[wxqc] Temperature Measurement Problems

[Dave Helms]

Hi Jefferey,

I looked at your neighbors data and your recent reports. 
http://www.findu.com/cgi-bin/wxpage.cgi?call=CW4066&last=720

Its been warm and the sun is still relatively high inclination for your 
latitude which causes at least some elevated temperatures in stations 
receiving direct sun, particularly those which have passively aspirated 
radiation shields (which is the norm for most weather stations).  Russ 
references a study made by Gearld Gill (e.g. the "Gill" shield) that 
documented elevated temps in passively aspirated shields here:  
http://www.wxqa.com/shields.html

The other issue you picked up on is the proximity to the trees.  Its 
been dry in your area, http://www.drought.unl.edu/dm/monitor.html, and 
outside of the tree canopy, the soil is getting baked dry and holding 
more and more summer heat.  However in your local area, the combination 
of shade and resulting moderated soil temperatures help moderate your 
local temperatures.  We also see situations where stations in the outter 
ring of city suburban regions appear to be (are in fact) cooler than 
stations closer to the city heat  islands (this is the case with my 
station with corn fields to my north and the DC metro concrete jungle to 
my south). 

So in my opinion, you are very accurately measuring temperature for your 
local area.  This is exactly the type of micro-climate we want to 
characterize with very dense CWOP station network.  I know the MADIS 
QCMS statistics show your station as having mean temperature too cool, 
but I believe your "cool" bias is real so I would not be concerned about 
the difference.  As your area gets stronger winds and lower sun angles 
with the advance of the fall season, your cool bias will be reduced and 
you will get a "green check". 

For not knowing much, you seem to have figured out great deal!

Dave
CW0351

Jeffrey Mack wrote:

> I recently installed a Davis Vantage Pro2 aspirated weather station 
> and began collecting data and feeding it to CWOP. So far, my 
> temperature data is not meeting the CWOP quality goals determined by 
> comparing my measures with predicted values for my location. The 
> neighborhood we live in has many tall oak trees and our yard backs up 
> to a wooded forest preserve area. I situated the Davis temperature and 
> humidity sensors on a 5' post approximately 50 feet from the edge of 
> the wooded area and about 35' from our house. The anemometer is 
> attached to a tv antenna mast on our roof about 30' feet up. Presently 
> this site is in full sunlight from approximately 10 AM to about 3:30 
> PM. In the morning hours the site is shaded by our house and in the 
> afternoon it is shaded by the woods.
>
>  
>
> Our temperature readings are consistently below the predicted values 
> with a noticeably bigger difference that often occurs beginning around 
> 12 noon local time. However the nearest other reporting site  (1 ½ 
> miles away), DuPage Airport, reports temperature that follow our 
> readings noticeably closer than the predicted values. How are the 
> predicted data in the analysis calculated? And are my readings 
> possibly more accurate due to the use of an aspirated temperature 
> shield vs. nearby stations using  non-aspirated shields which may tend 
> to maintain more heat as the day goes on? Or am I simply being 
> affected adversely by the proximity of the wooded area. But if that be 
> the case, why is DuPage closer to my readings than to the predicted 
> readings?
>
>  
>
> I am curious about how one assesses the quality of a temperature 
> reading in general. If one measures temperature in an area where there 
> are numerous trees, is this reading any less accurate than one taken 
> in area without trees?
>
>  
>
> Here are links for several days to our data and analyses:
>
>  
>
> http://weather.gladstonefamily.net/qchart/C4066?date=20050817&addnl=KDPA&Add+to+charts=Add+to+charts&.cgifields=addnl 
> <http://weather.gladstonefamily.net/qchart/C4066?date=20050817&addnl=KDPA&Add+to+charts=Add+to+charts&.cgifields=addnl>
>
>  
>
> http://weather.gladstonefamily.net/qchart/C4066?date=20050816&addnl=KDPA&Add+to+charts=Add+to+charts&.cgifields=addnl 
> <http://weather.gladstonefamily.net/qchart/C4066?date=20050816&addnl=KDPA&Add+to+charts=Add+to+charts&.cgifields=addnl>
>
>  
>
> http://weather.gladstonefamily.net/qchart/C4066?date=20050815&addnl=KDPA&Add+to+charts=Add+to+charts&.cgifields=addnl 
> <http://weather.gladstonefamily.net/qchart/C4066?date=20050815&addnl=KDPA&Add+to+charts=Add+to+charts&.cgifields=addnl>
>
>  
>
> http://weather.gladstonefamily.net/qchart/C4066?date=20050814&addnl=KDPA&Add+to+charts=Add+to+charts&.cgifields=addnl 
> <http://weather.gladstonefamily.net/qchart/C4066?date=20050814&addnl=KDPA&Add+to+charts=Add+to+charts&.cgifields=addnl>
>
>  
>
> http://weather.gladstonefamily.net/qchart/C4066?date=20050813&addnl=KDPA&Add+to+charts=Add+to+charts&.cgifields=addnl 
> <http://weather.gladstonefamily.net/qchart/C4066?date=20050813&addnl=KDPA&Add+to+charts=Add+to+charts&.cgifields=addnl>
>
>  
>
> I'm sure there's a lot that I don't understand about what is happening 
> here so I will appreciate any help and suggestions to improve both the 
> quality of data that I am providing and my understanding of the science.
>
>  
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>------------------------------------------------------------------------
>
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