Air moves from high pressure to low pressure.

 

Air that is less dense than the air around it will rise until reaching equilibrium.

 

Not sure where you got the idea that low pressure air rises.

Areas of high and low pressure are caused by ascending and descending air. As air warms, it ascends leading to low pressure at the surface. As air cools, it descends leading to high pressure at the surface. This is illustrated in the diagram below.

No diagram attached, understand that those events are taking place over huge areas covering continents or oceans and not an area like an airport or a city. This is one way that lower pressure systems can form.

 

Hopefully this difference is clear when contrasted to how you will encounter cooler and lower pressure air at higher altitudes when you climb. This mechanic is not related to the initial question.

Basically in a low pressure system air is rising and cooling?

I can't really speak to that as I never really delved into reading about the macro level, but I don't believe it can be generalized that way.

 

It would make sense to me to say that a low pressure system caused by a large mass of air over a desert being heated would rise resulting in lower pressure.

 

I'm not sure it would be correct to say the same about a low pressure system created by a trough

http://www.metoffice.gov.uk/media/pdf/a/t/No._11_-_Weather_Charts.pdf

low pressure systems are caused by warmer air rising and this leaves low pressure at the surface

Driver,

 

just look at the "gas law" or state equation:

 

P ~ T * _p 

 

This reads that, on an air mass, pressure P is proportional to the Temperature and the Density ( actually to their product ), so... varying any of the three variable affects the others. It is actually

 

P ~ T * _p * C  where C is usually expressed in terms of erg/g K...

 

If we forget about the C, and on the first relation we imagine just the density varying, then for constant T, if the density increases the pressure increases and the way around...

If T varies, you can imagine various possible combinations of P and density to account for example for a non-varying P. The same applies for a variation in P regarding T.

 

We can say that in regions with equal temperature ( at the surface ) but different surface pressures ( those plotted on the surface charts ), the air column above the region with lower pressure is less dense than the one above the colder region, so, _p varies between those two, but one can be at the center of an high pressure system, and the other at the center of a depression.

 

So.... you can now imagine the air columns:

 

 

                                                                     getting warm                                        warm                                        ------------

                                                                       ------------                                          ------------                                     |             |

                                                                       |            |                                           |            |                                     |             |

                                                  getting cold  |            |                          cold           |            |                                     |             |

------------   ------------                    ------------     |            |                       ------------     |             |                  -----------     |             |

|            |   |             |                    |            |     |             |                       |            |     |             |                  |            |     |             |

|     A     |   |     B     |                    |            |     |             |                       |            |     |             |                  |            |     |             |

|            |   |             |                    |   A1          |   B1      |                       |  L₁        |     |  H₁     |                  |  H₂     |     |   L₂       |

|            |   |             |                    |            |     |             |                       |            |     |             |                  |            |     |             |

=======  =======                    =======     =======                      =======     =======                  =======    =======

 

 

First case: A and B air columns / masses that have identical mass, and the same surface T;

2nd  case: A column of colder, denser air can, even if shorter, exert the same pressure as the one created by a higher column of warmer, less dense air, so air getting colder shrinks, while the air getting hotter expands, but the surface pressure is the same in this case;

3rd  case: exemplifies a situation where surface pressure H1 is higher than L1, although the air in the higher column is hotter than the air in the lower column, for a same level in the troposphere there being more air above in column H1, than in the corresponding L1 level, the warm air in altitude is associated with an anticyclonic region while the colder air in altitude with a Low. Winds in this case will blow from the H1 column towards L1 for equilibrium... and, with time, we transit to a reverse situation...

Last case: For you to explain Driver ;-)

 

And... looking again at the First case above, with columns A and B, imagine that column A contains saturated air and column B dry air, and they're both at the same T. On each of the two columns will surface P attain the higher value? Or, putting it in another way... Is humid air heavier than dry air, at the same temperature and level?

 

 

BTW: Regarding one of your initial question about the circulation in turn of a Low vs High on the Northern Hemisphere, I'm not sure if it was explained that while there is always a force ( coriolis ) pulling to the right, near a Low, the pressure gradient force is superior, and that's why it starts circulating CCW.

Just one more thing.... since we're on a flight simulation Portal :-)

 

- Among the various available flight simulators, which one models the "Corilois" force?

- And... which one models the geopotential height, meaning non-ISA pressure gradient?

- Which one models both?

- Among the various available flight simulators, which one models the "Corilois" force?

 

In which way PSX models coriolis force?

It doesn't :-)

 

The answers: 1) Flight Gear models the Coriolis force; 2) PSX models geopotential height and tropopause "folding", 3) None models both....

:-) But what do you mean when you say it models coriolis force? For the weather?

For the faster aircraft.

 

It's irrelevant for a b744, but was a factor for the Concorde, and it is for a strategic supersonic aircraft, for the Space Shuttle, etc...

 

Weather-wise it is not modeled :-)

Cool!

Can't make sense of that diagram lol. Never knew all this would be so hard lol

Check this out guys

 

http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/pilot_handbook/media/PHAK%20-%20Chapter%2011.pdf

Nothing wrong with the FAA text, only not a full explanation - after all that's not what a pilot must know...

 

As a glider pilot, weather and it's implications in my RL flying activities made me look further into it.... Then, working at the MetOffice and being married to a meteorologist also helps :-)