[wxqc] Temperature Measurement Problems

Fri Aug 19 00:23:14 EDT 2005

  _____  

From: wxqc-bounces at lists.gladstonefamily.net
[mailto:wxqc-bounces at lists.gladstonefamily.net] On Behalf Of Dave Helms
Sent: Thursday, August 18, 2005 10:03 PM
To: Discussion of data quality issues
Cc: kenneth.labas at noaa.gov; Nolan Doesken; jim.allsopp at noaa.gov
Subject: Re: [wxqc] Temperature Measurement Problems

Hi Jefferey,

I looked at your neighbors data and your recent reports.  
http://www.findu.com/cgi-bin/wxpage.cgi?call=CW4066
<http://www.findu.com/cgi-bin/wxpage.cgi?call=CW4066&last=720> &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
<http://weather.gladstonefamily.net/qchart/C4066?date=20050817&addnl=KDPA&Ad
d+to+charts=Add+to+charts&.cgifields=addnl>
&addnl=KDPA&Add+to+charts=Add+to+charts&.cgifields=addnl

http://weather.gladstonefamily.net/qchart/C4066?date=20050816
<http://weather.gladstonefamily.net/qchart/C4066?date=20050816&addnl=KDPA&Ad
d+to+charts=Add+to+charts&.cgifields=addnl>
&addnl=KDPA&Add+to+charts=Add+to+charts&.cgifields=addnl

http://weather.gladstonefamily.net/qchart/C4066?date=20050815
<http://weather.gladstonefamily.net/qchart/C4066?date=20050815&addnl=KDPA&Ad
d+to+charts=Add+to+charts&.cgifields=addnl>
&addnl=KDPA&Add+to+charts=Add+to+charts&.cgifields=addnl

http://weather.gladstonefamily.net/qchart/C4066?date=20050814
<http://weather.gladstonefamily.net/qchart/C4066?date=20050814&addnl=KDPA&Ad
d+to+charts=Add+to+charts&.cgifields=addnl>
&addnl=KDPA&Add+to+charts=Add+to+charts&.cgifields=addnl

http://weather.gladstonefamily.net/qchart/C4066?date=20050813
<http://weather.gladstonefamily.net/qchart/C4066?date=20050813&addnl=KDPA&Ad
d+to+charts=Add+to+charts&.cgifields=addnl>
&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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