Chemistry-climate interactions in the Goddard Institute for Space Studies general circulation model 2. New insights into modeling the preindustrial atmosphere

Abstract

We investigate the chemical (hydroxyl and ozone) and dynamical response to changing from present-day to preindustrial conditions in the Goddard Institute for Space Studies general circulation model. We identify three main improvements not included by many other works. First, our model includes interactive cloud calculations. Second, we reduce sulfate aerosol which impacts NOx partitioning hence Ox distributions. Third, we reduce sea surface temperatures and increase ocean ice coverage which impact water vapor and ground albedo, respectively. Changing the ocean data (hence water vapor and ozone) produces a potentially important feedback between the Hadley circulation and convective cloud cover. Our present-day run (run 1, control run) global mean OH value was 9.8 × 105 molecules cm-3. For our best estimate of preindustrial conditions run (run 2) which featured modified chemical emissions, sulfate aerosol, and sea surface temperatures/ocean ice, this value changed to 10.2 × 105 molecules cm-3. Reducing only the chemical emissions to preindustrial levels in run 1 (run 3) resulted in this value increasing to 10.6 × 105 molecules cm-3. Reducing the sulfate in run 3 to preindustrial levels (run 4) resulted in a small increase in global mean OH (10.7 × 105 molecules cm-3). Changing the ocean data in run 4 to preindustrial levels (run 5) led to a reduction in this value to 10.3 × 105 molecules cm-3. Mean tropospheric ozone burdens were 423, 306, 305, 305, and 310 Tg for runs 1-5, respectively. Copyright 2001 by the American Geophysical Union.