Correlations between OH, NaD and OI 5577 Å emissions in the airglow

CORRELATIONS

H. T-HI,

BETWEEN OH, NaD AND IN THE AIRGLOW

01 5577 is, EMISSIONS

P. P. RAT&ST& B. R. -HA,D.M.~MCHandY.SW

Institute de Pesquisas Eapaciais (INPE),+Conselho National de Desenvolvimento Cientffico e Tecnolcigico (CNPq), 12.200 - Sao Jose dos CIampos,SP, Brasil

AbMracLSmultaneous measurementsof the night airglow 015577 A and OH (8,3) band have been carried out at Cachoeira Pauliita (23’S, 45”W), Brazil since 1976. Cross correlation analysesbetween the nocturnal variations of these emissions and also witb the OH rotational temperature (ROT) for various time shifta are presented. It is found that OH (8,3) is well correlated with ROT but with a time fag of about 1 h. The variations of 015577 A tead OH (8,3) by about 2-3 h and ROT covaries with 5577 8, with a time tag less than 1 b. For the sake of comparison, 015577 %L,OH and NaD data from a number of IQSY stations have been anaiysed. It is noted that (1) 01 5577 A leads OH by about 2 h at mid-latitude stations and (2) OH is well correlated with Na 5893 w with a time lag of less than 1 h. The presence of the phase lagged correlation patterns between OH/5577 A, OH/ROT and OH/NaD indicates vertical propagation of a wavelikeperturbation of the upper atmosphere. WI‘RDDUCIZON

Geophysical Years (195% 19591, air&w 01 5577 A, NaD 5893A and OH band observations have been carried out systematically at various locations, Short term, long term and spatial variations of these emissions have been thoroughly investigated (Silverman, 1970). Witb respect to the relationship between the emissions, a correlation has been shown to exist between OH and NaD (Weill, 1967; Rao and Kulkarni, 1971), but not between OH or NaD with 5577 A. Rao and Kulkarni (1971) have mentioned that there is no obvious correlation between OH and 5577A or NaD and 5577 A. Takahashi et at. (1977) showed a similar tendency for the nocturnal variations of OH (8,3) and 5577 8, with respect to the post-midnight intensity increase, but the correlation coefficientr, found were low. On the other hand, a large amount of data of the IGY and IQSY stations has been analysed by Fukuyama (1976), who found the presence of a semi-diurnal variation in the 5577 A intensity and a longer period oscillation for OH and NaD. He suggested that the oscillations were produced by the solar semi-diurnal tide in the case of 5577 8, and by the diurnal mode in the case of OH and NaD. It seems, therefore, that these three emissions are contr$ed by a number of different meehanisms. In fact, in the altitude region of 8%lOOkm, where the emissions occnr, dynamical and photochemical processes are very active. It should be noted, however, that all the three emissions depend on the recombination processes of atomic oxygm, Since

the International

801

The emission heights are close together and the emission layers overlap. Therefore some relationship between them should exist. In this paper we show that the apparent lack of correlation observed by Rao and Kulkarni and Takahashi et al., results from a phase difference between the variations of the various emissions and that when this phase lag is taken into account the oscillations in the emissions are found to be well correlated. The data used here, 5577 A, OH (8,3) and the rotational temperatnre (ROT) have been measured at Cachoeira Paulista (22,7”S, 4.5.O*W), between May 1976 and May 1977. Instrumentation and the data reduction of the 5577 A and UH (8,3) measnrements have been descriid in Sahai et fit. (1974) and Takahasbi et al. (19741, respectively. In order to allow for the F-region component of 5577 A, 20% of the 01 63008, intensity has been subtracted from the observed 5.577 8, intensity (see Silverman, 1970). The IQSY data from Haute Provence (44”N), Abastumani (42”N), Dodaira (36‘Nj, Kitt Peak (32”N), Mt. Abu (25”N), Haleakala (21°N), Poona (19”N) and Tsumeb (19’S) have also been analysed, in order to investigate any possible latitudinal variation in the correlation patterns.

The general characteristics of the observed uocturnal variations of OH (8,3), rotational temperature and 5577 A were presented by Takahashi et a#. (3977)_ Concerning the seasonal variation_ 5577 is,

H. TAKAHASHI,P. P.

802

BATLWA, B. R. CLEMESHA,

shows a semi-annual oscillation with maxima in April and September. No significant seasonal variation has been observed in the OH (8,3) intensity, except that ROT shows a slight increase in March and April. It is difficult to see any common features in the nocturnal variations of the three parameters for individual nights. In general, however, it is noted that:

(3) ROT usually has the same variation as the OH (8,3) intensity but sometimes covaries with 5577 A. In order to examine the relationship between the three parameters in more detail, cross correlation coefficients, T(T), for various time shifts have been calculated from r(7) =

(1) the variation of 5577 A tends to be anti-phased

(2)

D. M. SIMONICH and Y. SAH~U

with OH (8,3), not only in the case of short period (less than 6 h) but also for long period variations (more than 8 h); both the emissions frequently increase after midnight, in this case 5577 A normally leads OH (S, 3);

ctM+T)-~XYW-Y) Et {X(t+T)-f}Z~{y(t)-~}2]1'2'

where x(t) and y(t) are a pair of values of the parameters at time t, i and jj are the nightly mean values of these parameters and T is time shift from -4 to +4 h. In Fig. 1, typical nocturnal variations of the three parameters are shown, together with the

4 tbl AT

4 (cl AT

AT -IO,L

16

,

20

I

I

I

I

22

0

2

4

J

VARIATIONS OF OH ROTATIONAL

Also

TEMPJZRATURE

I -2

0

Time lag,

(8,3) (W

(ROT)

1’1’1

6-4

L.S.T. FIG. 1. N -L

(BROKEN

L&, LINE)

111 2

01 557714 (D(~~TEDL& ON SOME S-

4

h

AND OH

NIGH’E.

correlation coefficientsbetween OH (8,3)/5577 8, (full line), OH (8,3)/ROT (broken line) and ROT/5577 A (dotted line) with time shift for each night.

shown are the variations of the

(1)

Comlatiom

-4

between OH, NaJDand OI5577 A emissions in the airglow

-3

-2

-I

0

I

Time lag,

FIG. 2. vARL4TION OF THE LINE), OH (8,3) ANDROT

GRAND

CORRELATION

(BROKEPJ -)

AND

2

3

BElWEFiN

ROT .uw 5577 A @m-rm

-4To+4h.

(1) 5577 A leads OH (8,3) by about 2-3 h; (2) ROT leads OH (8,3) by about 1 h; (3) 5577 8, leads ROT by about 0.5 h. Furthermore, it is interesting to note that, examining the individual days, the time lag between OH

4

h

COEiFFICIENrS

time shifted correlation patterns. Figure l(a) shows wavelike variations of the three parameters with a 6 h period. Very strong correlation can be seen. It should be noted that 5577 A leads OH (8,3) by about 1 h, ROT also leads OH (8,3) by about OS h and there is no obvious time lag between 5577 A and ROT. Figure l(b) shows an example of short period anti-phased variations of OH (8,3) and 5577 A. On this occasion 5577 8, leads OH (8,3) by about 2 h and ROT leads OH (8,3) by 1 h. Figure l(c) shows a day when large variations of ROT (AT more than 20 K) were observed. ROT is well correlated with 5577 A with a 0.5 h time lag, whereas OH (8,3) lags behind ROT by about 1 h. It should be noted that this was a magnetically disturbed night a I& = 31) and there was an enhancement of 01 6300A at around 2230L.S.T. Figures l(d) and l(c) show Iong period variations with the two emissions anti-phased and in-phase, respectively. Phase lags between the parameters are clearly seen in the correlation curves. In order to investigate the general trends of the correlation patterns, conjoint correlations were calculated using expression (l), carrying out the summations over all data pairs for all the available nights of data, using the nocturnal averages for X and y. In this way any possible influence of the day to day or seasonal variations on the correlation coefficient is removed. The results of this analysis, applied to the 55 days of data, are shown in Fig. 2. It may be seen that:

803

OH (8.3) AND 5577 8, (FULL LINE) WlTHTLMESwm FROM

(8,3) and ROT is larger when the period of variation is longer. In Fig. 3 we have plotted histograms of the frequency of occurrence of a given correlation coefficient, calculated with and without a time lag. 12

OH 8315577

IO

Atmt2

h

0

&=+I

0

h

t 6

I1

ROT/5577

IO

At=+

B

t

t/2 h -

6!-

I I -1

I

I

_I

4 2 r -' ~ -I.0-0.8-0.6-0.4-0.2

~

I.

0.2 0.4 0.6 0.a

1.0

Cormlotion coefficient FIG.

3. HKIWXUM

OF THE

FRFQIJFi.NC!Y OF OccuRRENcE

OFCORFtELATIONCO~CIENTBE

OH (8,3)/ROT W

-1

AND

m wrm

ROT/5577 A

GIVEN -).

OH (8,3)/5577 A, 8, wrm TIME LAG ZERO TIME

LAG,

At

(BROKEN

804

H. T-r%,

and Y. SAHAI P. P. BATISTA, B. R. C&MESH& D. M. S~MONBXI

The appro~ately equal spread about zero, of the OH15577 A correlation coefficient for zero time lag, explains why Rao and Kulkarni (1971) observed no significant correlation between these parameters. Daily mean values of the three parameters have also been examined, to check for day to day covariation. No correlation between OH (8,3) and 5577 8, was found, but there is a small positive correlation between OH (8,3) and ROT. Gmrelation between the daily mean values of 5577 8, and ROT is high (I =0.67) and the linear regression coefficient is 20 R K-‘. These daily means are plotted in Fig. 4 together with the regression line. This strong dependence of the 5577 A intensity on rotational temperature, however, does not necessarily imply a direct temperature dependence of the emission. Day to day variations, in the flux of solar U.V. radiation, could cause correlated fluctuations in the temperature and the rate of dissociation of molecular oxygen. It should also be remembered, of course, that ROT is not the temperature at the height of the 5577 A emission. Nevertheless, it should be noted that 5577 A is much better correlated with ROT than is OH, and a temperature dependence of the 0(‘S) excitation mechanism cannot be ruled out. lQSY DATA

In order to examine the global characteristics of the time lagged correlations between OH, 5577 A and NaD, the IQSY data for 1964 and 1965 (Smith et al., 1968) from the stations, Haute Provence (44WJ Abastumani (42”N), Dodaira (36”N), Poona (WN) and Tsumeb (19’S) were analysed in the

_-5577/RO-r

P 300

-

200

-

a. C r f

100 -

Rotational &G.

4. DAILY

MEAN

VAJXFS

temperatu~, OF 5577ii

l'IONALTl3dPERA'iURE.

K

AND OH ROTA-

Tsumsb (19%

Time lag,

h

FIG. 5. VARIATIONS OFTHEGRANDCORRELATIONCOEFFEOH AND 015577 ti (FwLL L@JE) AND clEWFiB_ OH AND Na 5893A (BROKEN LINE) WITH TAME SHIFT AT VARIOUS LocATIoNs.

same manner as the Cachoeira Paulista data (5577 A data were used without subtraction of the F-region component). Figure 5 shows the correlation patterns for each station. Again, the phase shifted patterns are obvious, showing about 2 h of time lag between OH and 5577 A. Poona does not show any pattern. This appears to be due to the fact that the OH intensity decreases monotonically throughout the night and does not show any short term variation (Chiplonkar and Tillu, 1967). Haute Provence shows very good correlation between OH and NaD at time lag zero but, except for Poona, the other stations show a time lag of about 0.5 h. These results show that maximum correlation between OH and NaD occurs for smaller time lags than does maximum correlation between OH and 5577 A. In Fig. 6, correlation patterns between NaD and 5577A are shown for the stations Kitt Peak (32”N), Mt. Abu (25”N) and Haleakala (21”N). Very uniform sine wave patterns are seen for Kitt Peak and Mt. Abu, showing maximum correlation at I equal to 2-3 h. These wavelike patterns indicate that both the emissions have a period of variation of about 10-12 h. On the other hand, Haleakala shows a very low correlation coefficient and a less uniform pattern.

Correlations between OH, NaD and 015577 8, emissionsin the airglow

Mt. Abu (25.N)

Haleakalat21.N)

-5

-6

-4

-2

0

Time lag, FIG.

2

4

6

h

6. As INFIG. 5 EXCEPTFOR Na 5893 8, AND 5577 A. DISCUSSION

There are several mechanisms which might contribute to the night-time intensity variation of the OH, NaD and 5577 A emissions. Firstly there is the change of photochemical equilibrium leading to a change in the mixing ratio of an atmospheric constituent, such as the atomic oxygen or ozone, in the mesopause region. This factor should be irnportant at altitudes below 85 km, where the recombination processes of atomic oxygen are rapid (Shimazaki and Laud, 1972). In the case of the OH emission, which is located at around 85 km, the intensity should decrease monotonically throughout the night because the ozone production rate decreases owing to the loss of atomic oxygen. 5577 8, should, however, remain constant because the emission layer is located at around 95 km where atomic oxygen does not change from day to night (Shimazaki and Laud, 1972). Secondly, it is possible that a variation in the turbulence could lead to an increase in eddy difhrsion during the night. Moreels et al. (1977) have calculated the effect of eddy diffusion on the OH emission. They showed that an increase in the OH intensity, of the right order of magnitude to explain the post-midnight maximum frequently observed, can be obtained by an increase of the eddy dithrsion coefficient by a factor of 10. Thirdly, a change of temperature and density caused by propagation of atmospheric tidal or gravity waves might contribute to the variation. Gadsden and Marovich (1969) have examined the effect of adiabatic pressure wave propagation in the 5577 8, emission layer. The effects of the semidiurnal solar tide in the 5577 A and OH emissions

805

have been investigated by Petitdidier and Teitelbaum (1977) and Takahashi et al. (1977). They showed that a density variation of a few per cent, at the height of the emission layer, is sufiicient to explain the intensity variations. Both the OH and 5577 A emissions depend on three body recombination processes whose reaction rates are sensitive to temperature and thus the intensity of emission should be sensitive to density and temperature variations. A downward transport of atomic oxygen, due to an increase of turbulence, as suggested by Moreels et al. (1977), might explain the presence of the phase lag between OH, NaD and 5577A. This, however, does not explain the time lag between OH (83) and ROT. We believe that a more reasonable explanation is that both temperature and density are modulated by the downward propagation of a wavelike disturbance. In this case, the time lag between OH (8,3) and ROT can be explained by the phase difference between the density and temperature fields predicted by tidal theory (Chapman and Lindzen, 1970). The time lag of about 2-3 h, between the 5577A and OH (8,3) emissions, would be equal to the time taken for a perturbation to propagate from the height of peak 5577 8, emission to the height of peak OH (8,3) emission. In this content, it should be pointed out that Clemesha et al. (1978) have shown excellent correlation between variations in the NaD nightglow and downward propagating perturbations in the sodium density distribution. Recent rocket and satellite measurements of the 5577 A emission profile show that it is located around 95 km (Offerman and Drescher, 1973 and Wasser and Donahue, to be published). The OH emission height has been reported to be at around 85 km (Rogers et al., 1973; Frederich et al., 1978). Calculated emission profiles based on a model atmosphere show reasonable agreement with the observed ones (Shimazaki and Laird, 1972; Moreels et al., 1977). It seems, then, that there should normally be a height difference of about 10 km between the two emission layers. Taking the average time lag between variations in OH (8,3) and 5577 A as 2 - 2.5 h, a vertical propagation velocity of the order of 4 km h-l is obtained. This velocity is a little higher than the velocities of propagation observed by Megie (1976) and Clemesha et al. (1978), for vertical structure in the mesospheric sodium layer. The 0.5 h time lag between the OH and NaD emissions, together with this velocity, suggests that the sodium emission region is centered on a height 2km above the peak of OH

806

H. TAKAHASHI, P. P. BATISTA, B. R. N,

emission, i.e. the height of peak emission is approximately 87 km. This result may be compared with the height of 89 km found by Clemesha et al. (1978). In the limited IQSY data, the northern middle latitude stations seem to show better correlation patterns than the northern lower latitude stations, for example, Haleakala and Poona. This would suggest a diBerence in the dynamics of the upper mesosphere between mid and low-latitudes. Fukuyama (1976) has pointed out that the nocturnal variation of 5577 8, at mid-latitudes might be related to the semi-diurnal tidal oscillations, whereas the diurnal mode should be more effective at lower latitudes. However, the southern lowlatitude station (Tsumeb) shows similar correlation patterns to that of the northern mid-latitude stations. This point needs to be investigated by analysing the airglow variation at a large number of stations.

CONCLUSION

A study of the correlations between the upper mesosphere emissions of OH, NaD and 015577 .&, shows that the OH intensity variations lag the rotational temperature (ROT) variations by about 1 h, the NaD variations by about 30 min and the 5577 A variations by 2-3 h. Model calculations for the OH and 5577 A emissions show that the time lag between them is consistent with the nocturnal variations being largely due to atmospheric density perturbations propagating downwards with a velocity of about 4km h-l. The time lag between OH and NaD indicates that the NaD emission originates from a region about 2 km above the height of the OH emission. A good correlation is observed between the 5577 A emission and ROT, with the former leading by less than 1 h. It is not clear whether this correlation is entirely due to the fact that density perturbations which influence the 5577 A emission are accompanied by temperature perturbations which affect ROT or whether a temperature dependence of the atomic oxygen excitation mechanism is involved. The daily mean values of 5577 8, are not significantly correlated with OH, but are strongly correlated with ROT, the emission intensity increasing by 20 R K-‘. This correlation does not necessarily indicate a causal relationship, both effects perhaps resulting from variations in the solar U.V. flux.

D. M.

fh4ONICH

and Y. SAHAI

Acknowledgement-This work was partly supported by the “Fundo National de Desenvolvimento Cientffico e Tecnol6gico (FNDCT),” under contract FINEP CT/271.

REFERENCES

Chapman, S. and Lindzen, R. S. (1970). Atmospheric Tides. Reidel, Dordrecht. Chiplonkar, M. W. and Tillu, A. D. (1967). A photometric study of the (9,4) and (7,3) OH emission bands in the night airglow at Poona. Indian J. pure appl. whys. 5, 87. Clemesha, B. R., Kirchhoff, V. W. J. H. and Siionich, D. M. (1978). Simultaneous observations of the Na 5893 A nightglow and the distribution of sodium atoms in the mesosphere. J. geophys. Res. 83, 2499. Frederich, J. E., Rusch, D. W. and Liu, S. C. (1978). Nightglow emissions of OH (pn): comparison of theory and measurement in the (9,3) band. J. geophys. Res. 83, 2441. Fukuyama, K. (1976). Airglow variations and dynamics in the lower thermosphere and upper mesosphere-I. Diurnal variation and its seasonal dependency. J. atmas. terr. Phys. 38, 1279. Gadsen, M. and Marovich, E. (1969). 5577 8, nightglow and atmospheric movements. J. amux. terr. Phys. 31, 817. Megie, G. (1976). Contribution & l’btude du comportment de l’atmosph&re B la mksopause obtenue par sondage laser du sodium. These de Doctorat D’etat. L’universit& Pierre et Marie Curie, Paris. Moreels, G., Megie, G., Valiance Jones, A. and Gattinger, R. L. (1977). An oxygen-hydrogen atmosphere model and its application to the OH emission problem. J. atmos. terr. Phys. 39, 551. Offermann, D. and Drescher, A. (1973). Atomic oxygen densities in the lower thermosphere as derived from in situ 5577 %, night airglow and mass spectrometer measurements. J. geophys. Res. 78, 6690. Petitdidier, M. and Teitelbaum, H. (1977). Lower thermospheric emissions and tides. Planet. Space Sci. 25, 711. Rao, V. R. and Kurkami, P. V. (1971). Interrelation of the different night airglow emissions (5577 A, 5893 8, and OH bands) in the lower ionosphere. Indian J. pure appl. Phys. 9,644. Rogers, J. W., Murphy, R. E., Stair, A. T., Ulwick, J. C., Baker, K. D. and Jensen, L. L. (1973). Rocket-borne radiometric measurements of OH in the auroral zone. J. geophys. Res. 78, 7023. Sahai, Y., Teixeira, N. R., Angreji, P. D., Bittencourt, J. A. and Takahashi, H. (1974). Tropical F-region nightglow enhancement in the Brazilian sector. Ann. Geophys. 30, 397. Shimazaki, T. and Laird, A. R. (1972). Seasonal effects on distributions of minor neutral constituents in the mesosphere and lower thermosphere. Radio Sci. 7,23. Silverman, S. M. (1970). Night airglow phenomenology. Space Sci. Rev. 11, 341. Smith, L. L., Roach, F. E. and McKennan, J. M. (1968). IQSY night airglow data. World data Center A, Upper Atmosphere Geophysics. U.S. Department of Commerce.

Correlations between OH, NaD and 015577 A emissions in the airglow Takahashi, H., Clemesha, B. R. and Sahai, Y. (1974). Nightglow OH (8,3) band intensities and rotational temperature at 23”s. Planet. Space Sci. 22, 1323. Takahashi, H., Sahai, Y., Clemesha, B. R., Bat&a, P. P. and Teixeira, N. R. (1977). Diurnal and seasonal variations of the OH (8,3) airglow band and its correlation with 015577 A. Planet. Space Sci. 25,541.

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WeiIl, G. M. (1967). Airglow observations near the equator, in Aurora and Airglow (Ed. B. M. McCormat), p. 407. Reinhold, New York. Wasser, B. and Donahye, T. M. Atomic oxygen between 80 and 120km; evidence for a latitudinal variation in vertical transport near the mesopause. J. geophys. Res. To be published.