Reconstructing the East Asian Monsoon Response to the 1815 Tambora Eruption;
a Test of Model Simulations with Paleoclimate Data

Ph.D. Candidate: James A. Bradbury

Advisor: Raymond S. Bradley

Collaborators:
Wei-Chyung Wang
Atmospheric Sciences Research Center, State University of New York, Albany, 251 Fuller Road, Albany, New York 12203

Caspar M Amman
National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80307-3000

Abstract

Our primary objective is to test the skill of dynamical climate modeling experiments with respect to the East Asian monsoon system. In particular, we aim to examine the models’ response to volcanic aerosols by studying both regional and large-scale patterns of temperature and precipitation change in response to this forcing. Comparing historical paleoclimate records from China with results from both global and regional climate model experiments, we focus on several ensemble simulations of the 1815 Tambora eruption. Diagnostic analyses examine the direct radiative effects of volcanic forcing as well as the dynamical response. Thus, an important added benefit to this project will be a fundamental improvement of our understanding of how the East Asian monsoon system responds to major volcanic eruptions.

Summary

Episodic volcanic eruptions inject huge quantities of sulfuric gases into the stratosphere, which gradually convert to sulfate aerosols and cause non-uniform perturbations of the earth’s radiative balance and significant global and regional climatic effects for up to 3 years following individual events. In collaboration with the National Centers for Atmospheric Research (NCAR), global climate model (GCM) simulations are being used to better understand the thermodynamic effects of volcanic eruptions on the global climate system by forcing each model with reconstructed estimates of past stratospheric volcanic aerosols.

The global model provides a reasonable basis for analyzing the processes by which large-scale atmospheric circulation responds to global-scale volcanic aerosol forcing, however, the coarse spatial resolution of GCMs commonly results in some undesirable, significant regional biases – in the lee of the Tibetan Plateau, for example. Since this study targets the East Asian region, a finer spatial resolution regional climate model (RegCM) is also being used, in collaboration with the State University of New York at Albany (SUNYA), to more reliably represent the complex spatial structure and seasonal evolution of the EAM system. Driven by boundary conditions prescribed from GCM output and the same external volcanic forcing, the RegCM is used to study the dynamical and radiative processes by which global volcanic forcing translates into regional climate change in East Asia.