Ion Density in the Stratosphere

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1 Iteratoal Joural of Physcs ad Applcatos. ISSN Volume 3, Number 1 (11), pp Iteratoal Research Publcato House Io Desty the Stratosphere Nagaraja Kamsal 1 ad S. Chadramma,* 1 Departmet of Physcs, Bagalore Uversty, Bagalore 56 56, Ida E-mal: kamsalagaraj@yahoo.com Departmet of Physcs, Yuvaraja s College, Uversty of Mysore, Ida * Correspodg Author E-mal: s_chadramma@yahoo.com Abstract Stratospherc o desty s oe of the mportat parameters for uderstadg the electrcal state of the rego ad s sestve to the presece of aerosols. A prelmary effort s made to study the behavour of o desty ad ts varato. Small os cosstg of aggregates of a few molecules determe the stratospherc electrcal parameters such as moblty, o desty, coductvty etc. The small o desty s cotrolled by the ozg mechasms for the producto of os ad electros ad the loss processes for these charged partcles. Io producto stratosphere s chefly due to galactc cosmc rays, ad the loss processes due to recombato ad attachmet. Free electros do ot exst at stratospherc heghts. The prmary postve o ad the electros are coverted to complex clusters of postve ad egatve os. The equlbrum o desty s govered by the equato of cotuty for the producto ad loss of these os. A smplfed model approach s adopted to study the effect of aerosols o the equlbrum o desty. Keywords: small os desty, stratosphere, ozato, recombato coeffcet. Itroducto At the preset tme, there s a great deal of terest o perturbatos due to athropogec actvtes the atmosphere ad ther mpact o global clmate chage. It has recetly bee realzed that such flueces are ot oly cofed to the lower atmosphere but may also affect the mddle ad upper atmosphere 1,. However, t was ot kow whether these chages also mpact o the o composto of the atmosphere. I fact, Beg ad Brasseur 3 postulated that huma actvtes mght

2 118 Nagaraja Kamsal ad S. Chadramma fluece the tropospherc o composto, as well ad Beg ad Mtra 4 have examed a potetally mportat role of chages the atmospherc eutral costtuets ad thermal structure o the dstrbuto of stratospherc ad mesospherc ozato ad reported a sgfcat varato several oc parameters. The o moblty, small o umber desty ad electrcal coductvty are mportat parameters for uderstadg the electrcal ature of the atmosphere. The small os cosstg of aggregates of a few molecules practcally determe the electrcal coductvty over the rego. Ios are formed the Earth s troposphere by umerous processes. Near to the surface of the Earth, radato emtted by radoactve materals ad rado gas plays a mportat role the ozato processes 5,6. The most mportat ozato source of ar ozato at stratosphere s galactc cosmc rays (GCR). Prmary charged speces formed by ar ozato clude free electros ad the smple molecular os of N ad, ad atomc os of N ad. Free electros attach rapdly to leadg to. Thereafter prmary postve os ad udergo o-molecule-reactos leadg to secodary postve ad egatve os, mostly complex cluster os. Ultmately os are lost by o-o recombato, ad aerosol rch ar masses, also by attachmet to aerosol partcles. The umber desty of the os s cotrolled by ozg mechasms for the producto of os ad electros ad the loss processes of these charged speces. At ths level, the o producto s chefly due to galactc cosmc rays comg form the extraterrestral org. The resultg electros ad postve os rapdly udergo hydrato reactos whch lead to the formato of egatve ad postve molecular o clusters referred to as small os. ly sgly charged os are mportat sce the cross secto for the producto of multply charged os by partcle mpact s smaller tha those for the producto of sgly charged os by a order of magtude or more. Further, the multply charged os that are formed wll rapdly udergo charge trasfer reacto wth eutral molecules to result sgly charged os. The small os have mobltes large eough to move apprecable uder the fluece of electrc feld ad thus determe the electrcal coductvty of the atmosphere, partcularly stratosphere. Thus, the aerosol loadg o the stratosphere has a bearg o the correspodg coductvty the rego. The aerosols reduce the stratospherc coductvty by a) covertg the hghly moble small os to less moble aerosol os through o-aerosol attachmet (coeffcet β) ad b) eutralzg the small os through the aerosol o-small o recombato (coeffcet α s ). Although the charged aerosol-aerosol recombato (coeffcet α a ) makes the o-aerosol attachmet rate faster, α a s small compared to β ad α s. There are lmted studes o the stratospherc o desty. The Io-aerosol model equatos The smplfed Io-aerosol model used ths study s show Fg. 1 ad the detaled reacto paths for the formato of dvdual cluster os are ot cosdered. The cosmc rays are the major role players the electrcal propertes of the atmosphere ad the global electrc crcut (GEC) by mapulatg atmospherc coductvty,

3 Io Desty the Stratosphere 119 oospherc potetal, vertcal curret ad vertcal oospherc potetal gradets. The cosmc rays beg hgh eergy charged partcles peetrate to the lower atmosphere ad are also fltered by the geomagetc feld. The flterg effect becomes varable tme wth the magetospherc currets that grow durg the perods of magetc actvty allowg partcles of a gve eergy to peetrate to lower lattudes, where these partcles produce ozato. The o producto rate peaks at dfferet heghts depedg o the eergy of cosmc ray partcle. It creases wth lattude ad decreases wth solar actvty. I the polar stratosphere, the o producto s maly by lower eergy GCR, whch s strogly modulated by the solar wd magetc felds the terplaetary space. C S M IC R N E U T N e H Y D R A TI Postve o clusters α Negatv e o clusters β β A E R S Postve aerosol os α a Negatv e aerosol α s Fgure 1: Schematc represetato of Io-aerosol model for the stratosphere. The producto mechasm of stratospherc os starts wth the ozato of ad N by GCR to form the precursor postve os ad N. However, N mmedately coverts to by charge exchage wth. hydrato, water cluster os are formed of the type H (H ), represetg the sum of all major water cluster os, where s a postve teger. The most abudat o speces observed the troposphere ad the stratosphere are complex cluster os cotag H S 4, H, HN 3, (CH 3 ) C ad CH 3 CN molecules attached to core os 7. The loss of os the stratosphere s maly due to o-o recombato ad attachmet processes. The value of o-o recombato for both two body ad three-body recombato coeffcets ad that of effectve attachmet coeffcet β has the value 1 6 cm 3 s 1. The total umber destes of postve ad egatve os are assumed to be equal from the charge eutralty crtero. The equlbrum o destes are computed from the equato of cotuty. The attachmet coeffcets β ad β for of postve ad egatve os wth the eutral aerosols are cosdered to be equal (.e., β =β = β). Smlarly, the correspodg o-aerosol recombato coeffcet α s ad α s- are also assumed to be equal the preset study, although these are kow to be slghtly dfferet. It s foud that the results of ths study are ot altered by these assumptos. Equato of cotuty for stratospherc os s gve by 5 :

4 1 Nagaraja Kamsal ad S. Chadramma d dt d dt = q α q α = βz (1) () Where Eq. (1) refers to the o desty ( ) absece of aerosols. Eq. () refers to the o desty ( ) presece of aerosols. postve / egatve o desty Z aerosol umber desty At equlbrum Eq. (1) ad () reduces to q α = = q α (3). e., q α α βz βz = q = (4) βz = ( βz) α 4qα. e., βz = α βz α q α (5) ly postve sg before square root s cosdered sce egatve sg leads to dvergece of the soluto of o destes. If we kow values of q ad α from parametrc formula, oe ca estmate ad from the kowledge of β ad Z values. Heght profles of Z are obtaed from Turco et al. 8 for the szes.1,.1 ad.1 μm ad the correspodg β values from Grgel et al. 9. It s well kow that ( )=Δ gves the decrease equlbrum o desty due to the presece of aerosols, ad ths s desgated as the charged aerosol desty, A. However, Δ << ad hece t s assumed that the loss of due to recombato wth A s eglgble compared to the o recombato loss. The loss of charged aerosols due to recombato wth opposte charged os s gve by A. From the equato of cotuty for the producto ad loss of charged aerosols oe ca wrte, βz βz α s = = (6) Δ Usg values of q, α, Z ad β ad by makg use of the Eqs.(3) to (5), values of α s estmated. Eqs. (3) abd (4) are rearraged to express the depleto of stratospherc os as Δ/ ad quatty (βz) s computed terms of / as:

5 Io Desty the Stratosphere 11 Δ βz β Z = α α Δ = (7) The relato betwee β ad r s kow, the percetage of depleto of stratospherc os for a gve aerosol umber desty s computed. Ths type of study s essetal predctg the cotrbuto of aerosol o o depleto partcularly durg ehaced aerosol codtos such as volcac erupto. Results ad dscusso The heght profles of o producto rate (q) for the stratospherc heght from 1 to 5 km s show Fg.. It clearly shows that the ozato rate decrease as heght creases wth a maxmum of 35 o-pars cm -3 s -1 at the top of troposphere or begg of stratosphere ad.4 o-pars cm -3 s -1 at the top of the stratosphere. The ozato rate decreases learly wth creasg heght. The curve follows a best ft wth a thrd order polyomal Y = X1.8 X X 3. The lear ft has exact matchg wth the profle ad has a regresso coeffcet of 99.84% wth a stadard devato of.5%. A small devato from the ft s observed for the heghts at 15 ad 5 km. Fg. also shows the varato of o-o recombato coeffcet (α ) for the stratosphere. The recombato s havg parallel varato wth ozato rate ad decreases learly as heght creases up to a alttude of 3 km ad the decreases expoetally ad gets saturated beyod 4 km. Fgure : Profles of ozato rate (sold le) ad recombato coeffcet (dashed le). The polyomal ft s made for the ozato rate.

6 1 Nagaraja Kamsal ad S. Chadramma The electrcal state of the atmosphere sometmes shows rapd chages the lower atmosphere. Measuremets showg such rapd chages of the electrcal parameters wth creasg alttude ear the exchage layer have bee reported by may workers 1,11 ad the results gve by them mostly show the fluece of meteorologcal codtos 1. The Fg. 3 depcts the heght profles of o destes for aerosol free ad aerosol atmosphere. The o desty reduces as heght creases ad may be due to the reducto ozato rate ad also ehaced aerosol cocetrato as oe moves up. The fluece of aerosols o o cocetrato s very clearly see ad has a marked depedece o aerosol umber desty ad sze. Mmum of 5% reducto o desty due to the presece of aerosols s observed. The effect of large aerosol s eglgble at hgher alttudes, ad the effect of small aerosol s eglgble at lower alttudes. The expermetal measuremet 13 of o desty at Thumba, Ida agrees well wth model estmated values from ths study. The mportace of small aerosols modfyg stratospherc o desty s clearly see. The results show good agreemet wth the observatos made by Morta et al. 1 partcularly the rego of 1- km. Fgure 3: Profles of o destes presece ad absece of aerosols. Refereces [1] Beg, G., 6, Treds the mesopause rego temperature ad our preset uderstadg- a update, Phys. Chem. Earth, 31, pp [] Srvas, N., Prasad, B.S.N. ad Nagaraja, K., 1, A o-aerosol model study for the stratospherc coductvty uder ehaced aerosol codto, Id. J. Rado Space Phys., 3, pp

7 Io Desty the Stratosphere 13 [3] Beg, G. ad Brasseur, G., 1999, Athropogec perturbatos of tropospherc os, Geophys. Res. Lett., 6, pp [4] Beg, G. ad Mtra, A.P., 1997, Atmospherc ad oospherc respose to trace gas perturbatos through the ce age to the ext cetury the mddle atmosphere, part I Chemcal composto ad thermal structure, J. Atmos. Sol. Terr. Phys., 59, pp [5] Nagaraja, K., Prasad, B.S.N., Srvas, N. ad Madhava M.S., 6, Electrcal coductvty ear the Earth s surface: Io aerosol model, J. Atmos. Solar Terr. Phys., 68, pp [6] Nagaraja Kamsal, Jayat Datta, ad Prasad, B.S.N., 9, Measuremet ad Modelg the Atmospherc Electrcal coductvty for motorg the Ar polluto, Adv. Space Res., 44, pp [7] Beg, G., 8, Global chage duced treds o composto of the troposphere to the lower thermosphere, A. Geophys., 6, pp [8] Turco, R.P., Too,.B., Hamll, P. ad Whtte, R.C., 1981, Effect of Meteorc debrs o stratospherc aerososl ad gases, J. Geophys. Res., 86, pp [9] Grgel, W., Kaselau, K.H. ad Muhlese, R., 198, Recombato rates of small os ad ther attachmet to aerosol partcles, Pure Appl. Geophys., 116, pp [1] Sagaly, R.C. ad Faucher, G.A., 1954, Arcraft vestgato of the large o cotet ad coductvty of the atmosphere ad ther relato to meteorologcal factors, J. Atmos. Terr. Phys., 5, pp [11] Sagaly, R.C. ad Faucher, G.A., 1956, Space ad tme varatos of charged ucle ad electrcal coductvty of the atmosphere, Quart. J. Roy. Meteor. Soc., 8, pp [1] Morta, Y., Ishkawa, H. ad Kaada, M., 197, the recet measuremets of atmospherc o desty from the groud to the stratosphere, J. Meteor. Soc. Jp., pp [13] Mural Das, S., Saskumar, V. ad Sampath, S., 1983, Measuremet of electrcal coductvtes, o desty ad mobltes the mddle atmosphere over Ixa, Id. J. Rado Space Phys., 16, pp. 15-.

Absorption in Solar Atmosphere

Absorption in Solar Atmosphere Absorpto Solar Atmosphere A black body spectrum emtted from solar surface causes exctato processes o atoms the solar atmosphere. Ths tur causes absorpto of characterstc wavelegths correspodg to those atoms