Atmospheric composition, mass and structure - Atmosphere, Weather and Climate - page 21

Figure 2.10 Changes in stratospheric ozone
content (per cent per decade) during March to
May and September to November 1978 to 1997
over Europe (composite of Belsk, Poland, Arosa,
Switzerland and Observatoire de Haute Provence,
France) based on umkehr measurements.
Source : Adapted from Bojkov et al . (2002), Meteorology
and Atmospheric Physics , 79, p. 148, Fig. 14a.

10 km

MAM
SON

9 45

8 40

7 35

6 30

5 26

4 21

3 17

2 12

-10 -8 -6 -4 -2 0 2 4 6

% change per decade

0.5

0.4

0.3

0.2

0.1

0

1300 1400 1500 1600 1700 1800 1900 2000

Year AD

Figure 2.11 Record of volcanic eruptions in the GISP 2 ice core and calibrated visible optical depth for AD 1300 to 2000, together
with the names of major volcanic eruptions. Note that the record reflects eruptions in the northern hemisphere and equatorial region
only; optical depth estimates depend on the latitude and the technique used for calibration.
Source : Updated after Zielinski et al . (1995), Journal of Geophysical Research 100 (D), courtesy of the American Geophysical Union, pp. 20,
950, Fig. 6.

centration derived from volcanic dust is extremely
irregular (see Figure 2.11), but individual volcanic emis-
sions are rapidly diffused geographically. As shown in
Figure 2.12, a strong westerly wind circulation carried
the El Chichón dust cloud at an average velocity of

20 m s -1 so that it encircled the globe in less than
three weeks. The spread of the Krakatoa dust in 1883
was more rapid and extensive due to the greater amount
of fine dust that was blasted into the stratosphere.
In June 1991, the eruption of Mount Pinatubo in the