Hi all
Been lurking for a while but joined up to ask this question.
We've seen a lot of convergence lines on the surface pressure charts lately - culminating in 3 close together on the attached Met Office chart from yesterday. They are rarely marked at all on charts, and I'm guessing they're only being marked because they are potentially the most significant source of precipitation in the absence of any meaningful fronts.
The usual explanation of convergence lines I've found online tends to talk about onshore breezes in summer, acting in the opposite direction to the geostrophic wind. This forces air upwards, creating persistent cloud and, potentially, locally high precipitation. That's easy enough to understand.
But the recent convergence lines we've seen on the chart have all been parallel to isobars. The geostrophic wind implied by the pressure gradient would all be in one direction, so my question is, how can convergence lines form here? Where does the opposing wind come from? And how can you have 3 of them parallel to each other in such close proximity, which would imply 6 reversals of wind direction (3 of which must be against the pressure gradient) in the space of a couple of hundred miles?
Are they the remnants of fronts? Rolling air masses? What's actually going on to create them and make them persist?
Thanks
