Wind speed from barograph?

[Thistle]

The wind speed is proportional to the rate of change of pressure.
The slope of the line on a barograph chart is proportional to the rate of change of pressure.
So I should be able to measure the slope of the line on the chart and convert this to a wind speed.

An easy way to do this would be to draw a series of lines (as diagonals of a circle) on a sheet of acetate at, say, 10 degree intervals, and to calibrate these as wind speeds.

If it's that easy, why hasn't someone done it before or am I being stupid (again!)? If I'm right, how do I calibrate the chart? What slope of line relates to what wind speed?

(I know it will depend on the size of the barometer drum but a common size has a circumference of 287.5mm for 7 days and 76mm tall for a pressure change of 100mb.)

 

[danielefua]

The wind speed is proportional to the rate of change of pressure.

Wrong. The wind speed is proportional to the horizontal gradient of the pressure. Distance variation, NOT time variation of the pressure field.
In first approximation if you assume that the pressure field shape is not changing as it moves (it is said to be advected) you could use the horizontal wind and the rate of change measured with your barometer to compute the horizontal gradient.
You should take into account also the horizontal wind so it sounds more like a snake biting its own tail and, I insist, it would even be only an approximation.

This is why nobody did it before!

Daniel

 

[neilf39]

I though the best you could do is check the rate of change, so how many mBit drops/rises over a few hours, to give a rough estimate of the wind strength likely to hit. Extracted this from the interweb and is also a rule of thumb in the RYA coastal skipper weather bit I seem to remember.

"Predict the resultant wind speed (in Beaufort Scale Numbers) using this rule of thumb. A 1 mb/hour change will give you F6 over the sea. 2 mb/hour will give F7-8 over sea, and 3 mb/hour will yield above F8 over the sea. Keep in mind that over land the wind speed will be about F2 less than over the sea. Also this tends to be gusty wind, and the peak wind will register higher."

Given how wide ranging the speeds are for a single F number it is very approximate.

You can do it from a pressure chart by measuring the distance between the isobars and applying some correction factors but this is approximate too.

 

[VicS]

You can get an estimate of wind speed by using the "geostrophic scales" printed on weather maps and isobars drawn at 2mb intervals . see below.

Draw the chart from the info broadcast in the shipping forecast

( sorry very out of date weather map)

 

[alan_d]

An easy way to do this would be to draw a series of lines (as diagonals of a circle) on a sheet of acetate at, say, 10 degree intervals, and to calibrate these as wind speeds.

I don't think circles have diagonals, did you mean diameters?

 

[grumpy_o_g]

The wind speed is proportional to the rate of change of pressure.
The slope of the line on a barograph chart is proportional to the rate of change of pressure.
So I should be able to measure the slope of the line on the chart and convert this to a wind speed.

An easy way to do this would be to draw a series of lines (as diagonals of a circle) on a sheet of acetate at, say, 10 degree intervals, and to calibrate these as wind speeds.

If it's that easy, why hasn't someone done it before or am I being stupid (again!)? If I'm right, how do I calibrate the chart? What slope of line relates to what wind speed?

(I know it will depend on the size of the barometer drum but a common size has a circumference of 287.5mm for 7 days and 76mm tall for a pressure change of 100mb.)

Here you go http://www.weathercharts.org/ukmomslp.htm#top

 

[danielefua]

Here you go http://www.weathercharts.org/ukmomslp.htm#top

Jolly good! Here in Italy we gonna have a great weather! Sorry for you, brit chaps!

Daniel

 

[Thistle]

Thanks all. Back to the drawing board.