Topic: 2 question Elevation and Height Above Ground .

[davidmc36]

Shouldn't HOG be where your barometer is situated?

No. Elevation is supposed to be where you barometer is located. The fact that WU has removed this functionality (to dial it in) means that they think we are too stupid to handle that. So they go by terrible map data and use ground level as the elevation.....they are the stupid ones. Nobody cares about ground level...that isn't where the barometer is. Sure it might be close but it introduces a margin of error.

To WU credit I get what they are doing. There are a lot of people that are confused. If they left elevation up to the user then many were entering in the height of their poles where their station was situated instead of their elevation above sea level (plus height above ground for the barometer). But many people are also confused and think the barometer is outside up on the pole. I think WU should have left the ability to customize for those that know what they are doing.

That leaves Height Above Ground to specify. This is supposed to be for your anemometer.

OK, no. I meant to say shouldn't HOG be the correction factor for the barometer?

If so, mine needs a -8 ft.

[CW2274]

As it relates to Weather Underground your height above ground is the height of your anemometer.

Seriously? If so, that's really stupid. The only thing that matters in PWS land relative to elevation is your pressure, and that the height of your console MSL, nothing more, nothing less.

The height above ground of the PWS anemometer is sometimes used for tracking storm damage from winds.  In other words, they consider the height of the anemometer above ground as well as the wind reading to "normalize" the wind data.

Wow. Like their isn't a million variables that could render that data completely useless.

Also, if you read the CWOP manual on siting, it mentions noting the anemometer height in the metadata.  That's what wunderground is doing here.

Fine and dandy.....for wind data. Certainly has nothing to do with pressure data.

For example, Weatherflow asks for height above ground for their "Air" sensor.  They add it to the internet-reported elevation for pressure calculations.

Of course they do. The barometer is in the "Air" unit, not a console (or whatever variations it may be called) like everyone else.

[nincehelser]

As it relates to Weather Underground your height above ground is the height of your anemometer.

Seriously? If so, that's really stupid. The only thing that matters in PWS land relative to elevation is your pressure, and that the height of your console MSL, nothing more, nothing less.

The height above ground of the PWS anemometer is sometimes used for tracking storm damage from winds.  In other words, they consider the height of the anemometer above ground as well as the wind reading to "normalize" the wind data.

Wow. Like their isn't a million variables that could render that data completely useless.

Also, if you read the CWOP manual on siting, it mentions noting the anemometer height in the metadata.  That's what wunderground is doing here.

Fine and dandy.....for wind data. Certainly has nothing to do with pressure data.

For example, Weatherflow asks for height above ground for their "Air" sensor.  They add it to the internet-reported elevation for pressure calculations.

Of course they do. The barometer is in the "Air" unit, not a console (or whatever variations it may be called) like everyone else.

The baro sensor being in a console doesn't change things.

[CW2274]

Never said it did. Knowing the height MSL of your barometer is essential for correct pressure readings, doesn't matter if it's up a flag pole, buried in your basement, whatever....

[nincehelser]

Never said it did. Knowing the height MSL of your barometer is essential for correct pressure readings, doesn't matter if it's up a flag pole, buried in your basement, whatever....

Then what's your point about Weatherflow?

[CW2274]

Never said it did. Knowing the height MSL of your barometer is essential for correct pressure readings, doesn't matter if it's up a flag pole, buried in your basement, whatever....

Then what's your point about Weatherflow?

My point? None other than confirming why they ask for the height of the Air. If the barometer wasn't housed in it, they wouldn't care.

[nincehelser]

Never said it did. Knowing the height MSL of your barometer is essential for correct pressure readings, doesn't matter if it's up a flag pole, buried in your basement, whatever....

Then what's your point about Weatherflow?

My point? None other than confirming why they ask for the height of the Air. If the barometer wasn't housed in it, they wouldn't care.

I thought that was obvious with my statement.  Care to opine why they also ask for the height above ground for the Sky?

[CW2274]

Nope, and frankly, don't care.

[nincehelser]

Nope, and frankly, don't care.

Metadata for the anemometer.

It's a good thing to know when you're dealing with wind data, as everyone isn't going to have theirs mounted at 10 meters.

[ValentineWeather]

Here is the 10-meter height adjustment published by Cumulus software.  This only works provided there are no obstructions, example open field or distance of 10x the height from the nearest obstruction. 

Compensation
As it says at FAQ#Where_should_I_position_the_wind_sensors the UK expects an anemometer to be 10m agl. Raising an anemometer to a height of 10 metres in an open space requires a strong mast with tensioned wires, and is not always possible, especially for weather enthusiasts, therefore one must build in a compensation figure (or multiplier) in order to take into account the height factor.

It is generally accepted that the following formula will provide a multiplier to compensate for lower height anemometer (where h is the height of the anemometer in metres above ground level).

= 1/(0.233 + 0.656*log10(h+4.75))
Examples:
Height (metres)   Multiplier
0.5   1.42
1.0   1.37
1.5   1.32
2.0   1.29
2.5   1.25
3.0   1.22
3.5   1.20
4.0   1.18
4.5   1.15
5.0   1.13
5.5   1.12
6.0   1.10
6.5   1.08
7.0   1.07
7.5   1.06
8.0   1.04
8.5   1.03
9.0   1.02
9.5   1.01
10   1
Wind Multiplier in Cumulus
Within Cumulus it is possible to set a multiplier which will be used to upscale your actual reading from your anemometer to take into account its lower height. Use the formula above (or the table of examples) to locate your multiplier. Remember you are measuring the height of your anemometer from the ground in metres.

[Old Tele man]

That Cumulus equation is also be found on page 213 of Stephen Burt's book, The Weather Observer's Handbook, with these cautionary comments:

"It must be stressed that these factors apply only to mean speeds in an open location over relatively long periods (days or months), and that the variation of speed with height will vary with atmospheric conditions minute-by-minute, hour-by-hour, and day-by-day. Individual spot readings over short periods, and observations made in obstructed or sheltered sites, may depart significantly from these averages. The correction factors do not apply to gust speeds, which vary much less with height. Gust speeds should be reported without applying any corrections."

[CW2274]

That Cumulus equation is also be found on page 213 of Stephen Burt's book, The Weather Observer's Handbook, with these cautionary comments:

"It must be stressed that these factors apply only to mean speeds in an open location over relatively long periods (days or months), and that the variation of speed with height will vary with atmospheric conditions minute-by-minute, hour-by-hour, and day-by-day. Individual spot readings over short periods, and observations made in obstructed or sheltered sites, may depart significantly from these averages. The correction factors do not apply to gust speeds, which vary much less with height. Gust speeds should be reported without applying any corrections."

Like I said on page 1, waaaaay too many variables with the wind, let alone surrounding terrain and obstacles. It is by far our most dynamic measurement (certainly velocity), even more so than precipitation. I'm sure the formula(s) work sometimes, somewhere, but AFAIC, not worth the consideration as a whole for true usable data.