[wxqc] Dew Point Error for CW6532 Tucson

[Evan Bookbinder]

Phil,

You can check your thermometer's/hygrometer's (dewpoint) accuracy with a sling psychrometer or other calibrated measuring device, but I'm willing to bet that they're measuring correctly.

The first thing that catches my eye is that you have the temp/dpt attached to a 6 ft. sensor from your rooftop (not familiar with the term parapet, so maybe I'm wrong). While this is fine for the anemometer and even the rain gauge, the temperature/dpt sensors should be located at 2m off the ground (5-6 feet). Very sharp inversions can set up at night, on the order of 5-10F within 30-40 feet of the surface, especially where terrain and standing water bodies are an issue. Likely you're sampling a "different airmass" above your roofline than you would be closer to ground level. 

Evan


  ----- Original Message ----- 
  From: Phil Gilmer 
  To: wxqc at lists.gladstonefamily.net 
  Sent: Tuesday, October 03, 2006 9:44 PM
  Subject: [wxqc] Dew Point Error for CW6532 Tucson


  Hi,

  I have a relatively new (June 06) Davis Vantage 2 set up on my roof (6' mast attached to the parapet) here in the foothills of the Rincon Mountains in Tucson and am recently getting reported errors for dew point. I notice there is also a significant difference in my temperatures at night vs the analysis (my actual readings are higher by over 10F just before sunrise ) which are explained in the quality report as likely due to proximity to metro area. Do you think I need to consider having the sensor re-calibrated? 

  There is a significant mean error in your dew point readings. You may need to calibrate your dew point sensor. Adjust your sensor to read 3.0 °F higher. Your readings are not within an acceptable error range. The automated problem analysis cannot identify the problem. You can sign up on the wxqc mailing list and post information about this situation there. This is may be caused by poor siting of the sensor (e.g. under eves, in screen porch, or in thick tree coverage). For information on siting, see CWOP Station Guide.

  I agree with the post I saw today re posting known error factors; these would be good to know..... Also wonder how much data (days, weeks?) are considered a valid statistical sample?

  By the way the unit is on the tallest part of the house and not near flues or vents. The house is situated on a ridge that is approx 40-50 ft higher than the arroyos on either side. The drive way goes through one of the arroyos and if I walk thru at night or early in the morning the temperature is noticeably cooler near the bottom. Also noticed the rare fog collects there as well. Please let me know what you think or if you could use more information. Thanks! 


  Phil




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