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Hi all. Does any of you know the formula to use to convert percent of total possible sunshine hours to actual sunshine hours?
Some Wikipedia articles have changed from sunshine hours to percentages recently and I was more used to the former.
When it comes to the ANNUAL percentage value, it is quite straightforward, I think:
For example, the Wiki article says that Chicago has 56% of the total possible sunshine hours in a year.
I just figured that the total possible sunshine hours YEARLY for any place on Earth is just the total hours in a year divided by two. So, it should be 365 days multiplied by 24 hours. But is really 365 the value used for the total days in a year? Isn't it 360? (And, so, accordingly, isn't 30 days the value used for the total days in any month?).
Anyway, I used 360, which multiplied by 24 gives 8640, which divided by 2 gives 4320. So, 56% of 4320 would be 4320 times 0.56 = 2419.2 total sunshine hours annually in Chicago.
Is this the right way of doing this?
And what about the total hours for each month? Here matters complicate a bit, since latitude come into play.
This won't be much use to you for Chicago, but this is a table of maximum possible sunshine hours per day for my part of the world (assuming sunshine recorders can pick up 100% of possible sun, which they can't):
Go there, pick the city you're interested in, and take day length on the 15th of each month which more or less accurately represents the average, multiply by number of days in the month.
Bear in mind that depending on the measurement method a deduction may need to be made from the possible durations (all assuming of course there are no artificial obstructions to the daylight). For non-electronic methods in most latitudes subtracting 30 mins per day is common, and is used in NZ. For the US (except perhaps for the Blue Hill site) no deduction should be made.
This won't be much use to you for Chicago, but this is a table of maximum possible sunshine hours per day for my part of the world (assuming sunshine recorders can pick up 100% of possible sun, which they can't):
Thanks for that, ben. It seems that I could use that table to calculate the maximum possible sunshine hours per day at any other latitude, providing there's no other factor I'm missing.
Quote:
Originally Posted by dhdh
Go there, pick the city you're interested in, and take day length on the 15th of each month which more or less accurately represents the average, multiply by number of days in the month.
This also sounds good, thanks dhdh.
Quote:
Originally Posted by RWood
Bear in mind that depending on the measurement method a deduction may need to be made from the possible durations (all assuming of course there are no artificial obstructions to the daylight). For non-electronic methods in most latitudes subtracting 30 mins per day is common, and is used in NZ. For the US (except perhaps for the Blue Hill site) no deduction should be made.
London records 1653 hours but the recording equipment has a burn threshold of 139.5 W/m2 at Kew Gardens (other stations use electronic sensors but the Met Office adjusts all measurements to be in line with old CS recordings). The WMO standard is 120 W/m2 which would give Kew around 1920 hours.
When Chicago recorded it's sunniest month on record back in July 1916, it used a sunshine recorder that required TWICE as many lagleys to initiate measurement than what went into use in 1953 when the NWS switched to the Foster equipment
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Even though the 1931-1960 sunshine hours for Chicago was still around 2600 hours as it is today. You would think that that 2600 hour line would be shifted much more for that time period when 23 of the 30 years used a sun measuring device that required twice the strength...
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But when I inquired to find out why, a local meteorologist stated that the difference between the 87 watts per sq meter that the Foster sunshine recorder uses, and the current WMO standard of 120 watts per sq meter is usually negligible
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Last edited by chicagogeorge; 06-09-2013 at 11:08 AM..
As I've said before - no way do I believe a Chicago mean anywhere near 2600 hours of "bright" sunshine, or even probably 2400, when compared to burn method results.
Is it just me or did wikipedia change back to the total monthly and yearly sunshine instead of the %?
When I go to Chicago or New York it is back to the monthly totals.
While Sydney still has mean daily sunshine hours which is every worse tbh.
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