Saturday, December 18, 2010

Canadian Heat Waves Part 4E

Count of Days for each Degree Deviation from Baseline.

To see if there is any change over all in temps, not just the extreme ends, requires a counting of the number of days at each degree C deviation from each station's baseline.

This produces a large matrix of deviations from baseline of a range between -40 and 21 in columns, each year in rows and the count of days in each intersecting cell.

The highest number of days should be around the baseline (zero), and looks like this:

A nice normal distribution curve. Each individual year will show the same shape. But does the apex change over the years? Is "global warming" shifting the apex?

Not over all, however, the 1930's and 1940's has the highest shift in the apex.

Is the count changing for each degree above or below the baseline. That is, if summers are indeed cooling then the number of days at temps above the baseline should be dropping. Indeed they are:

Because there are a different number of over all days in the last years (due to missing records), this was done as a percent of each year's count of records. 5C, 6C and 7C anomalies above the baseline are dropping. Fewer days are in each of those ranges. The drop is steeper with 8C, 10C and 12C above baseline:

15C is a nice example of the 1930's being exceptionally hot with more days in this range than any other time in the past 100 years:

But what about the other end, below the baseline, is that changing with time? Doesn't appear to be, -5C, -10C and -15C deviations are flat trends:

So what is happening is since 1920, at least, there are fewer days in the hotter ranges of the year. Not changes in the mid-range temps. This shows a narrowing of the range of swings in temps. And it is not not just the highest of TMax, but all the range of temps of TMax above the average. Summers are not getting as hot today than they did in the 1930s and 1940's.

So if the above baseline is losing days, but the but the below baseline is not changes, where are those days going? They are going into the range very close to the baseline. This is the change in the share the deviation from the baseline is zero:

So over time since the 1920's at least, the bell shape of each year is tending to narrow with fewer days above the baseline, but taller near the baseline. Something to test for.

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