@article{lackmann_miller_robinson_michaelis_2021, title={Persistent Anomaly Changes in High-Resolution Climate Simulations}, volume={34}, ISSN={["1520-0442"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85106939084&partnerID=MN8TOARS}, DOI={10.1175/JCLI-D-20-0465.1}, abstractNote={AbstractPersistent anomalies (PAs) are associated with a variety of impactful weather extremes, prompting research into how their characteristics will respond to climate change. Previous studies, however, have not provided conclusive results, owing to the complexity of the phenomenon and to difficulties in general circulation model (GCM) representations of PAs. Here, we diagnose PA activity in ten years of current and projected future output from global, high-resolution (15-km mesh) time-slice simulations performed with the Model for Prediction Across Scales-Atmosphere (MPAS-A). These time slices span a range of ENSO states. They include high-resolution representations of sea-surface temperatures and GCM-based sea ice for present and future climates. Future projections, based on the RCP8.5 scenario, exhibit strong Arctic amplification and tropical upper warming, providing a valuable experiment with which to assess the impact of climate change on PA frequency. The MPAS-A present-climate simulations reproduce the main centers of observed PA activity, but with an eastward shift in the North Pacific and reduced amplitude in the North Atlantic. The overall frequency of positive PAs in the future simulations is similar to that in the present-day simulations, while negative PAs become less frequent. Although some regional changes emerge, the small, generally negative changes in PA frequency and meridional circulation index indicate that climate change does not lead to increased persistence of midlatitude flow anomalies or increased waviness in these simulations.}, number={13}, journal={JOURNAL OF CLIMATE}, author={Lackmann, Gary M. and Miller, Rebecca L. and Robinson, Walter A. and Michaelis, Allison C.}, year={2021}, month={Jul}, pages={5425–5442} } @article{tierney_robinson_lackmann_miller_2021, title={The Sensitivity of Persistent Geopotential Anomalies to the Climate of a Moist Channel Model}, volume={34}, ISSN={["1520-0442"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85106894701&partnerID=MN8TOARS}, DOI={10.1175/JCLI-D-20-0254.1}, abstractNote={AbstractHigh-impact events such as heat waves and droughts are often associated with persistent positive geopotential height anomalies (PAs). Understanding how PA activity will change in a future warmer climate is therefore fundamental to projecting associated changes in weather and climate extremes. This is a complex problem because the dynamics of PAs and their associated blocking activity are still poorly understood. Furthermore, climate change influences on PA activity may be geographically dependent and encompass competing influences. To expose the salient impacts of climate change, we use an oceanic channel configuration of the Weather Research and Forecasting Model in a bivariate experiment focused on changes in environmental temperature, moisture, and baroclinicity. The 500-hPa wind speed and flow variability are found to increase with increasing temperature and baroclinicity, driven by increases in latent heat release and a stronger virtual temperature gradient. Changes to 500-hPa sinuosity are negligible. PAs are objectively identified at the 500-hPa level using an anomaly threshold method. When using a fixed threshold, PA trends indicate increased activity and strength with warming but decreased activity and strength with Arctic amplification. Use of a climate-relative threshold hides these trends and highlights the importance of accurate characterization of the mean flow. Changes in PA activity mirror corresponding changes in 500-hPa flow variability and are found to be attributable to changes in three distinct dynamical mechanisms: baroclinic wave activity, virtual temperature effects, and latent heat release.}, number={12}, journal={JOURNAL OF CLIMATE}, author={Tierney, Gregory and Robinson, Walter A. and Lackmann, Gary and Miller, Rebecca}, year={2021}, month={Jun}, pages={5093–5108} }