Meteorology question

[double_barrel]

Originally Posted by Luc Lion

Double_barrel,

- for the first question, the right answer is c "remains the same".
Generally speaking, the total water content of a parcel of air remains constant.
With varying temperature, the vapour content diminishes and transforms or water or ice (cooling), or the water/ice content transforms into vapour (warming) ; but the total water content remains the same.
This of course becomes invalid when the water droplets coalesce and fall as rain (water content reduction). It is also invalid for the parcels in immediate contact with a patch of water or a some ground with moisture (water content increase). So these are exceptions to the general rule "remains constant".

Thanks. I would understand that the total water content remains unchanged as a parcel of air cools. But I cannot understand how its potential for airframe icing does not increase as the water gets colder. Maybe I am misreading the question!

Originally Posted by Luc Lion

- the second question is badly worded ; there are 2 correct answers.
Both the "geostrophic wind" and the "gradient wind" are models for wind and not real wind and both are modeled so that they follow the curves of the isobars.
The difference between the 2 is the computed speed of the wind.
In the geostrophic model, the speed is such that the Coriolis force compensates the pressure gradient force and no other force is considered.
In the gradient model, the speed is such that the Coriolis force compensates the pressure gradient force plus or minus the centrifugal pseudo-force.
As a result, the gradient wind blows parallel to the isobars at a less than geostrophic speed when the isobars curve around a low pressure (a lower Coriolis force is needed for compensating the gradiant force reduced by centrifugal pseudo-force) and the gradient wind blows parallel to the isobars faster than geostrophic speed around a high pressure (a higher Coriolis force is needed for compensating the gradiant force increased by centrifugal pseudo-force).
So both answers b and c are correct but the book answers "c" as if the question was
"Which wind blowing around curved isobars has a speed closer to real wind speed ?"

These geostrophic vs gradient models are well explained on this internet page:
Gradient Wind: non-geostrophic winds which blow parallel to isobars

Very helpful, thanks!