Below average months in New Zealand

[J07]

Below average months have become fairly rare in the UK in "The christmas pudding" (TM? :lol: ). Thought I would start checking it out for New Zealand. I believe we get more below average months. But the overall change is most likely smaller since we are surrounded by the odd spot of water or two.

Just for the moment, looking at 2007, we have:

J 16.7 -0.4

F 17 0.9

M 16.6 0.9

A 13 -0.5

M 12.4 1.7

J 7.9 -0.6

J 8.1 0.2

A 9.1 0.4

S 10.5 0.1

O 11.7 -0.5

N 13.4 -0.3

D 16.1 0.5

On the left, the average temperature, on the right is the anomaly.

So, 5 below average months in 2007, and 7 above average. Perhaps the only *significant* temperature anomaly though was in May. Coming after a cold April, May 2007 turned out to be the warmest May in history (similarly in Australia). It gave a true Indian Summer. Following on from this, a cold June. Interesting that the warm pattern disappeared just in time for the first week of June where there were snowstorms and in Queenstown (sub-alpine resort town) their Annual Winter Festival had to be postponed (!!!).

Other months did not have such large temperature discrepancies. However, it's very much a case of data getting smeared again. Many people would consider November 2007 to have been a warm month, this is because the summer drought began halfway through that month (it's still persisting for many) and also because record temperatures were recorded in many regions. However, the tale-end of miserable October lagged into early November and pushed the average down.

IMO, it's worth noting that consistently the sunshine hours seem to be increasing year-in, year-out. It does not appear correlated with temperature and seems to be a trend that continues despite cold years and warm years. I wonder if this is a permanent factor that is appearing.

For example, in 2007, Wellington recorded a 10% increase in sunshine hours. This is actually a fair increase (in the region of 200hrs). Perhaps the bulk of this came in August 2007, where the temperature was bang on average, but the sunshine hours recorded were 180. This is in the region of 50% greater than normal.

Unfortunately, I've not yet worked out what sites are chosen to take the average temperatures from which to decide a "national average". On one extreme, you have towns in the south island interior which get 70 air frosts per year even in a warm year, and on the other there is Northland, where in places the average daytimes highs are about 24C in summer and 17C in winter with frost never occurring.

I will look more into this.

[BrickFielder]

The amount of sunshine hours could be linked to El Nino and La Nina with a bias towards El Nino at the moment you might expect cloud cover to reduce in some areas. It would therefore be interesting to see the sunshine hours so far for 2008. Equally it could be related to the antartic dipole which looks to be switching now.

[johnholmes]

I would not attempt to take a national average; the two islands have such differing weather patterns/climates, that one for each island might be an idea?

[J07]

The amount of sunshine hours could be linked to El Nino and La Nina with a bias towards El Nino at the moment you might expect cloud cover to reduce in some areas. It would therefore be interesting to see the sunshine hours so far for 2008. Equally it could be related to the antartic dipole which looks to be switching now.

Connection very slow at the moment so I can't do the looking up.

However, I do know that last summer was mostly El Nino, and this summer is mostly La Nina. In Wellington at least, this year has seen 15 more hours of sunshine in the summer period, essentially a meaningless change considering there was one extra day of summer and we average about 7.5 hours of sunshine per day.

I recall that January 2007 was noted as an especially cloudy month nationally.

So at the moment I don't see that El Nino increases sunshine relative to La Nina, but more exhaustive enquiries would be needed.

In NZ, El Nino leads to more SW winds, whilst La Nina gives more NE winds.

It is true that Southland had record high sunshine hours this summer, whilst Northland had record low sunshine hours! The mid-lat anticyclones were further south than normal which on occassions led to Northland being caught up in the beginnings of the trade winds, leading to soggy, cloudy conditions.

How does the antarctic dipole effect sunshine, and what is it exactly?

[J07]

I would not attempt to take a national average; the two islands have such differing weather patterns/climates, that one for each island might be an idea?

NIWA release their "national average temperature" for each month, I don't know how they calculate it. A problem with doing it myself is that the only consistent locations for which they release monthly means are the "five main centres" (Auckland, Hamilton, Wellington, Ch'Ch, Dunedin). Having looked at some figures, the national average temperature does NOT equal the average of the means recorded for these locations. So I remain at a loss as to which stations they use.

If I were to do it myself, I could have a NI mean from Auckland, Hamilton and Wellington and a SI mean from Ch'Ch and Dunedin. However, I would be concerned that these would not truly represent each island genuinelly. It would cover most of the population of the country, but not the distinct climates of all the regions and hence the islands.

The South Island mean would be the worst, with only two cities, and both located on the Pacific Coast, it just wouldn't represent the warmer, sunnier north, nor the incredible wet west, nor the cold and dry interior.

Perhaps the CET has the same issue, but then you could argue that its real strength is in the long record of data and it helps that the weather varies less across the UK than it does over New Zealand.

When it comes to other locations, NIWA only release their mean temperatures if they were particularly interesting for that month- eg when somewhere had its mean monthly maxima 4C above normal.

Just as a quick shot, using January data I get a NIM of 19.7C and a SIM of 17.2C. That's using NIWA's "5 main centres data".

If I include all other data they release for that month I get a new NIM of 20.0C and a SIM of 18.0C. Of course, I could not repeat that for every month of the year since they would not choose to share the mean monthly temperature of Whatawhata (where? Exactly) every single month.