Question for TonyT re an "old" Ch'ch reading

[RWood]

Re this claim from someone on another forum:

"I went back to an old edition of The Press (5/1/98) at the library, and it reported that Blues Skies weather forecaster Tony Trewinnard recorded a temperature of 36.4 deg on January 3, 1998 at his Christ's College weather station (Christchurch). Compare this with the official Christchurch Gardens temperature of 33.8 deg for that day."

Can TonyT please comment on this, and on whether such differences were typical of the site (and some reasons if so?)

[TonyT]

We set up an electronic station to provide the Press with readings they could access via computer to use in their newspaper. They needed to get data by 6pm each day, whereas the readings in the Botanic Gardens are done manually so arent available till 9am the next morning, and would therefore be 2 days old by the time they get read.

We set up the station at Christs College so it was very close to the Botanic Gardens site, probably no more than 500m away.
The temp sensor was a good one, in a metal shield. It was mounted at the right height, but the exposure wasnt brilliant, on a river bank, over grass but only 3-4m away from a building. It was the best we could do with the technology we had and the budget etc. The shield wasnt aspirated, so on light wind days (and the site was quite sheltered from prevailing winds, but then so is the Gardens site with all its trees around), the temps were on the high side.

I would always take the GArdens reading in preference over the Christs College one, as the College site was never intended to be archival, but the College site served its purpose of allowing the newspaper to get more up to data data for its readers.

On a more general note, the Gardens site for all its exposure problems is a much better site in my opinion than the Airport - you only have to look at the two environments to see which one is representative of the population of the city and which one is not.

Also, the difference in the two readings you quote does highlight the variations over quite small distances which can occur due to measurement techniques and environmental differences. There is never any "right answer" to questions like "what is the highest temperature?", you can only report what you measure and hope that the measurement is representative.

[RWood]

Thanks Tony, very interesting. You make a good point about the Gardens and Airport sites are far as representativeness goes - the "centre of gravity" of Ch'ch's population would certainly seem to be more like the former. On the other hand in the case of Dunedin, significant suburban hill population and higher night minima near the harbour mean that overall Musselburgh has a daily mean which is a bit high to be an average for the city. Kelburn is probably OK for Wellington city, or perhaps a tad cooler than the average location here.