Jahresbericht 08 - PMOD/WRC

Scientific Research Activities
Influence of Galactic Cosmic Rays on Atmospheric Composition and Temperature
Eugene Rozanov and Tatiana Egorova in collaboration with Marco Calisto and Thomas Peter IAC ETH, Zurich
We investigated the influence of Galactic Cosmic Rays
on atmospheric chemistry and temperature using a
Chemistry-Climate model and the most recent parameterization
of ionization rates. The implementation of
Galactic Cosmic Rays in the model causes a ~40% increase
of reactive nitrogen in the entire troposphere
and a ~9 % tropospheric ozone increase over high latitudes,
however, the temperature response is not statistically
significant.
Galactic Cosmic Rays provide an additional source of reactive
nitrogen and hydrogen in the atmosphere due to ionisation
of neutral species. The effects of Galactic Cosmic
Rays on the atmosphere have only been estimated with
simple models and their implications for past trends in atmospheric
ozone and temperature have not been properly
established. Galactic Cosmic Rays forcing was not taken
into account in simulations of the past atmosphere in the
framework of the Chemistry-Climate Model validation
(CCMval) campaign. Therefore, it is important to estimate
the influence of Galactic Cosmic Rays on atmospheric
composition and climate and formulate a recommendation
about their significance in the future.
To answer this question we performed two 13-year (1976-
1988) long transient simulations with the CCM SOCOL
v2.0 model with and without a Galactic Cosmic Rays
source. The ionization rate due to Galactic Cosmic Rays
was adopted from the recent paper by Usoskin and Kovaltsov
(2006). The source of reactive nitrogen and hydrogen
was parameterized according to Porter et al. (1976)
and Solomon et al. (1981). The atmospheric response to
Galactic Cosmic Rays was calculated as the difference between
the results of the run with Galactic Cosmic Rays and
the reference run without Galactic Cosmic Rays, which
gives the upper limit of their effects and also allows the statistical
significance of the obtained atmospheric response
to be estimated.
The results show, that Galactic Cosmic Rays produce a
substantial amount of NOx. The simulated NOx increase
shown in Figure 1 exceeds 30% in the southern polar troposphere,
whereas over low and middle latitudes the NOx
increase only reaches 10-20% and is confined to the upper
troposphere/lower stratosphere. The significant increase of
ozone (see Figure 2) up to 10 % is mostly confined to the
troposphere over the southern hemisphere, where ozone
production via smog reactions is most sensitive to additional
NOx due to low background NOx mixing ratios. The
annual mean temperature response (not shown) is not statistically
significant. From these results we can conclude
that Galactic Cosmic Rays may generally be important in
the troposphere over southern high latitudes.
Altitude (km)
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Figure 1. Annual mean percentage changes of zonal mean NOx due to
GCR implementation. The areas where changes are significant to better
than the 95 % confidence level are shaded.
Altitude (km)
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Figure 2. Annual mean percentage changes of zonal mean ozone due to
GCR implementation. The areas where changes are significant to better
than the 95 % confidence level are shaded.
References: Porter H.S., Jackman C.H., Green A.E.S., Efficiencies for
production of atomic nitrogen and oxygen by relativistic
proton impact in air, J. Chem. Phys., 65, No.1, 1976.
Solomon S., et al., The effect of particle precipitation
events on the neutral and ion chemistry of the middle
atmosphere: II. Odd Hydrogen, Planet. Space Sci., 29,
No. 8, 885 – 892, 1981.
Usoskin I.G., Kovaltsov A., Cosmic ray induced ionization
in the atmosphere: Full modeling and practical
applications, J. Geophys. Res., 111, D21206, doi:
10.1029/2006JD007150, 2006.
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