Interannual Variations in the Hydroxyl Radical: Dynamical Drivers and the Mean Meridional Gradient Ratio (Invited Presentation)

Reaction with the hydroxyl radical (OH), the atmosphere’s primary oxidant, is the main loss for a large number of trace gases, including greenhouse gases like methane and stratospheric ozone-depleting hydrochlorofluorocarbons. While observations show strong correlations between OH drivers (e.g., carbon monoxide (CO), water vapor (H₂O)) and climate modes of variability (e.g., the El Nino Southern Oscillation, the Madden-Julian Oscillation and the Indian Ocean Dipole), the associated dynamical mechanisms are poorly understood. Here we examine the correlation between interannual variations in the concentrations of OH and various meteorological (e.g., outgoing longwave radiation, water vapor, temperature) and chemical (e.g., CO, H₂O, ozone) fields, using output from the Chemistry-Climate Model Initiative (CCMI). We begin by quantifying the temporal regression slope between OH and each field,χ, (dOH/dχ) using simulations produced with the Goddard Earth Observing System chemistry climate model. We show that the sign and magnitude of dOH/dχ can be approximated by its climatological meridional gradient ratio (i.e., the gradient of OH divided by the gradient of χ). We then expand our analysis to the entire CCMI model ensemble and show that the intermodel spread in correlated OH-χ variability is related to the intermodel spread in the mean meridional gradients of OH and χ. Our results suggest that knowledge of the meridional gradients of OH and its dynamical drivers can help constrain their correlated temporal variability.