OPINION: March 22 is the autumn equinox, when the tilt of the planet in relation to the sun in New Zealand means the days are shorter and the nights longer. In The Lies of March: Does autumn exist in Auckland? I presented the theory that Auckland and Northland basically has two seasons – warm and cold, with varying degrees of rainyness in Auckland, and two transitional months of May and September, rather than two three-month transitional seasons.
But enough of what I think about whether or not there is a true autumn in Auckland and Northland, whether we have four equal length seasons, and even if this region is subtropical or not – let's see what the experts say.
First up – it really does seem to be a matter of opinion.
"You can define seasons any way you like!" says meterologist Bob McDavitt at the Metservice (the government agency on climate and the weather). There are, as discussed in the last column, different ways of defining seasons, favoured by different countries, cultures and languages.
"Being a logical person I divide seasons into four each year, based on our orbit around the sun, between equinoxes and soltices." But, I ask, are they four seasons of equal length here in Auckland? "Climatologists use the four seasons making them of four equal three-calendar months for practical purposes – so we can compare monthly norms."
Georgina Griffiths, a climate scientist based in Auckland with the National Institute of Water and Atmospheric Research (NIWA), also has no problems with our existing system – "Yes, I do believe in the seasons. We have four distinct seasons – every year is different though." I ask her what she thought about the March 1 being the beginning of autumn in Auckand and Northland.
'Good for druids'
"Yes. The minimum temperature is cooling and the weather is starting to transition." But isn't the beginning of March a bit arbitary, I ask. "I'm comfortable with that. We have a standard calendar year and we base it on the calendar." And what about the system where you begin autumn at the equinox? "If you're a druid..." she jokes.
I mention the Swedish system where they wait for there to be a mean temperature change to announce a change of season. "That's an interesting way of doing it," says Griffiths. "But a (temperature) threshold is arbitary as well."
There is certainly an argument for a subtle autumn in this region. Morning and evening temperatures are noticeably cooler than in February, and, says Griffiths, the wind changes. How can you tell it's autumn? "Wind and rainfall," says Griffiths. "To the people who live here – we're used to the climatology and recognise the seasons" (even though the daytime temperatures do not change at all or very minimally).
"For me it's about the wind directions, not the temperature. We get south westerly winds from the Tasman for instance.
"Autumn means a lot of different things to different people because it's activity based, ie, if you're sail like I do, or are a mountain climber and so on.
"Scientifically speaking, there are more highs (in the temperature) in summer, and in autumn we transition to more mobile features like cold fronts."
Bob McDavitt, also works from Auckland, and says of this region: "When you get dewey mornings and the mushrooms come out, then it's obviously autumn. And," he adds, "it's the when the leaves fall." I ask if you define autumn here as the season when leaves fall, does that mean that autumn depends on the people who live here – that before Europeans came here with their deciduous trees there wasn't an autumn, and now there is?
He pauses. "Then I would say it's the season of mushrooms."
Daylight saving
He adds that for the purposes of dairy farming, big business here in Aotearoa/New Zealand, autumn begins when daylight saving changes. "Autumn is the season when the nights get longer on the equinox, or when daylight saving changes. And autumn is when the bees close down.
"Obviously there is a difference between the north and south (of the country). There is an argument that up north there are fairly stable temperatures that change very quickly." Would my theory about the warm and the cold season with transitional months fit that then? "Yes, it would, but we use different terminology." He mentions research of this nature where transitions are called shoulder seasons.
Dr James Renwick is a Wellington based climate scientist at NIWA. I ask him if our season system is based on a European category rather than logic. "Yes, pretty much. It's arbitary. You have to have the dividing line somewhere if you're going to have defined seasons. We follow the UK and the European standard.
"In the US they use the astronomical seasons more and if we followed their system we would follow the solstice and the equinox – which makes the season changes about three weeks out of the calendar ones, with summer beginning at around Christmas time and our summer solstice – and lots of people say that the really good weather doesn't start until after Christmas. And autumn would begin now at the equinox.
"New Zealand is stuck in the middle of the roaring forties (the lattitude), and we are surrounded by ocean so we are hugely affected by ocean temperatures which don't warm or cool very much. We can get any kind of weather any time of the year."
He adds, "Auckland especially, but the whole of the Northland peninsula is pretty narrow and therefore close to the sea, so that the whole area is governed by the sea and the temperature changes are pretty moderate.
"The concept of four seasons of three months duration comes from Europe. It's something imposed by the European colonisation around the globe. It works well in Canterbury for instance. But for most of the north – sure – autumn is a relatively short season. Researchers here at NIWA are allowing for long summers and short autumns, and a more flexible season length."
How does he describe autumn? "It's the 'season of mists and mellow fruitfulness', I think is what Keats said. It's the harvest season with fruit ripe for the picking and pumpkins – the end of the growing season, like the Americans celebrate with Thanksgiving around their autumn equinox.
"And one thing you can't avoid is the length of the days getting shorter."
And that begging question – is Auckland and Northland subtropical? "Northland is not quite subtropical," he says. "Winter is too much like winter.
"But wait another 50 years and we might be in business."
Ali Bell
