Impact of radiation on the formation of potential vorticity anomalies

Radiation in the atmosphere drives atmospheric dynamics on all scales from locally in a cloud via weather systems to global weather and climate and also interacts strongly with physical processes. Radiative heating and cooling can have a significant effect on the dynamics of extratropical cyclones (Schäfer and Voigt 2018), but the impact has been less extensively studied than for other sources of diabatic heating. Attinger et al. (2019) found that radiative heating and cooling can both increase and decrease cyclone strength measured by potential vorticity (PV) in different regions of a marine pacific cyclone, while Attinger et al. (2021) analysed cyclone composites and found that radiation can have a comparable impact on potential vorticity generation along the cold front as convection and condensation for cyclones in a cold environment.

We investigate the local and global effects of radiation-dynamics interaction by analysing accumulated heating rates and potential vorticity both locally in the grid-boxes and accumulated along trajectories. We find a significant effect of longwave radiation on both potential temperature and potential vorticity in the Northern Hemisphere, particularly in the lower troposphere. There is a pronounced land-sea contrast and impact of orography. The impact is concentrated at the top of cloud layers, particularly low clouds, showing the importance of cloud-radiation-dynamics interaction for dynamic development. We investigate in which regions and parts of cyclones radiative effects are particularly important.

 References:

Attinger, R., Spreitzer, E., Boettcher, M., Wernli, H., & Joos, H. (2021). Systematic assessment of the diabatic processes that modify low-level potential vorticity in extratropical cyclones. Weather and Climate Dynamics, 2(4), 1073-1091. https://doi.org/10.5194/wcd-2-1073-2021

Attinger, R, Spreitzer, E, Boettcher, M, Forbes, R, Wernli, H, Joos, H. (2019), Quantifying the role of individual diabatic processes for the formation of PV anomalies in a North Pacific cyclone. Q J R Meteorol Soc.; 145: 2454– 2476. https://doi.org/10.1002/qj.3573

Schäfer, S. A. K., & Voigt, A. (2018). Radiation weakens idealized midlatitude cyclones. Geophysical Research Letters, 45, 2833– 2841. https://doi.org/10.1002/2017GL076726