Stratospheric correlation between nitric acid and ozone

An extensive data set of nitric acid (HNO 3 ) and ozone (O 3 ) measurements has been collected in the lower and middle stratosphere with in situ instruments onboard the NASA WB‐57F aircraft and remote sounding instruments that include the JPL MkIV Interferometer, the Aura Microwave Limb Sounder, and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer. The measurements utilized in this study span a broad latitudinal range between the deep tropics and northern high latitudes. The data are used to establish the robustness of the HNO 3 ‐O 3 correlation in the stratosphere and the latitudinal dependence in the correlation. Good agreement is found among the HNO 3 ‐O 3 correlations observed with the various instruments. Comparing HNO 3 ‐O 3 correlations relaxes the coincidence criteria necessary when making direct comparisons of HNO 3 measurements and allows meaningful comparisons between data sets that are not closely matched in time or space. The utility of this correlation is further demonstrated by establishing vertical profiles of proxy HNO 3 mixing ratios using the observed correlation and widely available ozonesonde data. These profiles expand the range of data available for validating remote measurements of HNO 3 . The HNO 3 ‐O 3 correlation is also demonstrated as a diagnostic for identifying locally enhanced HNO 3 in the upper troposphere. In situ measurements of HNO 3 near the tropical tropopause during the Aura validation campaigns are consistent with ACE‐FTS observations, with both revealing extremely low mixing ratios (<125 ppt) and a HNO 3 minimum in this region.