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 [email protected]:
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:
[email protected] 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)
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 [email protected].
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 [email protected]
===============================================================
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.
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-user/aeecc208-93ef-451c-98c3-b83f96e83523%40gmail.com.
