A43D-01
The 1982 El Chichón Volcanic Eruption: A Review of the Aerosol Cloud Distribution and Observed Climatic Effects
The El Chichón volcano erupted on April 3 and 4, 1982, injecting about 7 Mt of SO2 into the stratosphere. Satellite remote sensing using visible imagery showed that the cloud took three weeks to be transported around the world. Errors of longwave satellite retrievals of sea surface temperatures showed that the cloud stayed in the latitude band of 0-30°N throughout the summer. At the same time a large El Niño developed. By removing the El Niño signal from surface air temperature patterns, observations show winter warming of Northern Hemisphere continents in the 1982-1983 winter, a now well-understood enhancement of the positive phase of the Arctic Oscillation. Climate model simulations have not been able to show that the El Chichón eruption had any impact on the initiation or strength of the El Niño.
A43D-02
Wider Caribbean Temperature Anomalies in the Lower Stratosphere and Surface Following the 1982 El Chichón Volcanic Eruption.
Using available surface data from meteorological stations and lower troposphere measurements from a satellite instrument, monthly mean anomalies of the lower stratosphere and surface temperature over the Wider Caribbean region were studied following the 1982 El Chichón volcanic eruption. Global and regional temperature anomalies both in the lower stratosphere and surface are compared. In the lower stratosphere the well known global decaying temperature trend is the same for the region, with more variability as it was expected. Signals from El Chichón and Mt. Pinatubo are present both in the global and regional anomalies. In the surface there are positive anomalies during almost all the 1982 year, associated to the El Nino event. The seven strongest El Nino events after 1949 were selected. The series of Wider Caribbean monthly mean temperature anomalies regional averages for the seven El Niño events was calculated. Then superposed epoch analysis was used to determine the mean trend for the ensemble of the seven events. Then the El Niño event effect over the monthly mean temperature anomalies for 1982 was subtracted. Results reveal the sensitivity of the Wider Caribbean region to the type of radiative forcing produced by volcanic clouds. Comparisons with former results for individual sites in the region are conducted.
A43D-03
The 1982 El Chichon Eruption: The Birth of Volcanic Sulfur Dioxide Monitoring From Space
The 1982 eruption of El Chichon inspired a new technique for monitoring volcanic clouds using satellites. Data from the Total Ozone Mapping Spectrometer (TOMS) instrument on the Nimbus-7 satellite were used to identify sulfur dioxide in the volcanic cloud and to map the extent of the cloud. For the first time the sulfur dioxide mass in even the largest explosive eruption plumes could be determined. The sizes of eruptions could be measured over 4 orders of magnitude. The position and area of volcanic clouds was determined as the clouds drifted globally with the winds over weeks of time after the eruption. The loss of sulfur dioxide by conversion to sulfate was observed. In addition, volcanic ash clouds were mapped using the TOMS aerosol data. Using sulfur dioxide as a tracer, magmatic eruptions could be discriminated from steam-driven, phreatic eruptions. The data from the El Chichon eruption are reanalyzed using the latest version of the TOMS instrument calibration (V8). They show the shearing of the eruption clouds in three weeks into a globe-circling band while still anchored over Mexico. The measured sulfur dioxide mass in the initial March 28 eruption was 1.6 Tg; a second eruption on April 3 produced 0.3 Tg more, and the climactic April 4 eruption added 5.6 Tg, for a cumulative total of 7.5 Tg, in substantial agreement with estimates from prior TOMS data versions. The TOMS derived sulfur dioxide mass is an order of magnitude higher than the petrologic estimate that is based on the lost sulfur in glass phases of the tephra. This "excess sulfur" brought rise to a reevaluation of the pre-eruptive magmatic processes in volcanoes and a better understanding of eruptions.
A43D-04 INVITED
Physical Properties of the Ash from El Chichon Eruptions and Solar Radiation Extinction as a Measure of its Climate Impact
The eruptions of El Chichon Volcano in southern Mexico in late March and April 1982 and Pinatubo in the
Philippines in June 1991 provided the greatest volcanic clouds in the stratosphere in the last century, perhaps
indeed the greatest since the Krakatau eruption (Indonesia) on 27 August 1883. Curiously enough it was almost
the hundredth anniversary of the great explosive Krakatau eruption when we experienced the El Chichon
eruptions.
Today 25 years later we shall meet and discuss the main aspects of the El Chichon eruption and what we have
learned from this historical event. Here we shall concentrate on some of the observed effects on climate.
The experimentally determined refractive index n = 1.53 - 0.001i of the ash particles shows a very small aerosol
absorption expressed as the imaginary component of the refractive index (0.001) which implies that the aerosol
scattering is quite high. These results provide the physical basis to understand the atmospheric impact from sea
level up to the stratosphere of the aerosol cloud all over the world: Regional increases of air temperature and
solar radiation depletion with large and variable aerosol optical depths while the resultant stratospheric dust
cloud traveled completely around the Earth. Finally it is shown that the tropical atmosphere was already perturbed
even before the El Chichon eruption due to the so-called "Mystery Cloud" (Nyamuragira´s Volcano eruption in
December 1981)
http:www.ucol.mx
A43D-05
An Estimate of the Global Loading of Fine Ash from Volcanic Eruptions
Volcanic eruptions produce copious amounts of ash and gases. Most of these emissions do not penetrate the tropopause and have little effect on global climate. Estimates of the global emissions of sulphur dioxide gas from volcanoes have been made using satellite sensors, notably TOMS and TOVS, but little attention has been paid to the amount of particulate matter released into the atmosphere by volcanoes. Fine volcanic dust or ash with particle diameters <10 microns can remain in the atmosphere for sufficient time that long-range transport takes place, sometimes causing the ash to reach higher altitudes than anticipated. Ash fall onto the oceans can also fertilize the sea with potential consequences on ocean productivity and carbon dioxide drawdown. Here I analyse 6-years of MODIS satellite data to determine the particle size distribution statistics (mean, mode, skewness and kurtosis) and infrared opacity of ash to estimate the global loading of fine ash from volcanic eruptions. The implications of the results for local and global climate will be discussed.
A43D-06
Volcanic Aerosol Simulations of El Chichón and Pinatubo: Stratospheric Impacts and Decay Rates
Using the AER 2-D sulfate aerosol model, we simulate the eruptions of El Chichón, Mt. Pinatubo, and a significantly larger hypothetical eruption. Interannual stratospheric transport based on NCAR-NCEP reanalysis-2 data [Fleming et al., 2007] is used for the historical periods (1982-1990, 1991-1999), thus including QBO and El Nino effects. Aerosol decay rates are compared with available observations, and calculated aerosol size distributions for the different eruptions are contrasted. We show that e-folding decay rates of aerosol extinction vary almost linearly with effective radius. Impacts on zonal-mean ozone density are shown, along with changes in radiative forcing.
A43D-07
Volcanoes and ENSO over the past millennium
We reassess the controversial claim that (El Niño) events might be partially caused by radiative forcing due to volcanic aerosols. Building on the work of Mann et al. (2005), we use estimates of volcanic forcing over the past millennium (Crowley 2000) and a climate model of intermediate complexity (Zebiak and Cane 1987), to draw a diagram of El Niño likelihood as a function of the intensity of volcanic forcing. We show that in the context of this model, only eruptions larger than that of Mt Pinatubo (1991, peak dimming of about 4 W/m2) can shift the likelihood and amplitude of an El Niño event above the level of the model's internal variability. This reconciles, on one hand, the demonstration by Adams et al. (2003) of a relationship between explosive volcanism and El Niño; and, on the other hand, the ability to predict El Niño events of the last 148 years without knowledge of volcanic forcing (Chen et al. 2004). We then focus on the strongest eruption of the millennium (1258 A.D.), and show that it is likely to have triggered a moderate-to-strong El Niño event in the midst of prevailing La Niña conditions induced by increased solar activity during the well-documented Medieval Climate Anomaly. Compiling paleoclimate data from a wide array of sources, we document a number of important hydroclimatic consequences for neighboring areas. We propose, in particular, that the event briefly interrupted a solar-induced megadrought in the Southwestern US. Most of the time, however, volcanic eruptions are too small to significantly affect ENSO statistics.
A43D-08 INVITED
Interactions Between Volcanic Eruptions and El Nino Studies with a Coupled Atmosphere- Ocean Model
Major volcanic eruptions have a significant impact on stratospheric and tropospheric climate, atmospheric composition and circulation. After large tropical eruptions observations and subsequent years model simulations show abnormally warm winters over the Northern Hemisphere continents in years following the eruption. During the winters following the three biggest eruptions in the last decades (Agung, El Chichon and Pinatubo) El Ninos took place. It is currently uncertain to what degree ENSO influences the atmospheric response to volcanic forcing and or in which way a volcanic eruption influences the strength and the timing of an El Nino event. Fully coupled Atmosphere-Ocean GCMs are therefore an important tool to improve our current understanding of the atmosphere and ocean response to the combined effects of El Nino and large tropical volcanic eruptions. We have carried out a series of Pinatubo experiments with the coupled atmosphere ocean circulation model, the ECHAM5/MPIOM . The volcanic radiative forcing is calculated online in the model using a realistic spatial- temporal distribution of aerosol optical parameters derived from satellite observations. We present results of at least five ensembles of simulations when the volcanic eruption appears for different states of ENSO: before the onset and during an El Nino event, during a La Nina episode and for a climatological mean. Each ensemble run has been performed for two years. The discussion includes the changes in atmospheric and ocean circulation and in planetary wave propagation. Special emphasis will be placed on the circulation changes in Northern Hemisphere winter.
A43D-09
Volcanic Climate Impacts and ENSO Interaction
Strong explosive volcanic eruptions could produce global stratospheric aerosol clouds affecting the Earth's radiative balance. The climate response to volcanic impact forms as a result of interaction of associated thermal and dynamic perturbations with the major modes of climate variability, e.g., Arctic Oscillation (AO) and El Niño- Southern Oscillation (ENSO). The paleo proxy data even suggest that strong tropical eruptions could increase the likelihood of El Niño. It was also observed that strong low-latitude eruptions affect mid-to-high-latitude circulation, forcing an anomalously positive phase of AO; however the AO responses to volcanic forcing might depend on ENSO phase. The strongest explosive eruptions of the second half of 20th century - Agung, El Chichón, and Pinatubo - occurred in El Niño years. El Niño of 1982, coinciding with the year of the El Chichón eruption, was especially strong and significantly affected climate response. To better quantify ENSO-Volcano-AO interaction in this study, we employed a coupled climate model (GFDL CM2.1) and specifically designed the numerical experiments to study how volcanic eruptions could perturb AO and ENSO and how the ENSO phase could affect the AO sensitivity and global climate response. As a test we have chosen the strongest and the best observed eruption to occur in the 20th century, the June 1991 eruption of Mt. Pinatubo. To synchronize volcanic eruptions and specific ENSO phase we have chosen initial conditions from those years of the 300-year control run that exhibited, respectively, El Niño, La Niña, or neutral ENSO phase and conducted ten 20-year ensemble runs with El Niño and La Niña initial conditions, and thirty 5-year runs for neutral initial conditions. We found that in CM2.1 simulations volcanic forcing can not affect the phase of ENSO. However, the surface air temperature anomaly depends significantly on ENSO. The maximum cooling for El Niño cases tends to shift to the second year after the eruption. In La Niña cases maximum cooling appears in the year when eruption occurred. However, the temperature responses appear to be very similar in both El Niño and La Niña cases when SST effect was removed, suggesting linear superposition of global responses to volcanic forcing and SST. Because of high climate variability in the coupled model we could not obtain a definite conclusion about differences of the AO sensitivity to volcanic forcing for El Niño and La Niña initial conditions.
A43D-10 INVITED
Indirect Climatic Effects of Major Volcanic Eruptions
The direct effects on climate, related to atmospheric emissions to the atmosphere following major volcanic eruptions, are well-known although the sparseness of such eruptions make detailed study on the range of such variations difficult. In general terms, infrared absorption by volcanic emissions to the stratosphere result in local heating early in the event when gaseous sulfur compounds exist. This early period is followed by gas to particle conversion, on a time scale of 1-2 months, promoting the formation of sulfuric acid-water droplets. Coagulation and droplet growth result in the "volcanic stratospheric aerosol layer" which is related to the predominant direct climatic effect of large eruptions, the cooling of the troposphere by backscattering of solar visible radiation to space with a recovery time scale of 1-2 years. In this paper we will discuss some of the less-known "indirect" effects of the volcanic stratospheric aerosol on climate. We label them indirect as they act on climate through intermediary atmospheric constituents. The intermediaries in the volcanic indirect climatic effect are generally atmospheric greenhouse gases or other atmospheric gases and conditions which affect greenhouse gases. For example, cooling of the troposphere following major eruptions reduces the growth rate of atmospheric carbon dioxide related to respiration by the terrestrial biosphere. In addition, redirection of part of the direct solar beam into diffuse radiation by the volcanic stratospheric aerosol stimulates plant photosynthesis, further reducing the carbon dioxide growth rate. The growth rate of the second-most important atmospheric greenhouse gas, methane, is also affected by volcanic emissions. Volcanic stratospheric aerosol particles provide surface area which catalyzes heterogeneous chemical reactions thus stimulating removal of stratospheric ozone, also a greenhouse gas. Although major droughts usually related to ENSO events have opposite effects on carbon dioxide, as have increased emissions by the industrial world, it will be argued that the dearth of major volcanic eruptions since that of Pinatubo in 1991 needs to be considered in explaining the enhanced carbon dioxide growth rates experienced over the past 10 or so years.
A43D-11 INVITED
Sulphur Release from Holocene Basalt Eruptions in the East Volcanic Zone, Iceland
SO2 emissions by basaltic eruptions are significant contributors of atmospheric sulfur because of high initial sulfur contents in basaltic magmas. The Eastern Volcanic Zone (EVZ) is a young (<3 m.y. old) and developing rift zone in south central Iceland, characterized by basaltic volcanism. It is the most productive of the currently active volcanic zones, with >205 km3 of basaltic magma erupted in the Holocene. Subaerial fissure eruptions account for 130 km3 (63%) of the magma volume and ~80 km3 was expelled in subglacial eruptions at the Katla, Grimsvotn and Bardarbunga volcanoes. Fourteen flood lava eruptions account for about 87 km3 (44%) of the total magma volume or 74% of the subaerial production. The three largest Holocene flood lava eruptions in Iceland, the 1783-84 Laki (15 km3), 934-40 Eldgja (20 km3), and ~8500 BP Thjorsa (22 km3) events, all occurred within the EVZ. The magnitude of these three events is underpinned by the volume of magma expelled, which is about 28% of the Holocene magma output. Flood lava eruptions are prolonged eruptions (months to years) characterized by recurring eruption episodes. Each episode begins with a short-lived explosive subplinian phase, supporting >10 km high eruption columns, followed by a longer lasting lava effusion phase. The bulk of the sulphur is vented into the atmosphere by the explosive phases and therefore prolonged flood lava eruptions can maintain elevated H2SO4 aerosols loading for periods of months to years. Petrologic estimates indicates that the fourteen EVZ flood lava eruptions emitted ~700 megatons (Mt) SO2 into the atmosphere in four 600- to 850-year-long eruption periods occurring at 8-9 ka, 6-7ka, 3-4 ka and 0.2-1.1ka BP. Between 98 and 328 Mt SO2 were emitted in each eruption period, with 5 to 210 Mt SO2 mass loading by individual eruptions. Consequently, and analogous to the 1783-84 Laki eruption, the effects of these eruptions may have been felt on a hemispheric scale for several years. Over the last 9000 years basaltic eruptions within the EVZ have released ~1500 Mt of SO2 into the atmosphere, which on an annual basis equates ~10% of the current global volcanic sulfur flux. About 30% of this sulfur mass is background emissions because it was produced by small explosive subglacial eruptions that have occurred at a steady rate of 10-15 eruptions/century throughout the Holocene. The rest of this sulfur mass was released periodically by subaerial fissure eruptions, including the contribution from the EVZ flood lava events. This is, however, a minimum estimate for the total Holocene SO2 emissions by EVZ volcanism because (1) the volume figures given here for the erupted magma volumes are conservative estimates, (2) it ignores the possible SO2 contribution by degassing of unerupted magma, and (3) does not take into account the contributions from the intermediate (andesite) and silicic (dacite to rhyolite) eruptions to the sulfur emissions, which make up >15% of the erupted Holocene magma volume in the EVZ.
A43D-12
New Perspectives on the Climatic Impact of the 1600 Eruption of Huaynaputina Volcano, Peru
A critical test of the new understanding of volcanic aerosols developed since 1982 is to determine if it can predict the effects of larger eruptions than those that have occurred since El Chichon. To do that, requires detailed information about the effects of specific large eruptions. We have been investigating the human and climatic impacts of the 1600 eruption of Huaynaputina volcano in Peru. The estimated Volcanic Explosivity Index for this eruption is 6, which is comparable to that of the 1815 eruption of Tambora volcano in Indonesia, which produced global cooling and led to crop failures, famine and social unrest. On the basis of tree-ring data, Briffa et al. (1998) suggested that the most severe short-term Northern Hemisphere cooling event of the past 600 years occurred in 1601, the year following the Huaynaputina eruption. In order gain a better understanding of the nature and extent of this cooling, we have been collecting annual time series that provide information about climatic conditions during time intervals that bracket the Huaynaputina eruption. Among the time series that we have examined (or plan to examine) are ice conditions in the harbors of Tallinn, Estonia, and Riga, Latvia and in Lake Suwa in Japan: cherry blossom blooming (sakura) dates from Kyoto, Japan; records of agricultural production from China and Russia; tithe records from the Spanish colonial empire; dates of the beginning of the wine harvest in France and the rye harvest in Sweden; prices of agricultural commodities in Europe; and river flows from the Nile and the Colorado. Often, in the records we have examined, 1601 shows up as one of the coldest years, if not the coldest year. In addition, the worst famines in Russian history took place between 1601 and 1603, which eventually led to the overthrow of Tsar Boris Gudonov. Thus, there is considerable evidence that the climatic impacts of the Huaynaputina eruption were comparable to those from the Tambora eruption. This result is important because it documents that significant global cooling events can be generated by South American volcanoes as well as Indonesian ones and that such events might occur with a return frequency of as little as 200 years.