Enhanced Blocking Frequencies in Very‐High Resolution Idealized Climate Model Simulations

• Published in: Geophysical research letters 2024-11, Vol.51 (22), p.n/a
• Main Authors: De Luca, P., Jiménez‐Esteve, B., Degenhardt, L., Schemm, S., Pfahl, S.
• Format: Article
• Language: English
• Subjects: Atmospheric blocking; blocking; Blocking events; Climate; Climate and weather; Climate change; climate modeling; Climate models; Cold waves; Convection; Convection heating; Diabatic heating; Drought; Extreme values; Global climate; Global climate models; Heat waves; High resolution; ICON; idealized; Planetary waves; Pressure anomalies; Representations; Rossby wave breaking; Rossby waves; Simulation; very‐high resolution; Wave breaking; Weather; Weather patterns
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2024GL111016

Atmospheric blocking is a key dynamical phenomenon in the mid‐ and high latitudes, able to drive day‐to‐day weather changes and meteorological extremes such as heatwaves, droughts and cold waves. Current global circulation models struggle to fully capture observed blocking frequencies, likely because of their coarse horizontal resolution. Here we use convection permitting, nested idealized model simulations for quantifying changes in blocking frequency and Rossby wave breaking compared to a coarser resolution reference. We find an increase in blocking frequency poleward and downstream of the area with increased resolution, while the exact regions depend on the blocking index. These changes are probably due to a more accurate representation of small‐scale processes such as diabatic heating, which affect Rossby wave breaking and blocking formation downstream. Our results thus suggest an improved representation of blocking in the next generation of high‐resolution global climate models. Plain Language Summary Atmospheric blocking is a persistent weather pattern associated with high‐pressure anomalies that is able to drive meteorological extremes such as heatwaves and drought in summer, and cold waves in winter. Having blocking well represented in state‐of‐the‐art climate models is of paramount importance, however these models fail in simulating the frequency of blocking events, likely because their grid resolution is not high enough for resolving small scale physical processes important for the development of blocking episodes. Here we use very‐high resolution model simulations for quantifying blocking frequencies and the mechanisms driving these episodes. Our simulations are idealized, in the sense that they do not fully represent the Earth's system but allow us to focus on key physical mechanisms driving the blocking events. Our results show that using a very‐high resolution enhances blocking frequencies when compared to a lower resolution grid. The findings point toward the importance that unresolved physical processes play in generating blocking events that can only be simulated at very‐high resolution and can be of importance for the next generation of climate models. Key Points Blocking frequency increases downstream and poleward of sea‐surface temperature front with convection permitting atmospheric resolution The specific region of increased blocking depends on the blocking index Changes in diabatic heating and Rossby wave breaking play a fundamental