Chester County PA - Analytical Battle of Actual vs. Altered Climate Data

[ChescoWx]

6 hours ago, chubbs said:

Nope. The Chesco COOPs cool significantly relative to the SE PA Division data from the PA climatologist. Regression isn't a good tool because the station changes are sudden not gradual and you picked an interval that started after the initial Coatesville move and ended before the West Chester move took full effect. If you widen the interval to 1941-1975, the difference in slope is large.

Per table below, comparing the five years before the first move and the five years after the last move, the Chesco COOPs cool by 1.7F relative to the SE Pa Division. Note that the Pa SE Division includes the Chesco Coops so the two items compared are not independent. For that reason it is not surprising that the delta for the SE PA is slighly smaller than ABE. 

Funny seeing your persistent effort to dismiss what the the raw data from Chester County clearly shows.  The 3 stations each cooled significantly after the 1945-1970 moves: first Coatesville cooled relative to Phoenixville and West Chester; then Phoenixville cooled relative to Coatesville and West Chester; and finally West Chester cools relative to Coatesville and Phoenixville.  Clear as day in the raw COOP data.

 

 

All three stations cooled at statistically the same rate as the surrounding stations. Additionally, in looking closer at potential TOB adjustments one may wonder why the West Chester 2NW and Coatesville 1SW records which predominantly relied on morning (AM) observations...so one would think the Raw TOB Distortion of an AM reading captures a naturally lower minimum, meaning the raw data was technically already too cool correct? The NCEI Adjustment you would think logically would be to correct for morning bias at Coatesville and West Chester by warming the historical record. However, NCEI's automated, grid-wide homogenization algorithms actually did the opposite by applying additional sweeping chilling adjustments to both of these stations data from 1895 through 1982. 

[ChescoWx]

Of course @chubbsWidening the interval to 1941 - 1975 does not change the previous answer. Both series show a real, statistically significant cooling trend on their own — this isn't noise, and it fits the well-documented mid-century cooling that shows up across the eastern US from the 1940s into the 1970s.

Are the two trends statistically the same?

This is the more interesting question, and the answer depends on the test:

• Naive comparison (treating the two trends as independent): the difference in slopes (−0.66 vs. −0.46 °F/decade) gives t = −0.92, p ≈ 0.36 — not remotely significant. By this test they're indistinguishable.
• Paired comparison (the right test here, since both series describe the same regional weather in the same years — they're correlated at r = 0.83, so a paired test on the year-by-year difference is more powerful): the difference series trends at −0.021 °F/yr (−0.21 °F/decade), 95% CI [−0.042, +0.001], p = 0.057.

So the more rigorous test lands just on the wrong side of the conventional 0.05 cutoff — the station data cooled somewhat faster than the division average, and that gap is close to, but doesn't quite clear, statistical significance. The honest read: the two trends are not clearly, statistically different so no need to cool the raw data further as they are already a strong match.