Maynooth Optical Aeronomical Facility

Maynoo h Op ical Ae onomical Facili y F ancis J. Mulligan S . Pa ick's College Depa men o Expe imen al Physics Maynoo h, Co. Kilda e, I eland E-mail: mulligan@ axl .may.ie Rick J. Niciejewski Uni e si y o Michigan Space Physics Resea ch Labo a o y Depa men o A mosphe ic, Oceanic and Space Sciences 2455 Haywa d Ann A bo , Michigan 48109 1 In oduc ion a e impo an in helping o elucida e he complex dynamical and chemical p ocesses ha in luence a mosphe ic compo- si ion. Balloon' and ocke -bo ne2 expe imen s ha e enabled a mosphe ic scien is s o make measu emen s in he opo- sphe e and s a osphe e, while sa elli es such as Dynamics Explo e II ha e p o ided global co e age a much highe al i udes.3 The mesopause, loca ed nea an al i ude o 87 km, has p o ed o be one o he mos di icul egions o s udy expe imen ally, being oo high o balloon and oo low o sa elli e obse a ions. The majo i y o obse a ions in his egion ha e been ob ained ei he by ocke sounding o by emo e sensing o na u ally occu ing emissions in he in- a ed, isible, o ul a iole spec um. Rocke expe imen s p o ide excellen co e age in al i ude a a pa icula ime and loca ion, bu hey a e no capable o p o iding long- e m measu emen s. Lida echniques o e he g ea es po en ial o p o iding high- esolu ion empe a u e and wind measu e- men s a s a osphe ic and mesosphe ic al i udes, bu i is only e y ecen ly ha lida echniques ha e de eloped so ha he egion nea he mesopause can be s udied using his echnique.4 The measu emen o a mosphe ic empe a u e and wind eloci y by obse ing ai giow emissions con ined o na ow al i ude bands con inues o be one o he mos cos - e ec i e me hods a ailable. Essen ially all ai glow s udies a e made du ing he hou s o da kness, because o he di icul y o disc imina ing agains he o e whelming sola backg ound du ing dayligh hou s. Many measu emen s ha e been made a high la i udes, whe e good wea he condi ions, oge he wi h con inuous da kness in win e , allow long se ies o obse a ions o be ob ained.57 I eland is no an ideal loca ion in which o place an obse ing Pape 01-024 ecei ed Ap . 25, 1994; e ised manusc ip ecei ed Aug. 29, 1994; accep ed o publica ion Aug. 29, 1994. 1994 Socie y o Pho o-Op ical Ins umen a ion Enginee s. 009 I-3286/94/$6.00. si e o g ound-based op ical obse a ions. Poo and e y a iable wea he condi ions oge he wi h high ela i e hu- midi y and he absence o sui able high-al i ude obse ing si es pose he g ea es p oblems. The e y di icul y o ob- aming such measu emen s, howe e , ende s hei signi i- cance all he g ea e , pa icula ly in helping o cons ain global a mosphe ic models ha o en su e om a lack o da a poin s in ce ain la i ude and longi ude sec o s. Figu e 1 aken om Re . 8 shows he global dis ibu ion o op ical s a ions in ol ed in uppe a mosphe e s udies.8 I eland's po- si ion on he wes e n pe ime e o Eu ope ep esen s an im- po an loca ion in illing he oid be ween he Uni ed S a es and mainland Eu ope. Qui e dis inc om he ole ha an a mosphe ic obse ing si e in I eland can play as an elemen in a global g id o s a ions, i s la i ude is in he cen e o he ange whe e high al i ude (—82 km) noc ilucen clouds (NLCs) a e obse ed du ing wiligh in summe . NLCs a e obse ed mos e- quen ly in he la i ude egion 50° o60° on ei he side o he equa o in summe mon hs, when he sun is be ween 6° and 1 6° below he ho izon. They a e impo an in mesosphe ic physics because hey lie close o he mesopause, and because i appea s ha hei equency o occu ence is on he inc ease. I is belie ed ha his may be ela ed o inc easing concen- a ions o me hane coupled wi h dec easing mesosphe ic empe a u es. The ideal zone o iewing hem9 is 53° o57°. F om his poin o iew, I eland should be a good loca ion om which o unde ake a s udy o he co ela ion be ween noc ilucen cloud o ma ion and mesopause empe a u e. The ole o in e nal g a i y wa es in main aining he he - mal s uc u e o he mesopause is cu en ly he subjec o a numbe o in es iga ions .'0 1 2 These wa es p opaga e h ough he s a osphe e and mesosphe e and dissipa e hei ene gy nea he mesopause. T oposphe ic con ec ion, o o- g aphic e ec s, and e en la ge-scale ocean wa es a e be- lie ed o be sou ces o hese wa es. I eland's loca ion a he edge o a as expanse o open wa e wi h a p e ailing wes- e ly wind sugges s ha i migh also be a good place om OPTICAL ENGINEERING/Decembe 1994 / Vol. 33 No. 12/3853 Abs ac . G ound-based measu emen s o uppe a mosphe ic pa ame- e s, such as empe a u e and wind eloci y, can be made by obse ing ai glow emissions ha ha e a well-de ined al i ude p o ile and ha a e known o be ep esen a i e o he emi ing egion. We desc ibe he op- ical obse a o y a Maynoo h (53.23° N, 6.4° W) a which wo ins u- men s, a Fab y-Pé o in e e ome e and a Fou ie ans o m spec om- e e , a e used o eco d a mosphe ic ai glow emissions in I eland a isible and nea -in a ed wa eleng hs, espec i ely. Desc ip ions o he ins umen s, da a acquisi ion, and analysis p ocedu es a e p o ided, o- ge he wi h some sample esul s. Subjec e ms: op ical obse a o ies; ai glow obse a ions; g ound-based; meso- sphe ic measu emen s. Op ical Enginee ing 33(12), 3853—3860 (Decembe 1994). Measu emen s o a mosphe ic pa ame e s such as empe a- u e and wind eloci y, as a unc ion o ime and loca ion, 80 60 40 20 0 20 40 60 MULLIGAN and NICIEJEWSKI Fig. 1 Wo ldwide map o op ical a mosphe ic obse a o ies (a e Re . 8). which o sea ch o sho -pe iod (10 o 20 mm) g a i y wa es, since i has been sugges ed ha he in e ac ion o s ong winds wi h moun ains migh be a sou ce o lee- ype g a i y 2 This pape desc ibes a small op ical obse a o y loca ed on he campus a Maynoo h College (53.2°N,6.4° W), which houses a Fou ie ans o m spec ome e and a Fab y-Pé o in e e ome e , o he pu pose o measu ing empe a u e and wind eloci y in he uppe mesosphe e and lowe he mo- sphe e egion. Desc ip ions o he ins umen s, da a acqui- si ion, and analysis p ocedu es a e p o ided, oge he wi h some sample esul s. Da a eco ded a Maynoo h o m pa o a g ound-based alida ion campaign o he Uppe A - mosphe e Resea ch Sa elli e, h ough a collabo a ion wi h he Space Physics Resea ch Labo a o y o he Uni e si y o Michigan. 2 Ins umen Desc ip ions 2.1 Fou ie T ans o m Spec ome e The Fou ie ans o m in a ed (FTIR) spec ome e is based on a Michelson in e e ome e design and was supplied by Bomem Inc. A he moelec ically cooled InGaAs de ec o is employed, which has maximum sensi i i y in he wa eleng h egion 1 o 1.65 im. This ange includes he o a ional bands associa ed wi h ( =2) ib a ional ansi ions o he hy- d oxyl molecule. An in e nal He-Ne lase p o ides accu a e da a sampling, and he ins umen has a maximum esolu ion o 2cm .In his s udy, he esolu ion is se a 4 cm ,which enables a comple e in e e og am o be acqui ed in abou 5s and ep esen s a comp omise be ween in eg a ion ime and esolu ion. The ins umen has a ield o iew o 1 .5deg and ypically 50 in e e og ams a e coadded o inc ease he signal- o-noise a io. The composi e in e e og am is apod- ized using he Hanning window, and a spec um is ob ained by Fou ie ans o ming he apodized in e e og am. The el- a i e spec al esponse o he de ec o is de e mined by cal- ib a ion wi h a low b igh ness sou ce (LBS) whose a ea is su icien o comple ely ill he ield o iew o he ins umen and is simila in cons uc ion o ha desc ibed by Dandeka and Da is.'3 The calib a ion o he low b igh ness sou ce is aceable o a p ima y s anda d, and we es ima e ha adi- ances calcula ed on he basis o his sou ce a e accu a e o 10 o 15%. Figu e 2, eco ded sho ly a e midnigh on 5 Sep embe 1993 wi h an in eg a ion ime o 4.5 mm, is a ypical spec um showing bo h he OH(3,l) and (4,2) ib a ion- o a ion bands. The al i ude o maximum emission o hese bands in he nigh ai glow is nea 87 km. 2.2 Fab y-Pé o In e e ome e The Fab y-Pé o in e e ome e (FPI) was designed and con- s uc ed in he Depa men o Expe imen al Physics a May- noo h College, wi h a iew o eco ding he spec al line 3854 IOPTICAL ENGINEERING I Decembe 1 994 I Vol. 33 No. 12 180 160 140 120 100 80 60 4020 0 20 40 60 80 100 120 140 160 180 C.02.O>(I)Ca,C MAYNOOTH OPTICAL AERONOMICAL FACILITY Da a acquisi ion and con ol 80386 compu e and CAMAC modules p o ile associa ed wi h he a omic oxygen emissions a 557.7 and 630 nm; wa eleng h selec ion is achie ed using na ow passband il e s (2 and 6 A, espec i ely). De ails o he in- s umen pa ame e s a e lis ed in Table 1 .Thede ec o , which was p o ided by he Uni e si y o Michigan, is one o a se ies o de ices de eloped o he Fab y-Pé o in e e ome e on boa d he Dynamics Explo e II sa elli &4 and has also been used o g ound-based s udies a high I comp ises an S20 pho oca hode o diame e 1 .2 cm, h ee mic ochannel pla es as he gain elemen , and an anode comp ising 1 2 con- cen ic annuli each o equal a ea. The de ice ope a es as i i we e 12 dis inc pho omul iplie ubes, wi h a sepa a e coun ing channel o each anode. Da k coun s a e educed by cooling he de ec o using a he moelec ic coole , which educes he empe a u e a he ca hode by abou 40°C below ambien . Condensa ion on he de ec o window is p e en ed by he use o a he mopane window. The Fab y-Pé o pla es a e op ically con ac ed using h ee ze odu space s, 1 cm in heigh , and a e moun ed in a igid in a cage enclosed in a p essu e-sealed aluminium housing. Fine pa allelism adjus men is achie ed by applying p essu e o he pla es o e he ze odu space s ia in a sp ings. The con ac a ea be ween he housing and he Fab y-Pé o pla es is kep o a minimum o educe he conduc ion o hea o he d alon h ough he moun . Fab y-Pd o inges a e ocused on o he de ec o ia a 1- n ocal leng h lens. The op ical sys em is such ha he 12 channels o he de ec o in e cep abou 60% o a ull ee spec al ange. The choice o op ical pa ame e s is a co n- p omise be ween ob aining a good desc ip ion o a line p o ile in he 12 channels, i.e., ha he sky p o ile s addles a leas 6 o 7 channels, while a he same ime enabling he back- g ound signal le el o be es ablished accu a ely. Posi ioning o an in e e ence inge in he cen e o he 1 2 channels is achie ed by changing he p essu e in he sealed é alon hous- ing ia a mo o -d i en p essu e con olle , which is unde he con ol o he da a acquisi ion compu e . The p essu e con olle also plays a i al ole in de e mining he ins umen esponse as desc ibed in Sec. 3. The con ol and in e ace elec onics a e a combina ion o comme cial uni s and labo a o y speci ic modules designed and cons uc ed wi h he measu emen s in mind. The high ol age o he de ec o oge he wi h he p eampli ie s, dis- c imina o s, and pulse shape s we e buil a he Uni e si y o Michigan. This dedica ed elec onics is con olled by an- alog and digi al I/O lines om he da a acquisi ion compu e . Pulse coun ing is achie ed h ough he use o CAMAC ime and coun e modules, which a e also unde he con ol o he compu e . A simpli ied block diag am o he en i e ins umen is shown in Fig. 3. Figu e 4(a), eco ded on 26 Sep embe 1993 a 2:34 uni e sal ime (U.T.) wi h an in eg a ion pe iod o 2 mm, is a ypical sky p o ile ob ained when obse ing he a omic oxygen 0'S 557.7-nm emission. A midla i udes, his emission comes p edominan ly om an al i ude nea 95 km. Channels 10 and 12 ha e conside ably di e en da k Fig. 3 Block diag am o Maynoo h Fab y-Pé o in e e ome e . OPTICAL ENGINEERING / Decembe 1994 / Vol. 33 No. 12 / 3855 4.0 Nea in a ed spec um eco ded a Maynoo h 5 h Sep embe .1993 0.4 UT. Table 1 Maynoo h Fab y-Pé o in e e ome e cha ac e is ics. 0.06000 6400 6800 7200 7600 8000 Wa enumbe (cm-I) Pla e diame e 12.7 cm Pla e sepa a ion 1 .0 cm Re lec i i y (A) a 557.7 nm 0.82 F ee Spec al ange 0.155 A Ins umen al inesse 10 Objec i e lens =100 cm Field o iew 0.34°(ha angle) In e e ence il e 0.6 nm (T,,, = 40%) De ec o Type ITT F3035 concen ic ing anode; mic ochannel pla e elec on mu iplie S20 pho oca hode; 12 mm diame e (TE cooled). Spec al calib a ion F equency s abilized He-Ne lase Signal in eg a ion ime 5 minu es o in ensi ies > 100 A Fig. 2 Nea -in a ed spec um eco ded sho ly a e midnigh a Maynoo h on 5 Sep embe 1993 (in eg a ion ime: 4.5 mm). (a) (b) Fig. 4 (a) 01S 557.7-nm p o ile eco ded a Maynoo h on 26 Sep embe 1993 a 2.34 UT (in eg a ion ime: 2 mi, (b) Bes - i syn he ic Q15 557.7-nm p o ile (in leas -squa es sense) o ha shown in (a) o an emission empe a u e o 208 K and a line-o -sigh eloci y o 24 m/s. 3856 / OPTICAL ENGINEERING / Decembe 1994 / Vol. 33 No. 12 =ln{ N1E(J') Q (T o )S — kT o 1 6000 1 4000 1 2000 1 0000 6000 6000 4000 2000 0 U,C00 MULLIGAN and NICIEJEWSKI 1 6000 1 4000 1 2000 1 0000 8000 U,C00 6000 4000 2000 0 Channel Channel coun s and sensi i i y compa ed wi h channels 1 o 9 as in- F _E( J')l dica ed in Fig. 4(a). The absence o coun s in channel 11 was Q '(T o ) 2(2 J' + 1) expL kT o j(2) caused by he ac ha channel 1 1 was inope a i e in he de ec o employed in his s udy. Equa ion (1) may be con e ed o a linea equa ion in he 3Tempe a u e Calcula ion Technique ollowing o m: 3.1 OH Emission ln1 Ro a ional empe a u es o hyd oxyl emissions a e de e - 2(2J' + l)A(JVJ V)} mined om he in ensi y dis ibu ion o he o a ional lines. The li e ime o he ib a ional s a e is su icien ly long-li ed (3) o he emi ing molecule o each he mal equilib ium wi h i s su oundings'6; he o a ional le els a e hus popula ed The o a ional empe a u e can be ob ained om he slope acco ding o a Bol zmann dis ibu ion. Fo an emission a a o a plo o he le -hand side e sus E ( J'). Fo an emi ing empe a u e T o ' he in ensi y o a o a ional line is gi en sou ce in he mal equilib ium, such a plo is a s aigh line. by'7: The unce ain y o he linea i is a measu e o he empe - a u e unce ain y. The in e cep on he plo may be used o I( J', '9J", ' ) = de e mine he in ensi y o he emission. Ins umen esponse is measu ed a he beginning and end 2(2J' + 1) [— E(J')] o each obse ing nigh . Following a nigh o obse a ions, NV'A(J', '3J", ") exp kT '(1) each spec um o he o m shown in Fig. 2 is co ec ed o Q'(T o ) o ins umen esponse and p ocessed acco ding o he me hod ou lined abo e. In his s udy, he h ee mos in ense lines whe e N is he numbe o molecules in he ' ib a ional P1(2), P1(3), and P1(4) o he ansi ion om ib a ional s a e le el, J ' is he uppe o a ional s a e angula momen um, 3 o ib a ional s a e 1 a e used o ob ain he empe a u e. A(J'V'JV') is he Eins ein coe icien o spon aneous emis- These a e among he mos in ense lines in he spec um and sion om ib a ion- o a ion s a e ( J', ') o s a e J", ", and a e no a ec ed o any signi ican ex en by wa e apo ab- E(J') is he e m alue o he uppe s a e. The e m Q, is p'7 This esul s in a sequence o empe a u e and he pa i ion unc ion o s a e sum and is gi en by in ensi y alues o he nigh in ques ion. Figu e 5(a), which MAYNOOTH OPTICAL AERONOMICAL FACILITY Mesopause empe a u e calcula ed om OH(3, 1 ) band, 1 s Sep embe , 1 993 240 I 230 220 a) 210 Cua 200 EI180 170 I 20 21 22 23 012345 Time U.T. (a) In eg a ed band in ensi ies o OH(3, 1 ) band, 1 s Sep embe , 1 993 140 J I30 :+ 120 110 . 100 I+0 a) 90 ," +++I II —80 I 1+C11 II 70 •1 60 III 20 21 22 23 01234 Time U.T. (b) Fig. 5 (a) Tempe a u e alues calcula ed om OH(3,1) spec a e- co ded by he Maynoo h FTIR on nigh o 1—2 Sep embe 1993. (b) In eg a ed band in ensi ies o OH(3,1) emission eco ded by he Maynoo h FTIR on nigh o 1—2 Sep embe 1993. shows he a ia ion in de i ed empe a u e du ing he nigh o 1—2 Sep embe 1993, is ypical o he esul s ob ained h oughou he yea . Eins ein coe icien s we e ob ained om Mies.'8 Pa i ion unc ion alues we e ob ained om K as- so sky, She o , and Ya in,19 while o a ional e m alues we e aken om Coxon.2° Figu e 5(b) shows he co espond- ing in ensi y a ia ions o he same nigh . S a is ical e o s on bo h o a ional empe a u e and band in ensi y ob iously depend on ai glow in ensi y, which was ound o a y by as much as a ac o o 3 du ing a single nigh . A imes o s ong OH emission, s a is ical unce ain y in he calcula ed o a- ional empe a u es d opped o as low as K. Typically, abou 170 spec a we e eco ded in a single nigh du ing midwin e , dec easing o only abou 50 in midsumme . 3.2 Oxygen 01 S Emission The Dopple b oadening o an emission line, wi h an un- shi ed nominal wa eleng h X0 om a sou ce in he mal equi- lib ium a a empe a u e T is gi en as 1/2 [2kTln(2)] ,(4) whe e k is Bol zmann' s cons an , c is he speed o ligh , and m is he mass o he emi ing a om. Any line-o -sigh Dopple shi X is used o de e mine a wind eloci y ec o om he ela ion =—c . (5) xo Combiningobse a ions om each o he ca dinal di ec ions (no h, sou h, eas , wes ) allows a wind eloci y ec o o be de e mined o he obse ing s a ion. The spec al line eco ded by he Fab y-Pé o in e e - ome e is a con olu ion o he Dopple b oadened emission line sou ce and ins umen al b oadening. I is he e o e nec- essa y o decon ol e hese wo e ec s be o e a ibu ing a empe a u e o he emi ing egion. In his s udy, he ins u- men al p o ile was de e mined by eco ding he ou pu om he ins umen when illumina ed uni o mly by a equency s abilized He-Ne lase ha emi s a spec al line o negligible Dopple wid h a 632.8 nm. The esponse o each o he 12 de ec o channels is eco ded as a unc ion o p essu e o e h ee ee spec al anges. This allows he calcula ion o he ins umen al esponse in e ms o a se ies o Fou ie sine and cosine coe icien s o each channel as desc ibed by Killeen and Hays.2' These coe icien s a e hen co ec ed o he change in wa eleng h om 632.8 nm o he wa eleng h o he oxygen 0'S emission, which is a 557.7 nm. Syn he ic p o iles a e gene a ed by con ol ing he ins umen desc ip- ion wi h gene a ed Gaussian p o iles o known alues o empe a u e, wind eloci y, signal, and backg ound in ensi y. A nonlinea leas -squa es i ing app oach is used o de e - mine he op imum i be ween he gene a ed and eco ded p o ile. The alues o empe a u e, wind eloci y, signal, and backg ound in ensi y a e hen assigned o he emi ing al i ude a he ime o he obse a ion. Figu e 4(b) shows he bes - i syn he ic p o ile o he measu ed p o ile shown in Fig. 4(a) o an emission empe a u e o 208 K, and a line-o -sigh wind eloci y o 24 mIs. Figu e 6(a) shows an example se o empe a u es eco ded on 26—27 Sep embe 1 993 using his me hod, while Fig. 6(b) shows he co esponding zonal wind eloci ies. 4En i onmen al Conside a ions and Da a-Taking P ocedu e Theobse a o y was designed o allow he wo ins umen s o unc ion in daily una ended ope a ion. The obse e yp- ically ini ia es he obse ing p og am be o e lea ing in he e ening; he p og am hen wai s un il he sky becomes sui - ably da k as de e mined by a ligh senso , be o e commencing obse a ions. Wi h he app oach o dawn he ins umen s cease obse ing and e u n o he do man s a e. The layou o he obse a o y, wi h sepa a e ooms o he Fab y-Pé o in e e ome e , Fou ie ans o m spec ome e , and con ol oom, is shown in Fig. 7. The empe a u e o he oom housing he Fab y-Pé o in- e e ome e is con olled o be e han 0. 1°C so as o a oid unin ended shi s in he posi ion o he inge peak due o empe a u e e ec s. Ligh om he sky en e s he oom h ough a clea Pe spex dome and is di ec ed owa d he OPTICAL ENGINEERING / Decembe 1994 / Vol. 33 No. 12 / 3857 MULLIGAN and NICIEJEWSKI (b) Fig. 6 (a) Tempe a u e alues calcula ed om 01S 557.7-nm p o- iles eco ded by he Maynoo h FPI on nigh o 26—27 Sep embe 1993. (b) Zonal wind eloci ies (eas is posi i e) as a unc ion o ime om 557.7-nm emission eco ded a Maynoo h on nigh o 26—27 Sep embe 1993. Fab y-Pé o in e e ome e by a mi o sys em moun ed in he dome. The posi ion o he mi o in azimu h and al i ude is con olled by he da a acquisi ion compu e . A small ing hea e posi ioned a he base o he dome dissipa ing abou 250 Wo hea is su icien o keep he dome clea o con- densa ion a all imes. Du ing calib a ions, ligh om he sky is p e en ed om en e ing he oom by a shu e , which ac s as a e lec ion sc een o he calib a ion sou ce. The FTIR ins umen has been designed o be used in demanding condi ions, and i does no ha e he s ingen en i onmen al equi emen s o he Fab y-Pé o in e e om- e e . An iden ical ins umen has been employed o ob ain measu emen s om an ai c a du ing he Ai bo ne Lida and Obse a ions o he Hawaiian Ai giow Campaign (ALOHA-90).22 I is supplied wi h da a acquisi ion so wa e om he manu ac u e , which can be ailo ed o he use 's needs h ough he use o keys oke mac os. This ins umen was placed in a second oom in he obse a o y ha was i ed wi h an opening window, made om clea Pe spex. We de- cided o eco d all sky da a wi h he window in he open posi ion, due o he p esence o many abso p ion bands in Pe spex a in a ed wa eleng hs. A he s a o obse a ions o a pa icula nigh , he window is opened and a ime is s a ed. The ins umen is p o ec ed om he elemen s by a ain de ec o , which i ac i a ed causes he window o close and he ime o s op. Un o una ely, any da a eco ded a e he ime o he window closing has o be disca ded. In ensi y calib a ion o he FTIR is pe o med by eplacing he inpu mino by a demoun able low b igh ness sou ce. 5Resul s 5.1 Annual Va ia ions in Mesopause Tempe a u e Figu e 8 shows he imes du ing which OH obse a ions we e ob ained a Maynoo h du ing 1993. The FTIR ins umen was unc ional a all imes du ing he yea , and he gaps a e caused by unsui able wea he condi ions. This igu e is in- cluded he e as an indica o o he ac ion o ime a ailable o obse a ions in I eland. An a e age alue o empe a u e has been calcula ed o each nigh on which da a we e e- co ded a Maynoo h du ing 1993 and is shown in Fig. 9. The well-known win e -summe a ia ion o a midla i ude s a- ion, wi h he minimum in summe and maximum in win e , is clea ly e iden in hese da a. The gene ally accep ed ex- plana ion o his appa en in e sion is ha he cold summe (wa m win e ) mesopause is main ained h ough adiaba ic cooling (wa ming) p oduced by a s ong summe - o-win e me idional cell ha is d i en by b eaking e ically p opa- ga ing g a i y wa es.23 Also shown in he igu e a e he empe a u e esul s ob ained by Clancy and Rusch24 om da a eco ded by he Sola Mesosphe e Explo e (SME) sa - elli e o an al i ude o 86.5 km a a la i ude o 500N. The close co espondence be ween he SME esul s and he da a eco ded in his s udy helps o con i m ha he ins umen pe o mance and me hods used o calcula e empe a u es a e eliable. Figu e 9 also shows he p edic ions o he MSISE-90 model25 o an al i ude o 87 km a a la i ude o 53°N. The model p edic s a mean empe a u e o 1 85.7K,which is some 15 K below ha measu ed in his s udy. Resul s o a ha monic analysis applied o bo h he model and he measu ed em- pe a u es a e shown in Table 2 and a e in e y good ag eemen . 5.2 Combined Resul s om Bo h Ins umen s I is widely belie ed ha empe a u e luc ua ions a meso- pause al i udes, which ha e imescales o he o de o minu es o hou s, a e he esul o e ically p opaga ing acous ic g a i y wa es om lowe in he a mosphe e.6'7"7 Noxon26 was he i s o sugges ha conclusi e e idence o he pas- 3858 / OPTICAL ENGINEERING / Decembe 1994 / Vol. 33 No. 12 ( Time UT. (a) 310 290 270 a, 250 230 a.E, 210 190 170 1 5021 200 930926/27 100 i 0 > -100 -20021 22 23 01234 Time UT. FPIcompu e F lRcompu e Fig. 7 Layou o obse a o y a Maynoo h. I Con ol oom MAYNOOTH OPTICAL AERONOMICAL FACILITY Mon h Fig. 9 Compa ison o nigh ly a e aged empe a u es measu ed by he Maynoo h FTIR wi h esul s om Clancy and Rusch24 and p e- dic ions o MSISE-90 o he Maynoo h s a ion. sage o an a mosphe ic g a i y wa e could be ob ained by obse ing simul aneously di e en ai giow emissions o ig- ma ing om wo di e en al i ude egions. The al i ude o he peak emission o he OH band27 is cen e ed nea 87 km, while he 01S emission28 maximizes a 95kmin midla i udes wi h a small con ibu ion om he he mosphe e nea 250 km. I mus be ecalled, o cou se, ha hese laye s a e se e al kilome e s in dep h and ha hese a e he al i udes o he peak emissions only. Assuming ha he emissions ep esen he al i udes a he peak o he emission, we can calcula e pa am- e e s associa ed wi h e ically p opaga ing acous ic g a i y wa es. Figu e 10 shows empe a u e alues calcula ed om bo h he OH emission and he 0 S a omic oxygen emission o he nigh o 27—28 Sep embe 1993. To emphasize he co ela ion be ween he wo da a se s, he a omic oxygen esul s, which a e ep esen a i e o he highe al i ude, ha e been shi ed backwa d in ime by 20 mm. This is he esul ha one migh expec , assuming ha he empe a u e luc- ua ion obse ed in bo h emissions is he esul o a wa e mo ion p opaga ing upwa d om below he mesopause. The phase lag be ween he wo luc ua ions has been used o es ima e a e ical eloci y, assuming ha he al i ude di - e ence be ween he wo laye s is known. A knowledge o Annual componen Semiannual componen Mean empiK Ampli ude/K Phase/days Ampli ude(K) Phase/days OH(3, 1) 200 27±1 95±2 7±1 K .51±9 MSISE-90 185.68 30.1±0.2 95.3±0.6 9±0.2 K -99±1 270 250 230 0 210 0a-E190 Mesopause empe a u es calcula ed om OH(3,1) band and 01 S(5577) eco ded a Maynoo h Sep embe 27,1993 Time (UT.) Fig. 10 Combined empe a u e esul s o bo h FPI and FTIR on nigh o 27—28 Sep embe 1993. The FPI esul s ha e been shi ed backwa d in ime by 20 mm o illus a e he co espondence be ween he wo sepa a e da a se s. he e ical eloci y and he wa e pe iod, which can be ob- amed om ei he da a se , allows he e ical and ho izon al wa eleng h o be de e mined.29 These a e impo an pa am- e e s in de eloping models o g a i y wa e p opaga ion h ough he mesosphe e.3° Table 3 p esen s a lis o he pa- ame e s ha we e calcula ed om he wo da a se s eco ded a Maynoo h on 27—28 Sep embe 1993. The alues o pe iod, e ical, and ho izon al wa eleng h deduced a e consis en wi h he summa y o g a i y wa e pa ame e s epo ed by 6Summa y The Fou ie ans o m spec ome e desc ibed has been used o make obse a ions on all cloudless nigh s when he moon is low since Decembe 1992, while he Fab y-Pé o in e - e ome e has only been used ou inely since July 1993. The equen ly poo obse ing condi ions in I eland, oge he wi h a si e al i ude o only 60 m abo e sea le el, make i di icul o ob ain long sequences o obse a ions. Good-quali y OH spec a we e eco ded, howe e , wi h an in eg a ion ime o 5mm on 1 14 clea o pa ially clea nigh s du ing 1993. The Fab y-Pé o in e e ome e is much mo e sensi i e o sca - e ed ligh and could no be ope a ed nea ly as equen ly as he FTIR. Ne e heless, we belie e ha he esul s shown in his pape demons a e he easibili y o ob aining meaning ul geophysical measu emen s om I eland in spi e o he di - icul ies usually encoun e ed. Acknowledgmen s We acknowledge he con ibu ions o N. E. McKei h in in- i ia ing his p og am o esea ch a Maynoo h, and o OPTICAL ENGINEERING I Decembe 1994 I Vol. 33 No. 12 I 3859 Times o OH obse a ions Jan-Dec 1993 Table 2 Obse ed [OH(3,1) esul s o 1993] and p edic ed (MSISE-90) mean, annual, and semiannual a ia ions in mesopause empe a u e a Maynoo h. 12 8 a0; -4EI- -8 -12 Fig. 8 Times a which OH spec a we e eco ded a Maynoo h du - ing 1993. Measu ed and modelled mesopause OH empe a u es Maynoo h, Jan - Dec 1993 Jan Feb Ma Ap May Jun Jul Aug Sep Oc No Dec Mon h xX0H13,llMaynoo h1993 M515E90 p edic ions 1 Maynoo h U Sa eul eda aclancyand Ruoch119991 .OH(3,1) xIC 1 S (557.7) IC Xx's x xxx1*c U 0 (90a.E0I- 250 240 230 220 210 200 190 180 170 I 60 150 140 170 1 50 20 21 22 23 012 3 4 Jan Feb Ma Ap May Jun Jul Aug Sep Oc No Dec MULLIGAN and NICIEJEWSKI Table 3 In e nal g a i y wa e 1993, Maynoo h. cha ac e is ics, 27—28 Sep embe Quan i y Symbol Value Pe iod 120 mm. Angula equency m8.7 x 10 Ho izon al wa e speed Vh 155 m 5.1 Ho izon al di ec ion 9- Ho izon al wa eleng h ),, 1119 km Ho izon al wa enumbe k5.6 x 1O m1 Ve ical wa eleng h A46 km Ve ical wa enumbe k1.38 x 1O m-1 Ve ical wa e speed z 6.35 m Zeni h angle o p opaga ion iy 2.35 Assuming a backg ound wind o ze o m s. D. Gleeson, M. Ma in, W. Lanigan, and N. Mu phy o ab ica ing much o he ancilla y appa a us. The help o g ad- ua e s uden s J. Kea ing, D. Doyle, A. 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Williams, ' 'E on I : a da a base pe inen o he s udy o ene gy ans e in he oxygen nigh glow,' ' Plane . Space Sci. 34, 771—788 (1986). 29. R. H. Wiens, 5.-P. Zhang, R. N. Pe e son, and G. G. Shephe d, ''MORTI: A mesopause oxygen o a ional empe a u e image ," Plane . Space Sci. 39, 1363—1375 (1991). 30. D. W. Ta asick and G. G. Shephe d, ''E ec s o g a i y wa es on complex ai glow chemis ies 2. OH emission,' ' J. Geophys. Res. 97, 3195—3208 (1992). 31 . A. H. Manson, ''G a i y wa e ho izon al and e ical wa eleng hs: an upda e o measu emen s in he mesopause egion,' ' J. A mos. Sci. 47, 2765—2773 (1990). F ancis J Mulligan ecei ed BSc and PhD deg ees in expe imen al physics om S . Pa ick's College, Maynoo h, in 1978 and 1981, espec i ely. He was a lec u e in physical sciences a he Na ional Ins i- u e o Highe Educa ion in Dublin om 1981 o 1984. He became a membe o he acul y a S . Pa ick's College, Maynoo h, in 1 984, whe e he is cu en ly a senio lec- u e . D . Mulligan's main esea ch in e - es s a e in he ields o a mosphe ic sens- ing and elec on op ics. He has spen pe iods o esea ch a Ci y College, New Yo k, B ookha en Na ional Labo a o y, and he Uni- e si y o Michigan. In ecen yea s he has concen a ed on ins u- men a ion used o g ound-based ae onomical s udies. Rick J. Niciejewski ecei ed an MSc in 1981 and a PhD in 1987 om he Uni e - si y o Wes e n On a io in London, Can- ada. He joined he Space Physics Labo- a o y o he A mosphe ic, Oceanic, and Space Science Depa men o he Uni e - si y o Michigan as a pos doc o al ellow in 1 987, and became an assis an esea ch scien is in 1990. His cu en esea ch in- e es s a e in he ield o expe imen al ae onomy including op ical obse a ions o he e es ial ai giow and au o a. P ima y opics o in e es a e he he modynamics and wea he o he e es ial uppe a mosphe e and he applica ion o s a e-o - he-a echnology o emo e diagnos ics.