Geostrophic wind scale

[Mike1956]

Different spacing at different latitudes due to the chart projection used on the weather chart?

Mike

[StuM]

Sorry, I don't understand what you are actually asking. Care the rephrase your question?

[Hydra]

Different spacings at different latitudes result from the change in Coriolis force with the latitude.

Alain

[Mike1956]

Originally Posted by StuM

Sorry, I don't understand what you are actually asking. Care the rephrase your question?

Hi StuM,

Rephrasing question but it seems my question has already been answered.

I am aware for any chart or map to be produced on a flat sheet of paper a projection must be used, mercator or whatever. I was wondering if the distortion created by the use of the projection was the reason for needing a geostrophic wind scale.

I have before me a globe and a synoptic chart printed off the internet.

I have made some crude measurements as follows:

I have measured one degree of longitude at 70 deg LAT and 40 deg LAT in mm.

On the globe the measurements are 14mm and 31mm respectively.

On the synoptic chart the measurements are 13mm and 34mm respectively.

There does seem to be some distortion here but maybe does not account for the significant differences in the geostrophic wind scale?

I do have a basic understanding of Coriolis and once posted on a forum asking for someone to work me an example of the coriolis formula to assist my further understanding but no takers?.

Mike

[Brighteyes]

How do I use a geostrophic wind scale? | Weather FAQs

[Brighteyes]

Weather Facts: Geostrophic Wind - Weather UK - weatheronline.co.uk

[Hydra]

The "geostrophic approximation" considers that the wind speed is proportional to the pressure gradient (inversely proportional to the distance between isobars). But the ratio depends on the Coriolis force, which is proportional to the sine of latitude: the force is zero at the Equator (the reason why there are no hurricanes close to the Equator) and maximum at the poles.

On the sea surface, the real wind is much less than the geostrophic wind, due to friction.

Alain