Volcanic effects on climate: revisiting the mechanisms H.-F. Graf1, Q. Li2, and M. A. Giorgetta2 1Centre for Atmospheric Science, University of Cambridge, UK 2Max-Planck-Institute for Meteorology, Hamburg, Germany
Abstract. The characteristics of planetary wave energy propagation are being compared
based on NCEP reanalysis data from 1958 to 2002 between boreal winters after
strong volcanic eruptions, non-volcanic winters and episodes of strong polar
vortex lasting at least 30 days. It shows that in the volcanically disturbed
winters much more planetary wave energy is produced in the troposphere,
passes through the lowermost stratosphere and enters the upper stratosphere
than in any other times. This is contradicting earlier interpretations and
model simulations. Possibly the observed El Ninos coinciding with the three
significant eruptions in the second half of the 20th century
contributed to the planetary wave energy. In order to produce the observed
robust climate anomaly patterns in the lower troposphere, these planetary
waves are suggested to be reflected near the stratopause instead of
breaking. While a strong polar vortex is observed after volcanic eruptions
in the stratosphere and in the troposphere, specific episodes of strong
polar vortex regime exhibit much stronger anomalies and different dynamics.
Hence it is suggested that the climate effects of volcanic eruptions are not
being explained by the excitation of inherent zonal mean variability modes
such as Strong Polar Vortex or Northern Annular Mode, but rather is another
mode that possibly reflects upon the North Atlantic Oscillation.
Citation: Graf, H.-F., Li, Q., and Giorgetta, M. A.: Volcanic effects on climate: revisiting the mechanisms, Atmos. Chem. Phys., 7, 4503-4511, doi:10.5194/acp-7-4503-2007, 2007.