HR: 15:00h
AN: A43D-07    [Abstracts]
TI: Volcanoes and ENSO over the past millennium
AU: * Emile-Geay, J
EM: julien@gatech.edu
AF: Georgia Institute of Technology, 311 Ferst Drive, Ford ES&T, Atlanta, GA 30332, United States
AU: Seager, R
EM: seager@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, P.O. Box 1000, Palisades, NY 10964, United States
AU: Cane, M
EM: mcane@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, P.O. Box 1000, Palisades, NY 10964, United States
AU: Cook, E
EM: drdendro@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, P.O. Box 1000, Palisades, NY 10964, United States
AU: Haug, G
EM: haug@gfz-potsdam.de
AF: GeoForschungsZentrum, Telegrafenberg, Potsdam, D 14473, Germany
AB: 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.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 3374 Tropical meteorology
DE: 4255 Numerical modeling (0545, 0560)
DE: 4522 ENSO (4922)
DE: 4922 El Nino (4522)
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly