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Ekstinkciya v atmosfere

- oslablenie el.-magn. izlucheniya v zemnoi (planetnoi) atmosfere. E. obuslovlena summarnym deistviem poglosheniya i raseyaniya izlucheniya. Oslablenie izlucheniya s nachal'noi intensivnost'yu $I_0(\lambda)$ opredelyaetsya sootnosheniem:
$I(\lambda)=I_0(\lambda)\;e^{-\tau_e(\lambda)}$
gde $\tau_e(\lambda)$ - opticheskaya tolsha atmosfery dlya E. Optich. tolsha $\tau_e(\lambda)$ zavisit takzhe ot zenitnogo rasstoyaniya svetila z. Velichina $M(z)=\tau_e(\lambda,z)/\tau_e(\lambda,0)$ naz. vozdushnoi ili atmosfernoi massoi [ $\tau_e(\lambda,0)$ optich. tolsha pri z=0]. Dlya z<70^o $M(z)\approx\sec(z)$ i prakticheski ne zavisit ot $\lambda$ . Stepen' oslableniya sveta zemnoi atmosferoi chasto harakterizuyut koefficientom prozrachnosti atmosfery $p(\lambda)$ , kotoryi opredelyaetsya dlya svetila v zenite:
$p(\lambda)={I(\lambda,0)\over{I_0(\lambda)}}\;e^{-\tau_e(\lambda,0)}$ ,
ili v zvezdnyh velichinah:
m-m₀=-2,5 lg p .
Dlya lyubogo dr. zenitnogo rasstoyaniya
${I(\lambda,z)\over{I_0(\lambda)}}=p(\lambda)^{M(z)}$ .

Optich. tolsha dlya E. ravna summe $\tau_s(\lambda)+\tau_a(\lambda)$ optich. tolsh, obuslovlennyh processami rasseyaniya $\tau_s(\lambda)$ i processami poglosheniya $\tau_a(\lambda)$ . Izluchenie pogloshaetsya v zemnoi atmosfere gl. obr. v polosah poglosheniya molekul (sm. Prozrachnost' zemnoi atmosfery). Oslablenie izlucheniya iz-za processov rasseyaniya proishodit nepreryvno po spektru po zakonu $\sim\lambda{-\alpha}$ . Dlya releevskogo rasseyaniya, voznikayushego na optich. neodnorodnostyah, sravnimyh s razmerami molekul i vyzvannyh teplovymi dvizheniyami molekul (t.n. molekulyarnoe rasseyanie), $\alpha=4$ . Etim rasseyaniem ob'yasnyaetsya goluboi cvet neba.

Dlya aerozol'nogo rasseyaniya $\alpha$ lezhit v predelah ot 0 do 4, v zavisimosti ot razmera rasseivayushih chastic: v srednem $\alpha=1,3$ . Belesovatost' neba obuslovlena aerozol'nym rasseyaniem i zavisit ot razmerov chastic i ih indikatriss rasseyaniya. Polnaya optich. tolsha dlya processov rasseyaniya $\tau_s(\lambda)=\tau_R(\lambda)+\tau_A(\lambda)$ , gde $\tau_R(\lambda)$ i $\tau_A(\lambda)$ - optich. tolshi sootvetstvenno dlya releevskogo i aerozol'nogo rasseyanii.

Dlya dannogo mesta na Zemle naimen'shaya vozmozhnaya E. - releevskaya, ona prakticheski neizmenna vo vremeni, zavisit tol'ko ot vysoty h mesta nablyudeniya nad urovnem morya i yavl. poleznoi harakteristikoi mesta nablyudeniya.

$\lambda$ , mkm 0,2 0,3 0,4 0,5 0,7 1,0 5,0 20,0

$\varkappa_R(\lambda)\cdot 10^{10}/m$ 954,2 152,5 45,4 18,1 4,605 1,902 1,729 $\cdot 10^{-3}$ 5,571 $\cdot 10^{-6}$

Optich. tolsha $\tau_R$ , a sledovatel'no i koeff. prozrachnosti zemnoi atmosfery dlya releevskogo rasseyaniya, rasschityvaetsya po f-le: $\tau_R(\lambda)=\varkappa_R(\lambda) H(h)$ , gde H(h)- vysota odnorodnoi atmosfery, $\varkappa_R(\lambda)$ - pokazatel' oslableniya dlya releevskogo rasseyaniya. V tabl. privedeny znacheniya $\varkappa_R(\lambda)$ dlya nek-ryh dlin voln.

Chem blizhe nablyudaemyi hod prozrachnosti s dlinoi volny (vne polos poglosheniya zemnoi atmosfery) k releevskomu, tem bolee chista atmosfera i tem men'she izmeneniya ee prozrachnosti vo vremeni.

Lit.:
Martynov D.Ya., Kurs prakticheskoi astrofiziki, 3 izd., 1977; Makarova E.A., Haritonov A.V., Raspredelenie energii v spektre Solnca i solnechnoaya postoyannaya, M., 1972; Handbook of geophysics and space environments, ed. by S. Valley, N.Y. - [a.o.], 1995.

(E.A. Makarova)

E. A. Makarova, "Fizika Kosmosa", 1986
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$\lambda$ , mkm	0,2	0,3	0,4	0,5	0,7	1,0	5,0	20,0
$\varkappa_R(\lambda)\cdot 10^{10}/m$	954,2	152,5	45,4	18,1	4,605	1,902	1,729 $\cdot 10^{-3}$	5,571 $\cdot 10^{-6}$