Analysis of Biases in Mox's Fallbrook Temperatures

T. Chester and G. Moxon

The plots below show a comparison of Mox's temperatures in 11/1996 thru 9/1997 to the official Fallbrook temperatures:

(Click on graph for bigger and better image.)

(Click on graph for bigger and better image.)

Two lines are shown for comparison: one that represents identical temperatures, and one where Mox's temperatures are 10o hotter than the official temperatures. (10o is an interesting comparison since it could result from a typo in the tens digit.)


The high temperature bias turns out to be directly related to the elevation of the sun, as shown in the following plots. The leftmost plot plots the bias versus date; the rightmost plot plots the bias versus official high temperature.

(Click on graph for bigger and better image.)

(Click on graph for bigger and better image.)

The bias is well correlated with date. It peaks at the summer solstice, where the sun elevation is the highest, and is a minimum at the winter solstice, where the sun elevation is the lowest. The bias is poorly correlated with the official high temperatures.

A similar bias is also present in high temperature data collected by T. Chester using a thermometer in Altadena that was placed virtually identically to the position of Mox's thermometer in Fallbrook. Both thermometers were placed about a foot lower than the roof on the north side of a structure. This placement seems so eminently reasonable that both of us independently made that choice, but radiation and conduction from the roof through the structure is apparently enough to create the observed bias. After all, roofs heat up to above the mid-100o range in the full summer sun, which provides plenty of heat radiation and heat conduction a foot away from the roof, even if it is on the other side. This heat input is what causes attics to get so hot in the summer sun as well.

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Copyright © 1997 by Tom Chester and Gaylord Moxon.
Permission is freely granted to reproduce any or all of this page as long as credit is given to us at this source:
Comments and feedback: Tom Chester | Gaylord Moxon
Last update: 30 December 1997.