TL;DR: In this article, a new capability to predict the climatic response to a large tropical eruption for the succeeding 2 years will prove valuable to society, as well as to detect and attribute anthropogenic influences on climate, including effects of greenhouse gases, aerosols, and ozone-depleting chemicals.
Abstract: Volcanic eruptions are an important natural cause of climate change on many timescales. A new capability to predict the climatic response to a large tropical eruption for the succeeding 2 years will prove valuable to society. In addition, to detect and attribute anthropogenic influences on climate, including effects of greenhouse gases, aerosols, and ozone-depleting chemicals, it is crucial to quantify the natural fluctuations so as to separate them from anthropogenic fluctuations in the climate record. Studying the responses of climate to volcanic eruptions also helps us to better understand important radiative and dynamical processes that respond in the climate system to both natural and anthropogenic forcings. Furthermore, modeling the effects of volcanic eruptions helps us to improve climate models that are needed to study anthropogenic effects. Large volcanic eruptions inject sulfur gases into the stratosphere, which convert to sulfate aerosols with an e-folding residence time of about 1 year. Large ash particles fall out much quicker. The radiative and chemical effects of this aerosol cloud produce responses in the climate system. By scattering some solar radiation back to space, the aerosols cool the surface, but by absorbing both solar and terrestrial radiation, the aerosol layer heats the stratosphere. For a tropical eruption this heating is larger in the tropics than in the high latitudes, producing an enhanced pole-to-equator temperature gradient, especially in winter. In the Northern Hemisphere winter this enhanced gradient produces a stronger polar vortex, and this stronger jet stream produces a characteristic stationary wave pattern of tropospheric circulation, resulting in winter warming of Northern Hemisphere continents. This indirect advective effect on temperature is stronger than the radiative cooling effect that dominates at lower latitudes and in the summer. The volcanic aerosols also serve as surfaces for heterogeneous chemical reactions that destroy stratospheric ozone, which lowers ultraviolet absorption and reduces the radiative heating in the lower stratosphere, but the net effect is still heating. Because this chemical effect depends on the presence of anthropogenic chlorine, it has only become important in recent decades. For a few days after an eruption the amplitude of the diurnal cycle of surface air temperature is reduced under the cloud. On a much longer timescale, volcanic effects played a large role in interdecadal climate change of the Little Ice Age. There is no perfect index of past volcanism, but more ice cores from Greenland and Antarctica will improve the record. There is no evidence that volcanic eruptions produce El Nino events, but the climatic effects of El Nino and volcanic eruptions must be separated to understand the climatic response to each.
TL;DR: The eruption of Mt Pinatubo in June 1991 caused the largest perturbation this century to the participate content of the stratosphere, which put an end to several years of globally warm surface temperatures as discussed by the authors.
Abstract: The eruption of Mt Pinatubo in June 1991 caused the largest perturbation this century to the participate content of the stratosphere. The radiative influence of the injected particles put an end to several years of globally warm surface temperatures. At the same time, the combined effect of volcanic particles and anthropogenic reactive chlorine has led to record low levels of stratospheric ozone.
TL;DR: In this paper, the authors examine aspects of importance, or possible importance, to meteorology, such as the dust veils created in the atmosphere, particle sizes and distribution, heights, fall speeds and atmospheric residence times.
Abstract: After defining the terms commonly used in reporting volcanic eruptions and noting previous approaches to assessment of their magnitudes, this study proceeds to examine aspects of importance, or possible importance, to meteorology―principally the dust veils created in the atmosphere, particle sizes and distribution, heights, fall speeds and atmospheric residence times. Later sections deal with spread of the dust by the atmospheric circulation and the direct effects apparent upon radiation, surface temperature and extent of ice in the polar regions. These effects, as well as various crude measures of the total quantity of solid matter thrown up, are used to arrive at numerical assessments of volcanic eruptions in terms of a dust veil index (d. v. i.). The latitude of origin of the dust (latitude of the volcano) receives some attention, and apparently affects the course of development of the atmospheric circulation over the three or four years following, at least in the case of great eruptions (d. v. i. > 100 over one hemisphere). Effects upon the extent of ice on the polar seas may be of somewhat longer duration, and thereby influence the atmospheric circulation over a longer period of years, since there seems to be some association with the cumulative d.v.i. values when successive great eruptions occur with only few years between. The time distribution of volcanic dust since the last Ice Age, and since a. d. 1500, are indicated in as much detail as the evidence permits. Some associations with changes of climate are suggested, but it is clear that volcanic dust is not the only, and probably not the main, influence in this. The appendices give a chronology of eruptions (including those which it seems possible to dismiss as regards any effect on world weather or climate) and a chronology of d. v. i. values. A third appendix displays by means of graphs the variation of some circulation parameters in January and July in the region of northwest Europe over the years immediately following forty of the greatest eruptions since 1680.
TL;DR: In this paper, it was shown that the surface area of volcanic aerosol reached a maximum at mid-latitudes of about 50 μm2 cm−3 (above a typical background value of about 0.75) at an altitude of 18-20 km in early 1983.
Abstract: It is now well established that heterogeneous reactions provide an important mechanism for Antarctic ozone depletion. Recent laboratory studies suggest that the same reactions that occur on HNO3/H2O ice clouds in the cold Antarctic stratosphere can also take place on sulfuric acid particles (e.g., volcanic and background aerosols) typical of lower latitudes, albeit at slower rates. The reduction in stratospheric ozone observed at northern mid-latitudes in late 1982 through 1983 following the volcanic eruption of El Chichon is investigated in terms of ozone loss through heterogeneous chemistry on the aerosol which formed in the stratosphere. The rates of the relevant heterogeneous reactions are believed to be critically dependent on (1) the aerosol surface area density and (2) the percent by weight sulfuric acid in the liquid particles. Direct measurements of both of these important quantities for El Chichon aerosol are described and used as a basis for model calculations of their possible effects on ozone and other trace species. The observed volcanic particle surface area reached a maximum at mid-latitudes of about 50 μm2 cm−3 (above a typical background value of about 0.75) at an altitude of 18–20 km in early 1983. This enhancement of surface area is about the same as that encountered in stratospheric clouds in the Antarctic, suggesting a possible basis for ozone depletion through heterogeneous chemistry. Observations of NO2 and HNO3 also suggest that heterogeneous reactions on both background and volcanic aerosol play a significant role in partitioning reactive nitrogen species in middle and high latitudes in winter. It is shown that heterogeneous reactions similar to those occurring in Antarctica may have been responsible for at least a portion of the anomalous ozone reduction observed at mid-latitudes in early 1983.
TL;DR: In this article, a spectral-, space-, and time-dependent set of aerosol parameters for 2 years after the Pinatubo eruption using a combination of SAGE II aerosol extinctions and UARS-retrieved effective radii, supported by SAM II, AVHRR, lidar and balloon observations was developed.
Abstract: Volcanic sulfate aerosols in the stratosphere produce significant long-term solar and infrared radiative perturbations in the Earth's atmosphere and at the surface, which cause a response of the climate system. Here we study the fundamental process of the development of this volcanic radiative forcing, focusing on the eruption of Mount Pinatubo in the Philippines on June 15, 1991. We develop a spectral-, space-, and time-dependent set of aerosol parameters for 2 years after the Pinatubo eruption using a combination of SAGE II aerosol extinctions and UARS-retrieved effective radii, supported by SAM II, AVHRR, lidar and balloon observations. Using these data, we calculate the aerosol radiative forcing with the ECHAM4 general circulation model (GCM) for cases with climatological and observed sea surface temperature (SST), as well as with and without climate response. We find that the aerosol radiative forcing is not sensitive to the climate variations caused by SST or the atmospheric response to the aerosols, except in regions with varying dense cloudiness. The solar forcing in the near infrared contributes substantially to the total stratospheric heating. A complete formulation of radiative forcing should include not only changes of net fluxes at the tropopause but also the vertical distribution of atmospheric heating rates and the change of downward thermal and net solar radiative fluxes at the surface. These forcing and aerosol data are available for GCM experiments with any spatial and spectral resolution.