This I understand, Jacques - What is "direct solar irradiance"? Is there someone at the sensor deciding that it's direct? That they confirm that a solar disk is visible? That, given a decent scope, that sun spots are resolvable? Nah, I don't think so. They're PYROheliometers, measuring heat energy. Again, that becomes an arbitrary value of what is "sunshine". This is an artifice, and does not measure "sunshine" in the manner that Karen describes. It does not measure shadow, or even quality of shadow. It does not suit my local needs for "sunshine", as I've already said that on a OVC day here in KPHX it's still above 200 w/m^2. It's just a measure of "whether or not my location has received xx% of the theoretical insolation available". That's a poor estimate of "sunshine". We need an umbrameter. I submit that that is a quasi-2d sensor that measures the "quality" of an umbra cast by a sphere onto a concave spherical surface opposite to the sky, is better than what we have now. Or, using the idea of an "extended point source", it stares relentlessly into the sky and adjudicates the quality of the visible disk of the sun. Either of those is far superior to the "sunshine" concept.
I grew up in Los Angeles CA, when it was leaving the worst of its smoggy phase. There were so many days described as "hazy", "very hazy", "mostly sunny", or "sunny". I live in Phoenix AZ now, where there isn't as strong as an inversion layer or effect. Little moisture in the atmosphere, either. My personal rule's not perfect, but I recognize a sunny day as a day where the sky is a certain shade of blue. All empirical. I've been in Paris, Rome, Madrid, London, Brussels, Oslo, Hong Kong, Beijing, Seoul, Tokyo, Sydney etc., where "yeah, it's kinda sunny (i.e., not obvious clouds between me and the sun), but it's more diffuse than it is direct. I choose not to call those "sunny days". OMG - too many "". YMMV %^) Cheers - Jon N7UV On Friday, May 3, 2024 at 5:35:41 PM UTC-7 Jacques Terrettaz wrote: > The WMO definition (threshold at 120 W/m2) is applicable only for the > measurements of *direct solar irradiance*, using pyrheliometric sensors > that are all the day moving to point always directly toward the sun > position, with the surface of the sensor always perpendicular to the axis > sun-sensor. > > Pyrometer sensors, such as the Davis radiation sensor, are measuring > mostly * global irradiance*. These sensors are not moving to follow the > sun, and the surface of the sensor is parallel to the ground. And not > pointed toward the sun With this type of sensors, the measured radiation ( > even in absence of clouds) is highly dependent on the sun elevation. > > see > https://library.wmo.int/viewer/68695/?offset=#page=333&viewer=picture&o=bookmark&n=0&q= > > > > > > Le 3 mai 2024 à 16:59, n7uv...@gmail.com <n7uv...@gmail.com> a écrit : > > 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. > > > -- 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+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/weewx-user/5d3b9814-8054-4552-b505-4bd5ee9e3f98n%40googlegroups.com.
