5. Conclusions
In terms of reactivities, by extending the ATom-1 (G2021) to the four seasons of ATom-1234, we find:
Our sensitivity analyses using ATom measurements has identified some clear direction and pitfalls, as well as providing a more robust view of chemical feedbacks:
Probability densities for these critical species from ATom are presented as possible performance metrics for CCMs.
Comparing H2O with mean profiles is difficult because of the 3 orders of magnitude change over the troposphere, and thus, we recommend that relative humidity over liquid water (RHw) be used to detect model bias. Here we present a clear bimodal distribution of RHw in the tropics as measured by ATom.
The full ATom data set, including reactive species and the derived reactivities along with other atmospheric components describing the origins and processing of the air masses, provides the most extensive sampling of tropospheric chemistry over the remote ocean basins to date. The objective flight planning and near-continuous climb/descent profiling provided full sampling of the 0-12 km troposphere over the oceans. The statistics, including the co-variations of critical species (2D probability densities, in G2021), provide an excellent measurement metric for CCMs. The model-derived reactivities provide a testbed for the chemistry modules used in CCMs and also for independent analyses of the origins and chemical evolution of the air that matters, those chemically hot air masses clearly seen in the ATom flights. The sensitivity analysis of the 24-hour reactivities provides some core data that we feel should become a standard part of CCM evaluations and inter-comparisons. With this analysis, based on 10 s (2 km) air parcels, we believe we have partially deconstructed the spatial scales and variability that defines tropospheric chemistry.
Acknowledgements. The authors are indebted to the entire ATom Science Team including the managers, pilots and crew, who made this mission possible. We thank the instrument teams (co-authors on the first paper, Guo et al., 2021) for this valuable data set. Primary funding of the preparation of this paper at UC Irvine was through NASA grants NNX15AG57A and 80NSSC21K1454.
Data Availability. The full ATom data set as well as the derived MDS-2 and RDS*-2 data for ATom 1, 2, 3 and 4 are posted on the NASA ESPO ATom website (https://espo.nasa.gov/atom/content/ATom). The final archive for ATom data will be at Oak Ridge National Laboratory (ORNL), see https://daac.ornl.gov/ATOM/guides/ATom_merge.html. The MATLAB codes and data sets used in the analysis here are posted on Dryad (https://doi.org/10.7280/D1Q699), which has been expanded from Guo et al., 2021 to include this paper’s data and codes.