Group seminar on 15. June, 14:15 CET
Modal statistics of atmospheric circulation
Atmospheric circulation can be described as a system involving waves with different spatio-temporal scales and their interactions. However, the current studies are focused only on the part of waves’ spectrum, and the theory of waves interaction is far from being completed. MODES Hough decomposition (Žagar and Tribbia, Eds., 2020) has the potential to add further physical insight into the 3D structure of circulation and its extremes.
In the first part of the talk, I will present a spectral climatology of atmospheric Rossby waves with ERA5 reanalysis data on 43 terrain-following levels for 1980-2019. The results showed that climatological Probability Density Functions (PDFs) of energy computed from Hough expansion coefficients are skewed for studied scales (total balanced circulation, the zonal mean state, planetary and synoptic Rossby waves). This aligns with previous findings based on numerical simulations with a barotropic quasigeostrophic model (Timofeyev, 2007).
In the second part, I will introduce verified criterion for detecting atmospheric circulation patterns associated with surface weather extremes, such as heatwaves. It has been found that the energy distribution of some modes significantly changes during heat waves on the surface; thus, it demonstrates the connection between atmospheric circulation and surface extremes.
Žagar, N. and J. Tribbia (2020). Modal View of Atmospheric Variability: Applications of Normal-Mode Function Decomposition in Weather and Climate Research. Mathematics of Planet Earth. Springer International Publishing. ISBN : 9783030609634
I. Timofeyev, "Systematic deviations from Gaussianity in models of quasigeostrophic turbulence", Physics of Fluids 19, 116603 (2007) https://doi.org/10.1063/1.2815728