  Past studies show that coupled model biases in European blocking and North
Atlantic eddy-driven jet variability decrease as one increases the horizontal
resolution in the atmospheric and oceanic model components. This has commonly
been argued to be related to an alleviation of sea surface temperature (SST)
biases due to increased oceanic resolution in particular, with a physical
pathway via changes to surface baroclinicity. On the other hand, many studies
have now highlighted the key role of diabatic processes in the Gulf Stream
region on blocking formation and maintenance. Here, following recent work by
Schemm, we leverage a large multi-model ensemble to show that Gulf Stream
precipitation variability in coupled models is tightly linked to the simulated
frequency of European blocking and northern jet excursions. Furthermore, the
reduced biases in blocking and jet variability are consistent with greater
precipitation variability as a result of increased atmospheric horizontal
resolution. By contrast, typical North Atlantic SST biases are found to share
only a weak or negligible relationship with blocking and jet biases. Finally,
while previous studies have used a comparison between coupled models and models
run with prescribed SSTs to argue for the role of ocean resolution, we
emphasise here that models run with prescribed SSTs experience greatly reduced
precipitation variability due to their excessive thermal damping, making it
unclear if such a comparison is meaningful. Instead, we speculate that most of
the reduction in coupled model biases may actually be due to increased
atmospheric resolution.
