[paul cotter (OP)]

Currently in Ireland and I assume in the UK the weather is miserably wet sabotaging my gardening efforts. The perceived wisdom is that the latitude of the jet stream is the determinant of whether we have cyclonic or anticyclonic conditions. Is the jet stream the ultimate arbiter or is it subject to some other phenomena?

[alancalverd]

Kind of.

Weather in these islands is dominated by the Atlantic depression - essentially a tongue of warm air with strong winds circulating anticlockwise and driven eastwards by the Gulf Stream and jet stream - opposed by the Arctic cyclone that delivers long periods of dry, cold, weak northeast to east winds, and occasional visits from the North African sirocco that dumps sand and dust over southeast England.

The progress of depressions is a fairly constant 30 knots at 5000 ft but the contest is modulated by wobbles in the jet stream and the Euopean continental pressure system.

Don't complain about the rain! Cambridge is looking a bit like a desert right now.

[paul cotter (OP)]

Thanks for the prompt reply, Alan. We are slightly north of Dublin, latitude wise and we often get that red dust, most noticeable on windscreens, so it is not just south England. The surroundings were looking like the Algarve a week ago but since the rains arrived all has changed with a mass of weeds everywhere.

[evan_au]

On a visit to the USA (many years ago), I was surprised by the number of references to the Jet Stream on the TV weather reports. It never seems to get a mention on Australian weather reports.

I understand that part of the reason is that the Polar Jet Stream circulates much closer to the poles than where I live in Australia, so it doesn't affect our weather very much. Around my latitude, there is a subtropical jet stream, but this is at a much higher altitude than the polar jet stream.
https://en.wikipedia.org/wiki/Jet_stream#Description

[Petrochemicals]

Earth_Global_Circulation_-_en.svg.png (368.23 kB . 1263x1024 - viewed 483 times)Absolutely, 4 jets on earth, cyclone and anti cyclone action, the great variable is where your weather is coming from, in western Europe if from the Atlantic it's wet, if from the landmass it's dry, different in different places.

I think in summer the polar jet is usually above the British isles, during the winter either on or below, the sun heats atmosphere in summer and the atmosphere expands northward.

[paul cotter (OP)]

Nice diagram, Petro, thanks. Unfortunately the polar jet is well to the south right now and looks like it is going to stay there. I don't suppose anyone has a method to shift it northwards?, I am not greedy, ~300miles should not be too much to ask?

[Petrochemicals]

Nice diagram, Petro, thanks. Unfortunately the polar jet is well to the south right now and looks like it is going to stay there. I don't suppose anyone has a method to shift it northwards?, I am not greedy, ~300miles should not be too much to ask?

More polar ice I believe, a cooler pole will weaken the pressure I think.

[alancalverd]

Er, no. Cold air is denser, so if the poles cool, the polar anticyclones (high pressure areas) expand and the core pressure increases.

[Petrochemicals]

Er, no. Cold air is denser, so if the poles cool, the polar anticyclones (high pressure areas) expand and the core pressure increases.

Pressure means the summer heating of the middle latitudes increace the pressure, but during the winter do not have the heating, sothe jet slips southward. In a similar fashion to the poles the glaciers of the mountains provide summer cooling.