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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<70o $M(z)\approx\sec(z)$ 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.

$\lambda$, mkm0,20,30,40,50,71,05,020,0
$\varkappa_R(\lambda)\cdot 10^{10}/m$954,2152,545,418,14,6051,9021,729$\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)


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