New paper! Chris O'Reilly and I looked at recent trends in the wintertime North Pacific jet stream - Has climate change shifted the jet? - Can models capture these recent trends? - How has this affected North American weather? doi.org/10.1029/2024... 🧵 - ThreadSky

mattpattclimate.bsky.social • 68 days ago

New paper!

Chris O'Reilly and I looked at recent trends in the wintertime North Pacific jet stream

- Has climate change shifted the jet?
- Can models capture these recent trends?
- How has this affected North American weather?

https://doi.org/10.1029/2024GL113561

🧵

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mattpattclimate.bsky.social•68 days ago

First of all, the North Pacific jet stream has shifted Northwards over the satellite-era (1979-present).

This has already been pointed out by Keel et al (2024) https://doi.org/10.1029/2024GL109500

mattpattclimate.bsky.social•68 days ago

However, we found that no CMIP6 climate model simulations could capture the magnitude of this shift.

mattpattclimate.bsky.social•68 days ago

This northward jet shift matters for North American weather - only models with a more northward jet trend could capture the observed winter drying trend over California and southern states.

This drying likely contributed to the LA fires in January.

mattpattclimate.bsky.social•68 days ago

So was this climate change? We extended the jet time series back using longer reanalyses. Turns out the jet shifted southwards just as quickly from around 1950-1979.

This suggests that we cannot rule out internal multi-decadal variability, likely in part driven by Pacific SST variability

mattpattclimate.bsky.social•68 days ago

So why couldn't the models capture this shift? One hypothesis was the pattern-effect - the fact that models have tended to show an El Nino-like warming in the Pacific, in contrast to La Nina-like trend in observations.

mattpattclimate.bsky.social•68 days ago

This could resolve some of the discrepancy, but the observations still lie at the tail of the model spread.

We don't have a firm answer to why this is, but a lack of model low frequency or inaccurate response to forcing could be important.

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