Giddy all

Sorry to be a pain and I am unsure of how important this question is in the overall scheme of things but I have a query about question 9 in exercise gm2. This is the question of what lat is the greatest wind difference between gradient wind and actual wind at 5000. The answer is given as 5degrees south with an explanation that the Coriolis affect is next to nothing at the equator. Surely this means that the difference between the two winds is minimal making the correct answer d. 35 degrees sth.

Where have I gone wrong please?

G'day,

Sorry this answer is so terribly late but perhaps it will be of use to someone:

With decreasing Coriolis force, the wind direction will tend to flow more with the pressure gradient. So, if there is little or no Coriolis force, the gradient wind will tend to flow directly into a low and directly out of a high.

That's why a surface wind veers (in the southern hemisphere) when compared to the gradient wind. Near the surface, the wind slows down (due to friction with the surface) and Coriolis has therefore less of an effect on the moving air. Less Coriolis force means the pressure gradient force wins out and the wind tends to flow more directly into the area of low pressure.

So, let's apply that now to the situation at 5^o South. There is little Coriolis force so the gradient wind (at 5000 ft) will tend to flow straight into the low pressure area.

What happens at the surface though? Well, the wind will slow as usual and any Coriolis force will have less of an effect. But, at 5^o South there is little Coriolis effect anyway so the surface wind hardly changes direction at all in comparison to the gradient wind.

Compare that to 35^o South: near the surface the wind slows and experiences less of a Coriolis force. At 35^o South the Coriolis force is quite significant and the slowing of the surface wind will cause a more significant veering of the wind direction.

Cheers,

Rich