Is our Barometer function accurate?

[beebox]

Hi all

Do u use your barometer on your Ambit to forecast weather?

It has been raining very often over here in Singapore, but the barometer reading is always the same, sometimes increasing by 1 even when it is raining outside.

One thing weird i notice is the altimeter value dropped when it is raining..

Am i missing something?

[gaijin]

Hi all

Do u use your barometer on your Ambit to forecast weather?

It has been raining very often over here in Singapore, but the barometer reading is always the same, sometimes increasing by 1 even when it is raining outside.

One thing weird i notice is the altimeter value dropped when it is raining..

Am i missing something?

Sounds like your Ambit is in Alti mode. Set it to either Baro or Auto and you will see the Barometer readings change appropriately.

HTH

[cobrapa]

Have to agree, check what alti-baro profile you have set. As I posted in another thread, I find the baro graph to have a large vertical scale, which makes weather changes not very obvious as well.

[or_watching]

Of course it's important to be sure to understand the Alti-Baro functions.

If these solutions don't help, please check you local weather information (like a TV station or airport). You should able to find hourly barometric information, and you can then tell us, with exact numbers, what your watch readings are vs expected. The nearer the station to your location the better.

How familiar are you with forecasting your local weather with a barometer? Since Singapore is in the tropics, the barometric variation is less than other places on the planet.

Here is one graph for the last 24hr for SNG.
At the time leading up to your post (about midpoint on this chart), there were only a few mb of pressure changes.

[beebox]

My ambit is usually in the barometer mode when i'm at home since the altitude remains pretty much the same.
The reference altimeter is the value below and usually when it is raining, the barometer value remains the same but the altimeter value will drop, which i find it weird.

[cobrapa]

Do you mean the value shown there as "ref 11m" when you say altimeter value? Or some other value?

Are you set to barometer mode for profile or are you in auto mode?

[or_watching]

Here's one tidbit I found. I don't know that it relates to the OP's situation, but I'd not heard of it before and maybe it's of interest to folks who care about the minutiae of millibars.

In the tropics there is a diurnal (daily 24hr cycle) pressure variation of 3mb (+1.5 to -1.5mb) that, as I read it, isn't present to the same extent outside the tropics. So this would seem to be a source of real-world variation not accounted for in the standard atmospheric model (elevation vs pressure at specific reference temperatures) which all barometric altimeters use.

And I *think* that 1mb = 8 meters of altitude in the standard atmospheric model. (I checked my math with one of those online calcuators, so I think so).
And so if I've done the the math right, that 3mb of total up and down would show up in as 25meters in apparent altitude swings throughout the day. Assuming the watch didn't move, there were magically no 'weather driven' pressure changes, and the watch was set in Alti mode, etc

Is that really what happens???
Or is all this exactly what the temperature compensation in the watching is supposed to take care of when computing elevation???


http://www.metlink.org/pdf/articles/..._tropics_1.pdf

[beebox]

Do you mean the value shown there as "ref 11m" when you say altimeter value? Or some other value?

Are you set to barometer mode for profile or are you in auto mode?

Yes, I was referring to the ref11m as the altimeter value.
My watch profile is set to auto mode and usually when I'm home, it will show this hpa reading which I believe is the barometer.

[cobrapa]

Wow, both interesting posts... So, the ref 11m display is the reference altitude. It will only change when you set the reference altitude, or if the watch changes from baro to alti mode, and vice versa. If you are seeing the altitude change, and you are not setting the reference altitude, then it sounds like the watch made an automatic change.

I wonder if or_watching has found the reason. Maybe the tropical swing triggers the auto switching? Or something else has triggered it. I would try switching to baro mode, to disable auto switching.

[or_watching]

I read up a bit more on this phenomenon, and honestly still don't fully understand the consequences.
Any chance there's Equatorial Meteorologist reading this???

a) The Table is called a 'correction to observed pressure.' Which to me, most simply, means you need to add/subtract it to get a usable value. e.g. to understand i) weather-system-related pressure changes or ii) altitude-related presussure changed.
b) at the root cause it's thermally driven by the sun's heat.
c) It's not like it's directly related to the local ambient temperature causing the pressure change. But it's like a pressure wave that travels around the equator and that gets it's impetus the earth's temp gradient, but that the temperature isn't within the wave itself. Again implying that the watches temperature compensation can't/doesn't correct for it.

I'm seriously thinking this means I need to take week off work and fly somewhere sandy, warm and tropical. With those fancy blue drinks and little umbrellas.