ter/spectrometerandaprotonprecessionmagnetometerareinoperationalong
withasurfaceozonesampler,acarbonmono-oxideanalyzerandaUVradiome-
ter(measuressolarultravioletirradiancebetween280and320nm). Thisarticle
highlights the neutraldensity and temperature measurements by thelidar as
wellasAtmospheric/Ionosphericparametersderivedbyotherinstruments.
1. Introduction
Atmosphericsciencestudies atMt. Abuhadstartedin theearly1950'swiththeOzone
observations using Dobson spectrometer at the Hill View building. Due to the very
good seeing conditionsandverylargenumberof cloud-freedays/nights,itwasrealized
by PRL's scientic community that an atmospheric sciences laboratory should be set
up at Gurushikhar, alongside the Infrared observatory. In 1994 a small atmospheric
scienceslaboratorywas builtandregularopticalaeronomyobservationswerestartedby
operatingavarietyofinstrumentsviz. thedayglowphotometer,nightglowspectrometer
etc. Theseinstrumentsarepassiveremotesensinginstrumentsandrecorddayandnight
glowsemanatingfromdierentionosphericheights. During1996-97,PRL'sexistingLidar
at Ahmedabad was shiftedto the atmospheric science laboratory at Gurushikhar with
a90 cm primary mirrorfor thestudy of middle atmospheric dynamics. Pollution free,
clearskyandreducedairmassatGurushikhar(altitude aboveMSL1.67km)facilitates
probing heights up to about 80 km. In Fig. 1, a panoramic view of the atmospheric
scienceslaboratoryalongwithvariousinstrumentshousedinsidethebuildingisshown.
Figure 1. Panoramic view of the atmospheric sciences laboratory at Gurushikhar and the
instruments: (A)AllSkyImaging(B)UVRadiometer(C)InsideViewofLidarLaboratory(D)
OzoneAnalyzerand(E)InsideViewofOpticalAeronomyLaboratory.
2. Lidar-based studies of the atmosphere
The Rayleigh scattering by air molecules in the region of 30 to 80 km has been used
extensivelyto determine the densityand temperatureof the atmosphere (Hauchecorne
andChanin 1980,1981 and referencestherein). Due to the presenceof aerosols(below
the altitude of 30 km) Rayleigh scattering can not be used to get neutral density and
temperature proles. Thereforein this altituderegionRaman scatteringhas been used
to obtainneutraldensity and temperature proles(Evanset al., 1997). Mie scattering
at532nmisusedto studythetropospheric andlowerstratosphericaerosols.
AtmosphericprobingusingLidarwasinitiatedatPRLintheearly1990's. Apowerful
Nd-YAGlaser-basedlidar(operatingat 532nm) witha40cmCassegraintelescopewas
set upat Ahmedabad in April 1992and used primarily for aerosol studies (Jayaraman
et al., 1995). The Lidar system was moved to the atmospheric sciences laboratory at
Gurushikhar in 1996-97. Since then regular measurements of density/temperature are
being made. A highpowerlaser beam ispumpedverticallyinto theatmosphereat 532
nm and Rayleigh backscattered signal at 532 nm (Rayleigh Lidar), Raman scattered
Figure 2. TypicallidarprobedprolesofdensityandtemperatureoverMt. Abu.
3. Optical aeronomy instruments at Gurushikhar
3.1 Allsky imagingof the ionosphere
A Multiwavelength All Sky Optical Imager was developed at PRL. It employs a 180
degreesh-eyelens,animageintensier(gain100,000)andaCCDbaseddetector. This
Imagerisbeingoperatedatthreedierentwavelengthsviz. 630.0nm,557.7nmand777.4
nmtostudy thepropertiesof (a)theionosphericplasma depletionsand (b)thegravity
wave parameters. The parameters that can be derived from this experiment include,
E-Wextent,degreeofdepletionandorientation withrespectto geomagneticeldlines.
Figure3. DensityperturbationsobservedoverGurushikharon5November1997.
estimated(Sinha etal.,1996, 2000,2003). AtypicalAllSky Imageat 630nmtakenby
PRL'sAll SkyImagerisshownin Fig. 4.
Figure 4. AtypicalimagetakenbyPRL'sMultiwavelengthAllSkyImagerat630nm.
3.2 The day/nightairglow studies
TemporalvariationsoftheairglowemissionfromO(
1
D)excitationsarebeingmonitored
regularlyusingaFabry-PerotSpectrophotometer. Usingthisinstrument,extensivestud-
Figure 5. Anexampleofdatarecorded byDayglowPhotometeronFebruary3,2002 at Mt.
Abu. TheY-axis(normalizedphotoncounts)indicatestheintensityoftheairglowemission.
4. Studies of ozone and trace gases
Anumberofground-basedinstrumentsareoperationalformonitoringtheconcentrations
ofseveral surfacetracegasesat Gurushikhar. Continuousmeasurementsof Ozone(O
3 )
andCarbonMonoxide(CO)arebeingmadesincethelast6-7years. Extremelyharmful
solarultravioletradiation(UV)isalsobeingmonitoredattheatmosphericsciencelabo-
ratory. TheUVradiometermeasuresglobalsolarultravioletirradiancebetween280and
320nm, peakingaround300nm,which ispartof thesolarspectrumthatis responsible
forsunburnsonhumanskin. (Laletal.,2000;Subbarayaetal.,2001;Nazaetal.,2003)
5. Summary
The atmospheric science laboratory at Gurushikhar, Mt. Abu is well-equipped with a
numberof state-of-the-artinstruments used to addressvarious geophysical phenomena
takingplaceintheEarth'stroposphere,stratosphere,mesosphereandionosphere. With
these instrumentsa study of coupling processes between dierent regions of the atmo-
sphereisbeingcarried out. Longtermdataof groundbasedactiveand passiveremote
sensing instruments are useful for modifying/improving existing standard atmospheric
signalshaveto traversethroughearth's atmosphereandionosphere, observationsof pa-
rameterssuch as cirrus clouds, aerosols, neutraldensity uctuations,and gravitywave
phenomenaareusefulforastronomersaswell.
Acknowledgments
ThanksareduetoHarishChandraandPRL'sLidargroupmembersforfull-edgedsup-
port in running lidar facility at Gurushikhar. Som Sharma thanks Shyam Lal, B.G.
AnandaraoandT.Chandrasekharfortheirencouragementandsupport. Wewishto ac-
knowledgeR.Sekar,D.Chakraborty,R.Narayanan,T.A.RajeshandS.Venkataramani
forproviding picturesanddetails oftheinstruments. This work hasbeensupported by
DepartmentofSpace,Governmentof India.
References
Chakrabarty, D., Sekar, R., Narayanan, R., Pant, Tarun K.and Niranjan K., 2004, J.Geo-
phys.Res.,109,A12309,doi:10.1029/2003JA010 16 9.
Chakrabarty,D.,Pant,TarunK.,Sekar,R.,Taori,Alok,Modi,N.K.andNarayanan,R.,2002,
Curr.Sci.,83,2,167-170.
Chanin,M.L.andHauchecorne,A.,1981, J.Geophys.Res.,86,9715.
Evans,KD,Mel,S,Ferrare,RichardAandWhiteman,DavidN,1997, AppliedOptics,36,12.
Hauchecorne,A.andChanin,M.L,1980, Geophys.Res.Lett., 7,565.
Jayaraman,A.,Acharya,Y.B.,Subbaraya,B.H.andChandra,H.,1995,Appl.Optics,34,6937.
Lal,S.,Naza,M. andSubbaraya,B.H.,2000, Atm.Env.,34,2713.
Naja,M.,Lal,S.andChand,D.,2003, Atmos.Env.,37,4205.
Sinha,H.S.S.,MisraR.N.,Chandra,H.,Raizada,Shikha,Dutt,N.Vyas,G.D.,1996, Ind.J.of
Rad.&Space Phys.,25,44.
Sinha,H.S.S.,andRaizada,Shikha,2000, Earth,PlanetsandSpace,52,549.
Sinha,H.S.S.,Rajesh,P.K.,Misra,R.N.,Pandey,R.,Dutt,N.,Dhadhania,M.B.andBanerjee,
S.B.,2003, BolivianJournalofPhysics,9,52.
SharmaSom,Sivakumar,V.,Chandra,H.,Jayaraman,A.andRao,P.B.,2005, Adv.SpaceRes.,
inpress.
Subbaraya,B.H.,Lal,S.andNaja,M.,2001, Mausam,52,97.
