Dynamical footprints of aerosols in extratropical atmospheric disturbances and circulation: A modeling analysis
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Synoptic-scale atmospheric disturbances occupy extratropics in wintertime and form extratropical “storm tracks”. These disturbances not only influence day-to-day weather variability but also modulate regional climates. The region of the North Pacific storm track is also known to be characterized by high concentrations of atmospheric aerosols, making it an ideal location for investigating the interaction between aerosols and extratropical disturbances. In the first part of the study, we investigate the aerosol indirect effects on the development of idealized baroclinic waves in the Weather Research and Forecasting (WRF) model. Doubling of cloud droplet number concentration (to mimic the aerosol indirect effects) in the model increases total cloud water in the model, enhances local latent heating and leads to a statistically significant strengthening of the wave. To take into account the effects of aerosol-convection interaction that had been omitted in the WRF experiments, the Superparameterized Community Atmosphere Model (SP-CAM) is adopted to examine the aerosol effects on developing extratropical cyclones in a more realistic environment. The result suggests that the growth rate of the cyclone is temporarily reduced with increased environmental aerosol concentrations. A convection–advection–moisture self-adjustment (CAMS) mechanism of aerosol–cyclone interaction is proposed to explain this finding. The last part of the study explores the collective effects of aerosols on multiple aspects of the northern extratropical circulation in boreal winter based on long-term perpetual winter simulations conducted with the SP-CAM. Analyses of local energetics of atmospheric disturbances reveal the underlying processes that lead to the strengthened activity of high-frequency (less than 10 days) disturbances and weakened activity of low-frequency (10 to 30 days) disturbances with an elevated level of aerosol emission. Also discussed are the implications of these findings for the short-term prediction of weather and long-term projection of climate change in the northern extratropics.