Linking Interannual and Inter-Model Variability in OH to Meteorological Variability

Chemistry climate model intercomparison studies show a large spread in the simulated distribution and trends of the tropospheric hydroxyl radical (OH), the atmosphere’s dominant oxidant and primary sink of many trace gases, including the greenhouse gas methane. While OH itself is too short-lived to undergo significant transport, its chemical precursors are affected by transport and meteorological processes. In this work, we illustrate how the simulated spatiotemporal variability of OH is affected by meteorology and the transport of species such as CO, NO₂ and O₃ that are chemically coupled to OH, and how satellite observations of these species can be used to constrain simulated transport processes. We use output from the Chemistry-Climate Model Initiative (CCMI) to explore these relationships across different models. In addition, we show how idealized tracers provide additional information by representing processes, such as transport from various source regions with different lifetimes, and stratosphere-troposphere exchange. We find that a combination of specific humidity and three idealized tracers can represent many of the spatial anomalies in tropical OH. We analyze the variability of OH with ENSO for different regions of the atmosphere and how this variability relates to the ENSO variability of its chemical and meteorological drivers as well as idealized tracers.