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Old 02-26-2019
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Re: ambient wind vs true wind

If you think of TRUE wind as an instantaneous report... if could be showing you a GUST or a LULL and neither would tell you want the AVERAGE TRUE wind is.

AMBIENT, I believe, refers to the average wind at a particular location

Usually when we say the wind is blowing 25 knots, for example... it's actual speed varies... 22, 24, 27 and so on...

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Re: ambient wind vs true wind

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Originally Posted by Jeff_H View Post
'Ambient Wind', 'Gust', and 'Apparent Wind' are three separate terms. Ambient wind and gusts are both true winds in that they are measured from a stationary position. They are solely meteorological. Ambient wind is the average steady wind measured at a stationary point such as a weather station like Thomas Point. As NOAA defines the term 'Ambient', it means, "Of the surrounding area or environment." Gusts are a sudden and short lived increase in wind speed above the ambient wind speed. NOAA defines gust as "A rapid fluctuation of wind speed with variations of 10 knots or more between peaks and lulls." but we all know it as that sudden increase in wind.

If this was a college entrance exam, 'Apparent wind' would the one term which one does not match the other two of the three. Apparent wind is the wind measured from a moving object, such as a boat under way. It is the wind that results from combining the velocity (speed and direction) of the true wind with the boat's velocity relative to that true wind velocity.

Jeff
What he said!

Thanks Jeff!

At least I was in the ballpark with "Maybe ambient wind is what you have standing on a rock and true wind is on a boat that current could be moving". Okay not nearly as eloquent, accurate, or complete as Jeff answer.

Also, relieved to know I had not forgotten a very necessary part of set and drift.

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Old 02-26-2019
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Re: ambient wind vs true wind

To say that the ambient wind is 20 knots with gusts to 30 knots is contrary to what the word ambient implies i.e. the same all over. Around here, the marine weather forecast will say wind speed 20 knots with gusts to 30...or, wind steady at 20 knots. You can't have winds steady (or ambient) with gusts. If NOAA says otherwise, I disagree.
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Old 02-26-2019
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Re: ambient wind vs true wind

The definition of ambient is the environment that surrounds you. An average doesn't seem to contradict that definition. I can't find a definition that says its the same all over.

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Old 02-26-2019
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Re: ambient wind vs true wind

Current has no practical measurable impact of wind.

If you are measuring wind on a not stable platform... such as a boat... your wind speed measurement will sum the vectors of

current speed and direction
boat speed and direction through the water

a stable platform reads the instantaneous wind speed which likely is not constant in speed and direction

When a weather service reports wind speed and direction... they will report an AVERAGE usually noting gusts.

I have not heard the term *ambient wind* used and other than meaning some sort of average... as true is an instantaneous measurement and not reliable because of variations over time... the reported wind term may be *ambient*.

wind... YMMV

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Old 02-26-2019
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Re: ambient wind vs true wind

From
https://www.ncdc.noaa.gov/crn/measurements.html#ws

Wind Speed
A Met One Model 014A anemometer measures wind speed (in meters per second) at each station. The datalogger samples the anemometer every two seconds. Every five minutes these two-second samples are averaged to obtain 5-minute values.

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Re: ambient wind vs true wind

Ok to confuse things more or maybe clarify (it's the offseason right) I found text that led to my question. The term there was not ambient wind it was ground wind.

It's from NauticEd Sailing School - Learn to Sail and Get Certified the course is, "learn electronic-navigation"

If anyone is interested here's the text:

By definition, the True Wind is the wind you feel when you are stationary with the water. Note that in this case the apparent wind equals the true wind.

Thus, we must define the difference between Ground Wind and True Wind. But wait, are they not the same? Well no! Think of this: In a current flowing at 5 knots, you stop the boat and drift perfectly with the current while measuring the wind speed. Since boat speed is zero, True Wind must equal Apparent Wind right? Right!

Now hop off the drifting boat and stand on a rock. The wind you feel will change. Since you are stationary now on the ground and with satellites, this is called the Ground Wind and you can see it is potentially significantly different from True Wind. But that’s not really a problem because since the sailboat operates in water albeit moving, the boat is not too concerned with Ground Wind. It’s almost like acknowledging that the Earth is spinning and moving through the solar system, the boat is not concerned with that at all.

The above discussion helped us understand that True Wind is the wind the boat feels when stationary with the water.

You probably had not considered that before, but it now makes sense. If we were operating in a high tidal current situation, by definition, when we tack the boat on moving water, the true wind must stay a consistent direction throughout all of the directions that the boat will head.

When sailing, you are more interested in the effect the wind has on the boat rather than measurements from a purely meteorological point of view, so True Wind is the preferred choice over Ground Wind.

However, racing navigators constantly convert between True Wind and ground wind to determine the accuracy of weather forecasts which use Ground Wind. This would be especially pertinent when navigating the Gulf stream off of the east coast of the USA or the EAC (East Australian Current)."

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Re: ambient wind vs true wind

An informative piece JoCoSailor but there is nothing in there about ambient wind, isn't that what we were discussing? The previous post by jblumhorst explains a bit about how wind is measured but again, no mention of ambient wind.
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Re: ambient wind vs true wind

Quote:
Originally Posted by paulinnanaimo View Post
An informative piece JoCoSailor but there is nothing in there about ambient wind, isn't that what we were discussing? The previous post by jblumhorst explains a bit about how wind is measured but again, no mention of ambient wind.
Right, that was my mistake I was confusing the two. "I found text that led to my question. The term there was not ambient wind it was ground wind.:

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Old 02-26-2019
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Re: ambient wind vs true wind

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Originally Posted by JoCoSailor View Post
What he said!

Thanks Jeff!

At least I was in the ballpark with "Maybe ambient wind is what you have standing on a rock and true wind is on a boat that current could be moving". Okay not nearly as eloquent, accurate, or complete as Jeff answer.

Also, relieved to know I had not forgotten a very necessary part of set and drift.
Ignore current for this concept when you think of apparent wind factor in the boat's speed over ground which factors in current a little bit but mostly speed through the water.

The apparent wind is the angle and wind speed the boat feels. What the wind indicator at the top of the mast shows would be your apparent wind angle. Which would factor in the true wind and the boats speed and course over ground. I thought the AC72s would be a good example of the difference between these because the boat speed could actually exceed wind speed so the angle difference between true and apparent is fairly significant.

Americas Cup AC72 true versus apparent wind | Sailing Blog by NauticEd

Jordan
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