Weather across the UK and Western Europe appear to be strongly affected by the position of the jet stream and its involvement in moving storms across the Atlantic.

From what i've read the temperature contrasts between the subtropical and polar air mass along with the corriolis force create a strong wind high up in the atmosphere.  What I want to know is why the jet stream migrates northwards and southwards with the seasons and meanders around a bit?

 I can understand why the jet stream might be slower during the summer as the temperature contrasts between the air massess are lower, but i still dont understand the physics of why it moves.

How do people think the jet stream will respond to climate change?