[wxqc] Text to Degrees

[Evan Bookbinder]

To determine average wind direction without having the 0 to 360 cross over 
problem, winds are broken down to their U (east/west) and V (north/south) 
components with the origin being in the center at calm. This ensures proper 
averaging irrespect to the arbitrary numeric values assigned in the compass.

For example, a due west wind of X mph would have a 100% positive U value of 
X and 0 for V; north would be 0,-X; east would be -X,0; and south wind would 
be 0,X. Other wind directions would be broken down into U and V using proper 
trigonometry.

Evan


----- Original Message ----- 
From: "Victor Engel" <brillig at gmail.com>
To: "Discussion of weather data quality issues" 
<wxqc at lists.gladstonefamily.net>
Sent: Sunday, April 08, 2007 12:52 PM
Subject: Re: [wxqc] Text to Degrees


> I'm not sure what an average wind direction even means. There are
> probably many approaches to averaging wind direction. One would be to
> imagine a line being drawn from an origin. The line is drawn one unit
> in the direction of the wind for each time interval. The first line is
> drawn from the origin. The next is drawn from the endpoint of that
> line, etc. The average direction is then the direction of the overall
> line from the origin.
>
> Of course, this is not well defined. Consider if the wind direction
> changed one degree every minute for 6 hours, in the same direction
> each time. What you'd end up with is a polygon with 360 sides ending
> up at the origin. Since it's at the origin, there is no direction.
>
> Another approach would be to think of the directions as baskets on
> corners of a 16-pointed scale. Each time you measure wind in a certain
> direction, add an item to that basket. The average would then be the
> direction the scale pointed, which would be the direction of the
> center of gravity of the baskets.
>
> But I'm not so sure average direction is even meaningful, except on
> the short term, where it's relatively consistent. Then you can use a
> simple average. In this case, what I do is add 180 degrees mod 360 if
> the number is close to 0 or 360, then subtract 180 degrees again mod
> 360 after performing the average.
>
> On 4/8/07, Norm Shea <Norm.Shea at kiawah-owners.org> wrote:
>>
>>
>> Is there an accepted protocol determining the predominant wind direction 
>> by
>> averaging?   I've converted wind directions from text to degrees using 
>> the
>> basic format
>>
>>
>> N     0
>>
>> NNE   23
>>
>> NE    45
>>
>> ENE   68
>>
>> E     90
>>
>> ESE   113
>>
>> SE    135
>>
>> SSE   158
>>
>> S     180
>>
>> SSW   203
>>
>> SW    225
>>
>> WSW   248
>>
>> W     270
>>
>> WNW   293
>>
>> NW    315
>>
>> NNW   338
>>
>>
>>
>> but I'm thinking that averaging is going to weight things.
>>
>>
>>
>> Thanks,
>>
>> Norm
>>
>>
>>
>> Norm Shea
>> Director, Lakes Management
>> Kiawah Island Community Association Inc
>> 20 Kestrel Court, Kiawah Island, SC 29455
>> Phone 843-768-2315 x 255  Fax 843-768-0298  Mobile 843-708-3608
>> Norm.Shea at kiawah-owners.org --- www.kiawah-owners.org
>>
>> _______________________________________________
>> wxqc mailing list
>> Post messages to wxqc at lists.gladstonefamily.net
>> To unsubcribe or change delivery options, please go to:
>> http://server.gladstonefamily.net/mailman/listinfo/wxqc
>>
>> The contents of this message are the responsibility of the author.
>>
> _______________________________________________
> wxqc mailing list
> Post messages to wxqc at lists.gladstonefamily.net
> To unsubcribe or change delivery options, please go to:
> http://server.gladstonefamily.net/mailman/listinfo/wxqc
>
> The contents of this message are the responsibility of the author.
>