A one-dimensional photochemical-dynamical-radiative time-dependent model was used to study the response of middle atmospheric temperature and ozone to solar UV irradiance variations with the period of 27 days. The model solar UV O(x), HO(x), NO(x), and CIO(x)families and modeled solar UV variations. The amplitude of the primary temperature response to the solar UV variation is plus 0.4 K at 85-90 km with a phase lag of about 6 days. A secondary maximum response of plus 0.3 K at 45-50 km appears with a phase lag of 1 day. There is a maximum positive ozone response to the 27-day solar UV oscillation of 2.5 percent at 80-90 km with a phase lag of about 10 days after the solar irradiance maximum. At 70 km the ozone response is about 1.2 percent and is out of phase with the solar variation. In the upper stratosphere (40-50 km) the relative ozone variation is small, about 0.2 percent to 0.3 percent, and there is a negative phase of about 4 days between the ozone and solar oscillations. These oscillations are in phase in the middle stratosphere (35-40 km) where there is again a maximum relative response of about 0.6 percent. The reasons for these ozone amplitude and phase variations are discussed

Brasseur, Guy

Chen, LI

London, Julius

English

NASA Technical Reports Server

N95- 10674
THE RESPONSE OF MIDDLE ATMOSPHERIC OZONE TO SOLAR UV
IRRADIANCE VARIATIONS WITH A PERIOD OF 27 DAYS
Li Chen
Department of Physics, University of Colorado, Boulder, Colorado 80309-0391
Guy Brasseur
National Center for Atmospheric Research, Boulder Colorado 80303-3000
Juhus London
Department of Astrophysical, Planetary, and .Atmospheric Sciences,
University of Colorado, Boulder, Colorado 80309-0391
ABSTRACT
A one-dimensional photochemical-dynamical-radia-
tive time-dependent model was used to study the re-
sponse of middle atmospheric temperature and ozone
to solar UV irradiance variations with a period of 27
days. The model incorporated the O=, HO=, NO_, and
CIO= families and modeled solar UV variations. The
amplitude of the primary temperature response to the
solar UV variation is +0.4 K at 85-90 km with a phase
lag of about 6 days. A secondary maximum response
of +0.3 K at 45-50 km appears with a phase lag of 1
day. There is a maximum positive ozone response to
the 27-day solar UV oscillation of 2,5% at 80-90 km
with a phase lag of about 10 days after the solar irradi-
ance maximum. At 70 km the ozone response is about
1.2% and is out of phase with the solar variation. In
the upper stratosphere (40-50 km) the relative ozone
variation is small, about 0.2% to 0.3%, and there is a
negative phase of about 4 days between the ozone and
solar oscillations. These oscillations are in phase in the
middle stratosphere (35-40 km) where there is again a
maximum relative response of about 0.6%. The rea-
sons for these ozone amplitude and phase variations are
discussed.
INTRODUCTION
Efforts toward detecting the responses of the mid-
dle atmosphere to the solar irradiance variations have
been pursued for over 50 years. Understanding of such
a response is crucial for (1) fully understanding the
photochemical behavior of the middle atmosphere and
the coupling between temperature and ozone and (2)
detecting possible changes in the atmospheric compo-
sition due to anthropogenic effects. Satellite results
are now available that show the ozone and temper-
ature responses to solar irradiance variations with a
period of 27 days (Keating et al., 1987; Hood, 1986,
1991). The purpose of this paper is to identify, through
comparing theoretical results with satellite results, the
main processes that control the ozone and temperatur(,
351
responses to solar irradiance variation. A one-dimen-
sional photochemical-dynamical-radiative time-depen-
dent model extending from 10 to 100 km with a ver-
tical resolution of 0.5 km was used to investigate the
responses of ozone and temperature in the middle at-
mosphere to solar irradiance variations with a period of
27 days.
MODEL DESCRIPTION
The model involves a total of 27 chemical spe- cies
and 43 chemical reactions. The model uses the follow-
ing families in order to avoid the mathematically stiff
systems that are due to the large dispersion in the chem-
ical lifetimes of the several species:
O= : 03 + O(1D) + O(3P),
HO==H+OH+HO2,
NO= = NO + NO2,
CI_ = C1 + CIO + HC1.
We used fixed profiles for NO= and CI= (Brasseur and
Solomon, 1985) in the model.
The dynamical (vertical diffusion) time constant var-
ies with altitude from 105 s at 100 km to 107 s at 30 km
(Brasseur and Solomon, 1985). For short-lived chemical
species with lifetimes shorter than the dynamical time
constant, concentrations were derived from photochem-
ical equilibrium:
Pi -Li =0,
where Pi is the production term (cm -a s -I) for a given
constituent i and Li is the destruction term (cm -3 s -1)
of the chemical species i. The species O, OOD), NO,
NO_, CIO, el, H, OH, and HO2 were assumed to be
short lived in the model.
For O_, H2, and H20 , which have long chemical life-
times and are therefore sensitive to dynamics and chem-
istry, the following continuity equation was solved:
/) 7s=',]
https://ntrs.nasa.gov/search.jsp?R=19950004262 2020-06-16T11:26:23+00:00Z
wheren = air density (cm-3), ni = the number density
of a given constituent i, and Kz = the vertical diffusion
coefficient (cm 2 s-l).
The net heat was transported as a tracer with an
altitude-dependent vertical-exchange coefficient. The
potential temperature was derived from the following
energy equation:
000n Ot Oz
where 0 = potential temperature (K), H = the solar
heating rate (K s-l), C = the IR cooling rate (K s-l),
p0 = pressure at the ground (1013 mb), p = pressure
(rob), and t¢ = R/Cp (0.286 for dry air).
The solar heating rate based on absorption by molec-
ular oxygen and ozone was modeled after Schoeberl and
Strobel (1978). A small contribution from water va-
por was prescribed. The cooling rate below 30 km was
parameterized from a model developed by Morcrette
(Brasseur et al., 1987) after taking into account the
emission and absorption of atmospheric radiation by
O3, CO2, and H20. Above 40 kin, an algorithm to com-
pute the radiative cooling due to carbon dioxide, which
has been developed by W. Wehrbein et al. (in prepa-
ration), was adopted. This method explicitly includes
non-LTE and multiple bands and utilizes the method
known as lambda iteration to calculate the populations
for each of the energy levels in each atmospheric layer.
A wideband model of ozone absorption in the 9.6-#m re-
gion (Rosenfield, 1991) was used in the model. A tran-
sition between the two models was used for the layer
between 30 and 40 kin.
The absorption cross sections of 02 (SRC + Hertz-
berg bands) and 03 (Hartley + Huggins + Chappuis
+ Hertzberg bands) (from WMO, 1985) and the ab-
sorption cross sections of H202 (190 350 nm) and NO_
(185-410 nm) (from DeMore et al., 1987) were used
in the model. The absorption cross section of 02 over
the Schumann-Runge band was calculated according to
Allen and Frederick (1982). Values for the photodisso-
ciation rates for water vapor (SRB + Lyman-a) and 02
(Lyman-a) used in the model were taken from Brasseur
and Solomon (1985). The solar irradiance at different
altitudes was approximated by using Beer's law, and"
tile solar irradiance at the top of the atmosphere was
from WMO (1985). The chemical reaction rates given
in NASA Reference Publication 1242 (Watson et al.,
1990) were used. All of the initial profiles and the ver-
tical diffusion coefficient used to develop the vertical
transport for chenfical species were taken from Brasseur
and Solomon (1985). Boundary conditions used in the
model are listed in Table 1.
RESULTS AND DISCUSSION
A 27-day sinusoidal oscillation of the daily average
solar irradiance was applied to the model as the ex-
ternal forcing. The amplitude of the solar flux relative
variation over a period of 27 days is a strong function of
TABLE 1.
10 km 100 km
O_ • = 0 • = 0*
H2 n =4.2E+ 12 _ = 5.E+ 7
H20 n = 3.06E + 14 • = 0
0 0 = 288 K (0 km) 0 = 12359 K
Note: n is the number density (cm -3) and _ is the flux
(cm -2 s-l).
* _ = O at 100 km is not a realistic boundary condition
for Oz. We found, however, that the sponge layer is about 7
km below the upper boundary after using different boundary
conditions. Therefore, we only show the results below 90
km.
wavelength. A 23% relative variation of Lyman-a with
a period of 27 days was taken in the model. The wave-
length dependence of 27-day relative amplitudes for the
period of maximum solar irradiance observed by SME
(8 July 1982 to 4 August 1982) was taken from London
and Rottman (1990). The variation of solar irradiance
(_ > 300 nm) was considered to be zero.
The model ran for a time period of 81 days start-
ing from the spring equinox (i.e., from calender day
80 today 161). The mean solar zenith angle at the
equator was calculated each day. The model runs were
performed for both constant solar irradiance and a si-
nusoidal solar irradiance variation with a period of 27
days. The response of the chemical species to the solar
irradiance variation was defined as the percent change
in species concentration between the two cases:
% response -- nsinu -- nconst X 100%.
nconst
where nco_t = chemical species density for the constant
solar irradiance and nsi_u = chemical species density for
the solar irradiance with sinusoidal variation.
The temperature response to solar irra_iiance varia-
tions, which is defined as the difference between the
temperature with a 27-day solar irradiance variation
and that with constant solar irradiance, is shown in
Figure 1. The primary maximum of the temperature
response, about 0.4 K, was found about 85-90 km about
5.8 days after the peak of the solar irradiance oscilla-
tion. This maximum results from the increasing absorp-
tion of solar irradiance over the Schumann-Runge con-
tinuum and the Schumann-Runge bands by molecular
oxygen. The secondary maximum, about 0.3 K, occurs
at about 45-50 km and is due to increased absorption
of solar irradiance over the Haxtley band by ozone. A
positive phase lag, about 1 da0z, was observed at about
50 kin, which is nmch shorter than that in the upper
layer (above 70 kin) and lower layer (below 40 kin). This
phenomenon occurs because the radiative lifetime of the
middle atinosphere (about 3-5 days) is shorter than the
352
70 k " / /
- ,, ,,,_
,50_- ii Pi i
i I',U .VG
2O, .......... J . . . J
I00
I., b " _'l_u _,. .
,1%"Ill_ •+ IIIII "
.......
,%_-" ',lll _+",._'--:///
," _ ¢'/
%111 i f
o,,,',,j ,:
:',,', ,',
• t
-0.12 J I
1 10 120 1:30 140 150
TIME (days)
ii_q e -
L_ x _
/i •j, ,
sl" x
I I
_IL _ t
'4x
160 170
Fig. 1. The temperature difference (K) between the
running model with solar irradiance variations
and with constant solar irradiance. Only the
results of the last 54 days are shown. Time is
day of the year starting from 1 January. The
solid vertical lines represent the times of so-
lar oscillation maxima, located on days 114.75
and 141.75. The dashed vertical lines repre-
sent the times of solar oscillation minima, lo-
cated on days 128.25 and 155.25. Solid con-
tours represent positive values; dashed con-
tours represent negative values.
9O
80
70
60
4O
3O
20
100
+)r,:,',,:,+,',l
L_', ',',', ',;, ,','°5 , _\\
,,, ,> ,,,.,,,
i i
i i
:-q :-,l
• i_',,, , _,,,°
"+,-el _" Cl_ 7 ,,
.... _.l ....... ,x.. _ ,21 ..... .%,.
110 120 130 140 150 160 170
TIME (d_ys)
Fig. 2. The ozone response to solar irradiance varia-
tions. For complete explanation, see Figure 1.
dynamical time constant (a few weeks). The tempera-
ture field at this height, therefore, results largely from a
trend toward a radiative equilibrium and is not strongly
dependent, on transport. Another reason is that the ra-
diative lifetime of the nfiddle and upper stratosphere
is shorter than that of the upper mesosphere and the
phase lag of the temperature response is dependent on
the ratio of the radiatiw_ lifetime to the perio(l of solar
irradiance oscillation (Hood, 1986). The ozone response
with t('ni1),,raturv f,,cdba,'k, whMl is tit(' vlfi'<'t of tern-
60
55
5O
_0
,.a
< 35
30
Z$
20
0.00
Fig. 3.
"x
• feedback
._" .... -_- without temp. feedback
O.IO 0.20 0.30 0.40
OZONE SENSITIVITY
Ozone sensitivity represents the amplitude of
the ozone response corresponding to a change
of 1% of the amplitude of the solar irradiance
variation at 205 nm. Without temperature
feedback means holding temperature constant
in the model (i.e., using 1976 U.S. standard
atmosphere).
perature on the ozone response to solar irradiance vari-
ations, is shown in Figure 2. The strong ozone increase
at 85-90 km results from photodissociation of molec-
ular oxygen by the Schumann-Runge continuum and
Schumann-Runge bands and subsequent recombination
of atomic oxygen with molecular oxygen. The phase
delay, about 10 days after solar irradiance maximum,
occurs because of the low concentrations of third bod-
ies necessary for the three-body recombination process.
The ozone decrease at 70-75 km at the time of solar
irradiance maximum results from the photodissociation
of H_O at that height by solar Lyman-c_. At lower levels
(e.g., around 40-50 kin), increased photodissociation of
molecular oxygen leads to an ozone increase. The neg-
ative phase lags (i.e., the peak of the ozone oscillation
before the peak of the solar irradiance oscillation) were
found in the upper stratosphere and lower mesosphere.
The peak of the ozone oscillation is about 7 days before
the peak of the solar irradiance oscillation at about 50
km.
The ozone sensitivity, which is here defined as the
ozone variation associated with a 1% solar irradiance
variation at 205 nm, and the ozone phase lag with tem-
perature feedback were compared with these two pa-
rameters without temperature feedback (the temper-
ature profile in the model is not changed with time)
in Figures 3 and 4. The value of the ozone response
with temperature feedback is generally smaller than
that without temperature feedback. An increasing so-
lar irradiance will increase the solar heating rate and
hence the temperature• An increasing temperature will
cause a higher photochemical destruction rate of ozone
and a lower rate of ozone production. The combination
of these effects produces a smaller ozone response to
353
6O
55
5O
40
30
25
20
-Ill
• r _, ;
I
w
-_- without temp. feedback
-5 0 5
OZONE PHASE LAG (days)
1
J
1o
Fig. 4. The phase lag is the difference between the
maxima (or minima) of the ozone response
and the maxima (or minima) of the solar ir-
radiance oscillation. Twenty-seven days were
added to the phase lag above the inflection
point. Without temperature feedback means
holding temperature constant in the model
(i.e., using 1976 U.S. standard atmosphere).
solar irradiance oscillations with temperature feedback,
as compared to the ozone response without temt)erature
feedback.
When compared with the previous results (Keating et
at., 1987; Hood, 1986; Brasseur et at., 1987), the ozone
sensitivity from our one-dimensional model agrees
qualitatively with observed data (Keating et al., 1987;
Hood, 1986) and quantitatively with theoretical values
(Brasseur et at., 1987). The difference between the the-
oretical values and the observed data may be caused
by the incomplete treatment of the temperature feed-
back in our model. We also ran our one-dimensional
model with a suggested observed temperature variation
associated with observed relative variations at 205 mn
(Keating et at., 1987; Hood, 1986; Hood et al., 1991).
The agreement between the calculated values and the
observed data was improved greatly.
ACKNOWLEDGMENTS
Support is acknowledged from NASA Graduate Stu-
dent Fellowship NGT-30060 and NASA Contract No.
NAS5-27263. The National Center for Atmospheric Re-
search is supported by the National Science Foundation.
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354


The response of middle atmospheric ozone to solar UV irradiance variations with a period of 27 days

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