IT is well-known that dynamical variability plays an important role in the year-to-year variations in stratospheric trace gases. Model simulations using constant emissions have further repeatedly…

This is a $335,981.02 grant awarded by the Shared Services Center of the National Aeronautics and Space Administration (NASA) to the University Corporation for Atmospheric Research (UCAR), a non-profit consortium that manages the National Center for Atmospheric Research (NCAR). The grant supports research to improve understanding of the role of dynamical variability and low-frequency phenomena like the Quasi-Biennial Oscillation (QBO) and El Niño-Southern Oscillation (ENSO) in driving decadal-scale changes in stratospheric trace gases and ozone. The research leverages satellite measurements, advanced climate modeling, and statistical analysis to address inconsistencies between observed and expected trends in stratospheric chlorine, ozone, and water vapor. The grant does not have a set-aside designation. UCAR frequently collaborates with university partners on its grant-funded atmospheric research initiatives.

IT is well-known that dynamical variability plays an important role in the year-to-year variations in stratospheric trace gases. Model simulations using constant emissions have further repeatedly demonstrated that this dynamical variability can result in unforced trends in trace gases over decadal timescales that complicate the detection of anthropogenically-driven trends. Yet we currently lack a mechanistic understanding of the processes that drive this decadal-scale variability and a quantification of its impact on trace gas trend detection and attribution. This proposal builds on a strong foundation of previous work that has used aura microwave limb sounder (MLS) measurements and the whole atmosphere community climate model (waccm) to establish a critical role for the periodicity and seasonal timing of the QBO as key drivers of decadal-scale variations of stratospheric circulation and tracers. The proposed work expands this analysis from a hemispheric to a global perspective, considers the role of enso in modifying and interacting with the QBO over decadal timescales, and develops a trend model for long-lived stratospheric tracers that incorporates physically-based indices describing the low-frequency variability associated with seasonal cycle QBO enso interactions. The proposal team combines established expertise in stratospheric transport and chemistry, analysis of satellite measurements, global modeling, and spatiotemporal statistics to tackle these challenging issues. We also bring a powerful new tool to bear in the form of a new waccm version with a realistic, internally generated QBO whose parameterization is dependent on convective activity and thus sensitive to changes in sea surface temperatures. The outcomes of our work are expected to advance our understanding of the apparent inconsistency of stratospheric HCL trends with known decreases in source gas emissions, the apparent decline in lower stratospheric ozone over the past ~20 years, the occurrence of rapid decreases in cold point temperature and lower stratospheric water vapor, and the cause of extremely low ozone in the lower stratosphere in 2011.