Sunshine hours vs percentage: How to convert? (record, statistically, normal)
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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.
Well, up to 1953, Chicago used the Marvin sunshine instrument which took twice as long to initiate and record sunshine than what the current WMO standard is for watts per sq meter, and then switched to the more accurate Foster... Irregardless, of the instrument, the 1931-1960 average sunshine for Chicago shows around 2600 hours.
And if by "burn method" you mean the Campbell-Stokes, then you would be using a very inferior measuring device
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In fact all the old sunshine instruments are subject to inaccuracies
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Btw, Chicago had 2818.8 hours of sunshine in 2012 (using the Foster 87Watts per meter sq) as recorded at Midway airport, the only station to still monitor sunshine.
The issue is more complex than you think, and I'm not going to re-litigate it in detail here, except to say the the treatment by US met. bodies of sunshine recording appears to have been cavalier to say the least. This subject has been discussed at great length in other threads in this forum, and I suggest you familiarise yourself with them. You could also try asking some questions of the UK's Philip Eden, who has an extensive knowledge of the issues and problems relating to a manual-electronic conversion exercise there. You are of course free to delude yourself about the amount of sunshine you experience in Chicago, the 2012 figure you're claiming being almost at the average level for Brisbane.
I spent 12 months in Chicago doing graduate study - the records showed a sunshine total for the period of somewhat over 2400 hours. Comparing it with my experiences in my country, I'd rate it as having had no more than about 2150, perhaps barely 2100.
My country has had both manual and electronic meaurements methods. Regardless of any limitations of manual methods - and all methods have their issues - there was a lengthy period of time when the manual records here for up to 100+ sites over the recording history were carefully centrally checked for consistency and the results overall agreed very well with climatological commonsense re intercomparisons and other indirect knowledege from cloudiness levels etc. In computing % possible values, allowance was made for attenuation at the start and end of the day.
. You are of course free to delude yourself about the amount of sunshine you experience in Chicago, the 2012 figure you're claiming being almost at the average level for Brisbane.
If I'm deluding myself, then it's with official instrumentation at one of our international airports which the observer Frank Wachowski has been with the NWS for nearly 50 years. It's his data, he is in charge of calibrating the instrument. This is one of the few remaining sunshine stations left in the country
Again reiterated until 1953 the instruments had a sunshine threshold was much greater then the current WMO standard
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I spent 12 months in Chicago doing graduate study - the records showed a sunshine total for the period of somewhat over 2400 hours. Comparing it with my experiences in my country, I'd rate it as having had no more than about 2150, perhaps barely 2100.
Did you have a sunshine recorder at your dorm room? If no, then you will excuse me if I don't take your "experience" in a very scientific manner. I have had direct correspondents with several local meteorologists. It's not like I'm a novice on this subject.
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My country has had both manual and electronic meaurements methods. Regardless of any limitations of manual methods - and all methods have their issues - there was a lengthy period of time when the manual records here for up to 100+ sites over the recording history were carefully centrally checked for consistency and the results overall agreed very well with climatological commonsense re intercomparisons and other indirect knowledege from cloudiness levels etc. In computing % possible values, allowance was made for attenuation at the start and end of the day.
That's great. Doesn't negate any of the evidence that I just presented.
Last edited by chicagogeorge; 06-09-2013 at 04:48 PM..
Btw, Chicago had 2818.8 hours of sunshine in 2012 (using the Foster 87Watts per meter sq) as recorded at Midway airport, the only station to still monitor sunshine.
A location in central southern England recorded 1612 hours of sun using a CS recorder during 2011, but according to a Kipp & Zonen electronic recorder, calibrated to 100 W/m2, it recorded 2646 hours! Adjusting it to 87 W/m2 it gets just over 3000 hours!
A location in central southern England recorded 1612 hours of sun using a CS recorder during 2011, but according to a Kipp & Zonen electronic recorder, calibrated to 100 W/m2, it recorded 2646 hours! Adjusting it to 87 W/m2 it gets just over 3000 hours!
About as sensible as that Chicago total?!
Edit: perhaps this guy should talk to the Blue Hill, Mass. observer - who probably has a more realistic notion of what constitutes "bright" sunshine!
As for his wisecrack about "dorms" (which I didn't inhabit, BTW) - you could take 100 rational weather-aware people from some towns in NZ & Aus that average around the 2400-2500 mark, put them in Chicago for a year claiming an equivalent total, and for sure not a single one of them would believe the claim of the latter!
Well what else but a wisecrack did you expect? First off, did you sit and measure sunshine? No. Can you tell if there was an hour of sunshine less per day as you claim? No. Have you spoken with professional meteorologists who know Chicago's climate like I have? No.
You didn't state when you spent 12 months in Chicago. What year? Second what is your source that 12 month period received 2400 hours of sun? It's nearly impossible to get sunshine data unless you sift through the NDCC for the monthly climate reports at Midway airport WHICH I DO. Do you? I doubt it.
I don't know about those adjustments for Southern England that B87 suggests. Remember, Chicago is at 41N latitude, not 51N where London sits..... That puts us in the Mediterranean part of Europe. Are you suggesting that we are less sunny? Why? We would have less of a marine layer than many Mediterranean cities.
I'm just stating what is fact. In 2012 using the Foster equipment at 87 watts per sq meter, Chicago recorded 2818.2 hours of sunshine at Midway International airport, and that through correspondence with professional meteorologists this is what was said about the difference between 87 watts and the WMO 120 watt threshold..... During interment cloudy days few minutes to in extreme cases an hour
Last edited by chicagogeorge; 06-10-2013 at 05:55 AM..
^^Whatever the truth is behind Chicago's 'real' sunshine stats, whatever the merits of the various measurement methods, I think we can safely dismiss claims of 3,000 hours sunshine in southern England as pure and organic horse manure.
I wasn't saying there were 3000 hours, but a sensor calibrated to 100W/m2 did record over 2600 hours, so that same sensor would have recorded 3000 hours had it been calibrated to 87W/m2.
You didn't state when you spent 12 months in Chicago. What year? Second what is your source that 12 month period received 2400 hours of sun? It's nearly impossible to get sunshine data unless you sift through the NDCC for the monthly climate reports at Midway airport WHICH I DO. Do you? I doubt it.
I got Midway summaries for 1967 and 1968 - via a chain of correspondence starting at a Chicago weather website that ultimately led to these reports titled
"Local climatological data
Annual summary with comparative climatological data, 19XX
Chicago, Illinois
Narrative climatological summary"
...there followed a very detailed commentary and a set of monthly statistics (Aug 1967-Julyh 1968 total calculated to be about 2460)
There was a small charge for extracting the data from NOAA or someone (can't remember exactly who levied the charge now).
You can scoff and bluster all you like. I have been reading screeds of stuff - reports, research papers etc - about sunshine recording for decades. I am acutely aware of sunshine levels wherever I happen to be. There has been the odd occasion in my town when a wrong or missing value has been transmitted from a surviving local manual site and I have picked up on these immediately and pointed out the mistake.
You and your contact's 87W/m2 instrument fail to convince me. I would suggest that the discrepancies with WMO standards would be very considerable on many occasions. My (recall only re impressions, but data is direct from the report with a calculation done for %values => hours) comments below clearly convey that the cloudier months produced the larger relative discrepancies.
Just to give you a flavour of some of the months I would comment on - though I don't any longer have my personal notes that I made at the time, understandably.
September 1967 - 250 hours (+/- 1-3) - with a good run of clear sky days this wasn't far off I think.
October 1967 - 158 hours - a considerably cloudier month stated to be around the 46% mark, value looks optimistic.
Nov 1967 - 94 hours (32%) - drab, and probably even less than that.
Jan 1968 - 118 hours (!!!) Very considerable cloudiness and the month gave the impression of being more like 60-70 hours tops. I recall fellow students on at least a couple of occasions when the sun peeked through briefly saying something to the effect "hey, thought that wouldn't happen till about March!"
Feb 1968 - 200 hours - I would have said nearer 160-170, but it was quite a sunny winter month.
March 1968 - the claimed 238 hours (64%) looked wildly optimistic. Ditto for April's 54%, in spades.
I have better things to do with my life than to continue these arguments about measurement methods with you - contact Philip Eden in the UK if you want. I'm done.
I got Midway summaries for 1967 and 1968 - via a chain of correspondence starting at a Chicago weather website that ultimately led to these reports titled
"Local climatological data
Annual summary with comparative climatological data, 19XX
Chicago, Illinois
Narrative climatological summary"
...there followed a very detailed commentary and a set of monthly statistics (Aug 1967-Julyh 1968 total calculated to be about 2460)
There was a small charge for extracting the data from NOAA or someone (can't remember exactly who levied the charge now).
Now they are free. I looked at dozens upon dozens of monthly reports from the Midway airport station. All very consistent
You and your contact's 87W/m2 instrument fail to convince me. I would suggest that the discrepancies with WMO standards would be very considerable on many occasions. My (recall only re impressions, but data is direct from the report with a calculation done for %values => hours) comments below clearly convey that the cloudier months produced the larger relative discrepancies.
So if reports and observations from the official observe you fail to convince you, then I guess nothing will. But the fact remains, we have trained observer who has worked with the National Weather Service for 50 years collecting this data. There is no reason to suspect that his work is erroneous.
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Chicago's sunshine records date back to 1893 and are among the most complete in the nation thanks to climatologist Frank Wachowski who took over the measurements in 1996. Based on sunrise and sunset, each day has a total number of minutes of possible sunshine, ranging from a low of 549 minutes around the winter solstice to a maximum of 913 minutes around the summer solstice. Wachowski employs a sunshine sensor that tallies the total number of minutes of sunshine received each day and that number is compared to the total possible minutes of sun using a simple ratio. For example, 400 minutes of actual sunshine on a day with 800 minutes of possible sun would register 50 percent of possible sunshine.
We went straight to our sunshine expert, Frank Wachowski, who has been
measuring Chicago's daily sunshine for more than 40 years. He noted
that September, even with just 30 days compared to March's 31, has more
minutes of daylight. Based on the number of minutes each day between
sunrise and sunset September has the potential for 22,463 minutes of
sunshine while March can only muster 22,218 minutes of sun -- even with the
extra day. Wachowski noted that July leads the year with 27,642 minutes
of possible sunshine, closely followed by June with 27,280 minutes. Not
surprisingly, December has the least sunshine potential, with just 17,130
minutes possible.
The information comes from an instrument called a sunshine recorder. It consists of two photoelectric cells: one exposed to the direct rays of the sun and another shielded from direct rays but otherwise exposed to diffuse skylight. When sun shines on the exposed cell, an electric signal is generated--a signal that is not balanced by the shaded cell. This electrical imbalance trips a relay and activates a recorder which tallies the minutes of sunshine.
This sunshine recorder--the only one in the Chicago area--is operated by Frank Wachowski, the official weather observer for the Midway Airport weather station. He provides this information to us.
The information comes from an instrument called a sunshine recorder. It consists of two photoelectric cells, one exposed to the direct rays of the sun and another shielded from direct rays but otherwise exposed to diffuse skylight. When sun shines on the exposed cell, an electric signal is generated--a signal that is not balanced by the shaded cell. This electrical imbalance trips a relay and activates a recorder that tallies the minutes of sunshine.
A new instrument being used today (and recommended by the World Meteorological Organization) is made by Kipp and Zonen Leaders in Radiation Equipment. It consists of three sensors--one that detects all direct and diffuse sunlight, and two others that look only at portions of the sky. Sunshine times are determined by differential measurements between the three sensors. Sunshine data from both systems are being collected by Midway Airport weather observer Frank Wachowski, and the results are being compared.
I have better things to do with my life than to continue these arguments about measurement methods with you - contact Philip Eden in the UK if you want. I'm done.
You have no evidence other then your own personal "feelings" and the 12 months you spent here. Far from scientific. I have official data from NOAA from 2 reference periods. 1931-1960, and 1961-1990.
Both support the notion that Chicago falls in the 2400-2800 hours range, more specifically closer to 2600 hours.
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