Spring has sprung: Understanding the four different season start dates

Monday, 23 September 2024

Spring has arrived, but did you know there are four possible start dates? Learn about astronomical, meteorological, solar, and natural signs of spring, plus get ready for daylight saving this Sunday.

Give yourself a round of applause, you got through winter.

The first of September marked the first day of Spring. September 23, marked the first day of Spring. Early August, when solar winter ended, marked the first day of spring. And several weeks ago when the blustery westerlies turned up and temperatures hit 20 degrees for those out east, marked the first day of Spring. It’s all a little confusing.

There are four seasons in a year: Summer, Autumn, Winter and Spring. Each season has four potential start dates: Meteorological, Astronomical, Solar and Mother Nature.

Astronomical Spring: September 23

Earth is on a lean. We have an axial tilt of 23.5 degrees. This is a good thing! As it’s the tilt that allows the variation in how much sun we get across the year, and gives us our seasons. This tilt means there’s a predictable variation in how much sunlight we receive, and the angle of that sunlight.

These are marked by the two equinoxes and two solstices. For us in NZ, our summer solstice (December 21) is the point or our yearly orbit around the Sun, when the southern hemisphere is tilted towards the Sun, and receiving the most amount of daylight. The sun appears almost directly above us, and we have our longest day. Our winter solstice (June 21) is the opposite.

There are four seasons in a year: Summer, Autumn, Winter and Spring. Each season has four potential start dates: Meteorological, Astronomical, Solar and Mother Nature, Stuff and ThreeNews’ resident weather expert Heather Keats says.

The southern hemisphere is tilted away from the sun, we receive the least amount of daylight, and have our shortest day. The equinoxes are when equal amounts of day and night are received in both hemispheres. The spring or vernal Equinox (September 21), and the autumnal equinox (March 21).

Solar Spring: August 8

If you can get your head around that tilt, and how our tilt over our yearly orbit around the sun influences the amount of sunlight and radiation we receive. Then understanding the solar seasons is easier.

Solar seasons are still split into three months each, but cover a calendar period that encompasses the overall amount of daylight within that period. Solar Winter is the period with the least amount of sunlight, runs for six weeks before and six weeks after the winter solstice or shortest day. Solar summer is the same, but covering the period of the most amount of sunlight. So six weeks before and six weeks after the summer solstice or longest day.

Meteorological Spring: September 1

This is the easiest to explain, and the easiest to remember. For ease of record keeping, seasons start on the first day of the month where an equinox or solstice occurs. This has been the convention since the early 1700’s. For statistical purposes and establishing climate trends - this makes sense. The whole world, and all Meteorological departments follow this protocol. Summer: December 1. Autumn: March 1. Winter: June 1. Spring: September 1.

Mother Nature: Insert date here

This is an observational and subjective approach to marking the seasons. There are key climate drivers, and certain triggers - like trade winds and the Hadley Cell. But generally spring starts when the daffodils and cherry blossoms are in bloom, baby lambs are crowding the paddocks and avocados are in season. You’ll notice key weather patterns too, sustained westerly flows, fast moving fronts, and a very unsettled and changeable weather period. Windy, wet, warm, cold, snowy, calm, frosty, thundery. All the weather.