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General Weather/Earth Sciences Topics => Aviation Weather => Topic started by: CW2274 on November 02, 2015, 06:49:26 PM

Title: To go True or Magnetic
Post by: CW2274 on November 02, 2015, 06:49:26 PM
At suggestions, I've started this for those who wish to discuss whether you calibrate your PWS anemometer vane to true north or magnetic, such as myself, pros and cons.
Title: Re: To go True or Magnetic
Post by: CW2274 on November 02, 2015, 07:22:30 PM
At suggestions, I've started this for those who wish to discuss whether you calibrate your PWS anemometer vane to true north or magnetic, such as myself, pros and cons.
That being said, I'm taking bets that I'm the only "magnetic" guy on this board..... ;)
Title: Re: To go True or Magnetic
Post by: ValentineWeather on November 02, 2015, 08:33:38 PM
CWOP wants true north in siting guide. http://www.wxforum.net/index.php?topic=21081.0;nowap
Title: Re: To go True or Magnetic
Post by: CW2274 on November 02, 2015, 08:39:04 PM
C.D.M.V.T.?

I used the "true" heading from this FFA picture for TIA:

(https://upload.wikimedia.org/wikipedia/commons/thumb/f/fa/TUS_airport_diagram.svg/674px-TUS_airport_diagram.svg.png)
Earles, I have no idea what you're talking about, so I'll dumb it down for myself. All runway headings shown are magnetic. The declination compass even shows 11.1 degrees east with an annual rate of 0.1 degrees west. Respectfully, what's your point? :-?
Title: Re: To go True or Magnetic
Post by: CW2274 on November 02, 2015, 08:44:47 PM
CWOP wants true north in siting guide. http://www.wxforum.net/index.php?topic=21081.0;nowap
For overall comparison sake, I'm sure they do, kinda hafta. Like I said, I'm probably alone, but I prefer the straight up comparison to the NWS/FAA sites in my area.
Title: Re: To go True or Magnetic
Post by: Dr Obbins on November 02, 2015, 09:27:48 PM
While we all strive for perfection, in reality how much does it really matter? If you are off by 5° what are the consequences?
Title: Re: To go True or Magnetic
Post by: ValentineWeather on November 02, 2015, 09:53:48 PM
I would say even getting within 40 degrees with eyeballs is a win. Much harder than you would think. I tweak afterward with software.
Title: Re: To go True or Magnetic
Post by: CW2274 on November 02, 2015, 09:55:09 PM
While we all strive for perfection, in reality how much does it really matter? If you are off by 5° what are the consequences?
It doesn't. None. Merely a topic of conversation. Akin to having a brand new SHT11 to use or going with a 15. I have a 15.
Title: Re: To go True or Magnetic
Post by: CW2274 on November 02, 2015, 09:58:50 PM
Quoting the lyrics "...whichever way the wind blows..."

11.1ºE in 2005 -- at 0.1ºW per year -- means in 2015 "true" north has drifted to 10.1ºE magnetic.
Ten now, thank you. Even I won't re-calibrate for that. ;)
Title: Re: To go True or Magnetic
Post by: CW2274 on November 02, 2015, 10:01:54 PM
I would say even getting within 40 degrees with eyeballs is a win. Much harder than you would think. I tweak afterward with software.
40!!! Remind me to NEVER let you operate on me! :lol:
Title: Re: To go True or Magnetic
Post by: ValentineWeather on November 02, 2015, 10:56:30 PM
I would say even getting within 40 degrees with eyeballs is a win. Much harder than you would think. I tweak afterward with software.
40!!! Remind me to NEVER let you operate on me! :lol:
That's for sure. Reason I said 40 degrees we moved a station and it looks 40 degrees off tonight. I won't know for sure until I visit tomorrow. Could be some local direction issue however. Thought it was dead nuts on.
Title: Re: To go True or Magnetic
Post by: ValentineWeather on November 02, 2015, 10:59:47 PM
Never substitute a Proctologist-MD for a Neurologist-MD.  \:D/

But I did stay at a Holiday Inn Express.
Title: Re: To go True or Magnetic
Post by: Scalphunter on November 02, 2015, 11:07:06 PM
http://flighttraining.aopa.org/magazine/1998/August/199808_METAR_Winds_True_or_Magnetic.html


this list airports that do not give wind in magnetic heading.

 Also marine weather reports use true  headings instead of  magnetic.

John


Title: Re: To go True or Magnetic
Post by: CW2274 on November 02, 2015, 11:38:58 PM
Never substitute a Proctologist-MD for a Neurologist-MD.  \:D/

But I did stay at a Holiday Inn Express.
   :lol:
Title: Re: To go True or Magnetic
Post by: CW2274 on November 02, 2015, 11:45:23 PM
http://flighttraining.aopa.org/magazine/1998/August/199808_METAR_Winds_True_or_Magnetic.html


this list airports that do not give wind in magnetic heading.

 Also marine weather reports use true  headings instead of  magnetic.

John
Wow, not saying it can't still be the same, but that article's 17 years old.
I was in the Navy for 5 years, but certainly never a mariner.
Title: Re: To go True or Magnetic
Post by: Harryca on November 03, 2015, 12:03:29 AM
Everything is EXACT...except for the EXCEPTIONS (ha,ha)!

Way back in the day when I used to attend classes at IBM, the instructors would invariably say things like, "This is the way it always works or this is always true EXCEPT..." which always got a few chuckles from everybody.
Title: Re: To go True or Magnetic
Post by: yahtah on November 03, 2015, 12:04:44 AM
I think the real question here is how do we set a standard for aiming the anemometer. I'm grappling with that same question as I consider siting my flagpole for this. I have a short pole for the system now and aimed it at Polaris as best I could. For a deeper discussion about "North" consider reading the WiKi about True, Celestial, and Magnetic Norths.

https://en.wikipedia.org/wiki/True_north

Magnetic North is changed periodically, so maybe Celestial is the more stable reference. "North" only refers to some arbitrary place until it is defined and fixed with a bench mark.
Title: Re: To go True or Magnetic
Post by: CW2274 on November 03, 2015, 12:24:12 AM
I think the real question here is how do we set a standard for aiming the anemometer. I'm grappling with that same question as I consider siting my flagpole for this. I have a short pole for the system now and aimed it at Polaris as best I could. For a deeper discussion about "North" consider reading the WiKi about True, Celestial, and Magnetic Norths.

https://en.wikipedia.org/wiki/True_north

Magnetic North is changed periodically, so maybe Celestial is the more stable reference. "North" only refers to some arbitrary place until it is defined and fixed with a bench mark.
I never even heard of "celestial north", and people thought I was making it too complicated!
Title: Re: To go True or Magnetic
Post by: CW2274 on November 03, 2015, 12:28:17 AM
I think the real question here is how do we set a standard for aiming the anemometer. I'm grappling with that same question as I consider siting my flagpole for this. I have a short pole for the system now and aimed it at Polaris as best I could. For a deeper discussion about "North" consider reading the WiKi about True, Celestial, and Magnetic Norths.

https://en.wikipedia.org/wiki/True_north

Magnetic North is changed periodically, so maybe Celestial is the more stable reference. "North" only refers to some arbitrary place until it is defined and fixed with a bench mark.
The standard is your preference. 99% use true. Even thought it's only 10 degrees difference for me, I use magnetic.
Title: Re: To go True or Magnetic
Post by: yahtah on November 03, 2015, 12:37:32 AM
Just asking what level of accuracy do you want? How far will you go to calibrate your instrument? GPS? Is it accurate?

HAhaha!  :lol: I aimed mine at Polaris when I had a clear night. Celestial.

JMHO.  :grin:
Title: Re: To go True or Magnetic
Post by: CW2274 on November 03, 2015, 01:00:14 AM
Just asking what level of accuracy do you want? How far will you go to calibrate your instrument? GPS? Is it accurate?

HAhaha!  :lol: I aimed mine at Polaris when I had a clear night. Celestial.

JMHO.  :grin:
Oh, that celestial! I thought that was true north because that's also what I used. I then dialed in my declination on the console.
As far as my level of accuracy, I have it dialed in to a presumable plus or minus of two degrees of magnetic. 
Title: Re: To go True or Magnetic
Post by: ValentineWeather on November 03, 2015, 12:44:53 PM
Well figured out why the station we moved yesterday anemometer wind direction was so far off. The phone app was off by 30+ degrees compared to real compass. Did several more calibrations with app twirling phone and it finally started agreeing with compass. Don't trust these apps on phones I guess. :sad: The reason I used it in first place, it had declination built-in when the gps is turned on.
Title: Re: To go True or Magnetic
Post by: CW2274 on November 03, 2015, 01:21:18 PM
Well figured out why the station we moved yesterday anemometer wind direction was so far off. The phone app was off by 30+ degrees compared to real compass. Did several more calibrations with app twirling phone and it finally started agreeing with compass. Don't trust these apps on phones I guess. :sad: The reason I used it in first place, it had declination built-in when the gps is turned on.
Does that mean you're coming to the dark side and going magnetic? :twisted:
Title: Re: To go True or Magnetic
Post by: ValentineWeather on November 03, 2015, 03:36:55 PM

Does that mean you're coming to the dark side and going magnetic? :twisted:

No  :-)
Title: Re: To go True or Magnetic
Post by: CW2274 on November 03, 2015, 05:00:40 PM

Does that mean you're coming to the dark side and going magnetic? :twisted:

No  :-)
Darth will not be happy. :twisted:         






Title: Re: To go True or Magnetic
Post by: CW2274 on November 03, 2015, 05:25:48 PM
The 4-Bears (weather Rock) corollary:

FUNCTIONALLY, this is *how* I determine(d) "true" north for my VP2:

1) SPRING EQUINOX - at exactly NOON, placed a rock on the ground at the TOP (end) of the shadow from the pole.
2) SUMMER SOLSTICE - at exactly NOON, placed a rock on the ground at the TOP (end) of the shadow from the pole.
3) AUTUMANL EQUINOX - at exactly NOON, placed a rock on the ground at the TOP (end) of the shadow from the pole.
4) WINTER SOLSTICE - at exactly NOON, placed a rock on the ground at the TOP (end) of the shadow from the pole.

The "straight Line" formed by the four rock locations "points" exactly NORTH - SOUTH.

Done four years ago, I "check" things every three months: "...shadow on rock? Yep...all's OK!" (wink,wink).
Ya but, that takes a whole year. Ain't gettin' no younger! :-|
Title: Re: To go True or Magnetic
Post by: RPinCA on January 18, 2016, 03:25:46 PM
@CW2274, from another discussion I know you were with ATC, and you know I'm a GA pilot. We know that ATIS broadcasts surface winds using magnetic direction, as it corresponds to magnetic runway headings. Winds aloft are reported in geographic (true/celestial) units. I've seen conflicting information on the net regarding what we should use in a PWS. On my own, macht nichts, I'll know what I chose. But when I hook up to Wunderground (et al), I presume they would want all reporting stations in correspondence. Where I live, magnetic variation is 13.75, so the question seems relevant.

I know you chose magnetic, and I suspect your ATC background played a role in this. I tried finding the answer at Wunderground, but couldn't. Correction... I just found the answer, but I'll finish this post. I used a feature of Google search I've found helpful. My query was

wind direction magnetic or true/site=wunderground.com

The "site=xyz.com" makes a big difference in search results. I thought you might find this interesting, and hope you'll take it in a positive spirit. This is the link for the answer: http://help.wunderground.com/knowledgebase/articles/129054-how-is-wind-direction-referenced (http://help.wunderground.com/knowledgebase/articles/129054-how-is-wind-direction-referenced)

"Wind direction is referenced to true north, not magnetic. The wind display has a marker located at the wind source, with a small arrow indicating the flow of the wind."

So, in the process of asking the question, I found the answer that seems important to this community. Whether or not you'll choose to leave the dark side is an open question.  ;)
Title: Re: To go True or Magnetic
Post by: CW2274 on January 18, 2016, 05:46:14 PM
@CW2274, from another discussion I know you were with ATC, and you know I'm a GA pilot. We know that ATIS broadcasts surface winds using magnetic direction, as it corresponds to magnetic runway headings. Winds aloft are reported in geographic (true/celestial) units. I've seen conflicting information on the net regarding what we should use in a PWS. On my own, macht nichts, I'll know what I chose. But when I hook up to Wunderground (et al), I presume they would want all reporting stations in correspondence. Where I live, magnetic variation is 13.75, so the question seems relevant.

I know you chose magnetic, and I suspect your ATC background played a role in this. I tried finding the answer at Wunderground, but couldn't. Correction... I just found the answer, but I'll finish this post. I used a feature of Google search I've found helpful. My query was

wind direction magnetic or true/site=wunderground.com

The "site=xyz.com" makes a big difference in search results. I thought you might find this interesting, and hope you'll take it in a positive spirit. This is the link for the answer: http://help.wunderground.com/knowledgebase/articles/129054-how-is-wind-direction-referenced (http://help.wunderground.com/knowledgebase/articles/129054-how-is-wind-direction-referenced)

"Wind direction is referenced to true north, not magnetic. The wind display has a marker located at the wind source, with a small arrow indicating the flow of the wind."

So, in the process of asking the question, I found the answer that seems important to this community. Whether or not you'll choose to leave the dark side is an open question.  ;)
I find it somewhat laughable that WU says magnetic is not even a viable choice, but for their purposes, I guess not. Yes, I've chosen magnetic for my personal use, but 99% of the public uses true. Another thing, the arrow in the example is pointing the wrong way as the point should face where the wind is coming from, not going to. I noticed that my local TV station now does it backwards too.
I'll stick with magnetic as I like to compare with the neighboring airports, dark side and all. ;)
Title: Re: To go True or Magnetic
Post by: RPinCA on January 18, 2016, 06:03:11 PM
Quote
Another thing, the arrow in the example is pointing the wrong way as the point should face where the wind is coming from, not going to.

I noticed this trend in display style, as well. I think you and I are "old school" and understand it points opposite of the way the wind is going (rewording intentional). I remember needing to learn this characteristic as a young man.

It appears we are entering a Least Common Denominator world, where it's simply easier to reach the broader public than it is to train the broader public. Intellectual "Collateral Damage" of the Internet Age. The practice is spreading, as you noticed. Even the Wunder Weather Station has an internal display screen that mimics the Wunderground style gauge, and it is a solid, well-designed product. The reasoning behind the WWS decision is sensible; the reasons behind the reasoning are not.

I'll admit with some chagrin, this subject had me imagining ways to make a mechanical wind vane that points with the wind. I think it is do-able, although I've not yet made a prototype. My guess is the traditional pointer is a historical consequence from the days of bows and arrows.
Title: Re: To go True or Magnetic
Post by: CW2274 on January 18, 2016, 06:05:20 PM
Quote
Another thing, the arrow in the example is pointing the wrong way as the point should face where the wind is coming from, not going to.

I noticed this trend in display style, as well. I think you and I are "old school" and understand it points opposite of the way the wind is going (rewording intentional). I remember needing to learn this characteristic as a young man.

It appears we are entering a Least Common Denominator world, where it's simply easier to reach the broader public than it is to train the broader public. Intellectual "Collateral Damage" of the Internet Age. The practice is spreading, as you noticed. Even the Wunder Weather Station has an internal display screen that mimics the Wunderground style gauge, and it is a solid, well-designed product. The reasoning behind the WWS decision is sensible; the reasons behind the reasoning are not.

I'll admit with some chagrin, this subject had me imagining ways to make a mechanical wind vane that points with the wind. I think it is do-able, although I've not yet made a prototype. My guess is the traditional pointer is a historical consequence from the days of bows and arrows.
Well put.
Title: Re: To go True or Magnetic
Post by: Randall Kayfes on February 01, 2022, 03:39:09 PM
Just for kicks and I mean kicks - Polaris the North Star is Declination: +89° 21' 42.44" So you can see that Polaris is about 18' from the Celestial North Pole which the earth's true north pole generally points to. Since Polaris is not on the Celestial Pole that means it circles it. So technically the Pole star aligns with the true north of the earth twice a day. Astronomers like me have to use Pole tables or programs to align our scopes with the celestial pole based on sighting and then offsetting Polaris. Also because of orbital and lunar considerations the true north pole of the earth can get ever so slightly out of alignment with the celestial pole as well. And Polaris is a double star, so which one do you use.

So, if you really want to be accurate...  :grin:   \:D/

(Just having fun - and remember don't trust atoms - they make up every little thing...)
Title: Re: To go True or Magnetic
Post by: davidmc36 on February 01, 2022, 05:40:37 PM
Well figured out why the station we moved yesterday anemometer wind direction was so far off. The phone app was off by 30+ degrees compared to real compass. Did several more calibrations with app twirling phone and it finally started agreeing with compass. Don't trust these apps on phones I guess. :sad: The reason I used it in first place, it had declination built-in when the gps is turned on.

Phone App. Ewwww! And the GPS will only help while moving.

If you have any desire to calibrate it to anything a 50 dollar compass can be a good piece of kit.
Title: Re: To go True or Magnetic
Post by: box on February 02, 2022, 05:32:25 AM
 Mag variation in these parts is around 1degree west so to all intents and purposes can be ignored