawn from the ion distributions at night. These are presented in this report. 1

2. Altitude Distributions of Positive Ions at Different Times of the Day. Noon and nighttime altitude distributions of ionic densities, as obtained from rocket-borne mass spectrometers during period of solar minimum activity (Holmes et al., 1965), are given in Fig. 1. Dashed curves are extrapolated. Important features of such distributions are given in Table 1. 2

Table 1. Characteristics of Positive Ion Distributions for 100-280 Km at Different Times of the Day. Noon Night Morning +~~~~~~~~~~ 1. At lower altitudes (around 140 km), 1. O0 is the predominant ion at 1. Percentagewise, different types the concentrations of NO and O0, higher altitudes and then rapidly of ions in the morning are the which are the major ions, are falls with the decreasing altitude, same as at noontime except nearly equal. so much so, that at 200 km, its that Og density is small at density becomes very small. lower altitudes. At these alti2. Above 180 km, 0 becomes the tudes, NO is the predominant predominant ion. 2. Around 240 km, Og and NO ion. densities become equal and 3. During daytime, the concentrations same as for daytime. There 2. Ng and N concentrations hardly + +2 of N2 and N hardly become greater is no diurnal density variations become greater than 1% of the ^ ~than 1% of the total ion content, of these ions at these altitudes. total ion content. although N~ production rate is high. 2 + (Istomin, 1963). 3. 02 percentage is small at lower altitudes. 4. N and N concentrations hardly become greater than 1%o of the total ion content.

3. Nighttime Ionic Processes In Figs. 2-6, the production and loss rates of 0, 0+ N+, NO+ 2' 2J and N ions at night for the altitude range 100-280 km are drawn. Due to the non-availability of data, these rates for N2 and 0 ions are calculated only for a small altitude range. It is desirable to calculate the loss and production rates of different species of ions for the whole altitude range as the importance of reactions vary with altitude. To calculate these rates at night, ion densities as obtained from rocket-borne mass spectrometers given in Fig. 1 are utilized. 0, 02 and N2 densities are obtained from CIRA 1965 for the mean solar condition, N and NO densities are obtained by Ghosh (1968). The rate coefficients and their temperature variations are the same as given in (Ghosh, 1967). Assuming the equilibrium of N+ ion at night by the following reactions N2 + N —-N + N N+ 02 + N NO0 + O N ion densities are obtained. It is seen from Figs. 2-6 that at night, the ionosphere is not in equilibrium. Only at localized regions, there is equilibrium between the production and loss rates. For 0, the equilibrium is around 220 km, for 02 around 240 km, for NO+ at 120 km. For N2, there is no production mechanism at night. For the greater part of the above altitude range, 02 loss rates are higher than the production rate and vice versa for NO. Major nighttime ionic processes and certain characteristics of nighttime processes between 100-280 km are shown in Table 2. 4

Table 2 NIGHT TIME IONIC PROCESSES FOR 100-280 Km Ion Major Production Process Major Loss Process Remarks 0 N +Oi O2+N (1) O0+N2 - NO ++N Due to the high loss rates of these reactions, 2i 2i 2 (2) O++NO-4 O0+N 0 density falls rapidly with decreasing alti(3) 0 +O0-+ 02+0 tudes. Around 220 km, the total loss and (arranged in order of production rates become equal. importance) O 0 O+NO-) 0+N (1) 0+N-4 NO +O Around 240 km, the total loss and production 2 2 2 0+0-> 0O+O (2) 02+N2.4 NO +NO rates of O0 become equal. At other altitudes 2 2 2 2 2 2 (rapidly falling rate (3) 0+NO-* NO +02 loss rates are higher and hence ions form a from 230 to 200 km) ^ ^cr~~~~~~~~~~+ small proportion of the total ion content at night. + -+ ANO+N N+ ~nil (1) N++O"-, O N2nil (1) N+O + Since there is no production mechanism and the loss rate being high, [Njlat night at 220 km is about two orders lower than that during daytime. NO O0+N2- NO +NO NO +e-e N+O Large production rate compared to the loss rate. O+NO2 * NO +02 Only one loss process. This accounts for the + + ~~~~~~~~~~~~~~~~~~~~~+ O0+N-* NO +O comparatively large NO concentration at night. N +0- NO++N O+N2- NO +N (important for ~+ 2^ 280-220 kmn) + +N N+N-N+N 2 N N +N-, N +N N +0O N N density is calculated from the equilibrium 2 2 ^ NOO++ between these reactions. The rates for both these reactions are small.

4. Calculated Rate Codfficients of Ionospheric Reactions The calculated rate coefficients of certain reactions between ions and neutral particles in the ionosphere as obtained from the altitude distributions of positive ions are given below. Comparison with the available data shows that there is a fair agreement between calculated and observed rate coefficients except for the reaction O +NO-)O+N Reaction Altitude Assumption made Calculated rate coeff. Observed rate coeff. 3 -1 3 -1 (cm sec ) (cm sec N2 ++0- 0+N2 130 Km Equilibrium of 0+, by 2. 2x10 11 6x10 for daytime this reaction and losses ionosphere (Donahue, 1966) by the three major loss processes given in Sec. 3. + + 0 (1)1. 4x109** -11 (1)O +NO-+ O0+N 130 Km Equilibrium of by (1)1 24x10 4xl(Goldan (2)0 +O24 2+ these processes (ssum- (2)3.6x10-11, 1966) 2. 6x10 at thermal energy ing the rate of the second (Warneck, (Warneck, 1967) process is half of that of daytime ionthe first process) and major osphere at 130 Km loss processes given in Sec. 3. (Donahue, 1966) (1)2+N-* NO +0 130 Km Equilibrium of NO+ by (1)2. 1x100 (1)1. 8x10 at thermal (2)0-+NO. NO++O^ these production processes (2)1x10- energy(Warneck, (3)02+N2- NO +NO (assuming their rates are (3)6. 6x10'4 - 2 2 (2)8x10 at thermal energy equal) and the only loss (Warneck, 1967) process, NO +e- N+O. 12xl-15at thermal energy (3) (Warneck, 1967) -14 (4x10 for daytime ionosphere at 130 Km (Donahue, 1966) * obtained from equilibrium at 220 Km ** calculated from equilibrium at 240 Km

Table 3 Effective Recombination Coefficients and Lifetimes of Positive Ions at Night Alt. O eff (cm3sec) r(sec) Km) 0ON + + N+ + + N+ NO+ 2 2 NO 0 2 N2 130 2 7x10-5 2. 1x10-7 1 0x101 1 3x10 140 9. 1x10-5 1.7x10-7 46 25x13 150 35x10-4 1.5x10-7 36 8 5x10 160 5.6x10-4 1.4x10-7 34 14x10 170 5-6x10-4 1.3x10- 34 1 5x10 180 5. 1x10-4 1.3x10-7 36 1-5x104 -3 190 3.7x10-4 1 2x10- 3-8 12x10 200 1 7x10-5 1.9x10-4 1.2x10-7 4.7x101 4 3 6.7x103 210 5 9x10-6 6.2x10-5 1-1x10-4 3-9x10-4 1.2x10-7 6-7x10 6 3 3.7 10 34x103 220 22 4x10- 2. 4x10- 4.2 x1-5 2.2x10- 1. 9.3x10 9 2 55 0 20x10 230 7 8x10 7 8-4x10-6 1.2x105 1.0x10-4 1- lx107 1. 3x10 l1x1 1 -7 1 10 9. 0x103

5. Lifetimes and Effective Recombination Coefficients of Positive Ions at Night The effective recombination coefficients (o (e) and lifetimes (T) of e ff different species of positive ions at night at different altitudes are given in Table 3. They are claculated from the formula (1) oi Loss rate of positive ions of the ith species eff + n. n 1 e and ( effne where + n. - density of positive ions of the ith type n - electron density, which is taken to be equal to the total positive ion density It will be seen from the above table that NO' has the highest lifetime, 4 3 10 - 10 sec, and that of N2 the least about 1 sec. The effective recombination coefficients of positive ions vary between 104 and 10 cm /sec. 6. Conclusions The analysis of altitude distributions of positive ion density at different times of the day for the altitude range 100-280 km shows the following: 1. At lower altitudes, 0 02 and N2 are produced mainly by photoionization and hence their densities have large diurnal variations. (Because of the high I. P., N2 can be produced only by photoionization). +2 2. NO is produced at low altitudes mainly by charge exchange processes and hence its density has small diurnal variations. 8

3. At high altitudes, N2 and 0 mostly, are produced by solar rays. + + NO and 02 to a large extent, are created by charge exchange processes. The densities of latter ions have small diurnal variations. In fact, at 220 km at night, their densities become equal and same as those for daytime. 4. N2 ion rapidly decays by undergoing ion-atom interchange with 0 and 02 producing mainly NO+ ions. + O4 NO++N 2 + O NO++NO This accounts for the low percentage of N which, during the whole day, seldom becomes greater than 1% of the total ion content. 5. 0 rapidly exchanges charge with N2, NO and 02 producing NO either directly or through the intermediate production of 0O. N2 NO +N / NO - O2+N- NO++O 0+ 2 2 + +N2 — NO++NO +NO — NO+O2+ At night O loss rate by these processes is not balanced by the rate of the single important production process involving N2 and 0 atoms. This accounts for the rapid O+ density fall at night. 6. In the low altitude range, O2 loss rates are greater than the production rates and explain its large density fall at night. 7. The final removal of charge from the ionosphere takes place mainly through the dissociative recombination of NO+ ions and electrons. 9

8. Calculations show that although the concentration of neutral NO molecules is small, the rates of ion-atom reaction involving it is of the same order as those involving major atmospheric constituents, N2 and 02. 9. It was shown by Ghosh (1967) that at daytime at each level in the altitude range 100-280 km, the total rate of production of all positive ions is approximately equal to their total loss rate. The equality does not hold at night indicating that the ionosphere is not balanced. 10

References Donahue, T. M., Ionospheric Reaction Rates in the Light of Recent Measurements in the Ionosphere and the Laboratory, Planet. Space Sci., 14, 33-48 (1966). Ghosh, S. N., Ionospheric Characteristics from Altitude Variations of Positive Ion Densities, Scientific Report No. 05627-9-S, Univ. of Mich. (1967). Ghosh, S. N., Distributions and Lifetimes of N and NO between 100 and 280 Kilometers, J. Geophys. Res., 73, 309-318 (1968). Goldan, P. D., A. L. Schemeltekopf, F. C. Feshenfeld, H. I. Schiff, and E. E. Ferguson, Thermal Energy Ion-Neutral, Reaction Rates, 2. Some Reactions of Ionospheric Interest, J. Chem. Phys., 44, 4095-4103 (1966). Holmes, J. C., C. Y. Johnson, and J. M. Young, Ionospheric Chemistry, Space Research, 5, 756-766 (1965). Istomin, V. G., Aeronomy Symposium, Cambridge, Mass. (1965). Nicolet, M. and W. Swider, Ionospheric Conditions, Planet. Space Sci., 11, 1459-1482 (1963). Warneck, P., Laboratory Rate Coefficients for Positive Ion-Neutral Reactions in the Ionosphere, J. Geophys. Res., 72, 1651-1653 (1967). 11

1200 16+ - Daytime.,_ j Nighttime gooL~~~~900-/ AR- \ - Total Ion Density (Day) 90 / 0\ / \^\ — ~ Extrapolated Curve ION CONCENTRATIONS l 60 I \\ 5.!, / I 24+ Q: I ^ ^ ^^>^ \ I 150 <^2002 16+ - V ^-' - 6 f> 100 I I a10 10 3 104 105 106 CONCENTRATION (CM3) Fig. 1. Day and nighttime altitude variations of positive ions during the last solar minimum activity period averaged from observations made by different investigators.

NIGHTTIME (3)0 +0 02 + 0 DAYTIME (4)O+ +NO —ON + N 2 (I)NO + e - N+O (5)O++N2-NO++N (2)TOTAL PRODUCTION RATE (6)TOTAL LOSS RATE = (3)+(4)+(5) 300- (7) N2+O-O++N2 0 250Ext ~(2)\ (1) ~ 200- (7) ~ 200 0 (3) (4) (5) (6) 150100I I I I l I 10-2 10 I 10 102 103 104 RATE (CM3 SEC' ) Fig. 2. Production and loss rates of O ions at night. For comparison the total production and loss rates of 0+ during daytime are drawn.

NIGHTTIME (3)02 + N -NO +0 0 2^~~ ~(8) 0 + NO - 0+ N (4) 0+2 N NO+ NO (5)2 + NO -NO+ 02 (9)N + 02 DAYTIME ( NO + eO (I)TOTAL LOSS RATE 300 (6)0 +e-" 0 + +0 ~+0 (2)TOTAL PRODUCTION RATE ~~(300 70 + -.O + (10) Nq2+02 O; + N2 22 (II)TOTAL LOSS RATE = (3) +(4) + (5) + (6) \ (2) (12)TOTAL PRODUCTION RATE =(7)+(8)+(9)+ (10) 250 (9) (10) CLx ^r^^^ y.^^ i^~j;<7J~~7 200- x < (6150 (3)x / 100 104 0-3 102 10' I 10 1010 10 RATE (CM3 SEC-1) Fig. 3. Production and loss rates of 02 ions at night. The total production and loss rates of during daytime are also drawn. duction and loss rates of 02 during daytime are also drawn.

NIGHTTIME DAYTIME (3)N+ O+ -2+ N+ (I)TOTAL LOSS RATE 2 2 2- 2 N ()N300 ^2 (2) PHOTOPRODUCTION RATE (4)N2 + 0NO 2~(2) O++N2 \(2) () 250 2Lr pe~ <(3)(4) x _ x a 200 \ F - 150100I I I I 10 I 10 102 103 RATE (CM3SEC') Fig. 4. Loss rates of N2 ions at night. For comparison the total production and loss rates of N2 during daytime are drawn.

NIGHTTIME (3)LOSS RATE = NO e-N + O (4)N2- NO+NO (8)02 NO- NONO02 (5) N + NO-NO' N (9)N +NO-NO-+N, wN~+ (10)0 + NO. NO+ N (6)N +02o \o2O*N 2(11)00 +N-NO*+O \02'N (1l) N-NOO vDAYTIME NO*+N (7z)N O - N0~ W(I)TOTAL LOSS RATE (7)N + O,,+N (2)TOTAL PRODUCTION RATE (12) TOTAL PRODUCTION RATE - SUM OF (4) TO (II) 300 N0 (1) \(2) 250- (5) (9) (6) (3) (7 —.rJX~~~^ 6 X (\'-2001505- ^<^ 0) / ) 100I I I I! I I 103 102 10' 10 o2 3 104 10oo 10 RATE (CM3 SEC-') Fig. 5. Production and loss rates of NO ions at night. The total production and loss rates of NO+ during daytime are also drawn.

NIGHTTIME (3)N+ N-N-+N2 DAYTIME (I)TOTAL LOSS RATE 30(4)N+ +0.0r (2)TOTAL PRODUCTION RATE e \'+ O N+ 300- "NO.,O 0 (5)N + NO- NO N (2) \(1) 250 x (5) (3),(4) wJ x 200.J 150 100 I I I I 10-3c 102 10O 1 10 102 RATE (CM3SEC1) Fig. 6. Production and loss rates of N ions at+night. For comparison the total production and loss rates of N during daytime are drawn.