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Apparent Temperature seems wrong
Posted: Sun 24 Feb 2013 12:37 am
by dw5869
Hi There
seems the Apparent Temperature has gone screwy , im using the latest version v1.9.3 (1053)
the only thing that has changed recently the wind sensor my my wx station became faulty (seems ants like to eat the eletronics) , so its reading 0 all the time, not sure if that is affecting the Apparent Temperature?
ive included the log files for last month and this month.
Re: Apparent Temperature seems wrong
Posted: Sun 24 Feb 2013 1:13 am
by beteljuice
If you have no wind speed, you effectively have no windchill factor.
Re: Apparent Temperature seems wrong
Posted: Sun 24 Feb 2013 11:35 am
by dw5869
Hi Beteljuice, i guess it depends what formula is used for the AT.
it used to be pretty close to the BOM reading near here, but lately its been off. so not sure if its when i upgraded to the later version or if it is indeed the wind sensor that is now thrown it out since its always 0km/h from the north.
maybe its time to get a new one rather then trying to fix the wind sensor, as a bonus the newer ones come with that solar sensor.
Code: Select all
WBGT = 0.567 × Ta + 0.393 × e + 3.94
where:
Ta
= Dry bulb temperature (°C)
e
= Water vapour pressure (hPa) [humidity]
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 [%]
Source: American College of Sports Medicine, Prevention of thermal injuries during distance running - Position Stand. Med.J.Aust. 1984 Dec. 876
Version including the effects of temperature, humidity, and wind:
AT = Ta + 0.33×e − 0.70×ws − 4.00
Version including the effects of temperature, humidity, wind, and radiation:
AT = Ta + 0.348×e − 0.70×ws + 0.70×Q/(ws + 10) − 4.25
where:
Ta
= Dry bulb temperature (°C)
e
= Water vapour pressure (hPa) [humidity]
ws
= Wind speed (m/s) at an elevation of 10 meters
Q
= Net radiation absorbed per unit area of body surface (w/m2)
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 [%]
Source: Norms of apparent temperature in Australia, Aust. Met. Mag., 1994, Vol 43, 1-16
beteljuice wrote:If you have no wind speed, you effectively have no windchill factor.
Re: Apparent Temperature seems wrong
Posted: Sun 24 Feb 2013 12:03 pm
by steve
dw5869 wrote:Hi Beteljuice, i guess it depends what formula is used for the AT.
Cumulus uses the formula that's linked to in the FAQ. That hasn't changed. It uses temperature, humidity, and wind speed, so if you have no wind speed that's going to affect the calculation.
Re: Apparent Temperature seems wrong
Posted: Sun 24 Feb 2013 12:22 pm
by dw5869
Thanks Steve, i guess that solves the mystery
hope the server move went well, wasn't able to get to the faq the other day, and as soon as i posted this question the website went offline...
steve wrote:dw5869 wrote:Hi Beteljuice, i guess it depends what formula is used for the AT.
Cumulus uses the formula that's linked to in the FAQ. That hasn't changed. It uses temperature, humidity, and wind speed, so if you have no wind speed that's going to affect the calculation.