When looking at some of my 'yearly' charts (see
https://fletchers-uk.com/weather/index.html), the other day, I was
struck by how low the 'peaks' in the Solar Radiation and UV graphs were.
On a sunny day in the summer (yes - we do have such days in Buffalo!), I
typically see Solar Radiation numbers above 900 and UV values above 7
for at least a couple of hours around solar noon, but the peaks of the
yearly graphs barely exceed 325 and 2, respectively. A (very) little
thought revealed the reason for this - the longer term charts average
the raw values recorded over periods of more than 24 hours (a week, in
my case), so the averages displayed on the charts include a large number
of entirely predictable nocturnal zero readings. In the depths of a
Buffalo winter, it is dark for 15 hours out of the 24, and even in high
summer here it is dark for a bit less than 9 hours out of 24.
'Straight' averages are easy to compute, and make reasonably good sense
for displaying the majority of weather-related measurements, which
typically have no particular diurnal pattern - or, at least, not such an
extreme one - but it doesn't seem totally to make sense to use them when
you know in advance that there is such a pattern. OTOH, it clearly
wouldn't be very useful just to record and display the daily peak values
for these measurements, since that would treat otherwise cloudy days
during which the sun appeared through the clouds for ten minutes around
noon in the same way as days on which the sun shone out of a cloudless
sky from dawn to dusk. Some averaging is needed.
One possibility that might produce (IMHO) more meaningful results is
'non-zero averaging' - do not count zero values in computing the
average. Solar Radiation rarely reads as zero during the day, so the
results of this calculation should correspond reasonably well to a
daytime-only average. Daytime UV readings, OTOH, are frequently zero if
it is reasonably heavily overcast, so 'non-zero averaging' would produce
misleadingly high 'average' values on days with variable cloud cover.
A second, and, I think, better, possibility would be to explicitly
record and average only daytime values for both readings - defining
daytime as being between sunrise and sunset for the date and the
station's location.
It might also be of interest to record and display the average daily
number of minutes/hours for which the reading exceeded a particular
threshold, and/or the level reached for at least a certain length of
time - the thresholds in each case being determined in advance - but
computing these results on the fly would likely be more challenging.
I am going to be playing with implementing these ideas over time, but I
would like to hear others' thoughts.
--
Peter R. Fletcher <[email protected]>
Home Page - https://pfletch.fletchers-uk.com
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