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Stratospheric sulfur and its implications for radiative forcing simulated by the chemistry climate model EMAC - PubMed

  • ️Thu Jan 01 2015

Stratospheric sulfur and its implications for radiative forcing simulated by the chemistry climate model EMAC

C Brühl et al. J Geophys Res Atmos. 2015.

Abstract

Multiyear simulations with the atmospheric chemistry general circulation model EMAC with a microphysical modal aerosol module at high vertical resolution demonstrate that the sulfur gases COS and SO2, the latter from low-latitude and midlatitude volcanic eruptions, predominantly control the formation of stratospheric aerosol. Marine dimethyl sulfide (DMS) and other SO2 sources, including strong anthropogenic emissions in China, are found to play a minor role except in the lowermost stratosphere. Estimates of volcanic SO2 emissions are based on satellite observations using Total Ozone Mapping Spectrometer and Ozone Monitoring Instrument for total injected mass and Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on Envisat or Stratospheric Aerosol and Gases Experiment for the spatial distribution. The 10 year SO2 and COS data set of MIPAS is also used for model evaluation. The calculated radiative forcing of stratospheric background aerosol including sulfate from COS and small contributions by DMS oxidation, and organic aerosol from biomass burning, is about 0.07W/m2. For stratospheric sulfate aerosol from medium and small volcanic eruptions between 2005 and 2011 a global radiative forcing up to 0.2W/m2 is calculated, moderating climate warming, while for the major Pinatubo eruption the simulated forcing reaches 5W/m2, leading to temporary climate cooling. The Pinatubo simulation demonstrates the importance of radiative feedback on dynamics, e.g., enhanced tropical upwelling, for large volcanic eruptions.

Keywords: chemistry climate model; radiative forcing; stratospheric sulfur; volcanoes.

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Figures

Figure 1
Figure 1

(top) EMAC simulated and (bottom) MIPAS observed COS in the tropics. Contours show the zonal wind in the 5°S–5°N latitude belt with increments of 20m/s (QBO).

Figure 2
Figure 2

(top) Simulated and (middle) observed SO2 in the tropics. (bottom) MIPAS data from individual retrievals for the lower stratosphere (same color scale, monthly averaged). Contours for QBO as in Figure 1.

Figure 3
Figure 3

(top) Simulated and (bottom) observed SO2 at 28 km altitude.

Figure 4
Figure 4

(top) Simulated and (bottom) observed SO2 at 40 km altitude.

Figure 5
Figure 5

Simulated SO2 at 40 km altitude (right) without meteoric dust sink and (left) additionally without enhanced H2SO4 photolysis. Typical subsets of longer simulations.

Figure 6
Figure 6

(first and third panels) Simulated and (second and fourth panels) observed SO2 at 17 km altitude. Here MIPAS data are the monthly values of Höpfner et al. [2013] or 5 day averages of individual retrievals. As a general rule, each sudden increase in the observed or calculated SO2 (Figure 6 third and fourth panels) is related to a volcanic eruption.

Figure 7
Figure 7

Simulated SO2 changes in ppbv at 17 km altitude (first and second panels, reference simulation minus sensitivity study) without DMS and (third and fourth panels, sensitivity study minus reference of Figure 6) with 5 times the anthropogenic SO2 emissions by China. In the white areas the values are slightly negative due to meteorological variability.

Figure 8
Figure 8

(left) Simulated SO2 after Pinatubo, tropics. (right) Simulated SO2 volume mixing ratios (decadal logarithm, lines) sampled as the three ATMOS campaigns of Rinsland et al. [1995] (symbols): black, ATLAS 1 (April 1992); red, ATLAS 2 (April 1993); and green, SPACELAB (May 1985; model here background of 2004 with same QBO phase as 1985).

Figure 9
Figure 9

Aerosol number (top) median radius and (bottom) concentration in the accumulation mode. The mode boundary of 0.07 μm is the minimum value for the radius (left) Pinatubo and (right) MIPAS period.

Figure 10
Figure 10

Simulated total sulfate aerosol volume mixing ratio, tropics. Contours, QBO as in Figure 1 (additional contours on the left).

Figure 11
Figure 11

Aerosol optical depth at 530nm above 185 hPa. The green lines show values derived from SAGE+CALIPSO (middle) and SAGE+OSIRIS (bottom) satellite observations, the black lines the simulations using the SO2 injections of Table 1, and the blue lines the simulation with a reduced number of small volcanoes as marked in the last column of Table 1. Data gaps in the SAGE data for Pinatubo are filled similar to Arfeuille et al. [2013].

Figure 12
Figure 12

Radiative forcing at the tropopause (185 hPa, solar + IR) by stratospheric aerosol. Estimates from observations for global forcing (bottom row) are indicated by crosses [Toohey et al., ; Solomon et al., 2011], to be compared with the red curves. The ERBE data for Pinatubo (left column) are for solar forcing at the top of the atmosphere. In the bottom left the green and the black curves are the total and solar forcing at the tropopause, respectively. The black curve in the bottom right is the reduced volcanic SO2 simulation also shown in Figure 11.

Figure 13
Figure 13

Aerosol total radiative heating, tropics.

Figure 14
Figure 14

EMAC simulated lofting of trace gases H2O and N2O due to aerosol heating.

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