Intensity variations and ratios of (9-4) and (7-3) hydroxyl bands in nightglow at Poona

Planet. Printed

Space Sci., Vol. 31, No. 4, pp. 423433. in Great Bntain.

0032ZO633/83/040423-I Pergamon

1983

I$O3.oOjO Press Ltd.

INTENSITY VARIATIONS AND RATIOS OF (94) AND (7-3) HYDROXYL BANDS IN NIGHTGLOW AT POONA S.R. GOGAWALE* Department

of Physics,

Poona

and A. D. TILLU University, Pune-411007,

India

(Received 24 August 1982) Abstract-The observed types of nocturnal intensity variations for the OH (9-4) and OH (7-3) bands during IQSY at this Station are further analysed using the theoretical band intensity distribution of Evans and Llewellyn (1972). A considerable agreement is noticed between observed and theoretical intensity ratios, 1(9%4)/1(7-3),for a major portion of the data (- 70%), which has a “continuous decrease” type of noctural intensity variation. This data is thereby satisfactorily explained on the basis of available information. For the remaining portion ofthe data( - 30x), which has “an increase followed by decrease” type ofintensity variation and higher intensities, the observed ratios are also systematically higher than the above. A satisfactory explanation is offered, bv postulating a second layer of emission, by examining closely several

aspects of ;he &her observational resuits. 1.

-

INTRODUCTION

Intensity variations of the hydroxyl nightglow were studied at this station during the IQSY (Chiplonkar and Tillu, 1966, 1967). The total intensities of the two bands, (9-4) and (7-3) were obtained and found to be in order of magnitude in agreement with the theoretical distribution of Chamberlain and Smith (1959, referred hereafter as CS). The ratio, 1(9-4)/1(7-3), was however much higher than that given by CS distribution. As against this the ratio is now found to be in much better agreement with that given by the intensity distribution of Evans and Llewellyn (1972, referred hereafter as EL), although the order of band intensities is not. We have, therefore, further analysed the observational data on the basis of EL intensity ratios.

2.

PREVIOUS

WORK DONE

2.1 Observations ofthe OH nightglow at Poona Observations were carried out at this station during IQSY (1964, January-March), for the OH (9-4) and OH (7-3) bands at 7748 and 8824 A respectively. The nocturnal variations of the intensities of these two bands and other relevant parameters have been reported by Chiplonkar and Tillu (1966, 1967) and reviewed later on by Tillu (1973). The pertinent points of these analyses are briefly mentioned below : (i) The intensities of two bands are highly correlated throughout the night and from night to night (see also Table I).

(ii) The nocturnal intensity variations showed two types, out of the three, predicted by Ballif and Venkateswaran (1963) on the basis of ozone-hydrogen mechanism. The type II, viz. “increase followed by decrease” was observed on 30% of nights. The type III, viz. “continuous decrease” was observed on remaining 70% of nights. The type I, viz. “continuous increase” was never observed. (iii) The observed mean intensity of OH(7-3) band was consistent with the theoretical intensity given by CS, however that of (94) band was considerably higher. It was then attributed to an uncertain correction, for contamination, by theneighbouring OH (5-l) band. (iv) Even the van Rhijn estimates of heights, which were generally considered to be unreliable for absolute determination of height of emitting layer, were within 5 km of each other for the two observed OH bands. The heights of the emitting layer were found to be 112 km for OH (7-3) band and 117 km for OH (94) band (Tillu, 1966; see also Table 9). (v) The intensity ratios of the OH bands, viz. I(9-4)/1(7-3), were systematically higher in view of (iii) mentioned above; e.g. the average value of this ratio over the entire period of observations was 0.347 + 0.069, which was significantly higher than 0.254, predicted by CS, even after taking into account the day to day scatter. The theoretical intensity ratios amongst the hydroxyl bands were considerably modified when Murphy’s (1971) transition probabilities were taken into account by EL. This new distribution gives a value of 0.3 13 for the intensity ratio of the two bands of our interest. Thus our experimental value is in substantially

* Present address: Department of Physics, S. P. College, Pune-411030, India. 423

424

S.

R.

and A. D. TILLU

G~GAWALE

TABLE~.NIGHTLYMEAN INTENSITIES,RATIOSANDCORRELATIONS FORTWO OH Date

BANDS

1(9-4)

I(7-3)

1(9-4) ~I(7-3)

Type

Correlation between 1(9-l) and I(7-3)

4325 4064 3805 3021 2472 2730 1592 1341 1304 1857 1331 1197 1139 4762

9675 9177 8061 6821 6294 6047 4118 3560 3454 4444 3105 2602 2769 11359

0.447 0.443 0.472 0.443 0.393 0.452 0.387 0.377 0.378 0.418 0.429 0.460 0.411 0.419

II II II II III II III III III II II II II II

0.50 0.64 0.94 0.96 0.95 0.96 0.93 0.96 0.98 0.97 0.98 0.92 0.95 0.54

530 445 453 578 634 235 312 353 408 292 448 370 348 192 340

1278 1137 1269 1557 1781 961 1086 1071 1339 909 1453 1111 1004 858 1292

0.415 0.391 0.357 0.371 0.356 0.245 0.301 0.330 0.306 0.321 0.308 0.333 0.347 0.224 0.263

II III III III III III III III III III III III III III III

0.83 0.89 0.89 0.94 0.96 0.89 0.98 0.90 0.95 0.93 0.96 0.90 0.93 0.80 0.88

190 191 196 295 226 352 223 239

691 607 653 990 826 1050 826 973

0.275 0.315 0.300 0.298 0.274 0.335 0.270 0.246

III III III III III III III III

0.92 0.95 0.89 0.89 0.97 0.97 0.94 0.57

January 1964 6 7 8 10 11 12 13 14 15 16 17 18 19 20 February 1964 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 March 1964 4 5 6 7 8 10 11 12

Average ratios : 0.437 + 0.017 II 0.319 kO.046 III 0.354f0.072 II+111

better agreement with the new theoretical ratio. This prompted us to look more closely into the observed ratios.

3. FURTHER ANALYSIS OF THE DATA 3.1 Intensity ratios Chiplonkar and Tillu (1966, 1967) derived the observed band intensities for the OH (9-4) band by subtracting the contamination due to intensity of OH (5-l) band using CS intensity distribution. Intensities of

the bands (9-4) and (5-l) were 710 and 930 R as per CS distribution, while these values are 451 and436 Rasper EL distribution respectively. Therefore the intensities of the (94) band and subsequently the ratios 1(94)/ 1(7-3) are revised by using the intensity distribution of EL and the response of the photometer. The corrections are less than 2%. These corrected intensities and ratios are presented in Table 1. We have used, following Chiplonkar and Tillu (1967) only the estimated average band intensities for obtaining the intensity ratios. This is because all the nights do not have exactly

Intensity

variations

and ratios of (9-4) and (7-3) hydroxyl

TABLE 2. PUBLISHEDSTUDIESFORRATIOSOFOH

1 2 3 4 5 6 I 8 9 10 11 12 13 14 15 16 17

Present paper

Only the ratios of 1(9_4)/I(7-3)

are collected

3.2 Ratios and intensity variations A casual inspection of Table 1 immediately reveals that the ratio 1(94)/1(7-3) is systematically higher for type II and lower for type III nights, than the average value. The average values of ratios and their S.E.s are presented for type II, type III and the total (II +III), at the end of Table 1. These values can be compared with the theoretical ratios of CS and EL given in Table 2. We find that : (i) the average ratio for the total is in agreement with the EL value within its day-to-day scatter, and is considerably higher than the CS value ; (ii) the type III data has a value of 0.319 which is in excellent agreement with EL value. However its scatter is comparable with that of the total data; (iii) the type II data has a very high value even compared to EL value, however, the ratios are highly consistent amongst themselves as indicated by its low value of day-to-day scatter. the relative

magnitudes

I(94) 1(7-3) 0.253

0.254 0.240 0.347

0.313 0.323

0.393 0.398 0.354

in this table in view of the interest of this paper.

equal amount of observational time. Hence finer difference made in the previous analysis regarding the “observed” and “estimated” intensities and their respective ratios will not be needed now; as only the estimated values will be used throughout. This table now forms the starting point for the analysis to be presented. The average value for the ratio 1(9-4)/1(7-3) now comes out to be 0.354+0.072 as shown in Table 1. It agrees with the EL value within the day-to-day scatter.

Considering

BAND~NTENSITIES

Several bands (4-l), (5-2) All bands Almost all bands (9-4), (7-3) Bands up to 1 p (4-u (5-2) (5-l), (94) (7-2), (8-3) All bands Almost all bands (8-3), (54) t9-5), (4-l) (9-4), (5-l), (8-3) Almost all bands All bands (9-4), (7-3)

Roach, Pettit and Williams (1950) Fedorova (1958) Chamberlain and Smith (1959) (CS) Krassovsky, Shefov and Yarin (1961) Chiplonkar and Tillu (1967) Broadfoot and Kendall (1968) Harrison (1969) Yano and Takahashi (1971) Kulkarni and Rao (1972) Evans and Llewellyn (1972) (EL) Harrison and Kendall (1973) Wiens (1974) Shagaev (1974) Fiocco and Visconti (1974) Good (1976) Llewellyn, Long and Solheim (1978) (LLS)

425

at Poona

Bands studied

Authors

No.

bands in nightglow

of average

values and their scatter, we feel that the type II and III data are really two distinct homogeneous groups, whereas possibly the total data is merely an inhomogeneous sum total of the two. We therefore present in Table 3 values of average intensities, S.D.s and skewness for these two types and the total (II + III). This table shows that S.D.s and skewness values for type III and the total are very nearly the same, whereas these are distinctly higher for type II; supporting the above suggestion that types II and III have significant differences in their behaviour. An attempt will be made in the later section to analyse the physical significance of these differences. The very clear and definite relationship between the ratios and the types as described above, now gives us a better and more quantitative criterion for classification ofnights. This is because most ofthe nights do not have

TABLE ~.CHARACTERISTICSOF THEOBSERVED OH DISTRIBUTION

Band

Type

(9-4)

II III Total (II + III)

(7-3)

II III Total (II + III)

Mean intensity (kR)

INTENSITY

S.D. (kR)

Skewness

2.53 0.62 1.15

2.08 0.78 1.54

0.88 0.67 0.68

5.41 1.63 2.69

4.44 1.87 3.29

0.99 0.55 0.51

426

S. R.

G~CAWALE

and

A.

D. TILLU

AVERAGENOCTURNAL INTENSITY VARIATION

AVERAGENOCTURNAL VARIATION

INTENSITY

OH( 7-3 1 x .3e24;

0’

1

22QO

-

a

ODD0

0

’

OHlO

.

OHtS-Ll x 77l.en’

* . O&O0

1

I.S., HRS

I.S.T.

HRS

FIG. 1. AVEKAGENOCTURNAL INTENSITYVAKIATION FOROH (73) BAND.

FIG.2. AVERAGE NOCTURNAL INTENSITY VARIATION FOROH (94) BAND.

observations extending over the entire duration of the night as required for type identification. Although the observed intensity variations have already been extensively analysed earlier with reference to the types of intensity variations predicted by Ballif and Venkateswaran( 1963), the average curves for types II, III (and also for total II + III) are, however presented here, in view of the further analysis, for the first time in Fig. 1 and 2 for the two OH bands (7-3) and (9-4) respectively. The values of the average intensities for respective types of data are also indicated in these figures which show that type II intensity variations are characterised by extremely large values of average intensities for both the bands.

confidence, the intensity of the total OH nightglow. Of course, there will be day-to-day scatter in these estimates also and hence analysis is pursued with reference to the average values of intensities given in Figs. 1 and 2. We present in Table4, type and its average ratio along with the values of total OH nightglow estimated from EL distribution, separately for the two OH bands. The values for type II however, differ considerably from EL value of 1 MR and also amongst themselves.

3.3 Intensity of the total OH nightglow In view of the overall agreement with the EL distribution we can now estimate, with more

4. DISCUSSION

4.1 Types of intensity variation and ratios As early as 1959, Chamberlain and Smith tried to estimate both the aspects, viz. total intensity of OH airglow and ratios of OH band intensities, i.e. the distribution of OH intensities in different vibrational

TABLE 4. ESTIMATED INTENSITY OF TOTAL OH NIGHTGLOW Total OH intensity estimated from band (in MR)

Type

(Nf;Ill) II+111 (N = 37) III (N = 26) II-III (Section 4.4) *Values

1(9-4) 1(7-3) 0.437f0.017 0.354 & 0.072 0.319kO.046 0.488

(7-3)

(9-4)

3.79 (3.41)* 1.87 (1.68) 1.13 (1.02)

5.66 (4.01) 2.59 (1.83) 1.21 (0.86) 1

MR

in the brackets are obtained by using LLS (1978) intensity distribution.

Intensity variations and ratios of (94) and (7-3) hydroxyl bands in nightglow at Poona rotational bands. To a certain extent it is surprising that initial investigations were more concerned about the estimates of total OH intensity in view of the considerable uncertainties in the absolute calibration of photometers or monochromators used. It would have been perhaps more profitable to be concerned with OH intensity ratios as these are more likely to be accurate even on any relative calibration and perhaps would give more, if not less, information than the determination of total intensity can offer. In fact, even for obtaining the total intensity, a certain OH intensity distribution has to be assumed as it is almost impossible to observe the entire range of OH bands simultaneously. To a certain extent, this lack or neglect is nowadays more than over compensated. We, therefore, do not go into the detailed discussion of intensity distribution of different vibrational bands which are continuously being refined (e.g. Llewellyn, Long and Solheim, 1978 ; referred hereafter as LLS). We prefer to restrict ourselves to the intensity ratio of OH (994) and OH (773) bands. A casual inspection of Table 2 immediately reveals that prior to 1961, reported values of these ratios were low, whereas these are higher since 1967 or so. These ratios are of three kinds, viz., (i) purely observational ratios such as of Chiplonkar and Tillu (1967), Harrison and Kendall (1973) etc., (ii) based upon laboratory determination such as of Good (1976) and (iii) combination of theoretical analysis and experimental observations as given by EL and LLS. Thetotal rangeofthisratioisfrom0.313 to0.398and can be considered as sufficiently narrow, in view of these different approaches involved. One is therefore tempted to conclude that these aspects are very nearly converging and understanding of this aspect of OH nightglow is almost complete. The present study is probably focussing for the first time on the involved relationship between types of OH intensity variation and intensity ratios, even though intensities and their ratios were studied independently. We have already sorted out that ratios are consistently higher for type II, not only than that of type III, but than all those ofthe other approaches mentioned above. The analysis presented here is perhaps possible since types of OH intensity could be separated out only in tropical stations as was first suggested by Wiens and Weill (1973) and now confirmed here. Wiens (1974) has further considered nocturnal variations of intensity ratios with a view to understanding the nocturnal behaviour of the ozonehydrogen mechanism. The present analysis can be considered as complementary to his, as we have

427

considered behaviour from night to night instead of during night. Analysis similar to his for the variations of ratios during the night at this station can be carried out and is contemplated for the near future. However, it can be anticipated that it will most probably confirm the results obtained by this author and hence is not included in the present investigations. 4.2 Total intensity ofOH nightglow This aspect has been considered by several approaches, theoretical as well as experimental, from time to time (see Table 5). EL have used photon emission rate of4.8. We have, therefore, given the values calculated by using this rate and hence are different from the original one. Leaving the exceptional value of 15.4 MR given by Hesstvedt (1969) these values range between 1 and 7.7 MR. Moreover, the results directly obtained from the dynamic model are consistently higher (except those obtained by Moreels et al., 1977) than those obtained from experimental values either in the laboratory or from nightglow observations. The effects of quenching as shown by LLS produces a difference in the total intensity from nightly value of 90&290 kR for the day as quenching increases. However, their nighttime value of 900 kR does not differ significantly from EL value of 1 MR obtained without considering the quenching effect. Thus, the quenching phenomenon may bridge the gap between experimental values and dynamic model results only to a certain extent. This may perhaps be fully bridged in future if entire OH system can be monitored simultaneously. We now examine the results presented in Section 3 (Table4) in the light of above discussion. It is possible to attribute values derived for type II, as close to those of the dynamic model, so that no further examination is necessary. Although the dynamic model itself predicts in general a type III behaviour the type II has also been occasionally obtained (Moreels et al., 1977). At this stage it is preferable to give more weight to intensity ratios than a pattern of behaviour or absolute intensity values because of uncertainties in both, experimental as well as in those of model values. Moreover the intensities of type III agree among themselves and with EL as well as LLS intensities. 4.3 Intensity ratios and quenching The effects of quenching on nightglow as well as dayglow have been considered by LLS. Their nightglow values for total intensity as well as for ratios, are of considerable interest to our analysis. Their ratio forI(94)/1(7-3)is0,398asagainst theELratioof0.313. If we look for our observed average ratio viz. 0.354 kO.072 (without any type analysis), we find that it is

428

S. R. GOGAWALEand A. D. TILLU TABLE5. INTENSITY OFTOTALOH NIGHTGLOW

No.

Author

2 3 4 5 6 7 8 9 10 11

Chamberlain and Smith (1959) Bates (1960) Wallace (1962) Ferguson and Parkinson (1963) Lytle and Hampson (1964) Hunt (1966) Hesstvedt (1968) Gattinger (1969) Hesstvedt (1969) (unpublished) Hesstvedt (1970) Shimazaki and Laird (1970)

12 13

Crutzen (1971) Gattinger (1971)

14 15 16

Hunt (1971) Hunten (1971) Evans and Llewellyn (1972)

17 18 19 20 21 22 23

Wood (1972) Evans et al. (1973) Good (1976) Nagy et al. (1976) Moreels et al. (1977) Hingane (1978) Llewellyn, Long and Solheim (1978)

1

Intensity in MR 5.8 5.3 6.9 4.8 5.0 4.8 2.4 4.8 15.4 3.8 2.4 7.7 1.7 5.3 3.2 5.8 4.5 1.0

2.3 0.85 1.4 1.3-1.7 2.0 6.5 0.90

consistent within experimental errors with both the values viz. 0.313 and 0.398. We have therefore computed the values oftotal OH airglow, on the basis of this new LLS distribution and these are also given in Table 4 in brackets just below the respective EL values. These new values are in considerably better agreement with the values calculated from intensities of each band. The intensities for type II and for the total are now closer to each other. Those for the total are closer as well as smaller. Those for type III are relatively more divergent but are still smaller. It is thus possible to suggest that the total intensities estimated on the basis of LLS are more acceptable than those obtained on the basis of EL distribution. There are only two points which do not allow this rosy picture to be true. The first is that ratio for type III, viz. (0.319 kO.046) does not agree with the LLS distribution even if the wide error bar is considered. The order of intensities for type II is still very large and does not agree with the total intensity expected even when quenching is included (viz. 0.9 MR). Moreover as we consider the agreement of ratios as more important than the types and the order of intensities, we have to choose the former (i.e. EL) pattern for the interpretation

Remarks All vibrational levels populated at the same rate Experimental 6 h after sunset Night time Experimental (dayglow) Midnight Midnight Midnight Midnight Midnight Midnight Static Model Midnight Dynamic Model Midnight Midnight Standard Midnight variable diffusion Midnight Number of photons not mentioned OH formed is excited 45% in v = 9 45% in u = 8 10% in v = 7 Midnight Nightglow rocket observations Laboratory studies Dynamic model Midnight Midnight Considering the quenching effect

to the latter one (i.e. LLS) and more elaborate interpretation for type II is therefore necessary than available from existing recent models. 4.4 Further interpretation of type II intensities In view of the observed relation between type III intensities,itsmagnitude,nocturnalintensityvariation, etc., we now presume that type III behaviour is the more prevalent pattern ofbehaviour at this station. The observed type II behaviour is assumed to be some kind of different phenomenon which is superimposed upon the type III pattern. This superimposed pattern changes the following characteristics : (i) order of intensities, (ii) nightly behaviour, (iii) ratio of intensities of (9-4) and (7-3) bands. With this assumption it is possible to subtract as a whole the observed pattern of type III, from type II to estimate the superimposed pattern on type III. We have presented in Fig. 1 and 2, pattern of nocturnal intensity variations obtained after subtracting type III pattern from type II for both the bands. It is obvious that these curves obtained after subtraction, now show a more

429

Intensity variations and ratios of (94) and (7-3) hydroxyl bands in nightglow at Poona TABLE 6. ESTIMATION OF THE INTENSITY OF THE SECONDARY SOURCE

Type

(9-4)

(7-3)

Ratio I(94) -1(7-3)

II III II + III II-III

2382 521 953 1861

5450 1634 2692 3816

0.437 0.319x 0.354 y 0.488 z

Average intensities of OH bands, in R

I&OH) = Total intensity of OH derived from Type III of (7-3) band = 1.13 MR (see Table 4). Therefore, the estimated intensity of the secondary source I,(OH) = y-x I,(OH) = 0.295 MR. Z-Y

distinct type II behaviour, as in the early part of the curves type II and III have opposite tendencies. Thus if our interpretation turns out to be anywhere near the truth, then curves obtained after subtraction are more distinct and closer to type II, as envisaged by Ballif and Venkateswaran in their classification. In other words our interpretation is that the observed type II is a sum total of type II and type III. We now wish to characterise more closely the estimated type II behaviour. We may crudely obtain the order of intensities by subtracting average intensities of type III from type II. Thus the values of I (94) and 1(7-3) are respectively, 1.86 and 3.82 kR and the ratio of I (9-4)/I (7--3) is 0.488. Thus we may need a highly preferential excitation of 9th level compared to 7th one as the ratio is considerably higher than for type III (which is 0.3 13 by EL and 0.398 by LLS distribution). We now note that our average ratio, viz. 0.354, for the entire data is due to sum of two groups of intensities, the normal type III with a ratio of 0.319 and preferred one of ratio 0.488. Ifthe normal source has total intensity of 1.13 MR (Table 4), the estimated intensity of preferred source with the above ratio turns out to be merely 0.295 MR (see Table 6). However, since this source has been mainly operative only for 11 nights instead of 37, its average intensity for those nights works out to be 1 MR again. Comparing the magnitude of intensity of 1 MR with the entries in Table 4, we feel that the proposed interpretation has a more attractive explanation for observed type II, than that based upon changes in ratio on the basis of quenching alone. We are in a position to give some more observational characterization for such a preferred additional excitation. For the sake of convenience we will now refer this source as secondary source and call the one

TABLE~.CORRELATIONSBEWEENINTENSITIESANDRATIOSFOR OH BANDS Type

Correlation coefficient for

II

II+111

III

I(94) and I(7-3)

0.996

0.997

0.999

1(9-4) I(94) and __ 1(7-3)

0.362

0.744

0.665

1(7-3) and __ 1(9-4) 1(7-3)

0.287

0.720

0.617

giving normal or type III variation as a primary source. This concept of secondary source will now be used to explain the observed correlations between intensities and ratios for which incidentally, no attention was given so far. 4.5 Observed correlations of ratios and intensities The correlations of ratios and intensities were also calculated and are listed in Table 7. These show that intensities for type II, III and for average are highly correlated. Thus whether the source is primary or secondary we do not have to propose entirely new mechanism for OH excitation at this moment. Entire analysis is still within the framework of ozonehydrogen mechanism. We next notice that the correlations between intensities and ratios are significant for type III and for average data, whereas these are insignificant for type II. We interpret this behaviour with the new concept of secondary source. We suggest that the secondary source changes the intensities and the ratios, even for type III, in a very modest manner. Thus the observed correlation between ratios and intensities is only an indication of small changes in intensities and ratios due to variations in the contribution of secondary source to the type III behaviour. A larger change causing a complete transformation of type III to II is also consistent with this picture, as for the average data the correlation is still larger. However for type II only the correlation is insignificant. This is because now the contribution of primary source which is expected to be constant is negligibly small to cause any variations in the ratios for type II. For this behaviour, the changes in the order of intensities are entirely due to the intrinsic variation of the secondary source only. This explains the large variability in type III ratios and almost constancy in the ratios of type II. Thus in a single stroke this new concept explains all the observed correlations. The secondary source would be almost indistinguishable experimentally, even after all the above

430

S. R. GOGAWALE

and A. D. TILLU

TABLE 8. ALTITUDE OF NIGHTGLOW OH EMISSION

No. 1. 2. 3. 4.

Meinel (1950) Roach, Pettit and Williams Lowe (1960) Packer (1961)

5. 6. 7. 8. 9. 10.

Tarasova (1963) Hunt (1966) Chiplonkar and Tillu Baker and Waddoups Hesstvedt (1969) Shimazaki and Laird Harrison (1970) Hunt (1971) Gattinger (1971) Llewellyn and Evans Tarasova (1971)

11. 12. 13. 14. 15. 16. 17. 18. 19.

23. 24.

(1967) (1967)

882-774 727 -

(1970) 830-846 1650-1890 900-1050 1120-1140 15OQ-2000 -

(1971)

analysis

and

height

characterization, region

be distinguished

of primary

2200 1270, 1600 1800 channels -

from

if it is operative source.

the primary

1640and1340

758-859 628-63 1

in the

However,

it will

if the height

of the

source is distinctly different. We explore this aspect in the next sub-section. secondary

4.6

Height of the secondary source of OH

For the determination

of the height

ofemitting

layer,

was used extensively in the sixties (e.g. St. Amand et al., 1955). However, the results were highly variable and erratic due to patchiness of the airglow and day to day changes in extinction. By the time we developed the analytical methods to overcome these deficiencies (Tillu, 1966), more reliable height determinations were available from Rockets and theoretical considerations (Table 8) and the utility of ground determinations was more or less lost. We now present in Table 9 our estimated heights to illustrate the relative differences between different bands and those of different types for the same band. In view of the

Remarks

80 70 78 90 83 78 80 110 97 86 85 95 85 85 85 82 79 85 87 89 87

722-737 760-l 040

Good (1976) Moreels, Megie and Valiance Jones and Gattinger (1977) Moreels and Herse (1977) Llewellyn, Long and Solheim (1978) Frederick, Rusch and Liu (1978)

25. 26. 27.

Altitude (km)

725-896 640-1160 -

(1950)

Makino and Hagiwara (1971) Evans and Llewellyn (1973) Peterson and Kieffaber (1973) Evans, Llewellyn and Valiance Jones (1973) Hunt (1973) Fukuyama (1974) Battaner (1975)

20. 21. 22.

same

Region studied (wavelength, in nm)

Author

Ground based Ground based Rocket measurements Rocket experiment Rocket experiment Rocket experiment Calculated Ground based Rocket experiment Calculated Calculated Rocket experiment Calculated Calculated Rocket experiment Rocket experiment Experimental Recalculated from ref. 14 here Photographic parallax Rocket experiment

85 85 80 75 87 84

Calculated Calculated Midnight Calculated Noon-time Rocket experiment Daytime calculated

85 85 85

Photographic parallax Recalculated from ref. 19 here Satellite experiment, calculated

improved accuracy of rocket data and those based upon the models; absolute values of these estimates only indicate that extinction correction in this analysis was on the lower side by about 2%. However, estimates are close for type III. Since, now type III is completely explained by dynamic model, we normalize average height of OH (average ofestimates for the two bands) as 85 km for type III and estimate on this basis for other

the van Rhijn method

TABLE 9. ESTIMATEDHEIGHTSIN km FORDIFFERENT OH BANDS AND THEIRTYPES Type

II III

II+111 II-III

0H(9-4)

OH(7-3)

137 107 116 -

122 106 111 -

(122)* (86) (91) (120)

*The values in brackets are normalized km as the average height for Type III.

(96) (84) (88) (102)

with respect to 85

Intensity

variations

and ratios of (94)

and (7-3) hydroxyl

type. These normalized estimates are given in brackets. We do get different heights for type II and for the total than type III. These differences are quite systematic. We may attach some importance to these differences in height for two different types as these have been corrected for patchiness as well as day to day changes in extinction as stated above(Tillu, 1966). At least, it gives us further characterization of the secondary source, which we now expect to be operative at relatively higher height than 85 km. As we have estimated the ratio of superposed pattern by subtracting the type III intensities, from those of type II, we can estimate for each band appropriate van Rhijn ratios after similar subtraction. The heights of secondary source for OH (94), OH (7-3) individually and for the average of the two bands were worked out in the above manner and are 120 km, 102 km and 111 km respectively. Although one need not give again more importance to exact location of this source, an approximate order of its place is certainly estimated by the present analysis. The higher value of height for OH was expected by Krassovsky (1963) in order to explain the observed occasional correlation between OH and 6300 A as due to an increase in circulation of the upper atmosphere. We incidentally have obtained correlation between OH and 6300 A for the nights presented here and correlation was relatively stronger for type II than type III (Tillu, 1966). The new interpretation developed here to explain the detailed characterization of type II intensities, although it appears very attractive, needs additional experimental support. Most of the investigators, except Gattinger (1971), mentioned in Table 8 have hardly given any hint of such secondary source. The above interpretation could be tested only with an analysis of a set of similar ground observations or by independent rocket observations. Moreover, since the secondary source is not expected to be active continuously it may have eluded the rocket observations so far. The only exception to this is the rocket observations of Evans et nl. (1973). In their studies of determining the altitude distribution of OH and 0, (‘ALP), they have found a second peak at 112 km region. By considering all possible errors they have suggested a possibility that this secondary peak can be attributed to OH emission. This concept of secondary layer of OH emission may not remain very strange as it appears now. At least this concept is now known to be valid for 5577 A airglow as confirmed by Gogoshev et al. (1979). Second layer is also observed for 0, (‘A,) by Evans et al. (1973). We may finally mention that in their preliminary analysis of the recent rocket observations Llewellyn and others (private communication) have also detected a second layer for OH nightglow.

bands in nightglow at Poona

431

5. CONCLUSlONS We have thus tried so far two possible interpretations for type II behaviour, of hydroxyl nightglow, as characterized by an increase in the intensity and in the ratio I (9-4)/I (7-3). The increase in ratio can be explained following LLS to a certain extent as a result of quenching process. However, it does not explain all the observed characteristics. e.g. its surprising correlation with 6300 A emission. We may mention as a final remark that the type II behaviour was explained on the basis ofdynamic model by Moreels et ul. (1977) wherein an increase in eddy diffusion coefficient was stipulated. Thus a secondary source having its origin around 110 km fits in much better as the value of eddy diffusion at 110 km is usually taken to be maximum. In view of the rocket observations, and the conclusions reached here independently by analysis of ground observations, the explanation in terms of increase in eddy diffusion coefficient seems more likely than one based upon quenching. Further, the two processes may also be complementary to each other. However, in view of the strong observed correlation, need of a different mechanism for the production of OH as suggested by Evans et al. (1973), may not be necessary. The present analysis has brought out a number of interesting relations between various observational parameters of OH bands. The observed intensity variations are clearly discerned into two distinct types. These types are characterized by different distributions of vibrational excitations and the differences are therefore manifested in day to day changes in ratios, correlations of ratios with intensities, estimated total OH intensities, scatter and skewness of intensity distributions and height from which these originate. Out of the two types of intensity variations, the common one is completely identified with that predicted by theoretical studies on the basis ofdynamic model. A new interpretation based on a concept of secondary source is evolved to explain the observed characteristic of the other type of intensity variation, viz. increase followed by a decrease. We expect that more refined theoretical analysis and experiments would be in a position to confirm the observed characteristics which are very well brought out.

REFERENCES

Baker, D. J. and Waddoups, R. V. (1967) Rocket measurement of midlatitude

night airglow emissions.

J. yeophys. Res. 72,

4881. Ballif, J. and Venkateswaran, S. V. (1963) On the temporal variation of OH nightlow. J. Atmos.Sci. 20, 1. Bates, D. R. (1960) The airglow, in The Physics ofthe Upper Atnz~sphere (Edited by Ratchcliffe, J. A.), p. 219. Academic Press, New York.

432

S. R. GOGAWALE and

Battaner, E. (1975) Transport phenomena and the chemical composition in the Mesosphere and Lower Thermosphere. J. atoms. terr. Phys. 37, 1175. Broadfoot, A. L. and Kendall, K. R. (1968) The airglow spectrum, 310&10,000 A. J. geophys. Res. 73,426. Chamberlain. J. W. and Smith. C. A. (1959) On the excitation rates and intensities of OH in the airglow. J. geophys. Res. 64,611. Chiplonkar, M. W. and Tillu, A. D. (1966) The nocturnal intensity variation of (7-3) and (9-4) OH bands at Poona. The Proc. of IQSY Symp, New Delhi, Dec., 15-l 7, p, 434. Chiplonkar, M. W.and Tillu,A.D.(1967)Aphotometricstudy of the (994) and (7-3) OH emission bands in the night airglow at Poona. Indian J. pure appl. Phys. 5, 87. Crutzen, P. J. (1971) Energy conversions and mean vertical motions in the high latitude summer mesosphere and lower thermosphere, in Mesospheric Models and Related Experiments (Edited by Fiocco, G.), p. 78. D. Reidel, Dordrecht. Evans, W. F. J. and Llewellyn, E. J. (1972) Excitation rates of the vibrational levels ofhydroxyl and nightglow intensities. Planet. Space Sci. 20, 624. Evans, W. F. J. and Llewellyn, E. J. (1973) Atomic hydrogen concentration in the Mesosphere and the hydroxyl emissions. J. geophys. Res. 78, 323. Evans, W. F. J., Llewellyn, E. J. and Valiance Jones, A. (1973) Altitude distribution of hydroxyl bands of the AV = 2 sequence in the nightglow. Can. J. Phys. 51, 1288. Fedorova, N. I. (1958) Infrared spectrum of the northern nightskyin the region 95(w 11,500A. Ann. Geophys. 14,365. Ferguson, A. F. and Parkinson, D. (1963) The hydroxyl bands in the nightglow. P/c:net. Space Sci. 11, 149. Fiocco, G. and Visconti, G. (1974) Simultaneous measurements of the OH* nightglow in the (94). (7-3) and (5-l) bands and elects ofquenching. J. atmos. few. Phys. 36,583. Frederick, J. E., Rusch, D. W. and Liu, S. C. (1978) Nightglow emissions of OH (X211): Comparison of theory and measurements in the (9-3) bands. J. geophys. Res. 83.2441. Fukuyama, K. (1974) Latitudinal distributions of minor netural Hydrogen-Oxygen constituents. J. atmos. terr. Phys. 36, 1297. Gattinger, R. L. (1969) Interpretation ofOH airglow emission. Ann. Geophys. 25,825. Gattinger, R. L. (1971) Interpretation of airglow in terms of excitation mechanisms. D. region nightglow, in The Radiating Atmosphere (Edited by McCormac, B. M.), p. 51. D. Reidel, Dordrecht. Gogoshev, M. M., Sargoichev, S., Gogosheva, T. Z. N., Kazakov, K., Taneva, B. and Mendev, I. (1979) Vertical distribution of airglow emissions in the equatorial ionosphere duringmoderate geomagnetic activity. COSPAR. XXII, Plenary Meeting. Bangalore, India, p. 54; C. 2.7. Good, R. E. (1976) Determination of atomic oxygen density from rocket borne measurement of hydroxyl airglow. Planet. Space Sci. 24, 389. Harrison, A. W. (1969) The night airglow spectrum, 1.02 p to 1.13 n. Planet. Space Sci. 17, 173. Harrison, A. W. (1970) Altitude profile of airglow hydroxyl emission. Can. J. Phys. 48, 223 1. Harrison, A. W. and Kendall, D. J. W. (1973) Airglow hydroxyl intensity measurements 0.6 n-2.3 p. Planet. Space Sci. 21, 1731. Hesstvedt, E. (1968) On the effect of vertical eddy transport on atmospheric composition in the Mesosphere and Lower Thermosphere. Geophys. Puhl. 27, 1.

A. D. TILLU

Hesstvedt, E. (1969) A photochemical atmosphere model containing Oxygen, Hydrogen and Nitrogen. Contract No. DAJA 37-69-COOll, U.S. Army European Research Office (unpublished). Hesstvedt, E. (1970) Theoretical study of the diurnal variation of hydroxyl emission. J. geophys. Res. 752337. Hingane, L. S. (1978) Theoretical Studies in Aeronomy. Ph.D. Thesis, University of Poona, Pune 7, India. Hunt, B. G. (1966) Photochemistry of ozone in the moist atmosphere. J. geophys. Res. 71, 1385. Hunt, B. G. (1971) A diffusive photochemistry study of the Mesosphere and Thermosphere and the associated conservation mechanism. J. atmos. terr. Phys. 33, 1869. Hunt, B. G. (1973) A generalized aeronomic model of the Mesosphere and Lower Thermosphere including ionospheric processes. J. atmos. terr. Phys. 35, 1755. Hunten, D. M. (1971) Airglow-introduction and review, in The Radiating Atmosphere,(Edited by McCormac, B. M.), p. 3. D. Reidel, Dordrecht. Krassovsky, V. I., Shefov, N. N. and Yarin, V. I. (1961) On the OH airglow. J. atmos. terr. Phys. 21,46. Krassovsky, V. I. (1963) OH emission in the upper atmosphere. Planet. Space Sci. 10, 7. Kulkarni, P. V. and Ramchandra, Rao. (1972) Correcting the OH contribution in emission line measurements in the night airglow filter photometry. Planet. Space Sci. 20, 2198. Llewellyn, E. J. and Evans, W. F. J. (1971) The dayglow, in The Radiating Atmosphere (Edited by McCormac, B. M.), p. 17. D. Reidel, Dordrecht. Llewellyn, E. J., Long, B. H. and Solheim, B. H. (1978) The quenching of OH* in the atmosphere. Planet. Space Sci. 26, 525. Lowe, R. P. (1960) CARDE IGY Rocket measurementsCARDE Technical memorandum 291/59. Lytle, E. A. and Hampson, J. H. (1964) Observation of the OH -day-glow. Nature iO2, 76. Makino. T. and Haeiwara. Y. (1971) Bull. Inst. Sauce. Aeronaut. Sci. Tokyo Univ. 7, 136. Meinel, A. B. (1950) OH emission bands in the spectrum of the night sky. II. Astrophys. J. 112, 120. Moreels, G., Megie, G., Valiance Jones, A. and Gattinger, R. L. (1977) An oxygenhydrogen atmospheric model and its application to the OH emission problem. J. atmos. terr. Phys. 39, 551. Moreels, G. and Herse, H. (1977) Photographic evidences of waves around the 85 km level. Planet. Space Sci. 25,265. Murphy, R. E. (1971) Infrared emission of OH in the fundamental and first overtone bands. J. Chem. Phys. 54, 4852. Nagy, A. F., Liu, S. C. and Baker, D. J. (1976) Vibrationally excited hydroxyl molecules in the lower atmosphere. Geophys. Res. Lett. 3, 721. Packer, D. M. (1961) Altitude of the night airglow radiations. Ann. Geophys. 17,67. Peterson, A. W. and Kieffaber, L. M. (1973) Photographic parallax heights of infrared airglow structures. Nature, Lond. 244, 92. Roach, F. E., Pettit, H. and Williams, D. R. (1950)The height of the atmospheric OH emission, J. geophys. Res. 55, 183. Shagaev, M. V. (1974) Fast variation of OH night airglow emission. J. atmos. terr. Phys. 36, 367. Shimazaki, T. and Laird, A. R. (1970) A model calculation of the diurnal variation in Minor constituents in the Mesosphere and lower Thermosphere including transport effects. J. geophys. Res. 75, 3225. St. Amand P., Pettit, H. B.. Roach, F. E. and Williams, D. R.

Intensity

variations

and ratios of (94) and (7-3) hydroxyl

(1955) On a new method of determining the height of the nightglow. J. atmos. terr. Phys. 6, 189. Tarasova, T. M. (1963) Direct measurements of the light of the night sky in the region I = 8640 A. Planer. SpaceSri. 11,437. Tarasova, T. M. (1971) Moscow IAGA meeting. Paper presented at Moscow IAGA meeting (Ref: Valiance Jones, A. (1973) Spnce Sci. Rev. 15, 355). Tillu, A. D. (1966) Twiliyht and Airglow Studies at Poona. Ph.D Thesis. University of Poona, Pune 7, India. Tillu, A. D. (1973) Night airglow at Poona. Proc. Indian Nat. Sci. Acad. 39, 397. Wallace, L. (1962) The OH nightglow emission. J. Atmos. Sci. 19, 1.

bands in nightglow

at Poona

433

Wiens, R. H. (1974) Diurnal variation of the (S-3)/(5-0) intensity ratio of nightglow OH at Adi Ugri. Planet. Space Sci. 22, 1059. Wiens, R. H. and Weill, G. (1973) Diurnal, Annual and Solar variations of the hydroxyl and sodium nightglow intensities in the Europe-Africa sector. Planet. Space Sci. 19, 1011. Wood, H. C.(1972) TheMeasurement and ZnterpretationojO, (‘Ag) Concentrations in the Atmosphere. Ph.D Thesis, University of Saskatchewan, Canada. Yano, K. and Takahashi, H. (1971) Observation of the intensity ratio between (5-l) and (9-4) bands of OH emission in the night airglow. Rep. Zonosph. Space Res. Japan. 25,301.