HR: 15:20h
AN: A43D-09    [Abstracts]
TI: Volcanic Climate Impacts and ENSO Interaction
AU: * Stenchikov, G
EM: gera@envsci.rutgers.edu
AF: Department of Environmental Sciences, Rutgers University, 14 College Farm Rd., New Brunswick, NJ 08901, United States
AU: Delworth, T
EM: Tom.Delworth@noaa.gov
AF: NOAA Geophysical Fluid Dynamics Laboratory, 201 Forrestal Rd., Princeton, NJ 08450, United States
AB: 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.
DE: 0370 Volcanic effects (8409)
DE: 3319 General circulation (1223)
DE: 3337 Global climate models (1626, 4928)
DE: 3367 Theoretical modeling
DE: 8409 Atmospheric effects (0370)
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly