Time series of
solar activity (bottom) and the North Atlantic Oscillation in two
model simulations,
without (blue) and with (yellow) solar forcing. Graphics, GEOMAR.
Long-term climate variability in the Northern Hemisphere
linked to solar variations
(September 15, 2015) The
natural, 11-year cycle of solar activity is apparently influencing long-term
climate fluctuations in the Northern Hemisphere. An international team of
scientists led by GEOMAR Helmholtz Centre for Ocean Research Kiel showed that
the so-called North Atlantic Oscillation, one of the dominant circulation
patterns on the Northern Hemisphere, is phased-locked to the decadal solar
activity with a delay of one or two years. The study appears today in the
international journal Nature Communications.
Are climate predictions over periods of several years
reliable if weather forecast are still only possible for short periods of
several days? Nevertheless there are options to predict the development of key
parameters on such long time scales. A new study led by scientists at GEOMAR
Helmholtz Centre for Ocean Research Kiel shows how the well-known 11-year cycle
of solar activity affects the long-time development of dominant large-scale
pressure systems in the Northern Hemisphere.
For their investigations the scientists used a coupled
ocean-atmosphere model. In addition, this model includes an interactive
chemistry module which can for instance cope with the effect of ultraviolet
radiation (UV) in the upper atmosphere. This additional component seemed to be
key to transmit the variations in the solar radiation which might have only a
small direct impact on the earth's surface, through a complex mechanism from
the stratosphere (10-50 km altitude) to the lower atmosphere.