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NorwegianWould
Joined: 07 Jan 2006
Posts: 23
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 Posted: Mon Jan 09, 2006 9:53 am Post subject: Wind chill calculation |
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Hi,
I would like to ask how wind chill is calculated. It seems to me that this figure changes with quite a high frequency in wview and I'd like to understand where it comes from. Does it use some sort of average (integrated) value for wind when the wind chill is calculated?
Jeremy |
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mteel
Joined: 30 Jun 2005
Posts: 435
Location: Collinsville, TX
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| Posted: Mon Jan 09, 2006 12:01 pm Post subject: |
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| Code: | // ... calculate the wind chill
float wvutilsCalculateWindChill (float temp, float windspeed)
{
double T1, T2, T3, T4;
double result;
if (temp >= 50.0 || windspeed <= 3.0)
{
return temp;
}
T1 = 35.74;
T2 = 0.6215 * temp;
T3 = -1.0 * (35.75 * pow (windspeed, 0.16));
T4 = 0.4275 * temp * pow (windspeed, 0.16);
result = T1 + T2 + T3 + T4;
return (float)result;
}
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For HILOW values, the high wind for a sample is used. For charting purposes and current values, the average wind for the sample period is used.
This is the standard wind chill formula currently in use by NOAA among others.
Obviously wind speed is the most dynamic weather reading. It makes sense that wind chill would change frequently as well.
Mark |
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NorwegianWould
Joined: 07 Jan 2006
Posts: 23
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| Posted: Mon Jan 09, 2006 12:21 pm Post subject: Wind chill calculation |
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| Quote: |
For HILOW values, the high wind for a sample is used. For charting purposes and current values, the average wind for the sample period is used.
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Ah, so how do I extend the sample period. Is that "ARCHIVE_INTERVAL" parameter in wview.conf, and if so, can it be set to more than 60000?
| Quote: |
Obviously wind speed is the most dynamic weather reading. It makes sense that wind chill would change frequently as well.
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Yes, that makes sense. But a more useful reading (for me) would be an averaged wind chill. For example if you want to go out for a walk or a hike, it is better to know what the average temperature 'feels like'. The VP2 console uses the 10 min average wind value, and I'd like to do that too. Is this possible with wview?
Jeremy |
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mteel
Joined: 30 Jun 2005
Posts: 435
Location: Collinsville, TX
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| Posted: Mon Jan 09, 2006 12:38 pm Post subject: |
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Hack the code - the 10-minute avg value is copied from the LOOP packet. I do not use it because I want to know the "instantaneous" readings for loop data (that's why they are called current conditions). Further, wview is moving away from using anything that is VP-specific. So if I were using it, I would change it now.
I wouldn't mess with your ARCHIVE_INTERVAL setting (misnomer, I should have called it SENSOR_INTERVAL or somesuch) - it is about to be changed to 15 seconds default with the new 3.0.0 release. VP HILOW packets will not be used at all and we need to poll for readings more (not less) often.
Chart data uses archive records which contain the wind speed average over the interval, so the chart data uses an "archive interval"-minute wind average for wind chill. That is 5 minutes for me and other values for others... |
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