More Met confusion.

[Pianorak]

Sorry, but I am back with more questions on Meteorology which I’ve got to sort out by tomorrow evening. Any help would be much appreciated.

(On the Geostrophic Wind, Thom p.212) The geostrophic wind . . . flows in a direction parallel to the isobars.

(On the Gradient Wind, Thom p.214) . . . In the northern hemisphere the result is a wind flowing parallel to the isobars. Balanced wind flow around curved isobars is called the gradient wind.

I can only guess that the clue may lie with “around curved” isobars. If so, what other isobars are there? Straight, rectangular, pentagonal?

Since both geostrophic and gradient wind flow parallel to the isobars, what exactly is the difference between them?
:confused:

[bookworm]

When isobars curve, there's a need to accelerate the air to make it curve with them. So in the N hemisphere, with the low on the left, and therefore a pressure gradient from right to left, you need more pressure gradient to make the wind follow isobars round a curve to the left than you would for the same speed of geostrophic wind with straight isobars. You need less gradient to make the air follow curves to the right.

As a result, the same gap between isobars causes a slightly stronger wind around a high and a slightly weaker wind around a low than would be predicted for straight isobars.

I have no idea why it's called a gradient wind. The terminology seems pretty dumb to me.

[Dufwer]

bookworm, I don't want to sound too pedantic but......

When you say "you need more pressure gradient to make the wind follow isobars round a curve to the left than you would for the same speed of geostrophic wind with straight isobars" I think you'll find that it's the reduction of wind speed, and hence reduction of geostrophic force that causes the wind to curve to the left, not a greater pressure gradient. Yes, I probably am being too pedantic :sad:

Have to agree with you on the name gradient wind being a bit dumb.

D

[bookworm]

Tighter isobars, same speed.
Same isobars, lower speed.

Chicken-egg-egg-chicken... :)

[NineEighteen]

Since both geostrophic and gradient wind flow parallel to the isobars, what exactly is the difference between them?Geostrophic wind is essentially theoretical wind. It's only really useful in understanding gradient wind. Amongst other things, Geostrophic wind can only flow along straight and parallel isobars. Isobars are rarely straight and so we usually consider a gradient wind. Additionally, a Geostrophic wind assumes no surface friction and therefore would only occur above the friction layer.what other isobars are there? Straight, rectangular, pentagonal? No, only straight or curved.

I hope this answers your question in time.

0918

[Pianorak]

Bookworm and Dufwer – Thanks for your stirling support. Never mind the finer points of the argument – all that matters right now is that, against all expectations, I HAVE PASSED. Not my best result at 85% but who cares. I found Met the most difficult exam and don’t want to hear the word Meteorology ever again (only joking – I know it’s of paramount importance). ;)

NineEighteen – Thanks for pitching in even if too late by a couple of hours! Shall try and digest it all once I have recovered from the ordeal! :O

[Airbedane]

Well done Pianorac.

Don't worry about the mark, anything more than 75% is a waste! All you need is a Pass.

By their very nature, CAA exams are of limited used to practical aviation. Certainly, they prove you have a certain knowledge, can understand a question with tricky wording and you can put an 'X' in the right place. Having got that out of the way, now is the time to learn Aviation Met.

Study the weather, the TAFS, the Actuals and the forecast charts, then note what happens in the real world. In time, you'll get the experience necessary to make the right 'weather' decision, but like all of us, including the Met Office, you'll have to make a few mistakes on the way.

The best bit of advice given to me was:"If there's any doubt, there's no doubt - divert or put it back in the Hangar"

A

[Pianorak]

Study the weather, the TAFS, the Actuals and the forecast charts, then note what happens in the real world.

Thanks Airbedane for a piece of good advice.