Cumulus Support

Posted: **Wed 09 Feb 2011 1:06 am**

steve wrote:Does your calculated value agree with the Cumulus <#apptemp> web tag? Hopefully!

Steve, I just created a PHP function with the information provided by 'fracto' and I have added the apparent temperature on my [link removed] (both, the calculated one and the one provided by Cumulus) - at the time of writing this message, both temperatures were equal.

Posted: **Thu 10 Feb 2011 9:30 pm**

Interesting to see slight differences. This can probably be explained by the computation processes used by the different languages. Since this is an empirical index, small differences are not important. I checked them in parallel for several hours, at higher dry bulb temperatures (summer here in Oz), and there were no differences that I noticed.

BTW, Ray, nice looking, comprehensive web page.

DN

Posted: **Thu 10 Feb 2011 10:04 pm**

Currently showing 0.9 and 1.6; I'm surprised there's such a difference.

Posted: **Thu 10 Feb 2011 10:17 pm**

I think the difference is because I'm using a slightly different formula for vapour pressure (there are quite a few).

Posted: **Sat 18 Jun 2011 11:43 am**

beteljuice wrote:If the original precedence is correct, then I think this is the way it should look (untested !!!)

Code: Select all

<script type="text/javascript">

/* Apparent Temperature

Version including the effects of temperature, humidity, and wind: AT = Ta + 0.33×e − 0.70×ws − 4.00

Ta = Dry bulb temperature (°C)

e = Water vapour pressure (hPa) [humidity]

ws = Wind speed (m/s) at an elevation of 10 meters

The vapour pressure can be calculated from the temperature and relative humidity using the equation: 

e = rh / 100 × 6.105 × exp ( 17.27 × Ta / ( 237.7 + Ta ) )

where: 

rh = Relative Humidity [%]

*/


my_Ta = <#temp>; // degrees C

my_e = <#hum> / 100 * Math.exp( 17.27 * my_Ta / ( 237.7 + my_Ta));

my_ws = <#wlatest> * 0.27777; // windspeed converted from km/h to m/s

my_AT = my_Ta + 0.33 * my_e - 0.7 * my_ws - 4; // precedence is my_Ta + (0.33 * my_e) - (0.7 * my_ws) - 4


// tidy up

my_AT = ( Math.round(100* my_AT)/100, 1).toFixed(1); // rounds up to one decimal with trailing .0 if required


document.write(my_AT);
</script>

Your code looks great Beatle Juice. I have tested it, and just a few adjustments:
replace the my_e with:

Code: Select all

my_e = <#hum> / 100 * 6.105 * Math.exp( 17.27 * my_Ta / ( 237.7 + my_Ta));

and:

Code: Select all

precedence is my_Ta + (0.33 * my_e) - (0.7 * my_ws) - 4

I used this. The original equation didn't work at the time, but may have been atributed to the following problem:

Code: Select all

my_AT = ( Math.round(100* my_AT)/100, 1).toFixed(1); // rounds up to one decimal with trailing .0 if required

should take out the ",1". I put:

Code: Select all

var AT = (Math.round(10 * AT)/10) .toFixed(1);

. Of course you can times by 100 then divide by 100. Makes no difference.
then change to this:

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document.write(my_AT + "<#tempunit>");

just to tidy it up.
I've tested it and compared it with the chart supplied here: http://www.bom.gov.au/info/thermal_stress/ and works well (spot on).
Thanks for all the hard work Beetle Juice. I was going to do it after finding the equation on the BOM.gov.au site, but once again, why re-invent the wheel when you have Sandaysoft.com!

Posted: **Sat 18 Jun 2011 2:25 pm**

Your code looks great Beatle Juice. I have tested it, and just a few adjustments:
replace the my_e with:
Code: Select all
my_e = <#hum> / 100 * 6.105 * Math.exp( 17.27 * my_Ta / ( 237.7 + my_Ta));

That and the extra ", 1"
My bad

- good job I put the "English" formula so you found it

Cumulus Support

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