Fair play Keygrip, just the few hundred students giving all sorts of weird and wonderful answers over the past few years is enough to make anyone cranky, especially if said students are majoring in Met. Sorry if rubbed anyone the wrong way!
Anywho, it's not a cut n paste job - it's all my own work! My standard of grammar is far too poor to get into a textbook.
I said these answers are bizarre as there seems to be a lot of confusion about fairly basic physical principles that I always thought were reasonably well covered in the PPL texts. Simplifications are absolutley fine, but there becomes a point when you start hammering a square peg into a round hole with a sledge hammer, so to speak. You start getting more problems building on these if the simplifications propagate to other areas where they don't fit and people may start second guessing other areas that they are already clear on. A lot of the reasons people have come up with on this thread mention the key principles but are couched incorrectly that leads to a haze (pun intended) of confusion.
For example the hoover and cushion analogy is nice as it does conceptually fit with the vertical motion in lows and highs, except when you think about it, the time scales of the dominant physical processes are so different it begins to fall apart. The mean vertical motion in a high or low is of the order a few m per hour, whereas a convective updraft is a few m per second - the observed build up of haze isn't really going to result from a 1/3600 difference in the vertical motion.
Similarly there's a bit of confusion about the temperature in miroc's post. I can understand what they are going but if you don't know the answer in the first place it can be very confusing. Here miroc is talking about the concept of potential temperature, which is the temperature air would have if it was transported adiabatically to 1000hPa, as we all know from experience that the coldest air is not present at the surface. A rising plume approximately retains its original potential temperature and the buoyancy that I talked about in my first post is defined by the potential temperature difference between the environment and the rising plume.
What I'm trying to do in my replies is to help others by pointing out where the concepts are applied correctly and incorrectly. In the case of the haze question there are multiple time and space scales involved where other concepts and simplifications don't mesh properly. Maybe most aren't really that interested in the long drawn out answer and its probably not that important in the grand scheme of things, but I'm going to give it anyways!
Cheers,
Gareth. (now 50% less cranky thanks to coffee injection).