Gloomy June

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RWood
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Re: Gloomy June

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A few more days before sunrise turns the corner ….
RWood
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Re: Gloomy June

Unread post by RWood »

BeaconHill wrote: Thu 21/06/2018 09:01 Wellington sure has been decidedly dull the last 6+ weeks. I started cycling to work on a daily basis at the start of 2017, and last June/July there were only a handful of evenings that meant it was getting dark soon after 5pm. This year it has been the norm that it has been getting very dark at that time.

It has all been made worse by the fact there have been so many days with some amount of rain (26 out of 32 days with some rainfall measured).
Screen Shot 2018-06-21 at 8.50.06 AM.png

But..... at least the sun is now setting later again!! (4:58pm vs 4:57pm)
Of more concern to me is that this year is shaping up to be the 6th in this decade (starting 2010) with sunshine below normal - well below in 3 of those 6 years. The average over that timespan is well short of the 1980s, 1990s and 2000s. I don't think the results are due to any deterioration in the measuring equipment, it really has seemed cloudier.
Razor
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Re: Gloomy June

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Question.... what actually is a sunshine hour? A lot of conditions at the moment would be boarderline ie light cloud layers, fog patches, etc

Whats the formal definition?
Christchurch Rocks
RWood
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Re: Gloomy June

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Razor wrote: Thu 21/06/2018 10:49 Question.... what actually is a sunshine hour? A lot of conditions at the moment would be boarderline ie light cloud layers, fog patches, etc

Whats the formal definition?
Depends on the instrument type - NZ formerly used Campbell-Stokes sunshine recorders (glass sphere, burn marks on card), now only a handful left while conversion to electronic methods continues.


https://en.wikipedia.org/wiki/Campbell–Stokes_recorder (references at foot of article)

The new instrument being used is the Kipp and zonen sunshine recorder (google that for references, e.g. https://link.springer.com/article/10.10 ... 014-1125-z )

The latter calculates direct solar radiation by a "differential method" and the tally is computed against a cutoff of 120 watts per square metre (this value was apparently chosen by the WMO after analysis of C-S outputs showed responses over a range of 70-280 watts/sq metre, with a mean of around 120.

There are a number of serious issues with consistency using C-S equipment, easy to find online. So far NZ results show that most sites record signifcantly higher values with K-Z equipment than they did with C-S - typically by 150-250 hours per annum, though in some cases by more than 300-350, though this may reflect a deterioration in the old equipment (or former site exposure, if the new placement or site is better).
Razor
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Re: Gloomy June

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Thanks!!! The kids were asking me about this on the school run now I can throw science at them :)
Christchurch Rocks
Razor
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Re: Gloomy June

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Meanwhile, its another gloomy day, fog first and now a solid layer of cloud looking like its settled in for most of the day...
Christchurch Rocks
RWood
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Re: Gloomy June

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Razor wrote: Thu 21/06/2018 12:06 Meanwhile, its another gloomy day, fog first and now a solid layer of cloud looking like its settled in for most of the day...
Got some early sun here, but still getting cloudy spells and some brief drizzle. Regarding sun records: the averages from decades of C-S measurement did seem to me to bear a fairly reasonable relationship to the perceived climates at sites, but for almost every site's records one can find periods or a number of individual months when the values looked somewhat anomalous when compared with "nearby" regional sites.

On the other hand, for me there is an issue with new methods using a fixed cutoff for measurement regardless of season, as in temperate or higher latitudes a bright winter sun is not the same as a bright summer sun.
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TonyT
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Re: Gloomy June

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The main problem (from a "science" standpoint) with the older CS instrument was that you are defining the parameter on the basis of the instrument used to measure it. Bright sunshine was defined as happening when there was a burn mark on the card. Lots of issues could affect that, like the type and thickness of the card, how damp the card was, how clean and scratch feee the glass ball was, etc. Let alone the issues with exposure (trees growing up on the horizon over a period of decades then one day being cut down etc. The problem with the KZ instrument is that we have changed the definition of bright sunshine to 120w/m2 of solar radiation, but its relatively easy to get that under high cloud conditions in NZ, especially on the east coast of both islands in westerly flow, and then it records sunshine which is "not bright" and should probably not be called sunshine at all. Likewise, in winter, full sun can be under 120w/m2, even well away from the horizon, so the KZ records nothing. The "science" of this is really messed up, but then the true scientist would probably say that "bright sunshine" is a pretty useless parameter anyway, and that measuring radiation on different wavelengths is much more useful. Debatable point.
The best way to measure sunshine is with TWO radiation sensors, one fully exposed to all light, and one with a shade ring so it never gets direct sunlight on it. You then calculate the ratio of the two, and derive whether its sunny or not from that. The ratio method is independent of season, it just says "if the shaded radiation is 50% of the exposed or less then its sunny".
Razor
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Re: Gloomy June

Unread post by Razor »

Thanks Tony. So its a moot point as to how many sunshine hours we have seen this week. Sounds like yea, nah, maybe... Nothing definitive till its published
Christchurch Rocks
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Re: Gloomy June

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Cleared up to a nice fine and sunny day - wall to wall sunshine. :smile:
Haven't seen that for a while now, even a frost this morning.
JohnGaul
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RWood
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Re: Gloomy June

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TonyT wrote: Thu 21/06/2018 13:40 The main problem (from a "science" standpoint) with the older CS instrument was that you are defining the parameter on the basis of the instrument used to measure it. Bright sunshine was defined as happening when there was a burn mark on the card. Lots of issues could affect that, like the type and thickness of the card, how damp the card was, how clean and scratch feee the glass ball was, etc. Let alone the issues with exposure (trees growing up on the horizon over a period of decades then one day being cut down etc. The problem with the KZ instrument is that we have changed the definition of bright sunshine to 120w/m2 of solar radiation, but its relatively easy to get that under high cloud conditions in NZ, especially on the east coast of both islands in westerly flow, and then it records sunshine which is "not bright" and should probably not be called sunshine at all. Likewise, in winter, full sun can be under 120w/m2, even well away from the horizon, so the KZ records nothing. The "science" of this is really messed up, but then the true scientist would probably say that "bright sunshine" is a pretty useless parameter anyway, and that measuring radiation on different wavelengths is much more useful. Debatable point.
The best way to measure sunshine is with TWO radiation sensors, one fully exposed to all light, and one with a shade ring so it never gets direct sunlight on it. You then calculate the ratio of the two, and derive whether its sunny or not from that. The ratio method is independent of season, it just says "if the shaded radiation is 50% of the exposed or less then its sunny".
That all accords with what I've come to realise over the years. There were always plenty of potential issues with CS measurement, and it's no wonder a close look at the data reveals anomalies. Also, quite a number of stations, over various epochs, tended to show a decrease in the latter part of the records, probably mostly due to either deteriorating transparency of the ball if not replaced, or a reducing horizon. The KZ issue using fixed cutoff really messes things up, and it's no surprise that in general the increases observed in summer months are much larger than those for winter ones. Equally no surprise that stations in Canterbury in particular are logging much higher values given the high cloud scenarios it experiences. New Plymouth might take a little more explaining, as an "improver" at the top end of the differences.

NIWA has stopped citing sunshine deviations in its monthly reports and has said it is investigating the sunshine issue, but I'm sure they'll stick to KZ. Maybe your idea in the last paragraph will fly one day?
JP.
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Re: Gloomy June

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JP wrote: Tue 19/06/2018 08:39 I can never remember such a long period of overcast gloomy weather. The record in 1981 was 59 hours of sunlight from memory so we have a good chance of beating that. I see over the weekend and late next week looks quite sunny so it could be close.

As others have said the higher temps have offset the sunshine, its weird waking up to 6-8c overnight temps in June!
Well Christchurch avoided beating the record from 1981 of 59 hours when June 2018 actually ended up at 80.4 hours of Sunshine. Funnily enough wellington actually recorded lower than Christchurch with only 79.5 hours.

https://www.star.kiwi/2018/07/its-offic ... on-record/
RWood
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Re: Gloomy June

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Christchurch had only 61 hours in July 1977. But these numbers are quite decent for cloudiness by comparison with some sites' efforts in non-winter months - e.g. 59 hours at Timaru in March 1979, let alone the infamous 60 hours at Waimate in December 1959.