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Also, one other interesting consideration…don’t discount how rapidly solar gradients can change:
An old college professor I knew used to try this trick T/F question on his first year physical geography students every year; He would say with a smile “Pittsburgh is only 4 hrs by motor car away from Baltimore, MD….does Baltimore, MD get 25% more sun hrs annually and 35% more sun hrs in winter months than Pittsburgh? Almost universally everyone fell for it - and firmly stated FALSE..
Let's see... Baltimore (58%) and Pittsburgh (45%). 58-45= 13 and then you take 13/45 x 100 = 28% more sunshine in Baltimore. I would think that Washington, DC (56%) would be about the same as Baltimore. You'll notice most of the cities along the Northeast I-95 corridor have about 56-58% of the possible year-round sunshine (NYC, Philly, Baltimore, DC). I still don't understand why Cleveland, OH (49%) averages more sun than Pittsburgh? I mean, Cleveland is literally next to Lake Erie.
I'm really enjoying this as I love science and am learning a lot. It would be great to hear what your friend in the UK thinks. He may have another twist on this. I recall reading that the F-F, and also from the email I got from NCDC, is that they consider daylight hours based (to be used in the % calc's) on the Navy's time of official sunrise and sunset (disc above horizon). Also that a visible disc on a clear day will burn the SC card at 120W per sq meter> They also make adjustments for the fact the yearly daylight hours are not the same from the equator to the poles. There is a slight variation.
Here is Canada:
The Canada map is interesting, though not too surprising - the very low values on the western seabord stand out. Re the visible disc and 120W psqm, met. scientists responsible for the updates to normals tables looked at that pretty closely and concluded that almost universally in NZ the first 15 and last 15 minutes of sunlight would not register. I'm pretty sure the daylight tables used would be the same as the Navy ones (from memory at 45S the yearly quota was about 4425 hours). With half an hour per day deducted, the adjusted "possible" would be about 4240 hours. Percentage values were listed as both relative to astronomical daylength and the reduced daylength, the latter after deducting further any estimated loss due to obstructions at the site.
For sure it was always a difficult task to try and keep consistency in C-S recording, but for about 5 decades all cards were sent to the national office (the number of concurrent observing sites peaked at about 85) and the results in my opinion seemed very consistent with other understandings of local and relative climatologies.
I will contact the UK guy - he may be a little slow to respond but it will happen.
So S-C measures sunshine "shortly" after sunrise using 120 Watts, same as F-F.
This from an article on S-C:
Advantages
The major advantage of this type of recorder is its simplicity and ease of use. There are no moving parts and it thus requires very little maintenance. The unit can be used anywhere in the world with little or no modification and is relatively inexpensive – they can be purchased for about $2000 USD.
Disadvantages
When the sun is low in the sky it may not have enough strength to properly burn the card and thus can only measure the amount of bright sunshine as opposed to visible sunshine. Rain may cause the card to be torn when removing it and thus making it difficult to read. In areas of high frost and during periods of freezing rain the sphere may be difficult to clean and may not be removed before the sun is shining again. However, the single biggest problem is in the reading of the cards. As the sun is covered and exposed by clouds the amount of burn on the card may be the same for 30 seconds as for 5 minutes. Thus, the reading of the card may differ from one observer to another.
From what I read here, the S-C measures "bright sunshine" at low angles, but won't record visible sunshine. F-F does not record visible sunshine, unless an observer does that maybe.
Interesting is that according to the US Navy our sunset time here is 4:39, and on a clear day the sun is still visible on the horizon. End of twilight is 5:09pm, then it is dark. So it may be light out, but that is not counted towards sun hours if it is clear.
. As the sun is covered and exposed by clouds the amount of burn on the card may be the same for 30 seconds as for 5 minutes. Thus, the reading of the card may differ from one observer to another.
Good confirmation points on the technology. The observer issue is certainly an important one, as I commented on in more detail in the PM. Even with the excellent centralised checking that was done here for many years, I noted some definitely suspect monthly records got through then - but not a high proportion. I think the main person doing the work was probably unavailable on some of those occasions. What may throw further light on that is a long-running project to transfer older paper daily records to the main databases - for temperature, rainfall, sunshine etc. Some sunshine anomalies may well get picked up in the process. The people doing this work were quite excited to discover a new national all-time low temperature, recorded in 1903. Comparison with nearby sites and anecdotal history convinced them that the record was genuine.
Also, one other interesting consideration…don’t discount how rapidly solar gradients can change:
An old college professor I knew used to try this trick T/F question on his first year physical geography students every year; He would say with a smile “Pittsburgh is only 4 hrs by motor car away from Baltimore, MD….does Baltimore, MD get 25% more sun hrs annually and 35% more sun hrs in winter months than Pittsburgh? Almost universally everyone fell for it - and firmly stated FALSE.
I realize that Windsor and Detroit are much closer…but little physiographic, climatic, and even manmade differences can add up to alot when a weather element is calculated annually.
Detroit to Windsor varies by around 27 minutes per day in sunshine totals. That could certainly be accounted for by small geographic changes, hills, obstructions( in early morn or evening), etc. I don't think this diff that odd after all the reading I've done on this last night. Also, if you look at the map of Canada, the contours run north-south and are increasing as you move west away from Windsor. The Detroit airport is around 21 miles directly west of the Windsor airport. It doesn't seem so far out there that Detroit airport would record more sun than Windsor. I seem to recall people on C-D from the UK claiming that Greenwich sun hours were different (I think by around 20 mins per day) from Heathrow due to Greenwich being a particularly cloudy part of London.
There must be some obstruction from a man-made object that is causing the lower sunshine totals because that area of Windsor/Detroit has virtually no large hills that could account for such a large difference. The geography there is relatively flat and neither city is on a large body of water.. the closest "large" body of water is Lake St. Clair and it's to the northeast and wouldn't have much effect on sunshine totals I don't think.
In addition to comparing US vs. Canadian border towns, it would also be interesting to compare US vs Mexican border towns to get a picture to see what the Mexicans are doing and how it compares.
Not sure if sunshine data exists for these places but you could compare:
Tijuana / San Diego
Nogales / Nogales
Ciudad Juarez / El Paso
Nuevo Laredo / Laredo
Matamoros / Brownsville
There must be some obstruction from a man-made object that is causing the lower sunshine totals because that area of Windsor/Detroit has virtually no large hills that could account for such a large difference. The geography there is relatively flat and neither city is on a large body of water.. the closest "large" body of water is Lake St. Clair and it's to the northeast and wouldn't have much effect on sunshine totals I don't think.
In addition to comparing US vs. Canadian border towns, it would also be interesting to compare US vs Mexican border towns to get a picture to see what the Mexicans are doing and how it compares.
Not sure if sunshine data exists for these places but you could compare:
Tijuana / San Diego
Nogales / Nogales
Ciudad Juarez / El Paso
Nuevo Laredo / Laredo
Matamoros / Brownsville
Interesting point. Any sunshine average citations for a site, regardless of technology, should also comment on any loss due to obstructions.
There must be some obstruction from a man-made object that is causing the lower sunshine totals because that area of Windsor/Detroit has virtually no large hills that could account for such a large difference. The geography there is relatively flat and neither city is on a large body of water.. the closest "large" body of water is Lake St. Clair and it's to the northeast and wouldn't have much effect on sunshine totals I don't think.
In addition to comparing US vs. Canadian border towns, it would also be interesting to compare US vs Mexican border towns to get a picture to see what the Mexicans are doing and how it compares.
Not sure if sunshine data exists for these places but you could compare:
Tijuana / San Diego
Nogales / Nogales
Ciudad Juarez / El Paso
Nuevo Laredo / Laredo
Matamoros / Brownsville
Possibly, but why the differences within London at Heathrow vs. Greenwich? Between Detroit and Windsor we are talking 170 hours spread over an entire year. 27 minutes a day. Look at the blown up map from Canada's weather service. Leaving Toronto you lose 200 hours very quickly heading northwest. I seriously don't think this in and of itself is enough to start lopping off 300 sun hours from US cities to compare to the rest of the world.
Let's see... Baltimore (58%) and Pittsburgh (45%). 58-45= 13 and then you take 13/45 x 100 = 28% more sunshine in Baltimore. I would think that Washington, DC (56%) would be about the same as Baltimore. You'll notice most of the cities along the Northeast I-95 corridor have about 56-58% of the possible year-round sunshine (NYC, Philly, Baltimore, DC). I still don't understand why Cleveland, OH (49%) averages more sun than Pittsburgh? I mean, Cleveland is literally next to Lake Erie.
No, no…you missed it lad…the question was related to annual number of sun hrs at Pitt and Baltimore; From what I remember, Pitt averages something like 1900/2000 hrs of sunshine annually (due to its proximity to the Great Lakes)….while Baltimore averages around 2500/2600 hrs of sun annually(2550 – 1900 = 25 % or so difference)….the same with the winter differences (look at the map of Feb a few pages ago) Pitt gets like 115 hrs of sun in Jan/Feb….while Baltimore gets like 165 hrs of sun in Feb. Most people would not think the sun hrs is so large in such a short distance between Pitt and Balt/DC.
As far as Cleveland getting more annual % than Pitt…I was unaware of that. The only thing I can think of is that that the Allegheny Mts in western PA tend to have a lot of fog – perhaps this impacts total annual %?
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