Hi Anton - As you point out, this method is fraught with issues, rendering a result that at best is a guesstimate. It is not Karen's "shadow" aspiration. It certainly does not fit my definition of "sunshine".
I live in Phoenix Arizona. A day with full, honest-to-goodness (by my definition) sunshine looks like this at my Davis wx station: [image: Screenshot 2024-05-03 073913.png][image: Screenshot 2024-05-03 073545.png] This undeniably represents "sunshine". (The missing bit in the early morning is due to the mountain ridge immediately east of my station.) Here's a screen shot of the past 7 days of sunshine: [image: Screenshot 2024-05-03 074219.png] I can promise you that on both 26 and 27 April the sky was BKN, and using Karen's approach of casting a shadow, both of those days had significant periods during the day where no obvious shadow was cast. BUT, while I don't have the evidence at the same temporal resolution as the previous two graphs for those days, I can all but guarantee that the insolation didn't drop below 200 w/m^2. So, according to the WHO definition, days 26 and 27 were also days of full sunlight. That's bogus. Yet, For Phoenix boosterism, they can claim even the days 26 and 27 as days of sunshine. In fact, even during the months of July and August, when we enter the monsoon, with full overcast and infrequent rain, rarely does the sensor drop below 200 w/m^2. Only when a T-storm cell passes directly over the station does it fall to 100 w/m^2 or less. My point is that "sunshine" is an ambiguous and arbitrary term, with the definition and the methods for determining situational and motivated not by observation, but by interpretation. Unless we all agree to set our sensors in a specific way, and to use the same arbitrary threshold values, one cannot directly compare one station's estimate of sunshine with another station's estimate. I look forward to seeing how Karen's new instrument behaves. I think I understand the principle, yet it too makes a boatload of assumptions to generate its result. And for that instrument, as the sun approaches zenith (here it gets to 80 deg at the summer solstice), the data from that sensor becomes even more ambiguous. Cheers - Jon N7UV On Friday, May 3, 2024 at 1:04:34 AM UTC-7 Anton vanNwnhzn@GMail wrote: > WMO (World Meteorological Organization ) defines sunshine-duration as the > accumulating time each day that direct sunshine-radiation exceeds a level > of 120 W/m2 > That definition is simple enough, and many PWSes calculate along that > setup, but 'devil is in the details'. > Perhaps puristic approach, but Sunshine might be very fluctuating in level > and will meet your sensor from different angles with different wavelengths. > 'Problem0' is that you need a form of calibration for your sensor, to be > sure that you have correct threshold for the calulation. > 'Problem1' then is that a computerized PWS takes periodic samples => you > never have the really actual coverage, unless with high frequency sampling. > 'Problem2' is related aspect that you have to cope with dips while filling > your database for the daily accumulation => the opposite of Problem1. > The combination of those 'problems' is more the hurdle to be solved in a > sturdy algorithm to get a sensible, practical result. > Op 3-5-2024 om 1:23 schreef n7uv...@gmail.com: > > Hi Karen - > > I went and read the paper that is referenced for the sunshine duration > method. It describes an empirical approach to estimating whether or not the > sun is "shining". To me, as you suggest, if I have a crisp, well-defined > shadow, then there is indeed a 6000 K point source in the sky. If I meausre > in a low humidity, low atmospheric turbidity environment, with low > atmospheric particulate count, that shadow should indeed be crisp and well > defined. If I measure in a location where the sun is clearly above the > horizon, but the shadow is less well defined due to those confounding > factors and others, I can still assert that it is sunny, yet it is a degree > less sunny than at the former location. > > If one looks at brewster76/ > > - util-archer <https://github.com/brewster76/util-archer/tree/master> > - /user <https://github.com/brewster76/util-archer/tree/master/user> > > /radiationhours.py > > > there is an arbitrary value (to be inserted by the user) on what > constitutes full sunlight. > > _____________________________________________ > Adds a new observation field to weewx: [sunshine_hours] > > If the radiation observed during an interval of time exceeds 120 W/m2, > then the interval is considered sunny, > and [sunshine_hours] is set the length of the time interval. > > When [sunshine_hours] is summed over a day, the result is the number of > hours during the day when radiation > exceeded 120 W/m2, or 'hours of sunshine'. > > The threshold of 120 W/m2 can be overwritten in weewx.conf: > > [RadiationDays] > min_sunshine = 120 > _______________________________________________ > > so, for Brewster76, 120 w/m^2 is the threshold. This is more or less > consistent with the original paper, which attempts to get the necessary > fudge factors on atmospheric clarity via long--term empirical observations > vs the theoretical value for the insolation at that minute at that > location. It by no means is a measure of the shadow, or just how crisp it > might be. > > Various places in the USA all claim to have the most sunshine. I always > wondered how they measured that, and what constituted sunshine. If indeed > it is via models like what is presented in the paper and the subsequent > code examples, it is just a marketing term. > > If there is a measuring device, I call it the umbrameter, that can > actually measure the depth of shadow cast, and quantitatively show that > indeed it is a sunny minute, that would be a cool instrument. I think a > quality video camera or other 2D sensor could inspect the image of the sun > and, through sufficient training, could say that "this image is within x% > of the expected image of the sun taken above the atmosphere, that would be > a useful instrument. > > Sunny days and sunshine duration appear to be a matter of opinion. > > Cheers - Jon N7UV > On Thursday, May 2, 2024 at 12:03:15 AM UTC-7 Karen K wrote: > >> n7uv...@gmail.com schrieb am Donnerstag, 2. Mai 2024 um 01:01:52 UTC+2: >> >> When I hear "sunshine duration", I'm not sure whether that means the >> duration that the scary fiery (I live in PHX %^) ball of plasma is at and >> above the horizon (which is already provided under the Celestial tab) >> [image: Screenshot 2024-05-01 155959.png] >> or something about the total energy delivered to a square meter of the >> ground over the period of a day. >> >> >> Sunshine duration means the time the sun is really seen in the sky and >> typically casts a shadow. The standard instrument to measure sunshine >> duration is the Campbell-Stokes sunshine recorder >> <https://en.wikipedia.org/wiki/Sunshine_recorder>. >> >> Sunshine duration is *not* total daylight time. >> >> If a cloud is situated before the sun, this is considered no sunshine. If >> clouds are elsewhere in the sky it does not matter. >> >> -- > You received this message because you are subscribed to the Google Groups > "weewx-user" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to weewx-user+...@googlegroups.com. > > To view this discussion on the web visit > https://groups.google.com/d/msgid/weewx-user/254b9f95-a013-48e4-bc48-a61346d38276n%40googlegroups.com > > <https://groups.google.com/d/msgid/weewx-user/254b9f95-a013-48e4-bc48-a61346d38276n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > > -- > > =============================================================== > Contactinfo voor Anton van Nieuwenhuijzen: > Email = ton...@gmail.com > =============================================================== > Deze E-mail en eventuele aanhangende files zijn > alleen bestemd voor de geadresseerde(n). > Als je deze E-mail ten onrechte hebt ontvangen, > dan aub verwijderen en de afzender informeren. > > -- You received this message because you are subscribed to the Google Groups "weewx-user" group. 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