For myself, I found that for a yearly chart, using a bar chart with the daily averages, and a crosshair to display the daily maximum, a comprehensive way to display solar readings.
Peter Fletcher schrieb am Donnerstag, 16. März 2023 um 00:29:26 UTC+1: > In order to look at different ways of presenting solar and UV radiation > data, I dumped the contents of weewx.sdb to a csv file and used Excel to > manipulate and chart the relevant data. The attached charts show daily > averages for solar and UV radiation for four-month summer and winter > periods in 2021 and 2021/22. More (probably 'simple') averaging would > probably be done in producing yearly charts for a website, but I thought it > helpful to get a somewhat more granular picture of the processed data. For > all the charts and both types of data, 'Avg ...' uses the current > calculation (simple averaging of all readings for the 24 hr day), 'NZ Avg > ...' represents the average of all non-zero readings acquired during the > 24hr day, and 'Day Avg ...' represents the average of all readings > (including any zeroes) recorded between sunrise and sunset (calculated for > my location and the date by the standard NOAA method). > > For solar radiation, in both seasons, the non-zero and daytime averaging > methods produce almost identical results (there are only a few places where > the two lines do not coincide), and the numbers generated are a bit more > than 1.6 times the simple average numbers in the summer and well over twice > the simple average numbers in the winter. This additional seasonal > difference is, of course, a result of the non-zero winter averages not > being 'diluted' by the zero values from the longer nights. The results of > the two more complex averaging methods make more sense to me as a way to > present solar radiation readings for long time-periods. Non-zero averaging > is computationally simpler and would probably be my preferred way to go. > > For UV radiation, the picture is rather different. Here, the simple > average numbers are again lowest, but the other two averaging methods > produce substantially different results, with non-zero averaging giving > (particularly in the winter) results up to three times those generated by > non-zero averaging. Here, I think daytime averaging makes more sense. As I > indicated in my earlier post in this thread, I thought that non-zero > averaging for UV radiation was likely to produce 'average' results that > were distorted by periods of sunshine during an otherwise cloudy day, and I > believe that this is a substantial contributor to what is happening here. > Assuming, however, that stations which have UV sensors generally also have > solar radiation sensors, it might be computationally simpler to average UV > radiation readings if/when the accompanying solar radiation values are > non-zero. > > Any thoughts or comments? > > On Saturday, March 11, 2023 at 4:05:18 PM UTC-5 Peter Fletcher wrote: > >> 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 >> >> -- You received this message because you are subscribed to the Google Groups "weewx-development" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/weewx-development/8247f6d8-59ad-4a8e-adf2-4ca6671b686bn%40googlegroups.com.
