ATPL Met Exam Question - can anyone help?

[Riccarton]

ATPL Met exam coming up soon and I just can't get my head around anything to do with direction in the southern hemisphere. Can anyone help with these two questions?

1. Flying away from a low pressure area in the southern hemisphere, near the surface, where is the wind coming from?

The answer is given as "left and slightly on the nose", but I just can't see the "left" bit, no matter how many diagrams I draw.

2. Area of highest turbulence in a polar front jetstream in the southern hemisphere?

Answer - looking downstream, on your right. Why the right?? Do jetstreams blow the opposite way in the southern hemisphere?

I'm totally confused and obviously missing something somewhere.

Thanks in advance to anyone who can offer any kind of explanation.

[Tinstaafl]

1. Wind flow is clockwise around a low in the S. hemisphere.

Flying away from the L means the wind must be from the left for it to also be flowing clockwise around the low.

The question also states that you're at a low altitude. These sorts of 'extras' in the stem of qestions are there for a reason ie bring to your attention some factor that changes as a result of the specified condition and must be considered to derive the correct answer.

Wind flow at Low altitude vs high altitude changes as a result of surface friction preventing flow being truly parallel to the isobars.

The pressure system mentioned is a Low so air will tend flow into the Low, in addition to clockwise around this S. hemisphere Low.

You're flying away from the low at low altitude (therefore friction effects), the wind has a tendency to flow into the low so there will also be a slight headwind component.

2. Highest turbulence is on the Polar side of the jetstream.

The polar jet blows from W to E (in both hemispheres)& you're facing downwind in the S. hemisphere ie facing East. The S. pole is on your right & therefore so is the polar side of the jet & its highest turbulence.



[This message has been edited by Tinstaafl (edited 26 March 2001).]

[Riccarton]

Tinstaafl,

Many thanks for taking the time to respond and for an explanation which makes it all crystal clear. I can't believe (and I'm embarrassed to admit!) that I've sat in a classroom for three months and failed to pick up on these points. I'm a borderline case on Met, but here's hoping I've now secured another mark or two.

You must be an Instructor (and if you're not, you should be!)

Thanks again! Hope I can reciprocate sometime.

[Speedbird252]

Hi Riccarton - remember one golden rule in Met:

Buys Ballotts law sates that - if you are in the northern hemisphere, and you have your back to the wind, the low pressure is on your left. Its the reverse for the southern hemisphere:

If you have your back to the wind in Oz, the low pressure system is on your right.

So on your cross country flights you will have a good understanding as to why you have to compensate for drift.

Regards my friend.

Anything else please feel free to e-mail me.

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