Airglow Studies in India - NISCAIRnopr.niscair.res.in/bitstream/123456789/36475/1... · Indian Journal of Radio & Space Physics Vol. 16, February 1987,pp.84-101 Airglow Studies in

Indian Journal of Radio & Space PhysicsVol. 16, February 1987,pp.84-101

Airglow Studies in India

v V AGASHEPhysics Department, Poona University, Poona 411 007

Received 19 November 1986

Airglow radiations in different portions of the eletromagnetic spectrum have been studied in many aspects at middleand high latitude stations, from ground-based observations, rockets and satellites. A variety of instruments have been de-veloped which focus on different principles of optical probing of the upper atmosphere. Tropical latitudes differ from themiddle and higher latitudes in terms of atmospheric structure, dynamics and the high input level of the solar energy duringthe daytime. Airglow studies in low and equatorial latitudes are less developed owing to the limited number of stations anddifficulties due to poor meteorological conditions. As a tropical country, India possesses certain advantages for airglowstudies; its geographical position is unique and there are no other airglow observatories in its longitudinal sector.

For the past many years, 'optical emissions from the earth's upper atmosphere' has been the subject of research at a fewinstitutions in our country. Different techniques have been developed, suitable for ground-based observations, and bal-loon and rocket-borne studies. Morphological, dynamical as well as application aspects have been included in these stud-ies. A stage is reached for taking a look at what has been achieved and what can be planned in future. In this review, the au-thor has sketched different stages of development of airglow studies in India and has suggested actions for future growth ofthe subject in the country.

1 IntroductionPhysics of the airglow is a diversified subject and

many scientists consider this to be the secret of itscharm. It is interesting to recall that the presence ofairglow emission from the night sky was noted in1895, purely as a nuisance, since it interfered with as-tronomical spectroscopic observations. Existence ofwhat is now termed 'airglow' was established photo-metrically by Yntema in 1909. Around 1910, airglowwas recognized as a detached phenomenon of physi-cal interest through the pioneering investigations ofFabry', Van Rhijn ', Babcock.', Slipher", Lord Ray-leigh", Dufay", McLennan and Shrum 7 and a 'fewothers. The book by Chamberlain" is a good startingreference for readers having historicalinterest in thissubject.

The word 'airglow' was introduced by Elvey? at thesuggestion of Otto Struve. Roach and Pettit!" beganusing the term nightglow to mean the nighttime air-glow. The terms dayglow and twilight glow logicallyfollowed.

Chamberlain" defines 'airglow' as consisting of thenon-thermal radiation emitted by the earth's atmos-phere, with the exception of auroral emission (ob-served at geomagnetic latitudes, ~ > 45), lightning,meteor trails, ctc.In the low latitudes, such as tropics,airglow is considered to be free from auroral emis-sions (See Fig. I).

The primary objective of airglow studies has beento monitor, in a remote sensing way and ill situ, chemi-cal composition and the structure of the atmosphere

84

and the physical processes which influence these,such as radiation and dynamics, under various geog-raphical and physical conditions. In the early days,realization of this goal was hampered because it wasnot possible to ascribe a height at which each airglowemission originates with any degree of certainty. VanRhijn 12 (1921) first gave the rather simple expressionfor the height of the emitting layer, assuming a planeparallel atmosphere. However, the practical difficult-ies of correcting for the effect of absorption and scat-tering of emission in the lower atmosphere renderthese so called Van Rhijn heights quite uncertain. Fora number of years, theoretical predictions of airglowintensity and its time variation suggested on the basis

I I I I 1

- -HIGHTGlOW. •• ..,..

AURORA6300 6300- 6300 _

6300.5577

- ~ AURORAL POLAR -TROPICS LATIT\XlE ZOIIE CAP

»e ~.1~1I.55771 5577

.l1ll -

0 1 I I I I I I I

400

100

o 10 20 30 40 50 60 70 80MAGNETIC lATITLOE IN DEGREES

Fig. 1-Latitude-height relationship of aurora. polar cap andNightglow(Rd:RoachandSmith")

AGASHE: AIRGLOW STUDIES IN INDIA

of Van Rhijn heights disagreed with experimental ob-servations of airglow emissions. A clearer pictureemerged after 1956 when the first rocket experimentsestablished emission height of the green line of atomicoxygen around lOOkm (Berg etal:", and Kooman etal.14

). These and later technological developmentshave played a significant role in the advancement ofour knowledge of airglow phenomenon and of earth'satmosphere.

2 Developments In Airglow ResearchTechnologically, four distinct stages of airglow re-

search may be recognised. The period before 1945forms the initial stage, during which ground-basedspectroscopy and visual photometry were experi-mental tools. Wavelength determination and identifi-cation of airglow emissions are the achievements ofthis period. Important basic characteristics of the air-glow phenomenon were established during this earlyperiod. The period following the World War II ush-ered in the second stage with new type of instruments.Development of photomultiplier tubes (PMT), opti-cal interference filters, and electronics, gave the muchneeded technological boost to the airglow research.Technology enabled extension of the range of airglowobservations to UV and IR regions of the spectrum.Instruments having ultra-fast time response could bebuilt using PMTs. These instruments facilitated mor-phological studies of different airglow emissions dur-ing the years 1950-60. The number of airglow obser-vatories increased during this period, enabling studyof global trends in time variations of airglow emissionintensities. This study revealed the need for interna-tional co-operative research effort in the study of at-mospheric phenomena. This led to the IGY and IGCprogrammes in which many countries in the worldparticipated. These programmes directed the fo-cussed attention of international scientific commun-ity towards atmospheric research. Airglow studiesthus got more organized and rapid progress was madein understanding the phenomenon.

The period I<Hi0- 70 may be called the decade ofmulti-diagnostie measurements involving study ofcorrelation between airglow and other ionospheriephenomena, rocket measurements and the beginningof satellite observations. During this period airglowresearch enjoyed spectacular growth. Important newdiscoveries were made in this period, such as the ex-istence of the tropical red arc, existence of E- andF-region components of 0(1 )5577 A nightglow emis-sion, detection of singlet delta emission of molecularoxygen and its relationship with mesospheric ozone,etc. With improved understanding of the airglowphenomenon, attention of the scientists turned to-ward applications. Kinetic temperatures are inferred

from interferometric measurements; fluctuations inOH nightglow intensities are interpreted in terms ofgravity waves. Relationships have been establishedbetween ionospheric phenomena and airglow.

Instrumentation advanced considerably duringthis period enabling study of dayglow emissions ofatomic oxygen, molecular oxygen, atomic sodium,etc., using ground-based systems. The detection ofdayglow emission at the ground is highly challengingdue to the solar continuum background being manyorders of magnitude higher than the dayglow emis-sion intensity. This technological break-through wasachieved through the use of high resolution opticalsystems, such as Fabry-Perot etalons used in tandem,in combination with narrow passband optical filter.The system becomes highly sophisticated and not ea-sy to handle. However, it was soon realized that if themeasurements are carried out from a high altitude,much simpler optical system becomes adequate.Hence most of the dayglow measurements during1965- 70 were carried out using either an aircraft, bal-loon or a rocket. High altitude balloons and rocketshave been used in large numbers for dayglow studies(Noxon!").

Studies of twilight emissions also received consi-derable attention during 1960-70. Here the majoremphasis was on the determination of abundancesand height distributions of alkali and other metalatoms, like calcium, strontium, barium, etc. Anotherarea of interest in twilight studies was the identifica-tion of physical processes like resonance scattering,pre-dawn enhancement of airglow emissionetc.(Hunten II,).

Since 1971, satellites and Spacelab missions are be-ing used, in addition to balloons and rockets, as highaltitude orhitting observatories for airglow research.In rocket experiments, useful sampling time for col-lecting scientific data is rather short. Experi-mentalsatellites now enable global monitoring of airglowemissions over prolonged periods. Spacelab has fur-ther advantage of having a fairly big size laboratorycomplex, accompanied by trained scientific assist-ance on board for deployment and operation of theinstruments and for accidental minor corrections. Inthe Spacclab missions, instruments are recovered af-ter the experiment and hence instruments havinghigher degree of sophistication and those requiringrather critical alignments or adjustments and re-covery, are flown in Spacclab.

It needs to be specially remembered that, althougha considerable advancement in observational meth-ods has recently taken place due to space vehicles andother high technology, the need for ground-basedmonitoring of the airglow phenomenon has not van-ished. Most of the advanced methods of airglow re-

85

INDIAN j RADIO & SPACE PHYS, VOL 16, FEBRUARY 1987

search described above, need the support of ground-based, regular methods of observation for establish-ing 'ground truth' and also as an important aid in theinterpretation of satellite and other data.

3 Airglow Studies in IndiaWith the above background, it would be interesting

to review developments in airglow research inIndia. In this standpoint, the present review differsfrom a subject review. Considering the upper atmos-pheric research scene in India around 1960, one findsthat many university groups were engaged in atmos-pheric research. Calcutta University had a strong re-search group and similarly there were a few othergroups. Atmospheric research groups in the nationalinstitutes were fully developed a little later, around1970. Among the Indian atmospheric researchgroups, a large number of them had major interest inionospheric research; a few strong groups were doingmodelling studies but hardly any groups were work-ing on reaction rate measurements in the laboratory.All these research areas are closer to airglow studiesand in fact some of these groups had partial interest inairglow research. Airglow research in India has un-doubtedly benefitted from the work of these groupswhose major interest was not airglow. In the presentreview. emphasis is on experimental airglow, to fol-low the natural trend of subject development in India.The term 'airglow' includes dayglow, twilight, andnightglow, as explained before. Oayglow research,being highly specialized. commenced later, in 1975,in our country. Prior to 1<)75, the term 'airglow re-search' implied nightglow and twilight studies.

3.] Beginning of Airglow Studies in IndiaNightglow studies in India began with Lord

Rayleigh's experimental work at Kodaikanal during1925-27, in which intensity of oxygen green line at5577 A was measured. Lord Rayleigh sent a numberof photometers, which had previously been calibrat-ed against a master photometer, to different parts ofthe world. Hernandez and Silverman'? have estimat-ed the mean intensity of the green line at Kodaikanalfrom Rayleigh's measurements to be 164 rayleighsrepresenting a midnight average for 54 nights.

The first spectra of nightglow were obtained byRamanathan IX at Poona. The green line appearedprominently. Later, Karandikar'" described in detailthe spectral characteristics by giving very long accu-mulated exposure extending over several nights. Healso studied the intensity variation of the green linefrom photographic photometry. Taking advantage ofblack-out conditions in 1<)42, Chiplonkar" studiedthe intensity variation of 5577 A radiation at Poonausing a visual photometer. Similarly. Ghosh " and

86

Mitra'? measured the intensity of nightglow atCalcutta. Night glow spectra were also studied byBappu+' from Hyderabad during 1947-49. These in-vestigations show that the lines observed in the tropi-cal region are identical to those observed at middlelatitudes. No new emission features have been report-ed. The relative intensities of different lines may how-ever, be different because of differences in the latit-udinal dependence.

3.2 Airglow Studies during the Period ]954-1970The next phase of nightglow studies in India started

after 1954. This phase ushered in the age of photo-electric photometers in India. Poona University andthe Physical Research Laboratory (PRL), Ahmeda-bad, have been the two main experimental centrescarrying out airglow research in India. In the beginn-ing, the gree line of atomic oxygen at 5577 A waschosen for study owing to its prominence in the visibleregion of airglow spectrum and also due to technolog-ical feasibility of its study. In this study, the mean in-tensity and the diurnal and annual intensity variationsof this emission line were established for the tropicalregion and compared with observed characteristics inthe middle and high latitudes (Chiplonkar and Kul-kami " and Kulkarni:"). IGY and IGC programmesgave a great impetus to the airglow studies in India.These programmes aroused interest in airglow re-search among other experimental groups. Twogroups, one at Uttar Pradesh State Observatory,Naini Tal, and the other at Kodaikanal observatory,took up airglow work for some time. PRL group alsocarried out airglow studies from Gulmarg in Kashmirfor some time.

After 1960 airglow studies were extended to in-cludeoxygen red line at 6300 Aand the sodium ernis-sion at 5893 A during the nightglow and twilight. Thisstudy revealed the characteristic azimuthal intensityvariation of the red emission which was subsequentlyrecognized as the signature of the tropical red arc(Chiplonkar and Agashe " and Kulkarni and Ra027).

Intensity measurements of Meinel OH bands:" in thenightglow were undertaken at Poona in 1965. PRLgroup undertook studies of luminescent chemical va-pour clouds?". Study of correlation between differentnightglow emissions was not conclusive perhaps ow-ing to difficulties in correcting for OH contributiontransmitted through different emission filters. In filterphotometry, it is fairly common to use two-colourmethod for subtracting out, from the raw data, con-tributions of unwanted emission. This makes the finalresult highly dependent on the characteristics of both.the set of filters used in the instrument and the part ofthe airg.low spectrum transmitted by them. There arcnumerous OH bands occurring. throughout the visi-


ble region of the airglow spectrum; there is also air-glow continuum which was not known well enough. Ifthe optical filters used in the airglow photometer arenot sufficiently narrow the derived emission line in-tensities may contain unknown percentage of OH orcontinuum contribution which will influence correla-tion.

3.3 Airglow Studies after 1970After 1970 airglow research in India took strides.

On the one hand, study of 0(1) 5577 and 6300A.emissions got further strengthened through the use ofa twin-channel photometer with extremely narrowband optical filtcrs " and through extensive measure-ments on Meinel OH bands:" - ):;.The first rocket ex-periment for measurement of 0(1) 5577 A. emissionwas conducted from Thumba by the PRL group".Similarly, measurements of dayglow emissions of so-dium were started at Poona ". In addition to filterphotometry, the PRL group also developed interfer-ometric systems for airglow studies.

This upward swing of research activity appears tobe continuing in the eighties. During the coming yearsinterferometric methods will be developed at Poonafor measurement of neutral temperatures and windswhereas the work being done by the PRL group willhe further strengthened. The ground-based measure-ments planned by different groups of OH nightglowwill be used for estimating meso spheric temperatureand for studying atmospheric gravity waves. Experi-ments involving measurement of IR dayglow havebeen carried out by the Poona University group fromground during the Indian total solar eclipse of 1980and recently in a high altitude balloon expcri-mcnt" - 411 from Hyderabad. Additional balloon ex-periments are planned during the IMAP-C period.Rocket experiments for the measurement of IR day-glow volume emission rate profile are also planned bythe PRL group. Experimental measurements onboard an Indian satellite are likely as also those on

Spacelab missions. Indian Middle Atmosphere Pro-gramme (IMAP) and its continuation till 1989 hasgiven much needed boost to applied airglow research.New groups such as NPL and Centre for Earth Sci-ence Studies (CESS), Trivandrum, have either takenup airglow research or have plans for it. Table 1 liststhe airglow observing stations past, present andplanned during the eighties.

4 Broad Areas of Activity in IndiaPast and present activity may be classified as

follows:

1. Study of nightglow emissions2 Dayglow studies3 Twilight emissions, general photometry of twi-

light4 Study of rocket-released chemical vapours5 Theoretical and laboratory studies

Regarding the last activity, theoretical studies are car-ried out by all the active groups to some extent. Somework on determination of reaction rate constants inthe laboratory is presently carried out in BARC,Bombay, particularly in relation to singlet delta oxy-gen and OH emissions.

4.1 Measurements of Nightglow EmissionsStatus of Indian measurements of nightglow emis-

sions is summarized in Table 2. Some further detailsare given in the following.

ATOMIC OXYGEN

The major emission of the nightglow in the visibleregion is the green line of atomic oxygen at 5577 A.,which is related in some respects to the red doublet ofatomic oxygen at 6300A. and 6364A.. The red dou-blet is referred to as "the red line of atomic oxygen at6300A.'. In India the most extensive measurementsare on atomic oxygen emissions and are made mostlyby ground-based photometers.

Table I - Airglow Observing Stations in India

Station Lat. Long. Geomag. Activity" Group/RemarksN E lat.

Kodaikanal 10.23° 77.4W I.W I (past) Observatory(Past)**

Mt.Ahu 24.tlOO 72.700 15° 1.2.3.4 PRL. AhmedabadNainital 21).50° 71).50° 11).4° I (Past) Observatory

(Past )***Poona IX.50° 73.12° 1)0 1.2.3 Poona UniversityTrivandrurn XS 7tl.6° O.So I (Planned) CESS. PlannedWaltair IXo X3° 1)0 1 NPL. New Delhi

* Activity classification is as given in the beginning of Sec. 4.** Airglow station was operated bv Kodaikanal observatorv around 1'16'1 and by the NPL group during 1'I7X-7'1.

*** Uttar Pradesh State Observatory. Naini Tal. Period of Operation 1'160- 7 S

87

INDIAN J RADIO & SPACE PHYS, VOL 16, FEBRUARY 1987

Emission

Table 2 - Indian Measurements of Airglow Emissions

Type of study and the research groups

Atomic oxygen 0(1) 5577 AAltitude: 100,300km

do

do

do

do

Atomic oxygen 0(1) 6300,6364AAltitude: 300 km

do

Atomic sodium D-Lines, 5890,5896AAltitude: 85-90 km

do

Meinel hydroxyl bands OH (7,2);(8,3); (9,3); (9,4)Altitude: 80-90 km

Meinel hydroxyl bands in thencar infraredAltitude: 80-90 km

Meinel hydroxyl bands OH (5,3)at 1665 nmAltitude: 80-<)0 km

Instrument and type ofmeasurement

Fast spectrographs, Ground-based, Cumulative exposure dur-ingnights

Visual photometer, Ground-based, Night observation

Photoelectric photometer (Twin-channel, narrow band filtersafter 1974), Ground-based,Nightglow and Twilight

Rocket photometer, Midnightmeasurement

Fabry- Perot interferometerWide-angle Michelson (WAMI)

Photoelectric photometer (Twin-channel, narrow band filters after1974 at P.U.), Ground-based,Nightglow, and Twilight

Fabry-Perot interferometerWide-angle Michelson (WAMI)

Photoelectric photometer,Ground-based, Nightglow, andTwilight measurement

Zeeman photometer, Spectralscanning polarimeter, Dayglow

Photoelectric photometer,Ground-based, Nightglow andTwilight measurements

Photography of the OH layerfrom the ground and Space labusing image intensifier camerasystem

IR photometer. Daytimemeasurement. Balloon-borne ex-periment

Spectroscopy of the night sky, Ramanathan,Karandikar, Bappu. Approx. period:1930-1936; 1948-1950

Diurnal intensity variation, Chiplonkar, Mitra,Ghosh (1942-1950)

Diurnal, azimuthal, annual intensity variation;Correlation with other nightglow emissionsand with other parameters: like geo-magnetic,solar activity, etc.; Separation into E and F re-gion components; Calculation of plasma pro-perties (F region), Oxygen atom densities, etc.(P.U., PRL, NPL, Naini Tal (Past), Kodaikanal(Past), CESS (Planned)

Volume emission rate profile of the E regioncomponent of the night glow; Calculation ofatomic oxygen abundance; Theoretical studies(PRL)

Ground-based measurement of Doppler tem-perature; Thermospheric winds; Study of at-mospheric structure parameters (PRL- Ongoing; P.U. - Planned)Diurnal azimuthal, annual intensity variation;Tropical red arc morphology, F-region dy-namics, Winds, Ionospheric drifts, Correlationwith other nightglow emissions & other par-ameters: like geo-magnetic, solar activity;Application of semi-empirical relation (P.U.,PRL, NPL, CESS (Planned), Naini Tal andKodaikanal in the past)

Ground-based measurement of Doppler tem-perature; Spread F; Winds; F-region, Ionos-pheric drifts, Plasma flow, etc. (PRL - 'On go-ing'; P.U. - Planned with WAMI set-up)

Diurnal azimuthal, annual intensity variation;Calculation of abundance, Covariation withother nightglow emissions, other parameters(PRL, p.u., Naini Tal - Past)

Diurnal and annual intensity variation, Calcu-lation of abundance (P.u.)

Diurnal annual intensity variation, OHchemistry, Correlations, Rotational tempera-ture, Diurnal variation of temperature.Fluctuations, Periodicities in rotational tem-perature variation. Atmospheric gravity wavesand tides, Mesopause winds (PRL. P.ll. NPL.CESS - Planned)

Photography of the OH layer to study travell-ing waves. Study of mesopause dynamics.Gravity waves. Tides. Winds (PRL)

Intensity variation. OH chemistry. Abundance.Mesopause dynamics (P.U.)

88

Contd.


Emission

Table 2- Indian Measurements of Airglow Emissions- Contd.Instrument and type of Type of study and the research groupsmeasurements

Molecular oxygen 02( IL\) 1270,1580 nmAltitude: 50-100 km

do

IR balloon-borne photometer,Daytime measurement

Intensity variation, Ratio I( 1270)1 I( 1580),Photo-chemistry of singlet delta oxygen andozone, Abundance of O,(I~g) and ozone (P.u.)

Volume emission rate profile of 02( I~g) Abun-dance of 02( I~g) ozone (PRL)

Rocket photometer, Daytimemeasurement

;.A

Nomenclature

Atomic lines

5198.55200.75577-

Nitrogen doublet

Oxygen green

5890 Sodium D-lines58966300 Oxygen red6364Aitglow continuum (See Note 3)

5700-5850 Int. max

0, Bands

3100-5000 Herzberg

7619( 0 - 0) Atmospheric

Meinel OH Bands (See Note 5)

6460-6690 OH(6,1)

OH(7,2)OH(8,3)OH(4,0)

6800-71007200-75007550-7760

Table 3 - Identified Airglow Spectrum(Visible-Near IR)

Average*intensityrayleighs

1-2

250

20-150

50-500

3to5R/A

600

6 to 8 kR

120

280460300

Emission**altitude

km

300

100(E-layer)

300(F-layer)90

250-400

90

Excitation mechanism & otherremarks

0+ + N, - NO+ + N, Followed byNO+ +e-N*(2D)+O(3P)Chapman and Barth Mechanisms(See text)Dissociative recombination of O{NaO + 0 - Na*(2 P) + O2, alsoNaH + 0 -Na*(2P)+ OHDissociative recombination of 02+

NO+0-N02+ hv(Other reactions are also proposed.)

Transition

0['5,,-'D,1

Na[' P, 2 - '51 21Na[2P'2 - '51,10[ID2-'PIJO['D2-'P21

90 0 + 0 + M - OW~:) + M. These are Ol'~: - '~g-)forbidden bands. Additional bands, notidentified, are also present in this re-gion.

80(Note 41 0 + 0 + M - OJ(l~g+) + M, Also O,(I~: -'~~-)0+ 0, - O!( I~:) + O,('~~-)

85

858585

-.7l'J ~ - - Jr3 ~

2 JrI.2 - 2.7T12

Exothermic reactionO,+H -02+0H*( V' ~ 9) produces excited OH mole-cules in the vibration levels up to ninth.The secondary mechanism for excita-tion to V' < 6, is given byHO, + 0 - 0, + OH*(V' < 6) its contribution to totaln(OH*)may vary with latitude.

*Notel: Average intensities listed above indicate normal levels. Airglow intensities are variable.""Note 2: Altitude of the peak of emission. It may be a broad region.

Note 3: Airglow continuum extends from 5200 to beyond 6500 A. Intensity has a broad peak at 5700-5850A.Note 4: Band origin at 8645 A. Intensity peaks of P&R at 8659 and 8629 A respectively.Note 5: Vib-rot bands within the ground state' JTstate of OH molecule in mesosphere. Out of P, Q and R branches, R forms the band-

head. Bands extend from UV to Far IR and are well resolved. Only a few bands are mentioned in Table 4. For details seeChamberlain".

The mean intensities reported for different periodsby different stations arc listed in Table 3. During thelGY, photometers at Poona and Mt. Abu were inter-compared, in a joint experiment, with international

airglow standard, in relation to absolute calibration of5577 A emission. This intercalibration has not beenrepeated subsequently; hence the probability of dif-ference in calibration during later period must be con-

89

INDIAN J RADIO & SPACE PI-IYS, VOL 16, FEBRUARY 1987

sidered. The green line is known to exhibit a solar cy-cle effect. The diurnal intensity variation is character-ized by a maximum and a pronounced minimum dur-ing the night (Fig. 2). On the magnetic equator, how-ever, diurnal variation (Fig. 3) is found to be differ-ent ". All Indian stations show a considerable varia-bility in the diurnal variation. It is now known that inthe earth's atmosphere, the green emission originatesin two distinct regions having altitudes of around100km and 300 km respectively. Following ionos-pheric terminology, these are called E- and F-regioncomponents respectively. Their excitation mechan-isms are assumed to be the following:

E-Region Component (100 km)

CHAP:v1A"I :v1f-.CHA"IISM

o + 0 + 0 - O2 + O( 1S) ... (1)

OR HARTH Mf-.CHA"IISM

o + 0 + M - Ot + M ... (2)

... (3)OJ + 0(3 P) - O2 + O( 1 5)

Reaction (3) is in competition with

OJ+M -02+ M

OJ + 0(-1 P ) - O2 + O( 1 D or ' P )and

OJ-O:?+hv

... (4)

... (5)

... (6)

In one of the detailed review papers, Bares:" has con-cluded "Much chemical kinetics remains to be donebefore the emission of 5577 A in the nightglow is un-derstood."

F-Region Component(300km)

IJISSOCIAIIVi". RI-.COMHI"IATIO"l 01' 0.:

0; +e- -0('S)+0('P)+2.7geV

NEYYAR DAM

'"~'"} 300

>"'...inzw...z-

B ZENITHR·O·O~

7'· NO"TH"-0'121

c

300

hrs I ST

Fig. 3-Diurnal variation of 0(1) 5577 and 6300 A nightglowemissions on magnetic equator (Nayyar Dam. Geog. X.S5°N.

76.Y3°E. Geomag. 0.63°S); Rccorrclation coefficient(Ref: Kulkarni and Raol~)

which is claimcd " to be at least five times as possibleas

... (8)

31 JAN. -1 FEB. ,1968~OO~--------------~-------------,III.J::..~300v>-o•..•..200>-r(fl2:lLJ 100t--z......

ZENITH

o 02hr s 1ST

O~ 0620 22

(·i!!. 2-Diurnal variation of Oil; 5577 and (d()O A niglllgl()\\< cruissions at Mt. Abu iRef: Kulkarni and Ra()~ . ('17 ( )

90

Since 0(1) 6300 Anightglow emission results fromO( 1 [)) state, many airglow stations found partialcorrelation between 5577 A and 6300A emissions.The correlation is likely to be stronger during en-hancement of F-rcgion nightglow!'. In a remarkablysuccessful attempt, volume emission rate profile oflower 5577 A layer has been measured in a rocket ex-periment from Thumba by the PRL group ". Therocket measurement, carried out on 3rd February,IlJ73 at 0035 1ST, shows the emission peak at102 ± 2 krn, with half-width of II ± 2 krn, volumeemission rate at the peak, 47 photons cm - 1S I and in-tegrated intensity approx, 65 raylcighs (Fig. 4).

French group operating airglow station in the tropi-cal region from Tarnanrassct. Algeria (Iat. 22.HOoN,long. 5.52°1::) have found that airglow emissions fall


into three groups+' of different co-variance and alti-tude, as shown in Table 4. The radiations of anyonegroup covary, while the correlation is poor betweentwo different groups. As stated above, an exception tothis classification comes from the double-peaked dis-tribution of 5577 A emission altitude. At high altitudewhere quenching of the (ID) state is negligible, the ra-tio of transition rates 5577 N6300Ais 114; experi-mentally this ratio is found to be constant". At low lat-

o 10 20 30 40 so5577 Jl. PHOTONS. cm-3 5-1

Fig. 4- Volume emission rate profile of 0(1) 5577 A E-Iayer,measured in a rocket experiment from Thurnba

(Ref: Kulkarni")

itudes, 5577 A intensities are systematically weakerthan at middle latitudes by about 40%. Analysis of theintensity gradient with latitude from a number ofstations confirms the existence of an equatorial"trough" of 5577 A emission (Christophe/"). Intensit-ies decrease regularly between 25° and 10° geogra-phic latitude in the Sahara (Fig. 5).Thus the equatorial5577 A lower layer exhibits very smooth variations inspace and time; enhancement cells46.47 typical of mid-dle latitudes do not appear. The world's minimum in-sensities must lie along a "5577 A Equator" shownschematically in Fig. 6 (Barbier et al.4R). Annual in-tensity variation of 5577 A emission is shown in Fig. 7for nothern, tropical and southern stations (Weill'"),

The behaviour of 0(1) 6300A emission of night-glow in the tropics is quite dynamic and different fromthat at middle latitudes. Except SAR, 6300 A exhibitsquite regular distribution and variation features atmiddle latitudes. In contrast to this, the high altitudeemission at 6300A in the tropics, undergoes abruptand intense variations closely related to the 'magneticanomaly' in the F_region27.30,49-53. The most spectacu-

Oct.26 1962

TAMANRASSET and AGADEZ

If 5577 (lower layer) isophotes

10~--~--~---r---T---'----~--?---~--~03 UT21 00

Fig. 5-A typical set of isophotes of 5577 A (E-Iayer) versustime and latitude (Ref: Wei1l44)

Table 4-Covariance Groups of Airglow Emissions

Group Emission Wavelength E. iissionA altitude

km

A Oxygen green 5577 <n0, Herzberg bands 3100- 5000 90Airglow continuum 5700-51l50 I(max) 900, Atmospheric bands 7619-1l645 IlO

B Sodium D-lines 51l9() & 51196 90Meinel OR hands. 31l00-Far IR 115

C Oxygen red 6300 & 63(14 250-400Atomic nitrogen 519H.5 & 5200.7 250-400

I. Emissions within each group are well correlated with one another, both through one night and in night-to-night fluctuationsthrough the whole lunation.

2. At a particular time of year, a nearly linear relationship exists between the intensities of any two emissions within groups (A)odB)

3. The groups (A! and (B) tend to vary independently: they may also appear to become coupled and vary in a parallel way forseveral hours.

(Vide Chamberlain", p. 517)

91


lar global feature known as 'tropical red are', appearsin the form of finely structured airglow intensity en-hancement. Two regions of maximum enhancementoccur symmetrically with respect to the dip equatoraround magnetic dip latitudes ± 12°, The regions are

wC:J 60~~4 30....Jc,C 0

30

AIRGLOW EOU.(5577 )

~:!:30....JCJ~ O~~r-~ __~A~I~R~GTLO~W~E~O~U~A~TO~R4 Jan Apr Jul Oct Jan SEASONfig. 6-Seasonal movement of zone of maximum and minimumintensities of 5577 A at middle latitudes (maxima) and near the

equator (minimum) (Ref: Weill+')

92

0.5

Haute Provence ~ 44"

Tamanrasse t

0.5

Ker'lueten " - 49"

O~~~-r-r~-'--r-~'--r-r~Jan Apr Jut Oct Jan

Fig. 7 -Seasonal variation of 5577 A at northern. tropical andsouthern latitude stations (Ref: Weill+")

statistically aligned on a world-wide and local scale,along the magnetic isoclines. In the ground-based air-glow observations (Figs 8 and 9), the tropical red arcappears as a broad subvisual band of enhancementwith a latitudinal extent of about 500 km at half in-

POONA

,o~ __------~~ ~-----------2-'40--1-S~T--~9/10 JAN 7!>

>- 200•...'"zUI•...~ 100

( c

o

o

W S E NAZIMUTH AN(OLf(O)

Fig. H-Ohservation of tropical red arc at Poona (Ref: Agasheand Gurao':')

f'IT. ABU JAN. II - F£I. I t 1961

aOlo _

~•..~ O'L.-~~ _

••••SOO•..~ 400

oc 300

o~•••

I • w ••AZIMUTH

USO400

300

aoo

o,~~--.---.-_300 0210100 7f!.n-_.100 y~ \~

0' L.--.--.---.- ....•::1 7d.1Y: ono100.-A· ',\..

o • • I

IOO[~o· I

IOOt~JOo 7S' -.....0-,

•• I , W ••

Fig. 4-Azimuthal variation of 63()() A nighlglow at Mt. Abu.showing the presence of tropical red arc (Ref: Kulkarni and

Raoc'l


tensity, extending across the sky in the east-west di-rection. Arc's altitude can vary between approxi-mately 200 and 400 km. In the early night hours, asmooth intensity variation appears to travel from eastto west as if the earth were rotating under a configura-tion fixed with respect to inertial space. Intensitysometimes appears to be progressively transferredfrom one fine structure to another. As the night pro-gresses, the arc slowly moves toward the equator.Throughout the night, the arc intensity generally dec-reases. The above characteristics of tropical red arcobserved at Tamanrasser':' are identical with thoseobserved at Mt. Abu and Poona~h.n.3().43.44':;''.Markedvariations in intensity and appearance occur with so-lar cycle activity. Higher intensities prevail and arc isdeveloped well during high solar activity period; alsoarc is formed at more northern latitudes compared tolow solar activity period. During low activity periodgeneral arc structure is absent and the structure de-generates into enhanced regions. At times of intensemagnetic storms, the tropical red arc system is oftenseverely altered 53.

A semi-empirical relation found by Barbier andfurther discussed by Peterson et a/.54 brings out rela-tionship between 6300 A intensity and ionosphericF-region parameters. This relationship has been usedin the analysis of airglow data at Indian stations+'. Di-urnal intensity variation of 6300 A(Figs 2a,b) shows aprincipal maximum before midnight and often a sec-ondary maximum in the post-midnight period is seen.Times of the principal maximum either coincide withtransit of tropical arc atzcnith or with the lowering ofthe height of 6JO() A layer which is related with ionos-pheric height, h'F, in view of semi-empirical relation(Fig. 10).Changes in h'F are described as ionosphericdrifts and may be explained on the basis of E x Bandneutral wind effects on meridional movement of ioni-zation (Behnke and Kohl"; Blamont"; Kohl'"). Overthe Indian tropical region, magnetic declinationo = 0, hence only the meridional component of thehorizontal wind vector is effective in producing ion-ospheric drifts. 6300A nightglow measurementsfrom Poona have been analyzed to estimate meridion-al component of horizontal neutral wind in the nigh-ttime ionosphere. It was found'" that estimates ofwind velocity made from movement of tropical redarc appear to be reasonable during the pre-midnightperiod. Nightglow measurements of 5577 and6300A carried out from Kodaikanal and Waltair bythe NPL group have been analyzed to determineatomie oxygen densities and atmospheric structureparamcters"?". Measurements of 6300 A nightglowcarried out by the PRL group using a Fabry-Perot set-up are under analysis to study line widths, kinetic tem-peratures, winds and spread F.

16300 --160 h'F ~ 300

120 280

80 260

40 240

1/1 220.cCJlClJ~ 120 3200L-

80 280 E>- ~r--

~I.f) 40 240 IZ ~WI- 200 ~Z- 200 MAY 1965 300

160 z ec

120 260

80 240

00 02 04

hrs 1STFig. to-Monthly average I 6300 A. and h'F at Mt. Abu Delhi

(Ref: Kulkarni':')

THE SODIUM D LINES AND OH BANDSPeak altitude of these emissions is between 80-95

km which is the upper part of mesosphere. In the past,sodium nightglow has been studied at Poona, Mt. Abuand Naini Tal but studies are less extensive. Mean in-tensity during the IGY-IGC period has been reportedaround 100 rayleighs. Diurnal variation shows a max-imum during the night. i vnnual variation has a maxi-mum in winter.

Sodium dayglow has been studied at Poena Uni-versity with a Zeeman photometer and a spectralscanning polarimeter. In the Zeeman photometer, anarrow band interference filter restricts scatteredbackground entering the instrument to a narrowwavelength region around 5893 A. Transmitted radi-ation is incident on a sodium vapour cell, maintainedslightly warm in a de magnetic field. Sodium atoms inthe cell scatter the incident radiation selectively inwavelength; cross-section for scattering peaks at Dline wavelengths when the magnetic field is 'off' and atZeeman shifted wavelengths when the field js 'on',The spectral scanning polarimeter consists of mon-ochromator with a twin-channel polarization unit.Dayglow measurements show" I a slight asymmetryaround noon in the diurnal variation and a small sea-sonal variation with maximum in winter.

93


In the past, studies ofOH bands were directed tow-ards morphology, diurnal and annual intensity varia-tion, etc. Observations from Mt. Abu and Poona Uni-versity showed that OH bands are fairly intense andextremely variable in behaviour (Fig. 11).Diurnal var-iation has different forms like (i) showing a maximumduring the night, (ii) continuously decreasing, (iii)con-tinuously increasing, (iv) showing periodic fluctu-ations, etc. Annual variation has a maximum in win-ter. Measurements= ..11.62 have not been sufficientlyextensive to show the effect of solar activity. Intensitymeasurements have been used (Figs 12-14) to makeorder-of-magnitude calculations of the intensity of

ZO 00 04 20 00 04 20 00 04OCT. 25-26. U

VDIC.19-ZO, ••

~, ..~/\,- 400....,"J

600

400

l:enz'"~z

~

NOV' 17-11,' ••

'v'\ •.~too"'•.----':-I---',,- -,-::-~-t-H.;.:C-.-,7---"~,,:-••.:..:...~

~

,

~

.ZO-II,....'" '-- ...

,.,, .,. ,.1 ...•,,'.. 400

20 00 04

- 0" (I-I)--- OM ('1'-1)

20 00 04 ZO 00 04

INOI.N STANOARO TIME

Fig. II - Diurnal variation of OH hand intensity at MI. Ahu(Ref: Rao and Kulkarni'"]

,,.•.

,----- ----- .•. _--

..II,,

\.\\\\\,\,

OH (9,3 ) BANDMAR.-MAY 1976.400r-

--------- --->-t: 200-(/)

zWI-Z

O~-~--~-~I--~--~--~I-~o w U 00 ~TIME,hrs 1ST

Fig. 12 - Diurnal variation of mean inrcnxity of OH (YJ) handat Poona (Ref: Agashe and Gurao "]

94

the total band system, and assuming ozone-hydrogenmechanism, concentration of OH* and ozone mole-cules has been calculated-" in an approximate man-ner.

The major emphasis in airglow OH studies has cen-tred around the chemistry of this minor atmosphericconstituent. It is known that the OH emission peaks in.the mesopause region of the middle atmosphere. Themesopause region occurring around 85 km repre-sents the regime of transition between the stratos-phere where complete mixing prevails and the lowerthermosphere where only binary collisions occur anddiffusive equilibrium holds for individual species.The temperature of the mesopause region is an im-portant physical parameter of vital interest in thestudies involving D-region ion chemistry and mesos-pheric dynamics. It was realized that the determina-tion of the rotational temperature of the OH bands inthe nightglow offers a means of observing from theground the mesopause temperature around 85 kmthroughout the night. Further, Krassovaskys obser-

N-0

><r--"I 41-u

Q)

III

0 I-uN

E<> 21-<,

0E'--'

,......, I-

"':1:0L-.I

0

.II,I\."....

\-, .._--- ---- .....•

'......... _-- --------- ....

20 00 0222TIME,hrs 1ST

Fig. 13- Variation of [OH*i molecules calculated from the dataof Fig. 12 (Ref: Agashe and Gurao")

-

2on I-Q I

[03J MOLI>< , 15 Z -I

"I MEAN 'V 1.0 x 10 em seeI

<> I FOR 70-100 km RANGEQ) \s: \,\

0 \<> \

\

N \

E \.u .,<, ....•. _ .._----

<,0 ",

~ "" ----- ---- --r;;;'

0L-J

0W 22 00 02

TIME, hrs 1ST

-

Fig. 14- Variation of integrated 10,1 molecules calculated fromthe data of Fig. IJ

AGASHE: J\IRGLOW STl;DIES IN INDIA

vation'" of infrasonic variations in the diurnal varia-tion of OH nightglow pointed to the feasibility of em-ploying these emissions as tracers of mesopause dis-turbances. Krassovasky considered effects of gravity-wave disturbances on a parcel of air in the mesopause.He found that gravity waves significantly alter OHdensities through modified chemical process. How-ever, density fluctuations resulting from dynamicaleffects are not the only ones occurring in the meso-

28-4-76

, I! ! ! !

27-1-76

160

12~~0~0~~~21~OO~~~2~~~~OOOO~~~-OO~~~-0~~~~-J~hrs 1ST

Fig. IS-Short and long periodicities in rotational temperaturefluctuations inferred from OH (7.2) measurements at Mt. Ahu

(Majmudar")

pause regime. Production rates of vibration ally excit-ed OH* molecules are temperature dependent. Thus,the fluctuations in the temperature T of the fluid par-cel associated with gravity-wave interaction will alsomodify OH chemistry and hence its density. In addi-tion to gravity waves there are also other dynamicaleffects, like tidal oscillations, which affect OH densit-ies. It is expected that the different dynamical pro-cesses will perhaps produce their characteristic peri-odicities in temperature fluctuations. Results of thesestudies33.35.64.65 from Indian airglow stations areshown in Figs 15, 16 and 17.

+40

-40t ~------------------~~~--------~=:>; +40

-40

Fig. 16-Diumal variation of U; the wave-induced horizontalcomponent of wind speed calculated from ~ TIT

(Ref: Majmudar-")

250ZOO1S0250

200150

250

200150250200150

25020015.0

250200

150

~-85

16-12-85~ ---------

~ I. - 3-86 1.-1.-86

I~

~s ~ss ------- ~5-3-86 5-4-86

I I~

~s r:::: ---- ---6-3-86 11-4-86

,

~9-1-86 8-5-86

~ ------- ~10-12-85 7-3-86,

14-12-8S ~ -------- 8-3-86~-~ --------11-1-86 9- s-ee

f-

~ ~ -----." "-----15-12-85 13-1- 86 9 - 3- 86 10- 5-115

21'0 01·0 05·0 21·0 01·0 05·0 21·0hrs 1ST

01·0 05'0 21·0 01·0 05·0

Fig. 17·- Diurnal variation of rotational temperature of meso-pause region estimated from OH 17.2) measurements at Poona

(Ref: Agashc 1'1 ul.hS)

95


Recent technological development in opto-elec-tronics, camera optics and computer-aided scanninghave enabled investigators to introduce new tech-niques in airglow research. Taking advantage of highintensity of OH emissions in the IR region, Frenchgroup carried out photography of the OH layer fromthe ground, using IR image intensifier-coupled came-ra system and computer-aided image processing'".They found that travelling wave disturbances couldbe photographed in the near IR region. Using thistechnique horizontal wave velocities and wind speedswere measured'". This technique has been success-fully applied in India by the PRL group. A number ofcampaigns have been conducted since 1979 from Mt.Abu, Gadag, Kemmangundi, Chitradurga (Karnata-ka) and Srinagar (J & K) to photograph the OH layerfrom the ground to study mesopause dynamics. Un-der the ISRO-CNES exchange programme, PRL isinvolved, in collaboration with CNRS, France, in ajoint experiment to photograph the mesospheric OHemission layer in the near infrared on board a Spacel-ab mission.

OH dayglow measurement using ground-basedphotometer has been reported by the Poona Ur?ver~-ity group38.6Kduring the Indian total solar echpse III

February 1980. A balloon experiment for the mea-surement of OH (5,3) bands in the dayglow has beenscheduled from Hyderabad during the IMAP-C peri-od.

4.2 Dayglow Emissions of Molecular OxygenIn 1954, Bates and Dalgarno discussed how and to

what extent solar radiation could be transformed intoan emission spectrum in the dayglow; where the infor-mation then available permitted, they gave upper li-mits for the intensity of the features to be expected.The major excitation processes appear to be chemicalreactions, fluorescent and resonant scattering, elec-tron impact, and photo-dissociation. All these occuras a result of sunlight incident upon the atmosphere.

Dayglow emission of molecular oxygen in the in-frared is caused by photo-dissociation of ozone bysunlight (2000-3000 A).

O)+hV-+02(1~g)+O(ID) ... (9)

Loss processes for excited oxygen molecules are:Radiative loss leading to dayglow emission at 1270nm and 1580 nm

02( I~g) -+ 02\'Lg) + hv

and the quenching loss

02(1~~) + M - 02(lLg-) + M

... (10)

... (11)

Singlet delta represents the first electronic excitedstate of molecular oxygen which gives rise to IR opti-

96

>C)a::wzw<1. 4I-

ZWI-

oo,o

DISTANCE ,.a)Fig. 18-'- Energy level diagram of oxygen molecule

calemissions at 1270 nm (0, 0 band) and 1580 nm(O,1 band) (Fig. 18).In the earth's atmosphere this emis-sion originates.in the 50-100 km region. In the spec-trum of day sky, this emission is very prominent, whenviewed at high altitude, above the scattering lower at-mosphere. The singlet delta state has a low spontane-ous radiative transition probability. Hence high spec-tral intensity of the dayglow implies a notable abun-dance of excited molecular oxygen, in the metastablesinglet delta state, in the mesosphere '.Excited oxy~enand ozone are both chemically reactive, and are Im-portant minor neutral constituents. of the ~e~os-phere, playing a vital role in the cherrustry and ioruza-tion processes of the D region. Due to its optical emis-sion, singlet delta state becomes one of the key mea-surable quantities and, using reactions (9) to (11),dayglow measurement provides a sensitive methodfor determining ozone at mesospheric altitudes.

Almost all measurements of singlet delta oxygendayglow have been concentrated at high latitude~('9.In India, ground-based measurements were carriedout by the Poona University group'" from G~dag inKarnataka, during the Indian total solar echpse of16th February, 1980. Eclipse measurements showedthat ozone concentration increases at all altitudesduring the eclipse (Fig. 19). At the eclipse mid-time,ozone concentration increases by more than a factorof two over its value at the first contact. After totality,ozone concentration decreases rapidly. Further anal-ysis showed that during the eclipse, destruction ofozone through reaction (9) progressively diminisheswhile its production continues unhindered throughthree-body chemical reaction."

O+02+M-O,+M ... (12)

Dayglow measurements using ground-basedphotometer are useful only during a total solar ecli~seor a late twilight. At other times, they suffer from m-tense background contamination due to scattered so-lar radiation at emission wavelengths, and depletion


FEBRUARY 16,1980GADAG, INDIA.1S·1."N 75'6°E

At 66 km

[oJ Centre _ 2.769CoJnrst

MIE [os! f •••rt~u 9 (O.l Firat -1'239"' '0Z

o~a::~zUJUZouUJZoNo

At 85 ~m10,) Centre!OwlFirat -2,500

[OS)fourth :1'885

lOolfi~

85 km

TOT.AL SOLAR ECLIPSE

Centre Fourth,t!' Contoc:t - first

1600 1700

TIME, hrs 1ST

Fig. I(}-Changes in [OJ] estimated from ground-based O2 (I ~g)intensity measurements (Ref: Agashe and Rathi"]

of detectable intensity reaching the ground level dueto strong absorption by oxygen molecules below theemitting region. Due to these reasons, dayglow mea-surements are preferred from a high altitude platformprovided either by an aircraft, balloon, rocket, ora sa-tellite. A balloon experiment has been scheduledfrom Hyderabad during the IMAP-C time-framewhen the first measurements of this emission from In-dia will become available". A rocket experiment forthe measurement of volume emission rate profile ofsinglet delta oxygen dayglow, planned for the sametime-frame by the PRL group, would be the first rock-et measurement from India.

4.3 Twilight Glow MeasurementsChamberlain defines the twilight glow as the air-

glow emission at a time when sunlight is shining on theemitting region of the atmosphere 'from below'. Thisis distinct from the dayglow where the sunlight entersfrom above, and from the nightglow where sunlight isabsent. The definition implies that the sunlight is re-sponsible for the excitation of the twilight glow in a di-rect or indirect manner.

At twilight, the upper atmosphere is available forstudy under transitional conditions. The inherent an-alytical advantage of twilight rests on the effectiveprobing of the upper atmosphere with altitude as anindependent parameter. Intensity measurements car-ried out during twilight may be of two types: (i) mea-surements of specific airglow emission features, likeatomic oxygen lines, alkali metal lines, oxygen bands,OH bands, etc., and (ii) measurement of sky bright-ness in a broad spectral region or 'white light'.

The first type of measurements are used for obtain-ing information about concentration of a species at aknown height in the atmosphere. The determinationof the abundance of the species can lead to an im-proved understanding of the physical state of the up-per atmosphere. However, there are very few studiesin India relating to this type of work. The second typeof measurements are relevant to the scattering pro-perties of tlre atmosphere and some work has beendone at Poona and Ahmedabad. In the past, Chiplon-kar et af.7°,7] made simplifying assumptions aboutscattering properties of the atmosphere and assumingthat only primary scattering by air molecules prevailsin the early part of twilight, obtained temperatureprofile. Recently, however, twilight observationshave been treated for a realistic situation, taking intoconsideration aerosol scattering. These studies areparticularly useful for studying stratospheric aerosollayer. For example, during a volcanic eruption largeamount of volcanic dust is injected into the stratos-phere which can be studied through twilight observ-ations. Stratospheric aerosol layer formed after ElChichon volcano eruption in Mexico was studied byPRL and Poona University groups 72-74 using this tech-nique.4.4 Studies of Chemiluminescent Vapour Clouds

Following a suggestion from Bates 75 to release so-dium vapour into the upper atmosphere to gain infor-mation on the natural sodium emission, both twilightand nocturnal rocket release experiments were start-ed around 1956. The experiment consists of releasingfrom a rocket, sodium vapour during twilight (solardepression 6°). The released vapours attain the am-bient conditions soon after the release ( < 2 min). Thecloud expands through molecular diffusion andwinds. The released vapours behave as tracers of at-mospheric winds, diffusion and temperatures. The al-titudes and brightness of the trail are measured byphotographing the trail from three stations and subse-quent triangulation. Later, other types of releaseshave been performed with a variety of chemicals. Thereleases are done either as trails or point releases. A~-ter a series of attempts to release resonant ions intothe atmosphere, a group at Max-Planck Institute wasable to release a barium vapour cloud which was ion-ized by the solar UV and which could be tracked aslong as the twilight condition was fulfilled. The mostimportant scientific output of the Ba releases was themapping of ionospheric magnetic and electricfields">" and ambipolar diffusion coefficient". TheBa atoms and ions have a number of emission lineswhose relative intensities may give information on theupper atmosphere.

In India, rocket vapour release technique was deve-loped by the PRLgrouparound 1963. In 1963-64, the

97


group carried out six rocket releases of sodium va-pour from TERLS, Thumba which are the ea~l~estex-periments near equator. These data were utilized toprobe the high shear region at 100-115 km whichshowed eastward zonal winds between 115-140 kmand westward above 140 km. Observations showed?"wind speeds in the range 130-170 km. From a series ofsuch experiments, Bhavsar et al.80.81 presented amean circulation pattern above 100 km and deter-mined diffusion coefficient and the turbopause heightto be 104 ± 1 km (Desai et al.82; Desai and Narayan-an?").

The PRL group also participated in an Indo-Ger-man collaborative campaign in 1968, during whichfour barium-strontium point releases were carriedout at four different altitudes ranging between 93 and207 km to determine vertical winds and turbulenceover Thumba='. The PRL group also participated in aCommonwealth collaborative campaign between In-dia and UK, during which artificial ion and neutralclouds were released at altitudes between 150 km and160 km, using Petrel rockets launched from TERLS,Thumba. These experiments enabled the study ofelectric field components, winds and the equatorialelectrojet over Thumba'". Anandarao and Raghava-rao'" also studied gravity waves and tidal winds in theequatorial thermosphere using the wind profiles re-ported by different observers. Recently, the PRLgroup has carried out these measurements over Sri-harikota Rocket Range (SHAR) having a dip latitudeSSN. These experiments were carried out usingmultiple Ba-Sa blob releases and rocket-released so-dium trail during the evening twilight on geomagneti-cally quiet and severely disturbed occasions using a

>-I-

~ 1·0WI-Z

w>~...J 0·5wcr

0·0 l...!::~~~~ __ ..L-_~lA..d. ••.••..••.......:JL~-200 -100 a 200

6cr(mK)Fig. ::'0-The spectral scan of Fabry-Perot spectrometer at14~7± 5 km (solid circles); The synthetic spectral line for 1500 K(continuous curve); The Jacchia 1<)77 model curve (IOO() K.dashed curve); Instrumental profile at S~<)6A (open circles); Theerror bar gets reduced as the point slides up the profile. (Ref; Gup-

ta e/(Ii.~h)

98

,00

260

i 220~...0:>0-

S .&0...40

.000

I,.f. $HAII

I OI-m-"a2III

/I

I/

II

II

//

//

/

",.",,",..,..,..

.."",,"/

/.1·00 '.00 UT

++

20001000 .~

TEMPERATURE ( K»

Fig. 21-Spectroscopically measured neutral temperature profile(continuous curve) along with the predicted Jacchia 1<)77modeltemperature profile (dashed curve),just two hours after a sudden

commencement occurrence (Ref: Gupta et a/.x,,)

photographic camera system and a high resolutionFabry-Perot spectrometer operated from ground.They found that whereas quiet day measurementsagree well with the Jacchia 77 model predictions, en-hanced temperatures prevailed during disturbedconditions'". The results are plotted in Figs 20 and21.

5 Future DevelopmentsIt is possible to focus on three aspects for further

development of airglow studies in India. These are:(i) Growth in the number of research groups parti-

cipating in airglow research.(ii) Development of new instrumental techniques

and data processing.(iii) New opportunities of experimentation using

balloons, rockets and satellites.For studying an extensive phenomenon like air-

glow it is advantageous to have a network of airglowobservatories spread out over the whole of India. Itwold be still better if a co-ordinated programmecould be implemented with participation of all the air-glow stations. One can have intercalibrated instru-ments at different sites and such a team work would bevery productive.

Filter photometer has been the most-applied in-strument for airglow research in our country in thepast years. A filter photometer is very useful in thestudy of faint light sources of known spectral charac-ter. The spectral element in a photometer, i.e. the in-terference filter, acts like a low resolution solid stateFabry-Perot interferometer. The photometric instru-mentation processes greater temporal resolution andgreatest instrumental sensiti~ity. ~ow~ver, thephotometer requires more care in application for ac-


curate absolute measurements, and its calibration ismore stringent. Another limitation of the filter photo-metry is that it can be applied for observing only thoseairglow features which can be isolated from neigh-bouring spectral features. In this respect a filterphotometer is less versatile than a grating spectrome-ter.

Recently, it has been established that ground-basedoptical techniques can be used to measure tempera-ture and winds in the upper atmosphere as well as thespatial variation of atomic or molecular densities.This is achieved following the optical Doppler meth-od through the use of the Fabry-Perot spectrometer.This method involves the measurement of airglowemission line intensity, Doppler widths and displace-ments. This technique has been applied to 0(1) 5577and 6300 A lines originating at 97 and 300 km re-spectively. It is believed that, in principle, the tech-nique should be applicable to the Na(I) 5890 A lineemitted around 90 km and perhaps to selected lines inthe hydroxyl bands, emitted from about 85 km. It hasalso been shown that a stable field-widened Michel-son interferometer offers an alternative approach.There is considerable scope for developing thesetechniques in India.

The ground-based airglow observations offer theobvious economic and logistic advantages in the diag-nostic probing of the state of upper atmosphere.However, ground-based measurements yield spec-tral intensities which represent integral of emissionrates over altitude. Hence information about the alti-tude profile of the airglow emission is missing fromthe ground-based observations. This puts severe res-trictions on interpretation of data in terms of basicmechanisms. Airglow emission from the excited spe-cies involves dynamical as well as photochemical pro-cesses which are altitude dependent. It is thereforenecessary to supplement ground-based observationswith rocket or satellite experiments which establish'space truth'. Historical sketch of developments givenin the earlier part of this paper contains examples ofthe need for such co-ordinated experiments. Elucida-tion of excitation mechanisms for the emission of 0(1)5577 and 6300 Alines in the early sixties could not bemade until information on altitudes of the emissionswas supplied by first rocket experiments. Similarly, arocket experiment was crucial to establish photo-chemical relationship between ozone concentrationand singlet delta oxygen dayglow intensity in the me-sosphere. Rocket measurement of 0(1) 5577 AE-layer emission has been the lone rocket experimentin India. The need for conducting more such experi-ments involving different emissions cannot be over-stated.

As a low latitude. equatorial station, India occupies

a unique position. Nearly all the airglow observato-ries in the world are at high latitudes and none is in ourlongitudinal sector. Airglow phenomena like tropicalred arc and morphological behaviour of hydroxylbands are more germane to low latitude region. Solarelectromagnetic radiation which controls middle at-mosphere structure and chemistry is intense at lowlatitudes. These and many other unexplored prob-lems are awaiting solution in the tropical and equato-rial region. Developments outlined above would en-able Indian aeronomers to make specific contribu-tions to the understanding of 'outer space' which is ra-pidly becoming a technological resource for all coun-tries of the world.

AcknowledgementsReprints of papers on past airglow work at Naini

Tal were supplied by the Director, Uttar PradeshState Observatory, Naini Tal. Airglow work at PoonaUniversity is supported by grants from ISRO underRESPOND and from the UGC under UGC-IMAPproject. The support and advice of space physicsgroups at PRL, Ahmedabad, TIFR, Bombay andVSSC, Trivandrum as well as administrative, finan-cial and other support from ISRO HQ, IMAP Pro-gramme Office, Bangalore and the Poona Universityauthorities were crucial in the balloon-borne airglowstudies at Poona University. Airglow studies in thePoona University have also benefitted through colla-borative research projects with Prof. G G Shepherd,York University, Toronto, Canada.

The author is grateful to Dr A P Mitra, DirectorGeneral, CSIR, New Delhi, for continued encourage-ment and help in the airglow work at Poona Univers-ity. Many stimulating discussions with Dr Mitra dur-ing the Singlet Delta Oxygen studies and also in theWorking Group meeting during the IMAP period arerecalled.

ReferencesI Fabry C, Astrophvs J( USA). 31 (I <)10) 3<)4.2 Van Rhijn P I. AstrophysJ(USA), 50 (1<)19) 356.3 Babcock H D. Astrophys J (USA). 50 ( 1<)19) 356.4 Slipher V M. Astrophys J ( USA). 49 ( I<)1<)) 266.S Rayleigh Lord. Astrophys J( USA), 50 (1<)1<)) 227.6 Dufay 1, c.R. Hebd Seances Aead Sci Ser II i Francei. 176

(1<)23),12<)0.7 Mclennan 1 C & Shrum G M, Proc R Sac London Ser A (GR).

108 (1<)25) 501.X Chamberlain 1 W. Physics of Aurora and Airglow(Academic

Press, New York), 1%1. 345.<) ElveyCT.AstrophysJ(USA).11I (1<)50)432.

10 Roach FE & Pettit H B.J Geophys Res( USA). 56 (I <)51) 325.II RoachF E& Smith L L.in AuroraandAirglow.edited bvB.M.

McCnrmac (Reinhold. New York), 1%7.2<). .12 Van Rhijn P I. Pub! A stroll Lab Groningen (Netherlands). 31

(Inl) 1.U Berg 0 E. Koomen M 1. Meredith L & Scolnik R. J Geophvs

Res( USA). 61 (I<)So\ :1()2.

99


14 Kooman M J, Scolnik R & Tousey R,J Geophys Res( USA), 61(1956)304.

15 Noxon J F, Space Sci Rev (Netherlands), 8 (1968) 92.16 Hunten D M, Space Sci Revi Netherlandsi, 6 (1967) 493.17 Hernandez G J & Silverman S M, Res Rep AFCRL 63-835,

Massachusetts, USA, 1963.18 Ramanathan K R, Indian} Phys, 7 (1932)405.19 Karandikar J V, Indian) Phys, 8 (1933) 547; 9 (1934) 245.20 Chiplonkar M W, Bull Astron Inst Czech (Czechoslovakia), 2

(1950) 79.21 Ghosh S N, Proc Natl/nst Sci(lndia), 2 (1943) 301.22 Mitra S K, Nature (GB), 155 (1945)786.23 Bappu M V K, Astrophys Ji USA), III (1950) 201.24 Chiplonkar M W & Kulkarni P Y, Indian} Meteorol & Gar

phys, 9 (1958) 133.25 Kulkarni P Y, Some problems in atmospheric optics, Ph D the-

sis, Poona University, Poona, 1958.26 Chiplonkar M W & Agashe Y Y, Alln Geophys(France), 17

(1961) 231.27 Kulkarni P Y & Rao Y R, Indian} Pure &App/ Phys, 9 (1971 )

631.28 Chiplonkar M W & Tillu A D, Indian} Pure &Appl Phys, 5

(1967)87.29 Desai J N & Narayanan M S, } Atmos & Terr Phys (G8), 32

(1970) 1235.30 Agashe Y Y & Gurao J B, Proceedings of the Symposium on

Solar Planetary Physics, Physical Research Laboratory,Ahmedabad, 3 (1976) 299.

31 Kulkarni P Y & Rao Y R, Indian} Radio & Space Phys, 1(1972) 181.

32 Kulkarni P Y & Rao V R, Ann Geophys'Francei, 28 (1972)475.

33 Majmudar N H & Kulkarni P Y, Indian} Radio &Space Phys, 4(1975)228. .

34 Agashe Y Y & Gurao J B, Indian} Radio & Space Phys, 6(1977)322.

35 Majmudar N H, Study of the upper atmosphere with OH andother airglow emissions, Ph D thesis, M S University ofBaroda, Baroda, 1977.

36 Kulkarni P Y,} Geophys Res ( USA), 81 (1976) 3740.37 Warkari H S, Tade M R & Tillu A D, Indian} Radio &Space

Phys, 6 (1977) 228.38 Agashe V V & Rathi S M, Planet &Space Sci( GB), 30 (1982)

507.39 Agashe YY,JoshiSS,Jahangir Ama, Nighut D N & Rathi SM,

paper presented to the National Space Science Sympo-sium, Guwahati, 19-22 February, 1986, Abstracts book, p172.

40 Agashe Y V, A Balloon Measurement of 0, (I Llg) Dayglowfrom Hyderabad during [MAP, IMA P Report (IndianSpace Research Organization, Bangalore), 1986. in press.

41 Bates D R, Planet & Space Sci( GB), 26 (1978) 897.42 Hernandez G, Planet &Space Scil. GB), 19 (1971) 467.43 Kulkarni P Y, Ann Geaphysi Francei; 30 (1974) 105.

44 Weill G, in Aurora and Airglow, edited by B M McCormac(Reinhold. New York), 1967,407.

45 Christophe-Glaume J, Ann Geophys (Frallce), 21 (1965) I.46 Roach F E, A nil Geophys (France), 17 ( 1961) 172.

47 Barbier D, Sun, Upper Atmosphere and Space, Vol I (M[TPress, Cambridge, Massachusetts, USA), 1%4,401.

48 Barbier D, Volot J & Pelissier J, Ann Geophys (France), 19(1(}63) 184.

49 Appleton E Y.} !ltmos & Terr Phys( GB), 5( I (}54) 348.SO Barbier D, Planet & Space Sci( GII), 10 (1963) 2(}.51 KingJ W,} /umos & Ten l'hys(GB), 30 (1%8) 391.

100

52 Agashe Y Y, Gurao J B, Influence ofAtmospheric Phenomenaon 0(1) 6300 A Nightglow Emissions at Poona, paper pre-sented to the Symposium on Sun Weather Relationship,Centre for Earth Science Studies, Trivandrum, 16- Hi July1981.

53 Gurao J B, A study of aeronomical processes in the tropics,Ph D thesis, Poona University, Poona, 1981.

54 Peterson Y L, Van Zandt T E & Norton R B, } Geophys Res(USA), 71 (1(}66) 2255.

55 BehnkeR& Kohl H,}Atmos & TerrPhys( GB),36(1974)325.56 Blamont J E,} Atmos & Terr Phys( G8), 37 (1975) 927.57 Kohl H,J Atmos &Terr Phys( (8), 38 (1976) 879.58 Agashe Y Y & Gurao J B, Interpretation of Airglow Intensity

Variation in Terms of Upper Atmospheric Dynamics. pa-per presented to the National Space Science Symposium,Indian Institute of Science, Bangalore, 3-6 February,1982.

59 Rao M N M & Murty G S N,} Atmos & Terr Phys (GB), 43(1981) 1253.

60 Rao M N M, Murty G S N & Jain Y C.} Atmos & Terr Phys(G8), 44 (1(}82) 559.

61 Tillu AD, Warkari H S,Jadhav D B & Tade M R, Low LatitudeAeronomical Processes, edited by A.P. Mitra, COSPARSymposium Series: Vol I (Pergamon Press, London), 1981,73.

62 Rao V R & Kulkarni P V. Indian} Radio & Space Phys, 2(1973)26(}.

63 Krassovasky Y I, Ann Geophys(France). 28 ([972) 739.64 Agashe V Y, Aher G R, Harpale Y M & Kshirsagar S K, Pro-

ceedings of the Workshop on IMA P Results, Bangalorc,14-16 November, 1984,8.

65 Agashe Y V, Pawar YR, NighutD N,Jahangir Ama& AherGR, paper presented to the National Space Science Sympo-sium, Guwahati, I (}-22 February, 1986, Abstracts book,p. [91.

66 Moreels G & Herse M, Planet & Space Sci (G8), 25 (1977)205.

67 Myrabo H K, Planet &Space Sci( GE), 32 (1(}84) 249.

68 Agashe Y V, Rathi S M & Pershad S K, Observations of TotalSolar Eclipse of 16th February 1980 (Indian National Sci-ence Academy, New Delhi), 1(}81, 87.

69 Evans W F J & Llewellyn E J, Radio Sci( USA), 7 (1972) 45.

70 ChiplonkarMW & Kulkarni PV, Bull Astron Inst Crechi Cze-chos/ovakiu),9 (1957) 128.

71 Chiplonkar M W, Agashe Y V & Tillu A D, lndian J Pure &Appl Phys, 3 (1965) 358.

72 Ashok N M, Bhatt H C,ChandrasekharT & DesaiJ N, Nature(GB), 300 (1982) 620.

73 Ashok N M, Bhatt H C, Chandrasekhar T & Desai J N.} At-mos &Terr Phys( GB), 46 (1(}84) 411.

74 Agashe V V & Jahangir Ama, Proceedings of the Workshop on/MA P Results, Bangalore, 14-16 November 1984,34.

75 Bates DR,} Geophys Res( US!I), 55 (1(}50) 347.

70 Haerendel G & Lust R. La rth' s Particles and Field,edited by BM McCormac (Reinhold, New York). 1968.271.

77 Haser L, in Aurora and Airglow, edited hv B M McCormac(Reinhold, New York), 1907. 3(}1. .

78 Lloyd K H, Res Rep AFCRL No. 268, Massachusetts. USA,1967.

79 Bhavsar P [) & Ramanuja Ran K . .\/)1/('1'Rest. Netherlandsi. 8(1%8)655.

XO Hhuvxar I' D. Narayanan M S s: Ramanuja Rao K .. Spnce Res! Netherlands; 9 (IW)l)) 37-1.


81 Bhavsar P D. Narayanan M S & Desai J N, Space Res(Ger-mally).16(1976)319.

82 Desai J N, Bhavsar P D, Raghavarao R & Narayanan M S,Space Res (Germany), 15 (1975) 267.

83 Anandarao B G, Raghavarao R & Desai] N. J Almos & TerrPhys(GB),40(1978) 157.

84 Anandarao B G, Desai] N, Giles M, Martelli G, Raghavarao R& Rothwell P, J Almos & Terr Phys( GB), 39 (1977) 927.

85 Anandarao B G & Raghavarao R, Space Res (Germany), 19(1979)263.

86 Gupta Ranjan, Desai] N, Raghavarao R, Sekar R, Sridharan R& Narayanan R, Geophys Res Left (USA), 13 (1986) inpress.

101

Documents

Airglow Studies in India - NISCAIRnopr.niscair.res.in/bitstream/123456789/36475/1... · Indian Journal of Radio & Space Physics Vol. 16, February 1987,pp.84-101 Airglow Studies in