Meteorology question.

[xxilim]

Hi guy's I'm studying for a met exam I have on Friday and I'm reading through synoptic meteorology at the moment.

I just finish reading about warm and cold fronts and how once the front passes the wind tends to back. That's pretty much all it said.
My question is what makes the wind back?
I'm not sure if I need to know this, or if it's something I have simply overlooked.


Oh and I'm in Australia by the way

[xxilim]

I've been thinking about it...

Any one tell me if this sounds right.

The Coriolis force is proportional to the wind speed.
With the passage of a cold front the advancing air is moving faster than the air it is replacing.
The slower air isn't subject to so much of a Coriolis force so it tends to flow across the isobars in towards the low pressure system.
The faster moving air tends to be more of a gradient wind because of an increase in the Coriolis force.
Which results in the backing of wind as the front passes.

That sounds right to me?

Any thoughts?

[Trevor Hale]

Hi Craig,

That sounds right to me, but I am no expert in this field.  I am sure there are more users here that can answer this question better then I, although I would have to expect this would not be on your test.  But you never know.

Good luck,

Trev

[jackpilot]

To the best of my "Northern hemisphere" knowledge, all the forces that affect the wind deflection are at their maximum at the edge of a cold front (iso, coriolis, centrif. etc) . After the passage a more "normal" flow resumes because these forces tend to relax. Coriolis of course as you mention, due to slower speeds, but slower speeds are induced by wider iso lines too. So the tendancy to flow straight from high to low is less "impeded" . Hence the shift.

Not sure it answers your question, ask your local Aero weather office they will be glad to
help.
JP

[xxilim]

Thanks Trevor, I don't expect it to be but it's nice to know.
It sort of annoys me when a book like this just says how it is.
It's handy to have a bit of reason behind it. 

[xxilim]

Sorry if I haven't interpreted that correctly Jack.

So to say all forces are at maximum would be to say a gradient wind exists.
To consider it a backing wind the preceding air mass would have had less of a pressure gradient, in turn less wind speed and less Coriolis force which should result in more flow towards the center of the low pressure system.

I'm going to head out to the MET office tomorrow at some stage, been meaning to for a few weeks now 

[fsaviator]

Here's some info:
http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/c2df8d9d7471617786256a020078083a!OpenDocument&Click=

Look in Chapter 8, page 64.  All sorts of info on fronts.

This is a very handy, although dated in some cases, reference.  I keep a hard copy around for RW flying.

Warren

[xxilim]

Thanks Warren,
I made it out to the local MET office today and had a chat to guy out there, even lent me a few books.
I told him how I thought the Coriolis force was the result of the change, although I didn't really get a complete answer he did agreed to some extent about my comment.
I think that's good enough for me 

[fsaviator]

That's the way to go.

I'll tell you, when I was getting my PPL, weather was the most confusing thing.  In fact, the guy that taught the ground school was the US Air Force Academy Meteorologist.  After I received my PPL, I called him up for further tutoring.  it's interesting stuff, but very perishable.  It's also very important, especially here in Colorado Springs where we can enjoy all four seasons in a day, and quite often do.  It's not unheard of to have snow, rain, fog, sun, and heat in one day, in June or July.

Warren

[xxilim]

You were lucky Warren, there's no such ground school where I am.
It's all self study for me and the general community isn't at all aviation orientated, it's all farming, so resources here are rather limited.
and there nearest ground school is 5 hours away!

[fsaviator]

See, that's my goal.

When I finally retire from the military, I plan on opening a Fixed Base Operator (FBO) in Southern Colorado where I bought some land on a grass runway.  I will then give ground and flight instruction, as well as maintain aircraft.

I'm working through Embry-Riddle for the training, as I have time.

Bringing full service flight instruction and aircraft maintenance to the heartland.

Cheers!

Warren

[warvet]

  Hmmmmm
I always thought Back wind was caused by my wife's burritos from my Cornholis  not my Coriolis , Who knew learn something new every day.lol
Tim

[xxilim]

Well passed it! 5 to go! 

[Trevor Hale]

Great Job.

Trev

[fsaviator]

Well passed it! 5 to go! 

Awesome...  Congrats!

Warren

[jackpilot]

Good feeling. Good 4U.
Jack

[MLeavy737]

hey xxilim,
  Dont sweat the WX stuff all that much. You will come to find out if and when you start flying professionally that your pretty much gonna be going no matter what lol..  All you have to know is dont fly through the RED (thunderstorms) and dont land if the WX is reported below mins

Good luck with the training/classes though!

Let me know if i can help at all.. Most of the theory is long forgotten but the practical stuff is well within reach

Mike Leavy