[thiel]

> The Prosser report outlines one of the primary reasons for the increase in CAT events as the intensification of the jet streams, driven by the warming of the planet. As global temperatures rise, the temperature gradients between the equator and the poles become more pronounced, strengthening the jet streams and increasing the likelihood of turbulence .

I was under the impression that, as the poles are MORE affected by global warming, the jet stream is becoming weaker? is that incorrect?

[the_sleaze_]

You might be thinking of the Gulf Stream, which is an oceanic current and definitively weakening, rather than the jet stream, which is an air current.

[wongarsu]

The jet stream is getting stronger (and its path becomes more erratic), but the reasoning provided in the article is simplified to the point of being wrong.

The projected warming at the North Pole is much stronger than the projected warming at the equator, decreasing the temperature gradient. However the moisture carrying capacity of air increases exponentially with temperature. Since the equator starts warmer, a given change in temperature has a bigger effect on moisture carrying capacity. It turns out that heating up the equator by one degree Celsius and the North Pole by 2 degrees Celsius increases the moisture capacity gradient, despite the temperature gradient dropping. And that increasing moisture capacity gradient strengthens the jet stream.

(at least that's the intuitive reason they were probably going for. In reality there are many factors and a good bit of "if we simulate it this keeps happening")

[BlueTemplar]

Thanks for the detailed explanation.

But I also thought that it was the jet stream getting weaker that caused it to meander more (which sounds like it could increase CAT events ??), which we seem to be observing ??

[quakeguy]

Exactly, air currents are becoming stronger with warmer conditions, but the gulfstream being a water current it is expected to become weaker.

[HPsquared]

The jet stream is also driven by temperature differences. Same with most wind and weather, it's all various forms of heat engine.

(Edit: though apparently the additional moisture in the Tropics more than counteracts any reduction in temperature difference: see link in Retric's comment)

[rob74]

To muddle things even further, there is a (jet) aircraft manufacturer called Gulfstream (https://en.wikipedia.org/wiki/Gulfstream_Aerospace).

...but I fully agree with the rest of your comment.

[buildsjets]

Not all Gulfstream aircraft are jets. Mine certainly isn’t. Piston powered, burns avgas, spins a propeller, goes around 130 knots.

[polar_low]

That is correct, as a longer term trend at least while paradoxically, we are also seeing periods of record strength in the Jet Streams.

The truth is there are many oscillations and teleconnections(themselves being impacted by global warming) which influences this temperature gradient on a local/seasonal basis. QBO, El Nino/La Nina and mountain torque events to name a few can move and shift heat at the tropopause in a short period of time and is why we see this wider variance at both ends of the spectrum.

[photochemsyn]

I think the seasonality of the polar environment is a critical factor - while warming is expect to decrease the average equator-to-pole temperature gradient (as all models predict faster polar warming than equatorial warming by a large margin), winter is still winter as the polar axis is tilted, so steep atmospheric gradients are expected over that seasonal period.

[badcppdev]

Got some references?

[mcmcmc]

They are cited in TFA

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/202...

[konschubert]

That’s also what I read:

The poles warm FASTER than the equator. Thus, the global temperature gradients are getting smaller.

And as a result, not only does the Jetstream weaken: as a result, weather patterns become more stable which leads to greater continuous periods of draught or flooding.

[Retric]

Your intuition is incorrect. Global warming increases the jet stream.

“The new study, by University of Chicago Professor Tiffany Shaw and NSF NCAR scientist Osamu Miyawaki, uses climate models to show that climate change intensifies this density contrast because moisture levels for air above the tropics will increase more than above the poles.”

https://news.ucar.edu/132935/jet-stream-winds-will-accelerat....

[elevation]

> The poles warm FASTER than the equator

The article cites the Prosser Report which contradicts this claim, but I find it hard to understand how this could be true for very long. Why wouldn't the atmosphere stabilize as gradients diminish?

[photochemsyn]

Because the earth's rotational axis is not perpendicular to incident sunlight (hence dark polar winters). As winter sets in, gradients steepen relative to warming equator. It's all complicated by the general increase of atmospheric water vapor as warming proceeds, which can have different effects depending on whether the water vapor is gaseous or forms cloud droplets, which reflect sunlight. It's a hard physics problem.

[coldtea]

jetstream != gulf stream

[HPsquared]

Jet stream is also driven by temperature differences, like basically all weather. Heat engines.

[Retric]

It’s a heat engine but more than just temperature changes are occurring.

“The new study, by University of Chicago Professor Tiffany Shaw and NSF NCAR scientist Osamu Miyawaki, uses climate models to show that climate change intensifies this density contrast because moisture levels for air above the tropics will increase more than above the poles.”

https://news.ucar.edu/132935/jet-stream-winds-will-accelerat....

[HPsquared]

I guess it's like someone putting water on the coals in a sauna and the people feel a huge wave of heat due to the increased heat transfer, even though they've literally cooled down the coals.

[HPsquared]

Fair enough, I guess it's a pretty non-linear system!

[siffin]

I also think some of the confusion is coming from the use of the term 'weakening'. It is true that the primary jetstream wind pattern is weakening relative to it's stabler state.

That weakening means the jetstream meanders more, with more latitudinal movement in its form.

The strength overall of the jetstream wind is weaker when it's meandering, but can also be much more intense in places.

This says nothing about humidity or energy or pressure, just windspeed and direction.