Altitude variations of cosmic ray induced production of aerosols: Implications for global cloudiness and climate
Atmospheric Sciences Research Center
State University of New York, Albany, New York
(J. Geophys. Res., 107(A7), 10.1029/2001JA000248, 2002)
Abstract. The indirect radiative forcing of atmospheric aerosols is sensitive to
particle size and concentration, which are influenced significantly by
nucleation processes. Via its role in aerosol formation, cosmic ray may
affect the cloud condensation nuclei abundance, and hence the global cloud
properties and climate. Systematic variations in ionization rates due to the
modulation of cosmic ray radiation by the solar cycle are sufficient to cause
notable variations in aerosol production, and we find that the signs of such
variations are altitude-dependent. Our study indicates that an increase in
cosmic ray fluxes generally leads to an increase in particle production in the
lower troposphere but a decrease in particle production in the upper troposphere.
The main reason of such an altitude-dependent influence is that the dependence
of particle production rate on ionization rate is a complex function of
ionization rate itself, as well as precursor gas concentration and ambient
conditions. The implications of altitude variations of cosmic ray-induced
aerosol production on global cloudiness and climate are discussed. In addition
to the reported positive correlation between cosmic ray variations and low
cloudiness, our analysis reveals that high cloudiness may be anti-correlated
with cosmic ray variations if volcano and El Ni�o impacts are excluded. The
observed different correlations between cosmic ray variations and low, middle
and high cloud anomalies appear to be consistent with the predicted different
sensitivities of particle production to cosmic ray changes at different
altitudes. A systematic change in global cloudiness may change the atmosphere
heating profile, and if confirmed, may provide the external forcing needed to
reconcile the different surface and troposphere temperature trends. Much more
work is needed to understand how and how much the cosmic ray variations will
affect the global cloud properties and climate.