AERO NOMICA ACTA

I N S T I T U T D ' A E R O N O M I E ' S P A T I A L E D E B E L G I Q U E 3 - Avenue Circulaire

B • 1180 BRUXELLES

A E R O N O M I C A ACTA

A - N° 213 - 1980

Stratospheric chemical and thermal response to long-term variability in solar UV irradiance

by

G. BRASSEUR and P.C. SIMON

B E L G I S C H I N S T I T U U T V O O R R U I M T E - A E R O N O M I E 3 - Ringlaan

B - 1180 BRUSSEL

F O R E W O R D

T h e paper "Stratospheric chemical and thermal response to long- term variability in solar UV irradiance" is accepted for publication in Journal of Geophysical Research, 86, 1981.

A V A N T - P R O P O S

L'article "Stratospheric chemical and thermal response to long-term variability in solar UV irradiance" sera publie dans Journal of Geo- physical Research, 86, 1981.

V O O R W O O R D

Het artikel "Stratospheric chemical and thermal response to long- term variability in solar UV irradiance" zal verschijnen in Journal of Geophysical Research, 86, 1981.

V O R W O R T

Die Arbeit "Stratospheric chemical and thermal response to long- term variability in solar UV irradiance" wird in Journal of Geophysical

Research, 86, 1981 herausgegeben werden.

/

S T R A T O S P H E R I C C H E M I C A L A N D T H E R M A L R E S P O N S E T O L O N G - T E R M V A R I A B I L I T Y IN S O L A R U V I R R A D I A N C E

b y

G. B R A S S E U R ^ a n d P . C . S I M O N Institut d ' A e r o n o m i e Spatiale 1180 B r u s s e l s - Belgium.

Ahst.rnr.t,

A theoretical a n a l y s i s of the chemical r e s p o n s e of the s t r a t o s p h e r e to possible long-term v a r i a b i l i t y of solar ultraviolet i r r a d i a n c e h a s been p e r f o r m e d , t a k i n g into account the thermal feedback effect on the reaction rates. Numerical v a l u e s of ultraviolet a n d v i s i b l e irradiation f l u x e s u s e d in t h i s w o r k are g i v e n for aeronomic modeling p u r p o s e s a n d a possible v a r i a b i l i t y related to the 1 1 - y e a r solar cycle is s u g g e s t e d on the b a s i s of recent a n d reliable o b s e r v a t i o n s of solar ultraviolet i r r a d i a n c e . T h i s v a r i a b i l i t y h a s been i n t r o d u c e d in a s t r a t o s p h e r i c two-dimensional model which simulates the zonally a v e r a g e d d i s t r i b u t i o n of the chemical species related to the o x y g e n , h y d r o g e n , n i t r o g e n a n d chlorine families. T h e r e s u l t s lead to a total ozone variation of the o r d e r of 3 p e r c e n t from the minimum to the maximum solar a c t i v i t y , with a maximum of about ten percent in the u p p e r s t r a t o s p h e r e . A t these h e i g h t s , the calculated temperature c h a n g e is close to 2 - 4 d e g r e e s . T h e N2O concentration a p p e a r s to be one of the m o s t s e n s i t i v e to l o n g - t e r m solar v a r i a b i l i t y a n d a monitoring of t h i s constituent would be useful to g i v e information on the solar v a r i a b i l i t y in the ultraviolet.

( * ) A s p i r a n t au F o n d s National de la R e c h e r c h e scientifique.

Résumé

Une analyse théorique du comportement chimique de ia stratosphère aux variations possibles à long terme du rayonnement solaire a été

réalisée en tenant compte de l'effet rétroactif des variations en tempéra-

ture sur les vitesses de réaction. Des valeurs numériques du flux

ultraviolet du soleil sont proposées pour les calculs aéronomiques et une

variation avec le cycle de 11 ans est adoptée sur base des observations

les plus récentes. Cette variation a été introduite dans un modèle à

deux dimensions donnant une distribution moyenne méridionale des

constituants oxygénés, hydrogénés, azotés et chlorés. Les résultats du

calcul donnent une variation pour le contenu total en ozone de l'ordre

de 3% avec le cycle de 11 ans, avec un maximum de l'ordre de 10% dans

la stratosphère supérieure où la température varie de 2 a 4 K. La

mesure systématique de la concentration en ^ O qui est très sensible

aux variations à long terme du flux ultraviolet solaire pourrait donner

une confirmation expérimentale sur celles-ci.

S a m e n v a t t i n g

Een t h e o r e t i s c h e a n a l y s e v a n h e t s c h e i k u n d i g a n t w o o r d v a n de s t r a t o s f e e r op een m o g e l i j k e v a r i a t i e op lange t e r m i j n v a n de z o n n e - b e s t r a l i n g s s t e r k t e w e r d o n d e r n o m e n , r e k e n i n g h o u d e n d met h e t e f f e k t v a n de t h e r m i s c h e f e e d b a c k op de r e a k t i e s n e l h e d e n . De n u m e r i s c h e w a a r d e n v a n de u l t r a v i o l e t en z i c h t b a r e b e s t r a l i n g s s t e r k t e s t r o o m d i e in d i t w e r k g e b r u i k t w e r d e n z i j n v o o r a e r o n o m i s c h e m o d e l i s a t i e d o e l e i n d e n g e g e v e n en een m o g e l i j k e v a r i a b i l i t e i t in v e r b a n d met de 1 1 - j a a r z o n n e - c y c l u s is op basis v a n r e c e n t e en b e t r o u w b a r e w a a r n e m i n g e n v a n u l t r a - v i o l e t z o n n e b e s t r a l i n g s s t e r k t e v o o r g e s t e l d . Deze v a r i a b i l i t e i t w e r d g e - b r u i k t in een t w e e - d i m e n s i o n e e l s t r a t o s f e r i s c h model d a t de zonaal g e m i d d e l d e d i s t r i b u t i e v a n de c h e m i s c h e c o m p o n e n t e n in v e r b a n d met z u u r s t o f , w a t e r s t o f , s t i k s t o f en c h l o r a a t f a m i l i e s s i m u l e e r t . De r e s u l t a t e n l e i d e n t o t een t o t a l e ozon v a r i a b i l i t e i t v a n o n g e v e e r 3 p e r c e n t v a n de minimum t o t de maximum v a n de z o n n e a k t i v i t e i t , met een maximum v a n o n g e v e e r 10 p e r c e n t in de h o g e r e s t r a t o s f e e r . Op deze h o o g t e is de v e r a n d e r i n g v a n b e r e k e n d e t e m p e r a t u u r d i c h t b i j 2 - 4 g r a d e n . De ^ O d i c h t h e i d b l i j k t een v a n de meest g e v o e l i g e v o o r de z o n n e v a r i a b i l i t e i t op lange t e r m i j n t e z i j n en de a a n h o u d e n d e w a a r n e m i n g v a n deze c o m p o n e n t z o u zeer n u t t i g z i j n om i n f o r m a t i e t e g e v e n o v e r de z o n n e v a r i a b i l i t e i t in h e t u l t r a v i o l e t .

- 3 -

Z u s a m m e n f a s s u n g

Die c h e m i s c h e R ü c k w i r k u n g e n d e r S t r a t o s p h ä r e f ü r V a r i a t i o n e n d e r U l t r a v i o l e t t e S t r a h l u n g m i t t h e r m i s c h e R ü c k w i r k u n g a u f d i e R e a k t i o n K o e f f i z i e n t e n , i s t u n t e r s u c h t w o r d e n .

Die n u m e r i s c h e W e r t e f ü r d i e UV u n d s i c h t b a r e L i c h t i r r a d i a t i o n d i e i n diese R e c h n u n g e n genommen s i n d , w u r d e n i n a e r o n o m i s c h e Modelle g e b r a u c h t . Die e v e n t u e l l e 1 1 - J a h r e V a r i a t i o n d e r S o n n e n a k t i v i t ä t i s t v o n neue u n d z u l ä s s i g e U - V B e o b a c h t u n g e n a b g e r e c h t n e t w o r d e n . Die V a r i a t i o n e n s i n d in einem z w e i - d i m e n s i o n e l l e n Modell mit zonale M i t t e l w e r t e d e r D i c h t e v e r t e i l u n g f ü r d i e M o l e k ü l e n d i e O , H , N u n d Cl e n t h a l t e n , b e r e c h n e t w o r d e n . Die R e s u l t a t e n l e i t e n a u f eine gesamte O^

V a r i a t i o n v o n u n g e f ä h r 3% z w i s c h e n das Minimum u n d das Maximum d e r

S o n n e n a k t i v i t ä t . Die g r ö s s t e V a r i a t i o n (10%) e n s t e h t i n d e r o b e r e n

S t r a t o s p h ä r e wo eine T e m p e r a t u r s w a n k u n g v o n 2 - 4 K a u c h r e s u l t i e r t .

Die I ^ O K o n z e n t r a t i o n i s t e i n e r d e r e m p f ä n g l i c h s t e n f ü r l a n g d a u e r

V a r i a t i o n e n . Eine k o n t i n u i e r l i c h e B e o b a c h t u n g d e r ^ O D i c h t e in d e r

S t r a t o s p h ä r e k ö n n t e g u n s t i g e I n f o r m a t i o n e n ü b e r d i e V a r i a t i o n d e r

S o n n e n u l t r a v i o l e t t e S t r a h l u n g g e b e n .

1. I N T R O D U C T I O N

S t u d i e s of the correlation between solar activity a n d the ozone concentration h a v e a long h i s t o r y . T h e p o s s i b i l i t y of s u c h a correlation which was f i r s t s u g g e s t e d b y H u m p h r e y s (1910) h a s led to much c o n - t r o v e r s y but n u m e r o u s i n v e s t i g a t o r s (Willett, 1962; L o n d o n a n d Oltmans, 1973; Paetzold, 1973; R u d e r m a n a n d Chamerlain, 1975; A n g e l l a n d K o r s h o v e r , 1973, 1976), s t u d y i n g the statistics of the ozone data, h a v e quoted a possible relationship between the content of t h i s constituent and the s u n s p o t n u m b e r . However the o b s e r v a t i o n s are c o n t r o v e r s i a l because of absolute a n d intercalibration e r r o r s a n d g a p s in data a c q u i s i t i o n .

T h e effects of solar f l u x variabilities on atmospheric minor c o n s t i t u e n t s h a v e been p r i o r to t h i s w o r k estimated b y means of o n e - dimensional models. F r e d e r i c k ( 1 9 7 7 ) , a n d R y c r o f t a n d T h e o b a l d (1978) h a v e s t u d i e d the chemical r e s p o n s e of the u p p e r s t r a t o s p h e r e a n d meso- s p h e r e to v a r i a t i o n s of the solar irradiance with the 2 7 - d a y s solar rotation period. In p a r t i c u l a r , F r e d e r i c k (1977) h a s determined the possible variation in the concentration of mesospheric ozone due to c h a n g e s in the Lyman a line i n t e n s i t y . Callis a n d Nealy (1978a, b ) , P e n n e r a n d C h a n g (1978) a n d Callis et al. (1979) h a v e estimated the chemical and thermal r e s p o n s e of the s t r a t o s p h e r e to U V v a r i a b i l i t y associated with the 1 1 - y e a r s u n s p o t cycle adopting v a r i o u s possible solar f l u x v a r i a t i o n s among which some are close to i r r a d i a n c e ratio s u g g e s t e d b y Heath a n d T h e k a e k a r a ( 1 9 7 7 ) . V e r y r e c e n t l y , Pollack et al. (1979) h a v e i n v e s t i g a t e d the possible climatic impact of U V v a r i a t i o n s for time scales e n c o m p a s s i n g the 27 d a y solar rotation period, the s u n s p o t p e r i o d , the solar magnetic period a n d much longer times.

T h e p u r p o s e of t h i s paper is to p r o p o s e numerical v a l u e s of U V a n d v i s i b l e solar irradiance f l u x e s in a form which is c o n v e n i e n t for

i

aeronomic modeling p u r p o s e s . The possible long-term variability of these fluxes will be discussed and a tentative amplitude of these changes v e r s u s wavelength will be proposed. The effect of such variability on the chemical and thermal structure of the stratosphere will be examined using a two-dimensional numerical model. In particular, the possible changes in the photodissociation rates of the atmospheric molecules will be studied and the modification of the rate constants due to the tempe- rature variations will be taken into account. Only the flux variability associated with the 11-year cycle will be considered since the change of the solar flux intensity related to the 27-day solar rotation is less than 10 percent above 175 nm (Heath, 1973; Hinteregger et al., 1977) and is of the same order of magnitude as the semi-annual variation in the solar constant (± 3.3%) associated with the variation in the S u n - E a r t h distance.

2. T H E S O L A R I R R A D I A T I O N F L U X A N D I T S L O N G - T E R M V A R I A B I L I T Y

Recently, Simon (1978, 1979) published a critical review of the available full d i s k measurements obtained d u r i n g the solar cycle 20, between 120 and 400 nm, pointing out the disagreements between the most recent data. Since that time, new measurement have been made by Heath (1979), Hinteregger (1980), Mount et al. (1980) and Simon et al.

(1980). Table I gives the most useful observations for aeronomic p u r -

poses including date, accuracy and wavelength intervals. In fact,

discrepancies of the order of 50 percent still exist for many data,

especially in wavelengths particularly important for the photodissociation

of molecular o x y g e n . Consequently, when dealing with atmospheric

modeling, a critical s t u d y is necessary for the choice of the best solar

irradiation flux values.

TABLE 1 : UV solar irradiance measurements relevant for aeronomy

Reference date of observation Wavelength Véhiculé Accuracy interval (nm)

Arvesen et al (1969) Aug.-Nov. 1967 300- 2500 aircraft + 25 - Ackerman et al (1971) May 10, 1968

Apr. 19, 1969 194- 224 balloon + 2 0 % Oct. 3, 1969

Broadfoot (1972) June 15, 1970 210- 320 rocket ⁺ 10%

Simon (1974, 1975) Sept. 23, 1972 196- 230

balloon

+ 2 0 % May 16, 1973 285- 355 balloon

Rottman (1974) Dec. 13, 1972

116- 185 rocket ⁺ 15%

Aug. 30, 1973 116- 185 15%

Samain and Simon (1976) April 17, 1973 151- 209 rocket + 3 0 % Brueckner et al (1976) Sept. 4, 1973 174- 210 rocket ± 20%

Heroux and Swirbalus Nov. 2, 1973 123- 194 rocket + 2 0 % (1976)

2 0 % Heroux and Hinteregger April 23, 1974 25- 194 rocket ⁺ 2 0 %

(1978)

Heath (1979) Nov. 7, 1978 160- 400 satellite + 10 - Simon et al. (1980) July 1, 1976 210-•240

balloon

+ 15%

July 7, 1977 275-•350 balloon + 10%

Hinteregger (1980) July, 1976 - Jan. 22, 1979

15-•185 satellite ⁺ 2 0 % Mount et al. (1980) June 5, 1979 120-•256 rocket + 15%

Simon et al. (1981) Sept. 14, 1979 210-•240

balloon

+ 15%

June 24, 1980 275-•350 balloon + 10%

Neckel and Labs (1981) 1960's 330-•1.248 ground + 1.5

In the lower thermosphere molecular oxygen is photodissociated by solar irradi ation flux ranging from 130 to 175 nm, corresponding to the Schumann-Runge continuum. Only the data of Rottman (1974) Mount et al. (1980), Hinteregger (1980) and Heroux and Swirbalus (1976) cover this entire wavelength range while values of Samain and Simon

(1976) and Kjedlseth Moe et al. (1976) begin at 150 and 140 nm respectively. They are not direct full disk irradiance measurements but they were determined from radiance measurements converted into mean intensities using the center-to-limb variation measured by Samain and Simon (1976). The main objective of the observations of Hinteregger (1980) made from the AE-E satellite is to determine the variation of the solar irradiance from 14 to 185 nm. The absolute values are refering to the solar irradiance measurements of April 23, 1974, obtained by means of a rocket experiment (Heroux and Hinteregger, 1978). For these reasons, the rocket measurements performed by Rottman (1974) by Heroux and Swirbalus (1976) and by Mount et al. (1980) seem to us, to be the most reliable observations for aeronomic purposes between 120 and 175 nm. We have chosen Rottman's data obtained on Dec. 13, 1972

- 1

to elaborate solar irradiance values averaged over 500 cm because this observation took place in the middle of the second part of solar cycle 20, and not the value of Mount et al. (1980) which correspond to a maximum of solar activity during the solar cycle 21. A,more complete discussion on these data is given by Simon (1981).

Below 90 km photodissociation of molecular oxygen is due to solar

radiation ranging from 175 to 240 nm. This process initiates the photo-

chemistry in the mesosphere and in the upper stratosphere. Unfor-

tunately, large discrepancies also exist in the wavelength range mainly

between 180 and 190 nm ( c f . f i g . 6 in Simon, 1978) although rather

good agreement exists at 175 nm between Rottman ( 1 9 7 4 ) , Heroux and

Swirbalus (1976), Brueckner et al. (1976) and Samain and Simon

(1976). Only full disk measurements are fully pertinent for aeronomic

purposes. Therefore Rottman's values obtained on Dec. 13, 1972 have

been adopted up to 180 nm. Between 180 a n d 195 nm, it seems a p - propriate to use an a v e r a g e between the available measurements in o r d e r to link Rottman's data with the v a l u e s of Simon (1974) a r o u n d 200 nm which h a v e been confirmed b y the new o b s e r v a t i o n s of Heath ( 1 9 7 9 ) . B e y o n d 210 nm, these latter measurements are lower b y a factor v a r y i n g between 7 a n d 13 percent t h a n the p r e v i o u s v a l u e s of Simon (1974) but 27 percent h i g h e r than the recent v a l u e s obtained b y Mount et al. (1980) up to 255 nm. A complete d i s c u s s i o n on the d i s c r e p a n c i e s between all these data h a s been p r e s e n t e d b y Simon (1981). C o n s e - q u e n t l y , the v a l u e s of Broadfoot ( 1 9 7 2 ) , g e n e r a l l y adopted for aeronomic p u r p o s e s for the w a v e l e n g t h s b e y o n d 230, would be adjusted t a k i n g into account the new measurements of Heath ( 1 9 7 9 ) , M o u n t et al.

(1980) and Simon et al (1980). N e v e r t h e l e s s , the lowest data of Mount need to be confirm especially b y new rocket o b s e r v a t i o n s i n c l u d i n g solar measurements b e y o n d 255 nm because at longer w a v e l e n g t h s , a r o u n d 290 nm, both Simon (1975) and Heath (1979) are in v e r y good a g r e e - ment with B r o a d f o o t (1972).

A c c o r d i n g to the d i s c u s s i o n already p u b l i s h e d b y Simon (1978) on the irradiance data available b e y o n d 290 nm, irradiation flux v a l u e s obtained b y balloon b y Simon (1975) h a v e been adopted u p to 330 nm.

T h e s e v a l u e s are, in addition, in good agreement with the satellite measurement of Heath (1979) a n d the new balloon o b s e r v a t i o n of Simon et al. (1980). T h e data of A r v e s e n et all (1969) were g e n e r a l l y u s e d from 330 nm u p to near i n f r a r e d . U n f o r t u n a t e l y the absolute scale u s e d for calibration s u f f e r s from uncertainties ( K o s t k o w s k i , 1974) and it seems preferable to c o n s i d e r the data of A r v e s e n et al. (1969) as a good relative spectral d i s t r i b u t i o n at medium resolution. T h e latter v a l u e s have to be adjusted to the data of Neckel a n d L a b s (1981).

Table II and I I I g i v e the solar irradiation f l u x p r o p o s e d for aero-

nomical calculations. T h e v a l u e s c o r r e s p o n d b y definition to a mean

solar activity and are a v e r a g e d o v e r several spectral i n t e r v a l s d e -

p e n d i n g on the w a v e l e n g t h r a n g e .

- 1 T A B L E U . 1.- Solar i r r a d i a t i o n f l u x q nr one A . U ; averaged over 500 cm

between 117 and 308 nm.

N ° A^- (nm i) A

(cm

) 1 Ly a 1 2 1 . 5 6 7 8 2 , 2 5 9

2 116. 3-117. 0 8 5 , 5 0 0 - 8 6 , 0 0 0 3 1 1 7 . 0 - 1 1 7 . 6 8 5 , 0 0 0 - 8 5 , 5 0 0 4 1 1 7 . 6 - 1 1 8 . 3 . 8 4 , 5 0 0 - 8 5 , 0 0 0 5 1 1 8 . 3-119. 0 8 4 , 0 0 0 - 8 4 , 5 0 0 6 1 1 9 . 0 - 1 1 9 . 8 8 3 , 5 0 0 - 8 4 , 0 0 0 7 1 1 9 . 8 - 1 2 0 . 5 8 3 , 0 0 0 - 8 3 , 5 0 0 8 1 2 0 . 5-121. 2 8 2 , 5 0 0 - 8 3 , 0 0 0 9 1 2 1 . 2-122. 0 8 2 , 0 0 0 - 8 2 , 5 0 0 10 1 2 2 . 0 - 1 2 2 . 7 8 1 , 5 0 0 - 8 2 , 0 0 0 11 1 2 2 . 7-123. 5 8 1 , 0 0 0 - 8 1 , 5 0 0 12 123. 5-124. 2 8 0 , 5 0 0 - 8 1 , 0 0 0 13 1 2 4 . 2 - 1 2 5 . 0 8 0 , 0 0 0 - 8 0 , 5 0 0 14 1 2 5 . ,0-125. ,8 79 , 5 0 0 - 8 0 , 0 0 0 15 125, .8-126. .6 7 9 , 0 0 0 - 7 9 , 5 0 0 16 12 r». .6-127 .4 7 8 , 5 0 0 - 7 9 , 0 0 0 17 127. .4-128 .2 7 8 , 0 0 0 - 7 8 , 5 0 0 18 128 .2-129 . 0 7 7 , 5 0 0 - 7 8 , 0 0 0 19 129 .0-129 . 9 77 ,000-77 , 5 0 0 20 129 .9-130 .7 7 6 , 5 0 0 - 7 7 , 0 0 0 21 130 .7-131 . 6 7 6 , 0 0 0 - 7 6 , 5 0 0 22 131 .6-132 .4 7 5., 5 0 0 - 7 6 , 0 0 0 23 132 .4-133 .3 7 5 , 0 0 0 - 7 5 , 5 0 0 24 133 .3-134 . 2 7 4 , 5 0 0 - 7 5 , 0 0 0

q ( h v . s e c .cm ) 3 . 0 x 1 0

8 6 . 8 8 x 10 2 . 7 9 x 1 0

7 . 3 0 x 1 0

6.51.

1 . 5 6 x 1 0

1 . 4 0 6 . 3 0 2 . 2 8 1 . 2 5

9 . 0 6 x 1 0

l i l 9 x 1 0

5 . 9 5 x 1 0

6 . 7 5 x 1 0

1 . 8 2 x 1 0

4 . 5 6 x 10

8 . 0 1 5 . 9 9 7 . 0 7

6 . 9 0 x 10 9 1 . 7 6

8 . 2 4 x 1 0

3 . 3 5 x 1 0

5 . 2 1

TAP» LE I I . 1 ( con L iiiuod )

N<

(nm) Av(cm ) q C n v . s e c .cm )

25 26 27

28

29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

1 3 4 . 2 - 1 3 5 . 1 - 1 3 6 . 0 - 1 3 7 . 0 - 1 3 7 . 9 - 1 3 8 . 9 - 1 4 0 . 8 - 1 4 2 . 8 - 1 4 4 . 9 - 1 4 7 . 0 - 1 4 9 . 2 - 1 5 1 . 5 - 1 5 3 . 8 - 1 5 6 . 2 - 1 5 8 . 7 - 1 6 1 . 3 - . 1 6 3 . 9 - 1 6 6 . 7 - 1 6 9 . 5 - 1 7 2 . 4 - 1 7 3 . 9 - 1 7 5 . 4 - 1 7 7 . 0 - 1 7 8 . 6 -

135. 1 1 3 6 . 0 1 3 7 . 0 137.9 138.9 140.8 142.8 144.9 1 4 7 . 0 149.2 1 5 1 . 5 153.8 156.2 158.7 1 6 1 . 3 163.9 166.7 1 6 9 . 5 172.4 173.9 175.4 1 7 7 . 0 178.6 180.2

74,000- 73,500- 7 3,000- 72,500- 72,000- 71,000- 70,000- 6 9 , 0 0 0 - 68,000- 6 7 , 0 0 0 - 66,000- 6 5 , 0 0 0 - 6 4 , 0 0 0 - 6 3 , 0 0 0 - 62,000- 61,000- 60,000- 59,000- 58,000- 57,500- 57 ,000- 56 ,500- 56,000- 55,500-

7 4 , 5 0 0 7 4 , 0 0 0 7 3 , 5 0 0 7 3 , 0 0 0 7 2 , 5 0 0 7 2 , 0 0 0 7 1 , 0 0 0 7 0 , 0 0 0 6 9 , 0 0 0 68,000 6 7 , 0 0 0 66,000 6 5 , 0 0 0 6 4 , 0 0 0 6 3 , 0 0 0 62,000

•61,000

•60,000

•59,000

•58,000 5 7 , 5 0 0 5 7 , 0 0 0

•56,500

•56,000

8 . 5 8 X 10 2. 0 9 X lo' 1. 39

1 . 18

1.42 6 . 8 0 3 . 8 1 5 . 3 0 7 . 0 9

1 . 1 0 X 10

1 . 2 2

1.78 2 .96 2 . 4 1

2 . 8 8

3. 57 6 .07 7 , 9 1

1.32 X 10 7.39 X 10 8 . 3 3

1 . 1 3

10 1.35

1 . 8 5

8

10

11 10

11

- 1 1 -

TABLE H . I . - (continued)

- 1 - 1 - 2

N° AA-(nm) Av(cm ) q(hv.sec .cm )

49 180.2-181 .8 55,000-55,500 1. ,98

50 181.8-183 .5 54,500-55,000 2. ,10

51 183.5-185 .2 54,000-54,500 1. ,89

52 185.2-186, .9 53,500-54,000 2. ,90

53 186.9-188 .7 53,000-53,500 3. ,88

54 188.7-190, .5 52,500-53,000 4, . 16

55 190.5-192, .3 52,000-52,500 5, ,60

56 192.3-194 .2 51,500-52,000 5, ,07

57 194.2-196 .1 51,000-51,500 7, .40

58 196.1-198, .0 50,500-51,000 1, .01

59 198. 0-200, .0 50,000-50,500 1 .20

60 200.0-202 .0 49,500-50,000 1, .44

61 202.0-204 .1 49,000-49,500 1, .80

62 204.1-206 .2 48,500-49 j, 000 2, ,08

63 206.2-208, .3 48,000-48,500 2. .45

64 208.3-210 .5 47,500-48,000 5, .09

65 210.5-212 .8 47,000-47,500 7, .12

66 212.8-215 .0 46,500-47,000 8. ,55

67 215.0-217 .4 46,000-46,500 9. 27

68 217.4-219 .8 45,500-46,000 1, .16

69 219.8-222 .2 45,000-45,500 1. .20

70 222.2-224 .7 44,500-45,000 1, .64

71 224.7-227 .3 44,000-44,500 1 .41

72 227.3-229 .9 43 ,500-44,000 1, .46

TABLE H . 1 . - (continued)

N° AX(nm) Av (cm ) q(hv .

73 2 2 9 . 9 - 2 3 2 . 6 4 3 , 0 0 0 - 4 3 , 5 0 0 1. 68

74 2 3 2 . 6 - 2 3 5 . 3 4 2 , 5 0 0 - 4 3 , 0 0 0 1. 45

75 2 3 5 . 3 - 2 3 8 . 1 4 2 , 0 0 0 - 4 2 , 5 0 0 1. 74

76 2 3 8 . 1 - 2 4 1 . 0 4 1 , 5 0 0 - 4 2 , 0 0 0 1. 54

77 2 4 1 . 0 - 2 4 3 . 9 4 1 , 0 0 0 - 4 1 , 5 0 0 2. 25

78 2 4 3 . 9 - 2 4 6 . 9 4 0 , 5 0 0 - 4 1 , 0 0 0 2. 05

79 2 4 6 . 9 - 2 5 0 . 0 4 0 , 0 0 0 - 4 0 , 5 0 0 2. 09

80 2 5 0 . 0 - 2 5 3 . 2 3 9 , 5 0 0 - 4 0 , 0 0 0 2. 03

81 2 5 3 . 2 - 2 5 6 . 4 3 9 , 0 0 0 - 3 9 , 5 0 0 2. 96

82 2 5 6 . 4 - 2 5 9 . 7 3 8 , 5 0 0 - 3 9 , 0 0 0 5, .45

83 2 5 9 . 7 - 2 6 3 . 2 3 8 , 0 0 0 - 3 8 , 5 0 0 4. .86

84 2 6 3 . 2 - 2 6 6 . 7 3 7 , 5 0 0 - 3 8 , 0 0 0 1 .19

85 2 6 6 . 7 - 2 7 0 . 3 3 7 , 0 0 0 - 3 7 , 5 0 0 1 .29

86 2 7 0 . 3 - 2 7 4 . 0 3 6 , 5 0 0 - 3 7 , 0 0 0 1 .17

87 2 7 4 . 0 - 2 7 7 . 8 3 6 , 0 0 0 - 3 6 , 5 0 0 1 .11

88 2 7 7 . 8 - 2 8 1 . 7 3 5 , 5 0 0 - 3 6 , 0 0 0 7 . 8 4

89 281.7-285.7 3 5 , 0 0 0 - 3 5 , 5 0 0 1 . 5 0

90 2 8 5 . 7 - 2 8 9 . 9 3 4 , 5 0 0 - 3 5 , 0 0 0 2 .12

91 2 8 9 . 9 - 2 9 4 . 1 3 4 , 0 0 0 - 3 4 , 5 0 0 3 .56

92 2 9 4 . 1 - 2 9 8 . 5 3 3 , 5 0 0 - 3 4 , 0 0 0 3 .33

93 2 9 8 . 5 - 3 0 3 . 0 3 3 , 0 0 0 - 3 3 , 5 0 0 3 . 0 8

94 303.0-307.7 3 2 , 5 0 0 - 3 3 , 0 0 0 4 .39

-1 - 2 ,

. cm , .13

14

>

.14

-13-

TABLEII..2.- Solar irradiation flux q at one A.U, averaged over 5 nm between 307 and 647 nm.

- 1 - 2

N° AA (nm) q (hv.sec .cm ) 95 307.5-312.5 4.91 x 10

96 312.5-317.5 5.53

97 317.5-322.5 6.04

98 322.5-327.5 6.97

99 327.5-332.5 0.49

100 332.5-337.5 7.52

101 337.5-342.5 8.13

102 34?.. 5-347.5 7,84

103 347.5-352.5 8.31

104 352.5-357.5 9.33

105 357.5-362.5 8.47

106 362.5-367.5 1.06 x 10

107 367.5-372.5 1.10 108 372.5-377.5 9.57 x 10 14

109 377.5-382.5 1.14 x 10 14

110 382.5-387.5 8.63 x 10

111 387.5-392.5 1.15 x 10

112 392.5-397.5 9.57 x 10*

113 397.5-402.5 1.70 x 10

114 402.5-407.5 1.70

115 407.5-412.5 1-78

116 412.5-417.5 .1.87

117 417.5-422.5 1-84

118 422.5-427.5 1.80

TABLE I I . 2 . - ( c o n t i n u e d )

N° AA (nm) q ( h v . s e c .cm ) 119 4 2 7 . 5 - 4 3 2 . 5 1 . 6 6 x 1 0

120 4 3 2 . 5 - 4 3 7 . 5 2 . 0 4 121 4 3 7 . 5 - 4 4 2 . 5 2 . 0 0 122 4 4 2 . 5 - 4 4 7 . 5 2 . 2 0 123 4 4 7 . 5 - 4 5 2 . 5 2 . 3 5 124 4 5 2 . 5 - 4 5 7 . 5 2 . 3 0 125 4 5 7 . 5 - 4 6 2 . 5 2 . 3 5 126 4 6 2 . 5 - 4 6 7 . 5 2 . 3 4 127 4 6 7 . 5 - 4 7 2 . 5 2 . 3 6 128 4 7 2 . 5 - 4 7 7 . 5 2 . 3 9 129 4 7 7 . 5 - 4 8 2 . 5 2 . 4 9 130 4 8 2 . 5 - 4 8 7 . 5 2 . 3 0 131 4 8 7 . 5 - 4 9 2 . 5 2 . 3 6 132 4 9 2 . 5 - 4 9 7 . 5 2 . 5 3 133 4 9 7 . 5 - 5 0 2 . 5 2 . 3 8 134 5 0 2 . 5 - 5 0 7 . 5 2 . 4 7 135 5 0 7 . 5 - 5 1 2 . 5 2 . 4 7 136 5 1 2 . 5 - 5 1 7 . 5 2 . 3 2 137 5 1 7 . 5 - 5 2 2 . 5 2 . 4 6 138 5 2 2 . 5 - 5 2 7 . 5 2 . 4 3 139 5 2 7 . 5 - 5 3 2 . 5 2 . 6 0 140 5 3 2 . 5 - 5 3 7 . 5 2 . 5 9 141 5 3 7 . 5 - 5 4 2 . 5 2 . 5 1 142 5 4 2 . 5 - 5 4 7 . 5 2 . 5 6

-15-

TABLE n . 2.- ( c o n t i n u e d )

- 1 - 2

N ° A* (nm) q ( h v . S e c .cm ) 143 5 4 7 . 5 - 5 5 2 . 5 2 . 6 1 x 1 0

144 5 5 2 . 5 - 5 5 7 . 5 2 . 5 7

145 5 5 7 . 5 - 5 6 2 . 5 2 . 5 5

146 5 6 2 . 5 - 5 6 7 . 5 2 . 6 1

147 5 6 7 . 5 - 5 7 2 . 5 2 . 6 3

148 5 7 2 . 5 - 5 7 7 . 5 2 . 6 8

149 5 7 7 . 5 - 5 8 2 . 5 2 . 6 6

150 5 8 2 . 5 - 5 8 7 . 5 2 . 6 8

151 5 8 7 . 5 - 5 9 2 . 5 2 . 6 0

152 5 9 2 . 5 - 5 9 7 . 5 2 . 6 7

153 5 9 7 . 5 - 6 0 2 . 5 2 . 5 9

154 6 0 2 . 5 - 6 0 7 . 5 2 . 7 0

155 6 0 7 . 5 - 6 1 2 . 5 2 . 6 4

156 6 1 2 . 5 - 6 1 7 . 5 2 . 6 2

157 6 1 7 . 5 - 6 2 2 . 5 2 . 6 7

158 6 2 2 . 5 - 6 2 7 . 5 2 . 6 2

159 6 2 7 . 5 - 6 3 2 . 5 2 . 6 1

160 6 3 2 . 5 - 6 3 7 . 5 2 . 6 4

161 6 3 7 . 5 - 6 4 2 . 5 2 . 6 2

162 6 4 2 . 5 - 6 4 7 , 5 2 . 6 6

TABLE II. 3.- Solar irradiation flux q at one A.U. averaged over 10 rim between 645 and 735 nm.

N' AA. (nm) q (hv.sec .cm ) ^ -

163 164 165 166 167 168 169 170 171

645-655 655-665 665-675 675-685 685-695 695-705 705-715 715-725 725-735

5.21 x 10 5.07

5.18 5. 15 5.11 5.03 5.00 4 . 9 1 4.90

15

TABLE III.- Solar irradiation flux q at one A.U. averaged over 1 run between 116 and 310 nm.

- 1 - 2 - 1

AA(nm) q(hv.sec .cm .nm )

116 - 117 9. .57 ^X 10

117 - 118 3. .34 ^X 10

118 - 119 8. .26 ^X 10

119 - 120 2. ,07 ^X 10

120 - 121 6. . 19

i o

121 - 122 3. . 17 ^X i o

122 - 123 2. .09 ^X 10

123 - 124 1, .54

124 - 125 1, . 12

125 - 126 1, . 17

126 - 127 1. :46

io

127 - 128 9, .71 ^X io

128 - 129 7. .50

129 - 130 7, .27

130 - 131 7. .29 ^X 10

131 - 132 1, .31

io

132 - 133 9, .70 ^X io

133 - 134 9 .40 ^X 10

134 - 135 8 .58 ^X io

135 - 136 2, .13 ^X 10

136 - 137 1 .39

137 - 138 1 .33

138 - 139 1 .36

139 - 140 3 .85

140 - 141 3 .27

141 - 142 2 .04

142 - 143 2 . 13

TABLE I I I . - ( c o n t i n u e d 1)

- 1 - 2 - 1 AA(nm) q ( h v . s e c .cm .nm )

143 - 144 2 . 6 0 144 - 145 2 . 4 9 145 - 146 2 . 8 3 146 - 147 3 . 8 1 147 - 148 4 . 6 3 x 10 9

148 - 149 4 . 9 8 149 - 150 4 . 7 4 150 - 151 5 . 2 4 151 - 152 5 . 5 4 152 - 153 7 . 4 0 153 - 154 8 . 4 0 154 - 155 1 . 3 6 x 10 ¹

155 - 156 1 . 2 6 156 - 157 1.19 157 - 158 1 . 0 1 158 - 159 9 . 5 0 x 10 ⁹

159 - 160 9 . 7 8 1

160 - 161 1 . 1 3 x 10

161 - 162 1 . 1 8 162 - 163 1 . 4 2 163 - 164 1 . 6 5 164 - 165 1 . 7 8 165 - 166 2 . 6 9 166 - 167 2 . 1 0 167 - 168 2 . 4 5 168 - 169 3 . 0 4 169 - 170 3 . 8 9 170 - 171 4 . 5 9

-19

TABLE I I I . - (continued 2)

-1 -2 -1 AÄ.(nm) qChv.sec .cm .nm )

171 - 172 4.69 172 - 173 4.96 173 - 174 4.84 174 - 175 5.78 175 - 176 6.46 x 1 0

176 - 177 7.00 177 - 178 7.80 178 - 179 8.89 179 - 180 8.74 180 - 181 1.07 x 10

181 - 182 1.34

182 - 183 1.35

183 - 184 1.35

184 - 185 1.16

185 - 186 1.50

186 - 187 1.83

187 - 188 2.10

188 - 189 2.20

189 - 190 2.35

190 - 191 2.35

191 - 192 3.05

192 - 183 3.16

193 - 194 2.60

194 - 195 4.20

195 - 196 4.05

196 - 197 4.79

197 - 198 5 . 3 2

TABLE III.- (continued 3 )

-1 -2 -1 A A ( n m ) q(hv.sec .cm .nm )

198 - 199 6.05 199 - 200 5.95 200 - 201 7.11 201 - 202 7.29 202 - 203 8.04 203 - 204 8.93 204 - 205 9.76 205 - 206 9.90 206 - 207 1.06 x 1 0

207 - 208 1.20 208 - 209 1.53 209 - 210 2.56 210 - 211 2.92 211 - 212 3.61 212 - 213 3.23 213 - 214 3.43 214 - 215 4.43 215 - 216 4.01 216 - 217 3.73 217 - 218 3.96 218 - 219 4.95 219 - 220 5.27 220 - 221 5.35 221 - 222 4.39 222 - 223 5.68 223 - 224 7.42 224 - 225 6.55 225 - 226 6.13

- 2 1 -

TABLE I I I . - (continued 4)

-1 -2 -1 AA.(nm) q(hv.sec .cm .nm )

226 - 227 4.68

227 - 228 4.69

228 - 229 6.22

229 - 230 5 . 5 3

230 - 231 6.54

231 - 232 5.83

232 - 233 6.43

233 - 234 5 . 4 0

234 - 235 4.65

235 - 236 6.76

236 - 237 5.87

237 - 238 6.38

238 - 239 5.04

239 - 240 5.61

240 - 241 5.22

241 - 242 6.39

242 - 243 8.86

243 - 244 8.03

,244 - 245 7.69

245 - 246 6.33

246 - 247 6.40

247 - 248 7.13

248 - 249 5.66

249 - 250 7.35

250 - 251 7.48

251 - 252 5.91

252 - 253 5 . 6 0

253 - 254 7.09

TABLE I I I . - ( c o n t i n u e d 5)

- 1 - 2 - 1 AA(nm) q ( h v . s e c .cm .nm )

254 - 255 7.80 x 10 1 2

255 - 256 1.14 x I Q 1 3

256 - 257 1.38 257 - 258 1.68 258 - 259 i . 75

259 - 260 1.41 260 - 261 1.34 261 - 262 1.36 262 - 263 1.60 262 - 264 2 . 3 3 264 - 265 3.65 265 - 266 3 . 7 5 266 - 267 3 . 5 0 267 - 268 3,64 268 - 269 3.52 269 - 270 3 . 4 3 x 1 0 1 3

270 - 271 4 . 0 0 271 - 272 3 . 1 8 272 - 273 2 . 9 5 273 - 274 2.81 274 - 275 1.90 275 - 276 2 . 7 8 276 - 277 3 . 6 0 277. - 278 3.36 278 - 279 2 . 3 3 279 - 280 1.26 280 - 281 1.59 281 - 282 3 . 2 8

-23-

TABLE I I I . - (end)

-1 - 2 -1 A\(nm) q ( h v . s e c .cm .nm )

282 - 283 4, .37

283 - 284 4, .71

284 - 285 3. .50

285 - 286 2 .03

286 - 287 4. .62

287 - 288 .38

288 - 289 4. .46

289 - 290 6. .65

290 - 291 9. . 12

291 - 292 8. .82

292 - 293 8, .04

293 - 294 8 .07

294 - 295 7. .56

295 - 296 8. . 17

296 - 297 7. .36

297 - 298 7. .97

298 - 299 6. .21

10

299 - 300 7. .32

300 - 301 6. . 10

301 - 302 6. .77

302 - 303 7. .38

303 - 304 9. .65

304 - 305 9. .37

305 - 306 8. .93

306 - 307 8. .89

307 - 308 1. .00

10

308 - 309. 9. .54

10

309 - 310 7. .55

As long ~term v a r i a b i l i t y of UV solar i r r a d i a n c e is q u i t e e v i d e n t at lyman a and below 100 nm ( V i d a l M a d j a r , 1975; Schrnidtke, 1978), such a v a r i a t i o n is e x p e c t e d at l o n g e r w a v e l e n g t h w i t h a m a g n i t u d e w h i c h has to be e s t a b l i s h e d . U n f o r t u n a t e l y , in t h e w a v e l e n g t h r a n g e of s t r a t o - s p h e r i c i n t e r e s t , t h e e v i d e n c e of v a r i a t i o n s d u r i n g solar c y c l e 20 is not c o n c l u s i v e as it was s t a t e d b y Simon (1978) and b y D e l a b o u d i n i e r e el aL ( 1 9 7 8 ) . T h i s is due to t h e inadequate time coverage of reliable data d u r i n g t h e solar c y c l e 20, to t h e u n c e r t a i n t i e s associated w i t h each o b s e r v a t i o n and to t h e absence of i n t e r c o m p a r i s o n in t h e c a l i b r a t i o n p r o c e d u r e s . N e v e r t h e l e s s , Heath and T h e k a e k a r a (1977) claimed an 1 1 - y e a r v a r i a b i l i t y of a f a c t o r of 2 at 200 nm on t h e basis of t h e i r own measurements p e r f o r m e d b y satellites and b y r o c k e t s since 1966. T h i s is i l l u s t r a t e d in f i g . 1 on w h i c h t h e f u l l s q u a r e s and t r i a n g l e s r e p r e s e n t t h e solar f l u x r a t i o f r o m minimum to maximum solar a c t i v i t y o b t a i n e d f r o m b r o a d b a n d p h o t o m e t r i c o b s e r v a t i o n s and t h e f u l l c i r c l e s t h e r a t i o o b t a i n e d b y means of a double monochromator e x p e r i m e n t . T h e solid c u r v e r e p r e s e n t s t h e solar v a r i a b i l i t y d e d u c e d b y t h e a u t h o r s . It s h o u l d be p o i n t e d o u t t h a t t h e r e are o n l y two p o i n t s a r o u n d 180 nm and t h a t t h e solar f l u x ratios o b t a i n e d a r o u n d 290 nm w i t h t h e double mono- c h r o m a t o r are 15-20 p e r c e n t h i g h e r t h a n those o b t a i n e d f r o m t h e b r o a d - b a n d d e t e c t o r s at t h e same w a v e l e n g t h . In a d d i t i o n , the a c c u r a c y of t h e basic measurements o b t a i n e d f r o m t h i s l a t t e r i n s t r u m e n t is ± 15 p e r c e n t and ± 30 p e r c e n t f o r t h e s h o r t e r and t h e longer w a v e l e n g t h r e s p e c t i v e l y and between ± 8 p e r c e n t and ± 3 p e r c e n t f o r t h e double monochromator d a t a . A linear r e g r e s s i o n calculation is shown b y t h e dashed lines f o r each set of solar f l u x r a t i o s . E x t r a p o l a t i o n of solar f l u x r a t i o at 340 nm f r o m t h e b r o a d b a n d d e t e c t o r measurements g i v e s a v a r i a b i l i t y of 25 p e r c e n t between i r r a d i a n c e s c o r r e s p o n d i n g to t h e maximum and to t h e minimum of t h e 1 1 - y e a r solar c y c l e . Such a value is in c o n t r a d i c t i o n w i t h t h e v a r i a b i l i t y based on t h e double monochromator d a t a . On t h e o t h e r h a n d , e x t r a p o l a t i o n of t h e l a t t e r data to s h o r t e r w a v e l e n g t h g i v e s a r a t i o of o n l y 0 . 7 at 200 nm. If v a r i a t i o n s w i t h t h e 1 1 - y e a r cycle in t h e u l t r a v i o l e t solar i r r a d i a n c e do e x i s t , t h e y are p r o b a b l y less t h a n those stated b y Heath and T h e k a e k a r a ( 1 9 7 7 ) .

- 2 5 -

ro CT) I

1.0

— 0.8 _X

o

é

c 0.6

o 0.4 r-

<

er broad - band detector

0.2 -

o L .

a 1966/1969 a 1966/1970 double monochromator ® 1975/1970

JL ^JL _L ^X

160 180 200 220 240 260 280 WAVELENGTH (nm)

300 320 340

Fig. 1.- Ratio of solar flux measured near solar-cycle minimum to that measured

near solar-cycle maximum versus wavelength claimed by Heath and

Thekaekara (1977). (Solid line). The full squares and triangles are

based on broadband photometric observations and the full circles on a

S u c h a comment seems to be confirmed b y H i n t e r e g g e r (1980) for o b s e r v a t i o n s performed between 1976 a n d 1979 for w a v e l e n g t h s below 185 nm, leading to a variability of 21% a r o u n d 180 nm d u r i n g that time and by new o b s e r v a t i o n s performed b y balloon in 1976 a n d 1977 (Simon et al. 1980) c o r r e s p o n d i n g to the minimim solar activity between solar cycle 20 and 21. V a r i a t i o n s between 210 and 240 nm o v e r the 11-year cycle may not exceed 20 percent if differences between o b s e r v a t i o n s are interpreted only as v a r i a t i o n s of the solar o u t p u t a n d not as e x p e r i - mental e r r o r s .

T h e p r e v i o u s c o n s i d e r a t i o n s lead us to adopt a solar i r r a d i a n c e ratio between the minimum and the maximum of the 1 1 - y e a r cycle v a r y i n g from 0.8 at 200 nm to 0 at 300 nm. T h e s e ratios are illustrated in f i g . 2 and h a v e been i n t r o d u c e d in o u r calculations.

3. T H E O R E T I C A L R E S P O N S E OF T H E S T R A T O S P H E R E T O U V

V A R I A B I L I T Y A S S O C I A T E D W I T H T H E 1 1 - Y E A R S U N S P O T C Y C L E

U s i n g a two-dimensional model of the s t r a t o s p h e r e which has been

d e s c r i b e d in several p r e v i o u s p a p e r s ( B r a s s e u r , 1976; 1978; B r a s s e u r

and B e r t i n , 1976; 1978), we have s t u d i e d the relationship between the

solar variability and the s t r a t o s p h e r i c minor c o n s t i t u e n t s at v a r i o u s

latitudes. T h e model has been u s e d with s t e a d y state conditions since

the r u n of the time d e p e n d e n t v e r s i o n for a period of 2 or 3 solar

cycles consumes a p r o h i b i t i v e amount of computer time. A thermal

scheme has been added to the chemical a p p r o a c h in o r d e r to take into

account the thermal feedback in the chemical r e s p o n s e s . T h e d i s t r i -

bution in the meridional plane of the following species is calculated :

O

, 0 (

P ) , 0 (

D ) , O H , H 0

, N

0 , N O , N O g , N g O g , H N O

, C H

,

C H g C I , CFCI

., C F

C I

, C C I

, C I , C I O , C I 0 N 0

, H C I . T h e water v a p o r

is being held c o n s t a n t ; since H

0 a p p e a r s to be less s e n s i t i v e to the

photochemistry than to the t r a n s p o r t , this h y p o t h e s i s s h o u l d not

s e r i o u s l y alter o u r c o n c l u s i o n s .

\

ro I oo

X O 0.8

L L E

£ c

L L 0.7

O 1—

< 0.6 cr 0.6 0.5

SOLAR LONG- VARIABILITY

180 200 220 240 260 WAVELENGTH (nm)

280 300

F i g . 2.- Long-term solar variability adopted in this w o r k . The curve represen-

T h e s t e a d y state a s s u m p t i o n needs f u r t h e r justification since species with long chemical lifetime ( N

0 , C H

, C F C I g , C F

C I

, e t c . . ) may be expected to r e s p o n d with a certain delay which is not negligible compared with 11 y e a r s . In fact, the variability of minor c o n s t i t u e n t s a p p e a r s with the h i g h e s t efficiency in the r e g i o n s where the p h o t o - c h e m i s t r y is the most active, that is where the lifetime of the species is the s h o r t e s t . A s s h o w n b y Callis and Nealy (1978) and b y Penner a n d C h a n g ( 1 9 7 8 ) , in their 1 - D models, the time lag for long lived species s u c h as N

0 is s i g n i f i c a n t o n l y in the altitude r a n g e where the magnitude of the variation is v e r y small. T h e calculated ozone c h a n g e b y these a u t h o r s u s i n g a full interactive time d e p e n d e n t calculation, is t h u s n e a r l y identical to that obtained with a s t e a d y state model.

O n the other h a n d , there may be s i g n i f i c a n t differences between s t e a d y a n d time-dependent calculations for more reactive species s u c h as H N O g , H

C>

a n d C I 0 N 0

leading in steady state models to e r r o r s in the calculations of both local a n d total ozone. A g a i n , t h i s effect and the possible s i g n i f i c a n t p h a s e difference with respect to solar activity a p p e a r s essentially in the lower s t r a t o s p h e r e where the relative ozone variation is the smallest. N e v e r t h e l e s s f u r t h e r i n v e s t i g a t i o n s h o u l d estimate the impact of seasonal v a r i a t i o n s in the calculations, p a r - ticularly in a two-dimensional r e p r e s e n t a t i o n .

In o r d e r to determine the concentration of c o n s t i t u e n t s ( o r family of c o n s t i t u e n t s s u c h as N O ( = N O + NO_ + H N O „ + C I 0 N 0 y 2 3 2

) or C I X ( = CI + C I O + H C I + C I 0 N 0

) we h a v e solved for each of them a c o n t i n u i t y equation. T h e meridional d i s t r i b u t i o n of the temperature T is obtained b y s o l v i n g the equation of e n e r g y c o n s e r v a t i o n .

A detained d e s c r i p t i o n of the model with the related numerical

method a n d the p h y s i c a l a n d chemical conditions is g i v e n in the

a p p e n d i x .

4. A N A L Y S I S OF T H E R E S U L T S

The model has been run for three different scenarios. In the first case, a solar flux q m e a n corresponding to average irradiance conditions is adopted; the second and third cases refer respectively to high

(q m ax m i n m . v ) and low (q ) solar activity. The fractional variation of a quantity X , expressed in percent, is then defined as :

.'JC X (q ) - X(q . )

max nun , „ j ^{x 1 0 0}

m e a n

The temperature variation however is expressed by its absolute value AT = T C ^ ) - T ( q m i n )

The primary effect of the solar flux variation as shown by figure 2 appears through a change in the photodissociation rates for the mole- cules absorbing below 300 nm. Figure 3 shows the relative variation of photodissociation frequencies for various stratospheric species. Due to larger variations of ultraviolet flux around 200 nm, compounds ab- sorbing mainly in the shorter wavelengths range are obviously more sensitive than constituents whose absorption peaks are observed in the visible or in the near UV. For example, when the solar irradiance increases from the minimum to the maximum, the production rate of ozone related to the dissociation of O^ increases more significantly than the dissociation of O^.

The second chemical response appears through the change in the

temperature distribution since chemical reaction rates are generally

temperature dependent. T h i s effect is not negligible as shown by the

following example which refers to simplified conditions. If a pure

oxygen atmosphere is assumed, the ozone concentration above 25-30 km

is given by (Nicolet, 1971)

RELATIVE VARIATION (percent)

Fig. 3.- Relative variation of the photodissociation frequency of various

stratospheric species as a function of the altitude and for a solar

zenith angle of 60 degrees.

where K = k„/k_ (see table I I I ) and where J - is the ratio of

C 3 U j U j

the C>2 and O^ photodissociation rates. The fractional variation in the ozone concentration can be written, if the molecular oxygen and total concentrations are assumed to remain unchanged,

A n (0

-3 ) 1 ' T 1 A„

3 ^ _1 ^ J 1 AK n ( O j - 2 J 2 K

The first term, which is the direct effect via the photodissociation rates, is positive ( f i g . 4) since AJ_ /J^, > AJ_ / J _ . The second term

C>2 C>2 O3 O3

which represents the indirect effect via the temperature change is ₂ negative since AK/K s - 2810 A T / T . In fact, the temperature depen- dence of the recombination rate nf O and O^ (reaction k ³ , see table 3) reduces the variation of the ozone concentration as computed when the temperature feedback is omitted. In the real atmosphere, the problem is more complex since the interaction with other constituents (HO x > N O x ' C I X , e t c . . . ) has to be taken into consideration and the full model calculation has to be performed. However, the temperature effect ap- pears mainly through the direct recombination of O and O^.

A third effect, which is not included in this work, could play a certain role, namely the variation of the total concentration which, according to the hydrostatic law, should be associated with any tempe- rature change. T h i s variation could affect the three body reaction rates (see for example reactions k^, a ( , e t c . . . , table IV in the appendix and the concentration of minor constituents above 35-40 km (Penner and Luther, 1980).

Figure 5 depicts the percent change in ozone concentration from

solar minimum to solar maximum, as computed in the 2-D model using

the full chemistry of table IV (see appendix). C u r v e (a) represents the

vertical distribution of O^ at 30 degrees latitude when the temperature

feedback is taken into account. In curve ( b ) the temperature is held

Fig. 4.- Relative variation of the ozone concentration versus altitude in a pure

oxygen atmosphere for a zenith angle of 60 degrees. The curve labelled

AJ/2J refers to the contribution of the change in the photodissociation

rates while the curve labelled AK/2K represents the effect of the

following temperature variations : AT = 0.4 K at 25 km, 1.1 at 30 km,

1.6 at 35 km, 3.0 at 40 km and 6.0 at 45 km.

PERCENT C H A N G E IN THE OZONE CONCENTRATION

F i g . 5.- Relative change of the ozone concentration versus

altitude at 30 degrees latitude (yearly mean)

related to the solar irradiance variation as

indicated in fig. 2. Curve (a) with temperature

feedback. Curve (b) with fixed temperature.

constant. In this latter case, the ozone concentration increases with the solar f l u x , the maximum variation (13 percent) appearing around 40 km.

This large increase of O^ in the upper stratosphere is due to the enhanced dissociation rate of molecular oxygen in this altitude range.

Moreover, in the vicinity of the stratopause (and in the lower meso- sphere), the enhancement of Og becomes smaller due to the increase of the OH and HC^ concentration. In the lower stratosphere, the increase of Og is relatively small since the penetration of UV radiation in the Herzberg continuum is reduced by the enhancement of the ozone content at higher altitude and by the fact that O^ becomes less sensitive to chemistry and photochemistry. In order to illustrate this point, f i g . 6 depicts the variation of the average ozone production rate at 35 and 20 km respectively. In the upper stratosphere of the equatorial regions, the photodissociation rate of O ² leading to the formation of 0 ³ is in- creased by more than 10 percent from solar minimum to solar maximum.

But in the lower stratosphere, due to the enhancement of the optical depth above this level, the production rate of ozone is reduced by a factor which increases with latitude ( i . e . with optical depth or solar zenith angle). At 20 km this reduction varies from about 2 percent at the equator to 10 percent at 60 degrees latitude. The loss rate of O ^s is also modified. It increases with solar flux in the upper stratosphere so that a new photochemical equilibrium is reached with a corresponding value of the ozone concentration. In the lower stratosphere, the loss rate decreases with increasing solar irradiance but the new ozone con- centration depends on the transport conditions which are kept un- changed in the present model.

When the temperature feedback is considered, the ozone variation as given by the model calculation, is reduced above 30 km and the maximum (10 percent) raises to about 45 km. This reduction is ex- plained by the negative correlation between O^ and temperature. Below 30 km, in the region where the peak of the ozone concentration is located, the ozone enhancement is slightly larger when the temperature

-35-

RELATIVE VARIATION OF THE OZONE PRODUCTION RATE

feedback is c o n s i d e r e d . A g a i n t h i s is related to t h e v a r i a t i o n of ozone at h i g h e r a l t i t u d e and t h e p e n e t r a t i o n of UV r a d i a t i o n down to t h e lower s t r a t o s p h e r e . With t h e s p e c t r a l d i s t r i b u t i o n of t h e solar v a r i a b i l i t y adopted in t h i s p a p e r , t h e r e l a t i v e change of t h e ozone column has t h e same o r d e r of magnitude (3 p e r c e n t ) in b o t h cases ( w i t h and w i t h o u t t e m p e r a t u r e f e e d b a c k ) . M o r e o v e r , as stated b y f i g . 7, t h e total ozone v a r i a t i o n AC> ³ /0 ³ does not show any appreciable l a t i t u d i n a l v a r i a t i o n if t h e proposed solar v a r i a b i l i t y is used in t h e model c a l c u l a t i o n . In f a c t , as shown in f i g . 8 , t h e e q u a t o r i a l regions are c h a r a c t e r i z e d b y a r e l a - t i v e l y large ozone enchancement at h i g h a l t i t u d e s and a small v a r i a t i o n at low a l t i t u d e s , while at h i g h e r l a t i t u d e s the ozone v a r i a t i o n is r e l a - t i v e l y c o n s t a n t between 20 and 45 km. T h i s e f f e c t can be e x p l a i n e d b y t h e feedback between the v e r t i c a l ozone d i s t r i b u t i o n and t h e p e n e t r a t i o n of t h e UV r a d i a t i o n responsible f o r t h e ozone f o r m a t i o n .

Fig. 9 shows, f o r comparison p u r p o s e s , t h e ozone v a r i a t i o n s at 30°

l a t i t u d e due to t h e f l u x v a r i a b i l i t y adopted in t h i s w o r k and those due to h i g h e r v a r i a b i l i t y proposed b y Heath and T h e k a e k a r a (1977). T h e magnitude of t h e C> ³ v a r i a t i o n is enhanced from 10 to 22 p e r c e n t at 45 km. Since t h i s last number is much l a r g e r t h a n t h e o b s e r v e d changes of t h e ozone c o n c e n t r a t i o n in t h e u p p e r s t r a t o s p h e r e ( A n g e l l and K o r s h o v e r , 1978a), t h e solar f l u x v a r i a b i l i t y g i v e n b y Heath and T h e k a e k a r a (1977) is p r o b a b l y l a r g e l y o v e r e s t i m a t e d . When t h e l a t t e r solar v a r i a b i l i t y is i n t r o d u c e d in t h e model c a l c u l a t i o n , the increase in the total ozone c o n c e n t r a t i o n shows a more p r o n o u n c e d l a t i t u d i n a l v a r i a t i o n ( f i g . 7 ) . T h i s e f f e c t can be e x p l a i n e d b y t h e f a c t t h a t , in t h i s l a t t e r case, t h e solar i r r a d i a n c e is modified as f a r as 350 nm, i . e . in a region where ozone is photodissociated and molecular o x y g e n is n o t . T h e r e f o r e , t h e v a r i a t i o n of t h e J ^ / J _ r a t i o is more s e n s i t i v e to

° 2 ° 3

t h e solar z e n i t h angle in t h e ease of t h e Heath and T h e k a e k a r a model t h a n in t h e case of t h e solar f l u x v a r i a b i l i t y as suggested in t h i s p a p e r .

- 3 7 -

LATITUDE (degrees)

Fig. 7.- Relative variation of the vertically integrated ozone concentration as

PERCENT C H A N G E IN THE O Z O N E CONCENTRATION

Fig. 8.- Relative variation of the ozone concentration versus altitude at different latitudes in response to the UV variability from solar minimum to maximum (fig. 2).

- 3 9 -

PERCENT CHANGE IN THE OZONE CONCENTRATION

F i g . 9.- Relative variation of the ozone concentration versus altitude for two

different solar flux variabilities (see f i g . 1 - solid line and fig.

T h e n u m b e r s obtained in the p r e s e n t computation are not in- c o n s i s t e n t with the a n a l y s i s of the ozone data b y Angell a n d K o r s h o v e r (1978a). T h e s e show in the N o r t h e r n Hemisphere where most stations are located a 5 percent increase in total ozone between the early 6 0 ' s and 70's and a 1 - 2 percent decrease between 1970 and 72. T h e a n a l y s i s of Angell and K o r s h o v e r (1978a) also indicates that the U m k e h r data in the N o r t h temperate latitudes s u g g e s t a 11 percent increase of the ozone concentration in the 32-46 km layer between 1964 and 1970.

O n the other h a n d , calculations of the possible modulation of s t r a t o s p h e r i c ozone due to the penetration v a r i a b i l i t y in the atmospheric of galactic cosmic r a y s ( R u d e r m a n a n d C h a m b e r l a i n , 1975) a n d the related formation of n i t r o g e n o x i d e s in the lower s t r a t o s p h e r e , mainly at h i g h latitude ( W a r n e c k , 1972; Nicolet a n d Peetermans, 1972; B r a s s e u r and Nicolet, 1973; Nicolet, 1975), have been performed. O u r model s h o w s that t h i s effect can be neglected in comparison with the ozone modulation due to U V v a r i a b i l i t y as adopted in this w o r k .

Finally the c o r r e s p o n d i n g c h a n g e s in the heating rate b y O ^ a b - s o r p t i o n a n d in the temperature d i s t r i b u t i o n as determined b y o u r 2 - D model are s h o w n r e s p e c t i v e l y in f i g . 10 a n d 11. T h e temperature in- c r e a s e s with solar f l u x mainly above 30 km because of the e n h a n c e d ozone heating b y U V f l u x e s . T h e effect which is most s i g n i f i c a n t in the equatorial a n d tropical r e g i o n s must be related to the meridional d i s t r i - bution of the ozone variation ( f i g . 9 ) . A comparison with the r e s u l t s obtained b y Callis a n d Nealy (1978) a n d , to a certain extent, b y P e n n e r and C h a n g (1978) indicate that the temperature variation v a l u e s o b - tained b y these a u t h o r s are s i g n i f i c a n t l y larger than o u r s .

It s h o u l d also be noted that Callis and Nealy (1978b) have d e r i v e d a negative variation of the ozone concentration in the u p p e r s t r a t o - s p h e r e while the r e s u l t s obtained b y Callis and Nealy (1978a), b y Penner and C h a n g (1978) and b y o u r s e l v e s show a positive v a r i a t i o n .

-41-

T

VARIATION OF THE STRATOSPHERIC HEATING RATE

. 1 0 — — - ipercenu

-8-

30 45

LATITUDE (degrees)

Fig. 10.- Meridional distribution of the relative variation

in the heating rate for the UV variability from

solar minimum to maximum (fig. 2).

I

•b.

30 45 60 LATITUDE (degrees)

Fig. II. Meridional distribution of the relative change in the temperature for

the UV variability from solar minimum to maximum (fig. 2).

The difference may be mainly due to the magnitude of the temperature change which as mentioned is much larger in the results of Callis and Nealy (1978b).

The stratospheric temperature trends observed since the 1960's have been analyzed by different authors (Angell and Korshover, 1978b;

Quiroz, 1979). The warming occuring prior to 1970 in the middle and upper stratosphere and the cooling recorded in the beginning of the 1970's shows a high correlation with solar cycle 20 as quoted by Quiroz (1979). This author has indicated that the corresponding temperature change from solar maximum (1969) to solar minimum (1975) varies among the stations from - 3 ° C to - 6 ° C in the upper stratosphere. These values are in fairly good agreement with our results at .45 km which provide a variation of 6°C at the equator and 3°C at 60 degrees. However, below 40 km, the computed temperature change seems smaller than the obser- vations. Moreover, the variations reported by Quiroz (1979) appears to be fairly uniform among most stations while our results show some latitudinal variations.

The effect of the UV variability on atomic oxygen is illustrated in f i g . 12. The enhancement at high altitude of the concentration as-

3 1 sociated with a higher solar flux value is due, for 0 ( P) and 0 ( D ) , to the increased concentration of ozone and to the increased rate of its photodissociation. In the lower stratosphere, the negative change of the 0 ( D ) concentration is due to the increased absorption of UV radiation by ozone, the concentration of which becomes larger at higher alti- tudes.

The percentage change of the hydroxyl and hydroperoxyl radicals concentration is represented in - f i g . 13. This graph shows a global increase with altitude of the HO variation, which can be explained by

1

a similar increase of the 0 ( D) variation with height. The presence of

OH and HO ^? radicals in the stratosphere is primarly due to the

PERCENT CHANGE IN 0 (

P ) AND O«

D) CONCENTRATIONS

RELATIVE VARIATION (percent)

Fig. 12.- Vertical distribution of the relative change in the average atomic

oxygen concentration at 30 degrees latitude for the UV variability from

solar minimum to maximum (fig. 2).

PERCENT CHANGE IN OH AND HO, CONCENTRATIONS

RELATIVE VARIATION (percent)

F i g . 13.- V e r t i c a l distribution of the relative change in the average hydroxyl and h y d r o p e r o x y l radicals concentration at 30 degrees latitude for the UV variability from solar minimum to m a x i m u m (fig.

2 ) .

atoms. A s stated above, the water vapor is held constant in the model.

However had water vapor been allowed to v a r y , there would have been a small increase of H^O (Penner and C h a n g , 1980) due to more oxi- dation of methane. T h i s should lead to an increase of the OH and H 0 2

concentration in the upper stratosphere and consequently for OH to a lower crossover point from negative to positive variations. These changes should have a limited impact on the CIO/HCI concentration ratio but the effect on ozone is not expected to be large.

The change in the HOp to OH ratio, which also appears, is related to the variation of 0 3 , 0 ( P ) , NO and CO which determines the value of this ratio. Near the stratopause, one can see that the factor n ( H 0 2 ) / n ( 0 H ) remains unchanged since it becomes almost independent of any concentration.

The relative variation of long lived species produced at g r o u n d level such as N 2 0 , C C I 4 , C F C I g and C F 2 C I 2 is illustrated in figure 14 and 15 assuming for these constituents a fixed concentration at g r o u n d level and steady state conditions. In both cases, large perturbations are obtained but these occur at high altitude where the concentration becomes relatively small. Nevertheless, the long term measurement of the concentration of such species around 40 km should give an in- dication of the real existence of a solar variability associated with the 11-year cycle. For N 2 0 , C C I 4 , C F C I 3 and CF^Ci^, the negative variation computed in the model is due to the increase in the photo- dissociation rate of these molecules. However, the production rate of C I X which is the product of the dissociation coefficient and the con- centration of halocarbons ( v a r y i n g with opposite s i g n s ) varies locally much less and its integrated value remains unchanged if the flux at g r o u n d level is kept constant (atmospheric release of chlorofluoro- c a r b o n s ) . Moreover it should be noted that C H g C I , the most important producer of C I X in the natural stratosphere, is positively correlated with the UV flux since its main destruction is due to the reaction with

- 4 7 -

LATITUDE (degrees)

Fig. 14.- Meridional distribution of the relative change in the nitrous oxide

45

40

^ 35

LU

g 30 I—I

< 25

20

15

- 6 0 - 4 0 -20 0 *• 2 0

RELATIVE VARIATION (percent)

F i g . 15.- Vertical distribution at 30 degrees latitude of the relative change in the concentration of CCI, , CFCl^ and CF2CI2 from solar minimum to maximum (fig. 2 ) .

-49-

h y d r o x y l radicals O H which are s l i g h t l y depleted when the solar i r - radiance i n c r e a s e s . T h e same effect a p p e a r s for methane. T h e cal- culations r e f e r r i n g to C I O a n d H C I indicate that the a v e r a g e c o n c e n - tration v a r i e s in both cases b y less than 4 percent.

O d d n i t r o g e n in the s t r a t o s p h e r e is formed b y the reaction be- 1

tween N^O and 0 ( D ) . T h e variation in the c o r r e s p o n d i n g p r o d u c t i o n rate, illustrated in f i g u r e 16, is negative and yields 30 percent above 44 km in the equatorial r e g i o n . T h e r e f o r e , the decrease of the N O

concentration ( f i g u r e 17) can be s i g n i f i c a n t mainly in the u p p e r s t r a t o - s p h e r e and s h o u l d contribute to increase the ozone concentration in this r e g i o n .

5. C O N C L U D I N G R E M A R K S

T h e r e are indications that the U V i r r a d i a n c e r e s p o n s i b l e for the photodissociation of several minor constituents a n d for the local heating in the s t r a t o s p h e r e , s h o w s time v a r i a t i o n s related to the 1 1 - y e a r solar cycle. However the variability s u g g e s t e d b y Heath and T h e k a e k a r a (1977) seems to be overestimated if a critical a n a l y s i s of the solar irradiance measurements is performed. T h e r e f o r e a more realistic d e p e n - dence on w a v e l e n g t h , based on several o b s e r v a t i o n s i n c l u d i n g recent balloon measurements, is s u g g e s t e d .

If s u c h a variation is applied to the s t r a t o s p h e r i c photochemical

and thermal calculations, a total ozone variation of the o r d e r of 3

percent from the minimum to the maximum solar activity s h o u l d be

expected. T h e l a r g e s t c h a n g e , namely 10 percent when the temperature

feedback is taken into account, a p p e a r s in the u p p e r s t r a t o s p h e r e . T h e

c o r r e s p o n d i n g calculations with the solar flux variability of Heath a n d

T h e k a e k a r a (1977) lead to ozone v a r i a t i o n s (24 percent at 45 km and 30

d e g r e s s ) which s h o u l d be detected with the c u r r e n t ozone n e t w o r k .

LATITUDE (degrees)

Fig. 16.- Meridional distribution of the change in the nitric oxide production rate for the UV variability from solar minimum to maximum (fig.

2). Temperature feedback taken into account.

-51-

RELATIVE VARIATION ( p e r c e n t )

Fig. 17.- Vertical distribution of the relative change in

the NO^ (NO + NC^) concentration at 30 degrees

latitude for the UV variability from solar minimum

to solar maximum (fig. 2). Temperature feedback

taken into account.