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Observational data suggests that the extent of Arctic sea ice influences mid-latitude winter weather. However, climate models generally fail to reproduce this link, making it unclear if models are missing something or if the observed link is just a coincidence. We show that if one explicitly represents the effect of unresolved sea ice variability in a climate model, then it is able to reproduce this link. This implies that the link may be real but that many models simply fail to simulate it.

The stratosphere contains under a fifth of the atmosphere's mass but through its variability has a significant influence at ground level. Features of the variability are high-latitude sudden stratospheric warmings and a tropical quasi-biennial oscillation. Much of the variability is dynamical due to waves from the troposphere interacting with the mean flow. Dynamical stratospheric variability, its representation and predictability in models and coupling to the troposphere are reviewed.

Supercells are amongst the most complex and dangerous severe convective storms due to their associated phenomena (lightning, strong winds, large hail, flash-floods, or tornadoes). In this survey we study the supercell synoptic configurations and convective environments in Spain using the atmospheric reanalysis ERA5. Moreover, supercells are grouped in hail (greater than 5 cm) and non-hail events in order to compare and analyze both groups. The results reveals statistical significant differences.

In 1972, Prof. Ed. Lorenz gave a talk titled "Predictability; Does the Flap of a Butterfly's wings in Brazil Set Off a Tornado in Texas?". The chaotic error growth that under-pins the "Butterfly Effect" is a strong limiter to weather forecast skill. Here, we look at the metaphorical butterfly associated with midlatitude storm formation. We show that models differ widely in the predicted error growth, and that a better representation in the ECMWF model could improve probabilistic forecast skill.

Persistent weather can lead to extreme weather conditions. One such atmospheric flow pattern, termed Recurrent Rossby wave packets (RRWPs), increases persistent weather in the Northern Hemisphere. Here, we show that RRWPs are also an important feature in the Southern Hemisphere. We evaluate the role of RRWPs and other atmospheric features during Southeast Australian heatwaves. We also study how RRWPs are related to other atmospheric features well-known for increasing heatwaves.

The Arctic is currently warming twice as fast as the global average. This results in enhanced melting and thus freshwater releases into the North Atlantic. Using a combination of observations and models, we show that atmosphere-ocean feedbacks initiated by freshwater releases into the North Atlantic lead to warmer and drier weather over Europe in subsequent summers. The existence of this dynamical link suggests that European summer weather can potentially be predicted months to years in advance.