Strong volcanic eruptions have a
climate impact. Volcanologists measure the power of an eruption by the volcanic
explosivity index VEI in order to scale and to compare the eruptions of
different volcanoes. Aside the volume of erupted material also the plume height
and frequency of eruption are considered. The scale is open-ended and starts from 0, for non-explosive eruptions. From a
climatological point of view only the stratospheric mass loading is of interest
since it resides long enough to alter the atmospheres radiation budget for
months. Grieser
and Schönwiese (1999) therefore introduced a climatologically corrected
VEIc which is proportional to the logarithm of the estimated stratospheric mass
loading.
Within the period from 1951 to 2000 5
volcanoes erupted with a climatologically corrected Volcanic Explosivity Index
VEIc>5. These are summarized in Table 1.
Table 1: The 5 volcano eruptions with a climatologically
corrected Volcanic Explosivity Index VEIc>5 within the period 1951 to 2000.
Name |
Date |
Country |
VEIc |
Agung |
3/1963 |
Lesser Sunday
Islands |
5.9 |
Fernandina |
6/1968 |
Galapagos |
5.4 |
Fuego |
10/1974 |
Guatemala |
5.3 |
El Chichon |
4/1982 |
Mexico |
5.8 |
Pinatubo |
6/1991 |
Philippines |
6.1 |
Furthermore Grieser and Schönwiese
(1999) applied a simple stratospheric transport model which takes into account
the tropical pipe and a non-local transport scheme with seasonal dependency.
This allows to calculate aerosol optical thickness for both hemispheres and
tropical and outertropical regions.[volcanic aerosol optical
thickness data]
A simple radiation transfer model is
used in order to estimate the volcanic climate forcing. It is calibrated with
respect to the Pinatubo eruption in 1991. Forcing anomalies are calculated. [volcanic forcing data]
Finally, a simple energy balance model
(EBM) is driven with the volcanic forcing, leading to modelled hemispheric
surface air temperature reactions. [sea surface temperature response data]
Grieser, J. and C.-D. Schönwiese,
1999: Parameterization of spatio-temporal patterns of volcanic aerosol induced
stratospheric optical depth and its climate radiative forcing. Atmósfera 12,
111-133.