Stratospheric ozone over the United States in summer linked to observations of convection and temperature via chlorine and bromine catalysis

An example of the dependence of heterogeneous catalytic conversion of inorganic chlorine (Cl_y ≈ HCl + ClONO₂) on temperature, water vapor, and sulfate loading is displayed in a manner that distinguishes rapid conversion of Cl_y to free radical form in the shaded region (with the threshold defined as 10% chlorine activation in the first diurnal period) from the unshaded region for which there is virtually no Cl_y to ClO conversion. These domains establish the photochemical framework for the analysis of convective addition of water, sulfate addition by volcanic injection or overt sulfate addition for SRM, or combinations thereof. The broad blue line dividing the perturbed and unperturbed domains corresponds to a sulfate reactive surface area of 2 μm²/cm³; the green line represents a shift in sulfate reactive surface area to 20 μm²/cm³.

(A) The geographic distribution of deep stratospheric convective injection from the NEXRAD weather radar 3D mapping of storms in the summer (May–August 2004–2013) that penetrate more than 2 km above the local tropopause. (B) The vertical distribution of inferred HCl as a function of potential temperature in the stratosphere over the United States in summer for two latitude bins (blue and red points), where HCl is calculated using in situ O₃ data from the NASA SEAC⁴RS mission. In situ measurements acquired by the National Oceanic and Atmospheric Administration chemical ionization mass spectrometer (CIMS) HCl instrument during the NASA AVE mission in June 2005 are included for comparison with the inferred HCl. Data acquired between 30°N to 50°N and 80°W to 105°W are shown. Also plotted are bin-averaged measurements of HCl acquired by MLS as a function of potential temperature, calculated from simultaneous measurements of temperature at the 100- and 68-hPa pressure levels (green squares). The dashed green lines indicate the range 1 SD from the mean for each 20 K potential temperature bin. The MLS satellite data were selected to be between 30°N to 50°N and 80°W to 105°W for June–August from 2004 to 2016. (C) The total number of storms that penetrate more than 2 km into the stratosphere over the central United States in May–August (black) and June–August (red) from 2004 to 2013 as a function of potential temperature. The calculated HCl mixing ratio is superimposed on the NEXRAD observations of frequency and penetration height.

High spatial resolution in situ temperatures (gray dots) obtained during the NASA SEAC⁴RS mission over the United States in summer 2013. The distribution in temperature is, in part, due to gravity wave-driven temperature fluctuations. Bin-average profiles for these data are plotted in the red circles, and the smoothed mean profile, T_ave, is represented by the solid red line. Similarly, the profile of minimum temperatures, T_min, is shown in the cyan circles and line. T_mid (blue line) is defined as the temperature profile midway between T_ave and T_min. The July/August mean of RO temperatures for the same region (black dashed line) demonstrates agreement between the in situ and RO data sets of 2 K or less. Finally, the “standard atmosphere” temperature profile for July that has been used in the AER 2D model, averaged over a region extending from 33°N to 52°N is shown in the solid black line.

The response of the four major rate-limiting steps in the catalytic removal of ozone to (A) temperature alone and (B) temperature plus convective addition of water vapor to a mixing ratio of 10 ppmv. The ozone loss rates, calculated using the AER 2D model, are shown after perturbation of temperature and/or water vapor. The three temperature profiles used in the model are shown in Fig. 4, and the temperature distribution is described in Observations of Temperatures in the Lower Stratosphere. A constant 10 ppmv water vapor perturbation between 12 km and 18 km is used to demonstrate the sensitivity in ozone loss rates as a function of altitude (see text).